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Selective Catalytic Reduction (SCR) diesel exhaust aftertreatment systems are virtually indispensable to meet NOx emissions limits worldwide. These systems generate the NH3 reductant by injecting aqueous urea solution (AUS-32/AdBlue®/DEF) into the exhaust for the SCR NOx reduction reactions. Understanding the AUS-32 injector spray performance is critical to proper optimization of the SCR system. Specifically, better knowledge is required of urea sprays under operating conditions including those where fluid temperatures exceed the atmospheric fluid boiling point. Results were previously presented from imaging of an AUS-32 injector spray which showed substantial structural differences in the spray between room temperature fluid conditions, and conditions where the fluid temperature approached and exceeded 104° C and “flash boiling” of the fluid was initiated.

In recent years, the GDI (Gasoline Direct Injection) technology has significantly spread over the automotive market under the continuous push toward the adoption of combustion systems featuring high thermodynamic conversion efficiency and moderate pollutant emissions. Following this path, the injection pressure level has been progressively increased from the initial 5-15 MPa level nowadays approaching 35 MPa. The main reason behind the progressive injection pressure increase in GDI engines is the improved spray atomization, ensuring a better combustion process control and lower soot emissions. On the other hand, increasing injection pressure implies more power absorbed by the pumping system and hence a penalty in terms of overall efficiency. Therefore, the right trade-off has to be found between soot formation tendency reduction thanks to improved atomization and the energetic cost of a high pressure fuel injection system.

In the current automotive scenario, particulate filter technology is mandatory in order to attain emission limits in terms of particulate matter for diesel engines. Despite the fact that the Diesel Particulate Filter (DPF) is often considered a mature technology, significant issues can result from the use of the engine fuel injectors to introduce into the exhaust pipe the fuel needed to ignite the particulate matter accumulated in the filter during its regeneration. The most important issue is lubricant oil dilution with fuel as a consequence of significant spray impact on the cylinder liner. As an alternative, the fuel required to start DPF regeneration can be introduced in the exhaust pipe by an auxiliary low-pressure injector spraying in the hot exhaust gas stream.

One of the favored automotive exhaust aftertreatment solutions used for nitrogen oxides (NOx) emissions reductions is referred to as Selective Catalytic Reduction (SCR), which comprises a catalyst that facilitates the reactions of ammonia (NH3) with the exhaust nitrogen oxides (NOx). It is customary with these systems to generate the NH3 by injecting a liquid aqueous urea solution (AUS-32) into the exhaust. The urea solution is injected into the exhaust and transformed to NH3 by various mechanisms for the SCR reactions. Understanding the spray performance of the AUS-32 injector is critical to proper optimization of the SCR injection system. Results were previously presented from imaging of an AUS-32 injector spray under hot exhaust conditions at the injector spray exit for an exhaust injection application.

Emission legislation for light and heavy duty vehicles is requiring a drastic reduction of exhaust pollutants from internal combustion engines (ICE). Achieving a quick heating-up of the catalyst is of paramount importance to cut down cold start emissions and meet current and new regulation requirements. This paper describes the development and the basic characteristics of a novel burner for diesel engines exhaust systems designed for being activated immediately at engine cold start or during vehicle cruise. The burner is comprised of a swirled fuel dosing system, an air system, and an ignition device. The main design characteristics are presented, with a detailed description of the atomization, air-fuel interaction and mixture formation processes. An atomizer prototype has been extensively analyzed and tested in various conditions, to characterize the resulting fuel spray under cold-start and ambient operating conditions.

A comprehensive experimental and numerical analysis of two state-of-the-art diesel AfterTreatment Systems (ATS) for automotive applications is presented in this work. Both systems, designed to fulfill Euro 6 emissions regulations standards, consist of a closed-coupled Diesel Oxidation Catalyst (DOC) followed by a Selective Catalytic Reduction (SCR) catalyst coated on a Diesel Particulate Filter (DPF), also known as SCR on Filter (SCRoF or SCRF). While the two systems feature the same Urea Water Solution (UWS) injector, major differences could be observed in the UWS mixing device, which is placed upstream of the SCRoF, whose design represents a crucial challenge due to the severe flow uniformity and compact packaging requirements.