Simulation Investigation Of Combustion Process Of Methanol Based On Non-equilibrium Plasma

Methanol, as coal products fuel, is one of the best choice of alternative energy in China due to Chinese energy situation. Based on the advantage and the prospect of methanol, it is meaningful to study the using of methanol for resolving the energy issue of automobile in China. However, methanol engines have hard cold start and high unregulated emissions problems. Therefore, non-equilibrium plasma assisted combustion provided a new idea to improve methanol engine combustion and emissions performance.This paper, firstly, numerically explore the discharge process of methanol-air mixture plasma by studying the mechanism of methanol-air plasma discharge process, the electron energy distribution characteristics and the production process of active particles; Secondly,using CHEMKIN pre-mixed model at fixed initial temperature, pressure and the concentration of the reactant components, study the plasma assisted combustion mechanism and analyze the performance of methanol combustion with non-equilibrium plasma; Finally,in order to explore the application of non-equilibrium plasma assisted combustion in methanol engine, use AVL FIRE with the establishment of methanol engine model to simulate the effect of air plasma assisted combustion, analyze the performance of methanol engine by air plasma-ozone assisted combustion. Conclusions are as follows:1. methanol-air plasma discharge process mainly include: the kinetic mechanism of electron impact excitation, dissociation and ionization, excited state quenching reactions,ions and electronic secondary recombination; The electron energy distribution characteristics are conducted by reduced field E/n, ionization degree and mixture composition; radicals are produced mainly in the electron collision between 3e V to 10 e V during the process of plasma discharge; Main active particles in methanol-air plasma are H, O, CH2 OH, CH3 and OH; it is suitable to produce radicals between 220 Td to 440 Td in plasma assisted combustion due to its high efficiency and low energy consumption.2. Plasma assisted combustion of methanol can decrease the ignition delay timeeffectively, in addition, oxygen atoms play a key role on the decrease of ignition delay time in plasma assisted combustion; the interval that system temperature reach to the peak value is shorter by using plasma assisted combustion; the conversion time between reactant to production has been decreased because of the addition of active particles in plasma assisted combustion.3. ozone, as the main active particles in air plasma produced in air intake manifold,have given a good performance in promoting methanol engine characteristics in cold start and emissions: at engine duty cycle, methanol engine combustion quality was improved and the emissions concentration was reduced, this is mainly caused by the ozone decomposition yields to oxygen atoms through the reactions: O3 + N2â†' O2 + O + N2 and O3 + O2â†' O2 + O+ O2, the subsequent reactions between oxygen atoms and methanol will produce new radicals to trigger series of oxidation chain reactions that can improve the performance of methanol engine’s combustion and emissions. At cold start condition, the combustion and emissions characteristics were bad without the ozone assisted combustion. After the addition of ozone, more and more methanol was combusted, methanol engine combustion quality was improved and the emissions concentration was effectively decreased, engine start more stable.Overall, methanol-air plasma assised combustion can effectively shorten the methanol ignition delay time and signigicantly accelerate combustion oxidation reaction rate,the methanol flame is more stable; ozone, as the main active particles in air plasma produced in air intake manifold, have given a good performance in promoting methanol engine characteristics in cold start and emissions.