Effect of high injection pressures and ambient gas properties over the macroscopic characteristics of the diesel spray on multi-hole nozzles (original) (raw)
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Study of liquid and vapor phase behavior on Diesel sprays for heavy duty engine nozzles
Applied Thermal Engineering, 2016
A lot of effort has been put in the past years into the understanding of the delivery and development of diesel sprays in engine-like conditions as it has been proved to be a very important step for the design of better and cleaner commercial engines. Due to the bigger share of passenger cars engines over heavy duty engines, the research has been mainly focused on the investigation using small nozzles. This paper studies two nozzles with diameters representative of those that can be encountered in heavy duty engines, with the objective of corroborating the conclusions gathered for small nozzles representative of passenger car engines. The experimental data have been acquired by state-of-the-art techniques and equipment, and serves two purposes: further the understanding of the physics involved in the injection event and spray evaporation; and provide a dataset to CFD models that can accurately predict the behavior of the injection event. The tests were performed in a constant pressure flow vessel that allows to simulate enginelike conditions (1000 K and 15 Mpa) with continuous flow. The injection system tested is a novel, common-rail, solenoid-actuated injector for heavy duty applications which operates up to 220 Mpa. All experiments were performed in non-reacting conditions. The extended test matrix allowed to determine the influence of several parameters such as rail pressure, gas temperature, gas density, and nozzle geometry on the air-fuel mixing and evaporation process, by analyzing the spray penetration and spreading angle. Mie scattering and double-pass Schlieren optical configurations have been used to measure global liquid and vapor penetration, respectively. The data proves that spray penetration at low temperature can be up to 15% faster than spray penetration at high temperature conditions at the same density for the nozzles experimented, which limits the usability of low temperature experiments to infer the behavior of the injector at high temperature conditions. The data also shows that the nozzle with the biggest diameter provided the highest value of stabilized liquid length as expected. Also, when vapor phase is reached, the temperature has negligible effect on the global diesel spray morphology, and no influence on the tip penetration or on the spreading angle.
Scaling spray penetration at supersonic conditions through shockwave analysis
Fuel, 2020
In the current paper, an investigation of the supersonic flow effect on shockwave generation and diesel spray penetration scaling has been performed. For this purpose, spray visualization tests have been carried out in a constant-pressure chamber at room temperature using shadowgraphy technique. Two working gases have been used: nitrogen, with similar thermodynamic characteristics to the engine environment, and sulfur hexafluoride, aimed at producing supersonic conditions at moderate injection pressure values. A total of 60 operating points, including different nozzle geometries, injection pressures and chamber densities have been studied. From the visualization study, two different kinds of shockwaves have been detected: normal or frontal, for moderate spray tip Mach (between 1 and 1.5); and oblique, when the Mach is higher than 1.5. The penetration results show that, for the same injection conditions in terms of injection pressure and chamber density, the spray propagation is equal for SF6 and N2 when the spray is on subsonic conditions, while penetration is higher for SF6 when supersonic velocity is reached. This behavior has been related to the density gradient appearing across the shockwave. A new methodology to extrapolate supersonic penetration from the well-known subsonic penetration law has been proposed, showing good agreement with the experimental results.
Effect of ambient pressure on penetration of a diesel spray
International Journal of Multiphase Flow, 2007
In the present experimental and theoretical work the propagation of a high-speed fuel spray at distances much longer than the breakup length is studied. The motion of the spray is modeled in two regions: the main region of the steady flow and the front region of the spray. The analysis yields the equation of propagation of the tip of the spray. These theoretical results have been validated against experimental data obtained from a common-rail diesel injection nozzle and from other data available in the literature. The importance of the shock wave propagation at the initial stage of the spray injection is demonstrated.
