gasoline direct injection
TRANSCRIPT
GASOLINE DIRECT INJECTION
IN SI ENGINES
SUBMIT TED BY
B. PAVAN VISWANADH P. ASHOK KUMAR
Y06ME011, III/IV B. Tech Y06ME003, III/IV B. Tech
[email protected] [email protected]
Mobile No :9291323516 Mobile No: 9392320010
DEPARTMENT OF MECHANICAL ENGINEERING
V.R.SIDDHARTHA ENGINEERING COLLEGE
(AUTONOMOUS)
KANURU:: VIJAYAWADA-7 A.P.
ABSTRACT:
Fuel supply system in Spark Ignition Internal Combustion Engines plays an important role in the
output power of an engine as well as its performance in terms of fuel consumption. For many years, carburetor
systems are used for the spark ignition engines. Fuel injection method has proved to be a good alternative in
terms of lower emissions and better fuel consumption compared to the carburetor systems. Earlier (before 1990)
due to high initial cost, fuel injection system was used only in aircraft engines and racing cars only. But now,
due to pressure to control air pollution and because of advantages of better power fuel economy, gasoline I
njection is being offered in large number of Spark Ignition Engines. In this paper an attempt is made to compare
the different types of fuel supply systems for Spark Ignition Engines with special focus given on fuel injection
systems (MPFI & GDI).
Key Words:
SI -Spark Ignition
CI -Compression Ignition
MPFI - Multi Point Fuel Injection
MPI - Multi Port Injection
EFI -Electronic Fuel Injection
GDI - Gasoline Direct Injection
EGR -exhaust gas ratio
NOX -Oxides of nitrogen
ECU -Electronic control unit
1.0 Introduction: The different ways of fuel supply in SI Engines are: i) Carburetor System ii) Fuel injection
Carburetor System is a proven technology for many years and is adopted is almost all SI Engines until 1990's. Due to the growing demand for energy conservation and control of pollutants, the fuel injection system has came in to lime light and is the widely used system for SI Engines over the last decade. In this method fuel i.e., gasoline is injected in the intake ports/manifolds of the engine and is quite commonly referred as MPI or MPFI.
In a way to further improve the performance of the SI Engine and better control of pollutants, an improved fuel injection method called GDI (Gasoline Direct Injection) has been focused for the development of SI Engines. In the GDI method, fuel is been directly injected into the cylinder like in CI
Engines.
2.0 Fuel Supply Systems :
The different possible fuel supply systems for SI Engines are described as follows:
2.1 Carburetor System:
In this method air and fuel are mixed in the required quantities in a device called carburettor before
supplying to the engine cylinder. Many complex subsystems are required for the effective working of
the engine as the engine is subjected to various operating conditions in practice. Even by using a modern
carburettor, which has many features, it still has some drawbacks as explained below:
In multi-cylinder engines the mixture supplied to various cylinders varies in quality and quantity since the induction passages are of unequal lengths and offer different resistances to mixture flow. The mixture proportion is also affected due to fuel condensation in induction manifold.
Carburettors, with their choke tubes, jets, throttle valves, inlet pipe bends, etc., do not give a free flow passage for the mixture. Thus there is loss of volumetric efficiency on this account.
The carburettor has many wearing part. After wear it operates less efficiently.
Freezing may take place at low temperatures, unless special means are provided to obviate this.
Surging of the fuel takes place when the carburettor is tilted or during acrobatics in aircraft, unless special means are adopted to avoid this.
Vapor lock in the fuel systems may result in hot weather.
There is possibility of back fire in intake manifold and popping in the carburettor in cold weather unless the flame traps or fitted. it involves and additional complications which tend to reduce the volumetric efficiencies.
All the above points lead to lower fuel consumption and improper utilization of engine capacity
2.2 Fuel injection:
The three different types of fuel injection methods are:i) Multi point fuel injection (MPFI) ii) Gasoline direct injection (GDI)iii) Electronic fuel injection (EFI)
2.2.1 Multi Point Fuel Injection: This MPFI system is to supply the proper ratio of gasoline and air to cylinders. These systems function under two basic arrangements, namely
i) Port injection ii) Throttle body injection
PORT INJECTION THROTTLE BODY INJECTION
In the port injection arrangement the injector is placed on the side of intake manifold near the intake port .The injector sprays gasoline into the air, inside intake manifold.
In the throttle body injection system an injector is placed slightly above the throat of the throttle body .The injector sprays gasoline into the air in the intake manifold.
The advantages of MPFI over the carburettor system can be summarized as follows:
Increased volumetric efficiency and hence increased power and torque, due to the absence of any restriction such as ventures and other metering elements in the air passage.
Better distribution of mixture to each cylinder and hence lower specific fuel consumption.
Lower mixture temperatures in the engine cylinders, despite the increase in power developed and hence possibility of employing higher compression ratios.
Engines fitted with gasoline injection system can be used in any tilt position, which will cause surge trouble in carburettors.
Even in MPFI Engines there are limits to fuel supply response and the combustion control because the fuel mixes with air before entering the cylinder.
