Editing Volumetric efficiency (section)

==Internal combustion engines==
Volumetric Efficiency in an internal combustion engine design refers to the efficiency with which the engine can move the ''charge'' of fresh air into and out of the [[Cylinder (engine)|cylinders]]. It also denotes the ratio of equivalent air volume drawn into the cylinder to the cylinder's swept volume.<ref>Internal Combustion Engines 3rd edition  Ferguson, Kirkpatrick-  Publisher John Wiley and Sons, 2016</ref>  This equivalent volume is commonly inserted into a mass estimation equation based upon [[Boyle's law|Boyle's Gas Law]]. When VE is multiplied by the cylinder volume, an accurate estimate of cylinder air mass (charge) can be made for use in determining the required fuel delivery and spark timing for the engine.

The flow restrictions in the intake and exhaust systems create a reduction in the inlet flow which reduces the total mass delivery to the cylinder. Under some conditions, [[Resonance|ram tuning]] may either increase or decrease the pumping efficiency of the engine. This happens when a favorable alignment of the pressure wave in the inlet (or exhaust) plumbing improves the flow through the valve. Increasing the pressure differential across the inlet valve typically increases VE throughout the [[Naturally aspirated engine|naturally aspirated]] range. Adding intake manifold boost pressure from a [[supercharger]] or [[turbocharger]] can increase the VE, but the final calculation for cylinder airmass takes most of this benefit into account with the pressure term in [[Boyle's law|n=PV/RT]] which is taken from the intake manifold pressure.

Many high [[performance car]]s use carefully arranged air intakes and [[tuned exhaust]] systems that use pressure waves to push air into and out of the cylinders, making use of the [[resonance]] of the system. [[Two-stroke engine]]s are very sensitive to this concept and can use [[expansion chamber]]s that return the escaping [[air-fuel mixture]] back to the cylinder. A more modern technique for [[four-stroke engine]]s, [[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 [[supercharger|supercharging]] or [[turbocharger|turbocharging]]. With proper tuning, volumetric efficiencies above 100% can also be reached by [[naturally aspirated engine]]s. The limit for naturally aspirated engines is about 130%;<ref>{{cite web|author=SohoPros |url=http://www.theoldone.com |title=ENDYN |publisher=Theoldone.com |access-date=2010-11-07}}</ref> these engines are typically of a [[DOHC]] layout with [[Multi-valve|four valves per cylinder]].  This process is called [[inertial supercharging effect|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.<ref>SAE 860032 "Optimization of multi valve four cycle engine design"</ref>

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.