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. The engine is a single cylinder, four stroke, water cooled, unthrottled, supercharged, variable compression, spark ignition engine having a swept volume of 507 cc (31 in3). 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 that when the torque reaches zero on leaning the mixture. In addition, the lean knocking limit is presented for some experiments. 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 residuals, turbulence, and heat transfer.