Using spray momentum flux measurements to understand the influence of diesel nozzle geometry on spray characteristics (original) (raw)
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Measurements of Spray Momentum for the Study of Cavitation in Diesel Injection Nozzles
In Diesel injection Systems, cavitation often appears in the injection nozzle holes. This paper analyses how cavitation affects the Diesel spray behavior. For this purpose two spray parameters, mass flux and momentum flux, have been measured at different pressure. We know that cavitation brings about the mass flux choke, but there are few studies about how the cavitation affects the momentum and the outlet velocity. The key of this study is just the measurement of the spray momentum under cavitation conditions.
Flow regime effects on non-cavitating injection nozzles over spray behavior
This paper deals with the influence of flow regime (laminar, transition or turbulent) on the internal flow behavior, and how it affects the spray development in diesel nozzles. In particular, the research described here aims at studying and quantifying the internal flow regime effects on the spray behavior. With this purpose, internal flow results, based on mass flow rate and momentum flux measurements performed on three different tapered nozzles and which helped to determine the flow regime, has been taken into account as a point of departure for the spray behavior analysis. Thus, in this work, spray macroscopic visualization tests have been performed and analyzed which clearly revealed a change in the behavior of the angle and penetration of the spray related to the change of the flow nature. Moreover, with all the experimental data available, it has been possible to relate macroscopic parameters of the spray with those describing the internal flow (momentum and effective velocity) or the geometry of the nozzle (length or diameter) through correlations.
Air/fuel mixing process in the combustion chamber of Diesel engines plays an important role on the combustion efficiency. This mixing depends on the particle size distribution in the spray, on the local velocity of fuel droplets in the spray and on the air entrainment. Nozzle geometry as well as nozzle internal flow conditions influence many of these spray properties. An experimental study of the influence of the nozzle geometry on these properties has been conducted. The spray structure and the particle size distribution are determined using image shadowgraphy, the axial velocities near the nozzle outlet have been measured using Laser Correlation Velocimetry. Gas velocities are measured using Fluorescent Particle Image Velocimetry. It is found that the cavitation plays a role of major importance on the atomization process and on the interaction between the liquid spray and the surrounding gas.
Experimental and numerical momentum flux evaluation of high pressure Diesel spray
Fuel, 2012
In the present paper, a detailed numerical and experimental investigation of high pressure Diesel spray evolution is reported. The analysis is mainly focused on the spray momentum flux measurement, which is increasingly used to characterise both the in-nozzle flow in terms of cavitation intensity and the flow uniformity among the different jets emerging from the same nozzle. In the present study, the potentially critical aspects of the spray momentum flux measurement methodology based on the impact force on a flat target have been investigated comparing CFD-3D results and experimental data pertaining to a wide range of operating conditions in terms of injection pressure, energizing time and back-pressure. The available experimental data, pertaining to a commercial common-rail injector, include the spray momentum flux time-histories and steady values, the injection rate and the spray imaging during momentum flux tests and free-jet evolution. Globally, a good agreement was found among experimental and numerical momentum flux histories; furthermore, CFD allowed to evaluate the significant contribution of the spray gaseous phase to the measured momentum flux, which rapidly tends to become predominant as the measurement station distance from the nozzle exit increases. The obtained results also suggest that some details of the measurement system can significantly affect the spray momentum detection accuracy. Hence, a detailed numerical analysis of the spray impact force was developed to evaluate the target intrusiveness, pointing out the irrelevance in terms of momentum flux time-history of the target presence into the simulated domain with respect to the free jet evolution. A practical strategy to define the optimal combination of target-diameter and nozzle-target distance, for each set of operating conditions, as a compromise between the extreme configurations of the involved parameters, is discussed.
2011
The improvements in the fuel injection system of diesel engines can significantly reduce the emission of harmful pollutants. Cavitation phenomenon inside a diesel injector plays a critical role in primary spray breakup and development processes. In this paper, a CFD analysis of the influence of internal flow through various nozzle geometries on the global characteristics of the spray, including spray tip penetration, sauter mean diameter (SMD) and spray pattern are discussed in a heavy-duty DI diesel engine. Cylindrical nozzles with different nozzle inlet R/D ratios and nozzle hole, L/D ratios are used in order to observe the individual effects of these geometrical parameters. With respect to the liquid-phase, spray calculations are done based on a statistical method referred to as the Discrete Droplet Method (DDM). The results show that the lower R/D ratio or the sharper nozzle inlet leads to lower spray tip penetration length, larger spray angle and smaller droplet sizes due to st...
