Abstract
Heavy EGR is applied for the purpose of improving the thermal efficiency, however increasing EGR incurs the aggravation of IMEP covariance due to low combustion speed. Even if large turbulence is given to increase turbulent combustion speed in a combustion chamber, this aggravation occurs in the cause of combustion instability under the further heavy EGR condition. It is important to understand this phenomenon for the enhancement of EGR and the improvement of thermal efficiency. In this paper, the factor of combustion instability under heavy EGR conditions was analyzed by using single cylinder engine test, optical engine test and 3D CFD simulation. As an analysis result by focusing combustion diagram, extremely low IMEP cycles occur when Karlovitz number becomes larger than 1.0. And the tendency of IMEP covariance depends on the amplitude of Karlovitz number.
