Investigation of the Effect of Operating Conditions on Knock Limited Spark Advance and Octane Requirement in Internal Combustion Engine

In this paper, the effects of engine operating parameters on knock occurrence crank angle, knock-limited operating conditions and also octane requirement for knock prevention were studied. To predict knock occurrence crank angle and knock intensity, an experimentally based Knock Integral Method is optimized according to experimental results and is incorporated with the qausi-dimensional thermodynamic model. Comparison of the results of this study and experimental results indicates that the model is able to predict the knock-limited operating conditions with minimum error in magnitudes (1.7º). As shown in previous works and literature an increase in the octane number of the fuel allows approximately an equal increase in the spark advance. The effects of intake air temperature and pressure, air/fuel ratio and compression ratio on octane requirement were studied and a good agreement with the literature is observed. The results of this study show that the knock occurence can be predicted by the numerical method via experimental ones, which are very expensive.