Volumetric efficiency


Volumetric efficiency

Volumetric efficiency in internal combustion engine design refers to the efficiency with which the engine can move the "charge" into and out of the cylinders. More correctly, volumetric efficiency is a ratio (or percentage) of what volume of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions. Therefore, those engines that can create higher induction manifold pressures - above ambient - will have efficiencies greater than 100%. Volumetric efficiencies can be improved in a number of ways, but most notably the size of the valve openings compared to the volume of the cylinder and streamlining the ports. Engines with higher volumetric efficiency will generally be able to run at higher speeds (commonly measured in RPM) and produce more overall power due to less parasitic power loss moving air in and out of the engine. There are several standard ways to improve volumetric efficiency. A common approach for manufacturers is to use larger valves or multiple valves. Larger valves increase flow but weigh more. Multi-valve engines combine two or more smaller valves with areas greater than a single, large valve while having less weight. Carefully streamlining the ports increases flow capability. This is referred to as Porting and is done with the aid of an air flow bench for testing.

Today, automobile engines typically have four valves per cylinder. Many high performance cars in the 1970s used carefully arranged air intakes and "tuned" exhaust systems to "push" air into and out of the cylinders, making use of the resonance of the system. Two-stroke engines take this concept even further with expansion chambers that return the escaping air-fuel mixture back to the cylinder. A more modern technique, variable valve timing, attempts to address changes in volumetric efficiency with changes in speed of the engine: at higher speeds the engine needs the valves open for a greater percentage of the cycle time to move the charge in and out of the engine.

Volumetric efficiencies above 100% can be reached by using forced induction such as supercharging or turbocharging. With proper tuning, volumetric efficiencies above 100% can also be reached by naturally-aspirated engines. The limit for naturally-aspirated engines is about 120%, these engines are typically of a DOHC layout with four valves per cylinder.

More "radical" solutions include the sleeve valve design, in which the valves are replaced outright with a rotating sleeve around the piston, or alternately a rotating sleeve under the cylinder head. In this system the ports can be as large as necessary, up to that of the entire cylinder wall. However there is a practical upper limit due to the strength of the sleeve, at larger sizes the pressure inside the cylinder can "pop" the sleeve if the port is too large.

Volumetric Efficiency is frequently abbreviated as "VE" when discussing engine efficiency.

Volumetric "Efficiency" should in no way be construed to be a measure of engine efficiency, the thermal efficiency of the engine, although it may have an effect on it. For instance, when a standard gasoline engine is at idle or otherwise at less than full throttle, the effective compression ratio of the engine is reduced, resulting in reduced cylinder temperature and pressure during combustion. The thermodynamic laws which apply to all heat engines dictate that the engine will be therefore operating with less than its optimum thermal efficiency.


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • volumetric efficiency — [1] A comparison between the actual volume of fuel mixture drawn in on the intake stroke and what would be drawn in if the cylinder were to be completely filled. In practice, a normally aspirated car engine does not take in an amount of an equal… …   Dictionary of automotive terms

  • volumetric efficiency — …   Useful english dictionary

  • Efficiency — as a technical term may refer to: * Algorithmic efficiency, optimizing the speed and memory requirements of a computer program * Efficient energy use, useful work per quantity of energy ** Energy conversion efficiency, desired energy output per… …   Wikipedia

  • efficiency — [1] The accomplishment of something with the least amount of effort, energy, or fuel. [2] Output of a device, system, or activity, divided by the input necessary to create the output. In a compressor the efficiency would be the work output, as… …   Dictionary of automotive terms

  • Four-stroke engine — Four stroke cycle used in gasoline/petrol engines. The right blue side is the intake and the left yellow side is the exhaust. The cylinder wall is a thin sleeve surrounded by cooling liquid. A video montage of the Otto engines running at the… …   Wikipedia

  • Ceramic capacitor — In electronics, a ceramic capacitor is a capacitor constructed of alternating layers of metal and ceramic, with the ceramic material acting as the dielectric. The temperature coefficient depends on whether the dielectric is Class 1 or Class 2. A… …   Wikipedia

  • Manifold (automotive) — In automotive engineering, an intake manifold or inlet manifold is the part of an engine that supplies the fuel/air mixture to the cylinders. An exhaust manifold or header collects the exhaust gases from multiple cylinders into one pipe. The word …   Wikipedia

  • Turbocharger — A turbocharger, or turbo, is an air compressor used for forced induction of an internal combustion engine. Like a supercharger, the purpose of a turbocharger is to increase the mass of air entering the engine to create more power. However, a… …   Wikipedia

  • Internal combustion engine — The internal combustion engine is an engine in which the combustion of a fuel (normally a fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine, the expansion of the high temperature and high …   Wikipedia

  • Continuous variable valve timing — offers a unique ability to have independent control of the intake and exhaust valves in an internal combustion engine. For any engine load criteria, the timing of intake and exhaust can be independently programmed [1]. The main variations of… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.