Effects of EGR at various loads on diesel engine performance and exhaust particle size distribution using four blends of RON70 and diesel

Partially premixed combustion (PPC) is an efficient way to produce low oxides of nitrogen (NOx) and soot emissions simultaneously at low and medium loads, and the combustion phasing can be controlled through the change of injection event. Previous studies demonstrate that PPC applying regular diesel fuel can be achieved with a low compression ratio (CR) diesel engine using more than 70% exhaust gas recirculation (EGR) at 8 bar indicated mean effective pressure (IMEP). While diesel PPC has a combustion efficiency lower than 90% due to the lower CR and excessive EGR conditions. If we want to get PPC on a higher CR engine using reasonable EGR rate and with a moderate injection advance, the easiest approach is to use fuels having higher octane number or equivalently lower cetane number. The combustion and emission characteristics of four blends with research octane number (RON) 70 are experimentally investigated at various loads with a sweep of EGR rates and compared to that of conventional combustion with regular diesel. The first blend is a primary reference fuel with a RON of 70, denoted as PRF. The other three blends are n-heptane/iso-octane blended with ethanol or n-butanol or toluene separately to obtain RON 70 as well, they are denoted as ERF, BRF and TRF. Tests are performed on a heavy duty diesel engine with a CR of 15.7 applying a single injection strategy in this study. The results indicate that the four blends are dominated by premixed combustion at low and medium loads and produce low NOx and soot emissions simultaneously. At high load, a large amount of fuel needs to be injected into the cylinder hence the relatively long injection duration prevents to have a separation between fuel injection event and combustion event. Then the convention diesel combustion has be used to ensure high fuel economy. Compared with other fuels, ERF and BRF yield considerably less particulate matter emissions resulting from their favourable equivalence ratios due to their oxygen content and higher volatility. The particle size distribution curves for all the test fuels in general shift towards bigger size as engine load is increased. Results also show that when more EGR rate is used the number concentration of nucleation-mode particles reduces and more accumulation-mode particles are generated.

Effects of EGR at various loads on diesel engine performance and exhaust particle size distribution using four blends of RON70 and diesel. Available from: https://www.researchgate.net/publication/309391432_Effects_of_EGR_at_various_loads_on_diesel_engine_performance_and_exhaust_particle_size_distribution_using_four_blends_of_RON70_and_diesel [accessed Aug 2, 2017].