Spray nozzles are used in many applications such as cleaning, cutting and spraying. Spray nozzles come in many varieties and are usually classified according to the specific mode of atomization. This paper is focused on plain orifice nozzle. This kind of atomizer is the most common and simple type. Plain-orifice atomizers are widely used for injecting liquids into a flow stream of air or gas with normally circular pattern. The injection may occur in a co-flow, a contra-flow, or a cross-flow stream. An enormous variety of processes make use of plain orifice nozzles such as diesel engine, jet engine, afterburners and ramjets. 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 [1]. In the case of high pressure flow, around 25 bar, fuel injectors these nozzles to generate finely atomized sprays. Droplet size and spray angle are critical because the large surface area and finely atomized spray enhance fuel evaporation area. Dispersion of the fuel into the combustion air is critical to maximize the efficiency of these systems and minimize emissions of pollutants. One of the most noticeable limitations of plain orifice is its narrow spray angel. Therefore, a little discrepancy between theoretical and practical data caused effective changes in engine performance. Unfortunately the available equations predict spray angle recklessly. Therefore this paper focuses on the analysis of equations to reach the most useful and acceptable relation, in order to predict spray angle of plain atomizer as accurate as possible [1,2].

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