Influence of the Spatially Resolved Nozzle Hole Exit Flow Distribution on Diesel Spray Development
SAE Technical Paper Series, 2007
The internal flow in Diesel injector nozzles significantly affects the spray formation, atomisation and air/fuel mixing rates. A multi-dimensional model has been developed to numerically predict the spray evolution patterns with particular focus on capturing the influence of the injector nozzle flow on the near-nozzle spray dispersion. The link to the internal flow is established by using as initial conditions for the injected fuel, the transiently and spatially resolved distribution of the flow field at the nozzle hole exit plane as calculated from a multi-dimensional and multi-phase nozzle flow simulation model. The local spray dispersion angle is estimated by assuming that the disintegration of the liquid jet is function of the distribution of liquid velocity, cavitation vapour volume fraction and liquid turbulence level at the exit of the injection hole. Results confirm that the internal nozzle flow and in particular formation of cavitation, significantly affects the initial spray dispersion angle in a transient manner, in agreement with flow visualisation experiments inside transparent nozzle replicas.
Atomization and Sprays, 2019
In this work, the effect of high injection pressures and ambient gas properties on diesel spray penetration and spreading angle are studied. To this end a multi-hole piezoelectric injector was used, and MIE-Scattering optical technique to visualize the spray. Injection pressures up to 270 MPa were used throughout the experiments. Additionally, the spray behavior going from subsonic to supersonic state was analyzed by controlling the ambient gas speed of sound, promoting in this way supersonic jets. For this purpose, measurements were done using three different ambient gases (SF 6 , CO 2 , and N 2) at isothermal conditions. The results showed that sprays near transonic or in supersonic state had a higher penetration rate than those in subsonic state. Furthermore, among the sprays near transonic or in supersonic state, those with higher Mach number had faster penetration. Differently, within the sprays at subsonic state, no significant variations in spray penetration rate were found, regardless of the difference in the Mach number. Shock waves appearances were pointed out as a possible explanation for the spray penetration variations observed. Finally, a statistical analysis is presented for the spray penetration under isothermal conditions and for each ambient gas.
Numerical simulation of unsteady nozzle flow and spray formation under diesel engine conditions
In this paper a numerical approach for the prediction of the unsteady atomization process of liquid fuel in Diesel engine is presented. The dependences between the transient nozzle flow and spray formation are analysed. For that purpose models to simulate unsteady nozzle flows including the transient behaviour of cavitation and two-phase atomization process are employed. Results of transient flow through various 3D nozzle shapes (one-and multi-hole nozzle) and the resulting spray development are discussed. The flow predictions agree well with quantitative characteristics of nozzle flows and spray structures and with experimental results obtained for the case of the flow in a high speed diesel injector.
A comprehensive study on the effect of cavitation on injection velocity in diesel nozzles
Energy Conversion and Management, 2012
Results when testing cavitating injection nozzles show a strong reduction in mass flow rate when cavitation appears (the flow is choked), while the momentum flux is reduced to a lesser extent, resulting in an increase in effective injection velocity. So as to better understand the origin of this increase in effective injection velocity, the basic equations for mass and momentum
Velocity field analysis of the high density, high pressure diesel spray
International Journal of Multiphase Flow, 2016
In this study, particle image velocimetry (PIV) measurements have been performed extensively on a nonreactive dense diesel spray injected from a single orifice injector, under various injection pressure and steady ambient conditions, in a constant flow chamber. Details of PIV setup for diesel spray measurement without additional seeding are explained first. The measured velocity profiles are compared to those obtained from other similar measurements performed in a different institution, as well as those obtained from a 1D spray model simulation, presenting in both cases a good level of agreement. In addition, the velocity fields under various injection pressures and ambient densities show the dominant effects of these parameters on the behavior of diesel spray. The self-similarity of the transverse cut profiles of axial velocity is evaluated, showing that the measurements are in agreement with the hypothesis of self-similar velocity profiles. Finally, the effect of injection pressure and ambient density on the velocity fluctuations is presented and analyzed as well. While the experimental results presented here could help to understand the complex diesel fuel-air mixing process during injection, they also provide additional spray velocity data for future computational model validation, following the main idea of the Engine Combustion Network.