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Gasoline direct injection (GDI) engines have become very attractive in transportation due to several benefits over preceding engine technologies. However, GDI engines are associated with higher levels of particulate matter (PM) emissions, which is a major concern for human health. The aim of this work is to broaden the understanding of the effect of hydrogen combustion and the influence of the three way catalytic converter (TWC) on PM emission characteristics. The presence of hydrogen in GDI engines has been reported to reduce fuel consumption and improve the combustion process, making it possible to induce higher rates of EGR. A prototype exhaust fuel reformer build for on-board vehicle hydrogen-rich gas (reformate) production has been integrated within the engine operation and studied in this work.

The paper presents analysis of performance and emission characteristics of a common rail diesel engine operating with RME, with and without EGR. In both cases, the RME fuel was pre-heated in a heat exchanger to control its temperature before being pumped to the common rail. The studied parameters include the in-cylinder pressure history, rate of heat release, mass fraction burned, and exhaust emissions. The results show that when the fuel temperature increases and the engine is operated without EGR, the brake specific fuel consumption (bsfc) decreases, engine efficiency increases and NOx emission slightly decreases. However, when EGR is used while fuel temperature is increased, the bsfc and engine efficiency is independent of fuel temperature while NOx slightly increases.

In the present work, the partial oxidation of diesel (US07), rapeseed methyl ester (RME) and low temperature Fischer - Tropsch synthetic diesel (SD), almost 100% paraffinic, was investigated for the purpose of hydrogen and intermediate hydrocarbon species production over a prototype reforming catalyst, for the potential use in hydrocarbon selective catalytic reduction (HC-SCR) of nitrogen oxide (NOx) emissions from diesel engines. The presence of small amounts of hydrogen can substantially improve the effectiveness of hydrocarbons in the selective reduction of NOx over lean NOx catalysts, particularly at low temperatures (150-350°C). In this study, the partial oxidation reactor was operating at the same input power (kW), based on the calorific values of the fed fuel. Hydrogen production was as high as 19%, from the partial oxidation of SD fuel, and dropped to 17% and 14% for RME and US07 diesel, respectively.

A prototype catalyst has been developed and integrated within the aftertreatment exhaust system to control the HC, CO, PM and NOx emissions from diesel exhaust gas. The catalyst activity in removing HC and nano-particles was examined with exhaust gas from a diesel engine operating on biodiesel - Rapeseed Methyl Ester (RME). The tests were carried out at steady-state conditions for short periods of time, thus catalyst tolerance to sulphur was not examined. The prototype catalyst reduced the amount of hydrocarbons (HC) and the total PM. The quantity of particulate with electrical mobility diameter in nucleation mode size < 10nm, was significantly reduced over the catalyst. Moreover, it was observed that the use of EGR (20% vol.) for the biodiesel fuelled engine significantly increases the particle concentration in the accumulation mode with simultaneous reduction in the particle concentration in the nuclei mode.

Multiple fuel injections with higher injection pressure are a way to improve diesel engine performance and lower emissions of unburned HCs, smoke, particulate matter and carbon monoxide (CO). However this method leads to a higher level of NOx emissions. A combination of higher pressure split injection and exhaust gas recirculation (EGR) has potential in controlling NOx emissions and engine performance simultaneously. The focus of this study is to investigate the effect of variation in injection pressure with split (pilot and main) injection, (with and without cooled EGR) on engine performance and emissions. The engine used is a common rail direct injection V6 Diesel fitted with turbo-charged variable turbine geometry (VTG) turbochargers, fuelled with ultra low sulphur diesel (ULSD).

The purpose of this study is to improve the carbon monoxide (CO) and total hydrocarbons (THC) conversion efficiency of a diesel oxidation catalyst (DOC) by enhancing the monolith thermal behaviour through modification of the substrate cell density and wall thickness. The optimisation is based on catalyst properties (light off performance, conversion efficiency, pressure drop and mechanical durability). These properties were first estimated using theoretical equations derived from literature in order to select commercially available substrates for further modelling studies. The thermal behaviour and conversion efficiency of the selected catalysts under diesel exhaust gas conditions were numerically studied using data from an EU5 diesel engine operating a New European Driving Cycle (NEDC). This simulation was carried out on a commercial exhaust aftertreatment modelling program, AXISUITE. The predictions were compared to a reference coated 400/4 catalyst.

Exhaust Gas Fuel Reforming has potential to be used for on-board generation of hydrogen rich gas, reformate, and to act as an energy recovery system allowing the capture of waste exhaust heat. High exhaust gas temperature drives endothermic reforming reactions that convert hydrocarbon fuel into gaseous fuel when combined with exhaust gas over a catalyst - the result is an increase in overall fuel energy that is proportional to waste energy capture. The paper demonstrates how the combustion of reformate in a direct injection gasoline (GDI) engine via Reformed Exhaust Gas Recirculation (REGR) can be beneficial to engine performance and emissions. Bottled reformate was inducted into a single cylinder GDI engine at a range of engine loads to compare REGR to conventional EGR. The reformate composition was selected to approximate reformate produced by exhaust gas fuel reforming at typical gasoline engine exhaust temperatures.

This paper describes the results of an experimental investigation of the exhaust gas assisted fuel reforming process as a means of achieving reduction of both smoke and NOx diesel engine emissions. Using a reforming mini-reactor with exhaust gas from a single-cylinder DI diesel engine, diesel fuel was reformed and a hydrogen-rich gas was produced. The effects of the reforming process on the engine operation were studied by adding simulated reformer product gas to the engine inlet. In this way, the engine was operated as if a reformer would have been incorporated in the exhaust gas recirculation system (EGR) system providing the engine with ‘reformed EGR’ (REGR). Lower levels of REGR resulted in simultaneous reduction of smoke and NOx while increased REGR reduced smoke further but tended to increase NOx.

The Reformed EGR (REGR) technique involves the injection of hydrocarbon fuel (e.g., diesel) into a catalytic reformer fitted into the engine EGR system, so that the produced hydrogen containing gas mixture is fed back to the engine as REGR. Thus, in effect the engine operates in a similar way to a dual fuelled engine with standard EGR. Depending on the reforming conditions, the composition and the calorific value of the REGR may vary and this affects the engine performance and emissions. In the present study, simulated REGR with different H2/CO ratios has been examined. The combustion of REGR with maximum H2 and minimum CO contents resulted in the highest reduction of NOx emissions. This case simulated the reformer operation where the CO is fully converted to H2 by promoting the exothermic water gas shift reaction (WGSR). The highest reductions of both smoke and fuel consumption were achieved in the case of simulating the reformer operation where the CO is not fully converted to H2.

Recent developments in diesel engines lead to increased fuel efficiency and reduced exhaust gas temperature. Therefore more energy efficient aftertreatment systems are required to comply with tight emission regulations. In this study, a computational fluid dynamics package was used to investigate the thermal behaviour of a diesel aftertreatment system. A parametric study was carried out to identify the most influential pipework material and insulation characteristics in terms of thermal performance. In the case of the aftertreatment pipework and canning material effect, an array of different potential materials was selected and their effects on the emission conversion efficiency of a Diesel Oxidation Catalyst (DOC) were numerically investigated over a driving cycle. Results indicate that although the pipework material's volumetric heat capacity was decreased by a factor of four, the total emission reduction was only considerable during the cold start.