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Next generation of fuels and injection technology system are growing attention in the transportation sector. The effects of castor oil of biodiesel (C30D) and two conditions (500 bar and 1000 bar) of fuel injection pressure (FIP) on soot nanoparticles characteristics and NOX emissions were performed in a direct injection (DI) diesel engine. The results showed that size distributions of soot particulate decreased from C30D combustion by 43.62% compared to the diesel combustion for different FIP. Furthermore, the soot particle number concentration decreased more with 1000 bar of FIP compared with 500 bar for both fuels tests. The combustion of C30D decreased the average number of primary particles (npo) by 44.35% compared with diesel. For an injection pressure, it was observed that high injection pressure (1000 bar) significantly decreased the npo by 11.6 nm and 25.4 nm compared to the 500 bar by 22.4 nm and 33.2 from C30D and diesel, respectively. In addition, the average diameter of soot primary particle (dpo) was smaller by 47.68% during C30D combustion than to the diesel combustion for all conditions of injection pressure. In case of engine performance, the BTE, BSFC increased from the C30D combustion compared with diesel under different FIP. It is indicated that increasing injection pressure improved the engine performance for C30D and diesel. In contrast, the high injection pressure and C30D increased the NOX emissions by 21.37% compared with diesel fuel.

The fuel combustion in diesel engines can be improved by adding nanomaterials to the fuel which result in an reduction in pollutant emissions and enhance the quality of fuel combustion. The engine performance and soot nanoparticles characteristics were evaluated in this study with adding nanoparticles of copper oxide (CuO2) to the rapeseed methyl ester (RME) and diesel under variable engine speeds. The addition of CuO2 to the RME significantly improve brake thermal efficiency (BTE) and decline the brake specific fuel consumption (BSFC) by 23.6% and 7.6%, respectively, compared to the neat RME and diesel fuel. The inclusion CuO2 nanoparticles into the RME and diesel led to decrease the concentration and number of particulate matter (PM)by 33% and 17% in comparison with neat RME and diesel without nano additives, respectively. Moreover, PM is significantly decreased by 31.5% during the RME combustion in comparison with neat RME and diesel under various engine speeds. It was also obtained that the number of emitted particles (npo) reduced by 23.5% with adding nanoparticles to the RME in comparison with diesel, while the diameter of soot nanoparticles (dpo) increased by 8.6% in comparison with diesel. Furthermore, the addition CuO2 to the RME decreased the size and number of particles more than to the diesel fuel.