EXHAUST SYSTEM OF COMBUSTION ENGINE

DEFINITION OF EXHAUST SYSTEM:Exhaust system is usually piping used to guide reaction exhaust gases away from combustion chamber. The entire system conveys burnt gases away from the engine and includes one or more exhaust pipes.The exhaust gas flow through:

Cylinder head to exhaust manifold. Exhaust manifold to muffler or silencer. Silencer to tail pipe.

Types of exhaust systems: Header back. Cat-back. Axle back.

Header back:Header back is aftermarket exhaust system, which include all the components from the outlet of the header to the final vent to open air.

Cat back:Cat-back exhaust systems replace exhaust components from the catalytic converter back. These systems typically include a muffler and tailpipe, but depending on the make and model, they can also come with a mid-pipe, X-pipe, H-pipe or a Y-pipe. Cat-back systems are among the most popular exhaust upgrades for several reasons.

Axle back:An axle-back exhaust system includes all the components from the rear axle to exhaust tip. Although cat-back and header-back systems can deliver more power gains, there are many benefits to opting for an axle-back system. A well designed axle-back exhaust system will provide power gains over the stock exhaust but is often less expensive than comparable cat-back or header-back systems. Axle-back exhausts are easier to install and can deliver the performance exhaust sound you want.

COMPONENTS OF EXHAUST SYSTEM Exhaust Manifold Exhaust Pipes Catalytic Converter Muffler The Tail Pipe

Exhaust Pipes: The exhaust pipes are responsible for transporting the burned exhaust

gases from the engine and the exhaust manifold and funneling them towards the car's tailpipe.

It can be cast iron or SS material. The pipes are used to create an effectively sealed pathway.

Types of pipes: There are basically two types:

Regular pipe Flexible pipe

Regular exhaust pipe is solid, typically available in straight lengths, bent configurations and elbows. Flexible exhaust pipe is flexible enough to bend with road conditions and accommodate thermal expansion of the system. The exhaust system may be sealed by welding joints or using exhaust clamps as a simple, effective way to seal overlapping pipes.

Exhaust Manifold:

An Exhaust Manifold is the upper end of the exhaust system.

It is attached directly to the side of the engine and is the first part of the exhaust system to receive the burned exhaust gases from the car's engine.

The exhaust manifold burns any fuel that was inadequately burned by the engine and funnels it down into the main exhaust system.

Due to high temperatures, excellent oxidation resistance, High-temperature strength, Thermal fatigue properties are required.

Catalytic Converter:

A catalytic converter is a device that uses a catalyst to convert three harmful compounds in car exhaust into harmless compounds.

• Hydrocarbons - in the form of unburned gasoline. • Carbon monoxide -formed by the combustion of gasoline.

Nitrogen oxides - created when the heat in the engine forces nitrogen in the air to combine with oxygen

Different catalysts:There are two different types of catalyst at work.

• Reduction Catalyst - first stage It uses platinum and rhodium to help reduce the (NO)x emissions. Example 2NO => N2 + O2 or 2NO2 => N2 + 2O2

• Oxidation Catalyst -second stage It uses platinum and palladium to help reduce the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them. Example 2CO + O2 => 2CO2

Pollutants from Car Exhaust:

• CO — carbon monoxide. The main source of CO in cities is the internal combustion engine, where it is produced by incomplete combustion.

• CO2 — carbon dioxide. The internal combustion engine contributes to the increased concentrations of CO2 in the atmosphere.

• (NO)x — nitrogen oxide forms when fuels are burned at high temperatures.

• HC — hydrocarbons. Much of the hydrocarbon fuel passes through the process unconsumed and is expelled into the atmosphere along with other exhaust fumes.

• Other pollutants such as C6H6 — Benzene and its derivatives and • SO2 — sulphur-dioxides are also present.

Muffler:• A muffler or silencer is a device for reducing the amount of noise emitted by

the exhaust of an internal combustion engine.• The main muffler absorbs the noise of the exhaust gas and is composed of an

outer shell, inner plates, inner pipes, end plates and other components.• It contains a deceptively simple set of tubes that are finely tuned to reflect the

sound waves produced by an engine so that they cancel each other out.

Design of muffler: Vector Muffler - for larger diesel trucks, uses many concentric cones. Spiral Baffle Muffler - for regular cars, uses a spiral-shaped baffle system.

Tail pipe:The tail pipe is end of the final length of exhaust pipe which ends with just a straight or angled cut where it vents to open air.

Importance of Exhaust System The exhaust system has three major functions:

To channel out the waste products of combustion out of the engine. To reduce the noise generated by the engine. To clean up the emissions, that are harmful to the environment. To reduce the pollution and to increase the efficiency of the engine.

Design criteria:An exhaust pipe must be carefully designed to carry toxic and/or noxious gases away from the users of the machine. Indoor generators and furnaces can quickly fill an enclosed space with poisonous exhaust gases such as hydrocarbons, carbon monoxide and nitrogen oxides, if they are not properly vented to the outdoors. Also, the gases from most types of machines are very hot; the pipe must be heat-resistant, and it must not pass through or near anything that can burn or can be damaged by heat. A chimney serves as an exhaust pipe in a stationary structure. For the internal combustion engine it is important to have the exhaust system "tuned" (refer to tuned exhaust) for optimal efficiency. Also this should meet the regulation norms maintained in each country. In China, China 5;In European countries, EURO 5; In India, BS-4, etc.