2.2.2: Gasoline Direct Injection (GDI)
Gasoline engines work by inhaling a mixture of gasoline and air into a cylinder, compressing it with a piston, and igniting it with a spark; the resulting explosion drives the piston downwards, producing power. Traditional (indirect) fuel injection systems pre-mix the gasoline and air in a chamber just outside the cylinder called the intake manifold. In a direct-injection system, the air and gasoline are not pre-mixed; air comes in via the intake manifold, while the gasoline is injected directly into the cylinder. In these lines, the efforts of Mitsubishi Motors have come to reality and in near future we can see all the commercial medium & high powered SI engines adopting GDI system.
The required technical features to incorporate GDI system are as follows:
Upright straight intake ports for optimal airflow control in the cylinder.
Curved-top pistons for better combustion.
High-pressure fuel pump to feed pressurized fuel into the injectors.
2.2.3 Electronic fuel injection:
Modern gasoline injection systems use engine sensors, a computer and solenoid operated fuel injectors to meter and inject the right amount of fuel into the engine cylinders this systems are called An Electronic Control Unit (ECU) receives the signals from the sensors and determines the opening time for the injectors. The pulse width is an indication of the period for which injector is energized and kept open. The computer decides and controls the injector pulse width based on the signals received from various sensors.
Improvement in volumetric effiency, manifold wetting is eliminated due to fuel being injected into or close to cylinder and need not flow through the manifold, formation of ice on the throttle is eliminated , better atomization and vaporization will make the engine less knock prone. There is a cold start injector which ensures easy engine start up in very cold weather. Although it has advantages it also has disadvantages such as high maintenance cost, difficulty in servicing, possibility of malfunctioning of some sensors.
3.0 Characteristics of GDI and MPFI Engines:
3.1 Lower fuel Consumption Mode:
In conventional gasoline engines, dispersion of an air-fuel mixture with the ideal density around the spark plug was very difficult. However, this is possible in the GDI engine. Further more, extremely low fuel consumption is achieved because ideal stratification enables fuel injected late in the compression stroke to maintain an ultra-lean air-fuel mixture.
Ultra-lean Combustion Mode : Under most normal driving conditions, up to speeds of 120 km/h, the GDI engine operates in ultra-lean combustion mode for less fuel consumption. In this mode, fuel injection occurs at the latter stage of the compression stroke and ignition occurs at an ultra-lean air-fuel ratio of 30 to 40.
Fuel Consumption During Idling : The GDI engine maintains stable combustion even at low idle speeds. Moreover, it offers greater flexibility in setting the idle speed. Compared to conventional engines, its fuel consumption during idling is 40% less.
Fuel Consumption during Cruising Drive : At 40 km/h, for example, the GDI engine uses 35% less fuel than a comparably sized conventional engine.
Fuel Consumption in City Driving : The GDI engine used 35% less fuel than comparably sized conventional gasoline engines. Moreover, these results indicate that the GDI engine uses less fuel than even diesel engines.
Emission Control: Previous efforts to burn a lean air-fuel mixture have resulted in difficulty to control NOx emission. However, in the case of GDI engine, 97% NOx reduction is achieved by utilizing high-rate EGR (Exhaust Gas Ratio) such as 30% that is allowed by the stable combustion unique to the GDI as well as a use of newly developed lean-NOx catalyst.
3.2 Superior Output Mode:
During high power conditions, fuel is injected during the intake stroke. This enables a homogenous, cooler air fuel mixer that minimized the possibility of engine knocking and there by delivering higher output.
Improved Volumetric Efficiency: Compared to conventional engines, the GDI engine provides better volumetric efficiency. The upright straight intake ports enable smoother air intake.
Increased Compression Ratio: The cooling of air inside the cylinder by the vaporization of fuel has another benefit, to minimize engine knocking. This allows high compression ratio of 12, and thus improved combustion efficiency.
In high-output mode, the GDI engine provides outstanding acceleration.
Compared to conventional MPI engines of a comparable size, the GDI engine provides approximately 10% greater outputs and torque at all speeds.
4.0 Comparisons between GDI and MPFI Engines :A detailed comparative study of the two fuel injection systems has been made and is shown in the following graphs.
4.1 Variation of fuel economy with air fuel ratio
4.2 Variation of cylinder pressure and rate of heat release with crank angle
4.3 Variations in torque and fuel consumption with A/F ratio
4.4 Comparisons of emissions
4.5 Variation of volumetric effiency and Fuel consumption with speed
5.0 CONCLUSIONS : By looking at the various fuel supply systems for SI engines, it can be concluded that fuel injection systems has wide advantages compared to conventional carburettor system. This is the reason why all most all cars in the world have been using this technology over the last decade. As the GDI technology proved to be efficient in terms of fuel consumption and controlled emissions, the SI engines in near future will adopt this. The limitations for this technology being, initial cost of the system, increased service problem as it has many wearing parts and they generate more noise. Over coming the above drawbacks in near future one can see GDI SI Engines on roads.
REFERENCES:
1. Internal Combustion Engines by V.Ganesan2. http://www.howstuffworks.com3. Internal Combustion Engines by H.N.Gupta4. Internal Combustion Engines by M.L. Mathur & R.P.Sharma