Development of simulation methodologies and analysis of advanced VVA and Cylinder Deactivation strategies for Diesel engines

Due to air pollution and global warming being very actual problems, the regulations demand increasingly stringent targets in terms of CO2 and pollutants emissions reduction. The main way to achieve less CO2 production is to improve the fuel economy of the vehicle, and diesel engines are usually more fuel-efficient compared to spark-ignited engines. Modern diesel engines are equipped with Diesel Oxidation Catalyst (DOC) to oxidize hydrocarbons and carbon monoxide, Diesel Particulate Filter (DPF) to reduce particulate matter emissions, and Selective Catalytic Reduction (SCR) to reduce NOx emissions. Such after-treatment components require proper temperatures in order to work effectively in reducing emissions. Thermal management strategies are then required, in order to obtain higher exhaust gas temperature, especially during cold start and low-load engine operation. While electronically controlled fuel injection systems, Exhaust Gas Recirculation (EGR), and Variable Geometry Turbochargers have become standard in diesel engines, air management through Variable Valve Actuation (VVA) has not yet achieved a large popularity. In gasoline engines, VVA is capable of obtaining major fuel improvements, because it can replace, at least partially, the throttling for the load control, reducing the correspondent pumping losses. Instead, in diesel engines the load control is achieved by adjusting the amount of injected fuel, and therefore VVA has less potential of reducing the pumping losses. However, VVA can be a key technology for improving the exhaust warm up, aspiring at having no fuel consumption penalties, and thus is becoming highly desirable also for diesel engines. A variable valve train can also be taken advantage of for implementing Cylinder Deactivation (CDA) strategies. At low loads, the torque target can be achieved also by a lower number of cylinders than the engine has, and then cylinders can be deactivated, by interrupting their fuel injection and closing the intake and exhaust valves for the entire CDA phases. The remaining active cylinders, during CDA phases, work with higher load than normal operation, resulting not only in lower fuel consumption, but also in higher exhaust temperatures. The work for this master thesis has been conducted in collaboration with FEV Italia s.r.l. and supported by their simulation team. An existing 4-cylinder 2-liters diesel engine model, developed in the commercial software GT Power and provided by FEV, has been modified to implement two different VVA strategies, Late Intake Valve Closure (LIVC) and Internal EGR (iEGR) through Exhaust Valve reOpening (EVrO), and CDA technologies. A calibrated Engine Control Unit (ECU) model, also provided by FEV and built in Matlab/Simulink environment, has been revised to adapt it for the strategies above. Co-simulations between the engine and the ECU models have been performed for evaluating fuel consumption and engine-out quantities, after a transient driving cycle with low loads. Then, a 0D after-treatment model has been used for evaluating the tailpipe emissions. The results analysis focused on the impact of LIVC, iEGR and CDA on fuel consumption, NOx engine-out and tailpipe emissions, in respect to the baseline simulation. The exhaust temperatures have also been of interest, in order to evaluate the efficacy of such strategies for the after-treatment system warm-up.