Numerical prediction of mixing process in a methane-fueled engine



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Texas Tech University


One of the most important factors controlling the combustion process within internal combustion engines is the charge mixing. The charge mixing process in a gaseous fueled engine is different than that in a liquid fueled engine. In a conventional liquid fueled engine, the liquid fuel goes through the process of vaporization before the gaseous mixing takes place. Gaseous fuels, on the other hand, are already in a vapor form and do not go through the vaporization process. Among the gaseous fuels, natural gas, which consists of about 90% methane, is gaining acceptance because of its low emission levels and alternative energy source concerns. Introducing methane into the conventional spark ignition engine intake system causes about a 10% engine power loss contributed by low density of the fuel. By introducing natural gas directly into the engine cylinder, this power loss can be reduced.

The present work concerns numerical prediction of in-cylinder methane/air mixing preparation. A computer-based solution procedure, which employs a finite-difference solution of general conservation equations of motion in a piston/cylinder assembly, has been developed to predict the fuel/air mixing characteristics. This solution procedure has been used as a predictive tool to investigate the dependence of charge mixing characteristics on the flow field in the absence of combustion. Computational results show that the flow field has a great effect on charge mixing. The fuel/air mixing characteristics at the time of initiation of combustion are satisfactorily close to the mixing requirements when the fuel charging is prescribed properly.