Experimental investigation of the combustion characteristics of Mahua oil biodiesel-diesel blend using a DI diesel engine modified with EGR and nozzle hole orifice diameter

Engine modification through reducing nozzle hole diameter (NHD) (i.e., from the base value of 0.28 to the modified value of 0.20 mm) has been shown as an effective strategy in improving engine performance, combustion, and emission parameters. However, it has also led to substantial increases in NOx emission as a major shortcoming. In light of that, the present study was aimed at overcoming this challenge through the application of a partially-cooled exhaust gas recirculation (EGR) system. More specifically, Mahua oil biodiesel-diesel blend (B20) and neat diesel were tested on a modified single cylinder diesel engine under five different engine loads (i.e., 2.46, 4.92, 7.38, 9.84, and 12.3 kg) and in the presence of varying EGR rates (i.e., 10, 20, and 30%). The results obtained revealed that the performance, combustion, and emission characteristics of the modified engine (3-hole nozzle with an orifice diameter of 0.20 mm) were improved for both neat diesel and B20 except in the case of NOx, in comparison with those of the conventional diesel engine (3-hole nozzle with an orifice diameter of 0.28 mm). The considerable increases in NOx emissions caused by the smaller orifice NHD could be successfully compensated for through the implementation of the partially-cooled EGR. Overall and based on the findings of the present study, the proposed engine modification in the presence of partially-cooled EGR rate of 10% could be recommended as efficient combustion conditions for 20% blend of Mahua oil biodiesel and diesel. However, further increments in the EGR rate and in particular at higher loads, adversely affected the performance and emission characteristics of the modified engine due to the recirculation of high amounts of unburnt soot, CO2, H2O, as well as of O2 deficiency.