Experimental Study of Dual-Fuel Diesel/Natural Gas High-Pressure Injection

[Image: see text] Dual-fuel diesel/natural gas direct-injection engine is promising and highly attractive due to its low-carbon emission and high thermal efficiency, and both high-pressure diesel and natural gas injections are critical for air–fuel mixing. This study presents an optical experimental investigation on the high-pressure dual-fuel diesel/methane injection process based on a constant-volume vessel test rig. The results show that the diesel penetration process of the dual-fuel injection experiences two stages: Stage I, the diesel tip penetration S(diesel), the diesel spray area A(diesel), and the diesel spray perimeter C(diesel) of the dual-fuel injection are smaller than those of the single diesel injection. Stage II, both the diesel and methane continue to penetrate forward, and S(diesel), A(diesel), and C(diesel) of the dual-fuel injection become larger than those of the single diesel injection do. The diesel injection pressure causes effect on the dual-fuel spray penetration. The diesel injection pressure directly causes linear influence on the two-stage dual-fuel injection characteristic. As the diesel injection pressure increases, the diesel spray meets the methane jet advancer and the cross point occurs linearly earlier. Furthermore, the dual-fuel injection is asymmetric and the methane gas jet enhances this asymmetry so that the spray cone shifts to the side of the methane gas jet.