City Research Online

Abstract

Investigations with 300MPa injection pressures show significant soot reduction, but the effect of such extremepressures on the in-nozzle flow has not been closely examined. The study of the in-nozzle flow is important becauseit dominates primary break-up characteristics and therefore the combustion efficiency. Moreover, the characteristicpressure drops in Diesel injectors may cause the fuel to cavitate, which leads to enhancements in the nozzleoutlet velocity, the spray cone angle and the fuel atomisation. In this work, the fuel property database is modelledusing the molecular-based PC-SAFT EoS with an eight-components surrogate based on a grade no. 2 Dieselemissions-certification fuel. The composition for the surrogate is (in mole fration): 2.7% n-hexadecane, 20.2% n-octadecane, 29.2% heptamethylnonane, 5.1% n-butylcyclohexane, 5.5% trans-decalin, 7.5% trimethylbenzene and15.4% tetralin. Then, this surrogate is utilised in simulations for a common rail 5-hole tip injector tapered nozzle.The needle is assumed to be still at a lift of 100μm, which is representative of the lift reached during pilot injection.The injector operating pressures start from 180MPa and reach 450MPa. The collector back pressure is 5MPa. Thedensity of the bulk fluid is assumed to vary according to a barotropic-like scheme, following an isentropic expansion.Results show an increase in the mass flow rate, following the square root of the pressure difference law and alsoin the outlet velocity, both as expected. Surprisingly, the cavitation is significantly reduced as the injection pressureincreases. A focused study on this particular phenomenon shows a significant decrease in the Reynolds numberin the sac, therefore the flow is found to be more stable and the pressure drop along the nozzle is smaller. Thereason for the lower Reynolds number is found on the heavy nature of Diesel fuels. While the sac average velocityincreases 15% between an injection pressure of 180MPa and 450MPa, the kinematic viscosity increases close to a70%.

Publication Type:	Conference or Workshop Item (Paper)
Additional Information:	This work is licensed under a Creative Commons 4.0 International License (CC BY-NC-ND 4.0).
Subjects:	T Technology > TJ Mechanical engineering and machinery T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments:	School of Science & Technology > Engineering

Export

Downloads