CHAPTER 1INTRODUCTION

1. INTRODUCTION

1.1. Internal Combustion EngineThe invention and development of the internal-combustion engine in the nineteenth century has had a profound impact on human life. Its these heat engines that have really changed the world. The internal combustion engine has become an integral part of the lives of every person on earth. Although the understanding of engine processes has increased and new inventions as well as better materials have improved the design, the basic engine principle is still the same. The internal-combustion engine offers a relatively small, lightweight source for the amount of power it produces. Internal combustion engines are devices that generate work using the products of combustion as the working fluid rather than as a heat transfer medium. All these engines do is burn fuel and convert its energy into work. To produce work, the combustion is carried out in a manner that produces high-pressure combustion products that can be expanded through a turbine or piston. Chemical energy of the fuel is first converted to thermal energy by means of combustion or oxidation with air inside the engine. This thermal energy raises the temperature and pressure of the gases within the engine and the high-pressure gas then expands against the mechanical mechanisms of the engine. This expansion is converted by the mechanical linkages of the engine to a rotating crankshaft, which is the output of the engine. The crankshaft, in turn, is connected to a transmission and/or power train to transmit the rotating mechanical energy to the desired final use. For engines this will often be the propulsion of a vehicle.

1.1.1. Classification of IC EnginesInternal combustion engines can be classified in a number of different ways:(a)Types of Ignition: Spark Ignition (SI), Compression Ignition (CI).(b)Engine Cycle: Four-Stroke Cycle, Two-Stroke Cycle.(c)Valve Location: I Head engine, L Head engine, F Head engine.(d)Basic Design: Reciprocating, Rotary.(e)Position and Number of Cylinders of Reciprocating Engines: Single Cylinder, In Line, V Engine, Opposed Cylinder Engine.

1.1.2. Various Parts of an IC EngineThe following is a list of major components found in most reciprocating internal combustion engines:

(a) Block: Body of engine containing the cylinders, made of cast iron or aluminum. In many older engines, the valves and valve ports were contained in the block. The block of water-cooled engines includes a water jacket cast around the cylinders. On air-cooled engines, the exterior surface of the block has cooling fins.

(b) Camshaft: Rotating shaft used to push open valves at the proper time in the engine cycle, either directly or through mechanical or hydraulic linkage .Most modern automobile engines have one or more camshafts mounted in the engine head (overhead cam). Older engines had camshafts in the crankcase. Camshafts are generally made of forged steel or cast iron and are driven off the crankshaft by means of a belt or chain (timing chain). To reduce weight, some cams are made from hollow shaft with the cam lobes press-fit on. In four-stroke cycle engines, the camshaft rotates at half engine speed.

(c) Crankshaft: Rotating shaft through which engine work output is supplied to external systems. The crankshaft is connected to the engine block with the main bearings. It is rotated by the reciprocating pistons through connecting rods connected to the crankshaft, offset from the axis of rotation. This offset is sometimes called crank throw or crank radius. Most crankshafts are made of forged steel, while some are made of cast iron.

(d) Connecting rod: Rod connecting the piston with the rotating crankshaft, usually made of steel or alloy forging in most engines but may be aluminum in some small engines.

(e) Combustion chamber: The end of the cylinder between the head and the piston face where combustion occurs. The size of the combustion chamber continuously changes from a minimum volume when the piston is at TDC to a maximum when the piston is at BDC. Some engines have open combustion chambers which consist of one chamber for each cylinder. Other engines have divided chambers which consist of dual chambers on each cylinder connected by an orifice passage.

(f) Cylinders: The circular cylinders in the engine block in which the pistons reciprocate back and forth. The walls of the cylinder have highly polished hard surfaces. Cylinders may be machined directly in the engine block, or a hard metal (drawn steel) sleeve may be pressed into the softer metal block. Sleeves may be dry sleeves, which do not contact the liquid in the water jacket, or wet sleeves, which form part of the water jacket. In a few engines, the cylinder walls are given a knurled surface to help hold a lubricant film on the walls. In some very rare cases, the cross section of the cylinder is not round.

(g) Carburetor: Venturi flow device which meters the proper amount of fuel into the air flow by means of a pressure differential. For many decades it was the basic fuel metering system on all automobile (and other) engines. It is still used on low-cost small engines like lawn mowers, but is uncommon on new automobiles.

(h) Fuel injector: A pressurized nozzle that sprays fuel into the incoming air on SI engines or into the cylinder on CI engines. On SI engines, fuel injectors are located at the intake valve ports on multipoint port injector systems and upstream at the intake manifold inlet on throttle body injector systems. In a few SI engines, injectors spray directly into the combustion chamber.

(i) Exhaust manifold: Piping system which carries exhaust gases away from the engine cylinders, usually made of cast iron.

(j) Intake manifold: Piping system which delivers incoming air to the cylinders usually made of cast metal, plastic, or composite material. In most SI engines, fuel is added to the air in the intake manifold system either by fuel injectors or with a carburetor. Some intake manifolds are heated to enhance fuel evaporation. The individual pipe to a single cylinder is called a runner.

(k) Piston: The cylindrical-shaped mass that reciprocates back and forth in the cylinder, transmitting the pressure forces in the combustion chamber to the rotating crankshaft. The top of the piston is called the crown and the sides are called the skirt. The face on the crown makes up one wall of the combustion chamber and may be a flat or highly contoured surface. Some pistons contain an indented bowl in the crown, which makes up a large percent of the clearance volume. Pistons are made of cast iron, steel, or aluminum. Iron and steel pistons can have sharper corners because of their higher strength. They also have lower thermal expansion, which allows for tighter tolerances and less crevice volume. Aluminum pistons are lighter and have less mass inertia. Sometimes synthetic or composite materials are used for the body of the piston, with only the crown made of metal. Some pistons have a ceramic coating on the face.

(l) Head: The piece which closes the end of the cylinders, usually containing part of the clearance volume of the combustion chamber. The head is usually cast iron or aluminum, and bolts to the engine block. In some less common engines, the head is one piece with the block. The head contains the spark plugs in SI engines and the fuel injectors in CI engines and some SI engines. Most modern engines have the valves in the head, and many have the camshaft(s) positioned there also (overhead valves and overhead cam).(m) Fuel pump: On newer cars the fuel pump is usually installed in the fuel tank. Older cars have the fuel pump attached to the engine or on the frame rail between the tank and the engine. If the pump is in the tank or on the frame rail then it is electric and is run by your cars battery. Fuel pumps mounted to the engine use the motion of the engine to pump the fuel, most often being driven by the camshaft, but sometimes the crankshaft. (n) Fuel filter: Clean fuel is critical to engine life and performance. Fuel injectors and carburetors have tiny openings which clog easily so filtering the fuel is a necessity. Filters can be before or after the fuel pump, sometimes both. They are most often made from a paper element, but can be stainless steel or synthetic material and are designed to be disposable in most cases. Some performance fuel filters will have a washable mesh, which eliminated the need for replacement.(o) Fuel injectors: Instead of a carburetor to mix the fuel and air, a computer controls when the fuel injectors open to let fuel into the engine. This has resulted in lower emissions and better fuel economy. The fuel injector is basically a tiny electric valve which opens and closes with an electric signal. By injecting the fuel close to the cylinder head the fuel stays atomized (in tiny particles) so it will burn better when ignited by the spark plug. In general, spark ignition engines consists of a spark plug essentially, but a compression ignition engine do not need a spark plug at all. (p) Spark plug: Aspark plugis a device for delivering electric current from anignition system to thecombustion chamberof aspark-ignition engineto ignite the compressed fuel/air mixture by anelectric spark, while containing combustion pressure within the engine. A spark plug has a metalthreadedshell, electrically isolated from a centralelectrodeby aporcelaininsulator. The central electrode, which may contain aresistor, is connected by a heavilyinsulatedwire to the output terminal of anignition coilormagneto. The spark plug's metal shell is screwed into the engine'scylinder headand thus electricallygrounded.(q) Lubricating system: The lubricating system addresses the need to properly lubricate an engine when its running. Properly lubricating an engine not only reduces friction between moving parts but is also the main method by which heat is removed from pistons, bearings, and shafts. Failing to properly lubricate an engine will result in engine failure. The lubricating pump forces themotor oilthrough the passages in the engine to properly distribute oil to different engine components. In a common oiling system, oil is drawn out of the oil sump through a wire mesh strainer that removes some of the larger pieces of debris from the oil. The flow made by the oil pump allows the oil to be distributed around the engine. In this system, oil flows through anoil filterand sometimes an oil cooler, before going through the engines oil passages and being dispersed to lubricate pistons, rings, springs, valve stems, and more.(r) Cooling system: A typical 4 cylinder vehicle cruising along the highway at around 50 miles per hour, will produce 4000 controlled explosions per minute inside the engine as the spark plugs ignite the fuel in each cylinder to propel the vehicle down the road. Obviously, these explosions produce an enormous amount of heat and, if not controlled, will destroy an engine. Controlling these high temperatures is the job of the cooling system. There are two types of cooling systems found on motor vehicles: Liquid cooled and Air cooled systems.

