Engine combustion network: Influence of the gas properties on the spray penetration and spreading angle

Abstract

In this work, three Engine Combustion Network (ECN) single-hole nozzles with the same nominal characteristics have been tested under a wide range of conditions measuring spray penetration and spreading angle. n-dodecane has been injected in nonevaporative conditions at different injection pressures ranging from 50 to 150 MPa and several levels of ambient densities from 7.6 to 22.8 kg/m 3 . Nitrogen and Sulphur Hexafluoride (SF 6 ) atmospheres have been explored and,in the first case, a temperature sweep from 300 to 550 K at constant gas density has been executed. Mie scattering has been used as the optical technique by employing a fast camera, whereas image processing has been performed through a home-built Matlab code. Differences in spray penetration related to spray orifice diameter, spreading angle and start of injection transient have been found for the three injectors. Significant differenceshave been obtained when changing the ambient gas, whereas ambient temperature hardly affects the spray characteristics up to 400 K. However, a reduction in penetration has been observed beyond this point, mainly due to the sensitivity limitation of the technique as fuel evaporation becomes important. The different behavior observed when injecting in different gases could be explained due to the incomplete momentum transfer between spray droplets and entrained gas, together with the fact that there is an important change in speed of sound for the different gases, which affects the initial stage of the injection.

Experimental study of the injection conditions influence over n-dodecane and diesel sprays with two ECN single-hole nozzles. Part I: Inert atmosphere

“…10 shows the h v behavior with parametric changes in operating conditions. As occurs in previous studies [7,19], in Fig. 11-left, it is possible to observe how ambient density causes an increment in h v as product of the enhancement in gas entrainment into the spray which is caused.…”

“…Finally, it is appreciable in Fig. 9 how these respective patterns are kept between fuels, but Spray C tends to have greater R-parameter and penetration than Spray D at low densities, and how the opposite occurs with high values of density, which can be explained by the h v rise with gas density [7] and how this reduces vapor penetration.…”

“…Many previous researches have been made in order to investigate the effects on spray liquid length and vapor phase development induced by engine parameters such as atmosphere conditions and injection pressure [15,16,6,17], injector design [18], and fuel characteristics [6,19]. Parametric influence on spray angle has also http been investigated in the past [7,20,21], determining interesting aspects as its strong dependency on the ambient density and the fact that the appearance of cavitation on diesel injector nozzles can make the spray angle wider evidenced by visualization of transparent nozzles [20,22], laser sheet illumination [23] and Xrays [24]. In addition to this, some studies have confirmed the increment of turbulence at cavitating conditions, which promotes the jet break-up and enhances the mixing process [25].…”

“…A fundamental step forward in the comprehension of these phenomena was achieved with the definition and experimental characterization of specific features of the injection process such as tip penetration, spreading angle, liquid length, ignition delay, liftoff length, among others [6,7]. Many authors have performed spray visualization experiments employing facilities such as optically accessible engines [8] and test rig cells [9,10] in order to analyze these parameters.…”

Spray flow structure from twin-hole diesel injector nozzles

“…However, while the 0°THN has a larger difference in K-factor and diameter than the 10°THN for its two nozzle holes (Table 1), it shows the least variability in penetration, suggesting these differences are not sufficient to give rise to the observed behavior. Variability in internal nozzle flow, whether from transient needle movement [49][50][51], instabilities in the internal flow, variation in line pressure [25] or cavitation dynamics [23] are possible causes.…”