پایان نامه دکتری با موضوع Non-equilibrium Plasma-Assisted Combustion
پایان نامه با موضوع
Non-equilibrium Plasma-Assisted Combustion
در سطح دکتری تخضض
خلاصه
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
iv
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.
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