PREMIER combustion characteristics of a pilot fuel-ignited dual-fuel biogas engine with consideration of cycle-to-cycle variations

Abstract

Biogas is a promising alternative to fossil fuels for internal combustion (IC) engines. The purpose of this study is to investigate the effect of PREmixed Mixture Ignition in the End-gas Region (PREMIER) combustion on biogas engine combustion. As the main component of biogas is methane (CH4), methane slip is of concern; improvement of combustion efficiency is important and PREMIER combustion may be useful to this end. Experiments were carried out using a dual-fuel gas engine under supercharged conditions, with an intake pressure of 200 kPa. Simulated biogas served as the primary fuel and diesel as the pilot fuel. The pilot fuel injection timing was varied. Cycle-to-cycle variations were considered to improve the accuracy of temperature estimations at the time of end-gas autoignition. As the addition ratio of carbon dioxide (CO2) to CH4 in the intake increased, the temperature at end-gas autoignition increased under the micro-pilot injection timing before knocking. The total energy input was reduced as the CO2 proportion increased. The fuel mass in the end-gas region decreased and the intensity of end-gas autoignition was reduced. The results indicated that knocking is unlikely even when micro-pilot injection timing is advanced when the CO2 proportion is high. As the injection timing advanced, combustion efficiency was improved. As the CO2 proportion increased, the combustion efficiency under the micro-pilot injection timing conditions before knocking was approximately 81 % for all conditions. This resulted in a high indicated thermal efficiency of approximately 42 % even when the CO2 proportion increased.