Air expenditure

The air consumption is a measure of the fresh gaseous charge supplied to an internal combustion engine . In addition to the degree of delivery, the air consumption is an important parameter for describing the gas exchange quality, whereby the air consumption rather allows a statement to be made about the quality of the intake system and process.

calculation

The air consumption is the ratio of the mass of fresh mixture actually supplied to a reciprocating piston engine (or its cylinder) during a work cycle to the theoretically possible mass , which results from the geometric displacement and the theoretical charge density in the ambient condition. This applies to engines with free suction. With supercharged engines , the state of the fresh charge downstream of the compressor or charge air cooler is taken into account. ${\displaystyle m_{\mathrm {G} }\ }$ ${\displaystyle m_{\mathrm {th} }\,}$ ${\displaystyle V_{\mathrm {H} }\,}$ ${\displaystyle \rho _{\mathrm {th} }\,}$

The fresh charge supplied (for a cylinder) or (for the entire engine) and thus the air consumption depend on various factors, v. a. Valve timing and opening cross-section of the valves as well as the speed and the geometrical relationships of the intake tract and combustion chamber, so that the air consumption usually remains below 1 (it could only be greater than 1 through resonance effects). ${\displaystyle m_{\mathrm {G} }\ }$ ${\displaystyle m_{\mathrm {G,ges} }\ }$

${\displaystyle \lambda _{a}={\frac {m_{\mathrm {G,ges} }}{m_{\mathrm {th} }}}={\frac {m_{\mathrm {G,ges} }}{V_{\mathrm {H} }\cdot \rho _{\mathrm {th} }}}={\frac {{\dot {m}}_{\mathrm {G,ges} }}{i\cdot n\cdot V_{\mathrm {H} }\cdot \rho _{\mathrm {th} }}}}$   or for a cylinder    ${\displaystyle {\frac {m_{\mathrm {G} }}{V_{\mathrm {h} }\cdot \rho _{\mathrm {th} }}}}$

In a gasoline engine with external mixture formation (outside the cylinder), the entire fresh charge supplied to the engine consists of:

${\displaystyle m_{\mathrm {G,ges} }=m_{\text{Kraftstoff}}+m_{\text{Luft}}\,}$

and for diesel engines and gasoline engines with direct injection :

${\displaystyle m_{\mathrm {G,ges} }=m_{\text{Luft}}\,}$

literature

• Richard van Basshuysen , Fred Schäfer : Handbook Internal Combustion Engine Basics, Components, Systems, Perspectives. 3. Edition. Friedrich Vieweg & Sohn Verlag / GWV Fachverlage, Wiesbaden 2005, ISBN 3-528-23933-6 .
• Franz Pischinger : Combustion Engines, Volume I and Volume II; Lecture reprint. Chair of Applied Thermodynamics, RWTH Aachen , self-published, 1987.