On-board online evaluation of the charge density in internal combustion engines through electrical discharge characteristics

We propose here a new method to evaluate the mixture charge density inside the combustion chamber of an internal combustion engine. This is an important parameter that is needed to optimize the spark timing and the amount of fuel that is introduced to the cylinder at each cycle, thus optimizing the engine operation for higher power, lower brake-specific fuel consumption, or lower pollutants’ emission at any altitude/ambient conditions. The evaluation of the charge density is performed at each cycle (on a cycle-to-cycle basis) by using the voltage–current characteristics of the spark plug gap. This real-time evaluation method may save two of the present in-use temperature and pressure gages, thus considerably increasing the reliability of the propulsion unit. Owing to the expected higher system reliability and system simplicity, small unmanned aerial vehicles, as well as small automotive engines of various types, may significantly benefit from this proposed method. The method principles, rationale, and some preliminary results are presented.