Investigation on Effect of Offset Orifice Nozzle on Diesel Combustion Characteristics

Compression ignition engines provide superior thermal efficiency over other internal combustion engines. Unfortunately the combustion process is diffusive combustion, meaning a lot of fuel is impinged the on the piston and cylinder wall. This creates cooling loss coupled with smoke, CO and THC. Minimization of the nozzle orifice diameter is a simple method widely used to shorten spray penetration. However, decreasing the nozzle orifice diameter also decreases fuel flow rate resulting in a prolonged injection and combustion process and reducing thermal efficiency. An offset orifice nozzle causes less fuel impingement by shorter fuel spray penetration without significant reduction of fuel flow rate. The offset orifice nozzle was made by shifting its alignment from the center of the sac to the edge of the sac following the swirl direction. A counterbore design was applied to maintain constant orifice length. This paper investigates the effects of nozzle orifice position on combustion characteristics under various injection pressures, injection amounts and oxygen concentrations. The experiments were carried out on a single-cylinder engine. The engine was installed with a standard nozzle or an offset nozzle. The single pulse injection experiment was conducted in order to clarify the effect of nozzle orifice position on combustion characteristics. The results showed the offset orifice nozzle provided similar ignition delay and shorter combustion duration compared with the standard nozzle. The offset orifice nozzle also provided higher gross ITE compared with the standard design nozzle under all test conditions. However the increasing gross ITE from the offset nozzle orifice diminished when injection amount increased.