Abstract
Natural gas (NG) direct injection (DI) technology benefits the engine with high efficiency and clean emissions, and the high-pressure gas fuel injection process causes crucial effects on the combustion. This study presents an optical experimental investigation on the high-pressure methane single-hole direct injection and premixed ignition combustion based on a visualization cuboid constant volume bomb (CVB) test rig. The experimental results show that the methane jet process is divided into two stages. The methane gas jet travels at a faster speed during the unstable stage I than that during the stable stage II. The injection pressure causes more influence on both the jet penetration distance and the jet cone area during stage II. The methane jet premixed flame is a stable flame with a nearly spherical shape, and its equivalent radius linearly increases. The methane jet premixed flame area also increases while the flame stretch rate declines. The methane jet premixed flame velocity rises as both the standing time and equivalent ratio increase. The methane jet premixed flame is a partial premixed flame, and the peak of the methane jet premixed flame occurs at greater equivalence ratio ϕ, i.e., ϕ > 2. As the injection pressure rises, the jet premixed flame equivalent radius increases, and the flame velocity linearly increases. The higher the methane injection pressure, the faster the jet premixed flame velocity.
Highlights
Accepted: 2 November 2021Natural gas (NG) is a low-carbon fuel, and is widely used in the practical industry such as power plants, and vehicle and marine engines to produce less harmful emissions (Koyun et al, 2012) [1]; (Samokhvalov et al, 2018) [2]
For a natural gas direct injection engine, the natural gas jets directly into the cylinder once a cycle, which means that this gas fuel injection is a pulsed injection [6]
Huang et al (2003) investigated the natural gas direction combustion process based on a rapid compression machine, and they reported that the direct injection high-speed fuel jet leads to faster flame propagation [8]
Summary
Natural gas (NG) is a low-carbon fuel, and is widely used in the practical industry such as power plants, and vehicle and marine engines to produce less harmful emissions (Koyun et al, 2012) [1]; (Samokhvalov et al, 2018) [2]. Huang et al (2003) investigated the natural gas direction combustion process based on a rapid compression machine, and they reported that the direct injection high-speed fuel jet leads to faster flame propagation [8]. Ishibashi and Tsuru (2017) adopted a shadowgraphy system to optically observe a natural gas jet and dual-fuel combustion progress in a rapid compression and expansion machine (RCEM), and their results show that the natural gas injection parameters such as the injection time delay and the injection angle cause great influence on jet entrainment [14]. Huang et al (2013) studied natural gas direct injection combustion on a constant volume vessel by schlieren photography, and they found that natural gas injection mode causes great influence on flame propagation [20]. A digital high-speed camera recorded the methane jet and combustion progress under conditions of different pressures
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