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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 order to evaluate the potentialities of bioderived diesel fuels, the effect of fueling a 1.9 l displacement HSDI automotive Diesel engine with biodiesel and fossil/biodiesel blend on its emission and combustion characteristics has been investigated. The fuels tested were a typical European diesel, a 50% biodiesel blend in the reference diesel, and a 100% biodiesel, obtained by mixing rape seed methyl ester (RME) and recycled cooking oil (CME). Steady state tests were performed at two different engine speeds (2500 and 4000 rpm), and for a wide range of loads, in order to evaluate the behavior of the fuels under a large number of operating conditions. Engine performance and exhaust emissions were analyzed, along with the combustion process in terms of heat release analysis. Experimental evidences showed appreciably lower CO and HC specific emissions and a substantial increase in NOx levels. A significant reduction of smoke emissions was also obtained.

The potentialities in terms of engine performance and emissions reduction of pure biodiesel were examined on a Common Rail HSDI Diesel engine, trying to define a proper tuning of the injection strategies to bio-fuel characteristics. An experimental investigation was therefore carried out on a typical European passenger car Diesel engine, fuelled with a soybean oil derived biodiesel. A standard European diesel fuel was also used as a reference. In particular, the effects of an equal relative air/fuel ratio at full load condition were analysed; further, a sensitivity study on the outcome of the pilot injection timing and duration at part load on engine emissions was performed. Potentialities in recovering the performance gap between fossil fuel and biodiesel and in reducing NOx specific emissions, affecting only to a limited extent the biodiesel emission benefit in terms of CO, HC and FSN, were highlighted.

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.

The effects of using blended renewable diesel fuel (30% vol.), obtained from Rapeseed Methyl Ester (RME) and Hydrotreated Vegetable Oil (HVO), in a Euro 5 small displacement passenger car diesel engine have been evaluated in this paper. The hydraulic behavior of the common rail injection system was verified in terms of injected volume and injection rate with both RME and HVO blends fuelling in comparison with commercial diesel. Further, the spray obtained with RME B30 was analyzed and compared with diesel in terms of global shape and penetration, to investigate the potential differences in the air-fuel mixing process. Then, the impact of a biofuel blend usage on engine performance at full load was first analyzed, adopting the same reference calibration for all the tested fuels.

In an earlier study, a novel type of diesel fuel injector was proposed. This prototype injects fuel via porous (sintered) micro pores instead of via the conventional 6-8 holes. The micro pores are typically 10-50 micrometer in diameter, versus 120-200 micrometer in the conventional case. The expected advantages of the so-called Porous Fuel Air Mixing Enhancing Nozzle (PFAMEN) injector are lower soot- and CO2 emissions. However, from previous in-house measurements, it has been concluded that the emissions of the porous injector are still not satisfactory. Roughly, this may have multiple reasons. The first one is that the spray distribution is not good enough, the second one is that the droplet sizing is too big due to the lack of droplet breakup. Furthermore air entrainment into the fuel jets might be insufficient. All reasons lead to fuel rich zones and associated soot formation.

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.

The internal combustion engine technological development is today driven by the pollutants and carbon dioxide (CO2) emission reduction targets imposed by law. The request of lowering CO2 emission reflected in a push towards the improvement of engine efficiency, without sacrificing performances and drivability. The latest generations of Diesel engines for passenger cars are characterized by increasing injection pressure levels (250 MPa for the current production). Enhancing the injection pressure has the drawback of increasing the energy needed to pressurize the fuel and thus the high-pressure fuel pump energy request. A small but not negligible quantity of fuel has to be burned in order to provide this energy, generating a contribution in CO2 emission. In this frame, the injector back-flow represents a significant energy loss for the fuel injection system and for the whole engine.

The recent implementation of new rounds of stringent nitrogen oxides (NOx) emissions reduction legislation in Europe and North America is driving the expanded use of exhaust aftertreatment systems, including those that treat NOx under the high-oxygen conditions typical of lean-burn engines. One of the favored aftertreatment solutions 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, typically at a 32% concentration of urea (CO(NH2)2). The solution is referred to as AUS-32, and is also known under its commercial name of AdBlue® in Europe, and DEF - Diesel Exhaust Fluid - in the USA. The urea solution is injected into the exhaust and transformed to NH3 by various mechanisms for the SCR reactions.

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.

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.

The use of hydrogen in internal combustion engines is an effective approach to significantly support the reduction of CO2 emissions from the transportation sector using technically affordable solutions. The use of direct injection is the most promising approach to fully exploit hydrogen potential as a clean fuel, while preserving targets in terms of power density and emissions. In this frame, the development of an effective combustion system largely relies on the hydrogen-air mixture formation process, so to adequately control the charge stratification to mitigate pre-ignitions and knock and to minimize NOx formation. Hence, improving capabilities of designing a correct gas jet-air interaction is of paramount importance. In this paper the analysis of the evolution of a high-pressure gas jet produced by a single-hole prototype injector operated with different pressure ratios is presented.