Normal and abnormal combustion investigations through UV-visible imaging in a DISI boosted engine fuelled with gasoline and PRFs

Extreme downsizing and new fuels have lead to challenges caused by irregular combustion phenomena in gasoline engines. Besides conventional knocking, further combustion anomalies occur during high load operation of boosted downsized engines. Thermal load and surface temperature of various combustion chamber components increase during abnormal combustion. Reported critical hot spots are the spark plug, the exhaust valves and squish edges. In case of insufficient heat dissipation, local temperature peaks can occur and induce surface ignition processes.
In this work, crank angle resolved imaging in the UV-visible spectral range is employed for investigating flame front characteristics during normal combustion, as well as surface ignition and light knock conditions.
Measurements performed at the ‘line of sight’ provided information on local wrinkling evaluated based on a statistical approach, with multiple frames taken at the same crank angle during consecutive cycles.
The experimental trials were performed at fixed engine speed (2000 rpm) on an optically accessible direct injection spark ignition (DISI) engine equipped with the cylinder head of a four cylinder 16-valves commercial power unit. Different ignition timings were investigated in boosted conditions at 1.5 bar absolute average intake pressure. Commercial gasoline with an octane rating of 95 RON and primary reference fuels were used for all investigated conditions.