8. Ultra-low mixture heat engines

8.1 Thermodynamics of lean-burn combustion

To improve the efficiency of a spark-ignition engine at low loads, a lean reactive air-fuel mixture should be preferred, as indicated by the laws of thermodynamics [BE 8 007] , but combustion instabilities and misfires must be controlled. The heat released in the combustion chamber is very high, with a marked risk of knocking and a significant rise in nitrogen oxides linked to the combustion temperature. In addition, it is necessary to return close to...