Indicated mean effective pressure oscillations in a natural gas combustion engine by recurrence plots

We investigate the nonlinear time series of Indicated Mean Effective Pressure ($\mathit{IMEP}$) of the spark ignition engine cyclic combustion process of a natural gas. By applying the embedding theorem and the recurrence plots technique, we show changes in the engine dynamics for different equivalence ratios. Especially, we provide arguments for intermittency behaviour.