1.2. Literature Review Hiwasea et.al [1] studied experimentally Multidimensional Modeling of Direct Injection Diesel Engine with Spl Multiple Stage Fuel Injections. they found that At motored condition, the maximum average cylinder pressure and temperature occur at 360o of crank angle and that corresponds to 57 bar and 1050 K respectively, while in case of continuous injection it corresponds to 51 bar and 940 K respectively at the end of fuel injection and the combustion is initiated just 3o ignition delay after fuel injection due to auto ignition process delay leads to peak values of 135 bar and 2422 K respectively at 5o ATDC. The pressure and temperature at 700o crank angle are 3.5 bar and 750 K respectively. In multiple fuel injections, just after first stage of 25% fuel injection the pressure and temperatures are found out to be 29 bar and 800 K respectively, while after second stage of 75% fuel injection it corresponds to 51 bar and 940 K respectively and the combustion is initiated just 3 ignition delay after fuel injection due to auto ignition process delay leads to peak value of 120 bar and 2276 K respectively at 8 aTDC, which is slightly lower than that predicted for the continuous injection case. It can be concluded from study that the combustion with split multiple stage fuel injection exhibits strong effects on combustion and provides controlled pressure and temperature inside the combustion chamber. It is also observed that a multiple injections with 25% fuel in the first pulse and 75% in second pulse can significantly reduce the NOx formation by 45% compared to the continuous fuel injection combustion. This is because of the fact that in case of continuous fuel injection the charge is highly inhomogeneous due to insufficient time for thorough mixing that resulted in higher combustion temperature, while in case of multiple injection, the charge gets more homogeneous because of early injection in split form which enhances the mixing intensity till second stage fuel injection and the combustion temperature reduces drastically, which is the most responsible factor for NOx formation.Sarsi Kiran Prabhala1, K. Sunil Ratna Kumar et.al [2] worked on DESIGN AND WEIGHT s produce power by converting chemical energy of the fuel into heat energy. This produces the useful mechanical work by converting the heat energy. In the process of converting this thermal energy into mechanical work, which is performed by increase in pressure which generates forces to move piston connected to crank shaft by piton connecting rod. The fuel combustion occurs inside the cylinder so this process is called internal combustion. The piston engine is known as internal combustion heat engine. It supplies air fuel mixture in to the cylinder where it gets compressed and later burnt resulting the power. The internal combustion engine are reciprocating type engines which are either spark ignition (SI) where the spark ignition engine are called as petrol engines or compression ignition (CI), where the compression engine are called as diesel engines. In a conventional SI engine, fuel and air are mixed together in the intake system, inducted through the intake valve into the cylinder where mixing with residual gas takes place, and then compressed during the compression stroke. Under normal operating conditions, combustion is initiated towards the end of compression stroke at the spark plug by an electric discharge. Following inflammation, a turbulent flame develops, propagates through the premixed air-fuel mixture (and burned gas mixture from the previous cycle) until it reaches combustion chamber walls, then it extinguishes. Combustion event must be properly located relative to the TDC to obtain max power or torque. Combined duration of the flame development and propagation process is typically between 30 and 90 CA degrees. If the start of combustion process is progressively advanced before TDC, compression stroke work transfer (from piston to cylinder gases) increases. If the end of combustion process is progressively delayed by retarding the spark timing, peak cylinder pressure occurs later in the expansion stroke and is reduced in magnitude. These changes reduce the expansion stroke work transfer from cylinder gases to the piston. The optimum timing which gives maximum brake torque (called maximum brake torque or MBT timing) occurs when magnitude of these two opposing trends just offset each other.S.Sunil Kumar Reddy, Dr. V. Pandurangadu, S.P.Akbar Hussain et.al [3] had worked on Effect of Turbo charging On Volumetric Efficiency in an Insulated Di Diesel Engine For Improved Performance. They found that the increase in the intake boost pressure improves the brake thermal efficiency of the engine. For the compensation of drop in volumetric efficiency of the insulated engine 4% intake boost pressure is required for turbocharging. Though the higher temperatures are available in the combustion chamber due to insulation, the increase in exhaust gas temperature is marginal. This is attributed to the higher latent heat of vaporization of alcohol. As the alcohol contains oxygen and more air is available in the turbocharging for combustion, the ignition delay is reduced. Due to the complete combustion of alcohol at higher temperatures the smoke emissions are also marginal. The higher temperature in the combustion chamber decreases the ignition delay and aids combustion but drops the volumetric efficiency. The degree of degradation of volumetric efficiency depends on the temperatures in the combustion chamber and it further increases the frictional horsepower due to thinning of lubricant. For improving the thermal efficiency of insulated engine, the volumetric efficiency drop is compensated by turbo charging in the present experimental work.Sasi Kiran Prabhala, K. Sunil Ratna Kumar et.al [4] had worked on DESIGN AND WEIGHT OPTIMIZATION OF IC ENGINE. Since the mileage of the automobile depends on the weight of the automobile and the major weight is engine, as the engine is the assembly of many components, we will take the particular component and optimization of weight is done i.e. with respective to its function. I C engine components like piston, connecting rod crank shaft are made of steel because of its good strength. Replacing the steel components with aluminium components will reduce the weight but the strength is not enough so they are taking the aluminium alloy such that the aluminium alloy exhibits the strength like the steel because of its alloying material and own property of less weight. Therefore if as many as components are replaced then automatically overall weight is reduced therefore the power required to run itself by automobile is reduced resulting in the increase in the mileage. Design of engine crankshaft, connecting rod and piston assembly is analyzed by using the standard forces acting on the piston of four stroke engine. By using steady state and modal analysis measure at different connection they obtained the forces acting on the connections with represent the movement of crank angle. By observing the analysis results of assemblies they can conclude that using aluminium alloy for both connecting rod and piston is more beneficial than using steel for piston. While comparing stresses of the modified assembly is having less stresses than previous assembly. Displacement and strains (strain is also having less value than previous model) are negligible. By changing the piston and connecting rod material we can reduce the load effect on crank shaft. So that crankshaft life will be extended. Aluminium is having very less weight comparing to the steel so that we can conclude that modified assembly is having more mechanical efficiency and also we can reduce the cost of the product and production (Aluminium products are manufactured in cold chamber castings, steel products are manufactured in hot chamber castings). Vincenzo De Bellis, Elena Severi, Stefano Fontanesi, Fabio Bozza et.at[5] worked on Hierarchical 1D/3D approach for the development of a turbulent combustion model applied to a VVA turbocharged engine. Part I: turbulence model. In their paper, part I, a 0D turbulence sub-model to be included in a phenomenological combustion model is presented. The model belongs to the K-k family and describes the energy cascade from the mean flow scale to the turbulence scale. Numerical analyses on a small twin-cylinder VVA turbocharged engine are presented. In order to validate the turbulence model, 3D-CFD simulations of the motored flow field inside the cylinder are carried out for different engine speeds and largely different intake valve lift strategies. Boundary conditions for the 3D simulations are preliminary derived from the 1D code. Without any case-dependent tuning, the 0D turbulence model is able to satisfactory fit the 3D findings for all the considered operating conditions, especially during the compression and expansion strokes. This demonstrates the capability of the model to sense both different flow conditions through the valves (according to the engine speed) and different strategies for the intake valve actuation. The proposed methodology represents a successful example of integration of a refined 3D approach and a simplified 0D one. The proposed turbulence model shows the capability, once tuned, to accurately estimate the temporal evolution of the in-cylinder turbulence according to the engine operating conditions.M.L.S Deva Kumar, S.Drakshayani, K.Vijaya Kumar Reddy et.al [6] worked on Effect of Fuel Injection Pressure on Performance of Single Cylinder Diesel Engine at Different Intake Manifold Inclinations. Now-a-days internal combustion engines play an important role in automobile field. There are various factors that influence the performance of engine such as compression ratio, atomization of fuel, fuel injection pressure, and quality of fuel, combustion rate, air fuel ratio, intake temperature and pressure and also based on piston design, inlet manifold, and combustion chamber designs etc. Growing demand on reduction of internal combustion engine fuel consumption with increase of its performance new designs and optimization of existing ones are introduced. Air motion in CI engine influences the atomization and distribution of fuel injected in the combustion chamber. Fuel injection pressure plays an important role in better atomization of injected fuel allows for a more complete burn and helps to reduce pollution. They work a single cylinder 5HP diesel engine is used to investigate the performance characteristics. The main objective of this work is to study the effect of the fuel injection pressure on performance and pollution of the single cylinder diesel engine at different intake manifold inclinations. They found that in cylinder flow structure is greatly influenced by the intake manifold inclination. It is found that at 600 intakes manifold inclination, at 180bar gives the maximum brake thermal efficiency. This work improves both performance and fuel economy. By varying the manifold inclination we get better performance than normal one. By increasing fuel injection pressure, pollution levels reduce due to complete combustion of fuel. They finally got that emissions are reduced at 200 bar with engine at 600 manifold inclinations at 180 bars has given efficient performance and less pollution. Different manifold inclinations compared to other pressures.

