Volumetric efficiency

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Volumetric efficiency

Volumetric efficiency in internal combustion engine

Internal combustion engine

The internal combustion engine is an engine in which the combustion of a fuel occurs in a combustion chamber inside and integral to the engine. In an internal combustion engine it is always the expansion of the high temperature and pressure gases that are produced by the combustion which apply force to the movable component of the engine, such as...
design

Design

Design is used both as a noun and a verb. The term is often tied to the various applied arts and engineering . As a verb, "to design" refers to the process of originating and planning for a product, structure, system, or component with intention....
refers to the efficiency with which the engine can move the charge into and out of the cylinders

Cylinder (engine)

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Volumetric efficiency in internal combustion engine

Internal combustion engine

Design

Cylinder (engine)

A cylinder is the central working part of a reciprocating engine, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically casting from aluminum or cast iron before precision features are machined into it....
. 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

Poppet valve

A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem....
or multiple valves

Multi-valve

In automotive engineering, an engine is referred to as multi-valve when each cylinder has more than two poppet valve. Such designs have been around since at least 1912 and perhaps earlier....
. 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

Cylinder head porting

Cylinder head porting refers to the process of modifying the intake and exhaust ports of an internal combustion engine to improve the quality and quantity of the gas flow....
and is done with the aid of an air flow bench

Air flow bench

An air flow bench is a device used for testing the internal aerodynamic qualities of an engine component and is related to the more familiar wind tunnel....
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

Resonance

In physics, resonance is the tendency of a system to oscillate at maximum amplitude at certain Frequency, known as the system's resonance frequencies ....
of the system. Two-stroke engines take this concept even further with expansion chamber

Expansion chamber

An Expansion chamber is an exhaust system used on a two-stroke cycle engine to enhance its power output by improving its volumetric efficiency....
s that return the escaping air-fuel mixture back to the cylinder. A more modern technique, variable valve timing

Variable valve timing

Variable valve timing, or VVT, is a generic term for an automobile piston engine technology. VVT allows the lift, duration or timing of the intake or exhaust Poppet valve to be changed while the engine is in operation....
, 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

Forced induction

Forced induction is a term used to describe internal combustion engines that are not naturally-aspirated engine. A gas compressor is added to the air intake instead, thereby increasing the quantity of oxygen available for combustion....
such as supercharging

Supercharger

A supercharger is an air Gas compressor used for forced induction of an internal combustion engine. The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally-aspirated engine, which allows more fuel to be provided and more work to be done per cycle, increasing the power output of the engine...
or turbocharging

Turbocharger

A turbocharger, or turbo, is a gas 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....
. With proper tuning, volumetric efficiencies above 100% can also be reached by naturally-aspirated engine

Naturally-aspirated engine

A naturally-aspirated engine is a piston engine internal combustion engine that depends solely on atmospheric pressure to draw in combustion air....
s. The limit for naturally-aspirated engines is about 120%, these engines are typically of a DOHC

Overhead camshaft

Overhead camshaft, commonly abbreviated to OHC, valvetrain configurations place the engine camshaft within the cylinder heads, above the combustion chambers, and drive the poppet valve or tappets in a more direct manner compared to overhead valves and pushrods....
layout with four valves per cylinder

Multi-valve

Sleeve valve

The sleeve valve is a type of valve mechanism for piston engines, distinct from the more common poppet valve. They saw use in some pre-World War II luxury cars, sports cars, the Willys-Knight car and light truck, and saw substantial use in aircraft engines of the 1940s, such as the Napier Sabre and Bristol Hercules and Bristol Centaurus....
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

Engine efficiency

Engine efficiency of thermal engines is the relationship between the total energy contained in the fuel, and the amount of energy used to perform useful work....
, the thermal efficiency

Thermal efficiency

In thermodynamics, the thermal efficiency is a Dimensionless quantity performance measure of a thermal device such as an internal combustion engine, a boiler, or a furnace, for example....
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

Compression ratio

The compression ratio of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber; from its largest capacity to its smallest capacity....
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

Thermal efficiency

In thermodynamics, the thermal efficiency is a Dimensionless quantity performance measure of a thermal device such as an internal combustion engine, a boiler, or a furnace, for example....
.