Turbo Charged Low Temperature Combustion - Experiments, Modeling and Control

Abstract: Both the global economy and the society in general are dependent on the availability of reliable transportation. Most transportation technology involves the use of internal combustion engines in one way or another. Because of the large numbers of internal combustion engines in use around the world, their emissions have a significant environmental impact. Therefore, considerable efforts have been invested into developing more sophisticated engine control systems and improving engine combustion behavior and post-treatment systems. These efforts have resulted in significant reductions in NOx, CO, HC, and particulate matter emissions and further improvements can be expected. Emissions of the green house gas CO2 were once unregulated, but has recently become the focus of considerable attention because of its role in global warming. The formation of CO2 in an internal combustion engine is directly dependant on its efficiency. This, together with the fact that the Earth's oil resources are finite and rapidly diminishing, means that there remains a need for improvements in engine efficiency. Homogeneous Charge Compression Ignition (HCCI) and Partially Premixed Combustion (PPC) are “low-temperature” combustion techniques that can, if implemented correctly, allow for the development of engines with improved efficiency and low emissions of particulate matter and NOx. The objective of the work described in this thesis was to obtain insights into how these low temperature combustion processes can be controlled so as to achieve a high degree of combustion stability, low noise, and reliable transient performance. A set of control-oriented models of HCCI engines were developed. These models capture the engines dynamic behavior and have been used to design controllers that were tested on a real Turbo Negative Valve Overlap (NVO) HCCI Engine. Engines using these controllers exhibited improved transient performance compared to engines using a more conventional controller design. A number of difficulties relating to load range and controllability were encountered in the studies on HCCI engines; it was suggested that PPC engines might suffer less from these problems. PPC represents a significant advance on HCCI in terms of controllability. However, in order to satisfy modern emissions criteria, it is necessary to operate PPC engines with extensive Exhaust Gas Recirculation (EGR). This presents some challenges relating to excessive rates of pressure increase during transient load increases. This problem was solved using a dual-injection strategy and model-based control. Low-load PPC operation is difficult with high octane fuels. Various methods for extending the load tolerated by PPC were proposed; some, such as switching to SI mode, were evaluated experimentally. To the best of the author's knowledge, these experiments were the first instances in which the mode of operation of an active engine was changed from SI to PPC and back. In both PPC and HCCI, combustion is highly sensitive to environmental conditions. Some of these are not easy to measure or understand with sufficient accuracy to predict their impact. Some kind of combustion event feedback is therefore necessary. To this end, piezo-electric pressure sensors, an ion current sensor and a high precision torque sensor were evaluated as feedback sensors that could potentially provide this data. The piezo-electric pressure transducer was found to be superior to the alternatives. Its readings are precise and provide accurate feedback on combustion timing. The ion current sensor was found to be a useful alternative at high and intermediate loads; unfortunately, at low loads, the signal-to-noise of the ion current signal is poor. An algorithm was proposed to improve the detection of the ion current, and was somewhat successful. Using a novel technique, data from the torque sensor was used in conjunction with combustion and black box models to obtain information on the combustion phasing.