Raouf Mobasheri, Zhijun Peng et.al [7] has worked on CFD Investigation of the Effects of Re-Entrant Combustion Chamber Geometry in a HSDI Diesel Engine. They had conducted a CFD simulation to analyze the effects of combustion chamber geometry and pilot injection timing for optimization of engine performance and amount of pollutant emissions in a high speed direct injection (HSDI) diesel engine. The computed in-cylinder pressure, soot and NOx were firstly compared with experimental data under various ITs and good agreement between the predicted and experimental values was ensured the accuracy of the numerical predictions collected with the present work. To study the effects of combustion chamber geometry, thirteen different configurations were selected and analyzed compared to the original piston bowl geometry. The results showed that for shallower bowls, decreasing the bowl depth shows a higher amount of NOx emissions and a deep bowl depth combined with a shallow bowl centre depth is disastrous for fuel economy. It was also found that the narrower width of combustion chamber has a higher unburned fuel air mixture region, and thus would have higher soot emissions but with slightly wider combustion chamber the optimum operating point could be obtained. In addition, a potential has been found to improve the NOx emission compared to the baseline injection case while the engines specific fuel consumption emissions remain approximately unchanged and soot formation could be slightly increased. In order to investigate the effect of combustion chamber, thirteen different piston bowl configurations have been designed and analyzed. For all the studied cases, compression ratio, squish bowl volume and the amount of injected fuel were kept constant to assure that variation in the engine performance were only caused by geometric parameters. The results showed that by changing the geometric parameters on piston bowl, the amount of emission pollutants can be decreased while the other performance parameters of engine remain constant. Tomasz Leaski, Janusz Sczyk, Piotr Wolaski et.al [8] has worked on RESEARCH OF FLAME PROPAGATION IN COMBUSTION SYSTEM WITH SEMI-OPEN COMBUSTION CHAMBER FOR GASOLINE SI ENGINES. They had made some conclusions. They studied of flame propagation using the combustion system with semi-open combustion chamber, designed for SI engines, carried out using a rapid compression machine and an experimental visualization engine, allowed to interpret the phenomena occurring during combustion process. It was stated that the assumed mechanism of combustion in this system can be achieved only when the outflow of burning mixture and exhaust gases from the prechamber to the main combustion chamber, through the orifice in the partition, starts when the piston is near TDC position (approximately 100 CA in relation to TDC).If the pressure difference between the prechamber and the main combustion chamber, allowing the outflow from the prechamber into the main combustion chamber is achieved for the bigger value of crank angle, the cross-section area of the gap between the partition and the piston crown is much larger than the orifice area in the partition, so that the outflow occurs through the gap, what will be reflected in the deterioration of the system performance. A stream of burning mixture and exhaust gases outflowing from the prechamber to the main combustion chamber through the orifice in the partition should travel through the main combustion chamber with a velocity greater than the flame front velocity in the standard combustion chamber, what will be resulted in performance improvement. A key problem for the proper operation of the combustion system with semi-open combustion chamber is to choose the appropriate value of ignition advance angle, depending on engine operating parameters (especially the engine speed and load) and combustion system parameters (prechamber volume, diameter of the orifice in the partition, ignition place), which, at the moment, is possible by experimental testing only. Visualization researches enable to determine the direction of changes in the design and structure of the system with semi-open combustion chamber, necessary for achieving positive results of the system operation.K.M.Pandey and T.Sivasakthivel et.al [9] worked on CFD Analysis of Mixing and Combustion of a Scramjet Combustor with a Planer Strut Injector. They found that in order to investigate the flame holding mechanism of the planer strut in supersonic flow, the two-dimensional coupled implicit RANS equations, the standard k- turbulence model and the finite-rate/eddy-dissipation reaction model are introduced to simulate the flow field of the hydrogen fueled scramjet combustor with a strut flame holder under different conditions, namely the cold flow and the engine ignition. They observe that the numerical method employed in this paper can be used to accurately investigate the flow field of the scramjet combustor with planer strut flame holder, and capture the shock wave system reasonably. The static pressure of the case under the engine ignition condition is much higher than that of the case under the cold flow condition due to the intense combustion process. There are three obvious pressure rises on the top and bottom walls of the scramjet combustor because of the impingement of the reflected shock wave or the expansion wave on the walls. This illustrates that there exists the complex shock wave/shock wave interaction and the separation due to the interaction of the boundary layer and the oblique shock wave.Ariz Ahmad et.al [10] worked on Analysis of Combustion Chambers in Internal Combustion Engine. Here various types of combustion chambers in petrol engines, diesel engines, gas turbine, jet engines and steam engines and how they are different from each other in terms of their design, fluid flow characteristics and mechanisms had been studied. He found that Combustion chambers play a vital role in internal combustion engine. The amount of heat that is produced depends upon the shape and size of combustion chamber. For improving engine efficiency and performance the combustion chambers of different shapes and sizes are being developed by Vehicle manufacturers to have a lead in the competition. New innovations in engine combustions technology have been developed to tackle the challenges set by government and societies. He found some few limitations which are there can be a potential heat loss and pressure loss when fluid flows through large cross- section area of combustion chamber. Sometimes during cold weather an external device like glow plugs are required for ignition. Maintenance can be hazardous due to presence of residual fuel or gas during shut down. Sometimes due to high pressures there can be potential cracks developments in the chamber which can interrupt the fluid flow thus, can have a significant consequence in the whole process. CFD flow simulation on pressure as well as surface plot and cut plot animations were done on can type and jet type combustion chambers. CFD flow simulations can further be done other parameters like viscosity, force etc. which will be represented in future research.Stefan postrzednik, Zbigniew Zmudka et.al [11] had worked on IMPROVING OF IC ENGINE EFFICIENCY THROUGH DROPPING OF THE CHARGE EXCHANGE WORK. They found that regular growing of the relative work exchange load on IC engine causes dropping of the engine efficiency. On the basis of theoretical analysis and experimental results it has been calculated that the relative charge exchange work can achieve value up to 40 % at part load of the IC engine. As a consequence of the growing of the relative load exchange work is the regular and significant drop in the IC engine efficiency from 55% down to ca. 25%. The main reason of this is the throttling process occurring in the inlet and outlet channels. It is directly connected with the quantitative regulation method commonly used IC engines. Here a new concept of theoretical thermodynamic cycle (also called eco-cycle) of IC engine is presented, in which the method of diminishing the emission of toxic substances suggests that combustion of lean air-fuel mixture, multistage fuel injection, recirculation of flue gases, after burning of the combustible substances, loading of additional water into a cylinder. Using the proposed solution (eco-cycle) in engines with combustion of lean air-fuel mixture the 3 way catalyst can be applied. This proposed solution leads to the diminishing of toxic substance emission and simultaneously to improving the engine efficiency

