An experimental study on the ion current characteristics in HCCI combustion

A study on the wave pattern variation of ion current signal is conducted on a single cylinder test engine by changing combustion boundary conditions such as inlet temperature, fuel-air equivalence ratio and compression ratio etc. The results indicate that ion current signal can be strongly influenced by combustion boundary conditions, and its root cause is the effects of in-cylinder temperature peak on the concentration of free ion. When temperature rises, resulting in better combustion, the concentration of free ion increases and the ion current signal becomes stronger; while the fall in temperature weakens the combustion and suppresses the generation of free ion, leading to weak signal and its phase lag relative to combustion tends to increase.