A Numerical Investigation of Natural Gas Injection Timing Effect on Low-Load Dual-Fuel Engines Combustion and Emissions

Dual-fuel engines powered with natural gas and diesel fuel have shown superiority in their application within the transportation and industrial sectors. Primarily aimed at significantly reducing the concentration of PM, NOx, and soot emissions generated by diesel engines, natural gas/diesel dual-fuel engines present themselves as an alternative to achieving net-zero emissions. However, these engines exhibit reduced thermal efficiency under low-load conditions with higher HC and CO emissions. This study aims to identify the impact of natural gas injection under low-load conditions on dual-fuel engines fueled by diesel and natural gas concerning combustion processes, performance, and emissions. Numerical CFDs investigate these impacts. While previous studies have addressed some aspects, further identification of phenomena occurring within the combustion chamber is necessary for a more comprehensive understanding. Numerical simulations involved open-cycle processes encompassing intake, compression, combustion, and exhaust cycles. Natural gas was injected into the intake manifold near the port when the intake valve was open. The study identified that advancing the natural gas injection timing led to increased combustion temperatures by about 7.7%, cylinder pressure by about 3%, and thermal efficiency by about 5.8% compared to retarding the natural gas injection timing. Additionally, torque values produced were relatively similar across varied timings for injecting natural gas, with only 1.6% differences. Furthermore, HC and NOx emissions significantly reduced with retarding the natural gas injection timing by about 13.5% and 30%, respectively, compared to advancing the timing. Unfortunately, extreme retarding or advancing of natural gas injection timing resulted in increased CO and soot emissions of about 16.8% and 8%, respectively. However, due to natural gas injection timing adjustments, the quality of combustion influences complex mixture stratification between natural gas fuel and air. Complex mixture stratification caused a decrease in combustion temperatures, subsequently impacting engine performance and emissions.