1.3 . Design of Combustion Chamber of an IC EngineA Combustion Chamber is a part in which combustion of fuel or propellant, in particular, is initiated in internal combustion engine. Combustion chamber is one of the most important components of the internal combustion engine. The piston bowl geometry, nozzle position and spray behavior plays a predominant role in the engine performance. The most important role of IC engine combustion chamber is to enhance the fuel-air mixing rate (swirl) in short possible time. The turbulence can be guide by the shape of the combustion chamber hence there is necessity to study the combustion chamber geometry in detail. So, in the near future, we need a combustion chamber which will produce better fuel economy, lower hydrocarbons (HC) emissions, smoke, carbon monoxide (CO), greater brake thermal efficiency (BTE) and maximum cylinder pressure, which in turn increases the engine performance. Since there is a strong necessity of research and innovation in combustion chamber design as with advent of new technologies in engine and fuel type innovations, this is indispensable. Moreover, whatever is the type of fuel, technology or engine used in present or in future, combustion will be always there as through combustion of fuel only, power is generated. Hence study of combustion chamber is of prime importance. Here in this paper we will study the various factors (like detonation, scavenging, volumetric efficiency, engine speed, fuel air ratio, exhaust and emission smoke etc.) affecting the combustion chamber efficiency which in turn affect the engine performance and also their optimizations.1.3.1. Types of Combustion ChamberThere different types of combustion chambers of different shapes and sizes. Different types of combustion chamber used in petrol or gasoline engines are: (a) T - Head type: This configuration provides 2 valves on either side of the cylinder, requiring two cram shafts. (b) L-Head type: A modification of T-head type combustion chamber is the L Head type which provides 2 valves on the same side of the cylinder and the valves are operated by a single camshaft. (c) I - head type: It is also called overhead valve combustion chamber in which both the valves are located on the cylinder head.(d) F-Head type: This arrangement is a compromise between L-head and I head types. Combustion chamber in which one valve is in the cylinder head and the other on the cylinder block are known as F-head combustion chamber. In diesel engine the combustion chambers are divided based on the injection type used. There are two types of injection used namely: (a) Direct injection: Also called as open combustion chamber, in this type of combustion chamber, the entire volume of the combustion chamber is located at the main cylinder and the fuel is injected into this volume the main advantage is minimum heat loss during compression because of lower surface area to volume ratio and no cold starting problems. The main disadvantage is high fuel injection pressure and necessity of accurate metering of fuel by the injection system. (b) Indirect injection: This type of combustion chamber the combustion space is divided into 2 parts one is the main cylinder and other is the cylinder head. The main advantage is that the injection pressure required is low. Drawbacks are cold starting problems because of this we require heater plugs, specific fuel consumption is high because of loss of pressure.

Different types of Direct Injection combustion chambers are: Shallow depth chamber: The depth of the cavity in the piston is quite small. This chamber is adopted for large engines running at low speeds. Hemispherical chamber: The chamber gives a small squish. The depth to diameter ratio for this chamber can be varied to given any desired a squish to give better performance. Cylinder chamber: It is a form of truncated cone with a base angle of 30 degrees. The swirl was produced by making the inlet valve for nearly 180 degrees of circumference .Squish can also be varied by varying the depth. Toroidal chamber: It has such a shape so as to provide a powerful squish along with the air movement within the toroidal chamber. Mask needed for inlet valve is very small so as to provide the powerful squish.Different types of Indirect Injection combustion chambers are: Swirl chamber: Chamber in which swirl is generated. Pre-combustion chamber: Chamber in which combustion swirl is induced. Air cell chamber: Both combustion and compression are induced.1.3.2 Historic View of Combustion ChamberA. T-Head Combustion Chamber.Ford utilized this design in his famous model T introduced in 1908. The T-Head had the disadvantage of Having two camshafts. Being very prone to detonation, the distance across the combustion chamber was long. There was violent detonation even at compression ratio of 4. This was also because the average octane number of petrol available at that time was 45-50.

B. I-Head or Side valve Combustion Chamber.In the period 1910-30 the side valve engine was commonly used in petrol engines. In the side valve engines, valves are placed side by side and are in the block. A side valve engine has an advantage both from a manufacturing and maintenance point of view. It is easy to enclose and lubricate the valve mechanism, and the detachable head can be removed for decarbonizing without disturbing either the valve gear or the main pipe work. The side valve design also affords a neat and compact layout. In this original form, however, it gave a poor performance because of the following main defects: Lack of turbulence as the air had to take two right angle turns to enter the cylinder and in doing so lost much of this initial velocity. Extremely prone to detonation due to large flame length and slow combustion process due to lack of turbulence.

1.3.3 Combustion Chamber Design Principles To achieve high volumetric efficiency the largest possible inlet valve should be accommodate with ample clearance round the valve heads. To prevent detonation the length or flame travel from the sparkling plug to the farthest point in the combustion space should be as short as possible. This consideration involves the location of sparkling plug, the position of the valves and the shape of the combustion chamber. Again, to reduce the possibility of denotation there should not be a hot surface in the end gas region. Exhaust valve being a very hot surface should not be in the end gas region. It means that the exhaust valve should be near the sparkling plug. It would also avoid surface ignition. Because of the hot surface it presents, the exhaust valve should be kept small, but to compensate for this high lift should be employed. Short combustion time is the prime consideration in all SI combustion chamber designs. This is achieved by creating the highest flame front velocity through the creation of correct amount of turbulence. Proper turbulence may be created by suitable positioning the inlet valve and design of inlet passage and streamlining of combustion chamber. The other method of producing turbulence is by squish. Turbulence created by squish is better as it does not adversely affect the volumetric efficiency. The shape of the chamber should be such that the greatest mass of the charge burns as soon as possible after the ignition (consistent with a smooth application of force) with progressive reduction in the mass of charge burnt towards the end of combustion. To ensure high thermal efficiency and satisfactory initial combustion conditions the heat flow should be minimum in the zone around the sparkling plug. For minimum heat flow the surface-volume ratio should be least. A hemispherical shape provides minimum surface volume ratio. A low surface-volume ratio also gives less air pollution. In the end gas region surface-volume ratio should be large so that there should be good cooling in the detonation zone. In other words quench space should be formed in the end gas region. In other word to be able to extend the mixture range as far as possible on the weak side and more especially on reduced load, it is essential that the sparkling plug shall be positioned that it will be scoured of any residual exhaust products by the incoming charges. The exhaust valve head should be well cooled by a high velocity water stream around it as it is the hottest region of the combustion chamber. There should be sufficient cooling of the sparkling plug by high velocity water stream around it to avoid pre-ignition effects at the large throttle openings. A slight pocketing of the plug greatly increases electrode and decreases fouling. There should be good scavenging of the exhaust gases. Thickness of the walls should be uniform for uniform expansion. On manufacturing grounds, it is desirable to employ a plain flat topped piston. To achieve maximum thermal efficiency for a given grade of fuel the highest possible compression ratio must be employed. It means working should be near the borderline of detonation but detonation or rough working should not occur under all running conditions.

