Experimental Investigation Of Microwave Resonance Plasma Ignition Of The Methane-air Mixture

The spark ignition system in accompany with the thermal plasma as the conventional ignition technique dates back more than a hundred years to the advent of internal combustion engines(ICEs). However, with the stringent regulations on engine-related emissions and increasing demands for higher thermal efficiency, the conventional spark ignition faces two difficult problems: one is that combustion stability for the gasoline engine will be poor due to the misfire, and the other is that the engine knock is likely to occur because of the single-point spark ignition and the subsequent flame propagation, thus suppressing the increase of the compression ratio.Compared with the thermal plasma caused by the conventional spark ignition, the non-thermal plasma produced by the microwave ignition is a promising way to improve the combustion characteristics. On the basis of the understanding of the effect of the plasma on the combustion and with the support of the National Natural Science Foundation of China, this work focused on the effect of a novel ignition technique called Microwave Resonance Plasma Ignition(MRPI) on the combustion performances and experiments were performed in a constant volume combustion chamber(low pressure and low temperature) and a rapid compression machine(high pressure and high temperature).Microwave Resonance Plasma Ignition referred that once a certain frequency pulsed microwave was delivered into a combustion chamber with a specific size and structure, the microwave resonance occurred in the whole chamber, thus leading to a strong electric field with the non-thermal plasma induced and then igniting the combustible mixture after breakdown.The experimental results were obtained from the former test beds by means of the visual images, combustion pressure curves and analysis of the exhaust gas components. It could be observed from the visualization results that compared with the conventional spark ignition technique at the same ignition energy, MPRI could generate the larger volume of the plasma and bigger initial flame kernel, which meant that MPRI had a potential for realizing space ignition. The differences in combustion pressure curves between two ignition modes reflected that MRPI offers the remarkable advantages of extending the ignition limits, enhancing the combustion stability and improving the energy conversion efficiency. The analysis of the exhaust gas components showed that combustion efficiency was improved due to more complete combustion with the use of the microwave and MRPI could be used as a new approach to realize methane reforming for achieving the clean hydrogen energy at the conditions of rich burn.The experiments on the rapid compression machine aimed at control the ignition timing of homogeneous charge compression ignition with the pulsed microwave delivered. However, it was not satisfactory that the microwave energy could not affect the combustion process of HCCI mode with the 2450 MHz-100 mJ pulsed microwave delivered.