A parametric study on the lean misfiring and knocking limits of gas-fueled spark ignition engines

Increasing emphasis on gaseous fuels as clean, economical and abundant fuels encourages the search for optimum operating conditions of gas-fueled internal combustion engines. In this context, this paper presents the experimental results of a parametric study on the lean operational limits of a Ricardo E6 engine using propane and liquefied petroleum gas (LPG) as fuels. Three different criteria for defining the engine lean limit are used. The first is associated with the first detectable misfire on leaning the mixture, the second is the first detectable firing under motoring conditions when the mixture is being enriched slowly, while the third is when the torque reaches zero on leaning the mixture. In addition, the lean knocking limit for some experiments is presented. The effects of speed, spark timing, compression ratio, intake temperature, intake pressure (supercharging), and relative humidity of intake air on the engine operational limits are presented and discussed in relation to chemical reaction rates, ignition delay, amount of residual gases, turbulence, and heat transfer. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.