Fundamental Research On Fast Burning Of Methane-Air Mixture By Jet Ignition

Natural gas engines are used widely, but problems such as low thermal efficiency and large cycle-to-cycle variation still exist. The lean burn can solve the problems, while leading to the slow burning speed. The purpose of this paper is to realize the fast burning of methane-air mixture. The study was carried out by experiments and numerical simulations.Experiments in constant volume combustion bomb (CVCB) with an orificed adaptor built in were carried out. The pressure, the rates of pressure rise and schlieren pictures were obtained. The effects of initial pressure, equivalence ratio and orifice diameter on the jet ignition were studied. The ignition and combustion mechanisms in the main chamber were classified into three patterns. The jet speed and the flame propagation speed in the main chamber were calculated. The experimental results showed that the fast burning of methane-air mixture was realized in CVCB with an orificed adaptor built in, by the effects of the jet which had higher energy and enhanced the air motion.The chemical mechanisms of methane-air mixture were reduced for time saving. Simulated results using the reduced mechanisms were compared with the results using the detailed mechanisms. Important reactions were analyzed. The results showed that the reduced mechanisms can be used in CFD simulations.The mathematical and physical models were built, and the simulated results were compared with the experimental results. The effects of the ignition energy and the time step on the early stage of the flame were discussed. The species concentration was analyzed in detail. The results showed that the burning occured due to the high concentration of H﹑O﹑OH, and the fast burning in the main chamber occurred because the appearance time of high concentration of H﹑OH was earlier.