Experimental investigation on effect of enhanced premixed charge on combustion characteristics of a direct injection diesel engine

This study deals the effect of premixed charge energy on combustion characteristics of a direct injection diesel engine of 7.4 kW rated power at a constant speed of 1,500 rpm. The premixed charge energy is varied from 25.4 to 56.4 % under three different modes; (i) conventional diesel mode (ii) H2-diesel dual-fuel mode, and (iii) partially homogeneous charge compression ignition (PHCCI) mode. The increase in premixed charge energy increases the premixed combustion phase, but diffusion and afterburning phase decrease. It is observed from the study that the heat release rate depends on both premixed charge energy and start of combustion. The highest energy share of 56.4 % was achieved with PHCCI mode. The in-cylinder peak pressure and heat released during premixed combustion phase increased from 7.66 MPa and 298 J/cycle with 25.4 % premixed charge (conventional diesel mode) to 8.1 MPa and 315 J/cycle with 56.4 % premixed charge (PHCCI mode). The NOx and smoke emissions decreased from 6.9 × 10−3 kg/kW h and 14.3 % opacity with 25.4 % premixed charge energy to 5.9 × 10−3 kg/kW h and 0.3 % opacity with 56.4 % premixed charge energy. A proper methodology for calculation of premixed charge energy in diesel engines is highlighted in this study. The effect of premixed charge on premixed, diffusion and after burning combustion phases is explained in detail.