Exhaust system


An exhaust system is used to guide reaction exhaust gases away from a controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine and includes one or more exhaust pipes. Depending on the overall system design, the exhaust gas may flow through one or more of the following:
An exhaust pipe must be carefully designed to carry toxic and 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 machines are scorching; the pipe must be heat-resistant and not pass through or near anything that can burn or be damaged by heat. A chimney is an exhaust pipe in a stationary structure. For the internal combustion engine, it is important to have the exhaust system "tuned" for optimal efficiency. Also, this should meet the norms of the regulations in each country. In China, China 5; In European countries, EURO 5; In India, BS-4, etc.,

Motorcycles

In most motorcycles, all or most of the exhaust system is visible and may be chrome plated as a display feature. Aftermarket exhausts may be made from steel, aluminium, titanium, or carbon fiber.
Motorcycle exhausts come in many varieties depending on the type of engine and its intended use. A twin-cylinder bike may have independent exhaust sections, as seen in the Kawasaki EX250, or a single exhaust section known as a two-into-one. Four-cylinder machines, super-sport bikes like Kawasaki's ZX series, Honda's CBR series, Yamaha's YZF series, latterly titled R6 and R1, and Suzuki's GSX-R, often have a twin exhaust system. A "full system" may be bought as an aftermarket accessory, also called a 4-2-1 or 4–1, depending on its layout. In the past, these bikes would come as standard with a single exhaust muffler. This practice lasted until the early 2000s when EU noise and pollution regulations effectively forced companies to use other methods to increase the motorcycle's performance.

Trucks

In many trucks / lorries, all or most of the exhaust system is visible, often with a vertical exhaust pipe. Usually, in such trucks, the silencer is surrounded by a perforated metal sheath to avoid people getting burnt from touching the hot silencer. This sheath may be chrome plated as a display feature.
Part of the pipe between the engine and the silencer is often flexible metal industrial ducting, which helps to avoid vibration from the engine being transferred into the exhaust system. Sometimes, a large diesel exhaust pipe is vertical to blow the hot, toxic gas well away from people; in such cases, the end of the exhaust pipe often has a hinged metal flap to stop debris, birds, and rainwater from falling inside.
In former times, exhaust systems of trucks / lorries in Britain were usually out of sight underneath the chassis.

Two-stroke engines

In a two-stroke engine, such as that used on dirt bikes, a bulge in the exhaust pipe known as an expansion chamber uses the pressure of the exhaust to create a pump that squeezes more air and fuel into the cylinder during the intake stroke. This provides greater power and fuel efficiency. See Kadenacy effect.

Marine engines

With an onboard diesel or petrol engine, below-decks on marine vessels:-
  • Lagging the exhaust pipe stops it from overheating the engine room where people must work to service the engine.
  • Feeding water into the exhaust pipe cools the exhaust gas and thus lessens the back-pressure at the engine's cylinders. In marine service, the exhaust manifold is often integral to a heat exchanger that allows seawater to cool a closed system of freshwater circulating within the engine.

    Outboard motors

In outboard motors, the exhaust system is usually a vertical passage through the engine structure, and to reduce out-of-water noise, it blows out underwater, sometimes through the middle of the propeller.