DESIGN OF EXHAUST SYSTEM

Summary:Formula SAE rules restrict the decibel output level of the car’s exhaust system to be less than 110 db. The Engine Control’s team is required to design, and fabricate and exhaust system which will meet FSAE’s rules, while maintaining the engine’s performance and efficiency.

Background:As a first year Formula SAE team with no prior exhaust design experience it is expected that the new design will improve over the past design using modern exhaust design principles. The current exhaust system underwent limited design with many weaknesses. One of the biggest downfalls of the current exhaust is the unequal length headers with lack of intermediate piping. Currently the exhaust gasses from each cylinder merge inside the muffler at different points inside the muffler body rather than merging at a certain point. A proper merge pipe should help to increase exhaust efficiency throughout the 6500 to 9500 RPM range where the engine will be spending most of its time. The current design is restrictive compared to many other teams’ designs which target for close to the noise level limit; the current muffler is close to 10 db under the current competition limit.

Problem Definition:To design a Formula SAE compliant exhaust system for CBR 600 that optimizes engine performance and efficiency while meeting the noise criteria outlined by Formula SAE rules.

Design Parameters:

Sound Level: The formula SAE rules state that the engines sound level must not surpass 110 db during any part of the competition. If the judges suspect excess exhaust noise after initial testing, a car may be retested at any point during the competition. The CBR 600 exhaust produces 94 db, while most aftermarket exhaust systems produce close to 100 db. When testing the current exhaust system values of about 101 db were consistent using the same measurement distances required during completion. This leaves a large amount of room for exhaust options as the noise level can be raised nearly 10 db over what it currently is. Most aftermarket exhaust systems produce great power gains with

just a 4 db increase in noise output. Below are the official 2012 Formula SAE noise measuring procedures.

B10.2 Noise Measuring Procedure

B10.2.1 The sound level will be measured during a static test. Measurements will be made with a free-field microphone placed free from obstructions at the exhaust outlet level, 0.5 m (19.68 inches) from the end of the exhaust outlet, at an angle of forty-five degrees (45°) with the outlet in the horizontal plane. The test will be run with the gearbox in neutral at the engine speed defined below. Where more than one exhaust outlet is present, the test will be repeated for each exhaust and the highest reading will be used

B10.2.4 Test Speeds The test speed for a given engine will be the engine speed that corresponds to an average piston speed of 914.4 m/min (3,000 ft/min) for automotive or motorcycle engines, and 731.5 m/min (2,400 ft/min) for “industrial engines”. The calculated speed will be rounded to the nearest 500 rpm. The test speeds for typical engines will be published by the organizers

B10.3 Maximum Sound Level The maximum permitted sound level is 110 dBA, fast weighting.

B10.4 Noise Level Re-testing At the option of the officials, noise can be measured at any time during the competition. If a car fails the noise test, it will be withheld from the competition until it has been modified and re-passes the noise test

Manifold Design:When designing the exhaust manifold for the FSAE car, a few crucial things are to be considered. The length of the pipe from where it exits the exhaust port to where both of the cylinder’s flows meet is known as the runner length. This runner length allows the horsepower/torque curves to be changed by varying them. A shorter runner will produce more peak HP, while the longer runner will shift the torque curve lower in the rpm band. It is estimated that the majority of competition will be run in the 6500 to 9500 RPM range. This is helpful to know, as the runner length can be tuned to perform best within the specified range.

Muffler Design:The main focus of muffler design is to meet the maximum sound requirements while maintaining engine performance and efficiency. The car’s system will be designed to utilize a sound absorption (straight through) type muffler rather than a sound canceling (baffled) muffler for the sole reason of increased flow from the absorption over the sound canceling muffler. The basics of this design revolve around the exhaust running through a perforated tube with filler material packed around it rather than running through chambers which muffle the sound. The filler material allows some of the sound to be absorbed into itself while maintaining good flow characteristics. The nature of this sound absorption muffler allows the noise level to be tuned with based on different filler materials inserted inside the case.

Flow Characteristics:Many performing 4 stroke motor bike exhausts in the recent years have developed expansion chambers designs to aid exhaust flow. When comparing the exhaust set-ups of these bikes to other 4 stroke vehicle their chassis layout allows for rather long exhaust runners. To optimize both exhaust flow and power output many performance exhausts have gone to a design that incorporates some sort of expansion chamber located close to the engine. Manufactures claim as much as a 8 percent increase in horsepower with the use of these header designs. The chamber creates a larger place for the expansions and contraction of exhaust gases much like a merge pipe in a modern 4-10 cylinder engine would. This merge pipe allows proper cylinder scavenging to occur where in an ordinary constant diameter pipe would not allow for this. Many of these expansion chambers lower the exhaust close to 1.5db which is also a benefit as a less restrictive muffler can then be used.

Materials of exhaust components:

Exhaust manifolds are generally simple cast iron or stainless steel units which collect engine exhaust gas from multiple cylinders and deliver it to the exhaust pipe.

Exhaust pipe is moderate ductility, excellent corrosion resistance and relatively low cost have made it a very popular exhaust system material. A commonly used grade developed in the 1960's for mufflers, type 409, is a chromium ferritic stainless steel having nominally 11% chromium and stabilized with titanium.

Muffler is moderate ductile ,excellent corrosion resistance and relatively low cost .A commonly used grade developed in the 1960`s for mufflers,

type 409, chromium ferritic stainless steel having normally 11% chromium and stabilized with titanium.