A study on combined effect of high EGR rate and biodiesel on combustion and emission performance of a diesel engine

•The second stage combustion delay in cylinder can be used for LTC determination.•For medium loads, soot of 30% EGR rate is the highest due to its path in Φ-T map.•Biodiesel needs a higher EGR rate for LTC mode trigger. Emission regulations put forward more and more stringent requirements on diesel engine exhaust emissions, especially on nitrogen oxides (NOx) and soot emissions. These two kinds of emissions present a trade-off relationship, which poses a challenge to meet the emission regulations simultaneously. This study was carried out on a four-cylinder, DI diesel engine to investigate the combined effect of high EGR and biodiesel on combustion and emission under different loads from 10% to 50% with different EGR rates from 10% to 62%. Cylinder pressure, combustion delay period, indicated mean effective pressure (IMEP), heat release rate (HRR), and NOx and soot emissions were measured or calculated. The results of experiments show that approximate isobaric curve of cylinder pressure arises with high EGR rate, and second stage combustion delay can be found from HRR curve, which indicates the engine is running at low temperature combustion (LTC) mode. With medium load, soot emission does not increase monotonically with the increase of EGR rate, instead, the highest soot emission occurs in medium EGR rates. In the soot-EGR diagram, the soot peak position of B20 moves to right compared with that of B0, which indicates that biodiesel needs a higher EGR rate for LTC mode trigger.