Edinburgh Napier University

  Using algorithmic tools derived from the methodology of Computational Singular Perturbation various autoignition problems are investigated. In the first problem, the autoignition kinetics of DME/air and EtOH/air stoichiometric mixtures are compared both at low and high initial temperatures. DME and EtOH are two isomer fuels, with thepotential for production from renewable sources, that have virtually identical thermochemistry. These isomer fuels have drastically different ignition delays because of their different kinetics. In particular, at sufficiently high initial temperatures, the first and largest part of the ignition delay in the DME and EtOH cases is dominated by two different sets of components of carbon chemistry, while the last and shortest part is dominated by the same hydrogen chemistry. In the DME case thetime scale that characterizes autoignition in the first part is promoted by single-carbon chemistry, while in the EtOH case the two-carbon chain retains its bond in that part, therefore, the hydrogenchemistry plays an important role in promoting the autoignition. These features generate a substantially shorter ignition delay for EtOH. At sufficiently low initial temperatures, in the DME case, it is shown that the low-temperature oxidation is dominated by reactions involving heavy carbonaceous species. Moreover, it is demonstrated that the outcome of the competition between two specific reactions is the cause for the exhibited negative temperature coefficient (NTC). In the EtOH case, the analysis points to the importance of carbonaceous species and in particular acetaldehyde.In the second problem, the effect of selected additives on the ignition delay of EtOH/air and DME/air mixture is investigated. CSP tools are utilized in an effort to determine algorithmicallywhich species to select as additives and it is established that CSP can identify species whoseaddition to the mixture can affect ignition delay. In the third autoignition problem, the reactions via which H2O-dilution influences ignition delayand chemical paths that generate NO, are examined, in the context of isochoric homogenous CH4/air autoignition. Both, the thermal and chemical effects of dilution are examined and it is concluded that the thermal effects result in a lower temperature at the end of the explosive stage, while among the most notable chemical effects are (i) the increased OH production throughout the explosive stage and (ii) the lower levels of O after this stage. Finally, the homogeneous autoignition dynamics of a stoichiometric H2/air mixture around thethird explosion limit is investigated using CSP tools, on the basis of two detailed chemical kineticsmechanisms; one that includes surface radical loses and one that does not. It is shown that very close to the third limit both the gas phase and the surface reactions contribute to its development.