The quest for high engine brake thermal efficiency (BTE) in medium size (140mm – 190mm bore), lean-burn gas applications becomes increasingly difficult as lower emission levels (250mg/Nm3 NOx) are targeted. A traditional approach to offsetting this negative trend has been to design the piston and the intake ports to create high turbulence and homogeneous mixtures leading to faster combustion burn rates with leaner mixtures. This paper proposes a new combustion strategy aimed at optimizing fuel-air mixture stratification in the main combustion chamber. This would result in maximum fuel concentration within a passive prechamber plug leading to high turbulence flame jet (HTFJ) penetration in the main combustion chamber and, therefore, faster combustion burn rates. Experimental correlation of a combustion model is provided for flame jet ignition in a quiescent, mildly stratified combustion chamber through three different cases. The first case uses a traditional J-gap spark plug; the second, a prechamber plug that is not optimized for the fuel distribution present in this combustion chamber. Finally, the third case makes use of a prechamber plug that has been configured to have properly oriented HTFJ. These three cases constitute the basis of the proposed combustion strategy leading to significant increase in engine brake thermal efficiency (BTE).

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