LDV Characterization of Air Entrainment in Transient Diesel Sprays

Cossali, Gianpietro; Brunello, G.; Coghe, A.

doi:10.4271/910178

Cited by 26 publications

(29 citation statements)

References 9 publications

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“…In 1998 Shelby [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] confirmed that the spray develops according a hollow cone - Figure 3-13, with three main temporal phases described as follows:…”

Section: The High Pressure Gasoline Injectionmentioning

confidence: 86%

“…The lift-off length has naturally a noticeable impact on the oxygen concentration at the beginning of the combustion -the longer it is the higher the amount of air entrained in the spray, reported to the amount of injected fuel, is. Thereby, the soot production, as demonstrated by Idicheria [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] or Siebers [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], see Figure 3-10, is lower with small orifices. In this last case a reduced diameter led to a quasi soot free combustion.…”

Section: Lift-off Lengthmentioning

confidence: 99%

“…Following the theory of Flynn, based on the combustion model from Dec [3][4][5][6][7][8][9][10][11][12][13][14][15][16], the volume between the nozzle hole nozzle and the lift-off is the state of PAH formation (Poly-Aromatic Hydrocarbons) which are soot precursors. In 2001, Higgins [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] emphasized the influence of the surrounding parameters like the injection pressure, the oxygen concentration or the ambient gas temperature and density on the position of this flame by measuring the OH concentration -see Figure 3-9. The lift-off length has naturally a noticeable impact on the oxygen concentration at the beginning of the combustion -the longer it is the higher the amount of air entrained in the spray, reported to the amount of injected fuel, is.…”

Section: Lift-off Lengthmentioning

confidence: 99%

“…Figure 3-10: soot incandescence (false colors) and OH chemiluminiescence (white); injection in a constant volume vessel, rail pressure 1000 bars, air temperature 1000K, air density 14.8 kg/m 3 [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] average position of the lift-off for 22 images natural emission of soot…”

Section: Lift-off Lengthmentioning

confidence: 99%

“…The Sandia conceptual model, based on Dec combustion scheme [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], involved the different theories presented above. The soot is formed at the head of the spray and then partially oxidized at its periphery.…”

Section: Pollutant Formationmentioning

confidence: 99%

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Influence of the Mixture Preparation on the Combustion in Direct Injection Engines

Gastaldi¹

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During the last two centuries, the development of the internal combustion engine has followed the evolution of the customer expectations. From the race for pure performances, high power, and fun to drive, perfectly well illustrated by the fabulous Mercedes 300 SL, the focus moved towards fuel efficient engines under the pressure of the still increasing oil prices. The well-known Diesel powertrain, up to this period limited to industrial vehicles, suddenly became the object of many researches, even for automotive manufacturers, specialists for sport cars. Technologic developments, mainly concerning turbocharging and injection, allowed the opening of the passenger cars market to CI engines due to acceptable noise, power and still unreachable efficiency. On the gasoline side, direct injection moved from racing to economic cars by the introduction of the stratified combustion. More recently, the pressure rose for dramatically reducing the air pollution, both in urban areas, by limiting NOx and soot, but also, at the scale of the earth, for managing CO 2 rejections and thereby enlarging the efforts on efficiency.The two first combustion systems described in this document are concerning spray guided and air guided design alternatives to obtain a fuel stratification, and thereby operate the gasoline engine without throttling the air intake, aiming at a better fuel efficiency.The first concept, called MID3S, was based on a 3 valve combustion chamber with a large squish area and a high compression ratio over 12; inspired from the May Fireball system, it was developed with a house made high pressure injector operating up to 80 bars with an outwardly opening needle. An ultra-lean flame-able mixture was formed at WOT in the vicinity of the spark plug for different operating points as low as idle, while the maximum performances were quite close to the targeted 37 kW/l. The efficiency was significantly improved compared to a similar MPI engine while CO and HC were quite acceptable. On the contrary, NOx and soot would have to be improved. The robustness of the squish aerodynamic motion was unfortunately balanced by the sensitivity of spray angle and penetration versus the back pressure and thereby late injection timings, creating plug wetting and fouling. The hollow cone structure of the fuel plume was clearly responsible of this behavior, especially because of the effect of the air entrainment inside the spray. An increase of the injection pressure from 30 to 80 bar, and probably upper, would probably reduce this effect. Concerning methodologies, a dedicated cylinder head was designed with two endoscope locations in order to visualize the interaction between spray, air, walls and combustion -or more precisely soot-with a high speed camera operating within visible wavelengths. The spray structure, formed by a succession of ligaments at the surface of the plume, was clearly emphasized in atmospheric conditions. The second design, called K5M, was based on an adjustable high tumble motion generated in the intake port. A s...

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