| Lean combustion and high compression ratio technologies have great potential for improving thermal efficiency,but these technologies will form a lean and high-pressure environment in the cylinder,making the combustion environment in the cylinder worse,especially in the case of ignited internal combustion engines.The gas is prone to problems such as difficulty in ignition and unstable early combustion.Relevant researchers draw on the theory of plasma combustion support and electric field combustion support,and propose microwave plasma assisted ignition technology.This technology can greatly increase the concentration of OH and other free radicals during ignition,and significantly improve the ignition performance.However,the study also found that with the increase of environmental pressure,the effect of microwave combustion assistance is getting worse and worse.When the internal combustion engine is actually working,the combustion in the cylinder is often under a high pressure environment,which makes the application of microwave assisted ignition technology in the internal combustion engine facing some bottleneck.Therefore,in this paper,from the perspective of microwave antenna performance,combined with numerical simulation and experiments research,the influence of antenna structure parameters and microwave parameters on microwave-assisted ignition is studied,and the coupling mechanism of antenna structure to microwave and plasma is analyzed.The content of the paper is mainly divided into two parts: The first part uses HFSS to construct the electromagnetic simulation model of microwave antennas.Then,the return loss of the center conductor diameter 1.1,1.3,1.5,1.7,1.9mm antenna at 2.45 GHz was measured through experiments.The experimental and simulation results are around 10 d B,and the maximum difference in energy feed rate is only 3.9%.Within the allowable error range,the accuracy of the microwave antenna numerical simulation method and the reliability of the simulation results are verified.HFSS simulation found that the influence of microwave antenna structure parameters on the antenna’s return loss and electric field strength is correlated,but they are not completely consistent.That is,when the microwave antenna reflects less energy,the strongest electric field cannot be guaranteed.The second part uses the constant volume combustion chamber developed by the research group to study the influence of different antenna structures and microwave parameters on the microwave-assisted ignition performance.The experiment includes 2bar discharge experiment and 2bar equivalent ratio 0.65 methane mixture combustion experiment.Through the discharge and ignition experiments of the traditional spark plug and the microwave-assisted ignition,it was found that the feeding of microwave can not only increase the flame propagation speed of the early fire core,but also change the shape of the fire core,induce the generation of folds,and occur glow phenomenon.Experiments with different antenna structure parameters have found that the microwave combustion effect is obviously different,and its trend is similar to the influence of the antenna structure on the electric field strength,indicating that the microwave antenna structure changes the microwave antenna electric field strength,which has different effects on the microwave combustion effect.This also shows that the electric field effect of microwave is an important mechanism of microwave-assisted ignition.Therefore,when designing the antenna structure,it is necessary to focus on the electric field strength to improve the microwave combustion-supporting effect.Experimental studies have found that when the microwave power is 1000 W,the microwave duration is 3ms,the microwave pulse frequency is 40 k Hz,and the microwave feed delay is 0ms,a better microwave combustion support effect can be achieved. |
