Evaluation of Diesel Spray with Non-Circular Nozzle - Part I: Inert Spray

Numerous studies have characterized the impact of high injection pressure and small nozzle holes on spray quality and the subsequent impact on combustion. Higher injection pressure or smaller nozzle diameter usually reduce soot emissions owing to better atomization quality and fuel-air mixing enhancement. The influence of nozzle geometry on spray and combustion of diesel continues to be a topic of great research interest. An alternate approach impacting spray quality is investigated in this paper, specifically the impact of non-circular nozzles. The concept was explored experimentally in an optically accessible constant-volume combustion chamber (CVCC). Non-reacting spray evaluations were conducted at various ambient densities (14.8, 22.8, 30 kg/m³) under inert gas of Nitrogen (N₂) while injection pressure was kept at 100 MPa. Shadowgraph imaging was used to obtain macroscopic spray characteristics such as spray structure, spray penetration, and the spray cone angle. Analysis from image processing showed expected result of lower penetration rate and higher spray cone angle as ambient density increased. Two slot nozzles with different aspect ratios but similar flow area as compared with one of the circular nozzles were tested. Given a certain minor-to-major axis ratio of the non-circular nozzle, spray penetration of non-circular nozzle can be longer or shorter than that of the circular nozzle. At a similar condition, the spray cone angle was smaller for the non-circular nozzle compared to that of the circular nozzle. A mathematical model based on the work of Hiroyasu & Arai [1] was applied to predict spray tip penetration for all the tested nozzles. The model was then modified to predict spray penetration of non-circular nozzles. Non-circular nozzles were shown to have an impact on spray break-up and spray penetration, that can potentially promote the level of mixing. Validated 3D CFD simulation was used to provide insight into the spray and combustion of a non-circular nozzle. Subsequently, longer ignition delay was observed for non-circular nozzle as compared to a circular nozzle through simulation results.