Plain-orifice atomizers

Plain-orifice atomizers are widely used for injecting liquids into a flow stream of air or gas. The injection may occur in a co-flow, a contra-flow, or a cross-flow stream. The best known application of plain-orifice atomizers is perhaps diesel injectors. This type of injectors is designed to provide a pulsed or intermittent supply of fuel to the combustion zone for each power stroke of the piston. As the air in the combustion zone is compressed by the piston to a high pressure, a very high pressure (83-103 MPa) is required to allow the fuel to penetrate into the combustion zone and disintegrate into a well-atomized spray. 

Another important application of plain-orifice atomizers is jet engine afterburner injectors. The fuel injection system typically consists of one or more circular manifolds supported by struts in a jet pipe. The fuel is supplied to the manifold by feed pipes in the support struts and sprayed into the combustion zone through the orifices in the manifold. Increasing the number of orifices and/or using a ringlike manifold may promote uniform distribution of liquid. To reduce the risk of blockage of orifices, a minimum orifice size of 0.5 mm is usually regarded as practical for kerosene-type fuels. 

One of the limitations of plain-orifice atomizers is the narrow spray cone generated. For most practical applications, large spray cone angles are desired. To achieve a wide spray cone, a simplex, i.e.,... 

Table 4.3. Correlations for Mean, Minimum and Maximum Droplet Sizes Generated in Pressure Jet Atomization by Plain-Orifice Atomizers... 

C. Xu, R. A. Bunnell, and S. D. Heister, On the influence of internal flow structure on performance of plain-orifice atomizers. Atomization Sprays, 11, 335-350, 2001. 

Pressure Atomization Plain- Orifice 25-250 Diesel engines, Jet engine afterburners, Ramjets Simple, Rugged, Cheap Narrow spray angle, Solid spray cone... 

The main applicatiOTi for plain orifice nozzles is in fuel combustion [1]. Therefore most correlations have been developed for this application [46—51]. Tanasawa and Toyoda [46] derived 24.5.i for diesel sprays in still air. Harmon [47] derived a correlation 24.5.ii that considered many different properties for both the liquid and the gas. In (24.52), liquid viscosity has very little impact on the SMD. Also, it predicts that an increase in surface tensitm will lead to finer atomization. This is contrary to the findings of most other experiments. Figure 24.31 shows a graph with both equations plotted plus (24.5.iii) by Merrington and Richardson [48], where do was set to 0.2 mm and (7l to 50 m/s. The diesel properties were taken from [50] as follows p = 826 kg/m, p = 2.744 mPa s and a = 0.0286 N/m. 

Abstract Plain orifice, or pressure atomizers are the most commonly used atomizers due primarily to their simplicity and ease of manufacture. This chapter provides background on the characteristics of these devices in terms of spray production and general behavior. Classical linear theories are reviewed to provide a basis for theoretical droplet size predictions. More recent developments assessing the unsteadiness within these devices, and its role in spray production, is also provided in subsequent discussion. The chapter closes with modem nonlinear simulations of spray production using modem numerical techniques. 

Chen, S. A., Lefebvre, A. H. (1994). Discharge coefficient for plain-orifice effervescent atomizers. Atomization and Sprays, 4(3), 275-290. 

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