Numerical study on the effects of intake valve timing on performance of a natural gas-diesel dual-fuel engine and multi-objective Pareto optimization

A natural gas-diesel dual-fuel engine is considered an attractive option for reducing the emissions of a diesel engine while maintaining high thermal efficiency. However, it is important to investigate and optimize the parameters of such an engine in dual-fuel mode. Intake valve timing is a major parameter affecting the air/fuel (A/F) ratio, which is an important factor in dual-fuel combustion characteristics. Here, a numerical study was performed to investigate the fundamentals of dual-fuel combustion and the effects of intake valve closure (IVC) changes in dual-fuel mode using a 1D engine simulation. As the natural gas energy proportion (NGP) increased, brake power decreased and nitrogen oxide (NOx) emissions decreased because of low combustion efficiency and a lower temperature in the cylinder. At each NGP, a change in IVC could increase combustion efficiency and affect NOx emissions by controlling the A/F ratio. Additionally, the start of diesel injection (SOI), a major parameter in a dual-fuel engine, and the IVC were selected as independent variables. Latin hypercube sampling (LHS) was used with these variables and a multi-objective Pareto optimization (MOP) was performed to optimize high thermal efficiency and low NOx emissions. As a result, optimal Pareto solutions were obtained.