Lean Misfire Limits of LPG Fueled S.I. Engine

The purpose of this research is to investigate the use of local, commercial LPG (liquefied petroleum gas) fueled Spark ignition engine in term of lean misfire limits. A 4-cylinder Suzuki, water-cooled, S.I. engine is tested under different operational conditions ( fuel/air equivalence ratio, ignition timing, engine speed and inlet air temperature ). The engine is tested at elevated inlet air temperatures to simulate the car engine operational conditions during summer season in Kuwait. Results show that ignition timing is strongly affecting the overall engine lean misfire limit. Experimental results showed that the combustion of LPG fueled S.I. engine can be improved by advancing ignition timing. Results also show that as the ignition timing advanced the lean misfire limit decrease due to the enhancement in engine combustion efficiency.

Experimental results show that as the fuel/air equivalence ratio leaned, the MBT ignition timing need to be advanced, where lean mixtures requires advancing in ignition timing to provide more time for reaction due to the excess presence of oxygen in the fuel/air mixture. The engine lean misfire limit increases as the engine speed increase, with the same effect of preheating inlet air temperature, and as the engine load increase, the lean misfire limit increase.