Virtual Valve Design for Three Dimensional Numerical Simulations of a Large-Bore Natural Gas Engine

One of the promising mixing enhancement technologies for natural gas engines currently used is high pressure fuel injection. Three dimensional computational simulations that can examine the entire injection and mixing process in engines using high pressure injection and determine the impact of injector design on engine performance are consequently of considerable interest. However, the cost of three dimensional engine simulations including a moving piston and the kinetics of combustion and pollutants production quickly becomes considerable in terms of simulation time requirements. The limiting factor is the modeling of the small length scales of the poppet valve flow. Such length scales can be two orders of magnitude smaller than cylinder length scales. The objective of this paper is to describe the development of a compatible virtual valve which can be substituted in three-dimensional numerical models for the complex shrouded poppet valve injection system actually installed in the engine to be simulated. Downstream flow characteristics of the jets from an actual valve and a virtual valve were compared. Various mixing parameters were evaluated in moving piston simulations that include the effect of the jet-piston interaction. Comparison of the results indicated that it is possible to design a simple converging-diverging fuel nozzle that will produce the same jet and subsequently the same large and turbulent scale mixing patterns as a real poppet valve.