A Novel Nozzle Orifice Design of a Heavy-Duty Diesel Engine to Achieve Higher Thermal Efficiency with Significantly Reduced Heat Loss

This study investigated a novel nozzle orifice design to improve thermal efficiency. The offset orifice nozzle has holes drilled offset of less than 0.5 mm from the radial center of the nozzle. Engine performance test and in-cylinder combustion observation were carried out by means of a heavy-duty diesel engine. The experimental results demonstrated that the offset orifice nozzle achieved significant improvements in both heat loss and thermal efficiency, regardless of the compression ratio and operating load conditions. However, the underlying mechanisms have not been revealed yet. Therefore, investigation into the mechanisms behind heat loss reduction and thermal efficiency improvements with the offset orifice geometry is the purpose for establishing design guidelines for optimization. It was revealed by the combustion visualization that the flame tip length of the offset orifice nozzle was shortened with significantly wider flame cone angle from very close to the orifice exit even though the fuel injection rate was slightly higher than that of the referenced radial orifice nozzle. The asymmetrical spray structure along with the nozzle internal flow were confirmed by a numerical simulation. From these findings, the main cause of heat loss reduction was assumed to be more homogeneous wall surface temperature distribution by the modified spatial flame distribution.