An Experimental Study on the Effect of Intake Pressure on a Natural Gas-Diesel Dual-Fuel Engine

Natural gas-diesel dual-fuel (NDDF) combustion can be a viable method to reduce diesel usage in compression ignition (CI) internal combustion engines. Potential benefits of NDDF engines in comparison to conventional diesel engines include decreases in particulate matter (PM) and carbon dioxide (CO₂) emissions. This study focuses on the effect of intake pressure on a dual-fuel engine with intake port injected natural gas (NG) and in-cylinder direct injected diesel at two typical engine operation conditions—low load-high speed and high load-low speed. The research work was performed on a heavy-duty, four-stroke CI, single-cylinder research engine at a NG-diesel energy ratio of approximately 3:1. The results show that when the intake pressure was increased, the indicated thermal efficiency (ITE) decreased and increased at the low load-high speed and high load-low speed conditions, respectively, for NDDF combustion. For the low load-high speed NDDF combustion, increasing intake pressure increased the carbon monoxide, methane, and soot emissions, but decreased the nitrogen oxide (NO_x) emissions. For the high load-low speed NDDF combustion, increasing intake pressure caused the methane emissions to increase, and the carbon monoxide, NOx, and soot emissions to decrease. In-cylinder temperature measured at the tip of the diesel injector showed that the injector tip temperatures were higher for NDDF cases compared to diesel cases and these temperatures could be correlated with the combustion phasing and the NO_x emissions. Increasing intake pressure caused lower injector tip temperatures for both NDDF operating conditions. Equivalent CO₂ emissions for the low load-high speed and high load-low speed NDDF cases were higher and lower than the corresponding diesel cases, respectively.