پایان نامه دکتری با موضوع Non-equilibrium Plasma-Assisted Combustion

As a promising method to enhance combustion, plasma-assisted combustion has

drawn considerable attention. Due to the fast electron impact excitation and dissociation

of molecules at low temperatures, plasma introduces new reaction pathways, changes fuel

oxidation timescales, and can dramatically modify the combustion processes. In this

dissertation, the radical generation from the plasma and its effect on flame extinction and

ignition were investigated experimentally together with detailed numerical simulation on

a counterflow CH4 diffusion flame. It was found that the atomic oxygen production

played a dominant role in enhancing the chain-branching reaction pathways and

accelerating fuel oxidation at near limit flame conditions. To understand the direct

coupling effect between plasma and flame, a novel plasma-assisted combustion system

with in situ discharge in a counterflow diffusion flame was developed. The ignition and

extinction characteristics of CH4/O2/He diffusion flames were investigated. For the first

time, it was demonstrated that the strong plasma-flame coupling in in situ discharge could

significantly modify the ignition/extinction characteristics and create a new fully

stretched ignition S-curve.

To understand low temperature kinetics of combustion, it is critical to measure the

formation and decomposition of H2O2. A molecular beam mass spectrometry (MBMS)

system was developed and integrated with a laminar flow reactor. H2O2 measurements

were directly calibrated, and compared to kinetic models. The results confirmed that low

and intermediate temperature DME oxidation produced significant amounts of H2O2. The

experimental characterizations of important intermediate species including H2O2, CH2O

and CH3OCHO provided new capabilities to investigate and improve the chemical

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kinetics especially at low temperatures.

A numerical scheme for model reduction was developed to improve the

computational efficiency in the simulation of combustion with detailed kinetics. A multi

generation Path Flux Analysis (PFA) method for kinetic mechanism reduction is

proposed and validated. In this method, the formation and consumption fluxes of each

species at multiple reaction path generations were analyzed and used to identify the

important reaction pathways. The comparisons of the ignition delays, flame speeds, and

flame structures showed that the PFA method presented a higher accuracy than that of

current existing methods in a broad range of initial pressures and temperatures.