Fuel Injection Optimization for Large-Bore Two-Stroke Natural-Gas Engines

Recent methane emissions regulations present a challenge for the large-bore, natural-gas-fueled engines used at over 1700 compression stations across the US. Poor air–fuel mixing in the main combustion chamber of these engines results in low combustion efficiency and the resulting methane emissions. High-pressure fuel injection is believed to be a significant development in improving air–fuel mixing in natural-gas engine combustion chambers. This study aims to determine the sensitivity of in-cylinder mixing to injection pressures using Computational Fluid Dynamics (CFD) simulations, determine the limits of high-pressure fuel injection, and explore high-momentum low-pressure fuel injection. The engine, modeled using Converge Studio for CFD, was a Cooper-Bessemer large-bore, four-cylinder, GMV-4TF spark-ignited natural-gas engine with direct injection. The model was simulated for four sets of configured cases—baseline; ideal mixing; injection pressure variation; and low-pressure, high-momentum injection. The results show that fuel injection at 700 psi and −115 degrees BTDC gives the best in-cylinder mixing and improved mixing, potentially reducing methane emissions by half. The optimal timing for the injection at different injection pressures was determined. The level of mixing in low-pressure fuel-injection systems was also improved by the high-momentum fuel injector design. It was concluded that mixing can be further improved in integral gas compressor engines through fuel injection optimization.