CI engines provide higher thermal efficiency compared to other internal combustion engines. On the other hand large amounts of smoke and NOx are produced during combustion. Smoke and NOx can be reduced by applying Premixed Charge Compression Ignition (PCCI) combustion. Unfortunately, the problems of PCCI combustion include unstable start of combustion and limited operating range. The multi-pulse ultrahigh pressure injection allows fuel to control PCCI combustion. The objective of offset orifice nozzle is to improve mixture formation and shorten spray penetration in order to increase thermal efficiency and control PCCI combustion. The offset orifice nozzle was designed by shift orifice aliment from into the sac center to edge of sac follow swirl direction. Counter bore design was applied to offset orifice nozzle in order to keep the constant orifice length as standard nozzle. This paper investigates the effect of nozzle orifice design on combustion characteristics under multi pulse ultra high pressure injection and PCCI combustion conditions. The experiments were carried out on a single cylinder engine at 0.55 MPa gross IMEP at 1,750 rpm. The injection pulses were 3 pulses equally mass main injection at 150, 200, 250, 300 and 350 MPa injection pressure. In case of standard nozzle orifice, 1st, 2nd pulse are PCCI followed by diffusive combustion in every injection pressure. For offset orifice nozzle orifice at 150 and 200 MPa 1st, 2nd pulse are also PCCI combustion. However when injection pressure is over 200 MPa, the 2nd pulse of rate of heat release become diffusive combustion. The offset orifice nozzle resulted in increased thermal efficiency, NOx and smoke. However significant differences between the smoke of offset orifice nozzle and standard nozzle were not found under injection pressure 300 and 350 MPa. The offset orifice nozzle also resulted in decrease CO and THC.
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