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The paper reports the results of an experimental investigation carried out on a prototype optically accessible compression ignition engine fueled with water in diesel emulsion (WiDE) and Diesel only. The effect of WiDE on combustion process evolution and exhaust emissions was investigated through standard engine benchmark and optical diagnostics. 2D chemiluminescent emission measurements centered at 690 nm were carried out during the whole combustion process to discriminate the soot emission from other excited chemical species. The emulsion was produced through a prototype designed microchannels emulsifier that can also work inline. The water concentration was 9.1%v with a small amount (0.2%v) of nonionic surfactant (SPAN80) used to stabilize the emulsion. Tests were performed comparing combustion and exhaust emissions of the reference commercial diesel fuel to the WiDE. For any investigated fuel and operating point, engine tests were carried out changing the injection interval to achieve the same chemical energy as the reference diesel (935 J/str). Compared to Diesel, the WiDE induced an increase in ignition time, enhancing the air/fuel mixing with a simultaneous reduction in both PM and NOx. The digital imaging and 2D chemiluminescence techniques highlighted a reduction in soot formation without significant changes on the soot oxidation rate. The results suggest the use of WiDE as a reliable method to improve NOx-soot trade-off of CI engines.

Reduction of NOX emissions and fuel consumption are the main topics in engine development, forcing the adoption of complex techniques and components, whose interactions have to be clearly understood for proper and reliable operations and management of the whole system. The investigation presented in this paper aimed at the development of integrated control strategies of turbocharging, high pressure (HP) and low pressure (LP) exhaust gas recirculation (EGR) systems for better NOX emissions and fuel consumption, while analyzing their reciprocal influence and the resulting variations of engine quantities. The study was based on an extended experimental program in three part load engine operating conditions. In the paper a comparison of the behavior of the main engine sub-systems (intake and exhaust circuits, turbocharger turbine and compressor, HP and LP EGR loops) in a wide range of operating modes is presented and discussed, considering open and closed loop approaches for variable nozzle turbine (VNT) control, and showing how these affect engine performance and emissions. The potential of significant decrease in NOX emissions through the integration of HP and LP EGR was confirmed, while a proper VNT management allowed for improved fuel consumption level, if an open loop control scheme is followed. At higher engine speed and load, further actions have to be applied to compensate for observed soot emissions increase.

An experimental investigation was performed with a view to comparing high and low pressure exhaust gas recirculation systems (HP and LP EGR) fitted on an automotive turbocharged diesel engine, focusing on analysing their influence on fuel consumption, pollutant emissions and the combustion process. Following the development of a prototype cooled LP EGR circuit, the main engine and turbocharger parameters were measured in six part-load operating conditions related to the European driving cycles. Different operating modes were considered, from the simplest and most commonly investigated (without EGR, with HP or LP EGR) to more complex schemes, namely the simultaneous application of high and low pressure recirculation and the addition of variable nozzle turbine (VNT) control. The extensive experimental database made it possible to confirm literature concerning the comparison of recirculating systems and the potential of LP EGR on engine intake temperature and NOx reductions. New aspects were also analysed, such as the balance of the high and low pressure EGR rate in order to achieve maximum NOx reductions in simultaneous applications, the interactions between EGR circuit management and the application of VNT control in order to improve the trade-off between fuel consumption and NOx and soot emissions.

An experimental study was developed to compare high and low pressure exhaust gas recirculation systems (HP and LP EGR) fitted on an automotive turbocharged diesel engine, analysing the effects of their control on fuel consumption, pollutant emissions and combustion process. An extensive range of operating modes was considered at different engine part-load conditions, starting from the reference one without EGR, then considering the simple activation of the HP or LP EGR circuit, followed by the simultaneous application of high and low pressure recirculation and the addition of variable geometry turbine (VGT) control. The paper focused on different goals: firstly, to highlight the change of selected operating parameters (intake pressure and mass flow rate, EGR fraction) in the different configurations affecting the development of in-cylinder pressure curves, ignition delay and combustion process. Secondly, to analyse how rate of heat release is affected by the different EGR and VGT control strategies. Finally, to justify the observed trends of fuel consumption, NOx and soot emissions according to the pressure diagrams and heat release curves, as LP EGR and a different VGT position allowed reductions of 2.1, 50 and 22.8% of these parameters referring to the standard operating mode in the presented experimental point.