Computational Modeling of Natural Gas Injection in a Large Bore Engine

The topic of this paper is the computational modeling and experimental visualization of gas injection in a large bore engine. The injection process is accomplished through the use of a mechanically or electrically controlled poppet valve. The objective of the paper is to more fully understand the significance of the poppet valve and the piston top in controlling the mixing of the injected fuel with the air in the cylinder. In this paper, the flow past the poppet valve into the engine cylinder is computed using computational fluid dynamics (CFD) for both a low (4 bar) and a high pressure (34 bar) injection process using unshrouded and shrouded valves. Flow visualization using planar laser induced fluorescence (PLIF) is used to visualize the actual fluid flow. The results indicate that for low pressures the gas flow around the poppet valve collapses downstream of the poppet. At high pressure, the gas flow does not collapse, but flows along the cylinder wall, producing poor mixing in the cylinder. To obtain satisfactory fluid flow at high pressure, the results indicated a shroud should be employed around the poppet valve to direct the gas into the center of the cylinder. Additional computations show that at top dead center, the flammable mixture and fuel mass fraction for the high-pressure injection are significantly greater than for the low-pressure injection.