Distinguishing between the thermal effect and active radicals' chemical effect in combustion reaction was implemented using an experimental apparatus with an argon plasma jet (Ar P.J.) and oxygen plasma jet (O2 P.J.) coupled with corresponding numerical simulation. It was conducted based on the idea that Ar P.J. has much higher temperature without active species whereas O2 P.J. includes abundant O radicals. The experimental results show that O2 P.J. is much more eligible for combustion promotion in both DME/air and CH4/air mixtures, which coincides with the numerical results showing that the ignition delay time is reduced more remarkably by adding O radicals than by increasing the temperature of the fuel/air mixtures. Although the level of effect differs according to the kind of mixtures used, it is generally more advantageous for ignition/combustion promotion to be conveyed as active radicals than as heat to fuel/air mixtures with the same supply of energy.
radicals, plasma jets, combustion promotion, chemical effect, thermal effect