The Influence of Hot Gas Jet on Combustion Enhancement for Lean Mixture in Plasma Jet Ignition

This study clarified the influence of hot gas jet on combustion enhancement effect for lean mixture in the plasma jet ignition. The hot gas jet was generated by the high temperature plasma and was ejected from igniter after plasma jet finished issuing. In combustion tests, propane-air mixture at equivalence ratio of 0.6 was used and the mixture was filled in the combustion chamber at atmosphere pressure and room temperature. For generation of the hot gas jet, the standard air was filled in chamber at same conditions and the hot gas jet was visualized by schlieren method in the absence of combustion. The combustion development processes were also visualized and the combustion pressure was measured. The discharge voltage, discharge current and the plasma luminescence were also measured. The plasma luminescence disappeared within 0.05 ms for any experimental conditions. When cavity depth was deep and orifice diameter was small, the maximum plasma luminescence height was short. However, the hot gas jet ejection velocity was increased as the cavity volume increased and orifice diameter decreased. At 0.5 ms after the ignition, both initial flame kernel and hot gas jet were similarly developed. However, the combustion was continuously enhanced after the hot gas jet disappeared. This is because the initial flame kernel was enlarged and turbulence was generated on flame front by the hot gas jet effect. In case of a large volume cavity and small diameter orifice of igniter, the flame propagation was enhanced and combustion duration was shortened. The high voltage discharge duration was very short as compared with combustion period and the initial flame kernel was similarly developed as hot gas jet, therefore the combustion enhancement effect of plasma jet ignition was mainly caused by the hot gas jet effect.