Cool flames may contribute to engine knock – the undesirable, erratic, and noisy combustion of low-octane fuels in internal combustion engines.[2] In a normal regime, the conventional flame front travels smoothly in the combustion chamber from the spark plug, compressing the fuel/air mixture ahead. However, the concomitant increase in pressure and temperature may produce a cool flame in the last unburned fuel-air mixture (the so-called end gasses) and participate in the autoignition of the end gasses.