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Effect of Spray-Wall Interaction on Air Entrainment in a Transient Diesel Spray
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Abstract
The influence of spray-wall interaction on air entrainment in an unsteady non-evaporating diesel spray was studied using laser Doppler anemometry. The spray was injected into confined quiescent air at ambient pressure and temperature and made to impact on a flat wall. The air velocity component normal to a cylindrical surface surrounding the spray was measured during the entire injection period, allowing to evaluate the time history of the entrained air mass flow rate. The influence of wall distance and spray impingement angle on air entrainment characteristics has been investigated and the results indicate that the presence of a wall increases the entrained mass flow rate in the region close to the surface, during the main injection period. Normal impingement appears to produce stronger effects than oblique incidence at 30 and 45 deg. A qualitative explanation of the results is also proposed, based on the drop-gas momentum exchange mechanism.
Air entrainment in steady and unsteady full cone sprays has been subject of experimental research only quite recently and few works have been published [1, 2, 3, 4, 5, 6, 7, 8 and 9] up to date. The reason of an increasing interest on the subject can be explained by the relevance that this phenomenon has in applied fields like internal combustion engines.
The importance of the phenomenon can be easily understood when considering that the interaction between fuel spray and surrounding gas is of capital importance for the combustion efficiency of DI diesel engines, and is, to a great extent, controlled by the fuel injection characteristics and flow mixing mechanisms, such as swirl and air entrainment. The last process is responsible of the first stage of the mixture formation, and controls spray combustion during early and main diffusion periods [10].
In a previous work [5] the air entrainment into an unsteady diesel spray injected into quiescent atmosphere at room temperature and pressure was measured by laser Doppler anemometry (LDA) and characterised in terms of entrained mass flow rate as suggested in [4], in order to compare the results to those obtained in steady turbulent gaseous jets [11]. In the near field zone investigated, up to 160 nozzle diameters (40 mm), the air entrainment into transient liquid jets resulted to be lower than that in steady gaseous jets, but larger than that in steady liquid jets [4]. The momentum exchange between liquid and gaseous phase was also evaluated and a dependence on the injection mass flow rate was deduced [5].
Recently, it has been found experimental evidence that increasing fuel injection pressure, coupled with retarded injection timing, reduces soot concentration [12], black smoke emission [13] and improves fuel consumption [13, 14]. This result has been interpreted as a consequence of augmented mixing and air entrainment, which makes mixture formation less dependent on air swirl. This is beneficial in the lower engine speed range, where swirl is always low.
In small DI diesel engines, when high fuel injection pressures are used, the spray is found to impact on the piston bowl before ignition starts [15, 16 and 17]. In fact, in the very earliest portion of the injection event, up to the point of maximum spray-tip velocity, the penetration process is dominated by the fuel delivery characteristics of the injection system [18], the air motion having very little effect. After the fuel is injected into the cylinder, sufficient time elapses (about 1 ms) before the formation of a combustible mixture and ignition occur, well enough to allow the dense core of the liquid jet to reach the piston bowl.
The spray impingement on the piston surface may be detrimental because liquid splashed above the bowl can increase hydrocarbon emissions. However, jet impingement produces strong turbulence, enhancing mixing of rich mixture in the core of the spray, and provides an additional mechanism for droplet break-up [14, 19].
Those findings prompted the idea of studying the influence of spray-wall interaction on air entrainment in an unsteady diesel spray, which is the subject of the present work. The influence of wall distance and spray impingement angle on air entrainment characteristics have been investigated and the results will be presented and discussed.