Terminology

Manifold or header

In most production engines, the manifold is an assembly designed to collect exhaust gas from two or more cylinders into one pipe. In stock production cars, manifolds are often made of cast iron. They may have material-saving design features such as using the least metal, occupying the least space necessary, or having the lowest production cost. These design restrictions often result in a cost-effective design that does not do the most efficient job of venting the gases from the engine. Inefficiencies generally occur due to the nature of the combustion engine and its cylinders. Since cylinders fire at different times, exhaust leaves them at different times, and pressure waves from gas emerging from one cylinder might not be completely vacated through the exhaust system when another comes. This creates back pressure and restriction in the engine's exhaust system, restricting the engine's actual performance possibilities.
Regardless of the negative attributes of steel tube exhaust outlet configurations, engineers who design engine components choose conventional cast iron exhaust manifolds because they list positive attributes, such as an array of heat management properties and superior longevity to any other type of exhaust outlet design.
A header is a manifold specifically designed for performance. During design, engineers create a manifold without regard to weight or cost but instead for optimal flow of the exhaust gases. This design results in a header that is more efficient at scavenging the exhaust from the cylinders. Headers are generally circular steel tubing with bends and folds calculated to make the paths from each cylinder's exhaust port to the common outlet all equal length and joined at narrow angles to encourage pressure waves to flow through the outlet, not back towards other cylinders. In a set of tuned headers the pipe lengths are carefully calculated to enhance exhaust flow in a particular engine revolutions per minute range.
A common method of increasing an engine's power output is using upgraded headers. The increased power output is often due to a result of a larger cross-section area of the pipes and designing the pipe lengths so that the pressure wave assists in exhaust scavenging. For inline-four engines and V8 engines, exhaust manifolds are usually either a 4-2-1 design or a 4-1 design.
Headers are generally made by aftermarket automotive companies, but sometimes can be bought from the high-performance parts department at car dealerships. Generally, most car performance enthusiasts buy aftermarket headers made by companies solely focused on producing reliable, cost-effective, well-designed headers specifically for their cars. Headers can also be custom-designed by a specialty shop. Due to the advanced materials that some aftermarket headers are made of, this can be expensive. An exhaust system can be custom-built for many vehicles and generally is not specific to the car's engine or design except for needing to properly connect solidly to the engine. This is usually accomplished by correct sizing in the design stage and selecting a proper gasket type and size for the engine.

Catalytic converter

Some systems eliminate the catalytic converter. It is a U.S. legal requirement to have a catalytic converter. Converters may not be removed from a vehicle that is used only for "off-road" driving in the United States. The main purpose of a catalytic converter on an automobile is to reduce harmful emissions of hydrocarbons, carbon monoxide, and nitrogen oxides into the atmosphere. They work by transforming the polluted exhaust components into water and carbon dioxide. There is a light-off temperature from which catalytic converters start to be efficient and work properly.
Catalytic converters can cause back pressure if clogged or not designed for the required flow rate. In these situations, upgrading or removal of the catalytic converter can increase power at high revs. However, the catalytic converter is vital to the vehicle's emission control systems. Therefore, a non-standard product can cause a vehicle to be unroadworthy.

Piping

The piping that connects all of the individual components of the exhaust system is called the exhaust pipe. If the diameter is too small, power at high RPM will be reduced. Piping diameter that is too large can reduce torque at low RPM and can cause the exhaust system to be lower to the ground, increasing the risk of it being hit and damaged while the car is moving.
On cars with two sets of exhaust pipes, a crossover pipe is often used to connect the two pipes. Typical designs of crossover pipes are a perpendicular pipe or angled pipes that slowly merge and separate.

Muffler

Original equipment mufflers typically reduces the noise level from the tailpipe by bouncing sound waves off of the back, front, and sides of the muffler. They are designed to meet the maximum allowable noise level required by government regulations. However, some original equipment mufflers are a significant source of backpressure.
Glasspack mufflers are straight-through design mufflers that consist of an inner perforated tube, an outer solid tube, and fiberglass sound insulation between the two tubes. They often have less back pressure than original equipment mufflers, but are relatively ineffective at reducing sound levels. Another common type of muffler is the chambered muffler, which consists of a series of concentric or eccentric pipes inside the expansion chamber cavity. These pipes allow sound to travel into them and cause the sound waves to bounce off the closed, flat ends of the pipe. These reflections partially cancel each other out, reducing the sound level.
Resonators are sections of pipe that expand to a larger diameter and allow the sound waves to reflect off the walls and cancel out, reducing the noise level. Resonators can be used inside mufflers or as separate components in an exhaust system.