We report our results on non-periodic experimental time series of pressure in a single cylinder spark ignition engine.
The experiments were performed for different levels of loading. We estimate the noise level in internal pressure calculating
the coarse-grained entropy from variations of maximal pressures in successive cycles. The results show that the
dynamics of the combustion is a non-linear multidimensional process mediated by noise. Our results show that so
defined level of noise in internal pressure is not monotonous function of loading.
