Experimental study of microwave resonance plasma ignition of methane–air mixture in a constant volume cylinder

Application of microwave induced plasma to ignition and combustion offer potential for energy saving and emission reduction in internal combustion engines (ICEs). In this paper, the concept of microwave resonance plasma ignition (MRPI) is proposed and investigated. Experiments were carried out in a cylindrical constant volume combustion chamber, which was designed not only to simulate the size and configuration of the real engine combustion chamber at the top dead center (TDC), but it also enables the generation of resonance to obtain strong electric field in the large space. The ignition source consumes low ignition energy similar to that of the traditional spark plug, yet offers the advantages of extending the ignition limit, enhancing the combustion stability and improving the energy conversion efficiency. Results showed that the ignition limit was expanded to equivalence ratio (ϕ) of 0.55 and 3.0 for the lean and rich mixtures, respectively. For ϕ = 0.70, due to the more complete combustion for the MRPI mode, the energy conversion efficiency was 13.4% higher than the SI mode. Initial ignition stage was captured by using a high speed camera.