Natural gas jet evolution and structural characterization of shockwaves downstream of an injector in a simulated engine environment.

This article focuses on the computational investigation of methane jet characteristics during fuel injection in compressed natural gas (CNG)-fueled internal combustion (IC) engines, analyzing the effects of varying fuel injection pressures (8, 16, and 24 bar) and ambient pressures (1, 2, and 4 bar) relevant to port and direct injection applications. Using Reynolds-averaged Navier–Stokes (RANS) simulations validated against experimental data, the study characterizes jet development, shockwave formation, turbulence, and energy conversion efficiencies across subsonic, moderately under-expanded, and highly under-expanded jet regimes defined by pressure ratios. Key findings include the identification of secondary instabilities at higher pressure ratios, limited jet penetration gains due to choking effects, consistent jet cone angles (~20°–25°) regardless of conditions, and energy transfer efficiencies around 80%–82% for pressure ratios above 4. The research provides detailed insights into jet structure, shock parameters such as Mach disk geometry, turbulence intensity localized mainly in shear layers, and vorticity patterns, contributing to optimized injector design and improved fuel-air mixing in CNG engines.