Gas Entrainment Characteristics of Diesel Spray During End of Injection Transient
Atomization and Sprays, 2009
In this study, gas entrainment characteristics of a diesel spray injected by a group of closely spaced twoorifices (group-hole nozzle) were investigated. Both free and wall-impinging sprays were considered. The gas entrainment characteristics of the group-hole nozzle spray were compared to those of single-hole nozzle sprays: one has the same total hole area with the group-hole nozzle, and the other has the same hole diameter. The gas entrainment characteristics of diesel sprays were investigated using a particle image velocitmetry technique coupled with a laser induced fluorescence technique (LIF-PIV technique). The spray tip penetration of the group-hole nozzle was the shortest among the applied nozzles in a free spray condition, while it was the longest in a wall-impinging condition. In the free spray condition, the gas entrainment of the spray was enhanced by the group-hole nozzle due to extensive momentum exchange with surrounding gas and superposed gas entrainment motion of the two-jets injected by the group-hole nozzle. After wall-impingement, the group-hole nozzle spray showed a stronger walljet vortex and increased gas entrainment compared to the single-hole nozzle sprays due to enhanced spray/wall interaction caused by the momentum interaction of the two-jets from the group-hole nozzle. Asymmetric shape of the group-hole nozzle spray resulted in an asymmetric gas velocity distribution of the spray both in the free and wall-impinging conditions.
Dynamic characteristics of pulsed supersonic fuel sprays
Shock Waves, 2008
This paper describes the dynamic characteristics of pulsed, supersonic liquid fuel sprays or jets injected into ambient air. Simple, single hole nozzles were employed with the nozzle sac geometries being varied. Different fuel types, diesel fuel, bio-diesel, kerosene, and gasoline were used to determine the effects of fuel properties on the spray characteristics. A vertical two-stage light gas gun was employed as a projectile launcher to provide a high velocity impact to produce the liquid jet. The injection pressure was around 0.88-1.24 GPa in all cases. The pulsed, supersonic fuel sprays were visualized by using a high-speed video camera and shadowgraph method. The spray tip penetration and velocity attenuation and other characteristics were examined and are described here. An instantaneous spray tip velocity of 1,542 m/s (Mach number 4.52) was obtained. However, this Communicated by K. Takayama.
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2010
Computational fluid dynamics results are presented providing information on the influence of multiple injection strategy on fuel vaporization characteristics under conditions typical of direct injection, turbocharged, high-speed automotive diesel engines. The fuel is assumed to be injected from a high-pressure common rail injector nozzle. Focus is given on the number of multiple injections and dwell-time on the evaporating spray plume development. Comparison between the different cases is performed in terms of liquid and vapour penetration curves, the spatial distribution of the air-fuel equivalence ratio and the fuel vapour spatial distribution difference between the cases considered. The results confirm that, under the operating conditions investigated, the liquid penetration length, known to freeze at a distance from the nozzle exit, is not significantly affected by the injection strategy, while vapour penetration follows the time-shift of the dwell-time. Longer dwell-times retard the diffusion of the vapour in the carrier gas. Although injection of small fuel quantities prior to the main pulse does not affect the liquid penetration, it contributes up to 5 per cent more stoichiometric fuel vapour present in the area of observed auto-ignition sites. Post injection and splitting of the main injection in two pulses modify the vapour distribution by creating two spatially separated fuel-rich zones.
Structure of high-pressure diesel sprays
A comprehensive set of computational and experimental results for high-pressure diesel sprays are presented and discussed. The test cases investigated include injection of diesel into air under both atmospheric and high pressure/temperature chamber conditions, injection against pressurized and cross-flowing CF 6 simulating respectively the density and flow conditions of a diesel engine at the time of injection, as well as injection into the piston bowl of both research and production turbo-charged highspeed DI diesel engines. A variety of high-pressure injection systems and injector nozzles have been used including mechanical and electronic high-pressure pumps as well as common-rail systems connected to nozzles incorporating a varying number of holes with diameters ranging from conventional to micro-size. Results from spray imaging, phase Doppler anemometry and CFD calculations of both the internal nozzle flow and the subsequent spray development have been combined to identify the relative importance of the geometric/operating parameters that control the structure of diesel sprays and areas of further research.
Experimental Thermal and Fluid Science, 2014
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.