Volumetric efficiency (VE) in
internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
engineering is defined as the
ratio
In mathematics, a ratio shows how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons is eight to six (that is, 8:6, which is equivalent to the ...
of the
mass density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematically ...
of the
air-fuel mixture drawn into the cylinder at atmospheric pressure (during the intake stroke) to the mass density of the same volume of air in the intake manifold. The term is also used in other engineering contexts, such as
hydraulic pumps and electronic components.
Internal combustion engines
Volumetric efficiency in an internal combustion engine design refers to the efficiency with which the engine can move the ''charge'' of fuel and air into and out of the
cylinders. It also denotes the ratio of air volume drawn into the cylinder to the cylinder's swept volume. More specifically, volumetric efficiency is a ratio (or percentage) of the mass of air and fuel that is trapped by the cylinder during induction divided by the mass that would occupy the displaced volume if the air density in the cylinder were equal to the ambient air density. The flow restrictions in the intake system create a pressure drop in the inlet flow which reduces the density (unless boosts like turbos or superchargers or cam tuning techniques are used). Volumetric efficiency can be improved in a number of ways, most effectively this can be achieved by compressing the induction charge (
forced induction
In an internal combustion engine, forced induction is where turbocharging or supercharging is used to increase the density of the intake air. Engines without forced induction are classified as naturally aspirated.
Operating principle Overvi ...
) or by aggressive cam phasing in naturally aspirated engines as seen in racing applications. In the case of forced induction volumetric efficiency can exceed 100%.
There are several ways to improve volumetric efficiency, but system-wide approaches are used to realize its full potential.
Many high
performance car {{Unreferenced, date=June 2019, bot=noref (GreenC bot)
A performance car is a car that exhibits above-average capabilities in one or more of the following areas: acceleration, top speed, cornering and braking. It is debated how much performance is ...
s use carefully arranged air intakes and
tuned exhaust
In an internal combustion engine, the geometry of the exhaust system can be optimised ("tuned") to maximise the power output of the engine. Tuned exhausts are designed so that reflected pressure waves arrive at the exhaust port at a particular t ...
systems that use pressure waves to push air into and out of the cylinders, making use of the
resonance
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...
of the system.
Two-stroke engine
A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being completed in one revolution of ...
s are very sensitive to this concept and can use
expansion chamber
On a two-stroke engine, an expansion chamber or tuned pipe is a tuned exhaust system used to enhance its power output by improving its volumetric efficiency.
History
Expansion chambers were invented and successfully manufactured by Limbach, a ...
s that return the escaping
air-fuel mixture back to the cylinder. A more modern technique for
four-stroke engine
A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either directi ...
s,
variable valve timing
In internal combustion engines, variable valve timing (VVT) is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with varia ...
, 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
In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement.
The current categorisation is that a supercharger is a form of forced induc ...
or
turbocharging
In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pr ...
. With proper tuning, volumetric efficiencies above 100% can also be reached by
naturally aspirated engines. The limit for naturally aspirated engines is about 130%; these engines are typically of a
DOHC
An overhead camshaft (OHC) engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion c ...
layout with
four valves per cylinder. This process is called
inertial supercharging and uses the resonance of the intake manifold and the mass of the air to achieve pressures greater than atmospheric at the intake valve. With proper tuning (and dependent on the need for sound level control), VE's of up to 130% have been reported in various experimental studies.
[SAE 860032 "Optimization of multi valve four cycle engine design"]
More "radical" solutions include the
sleeve valve
The sleeve valve is a type of valve mechanism for piston engines, distinct from the usual poppet valve. Sleeve valve engines saw use in a number of pre-World War II luxury cars and in the United States in the Willys-Knight car and light truck. ...
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.
Hydraulic pumps
Volumetric efficiency in a hydraulic pump refers to the percentage of actual fluid flow out of the pump compared to the flow out of the pump without leakage. In other words, if the flow out of a 100cc pump is 92cc (per revolution), then the volumetric efficiency is 92%. The volumetric efficiency will change with the pressure and speed a pump is operated at, therefore when comparing volumetric efficiencies, the pressure and speed information must be available. When a single number is given for volumetric efficiency, it will typically be at the rated pressure and speed.
Electronics
![Capacitor Miniaturizing 1970-2005](https://upload.wikimedia.org/wikipedia/commons/d/d2/Capacitor_Miniaturizing_1970-2005.png)
In electronics, volumetric efficiency quantifies the performance of some electronic function per unit volume, usually in as small a space as possible. This is desirable since advanced designs need to cram increasing functionality into smaller packages, for example, maximizing the energy stored in a battery powering a cellphone. Besides energy storage in batteries, the concept of volumetric efficiency appears in design and application of
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
s, where the "CV product" is a
figure of merit
A figure of merit is a quantity used to characterize the performance of a device, system or method, relative to its alternatives. Examples
*Clock rate of a CPU
* Calories per serving
*Contrast ratio of an LCD
*Frequency response of a speaker
* ...
calculated by multiplying the capacitance (C) by the maximum voltage rating (V), divided by the volume. The concept of volumetric efficiency can be applied to any measurable electronic characteristic, including
resistance,
capacitance
Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are ...
,
inductance
Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current creates a magnetic field around the conductor. The field strength depends on the magnitude of the ...
,
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
,
current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
,
energy storage
Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production.
A device that stores energy is generally called an accumulator or battery.
Energy comes in ...
, etc.
See also
*
Two-stroke power valve system {{Unreferenced, date=February 2018
The two-stroke power valve system is an improvement to a conventional two-stroke engine that gives a high power output over a wider RPM range.
Operation of a two-stroke engine
A ''stroke'' is the action of a pi ...
*
Variable compression ratio Variable compression ratio (VCR) is a technology to adjust the compression ratio of an internal combustion engine while the engine is in operation. This is done to increase fuel efficiency while under varying loads. Variable compression engines al ...
Notes
External links
2 Stroke Tuned Pipe (Expansion Chamber) Design Software
{{DEFAULTSORT:Volumetric Efficiency
Engine technology
Two-stroke engine technology
Engineering ratios