The effect of nozzle geometry over ignition delay and flame lift-off of reacting direct-injection sprays for three different fuels

Abstract

h i g h l i g h t sSimultaneous Schlieren and OH * chemiluminescence visualizations are carried out with different techniques. The effect of nozzle geometry is analyzed for three different fuels along a wide test matrix in reactive conditions. Analysis of spray tip penetration, lift-off length and ignition delay. A total of 162 different test conditions are evaluated in the high temperature/high pressure test rig. The experimental database will be published and available for model validation. a b s t r a c tThe influence of internal nozzle flow characteristics over ignition delay, and flame lift-off of reacting direct-injection sprays is studied experimentally for three fuels using two different nozzle geometries. This is a continuation of previous work by the authors, where, evaporative and non-evaporative, isothermal spray developments were studied experimentally for the same nozzle geometries and fuels. Current study reports the ignition delay through Schlieren technique, and flame lift-off length through OH * chemiluminescence visualization. The nozzle geometries consist of a conical nozzle and a cylindrical nozzle with 8.6% larger outlet diameter when compared to the conical nozzle. The three fuels considered are n-heptane, n-dodecane and a three-component surrogate to better represent the physical and chemical properties of diesel fuel. Reacting spray is found to penetrate faster than non-reacting spray due to combustion induced acceleration after ignition. Higher oxygen concentration, and ambient temperature enhance the reactivity leading to higher spray tip penetration. Injection pressure does not affect the reactivity significantly and hence, influences spray penetration through momentum-similar to a non-reacting spray. Both ignition delay and lift-off length are found to be shortest and longest for n-dodecane and n-heptane, respectively, while the surrogate fuel falls in-between the two pure component fuels. Both ignition delay and lift-off length are found to decrease with increase in oxygen concentration, ambient temperature, and density. The cylindrical nozzle, in spite of shorter lift-off length is found to have longer ignition delay, when compared to the conical nozzle. This could be due to better atomization leading to larger spread angle and evaporative cooling from the cylindrical nozzle compared to a conical nozzle. The longer ignition delay also leads to leaner equivalence ratios at the time of ignition.

On the Influence of the Slot Orifice in Diesel Common Rail Nozzle

“…According to Fig. (1), the chosen Slot cross section is formally related to the circular one by the following equations (1)(2)(3)(4), which are directly derived from the adopted section geometries. Table 1 After drilling, the two nozzles have been hydro-ground.…”

Injection systems in diesel engines and their theoretical-experimental study: a review

“…Liu et al [13], showed in their study how the low temperatures affect the combustion of the Diesel jet increasing the lift-off length and the delay time, together with low temperatures, the injection pressure has little significance over the length of the Lift-off and delay time. As the temperature affects the lift-off length, the geometry of the nozzle is another important parameter to be considered as demonstrated by Payri et al [14], which considered three fuels and two nozzles with different geometries; one consisted of a conical shape, while the other had a circular hole, but with a diameter 8.6% larger than the conical one. The results obtained experimentally indicated that the conical geometry has a longer lift-off length when compared to circular geometry, and a shorter delay time, highlighting that it may be due to the liquid length evaporating faster than in the circular nozzle.…”

Vapor phase penetration measurements with both single and double-pass Schlieren for the same injection event

“…Researchers have used Schlieren imaging to analyze the transient vapor phase of the diesel sprays in both nonreactive and reactive conditions. With this technique it is possible to measure simple macroscopic parameters, like spray tip penetration and spreading angle [2,3], to more complex variables, like ignition delay [4][5][6][7] or even lift-off length [8]. It is not only fundamental knowledge to understand how boundary conditions affect these variables, but the experimental data is necessary to validate computational tools, such as 1-D models or computational fluid dynamics (CFD).…”

“…It is not only fundamental knowledge to understand how boundary conditions affect these variables, but the experimental data is necessary to validate computational tools, such as 1-D models or computational fluid dynamics (CFD). The two most common Schlieren configurations are single-pass (SP) [2,[5][6][7][8][9] and double-pass (DP) [3,[10][11][12][13]. Typically, the first setup is used for axially drilled single-orifice nozzles, where vessels with multiple optical accesses allow line of sight visualization.…”