Transient heating effects in high pressure Diesel injector nozzles

Abstract

The tendency of today's fuel injection systems to reach injection pressures up to 3000 bar in order to meet forthcoming emission regulations may significantly increase liquid temperatures due to friction heating; this paper identifies numerically the importance of fuel pressurization, phase-change due to cavitation, wall heat transfer and needle valve motion on the fluid heating induced in high pressure Diesel fuel injectors. These parameters affect the nozzle discharge coefficient (Cd), fuel exit temperature, cavitation volume fraction and temperature distribution within the nozzle. Variable fuel properties, being a function of the local pressure and temperature are found necessary in order to simulate accurately the effects of depressurization and heating induced by friction forces. Comparison of CFD predictions against a 0-D thermodynamic model, indicates that although the mean exit temperature increase relative to the initial fuel temperature is proportional to (1-Cd 2) at fixed needle positions, it can significantly deviate from this value when the motion of the needle valve, controlling the opening and closing of the injection process, is taken into consideration.Increasing the inlet pressure from 2000bar, which is the pressure utilized in today's fuel systems to 3000bar, results to significantly increased fluid temperatures above 2 the boiling point of the Diesel fuel components and therefore regions of potential heterogeneous fuel boiling are identified.

Assessment of compressibility effects on internal nozzle flow in diesel injectors at very high injection pressures

“…Similar conclusions about the effect of the fuel properties have already been seen both experimentally and numerically for other kinds of biodiesel [27]- [31] and for winter fuel formulations [32]- [34]. Recently, a few authors [35]- [39] have showed that it is important to consider not only the changes in the fuel properties related to the fuel composition, but also those related to the different temperature and pressure conditions along the nozzle geometry, which are traditionally neglected.…”

Experimental assessment of the fuel heating and the validity of the assumption of adiabatic flow through the internal orifices of a diesel injector

“…Approaches have been made through one-dimensional modelling of the complete injector flow [9][10] [11] [12][13] [14] or three-dimensional modelling of the nozzle flow [4][15] [16][17] [18]. Some of these works assume that the flow is isothermal [11] [12][13] [14].…”

Purely predictive method for density, compressibility, and expansivity for hydrocarbon mixtures and diesel and jet fuels up to high temperatures and pressures

“…To accelerate this process and reduce costs, computational fluid dynamics (CFD) simulations are routinely used by manufacturers to evaluate, understand, and optimize FIE design and operation. Many numerical methods and approaches have been developed to simulate the performance of fuel injectors and provide insight into the physical processes taking place inside these systems [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Accurate simulation of the flow field within the FIE and phenomena observed further downstream (e.g., jet breakup and spray formation) is required to ensure their reliable predictive capability.…”