Computational Modeling of Natural Gas Injection in a Large Bore Engine

Abstract

The topic of this paper is the computational modeling of gas injection through various poppet valve geometries in a large bore engine. The objective of the paper is to contribute to a better understanding of 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 for both a low (4 bar) and a high pressure (35 bar) injection process using unshrouded and shrouded valves. Experiments using PLIF (planar laser induced fluorescence) are used to visualize the actual fluid flow for the valve geometries considered. The results indicate that for low injection pressures the gas flow around a typical poppet valve collapses to the axis of symmetry of the valve downstream of the poppet. At high pressure, the gas flow from this simple poppet valve does not collapse, but rather expands outward and flows along the cylinder wall. At high pressures, addition of a shroud around the poppet valve was effective in directing the supersonic flow toward the center of the cylinder. Additional computations with a moving piston show that at top dead center, the flammable volume fraction and turbulence intensity with high pressure shrouded injection are larger than for low pressure injection.

Effect of Valve Opening Manner and Sealing Method on the Steady Injection Characteristic of Gas Fuel Injector

“…Thus, it can be guaranteed that the gas jet of type B push-open valve will be attracted to the outlet axis direction while the pressure ratio is less than 5:1. According to the results of literature [19], with the increase of the inlet/outlet pressure ratio, it is easier to form the divergence phenomenon as shown in Figure 8. On the contrary, with the decrease of the pressure ratio, the jet tends to the outlet axis direction.…”

“…Then, the axial velocity and Mach number radial distribution on the cross section 50 mm and 90 mm downstream outlet, within the stable range, are plotted in Figure 14 There will be a considerable stagnation pressure loss when the gas fuel passes through injector. According to the results of literature [19], the actual jet velocity of one injector was completely subsonic under the inlet/outlet pressure ratio 4.06:1, while the theoretical velocity calculated according to the one-dimensional isentropic flow relationship was supersonic, as high as 1.6 Ma. This indicates that the stagnation pressure loss during injection process is high enough to affect the fundamental jet characteristic.…”

Development of a High Performance Natural Gas Engine with Direct Gas Injection and Variable Valve Actuation

“…The situation becomes more critical when the underexpanded jet issues from a gas injector featuring outward-opening poppet valve rather than an axisymmetric orifice. In fact, the latter generates a circular gas jet and the former a hollow cone jet that, depending on the injector geometry and NPR, may shortly collapse to the nozzle axis, maintain the conical shape onwards, or attach to adjacent walls [21,22]. Moreover, the cross section of the injector nozzle in reality varies with time during transient phases as the needle valve opens or closes.…”

“…Such variation is often complex since, along with the needle valve movement, not only the cross sectional area of the nozzle but also the absolute location of the nozzle throat changes. Many studies have investigated the hollow cone jets ejected from poppet-valve type injectors by means of fixed injector needle lift [12,15,16,22]. It was found, in consequence, that the injector flow initialization through gradual increase in inlet boundary pressure and the location of the boundary are crucial to the numerical model predictability [21].…”

Generation of Turbulence in a RCEM towards Engine Relevant Conditions for Premixed Combustion Based on CFD and PIV Investigations

“…This method was e.g. applied by Kim et al for CNG [32] and Gerke et al for hydrogen [19]. Scaling laws based either on an equivalent nozzle diameter [33,34] or modified inlet conditions [35] or a combination thereof [36] allow to model the far field of the jet without resolving the near field with its shock structures.…”