Misfire of spark ignited lean mixture of propane-air in a constant volume vessel.

Abstract

Misfire occurs when operating an internal combustion engine with air fuel ratio near the lean limit. To extend the misfire limit, the combustion chamber is redesigned to promote turbulence and swirl. An experimental study has been conducted in a constant volume vessel to investigate the effects of the swirling flow, the spark location, the spark energy, the spark gap and the equivalence ratio on misfire. The relationship between spark location and misfire is investigated for the three following ignition locations: quarter radius from the wall, half radius from the wall and three quarter radius from the wall. The instantaneous velocities are measured using hot wire anemometer. Mixtures of propane and air with equivalence ratios between 0.5 and 0.64 have been tested. Misfire was determined using the pressure trace and by visually inspecting the flame through the quartz glass. The misfire probability decreases as the mean swirling velocity and turbulence intensity decay. Also the misfire probability decreases as the ignition point is nearer to the center even though the turbulence intensity is higher than that near the wall. It is postulated that the rate of growth of the flame area (flame stretching) is higher near the wall, therefore the lean misfire limit is richer.