On the Impact of Piston Motion and In-Cylinder Charge Composition on Energy Release, Auto Ignition and Emission Formation in Premixed Charge Internal Combustion Engines

Sammanfattning: The results presented in this thesis can be divided into four areas of investigation: Investigation of the effect of new volume-crank angle relations on engine emissions, power and efficiency; investigation of nitrogen oxides effect on auto ignition and knock in SI engines; investigation of premixed SI and HCCI engine operation with the alternative fuels hydrogen and reformed methanol gas (RMG); software development of a detailed chemical kinetics zonal engine model. Model development of the in-house two-zone chemical kinetic code focused on expansion of the Jacobian matrix to allow simulations of variable in-cylinder charge. Addition of engine simulation sub-routines to achieve full cycle simulation capacity were made. The routines added handle flow through valves and both internal and external residual gas mixing. Also expansion of the solver and development of the code to achieve multi-zone capacity was made. Nitric oxide was, both in a modeling study and in an experimental study, found to have an impact on auto ignition. The modeling study showed a maximum auto ignition promoting effect at 500 ppm. The experimental study showed increased knock intensity when NO was added but no maximum promoting effect was noted. Premixed engine HCCI and SI operation fuelled with hydrogen and RMG was analyzed from operating range, power, efficiency and emission perspectives. For the SI cases empirical flame speed expressions based on the engine related parameters lambda, engine speed, minimum cylinder height and ignition angle were developed. In the efficiency discussions the reformation of methanol to hydrogen or RMG is taken into account. The range of operation was limited to lean combustion. Engine power when using the investigated fuels was found to be limited to about half of what is achievable in premixed operation on other fuels. Indicated efficiencies were found to be high and the emissions of NO from the HCCI operated engine were low but the low combustion efficiency at high lambdas resulted in high amounts of unburned fuel in the exhaust gas. Modeling of new relations of volume-crank angle dependence was made. The efficiency and the power of the engine modeled were not altered in any major way by changes in the volume-crank angle dependence as long as the expansion ratio was held constant. Engine emission of NO and CO could be altered by changes in the volume-crank angle dependence but the changes were not of the magnitude that the concept can replace the catalyst used to lower emissions from engines today.