In addition, water consumption decreases rapidly after 3000 rpm.
So, unstable operation occured. At lower engine speeds, it is seen
that heat losses increase due to heat transfer to the cylinder walls.
Because, there is enough time to transfer the heat at lower engine
speeds. It results the decrease of in-cylinder temperature. Thus, HC
formation occurs. Moreover, HC emissions are higher, because
flame goes out at cooler cylinder surface due to lower in-cylinder
temperature at lower engine speeds. At higher engine speeds,
flame is similarly quenched at cylinder surfaces due to heat losses
and gas leakages. Bayraktar and Durgun [52] showed that in-cylinder
pressure and temperature predicted for LPG was higher in a
spark ignition engine. It is possible to say that HC emissions
decrease at higher in-cylinder temperatures. In work