Research on the Influence of Advanced Exhaust Gas Recirculation Technology on the Combustion and Performance of an Equivalent Natural Gas Engine

In order to meet the emission requirements of the China VI regulations on natural gas (NG) engines, the China VI compliant NG engines generally adopt the equivalent combustion technology route with high-pressure exhaust gas recirculation (HP-EGR). However, the HP-EGR introduction mode heavily relies on engine exhaust pressure, which has negative impact on engine pumping work. In regards to this issue, study on an alternative EGR technology is very important to achieve high EGR introduction ability with low pumping work.In this research, an experimental study on an equivalent-NG engine used in extended-range hybrid vehicles was carried out. The influence of high-low-pressure EGR (HLP-EGR) technology on engine combustion, performance, and emission characteristics was analyzed. The potential of HLP-EGR in improving engine economy and reducing emissions was explored. The test results showed that the HLP-EGR achieved a better combustion quality, due to better intake air mixing uniformity and lower intake manifold temperature in comparison with the HP-EGR. As a result, the combustion phase was advanced and the pumping loss was significantly reduced. Finally, the brake specific fuel consumption (BSFC) of 50% and 100% engine loads were reduced by 1% and 3.9%, respectively. The increase in combustion efficiency and in-cylinder combustion temperature slightly reduced carbon monoxide (CO) and CH4 emissions at cost of higher nitrogen oxide (NOx) emissions. Specifically, an energy balance analysis was conducted. The pumping losses, heat transfer losses, and exhaust energy losses in HLP-EGR mode mainly contributed to the BSFC reduction in comparison with the HP-EGR mode.