Thermodynamic Simulation of HCCI Engine Systems

Abstract: This thesis focuses on engine system simulation using thermodynamics and chemical kinetic models to investigate the performance and efficiency of Homogeneous Charge Compression Ignition (HCCI) engines for stationary applications. It includes the development of software as well as models for engine, turbocharger, intercooler, inlet and exhaust manifolds, wastegate valve, inlet air humidifier, inlet air heater and more. The engine model can be classified as a one-zone, zero-dimensional and includes sub-models for in-cylinder heat transfer, exhaust port heat transfer, heat release and the valve flow process. The turbocharger model is developed in steps and is based on a polynomial fit to experimental compressor and turbine performance data. Inlet and exhaust manifolds are treated as well-mixed volumes. A simplified model for the humidifier is adopted in order to simulate a humid air motor (HAM) concept. The whole engine system is zero dimensional and the different system components are linked by means of mean values for mass flow, temperatures, pressures and gas composition. The NASA-polynomials are used for calculating thermal and transport properties. The extended Zeldovich mechanism is used as an indicator of significant NO formation. The models are validated through comparisons with experiments on mainly diesel and HCCI engines, both cycle and system results.HCCI engine cycle simulations are made, showing the influence of various engine parameters e.g. compression ratio, engine speed, air-fuel ratio, exhaust gas recycling, inlet pressure and valve timing. Mainly natural gas and landfill gas are studied. The self-stabilizing feature of HCCI ignition timing is investigated using chemical kinetics. HCCI engine system simulations are made, both with (to find ignition timing) and without chemical kinetics, investigating turbocharging and the influence of turbine size. The HCCI - HAM concept is investigated and compared to simpler systems.