Towards environmentally-friendlier diesel passenger cars
Recent advancements in automotive diesel engines have led to highly efficient operations accompanied with low emissions of CO2. Yet, as dictated by European regulations CO, HC, NOx and particulate discharges need to be further reduced. Motivated by this, this project focused on developing homogeneous combustion process for diesel engine passenger cars. The so-called Homogenous Charge Compression Ignition (HCCI) process can result in ultra low NOx and particulate emissions without compromising the efficiency of a diesel engine. Part of the project work involved an investigation of the fundamentals of turbocharger behaviour and spray formation in HCCI diesel engine operation at medium loads. Employing numerical simulations a large range of turbocharger-engine configurations were studied. One of the key issues was the turbo matching, as high Exhaust Gas Recirculation (EGR) rates and charge cooling is required under medium load operation conditions in HCCI mode. EGR systems are effective techniques to reduce the level of harmful NOx emissions of a diesel engine by introducing exhaust gas into the engine's intake system. Without burning, the exhaust gas takes up part of the combustion chamber's space, while lowering temperature and NOx emissions. In a turbocharged engine, high EGR rates may result into reduction of mass flow rates and boost of compression ratios. For the effective and reliable prediction of the turbocharger working conditions and hence, the engine's performance in HCCI mode, a computer model was generated. Additionally, characterisation of a newly produced innovative injection system was completed in an experimental test rig. Using laser-imaging techniques, monitoring and analysis of spray pattern formation was made possible by re-producing thermodynamic conditions similar to those created during advanced fuel injection. Moreover, the unknown analogies between parameters, such as fuel pressure, injection pulse duration, air density, air temperature and spray penetration, were also explored. Collaborations are sought with research institutions and/or automotive and heavy-duty engine manufacturers with experience on spray pattern formation in HCCI combustion mode operation and/or engine-turbo matching.
