Effects of Boost Pressure and Spark Timing on Performance and Exhaust Emissions in a Heavy-Duty Spark-Ignited Wood-Gas Engine

Abstract

Wood gas represents a viable energy source, particularly for stationary electric power generation, as it allows for a wide flexibility in fossil fuel sources and can be used as full supplement fuel in conventional heavy-duty (HD), turbocharged (T/C), spark-ignited (SI) engines. For such engines fuelled with wood gas, spark timing and boost pressure are critical parameters that affect both engine performance characteristics and NO and CO emissions. Thus, the main objective of this study is to investigate theoretically the effects of these parameters on the performance and exhaust emissions (NO and CO) of such an existing engine fueled with wood gas. The investigation is conducted by using a comprehensive two-zone phenomenological model. The predictive ability of model was tested against experimental measurements, which were obtained from the operation of such an engine fueled with wood-gas fuel under various operating conditions. The experimental results were found to be in good agreement with the respective computed ones obtained from the simulation model. From the comparative evaluation of the theoretical findings presented in this work, it is generally revealed that for a heavy-duty, turbocharged, SI wood-gas engine operating at 65% of (full) throttle valve opening (TVO), the increase of boost pressure accompanied by advanced spark timing could lead to a more efficient engine operation (i.e., decrease of the brake specific fuel consumption) with a slight improvement on its environmental behavior (i.e., decrease of specific NO and CO emissions). On the other hand, at 100% TVO engine operating point, the slight improvement of engine performance and environmental characteristics, which is achieved via the simultaneous increase of boost pressure and spark timing, is restricted by the occurrence of phenomena influencing its structural strength, because the maximum cylinder pressure becomes considerably higher compared to the respective one observed under normal spark timing and normal boost pressure operating mode.