Observation of two different cool flame regimes of diethyl ether in a counterflow burner

•Observation of two different cool flame regimes of diethyl ether.•Only high low-temperature reactivity fuels may cause this phenomenon.•Both cool flames have the same low-temperature chemistry reaction pathway.•The mechanism of autoignition-assisted cool flame is described.•The different regimes may trigger an uncontrolled combustion in advanced engines.