  We analyse the experimental time series of internal pressure in a four
cylinder spark ignition engine. In our experiment, performed for different
spark advance angles, apart from usual cyclic changes of engine pressure we
observed oscillations. These oscillations are with longer time scales ranging
from one to several hundred engine cycles depending on engine working
conditions. Basing on the pressure time dependence we have calculated the heat
released per cycle. Using the time series of heat release to calculate the
correlation coarse-grained entropy we estimated the noise level for internal
combustion process. Our results show that for a smaller spark advance angle the
system is more deterministic.
