Study on Optimization of Gas Injection Timing of a Marine Micro-pilot-ignition Dual-Fuel Engine

Natural gas (NG) injection timing of port-injection dual fuel engine has effects on its performance and emissions. The influence of the NG injection timing on the efficiency, the combustion and the emissions of the marine micro pilot ignition (MPI) dual fuel engine (substitution of 99%) is investigated by using the Computational Fluid Dynamics (CFD) method in this paper. The working processes of the different NG injection timing under different loads are simulated respectively. The results show that too early the NG injection causes the gas scavenged away from the exhaust valve during the valve overlap. Retarding NG injection timing under the high load will cause the $\mathrm{NO}_{\mathrm{x}}$ emissions increase first and then decrease, and has lower the Unburned Hydrocarbon (UHC) emission than that under the partial load. More than $90 \%$ UHC emission amount comes from the unburned methane (CH<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf>). In order to improve the indicated efficiency and the emission, the NG injection timing under different loads has been optimized, which provides a useful reference for improving the performance of the marine medium-speed dual fuel engine.