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The recent implementation of new rounds of stringent nitrogen oxides (NOx) emissions reduction legislation in Europe and North America is driving the introduction of new automotive exhaust aftertreatment systems. One of these technologies comprises a catalyst that facilitates the reactions of ammonia (NH₃) with the exhaust nitrogen oxides (NOx) to produce nitrogen (N₂) and water (H₂O). This technology is referred to as Selective Catalytic Reduction (SCR). The ammonia is delivered by a separate fluid supply and injection system to the exhaust in the form of AUS-32 (Aqueous Urea Solution), and is also known under its commercial name of AdBlue® in Europe, and DEF - Diesel Exhaust Fluid - in the USA. The development and application of current production AUS-32 injection systems typically rely on spray diagnostics techniques that were implemented for the gasoline port injector. These data are often obtained under standard room temperature conditions.

With increasingly stringent emissions regulations and concurrent requirements for enhanced engine thermal efficiency, a comprehensive characterization of the automotive gasoline fuel spray has become essential. The acquisition of accurate and repeatable spray data is even more critical when a combustion strategy such as gasoline direct injection is to be utilized. Without industry-wide standardization of testing procedures, large variablilities have been experienced in attempts to verify the claimed spray performance values for the Sauter mean diameter, Dv90, tip penetration and cone angle of many types of fuel sprays. A new SAE Recommended Practice document, J2715, has been developed by the SAE Gasoline Fuel Injection Standards Committee (GFISC) and is now available for the measurement and characterization of the fuel sprays from both gasoline direct injection and port fuel injection injectors.

Understanding the disintegration process and geometric effects on spray characteristics are of importance in the design of a high quality injector, because improving fuel atomization and targeting has been proved to be an effective way to reduce the exhaust hydrocarbon emissions for gasoline engines. To reveal the relationship between the internal flow and the spray characteristics, particle size measurements and computational fluid dynamics (CFD) were combined to analyze a set of orifices. The flow field inside the nozzle, as well as the direction and shape of the liquid jet in the vicinity of the nozzle exit, was numerically predicted. Spray droplet sizes were then measured for the same orifices. Interesting links were discovered between nozzle geometry and spray characteristics. The results indicate that the secondary flow inside the orifice hole, due to Vena Contracta phenomena, contributes greatly to the atomization and shape of the liquid jets.