Ion Current in a Homogeneous Charge Compression Ignition Engine

Homogeneous charge compression ignition (HCCI), has the potential to improve the fuel economy and to reduce NOx emission significantly. Spark plug in SI engine and fuel injector in diesel engine can be used directly to control the start of combustion and the combustion period. However, the combustion of HCCI engine is controlled by the chemical kinetic mainly due to the temperature histories in the cylinder. Therefore the combustion process of HCCI engine cannot be directly controlled. Ion sensors such as a spark plug or a gasket are useful to detect the combustion information in production engines. In this study, the ion current was measured in an HCCI engine with the heated charge mixture of fuel and air without EGR when the charge temperature, equivalence ratio and fuel were varied. Simultaneously in-cylinder pressure was measured and the rate of heat release was calculated. The relationship between the rate of heat release and the ion current is mainly discussed. In order to investigate the relationship between the rate of heat release and the ion current, the several parameters were defined. The present study indicates that there is a strong correlation between the peak location of differential ion-current and the second peak location of R.O.H.R.. In the case of Tc=373 and 353K, in spite of decrease of rate of heat release, there is a good correlation between the value of second peak in the rate of heat release, (dQ/dθ)_H and the differential value of ion current at θ_G, (dI/dθ)_H.