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The optimization of the piston bowl design has been shown to have a great potential for air–fuel mixing improvement, leading to significant fuel consumption and pollutant emissions reductions for diesel engines. With this aim, a conventional re-entrant bowl for a 1.6 L light-duty diesel engine was compared with two innovative piston designs: a stepped-lip bowl and a radial-bumps bowl. The potential benefits of these innovative bowls were assessed through 3D-CFD simulations, featuring a calibrated spray model and detailed chemistry. To analyse the impact of these innovative designs, two different engine operating conditions were scrutinized, corresponding to the rated power and a partial load, respectively. Under the rated power engine operating condition, a start of injection sensitivity was then carried out to assess the optimal spray–wall interaction. Results highlighted that, thanks to optimal injection phasing, faster mixing-controlled combustion could be reached with both the innovative designs. Moreover, the requirements in terms of swirl were also investigated, and a higher swirl ratio was found to be necessary to improve the mixing process, especially for the radial-bumps design. Finally, at part-load operating conditions, different exhaust gas recirculation (EGR) rates were analysed for two injection pressure levels. The stepped-lip and radial-bumps bowls highlighted reduced indicated specific fuel consumption (ISFC) and soot emissions values over different rail pressure levels, guaranteeing NOx control thanks to the higher EGR tolerance compared with the re-entrant bowl. The results suggested the great potential of the investigated innovative bowls for improving efficiency and reducing emissions, thus paving the way for further possible optimization through the combination of these designs. [ABSTRACT FROM AUTHOR]

The calibration of modern automotive diesel engines, stored in form of maps in the engine control unit, must fulfill stringent requirements in terms of smoothness, ensuring a subtle transition of control parameters between neighbor operating points. However, this could lead to penalties in emissions or fuel consumption. It is therefore necessary to develop a methodology capable of carrying out the engine calibration task in a quick and automatic way. In this paper, an original fully automated methodology for the generation of smooth calibration maps is proposed. Starting from a population of more than 80 optimized calibrations for 20 engine operating points, generated by means of a genetic algorithm-based multi objective optimizer, a final calibration was then selected in an automated way, on the basis of a trade-off between the performance of the calibration and the smoothness of maps. The results achieved clearly showed that in comparison with traditional methods similar level of smoothness can be achieved while having 5–10% lower NO x and soot emissions with an additional benefit of 1% in fuel consumption. Furthermore, the time required for the calibration task of an automotive diesel engine can be reduced by more than half. • Novel methodology to generate smooth calibration maps for automotive diesel engines. • Minimization of loss of optima due to manual smoothening procedures for calibration. • Capability of reducing the time and effort for the calibration by more than half. • Achievement of desired smoothness level with considerably lower emissions. [ABSTRACT FROM AUTHOR]

The effects of using a 30% by volume blend of a renewable fuel, called Farnesane, and fossil diesel in a small Euro 5 displacement passenger car diesel engine have been evaluated in this paper. Farnesane is a 15-carbon long molecule that can be obtained from the fermentation of biomass-derived sugars (such as sugar cane, amidaceous and cellulosic crops), which are first fermented to Farnesene and then hydrogenated to Farnesane. Farnesane has similar chemical and physical properties to diesel fuel, as far as its viscosity and density are concerned. Its higher Lower Heating Value (LHV) and cetane number mean that the biofuel has better combustion properties, and the lack of aromatics and sulfur could contribute to a decrease in smoke and particulate matter emissions. Tests were carried out on a small displacement Euro5 automotive diesel engine for passenger car applications. The impact that the Farnesane blend could have on engine performance was first evaluated at full load. The effects of the use of the Farnesane blend on engine emissions and fuel consumption were then evaluated at seven different part load operating points, considered representative of the New European Driving Cycle. Other experimental investigations have been carried out to fully exploit the benefits that could be obtained by adjusting the Exhaust Gas Recirculation (EGR) rates in order to take into account the different Soot–NO x and CO–NO x biofuel blend trade-offs. When the engine was fueled with the Farnesane blend in diesel at full load operating conditions, without any modifications of the ECU calibration, brake torque output levels that were comparable with the reference diesel could be observed over almost the entire speed range. At part load operating conditions, which are representative of the New European Driving Cycle, no significant variations in fuel consumption were found on a mass basis, for the same fuel conversion efficiency and CO 2 emissions for the Farnesane blend compared to the diesel. The specific CO and HC emissions were reduced significantly for the biofuel blend at low and medium loads, while only modest or even insignificant variations were registered at higher loads. The NO x emissions with the biofuel blend were generally comparable with those of the reference diesel fuel, while a noticeable reduction in smoke level was generally observed for medium and high load operating conditions. Finally, the Soot–NO x and CO–NO x trade-off, obtained from EGR sweeps, has highlighted the possibility of obtaining some further emission benefits through a better exploitation of the biofuel characteristics by means of a more extensive ECU recalibration. [ABSTRACT FROM AUTHOR]

Abstract: Different Exhaust Gas Recirculation (EGR) system architectures have been evaluated by means of both experimental tests and numerical simulation; in addition to the experimental tests, a one-dimensional fluid-dynamic engine model has been built in order to assess the potential of a Dual Loop (DL) EGR system – a combination of Short Route (SR) and Long Route (LR) EGR systems. Substantial reductions of the NO x emissions have been achieved using the LR EGR layout both under steady state and transient operating conditions: a reduction of up to 15% over the first 60s of the Extra Urban Driving Cycle (EUDC) was obtained with the LR layout. An optimal combination of LR and SR has led to a further reduction of 5% of the nitrogen oxide emissions, due to a faster response of the EGR system during transients. Finally some fundamental knowledge that can be used to control the EGR flow rate more accurately has been gathered, by means of the numerical simulation, especially for the Dual Loop EGR system layout. [Copyright &y& Elsevier]