Experimental and numerical analyses of cold EGR effect on combustion, performance and emissions of natural gas lean-burn engine with pre-chamber combustion system

The pre-chamber combustion system is an attractive strategy to enable the operation of spark-ignition engines in lean conditions and to maintain a suitable combustion process. Also, cold exhaust gas recirculation (EGR) system can be used during air dilution operation to overcome issues of emissions. In this research, an experimental and numerical investigation has been carried out to evaluate the potential of pre-chamber combustion system combining with EGR system. The results show that the use of pre-chamber combustion and cold EGR at the same time in a lean-burn engine considerably reduced mass release of NOx from 8.83 g/kWh to 4.40 g/kWh (50% reduction) and slightly increased CO emission, while it had no significant effect on CO2 emission. The engine output power and IMEP decreased by 3-4% per 5% of cold EGR and the efficiency slightly decreased (lower than 1%). A gradual increase in cold EGR volume from 0% to 20% reduced the indicated work availability and heat loss availability by approximately 1.4%; however, on the contrary, the exhaust gas availability and the combustion irreversibility declined by 1.1% and 1.4%, respectively. Moreover, exergy efficiency decreased from 41.9% to 40.6%, with a slight reduction in entropy generation. The results indicated that an ideal range could be defined for cold EGR in an engine equipped with the pre-chamber combustion system in which pollutant emission is at the lowest level, and the engine output power is maintained to a great extent. The ideal range for the engine used in this study was EGR = 10%.