Vinícius B. Pedrozo

Characterization of Low Load Ethanol Dual-Fuel Combustion using Single and Split Diesel Injections on a Heavy-Duty Engine

The first author would like to acknowledge the Brazilian Federal Agency for Support and Evaluation of Postgraduate Education (CAPES) for supporting the PhD studies of Mr. Pedrozo at Brunel University London.

Exploring the NOx Reduction Potential of Miller Cycle and EGR on a HD Diesel Engine Operating at Full Load

The reduction in nitrogen oxides (NOx) emissions from heavy-duty diesel engines requires the development of more advanced combustion and control technologies to minimize the total cost of ownership (TCO), which includes both the diesel fuel consumption and the aqueous urea solution used in the selective catalytic reduction (SCR) aftertreatment system. This drives an increased need for highly efficient and clean internal combustion engines. One promising combustion strategy that can curb NOx emissions with a low fuel consumption penalty is to simultaneously reduce the in-cylinder gas temperature and pressure. This can be achieved with Miller cycle and by lowering the in-cylinder oxygen concentration via exhaust gas recirculation (EGR). The combination of Miller cycle and EGR can enable a low TCO by minimizing both the diesel fuel and urea consumptions. In this work, Miller cycle with late intake valve closing (IVC) and EGR technology were investigated on a single cylinder common rail heavy-duty diesel engine at the high load operation of 24 bar net indicated mean effective pressure. The experiments were performed with a constant intake manifold pressure of 3 bar while optimizing the start of diesel injection to keep the peak in-cylinder pressure limit of 180 bar. The aqueous urea solution consumption in the SCR aftertreatment system was estimated to evaluate the effectiveness of the strategies in terms of TCO. The calculation was based on the engine-out NOx emissions and the Euro VI NOx limit. The results revealed that the use of the Miller cycle without EGR reduced NOx emissions by 35% and the net indicated efficiency by 4% when compared to the case with the baseline IVC at -178 crank angle degrees (CAD) after top dead center (ATDC). The introduction of 8%EGR decreased the levels of NOx by 54% while maintaining similar net indicated efficiency at the baseline IVC. The combination of Miller cycle with an IVC at -127 CAD ATDC and an EGR rate of 8% achieved the best trade-off between NOx and ISFC, decreasing the NOx levels by 57% and the fuel consumption by 1.6% compared to the baseline case. Soot emissions were maintained below the Euro VI limit of 0.01 g/kW h. Carbon monoxide emissions were maintained at low levels except for the combination of an IVC at 114 and an EGR rate of 8%. Unburned hydrocarbon emissions were slightly decreased with EGR and late IVCs likely due to relatively longer ignition delays and higher exhaust gas temperature. Overall, the analysis showed that the combination of Miller cycle with an IVC at -127 CAD ATDC and 8%EGR achieved the lowest total fluid consumption despite the reduction in net indicated thermal efficiency. Introduction Diesel engines have been the main power source in transportation sectors owing to their high torque output and superior thermal efficiency. However, conventional diesel combustion produces harmful exhaust emissions, particularly NOx and smoke, due to the presence of high local in-cylinder equivalence ratio and temperature during the mixing-controlled combustion [1]. The application of more stringent exhaust emissions and carbon dioxide (CO2) regulations have driven the development of cleaner and more efficient internal combustion engines [2]. In recent years, the main research focus has been on the reduction of NOx and smoke emissions while maintaining or increasing the engine efficiency. This has been achieved by the combination of in-cylinder measures and exhaust aftertreatment technologies, such as the SCR system [3]. However, there is an optimum balance between in-cylinder and aftertreatment control of NOx emissions, which is attained by minimizing the diesel fuel consumption and the aqueous urea solution used in the SCR system [4]. Therefore, it is favorable to reduce emissions and increase engine efficiency by an optimization of in-cylinder combustion process and the development of high efficiency aftertreatment system in order to reduce the total cost of ownership. As for the in-cylinder measures, low temperature combustion (LTC) concepts such as homogenous charge compression ignition (HCCI) and partially premixed charge compression ignition (PCCI) have shown potential to significantly reduce engine-out NOx and smoke emissions at the expense of lower engine efficiency and higher emissions of unburned hydrocarbon (HC) and carbon monoxide (CO) [5,6]. These LTC strategies are usually achieved by high levels of EGR, which allow for longer ignition delay and lower combustion temperatures [7]. However, the use of elevated EGR rates might not be practical at high loads because of the greater demand on the boosting system and the cooling system of the engine in order to maintain a reasonable excess of air while keeping an acceptable peak in-cylinder pressure [8]. Alternatively, Miller cycle can be used in an attempt to decrease the EGR requirements. This in-cylinder strategy can reduce NOx emissions by lowering the effective compression ratio via early or late IVCs while maintaining the original expansion ratio. Initially, Miller cycle was used to improve thermal efficiency by avoiding knocking combustion in gasoline engines [9]. In recent years, it has received more attention in diesel engines due to a potential NOx emissions reduction benefit obtained by lowering the peak combustion temperatures [10–12].