Technical Paper
Effects of Injection Timing on the Lean Misfire Limit in an SI Engine
1997-02-24
970028
A commercial DOHC 4-Cylinder sequential MPI SI engine was modified as a research single cylinder engine. And four kinds of cylinder head with the same combustion chamber geometry have been used to induce in-cylinder flow of different swirl ratio. To investigate the effect of injection timing on the lean misfire limit (LML), experiments have been made at selected engine speeds for each cylinder head. Fuel injection timing was varied while running the engine at a constant speed. And the LML was defined as the mixture ratio at which engine speed deviates more than 10 rpm from the present speed resulting in the engine instability which might be causing from misfire or partial combustion. Results show that LML or stability of engine is not affected by engine speed because early flame stability is dominated not by turbulence but by AFR around the spark plug at spark timing. Stratification of mixture resulting from port swirl and injection timing were shown to govern the LML.