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Citation
Cossali, G., Coghe, A., and Brunello, G., "Effect of Spray-Wall Interaction on Air Entrainment in a Transient Diesel Spray," SAE Technical Paper 930920, 1993, https://doi.org/10.4271/930920.Also In
References
- Ha, J. Norimasa, I. Sato, G.T. Hayashi, A. Tanabe, H. “Experimental Investigation of the Entrainnment into Diesel Spray” SAE paper 841078 1984
- Obokata, T. Inaba, K. Takahashi, H. “LDA Measurements of Diesel Spray and Entrainment Air Flow” Fourth Int. Symposium on Application of Laser Anemometry to Fluid Mechanics Lisbon 1988
- Obokata, T. Hashimoto, T. Takahashi, H. “LDA Analysis of Diesel Spray and Entrainment Air Flow” International Symposium COMODIA 90 231 236 1990
- Ruff, G.A. Sagar, A.D. Faeth, G.M. “Structure and Mixing Properties of Pressure-Atomized Sprays” AIAA 26th Aerospace Sciences Meeting Nevada 1988
- Cossali, G. E. Brunello, G. Coghe, A. “LDV Characterization of Air Entrainment in Transient Diesel Sprays” SAE paper 910178 Detroit 1991
- Brunello, G. Cossali, G.E. Coghe, A. “Fluidmechanics of Spray-Wall Interaction in Diesel Engines” 2nd Int. Conf on Fluidmechanics, Combustion, Emission, and Reliability in Recipr. Engines Capri, Italy 1992
- Hosoya, H. Obokata, T. “LDA Measurements of Spray Flow from a Single Hole Diesel Type Nozzle under Steady Conditions” 6th Int. Symp. on Appl. of Laser Techn. to Fluid Mech. Lisbon 1992
- Coghe, A. Cossali, G.E. “Experimental Analysis of Wall-Spray Structure by Laser Doppler Techniques” 6th Int. Symp. on Appl. of Laser Techn. to Fluid Mech. Lisbon 1992
- Elkotb, M.M. “Spray-Gas Stream Interaction in Diesel Engine” 4th Int. Conf. on Liquid Atomization and Spray Systems - ICLASS-'88 Sendai, Japan 1988
- Kamimoto, T. Aoyagi, Y. Matsui, Y. Matsuoka, S. “The Effects of Some Engine Variables on Measured Rates of Air Entrainment and Heat Release in a DI Diesel Engine” SAE paper 800253 1980
- Ricou, F.P. Spalding, D.B. “Measurements of Entrainment by Axisymetrical Turbulent Jets” J. Fluid Mech. 11 21 3 2 1961
- Kamimoto, T. Won, Y. “Soot Formation and Related Techniques for its Reduction in Diesel Engines” 2nd Int. Conf on Fluidmechanics, Combustion, Emission and Reliability in Reciproc. Engines Capri, Italy 1992
- Binder, K. Pfeffer, V. “New Results of Research into Mixture Formation in the Direct injection Diesel Engine” Int. Symposium COMODIA 90 557 564 1990
- Borman, G.L. Brown, W.L. “Pathways to Emission Reduction in Diesel Engines” 2nd Int. Conf on Fluidmechanics, Combustion, Emission and Reliability in Reciprocating Engines Capri, Italy 1992
- Arcoumanis, C. Hadjiapostolou, A. Whitelaw, J.H “Flow and Combustion in a Hydra Direct-Injection Diesel Engine” SAE paper 910177 Detroit 1991
- Shundoh, S. Kakegawa, T. Tsujimura, K. Kobayashi, S. “The Effect of Injection Parameters and Swirl on Diesel Combustion with High Pressure Fuel Injection” SAE paper 910489 Detroit 1991
- Binder, K. Gutman, M. Prescher, K. “Evaluation of High-Speed Schlieren Films of Diesel Fuel Sprays with an Electronic Image Processing System” 2nd Int. Conf. on Fluidmechanics, Combustion, Emissions and Reliability in Reciproc. Engines Capri, Italy 1992
- Harrington, D.L. “Interaction of Direct-Injection Fuel Sprays with In-Cylinder Air Motions” SAE paper 831728 1983
- Brunello, G. Callera, S. Coghe, A. Cossali, G.E. Gamma, F. “LDV and PDA Characterization of Spray-Wall Interaction” Gaithersburg, USA 1991
- Katsura, N. Saito, M. Senda, J. Fujimoto, H. “Characteristics of a Diesel Spray Impinging on a Flat Wall SAE paper 890264 1989