Abstract
The ion current signal in homogenous charge compression ignition (HCCI) engines is studied. The aim of this research is to show that a measurable ion current exists even in the very lean combustion (equivalence ratio
ϕ
=
0.35) in an HCCI engine. Numerical models using detailed chemical kinetics for propane combustion, including kinetics for ion formation, support the experimental findings. The effects of the equivalence ratio, the intake mixture temperature, and the applied bias voltage on the ion signal are studied through a series of experiments. The findings are compared to the numerical model results. The research shows that an inexpensive ion sensor may replace the expensive pressure transducers currently used in HCCI engines. The ion current signal is very sensitive to the equivalence ratio of the intake fuel–air mixture. Through numerical modeling, the N
2O mechanism is shown to be the significant source of Nitrogen Oxides (NO
x
) generation in HCCI combustion.