Effects of start of injection and exhaust gas recirculation on dual fuel combustion of isobutanol with diesel and waste cooking oil biodiesel in a diesel engine at higher loads

Dual fuel combustion (DFC) is one of the current emission reduction methods adopted widely for diesel engines. In DFC, high-octane fuels (alcohol) are port injected and high cetane fuels (diesel, biodiesel) are directly injected into the cylinder. However, DFC is reported to increase nitrogen oxides (NOx) compared to conventional combustion mode (CCM) at higher loads. Hence, to mitigate NOx emission in DFC of isobutanol (IB) with diesel, B20, and B100 fuels at higher loads (80 and 100%), the influences of start of injection (SOI) and exhaust gas recirculation (EGR) are investigated. The baseline SOI of DFC fixed at 27 degrees CA before top dead center (bTDC) is retarded to 25, 23, and 21 degrees CA bTDC, and varying EGR (10, 15, and 20%) is implemented at the baseline SOI. Significant NOx reductions of 47.11, 52.53, and 54.45% at the SOI of 21 degrees CA bTDC (at 100% load) and 41.74, 46.38, and 47.81% at 20% EGR (at 80% load) are achieved in the DFC of diesel, B20, and B100 respectively, visa-vis their CCM. In DFC of D-IB and B20-IB, retarded SOIs and 10% EGR exhibited better NOx/smoke trade-off than their CCM. Overall, all the DFCs with SOI of 25 degrees CA bTDC as well as 10% EGR is suitable operating conditions compared to CCM.