Temperature of diesel fuel spray at injector nozzle hole exit

Abstract

Fuel is injected into the cylinder of a diesel engine through a high-pressure injection system. For the particular system considered by Perkins Technology, fuel at a temperature of about 300 K arrives in the injector at approximately 1400 bar and is then injected into the cylinder in 1.5 ms by raising a needle and uncovering the nozzle holes. The cycle period between injections is 40 ms. Each injection contains 85 mm^3 of fluid. This corresponds almost exactly to the amount of fuel stored in the annulus around the needle below the spherical reservoir. The physical quantity of interest is the temperature of the fuel when it is injected into the cylinder. Temperature measurements in the fuel storage volume are hard to make. A thermocouple placed in the wall of the injector tip, however, has measured a temperature of 550 K.

The various contributions to the change in temperature of the fluid can be summarised as:
(a) -5 K from the adiabatic cooling
(b) 15 K from the convection near the nozzle
(c) ΔT_s/17 from the conduction in the annulus. This depends on the average temperature of the wall of the annulus, which is unknown, but certainly between 300 and 5.50 K, corresponding to ΔT_s = 0-250 K. Hence the smallest and largest rises in temperature are 0 and 15 K respectively.

The maximal rise in temperature of the fluid is hence 25 K. A more likely estimate might be 10 K.

Some useful data, in the absence of actual heat measurements inside the fuel reservoir around the needle, would be the temperature of the wall TB. Knowledge of its spatial variation would also be of interest, since it has just been been treated as an average in this report.