Numerical investigation of combustion characteristics of a single-cylinder linear engine fueled by natural gas under the influence of exhaust gas recirculation
Mohammad Alrbai, Matthew C. Robinson, Nigel Clark, Hassan Hayajneh
Abstract
The effect of applying the exhaust gas recirculation technique on the performance of a free-piston engine, including the resulting emissions, is introduced and assessed in this study. The simulation process has been performed over a single-cylinder, two-stroke free-piston engine that uses a homogeneous charge compression ignition. Two main sub-models that work implicitly to simulate the engine performance and emissions in an iterative simulation procedure using MATLAB® and Cantera toolbox. It was found that recycling a small percentage of the exhaust gases (∼10%) has a significant effect on reducing the engine emissions, like the NOx levels. Four different levels of EGR were applied in the simulations at 0%, 10%, 20% and 30%. Raising the percentage of the recirculated gases beyond a specific threshold will encounter a negative outcome by increasing the emissions of other particles, such as the UHC and CO. Moreover, it can lower the oxygen (O2) concentrations causing an incomplete fuel–air burning which reduces the combustion efficiency. The recirculation of 30% of the exhaust gases was aggressively able to reduce about 14 g/kWh of NOx at the ignition time compared to no recirculation, and about 8 g/kWh at the steady state.