CHAPTER 2IC ENGINE COMBUSTION CHAMBER ANALYSIS

2. DIFFERENT APPROACH TO IC ENGINE ANALYSISIn this topic we are going thorough study on the analysis of combustion in IC Engine. Here we are studying about different problems that arise in internal combustion engines. In addition to that, we study about the different effects on internal combustion engine such as effects of super-charging, turbulence etc. The different problems which we may encounter in an IC Engine are discussed below. 2.1 . Factors Affecting IC Engine (a) Detonation and Knocking: Knocking, in an internal-combustion engine, is sharp sounds caused by premature combustion of part of the compressed air-fuel mixture in the cylinder. In a properly functioning engine, the charge burns with the flame front progressing smoothly from the point of ignition across the combustion chamber. However, at high compression ratios, depending on the composition of the fuel, some of the charge may spontaneously ignite ahead of the flame front and burn in an uncontrolled manner, producing intense high-frequency pressure waves. These pressure waves force parts of the engine to vibrate, which produces an audible knock. Knocking can cause overheating of the spark-plug points, erosion of the combustion chamber surface, and rough, inefficient operation. It can be avoided by adjusting certain variables of engine design and operation, such as compression ratio and burning time; but the most common method is to burn gasoline of higher octane number. Detonation (generally caused by fuel with a low octane rating) is the tendency for the fuel to pre-ignite or auto-ignite in an engine's combustion chamber. This early (before the spark plug fires) ignition of fuel creates a shock wave throughout the cylinder as the burning and expanding fuel air mixture collides with the piston that is still traveling towards top-dead-center. The resulting knock/ping is the sound of the pistons slamming against the cylinder walls. Severe detonation can break pistons and destroy engines. Generally knocking is observed in diesel engines and detonation is observed in petrol engines. Both the phenomenon occurs due to excessive rise of cylinder pressure in engine cylinder. The diesel engines with highly advanced injection timings allows air fuel mixture to burn with enough time creating uneven pressure on cylinder wall resulting in hammering effect which is termed as knocking .In petrol engines sometimes the air fuel mixture is burned due to the in cylinder temperatures or the cylinder wall temperatures which is called as pre-ignition also. Such phenomena results in high combustion pressures due to uneven distribution ignition flames resulting in detonation.(b) Volumetric efficiency: It is the ratio of the actual volume of the charge drawn in during the suction stroke to the swept volume of the piston. The amount of air taken inside the cylinder is dependent on the volumetric efficiency of an engine and hence puts a limit on the amount of fuel which can be efficiently burned and the power output. The value of volumetric efficiency of a normal engine lies between 70 to 80 percent, but for engines with forced induction it may be more than 100 percent. Naturally aspirated engines can have volumetric efficiencies of more than 100% by using properly designed induction piping, utilizing resonance in the induction pipe (by selecting the induction pipe length according to the rotation speed at which maximum VE is desired) as well as the inertia of the air mass in the induction piping. Using inertia effects requires high air speeds in the induction system, which is normally accompanied by high flow losses. By careful design and streamlining of the inlet port and valves, much of the losses can be reduced to an acceptable level. Resonance and inertia effects are normally only used in high speed sports engines, for example as found in many modern motorcycles.(c) Power and mechanical efficiency: The amount of work an engine exerts is measured in foot * pounds of torque. The amount of power that an engine can do is measured in horsepower or watts.1 horsepower = (550 FT * LB) / Sec = 746 Watts = 2,545 BTU / HourTo convert torque into horsepower: (Torque * RPM) / 5,252*NOTE* Horsepower will always equal torque at 5,252 rpm, torque will always be greater than horsepower under 5,252 rpm, and horsepower will always be greater than torque over 5,252 rpm.There are many different ways to find the efficiency of an engine, and many different parts of an engine that you can rate the efficiency.Thermal efficiency is the percentage of energy taken from the combustion which is actually converted to mechanical work. In a typical low compression engine, the thermal efficiency is only about 26%. In a highly modified engine, such as a race engine, the thermal efficiency is about 34%. Mechanical efficiency is the percentage of energy that the engine puts out after subtracting mechanical losses such as friction, compared to what the engine would put out with no power loss. Most engines are about 94% mechanically efficient.This means that for a stock engine, only 20% of the power in fuel combustion is effective.(d) Specific fuel consumption: Specific fuel consumption, abbreviated SFC, compares the ratio of the fuel used by an engine to a certain force such as the amount of power the engine produces. It allows engines of all different sizes to be compared to see which is the most fuel efficient. It allows manufacturers to see which engine will use the least fuel while still producing a high amount of power.There are different types of SFC: TSFC, thrust specific fuel consumption, and BSFC, brake specific fuel consumption, are two of the most common. TSFC looks at the fuel consumption of an engine with respect to the thrust output, or power, of the engine. Airplane engines, for example, can be compared to see which will produce the most thrust while using the least amount of fuel.TSFC is expressed in the amount of fuel needed to provide a certain thrust over a period of time. This formula is written as pounds of fuel per hour of thrust. There are disadvantages to this formula, however. The most fuel efficient engine may not always be the best choice. A more lightweight engine may cut down on the need for more fuel to power it, and thus be a better choice even if a heavier engine has a lower TSFC.BSFC is used to calculate and compare how fuel efficient a reciprocating engine is. The reciprocating engine is a type of engine that uses pistons to create the motion that powers the engine. The most common type is an internal combustion engine, found in most vehicles today.The formula for measuring BSFC is the fuel rate over power. The fuel rate is expressed as the fuel consumption of the engine in grams per second and power is expressed as the amount of power the engine produces written in watts. The final answer for calculating BSFC is typically expressed in grams per kilowatt-hour.While specific fuel consumption has its advantages, it has its disadvantages as well. While it allows engines of all sizes to be compared, resulting in a chart that shows the most efficient engine, it can also leave out other important factors. The engine design, what it will be used for, and where it will be used all affect the engine's performance and specific fuel consumption can only make an educated guess at which engine will perform the best.(e) Exhaust and smoke emission: Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline/petrol, diesel fuel, fuel oil or coal. It is discharged into the atmosphere through an exhaust pipe, flue gas stack or propelling nozzle. In spark-ignition engines the gases resulting from combustion of the fuel and air mixture are called exhaust gases. This exhaust smoke is basically consist of nitrogen (N2), water vapor (H2O), and carbon dioxide (CO2), carbon monoxide (CO) from incomplete combustion, hydrocarbons (HC), from unburnt fuel, nitrogen oxides (NOx) from excessive combustion temperatures, ozone (O3), and particulate matter (mostly soot). They also contain a very infinitesimal amount of Lead (Pb) and Sulphur Dioxide (SO2) Exhaust gas temperature (EGT) is important to the functioning of the catalytic converter of an internal combustion engine. It may be measured by an exhaust gas temperature gauge. EGT is also a measure of engine health. Since, after combustion, there a is large amount of loss of energy in the form of heat energy going out through the exhaust gases of the combustion chamber, so in order to reduce this loss the exhaust gases are recirculate and also turbocharger is used to recover the exhaust losses by boosting the intake pressure.(f) Turbulence: If the explosive charge (mixture of air and fuel) is quiescent prior to ignition, combustion will not be efficient. For the DESIGN of high speed engines, it is necessary to mix air and fuel thoroughly. Through mixing leads to efficient combustion. The mixing of fuel with air is known as turbulence which may be caused by the velocity of the gases through the inlet valve and by the shape of cylinder head.(g) Scavenging of Engine: Scavenging is the process of pushing exhausted gas-charge out of the cylinder and drawing in a fresh draught of air or fuel-air mixture for the next cycle. This process is essential in having a smooth running internal combustion engine. If scavenging is incomplete, the following stroke will mix with a mix of exhaust fumes rather than clean air. This may be inadequate for proper combustion which leads to poor running condition. Scavenging is equally important for both two-stroke and four-stroke engine. However, it is more difficult to achieve in two-stroke engines. It is also equally important for both petrol and diesel engines. To increase the scavenging potential, the entire path from intake to exhaust to tailpipe must be tuned in sync with each other. This will ensure that the air flow is never interrupted. The acceleration and deceleration of this exhaust gas is what will hinder the scavenging potential. For example fast flowing heads and a tunnel ram intake combined with a poorly planned camshaft and exhaust system will cause the system to slow down and speed up through its journey, thus reducing its scavenging potential. So, to increase the scavenging potential the air must maintain a positive linear acceleration curve.

