Multi-Dimensional 3D-CFD/Chemical-Kinetics Modeling of Natural Gas–Diesel RCCI Engines: Combustion Phasing, Efficiency and Emissions

Abstract

Nowadays, low temperature combustion is a promising concept to implement in conventional internal combustion engines, as it provides lower emissions and higher thermal efficiency. In the current work, the combustion process of an NG/diesel Reactivity Controlled Combustion Ignition (RCCI) engine was investigated using a coupled 3D-CFD/chemical kinetics framework. The reduced chemical kinetics mechanism containing 57 species and 190 reactions was utilized to simulate the combustion of blended fuels. The results show that increasing premixed ratio (PR) (from 75% to 97%), while keeping constant the total input energy in RCCI engine, delays start of combustion (SOC) and CA50 and causes extended burning duration of diesel. In addition, the duration of methane combustion reduces in lower PRs in comparison with higher PRs. When dealing with injection timing, advancing the diesel injection (SOI) until specific value advances the SOC, but afterward retards the SOC. In fact, burning duration for early injection of diesel increases (from 4.2 crank angle degree to 7.4 crank angle degree) while burning duration of methane decreases (from 10.3 crank angle degree to 5.2 crank angle degree). By further advancing SOI timing, combustion efficiency decreases (from 87.5% to 82.8%) while gross indicated efficiency increases (from 40% to 43%). However, HC and CO emissions increase by earlier SOI timing while NOx emissions decrease.