Combustion Process in a Spark Ignition Engine: Analysis of Cyclic   Maximum Pressure and Peak Pressure Angle
  In this paper we analyze the cycle-to-cycle variations of maximum pressure $p_{max}$ and peak pressure angle $\alpha_{pmax}$ in a four-cylinder spark ignition engine. We examine the experimental time series of $p_{max}$ and $\alpha_{pmax}$ for three different spark advance angles. Using standard statistical techniques such as return maps and histograms we show that depending on the spark advance angle, there are significant differences in the fluctuations of $p_{max}$ and   $\alpha_{pmax}$. We also calculate the multiscale entropy of the various time series to estimate the effect of randomness in these fluctuations. Finally, we explain how the information on both $p_{max}$ and $\alpha_{pmax}$ can be used to develop optimal strategies for controlling the combustion process and improving engine performance. 
G. Litak, T. Kaminski, J. Czarnigowski, A.K. Sen, and M. Wendeker