2.2 Combustion in SI Engine 2.2.1 Stages of combustion(a) Ignition lag- There grows up, gradually at first, a small hollow nucleus of flames, much in the manner of a soap bubble.(b) Propagation- If the contains of the cylinder were at rest, this flame bubble would expand with steadily increasing speed until extended throughout the whole mass. In the actual engine cylinder, however the mixture is not at rest inject it is at high turbulence breaks the fundamental of flame into a ragged front, thus presenting far greater surface area from which heat is radiated, hence its advance is speeded up enormously. The rate at which the flame front travels in dependent primarily on the degree of turbulence, but its general direction of movement that of radiating outwards from the ignition point, it is not much affected.(c) After burning- Although the completion of the flame travel, it does not follow that at this point at whole of the heat of the fuel has been liberated, for even after the passage of the flame. Some further chemical adjustments due to reassociation, etc. and what is generally referred to as after burning, will is a greater or less degree continues throughout the expansion stroke.

2.2.2. Effect of Engine Variables on Ignition Lag(a) Fuel- The ignition lag depends on the chemical nature of the fuel. The higher the self-ignition temperature of the fuel, the longer is the ignition lag.(b) Mixture Ratio- The ignition lag is smallest for the mixture ratio which gives the maximum temperature. The mixture ratio is somewhat richer than the stoichiometric ratio.(c) Initial Temperature and Pressure- Increasing the intake temperature and pressure increasing the compression ratio and retarding the spark, all reduce the ignition lag.(d) Electrode Gap- The electrode gap is important from the point of view of the establishment of the nucleus of flame. If the gap is too small, quenching of the flame nucleus may occur and the range of fuel air ratio for the development of flame nucleus is reduced. The lower the compression ratio, the higher the electrode gap is required.(e) Turbulence- Ignition lag is not much affected by turbulence intensity turbulence is directly proportional to engine speed. Therefore increase in engine speed does not affect much the ignition lag, measured in mille seconds. Excessive turbulence of the mixture in the area of the spark plug is harmful, since it increases the heat transfer from the combustion zone and leads to unstable development of the nucleus of flame.

2.2.3. Effect of Engine Variables on Flame Propagation(a) Fuel-air ratio-With hydrocarbon fuels the maximum flame velocity accrue when mixture strength is 10% richer than stoichiometry. When the mixture is made leaner or is enriched and still more, the velocity of flame diminished. Scan mixtures release less thermal energy resulting in lower flame temp and flame speed. Very with rich mixtures have incomplete combustion (some C only burns to CO and not to CO2), which results in decrease of less thermal energy and hence flame speed is low.(b) Compression ratio-A higher compression ratio increases the pressure and temperature of the working mixture and decreases the concentration of residual gases. These favorable conditions reduce the ignition advance is needed. High pressure temperature of the compressed mixture also speed up the second phase of combustion increase in compression ratio increases the chances of engine to detonate.(c) Intake temperature and pressure-Increase in initial temperature and pressure increases the flame speed.(d) Engine load-With increase in engine load, the cycle pressures increases. Hence the flame speed increases poor combustion at low loads and necessity of the mixture enrichment are among the main disadvantage of SI engines which causes wastages of fuel and discharge of large amount of products of incomplete combustion like CO and poisonous products.(e) Turbulence-Turbulence accelerates chemical action by intimate mixing of fuel and O2 .hence turbulence allows the ignition advance to be reduced and therefore weak mixtures can be burnt. The increase of flame speed due to turbulence reduces the combustion time and hence minimizes the tendency to detonate. Turbulence increases the heat flow to the cylinder wall and in the limit excessive turbulence way extinguishes the flame. Excessive turbulence results in the more rapid pressure rise and the high rate of pressure causes the iron shaft to spring and rest of the engine vibrate with high periodicity, resulting in rough and vesting running of engine.(f) Engine size-The number of crank degrees required for frame travel will be about the same irrespective of engine size provide the engines are similar.

2.3 Knocking in SI EnginesKnocking(also calledknock,detonation,spark knock,pingingorpinking) in spark-ignitioninternal combustion enginesoccurs when combustion of theair/fuel mixturein the cylinder starts off correctly in response to ignition by thespark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.The fuel-air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for thefour-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive. Knocking, in an internal-combustion engine, sharp sounds caused by premature combustion of part of the compressed air-fuel mixture in the cylinder. In a properly functioningengine, the charge burns with the flame front progressing smoothly from the point of ignition across the combustion chamber. However, at highcompression ratios, depending on the composition of the fuel, some of the charge may spontaneously ignite ahead of the flame front and burn in an uncontrolled manner, producing intense high-frequency pressure waves. These pressure waves force parts of the engine to vibrate, which produces an audible knock. Knocking can cause overheating of the spark-plug points, erosion of the combustion chamber surface, and rough, inefficient operation. It can be avoided by adjusting certain variables of engine design and operation, such ascompression ratioand burning time; but the most common method is to burn gasoline of higheroctane number. 2.3.1. Various effect of engine variables on knock or detonations are as follow-(a) A low temperature(b) A low density(c) A long ignition delay(d) A non-reactive compositionThus the various engine variables affecting detonation can be classified under four factors, namely, the temperature factors, density factors, time factors and composition factors:(a) Temperature factors- increasing the temperature of the unburned mixture by a factor in design or operation will increase the possibility of knock in the SI engine because all combustion reaction leading to lower delay periods and grater formation of chemical species are accelerated by an increase in temperature loss. the temperature of the unburned mixture is increased by all the following factors:i) Raising the compression ratio- Increasing the compression ratio increases both the temperature and pressure (density of the unburned mixture).Increase in temperature reduces the delay period of the end gas. Increases in temperature as well as increase in pressure both lead to greater collisions of molecules resulting in greater formation of chemical species responsible for knocking. Hence in tendency to knock increases. For a given engine setting and fuel there will be a critical compression ratio above which knock occurs. This compression ratio is called the highest useful compression ratio. Materials with high heat conductivity coefficients such as aluminum alloys are desirable for high compression cylinder heads since a cool combustion chamber wall is essential for high compression without knock. However hot spot may develop because of poor circulation of the coolant or improper distribution of the metal. ii) Supercharging-It also increases both temperature and density. iii) Raising the inlet temperature-Delay period decreases, velocity of flame travel increases.iv) Raising the coolant temperature-delay period decreases.v) Increasing the load (opening the throttle)-An increase in the load increases the temperature of the cylinder and combustion chamber walls thereby raising mixture and end gas temperatures. Also the pressure of the charge is increased. Hence, the tendency to knock increases.vi) Raising the temperature of the cylinder and combustion chamber walls- The temperature o the end gas depends on the design of combustion chamber. Sparking plug and exhaust valve are two hottest parts in the combustion chamber and hence end gas should not be compressed against these.vii) Advancing the spark timing-When the spark is advanced, burning gas is compressed by the rising piston and therefore both temperatures and pressure (density) are increased. Thus tendency to knock increases with advanced spark timing and decreases with retarded spark timings, By retarding the spark timings the peak pressures are reached farther down on the power stroke and are thus of lower magnitude. If in a given engine the fuel quality is changed and knock takes place, retarding the ignition may eliminate the knock, but it will also reduce the engine power.(b) Density factors-Increase the density of the unburned mixture by any of the following methods will increase the possibility of knock in the engine.i) Increase the compression ratio.ii) Opening the throttle (increase the load)iii) Supercharging the engineiv) An increase in the inlet pressure increases the overall pressure during cycle. The high pressure in the end gas decreases the delay period which increases the tendency of the charge detonate. However n increase in the inlet pressure increases the flame velocity, which would reduce the tendency to detonate, but the first effect always predominates. Therefore, with increased pressure tendency to detonate always increases.v) Advancing the spark timings.

(c) Time factors-Increasing the time of exposure of the unburned mixture to auto-ignition conditions by any of the following factors will increase the possibility of knock in SI engines. i) Increasing frame travel distance- (combustion chamber design, spark plug position, engine size).the possibility of knock is increased by increasing the distance the flame has to travel in order to traverse the combustion chamber. Combustion chamber shape- In general, the more compact the combustion chamber, the better will be its anti-knock characteristics, since the flame travel and combustion time will be shorter. Further if the combustion chamber is highly turbulent, the combustion rate is high and consequently combustion time is reduced; this further reduces the tendency to knock. Location of spark plug A plug which is centrally located in the combustion chamber has minimum tendency to knock as the flame travel is minimum. The flame travel can be reduced by using two or more spark plugs. Location of exhaust valve-The exhaust valve should be located close to the spark plug so that it is not in the end gas region; otherwise there will be a tendency to knock. Engine size-The delay period is not very much affected by the size of the cylinder. However flame requires a longer time to travel across the combustion chamber of the large engine. The large engines therefore have a greater knocking tendency than smaller engines. The SI engine is therefore; generally limited to 100 mm bore.ii) Decreasing the turbulence of mixture- decreasing the turbulence of the mixture decreases the flame speed and hence increases the tendency to knock. Turbulence depends on the design of combustion chamber and one engine speed.iii) Decreasing the speed of the engine-A decrease in the engine speed decreases the turbulence of the mixture resulting in reduced flame speed. Also lower the engine speed, longer is the absolute time for the flame to traverse the cylinder which increases the time available for per flame reaction. Hence the tendency to knock is increased at lower speeds.

