Investigation of the Effect of Spark Plug Gap on Power Performance and Combustion Characteristics in a Gasoline Fueled SI Engine

Abstract

Spark plugs are typically designed to have a gap that is placed between the center and ground electrodes. The first effective parameter in sparking system would be the spark plug gap. Spark plug gap is a main factor affecting the performance of the engine depending on the engine structure. According to the specification of spark plugs for several different engines, the size of this gap varies 0.9–1.8 mm. The gap adjustment can be critical to proper engine operation, so gap should be fitted in order to have best engine performance. A narrow gap leads to weak spark to effectively ignite the fuel-air mixture. On the other hand, a gap that is too wide might prevent a spark from firing at all or may result in misfiring at high speeds. As spark plug ages, and because of oxidation and erosion of the electrodes, the gap will tend to widen therefore coil has to provide more energy in order to have the proper spark for optimized ignition. In this work the effects of different spark plug gaps in performance of Gasoline fueled SI engine are investigated. The investigation was performed using 3 different spark plug gaps (0.5, 0.75 and 1 mm) and two ignition timing values (11°and 15°CA BTDC) at 100% wide open throttle (WOT). Maximum power values were obtained at 0.75 mm spark plug gap for both ignition timing values of 11°and 15°CA BTDC.