Experimental Study on the Atomization of Plain Orifice Injector Under Uniform and Non-Uniform Cross Flowing Air Stream

Abstract

The effects of three parameters: air velocity, nozzle pressure drop and injector orifice diameter, on the spray characteristics of a plain orifice injector under uniform and non-uniform cross flowing air stream have been studied experimentally. For uniform cross flowing air stream, the results show that the effects of these parameters are interrelated. The exponents of these terms in a correlation are not constants. Based on a very large amount of experimental data, the following correlation has been derived for Sauter Mean Diameter. SMD = 8.28 • 10 4 V ¯ a A • Δ P ¯ f B • d ¯ C where: A = −1.59 −0.0044ΔP̄f −0.01 d̄ B = −0.13 −0.025 d̄ +0.34 Ma C = 0.36 −0.55 Ma −0.0032ΔP̄f (Va ≤ 140 M/s ; ΔPf ≤ 11 Kg·f/cm2 ; d ≤ 2.5 mm) For small orifice diameters, the drop size distribution parameter, N (Rosin-Rammler distribution ), decreases until a minimum then increases with air velocity. For large orifice diameters, it decreases with air velocity. N always decreases with the increases of nozzle pressure drop or orifice diameter. For non-uniform cross flowing air stream, atomizations under four velocity profiles with same averaged velocity and with a velocity recess of same shape but at different radial positions have been tested. The atomization data were compared with that of uniform cross flowing air stream. Two types of comparison were made based on: a) the undisturbed velocity, b) the averaged velocity, equals to the velocity of uniform cross flowing air stream. For former situation the atomization for non-uniform cross flowing air stream tested is always poorer. The influence from the velocity recess will be maximum at certain nozzle pressure drop. The experimental evidence obtained has shown that cross flow atomization is a combination of pressure atomization (at low air flow velocity) and airblast atomization (at high air flow velocity).

Air Blast Atomization as a Function of Pressure Loss for Large Air Flow Rates

“…This combined with different local velocity profiles with the jets could lead to the observed small differences in the SMD with fuel flow rate. The strong influence of the atomization air velocity profiles on the SMD has been shown by McVey et al (1988) and Zhang et al (1987). Thus, the influence of the fuel flow rate may influence the constant A in Eq.1, rather than the F/A term.…”

Experimental Study on Internal Mixing Sonic Flow Air Assist Atomizer for Heavy Oils

“…Sometimes a pressure swirl atomizer is used for atomization of these heavy oils. But inevitably, for these applications, a pressure swirl atomizer has several disadvantages, (1) as the flow passage is rather of small dimension and the fuel is not so clean, the atomizer is easy to be blocked, (2) particularly if fine atomization is required, then small droplets have less penetration, so the flame length is usually short, and in some cases, it is not suitable for some furnace applications. This short-coming is not only true for pressure swirl atomizer but also for prefilming airblast atomizer, Y jet internal mixing injector, and other atomizers.…”

“…It consists of two portions, mixing chamber and injector head. For mixing chamber, the design makes use of the cross flowing air stream atomization based on previous atomization studies [1][2]. The mixing chamber designed is rather different from the Y-jet internal mixing atomizer in [3].…”

“…Also the pressure in the mixing chamber is kept higher than critical pressure, the exit velocity of the air-spray jet is equal to or higher (for convergent-divcrgent exit nozzle orifices) than sonic velocity, that will further improve the atomization. From [1] [2], we know that, SMD aV -1.59 so the air velocity through the mixing chamber holes should not be low. The function of mixing chamber is to have primary atomization to form air-spray mixture.…”