(d) Composition The properties of the fuel and the fuel air ratio are the primary means for controlling knock, once the compression ratio and the engine dimensions are selected.i) Octane rating of the fuel- The tendency of an engine to knock is very much affected by the properties of the fuel used. In general, lower the self-ignition temperature of the fuel or greater its pre-flame reactivity, the greater the tendency to knock. Octane number is the measure of resistance to knock. Paraffin series have the maximum and aromatic series the minimum tendency to knock. The naphthene series comes in between the two.The following is the general relationship between molecular structure of the puffins and knocking tendency. Increasing the length of the carbon chain increases the knocking tendency. Centralizing the carbon atoms decreasing the knocking tendency. Adding methyl group (CH3) to the side of the carbon chain in the centre or position to decreasing the knocking tendency.In aliphatic hydrocarbon, unsaturated compounds show lower lesser knocking tendency that the saturated hydrocarbons, with the exceptions of the ethylene, acetylene and propylene, thus acetylene (CC) knocks much more rapidly than ethane (C-C). Napthenes and aromatic show the following general relationship between molecular structure and knocking tendency. Napthenes have grater knocking tendency than the corresponding aromatics. With increasing double bond the knocking tendency reduces. Lengthening of side chains increases the knocking tendency whereas branching of side chains decreases the knocking tendency.In general, for most hydrocarbons a more compact molecular structure is associated with a lower tendency to detonate. The knocking characteristics of a fuel can be decreased by adding small amounts of additives called dopesii) Fuel-air ratio. The most important effect of fuel- air ratio is on the reaction time or ignition delay. When the mixture. When the mixture is nearly 10% richer than stoichiometric (fuel-air ratio=0.08) ignition lag of the end gas is minimum and the velocity of flame propagation is maximum. The former effect, however, very much predominates and the knocking tendency is found to be maximum. (At this point the power is maximum).By making the mixture leaner or richer (than F/A~0.08)the tendency to knock is decreased. A too rich mixture is especially effective in decreasing or eliminating the knock due to longer delay and lower temperature of compression.iii) Humidity of air-increasing atmospheric humidity decreases the tendency to knock by decreasing the reaction time. The trends of the most of the above factors upon the knocking tendency of an engine gives the summary of variables affecting detonation is the SI engine and shows whether the various factors can be controlled by the operator.iv) Effect of deposits incomplete combustion of fuel lead to deposit of ash on the walls of the combustion chamber, which re later on augmented by dirt in air, and by unscavenged additive products. The proportion of combustion heat which normally flows through the chamber walls may be largely absorbed by these deposits, and transferred back to the fresh charge. Also by reducing the clearance volume to deposits increases the compression ratio. With a given fuel, the tendency to knock will increase withy the time as the deposits build up and become increasingly effective. In other words the octane requirement of the engine rises.Combustion chamber with highly polished surfaces have a greater knocking tendency than those coated with light carbon deposits which increases the heat absorption characteristics, but appreciable carbon deposits increase knocking tendency as explained above.2.3.2 Effects of Detonationi) Noise and Roughness- Mild noise is seldom audible and is not harmful. When the intensity of the knock increases a loud pulsating noise is produced due to the development of a pressure wave which vibrates back and forth across the cylinder. The presence of vibratory motion causes crankshaft vibrations and the cylinder runs rough.ii) Mechanical Damage- In most cases of knocking a local and a very rapid pressure rise is observed with subsequent waves of large amplitude. This gives rise to increased rate of wear. Erosion of piston crown, in a manner similar to that of marine propeller blades by cavitation, occurs. The cylinder head and valves may also be pitted. Detonation is very dangerous in engines having high noise level. In small engines the knocking noise is easily detected and the corrected measures can be taken; but in large high duty engines, such as in aero-engines it is difficult to detect knocking noise and hence corrective measures cannot be taken. Hence severe detonation may persist for a long time which may ultimately result in complete wreckage of the piston.iii) Carbon deposits- Detonation results in increased carbon deposits.iv) Increase in heat transfer- knocking is accompanied by increase in the rate of heat transfer to the combustion chamber walls. The increase in heat transfer is due to two reasons. The minor reason is that the maximum temperature in a detonating engine is about 150C higher than in a non-detonating engine, due to rapid complete of combustion. The major reason for increased heat transfer is the scouring away of protective layer of inactive stagnant gas on the cylinder walls due to pressure waves. The inactive layer of gas normally reduces the heat transfer by protecting the combustion chamber walls and piston crown from direct contact with the flame.v) Decrease in power output and efficiency- due to increase in the rate of heat transfer the power output as well as efficiency of detonating engine decreases.vi) Pre-ignition- the increase in the rate of heat transfer to the walls has yet another effect. It may cause local overheating, especially of the sparkling plug, which may reach a temperature high enough to ignite the charge before the passage of spark, thus causing pre-ignition. A n engine detonation for a long period would most probably lead to pre-ignition and this is the real danger of detonation.

2.4. Governing Equations (a) The continuity equation

(b) The conservative form of momentum equation (X- Direction)

(Y-direction)

(Z-direction)

(c) The Conservation Form of the Energy Equation

2.5. Optimization of process parameter:In optimization of process parameter we will discuss the methods to reduce the effect of process parameter which are mentioned above in IC engine performance. The methods adopted for optimization of process parameters are:(a) For Knocking: Anantiknock agentis agasoline additiveused to reduceengine knockingand increase the fuel'soctane ratingby raising the temperature and pressure at which auto-ignition occurs. The mixture known as gasoline, when used in highcompressioninternal combustion engines, has a tendency to knock "engine knocking" (also called "pinging" or "pinking") and/or to ignite early before the correctly timed spark occurs (pre-ignition, refer toengine knocking).(b) For volumetric efficiency: With the use of the Helmholtz resonator improvement in thevolumetric efficiencyof the engine is done and also to help with engine sound attenuation. This is possible due to the special features of the Helmholtz resonator designs. Also turbocharged engines can easily achieve a volumetric efficiency over 100%. For naturally aspirated engines, higher volumetric efficiency is achieved by using resonators integrated with the inlet manifold design.(c) For Improving Internal Combustion Engine Efficiency and power: The practical methods and new technology that help in increasing the efficiency of the internal combustion engines are as follows: Regenerative braking: As braking a car or automobile wastes the kinetic energy in the form of heat, regenerative braking is ideal method when you want to brake your vehicle to control speed (like when going downhill). In this electromagnetic braking is done as small motors absorb the energy and convert it into battery energy. Variable Injection Timing: This is already used in Maritime engines. At low loads and speeds, the injection is advanced allowing same mean effective pressure to be maintained. This not only increases the efficiency of the engine as the scavenge pressure is maintained, it also allows for lower quality fuel to be burnt. Variable valve timing: In this method the exhaust and inlet valves opening and closing time can be varied, affecting the efficiency of the engine. This method can increase the efficiency by 4 to 5%. Cutting off cylinders: In large engines in cruising or going downhill, half of the cylinders can be cut off thus reducing fuel demand. It cannot be done on small engines as the engine would become rough. Turbochargers: A turbocharger is an exhaust gas recovery device that increases boost air pressure thereby optimizing combustion. It increases efficiency by 7 to 8%. Direct Fuel Injection: In previous engines, the fuel was mixed with air and injected, but nowadays fuel is directly injected into the combustion chamber and mixing takes place according to the profile of the combustion chamber. It increases efficiency by 11 to 13%. Twin spark plugs and multiple injectors: As the flame front starts from the spark plug and proceeds outward, some fuel remains unburnt as ejected before the flame front can reach it. In a twin spark plug cylinder two flame fronts are created, causing better combustion. Using the correct viscosity of lubricating oil, as viscous oil can result in losses due to friction. Integrated starter and generator systems: In this system the engine is immediately stopped when idling and started when the accelerator is pressed.(d) For Emissions: To Increase engine efficiency some after treatment technologies are used to control advanced combustion engine exhaust emissions. All engines that enter the vehicle market must comply with the Environmental Protection Agency's emissions regulations. Harmful pollutants in these emissions include: Carbon monoxide Nitrogen oxides Unburned hydrocarbons Volatile organic compounds (VOCs) Particulate matterThese exhaust after treatment technologies include: NOx absorbers and selective catalytic reduction (SCR) to control oxides of nitrogen (NOx) Oxidation catalysts to control hydrocarbons (HC). Particulate filters to control particulate matter (PM).(e) For complete scavenging: To maximize scavenging three types of scavenging methods are used: Cross flow scavenging. Backflow or loop scavenging. Uniflow scavenging.(f) For improved turbulence: To improve the turbulence inside the combustion chamber by forming grooves, channels or passages through the squish areas will further enhance in-cylinder turbulence followed by multi flame front combustion. The effects of the grooves, channels and passages cause the air-fuel charge to be in a greater state of turbulence prior to ignition in the combustion chamber, which will result quicker and complete clean burn combustion. These grooves or channels or passages after ignition direct the flame front to cause multipoint ignition during the combustion cycle.

