Tuned exhaust

tuned exhaust system is an exhaust system for an internal combustion engine which improves its efficiency by using precise geometry to reflect the pressure waves from the exhaust valve or port back to the valve or port at a particular time in the cycle.

Ferrari V10 engine showing one of its two tuned extractor manifolds

Two-stroke engines

Yasuni aftermarket motor scooterexhaust system. The exhaust passes first through the expansion chamber at the bottom and then exits through the muffler above it.

A conceptual animation of a two-stroke engine with a tuned exhaust system using an expansion chamber. Exhaust gases are in grey, fuel/air mixture is green. In practice the fuel/air mix is unlikely to progress as far down the exhaust pipe as shown.

In many two-stroke engines, the exhaust port is opened and closed directly by the position of the piston rather than by a separate valve, which restricts the timing of its operation; Typically, the port remains open long after is optimum, allowing some of the incoming charge to escape. This can be partly addressed by use of a tuned exhaust system to deliver a pulse of positive pressure prior to the port closing, to retain the charge.

Alternatives

Direct-injection two-stroke diesel engines tend to use exhaust valves actuated either by camshafts or electronic control, rather than exhaust ports. This system is called uniflow scavenging. Opposed piston engines are inherently uniflow-scavenged, but these do use piston-controlled cylinder ports. Two-stroke opposed piston engines such as the Napier Deltic and Junkers Jumo 204 engines use one piston to control the inlet port and the other the exhaust, allowing more flexibility in timing. A variation of this approach is taken by the split-single engine, in which two cylinders share one combustion chamber, with the piston in one cylinder controlling the transfer portand the other the exhaust port.

Four-stroke engines

Extractor manifolds

Most non-turbo performance cars and high-performance four-stroke motorcycles use extractor manifolds (headers in American English), as do most non-turbo racing cars. Extractor manifolds are also available as aftermarket accessories to suit many engines.

Extractor manifolds offer the following advantages over the simple manifolds often fitted to non-performance engines:

  • Separating the gas flows from the individual cylinders so that undesirable inter-cylinder interference is avoided.
  • Maintaining an optimum gas velocity by carefully chosen tube diameter.
  • Allowing the individual cylinders to assist one another by means of the negative pressure waves generated at the collector, where the individual exhausts merge.[1]

This type of exhaust system can be used with or without a muffler, and so can be used on both race and road vehicles.

Aftermarket extractor manifold
Rotax 912s aero engine showing the tuned exhaust system
Collector on a racing car
Zoomie headers on a dragster

References

  1. The Design and Tuning of Competition Engines, Philip H. Smith, pp137-138
Exhaust gas Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline, petrol, biodiesel blends, diesel fuel, fuel oil, or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack, or propelling nozzle. It often disperses downwind in a pattern called an exhaust plume. It is a major component of motor vehicle emissions (and from stationary internal combustion engines), which can also include: Crankcase blow-by Evaporation of unused gasoline Motor vehicle emissions contribute to air pollution and are a major ingredient in the creation of smog in some large cities. A 2013 study by MIT indicates that 53,000 early deaths occur per year in the United States alone because of vehicle emissions. According to another study from the same university, traffic fumes alone cause the death of 5,000 people every year just in the United Kingdom. This diesel-powered truck emits an exhaust gas...
Exhaust system An exhaust system is usually piping 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: Cylinder head and exhaust manifold A turbocharger to increase engine power. A catalytic converter to reduce air pollution. A muffler (North America) / silencer (UK/India), to reduce noise. Exhaust manifold (chrome plated) on a car engine Muffler and tailpipe on a car Design criteria Exhaust system of the Opel Corsa B 1.2 petrol An exhaust pipe must be carefully designed to carry toxic and/or noxious gases away from the users of the machine. Indoor generatorsand furnaces can quickly fill an enclosed space with poisonous exhaust gases such as hydrocarbons, carbon monoxide and nitrogen oxides, if they are not properly ven...
Diesel particulate filter A diesel particulate filter (DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine. A diesel particulate filter (top left) in a Peugeot Off-road - DPF Installation Mode of action Wall-flow diesel particulate filters usually remove 85% or more of the soot, and under certain conditions can attain soot removal efficiencies approaching 100%. Some filters are single-use, intended for disposal and replacement once full of accumulated ash. Others are designed to burn off the accumulated particulate either passively through the use of a catalyst or by active means such as a fuel burner which heats the filter to soot combustion temperatures. This is accomplished by engine programming to run (when the filter is full) in a manner that elevates exhaust temperature, in conjunction with an extra fuel injector in the exhaust stream that injects fuel to react with a catalyst element to burn off accumulated soot in ...
Expansion chamber On a two-stroke engine, an expansion chamber or tuned pipe is a tuned exhaust system used to enhance its poweroutput by improving its volumetric efficiency. Scooter exhaust with expansion chamber and silencer History Direct comparison between different types of exhausts for the two-stroke engine, on the left you can see the engine and its exhaust, in the center the progression curves of the pressures (effective pressure in atmospheres) to the exhaust port (detection area highlighted in red), on the right the power curves of the various drains. A) Traditional discharge with constant section B) Discharge with divergent section C) Resonant expansion chamber with expansion chamber, in the power graph the influence of the exhaust back pressure valve is also highlighted Expansion chambers were invented and successfully manufactured by Limbach, a German engineer, in 1938, to economize fuel in two stroke engines. Germany was running short of petrol, which was at ...
Exhaust manifold In automotive engineering, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe. The word manifoldcomes from the Old English word manigfeald (from the Anglo-Saxon manig  and feald ) and refers to the folding together of multiple inputs and outputs (in contrast, an inlet or intake manifold supplies air to the cylinders). 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. For many engines, there are aftermarket tubular exhaust manifolds known as headers in American English, as extractor manifolds in British and Australian English, and simply as "tubular manifolds" in British English.These consist of individual exhaust headpipes for each cylinder, which then usually converge into one tube called a collector. Headers that do not have collectors are called zoomie headers. The most common types of aftermarket headers are made of mil...