“…Various modifications in engines such as exhaust gas recirculation (EGR), diesel oxidation catalyst (DOC), elective catalytic reduction (SCR) and diesel particulate filter (DPF) system have developed to minimize the pollutants. By varying various engine parameters like fuel injection timing [18,24], injection pressure, [6] compression ratio(VCR), [13][14][15][16][17][18][19][20][21] etc. and application of several techniques such as turbo charger, preheating, low heat rejection (LHR), and homogeneous charge compression ignition (HCCI) concept, etc [4,10,11], the performance, combustion, and emission characteristics of engines may be improved.…”