2.6. Different features of ANSYS(a) Geometry: We use the Geometry cell to import, create, edit or update the geometry model used for analysis. All geometry-specific options are described here; not all will be available at all times. These options are in addition to the common options described in Common Context Menu Options and Transfer Context Menu Options. In geometry we can import and export geometry between different analysis process. We can also create geometry in CAD and import them.(b) Mesh: The Model cell in the Mechanical application analysis systems or the Mechanical Model component system is associated with the Model branch in the Mechanical application and affects the definition of the geometry, coordinate systems, connections and mesh branches of the model definition. When linking two systems, we cannot create a share between the Model cells of two established systems. We can generate a second system that is linked at the Model cell of the first system, but we cannot add a share after the second system has been created. Likewise, we cannot delete a link between the Model cells of two systems. The Mesh cell in Fluid Flow analysis systems or the Mesh component system is used to create a mesh using the Meshing application. It can also be used to import an existing mesh file.(c) Setup: The Setup cell is used to launch the appropriate application for that system. We can define the loads, boundary conditions, and otherwise can configure our analysis in the application. The data from the application will then be incorporated in the project in ANSYS Workbench, including connections between systems.(d) Solution: From the Solution cell, we can access the Solution branch of our application, and we can share solution data with other downstream systems (for instance, we can specify the solution from one analysis as input conditions to another analysis). If we have an analysis running as a remote process, we will see the Solution cell in a pending state until the remote process completes.(e) Result: The Results cell indicates the availability and status of the analysis results (commonly referred to as post-processing). From the Results cell, we cannot share data with any other system.

CHAPTER 3RESULT AND DISCUSSION

3. RESULT AND DISCUSSIONIn our project work we study a four stroke Internal Combustion engine combustion chamber. In this time we only study first two stroke i.e. suction and compression while the others will be studied in later stage. Here we analyze only the variation of velocity of fuel air mixture inside the combustion chamber with respect to crank angle rotation.

3.1. Geometry:We used geometry decomposition process in our work. Before understanding how the geometry is decomposed into different sub volumes, we have to understand the process of decomposition in Design Modeler. The various engine parameters can only be assigned after installing ICE. Since we do not have access to ICE in ANSYS, so we opted for installing IC tutorial II.msh.gz. Details of various geometry input parameters are Different engine parameters are given table 1.In our studies we used IC engines having parameters like connecting rod of length 200mm, crank radius 20mm, engine speed of 1800 rpm , minimum lift of 0.2 mm . By using geometry decomposition we have created a geometry having 5 faces namely 1 inlet face, 1 outlet face, 4 cylinder faces ,we have used 2 types of valves namely InValve and ExValve . We have also used symmetry face option with 3 faces. Figure 7 shows the final geometry of the combustion chamber.

3.2. Meshing:The approaches for meshing the chamber region are given below.i) Chamber Meshing: The chamber head-upper faces are selected as the input. Element type is set to Element Size. Element Size is equal to Reference Size, which is set in the IC Mesh Parameters dialog box. Behavior for this body part it is set to hard.ii) Valve meshing: Body Sizing of valve is done under Mesh. Geometry shows the number of bodies selected (ch-upper, ch-lower, ch-invalve1body, ch-exvalve1body). Type is set to Element Size. Element Size is equal to Reference Size, which is set in the IC Mesh Parameters dialog box. Behavior for this body part it is set to soft.iii) Interface Between Piston And Chamber meshing: Face Sizing is the sizing method used for this part. When we click on Face Sizing under Mesh in the Outline, we can see the details. Geometry of the upper face of piston body is selected as the input. Type is set to Element Size. Element Size is equal to Reference Size, which is set in the IC Mesh Parameters dialog box. Behavior for this body part it is set to hard.

3.3. Boundary conditioni) Model: We use k epsilon model in our study. One of the most prominent turbulence models is k-epsilon model. it has been implemented in most general purpose CFD codes and is considered the industry standard model. It has proven to be stable and numerically robust and has a well-established regime of predictive capability. For general purpose simulations, the k-model offers a good compromise in terms of accuracy and robustness. While standard two-equation models, such as the k- model, provide good predictions for many flows of engineering interest, there are applications for which these models may not be suitable. Among these are: Flows with boundary layer separation. Flows with sudden changes in the mean strain rate. Flows in rotating fluids. Flows over curved surfaces.ii) Inlet boundary conditions: In the inlet boundary condition, we put turbulent intensity 5% and hydraulic diameter 0.03 m. total temperature of the system is maintained at 300K.iii) Outlet boundary conditions: In the outlet boundary condition, we put turbulent intensity 8% and hydraulic diameter 0.03 m. total temperature of the system is maintained at 300K.

3.4 Result Discussion i) Actual Valve timing: The actual valve timing diagram is shown in the figure At 0 crank angle (CA) the piston is at top dead center (TDC) after compression. So, at 0 CA both intake and exhaust valves are closed as shown in Figure.In x-axis we plot crank angle in degrees and in y-axis we plot valve lift in mm.. Here the green coloured curve represents inlet valve lift and the black coloured curve represents exhaust valve lift. From the graph we see that the exhaust valve remains closed up to around 140 degree of crank angle rotation, then it starts lifting up and reaches its peak round 250 degrees of crank angle rotation and after that it starts declining and closes at around 350 degrees. Similarly for the inlet valve it remains closed up to around 350 degrees of crank angle rotation and then starts lifting up and reaches the peak position at around 450 degrees of crank angle rotation, then it closes at around 575 degrees of crank angle rotation. ii) Variation of velocity with different crank angle: We study the velocity variation of the air fuel mixture inside the combustion chamber of a four stroke engine with respect to crank angle rotation; and hereby we concentrate on the variations that occur in the first two strokes i.e. suction and compression. The air and fuel mixture enters the combustion chamber via the inlet manifold through the inlet valve. This is called the suction stroke. During this stroke the piston moves from TDC to BDC and the exhaust valve remains closed in ideal engine cycles during this time. But in actual engines due to valve overlapping both the valves remain open together for better performance of the engine. But increase in this valve overlap period causes the disadvantage that a small amount of fresh charge directly exits through the exhaust valve thus reducing the volumetric efficiency and increasing the unburnt hydrocarbon emissions. The crank angle rotation occurs from 0 to 180 during the suction stroke. After the maximum intake of air fuel mixture into the combustion chamber, the inlet valve is closed and this air fuel mixture is compressed by the piston moving from BDC to TDC, thereby increasing the pressure and temperature of the combustible mixture to a maximum value sufficient for combustion to occur. In this stroke the crank angle moves through 180 to 360, completing one rotation of the crankshaft.

1