A Quantitative Survey of Combustion Intermediates towards Understanding of Plasma Assisted Combustion Mechanisms

Mississippi State University, Mississippi State MS

Investigators

Abstract

1066486 Wang The goal of this study is to understand the fundamental mechanisms of nonthermal plasma-assisted combustion (PAC) and to promote the interests of a diverse population in the fields of plasma, combustion, and clean energy. Among plasma-initiated radicals, ions, and excited neutral species, the radicals may play the most important role in the enhancement of PAC for increased combustion efficiency, reduced pollutant emissions, short ignition delay time, leaner fuel mixtures, etc. However, rate constants and kinetic mechanisms of the reactions involving radicals as well as other reactive species remain little known, to a large extent, due to the challenge of obtaining time-resolved, in situ experimental data on the absolute number densities of reactants/products of the reactions pre-, during-, and post-ignition. This proposal conducts a survey of absolute number densities of the combustion intermediates, leading to a better understanding of the role of radicals in PACs. The technologies developed in this project will be transportable to study other types of PACs and the scientific database generated in this project will benefit the greater PACs community. This work will help to explain how plasma can enhance combustion performance. The research effort includes: 1) Develop two novel combustion systems assisted by a continuous microwave plasma discharge with low-speed flows in ambient air and by a pulsed DC glow discharge with high-speed flows in a supersonic jet chamber; 2) Employ high sensitivity laser cavity ringdown spectroscopy (CRDS) technique to measure absolute number densities of multiple combustion intermediates in near real-time, in situ with high spatial resolution; 3) Use the generated particle densities database to establish the rate constants and kinetic pathways of key fundamental reactions, which will lead to the development of new kinetic mechanisms for PACs; and 4) Validate the kinetic mechanisms through characterization of the plasma sources and combustion properties by using a suite of functionally-combined diagnostic techniques. The novelty is three-fold: 1) CRDS is capable of measuring absolute number densities in near real-time, in situ; 2) CRDS in combination with a widely tunable (UV - mid-IR), narrow-linewidth laser source enables us to measure almost all important radicals and other reactive species; and 3) Combination of the simple fuel mixtures with two distinct plasmas will facilitate the initial kinetic modeling and the investigation of two major combustion attributes: flame behavior and ignition delay time. The research activities will help advance the current understanding of PAC mechanisms from entirely depending on high-temperature reaction mechanisms that have been established for combustion without nonthermal plasma to using the new reaction mechanisms that are built on an experimental database obtained temporally and spatially in combustions enhanced by a low-temperature nonthermal plasma. The social benefits of this study lie in the areas of fuel economy, pollution control, and technological limits of plasma/combustion operation in various applications. For instance, 48% of electricity in the US comes from combustion processes, where combustion efficiency, fuel reforming, and combustion pollution are critical issues. In aerospace applications, technological limits of combustion processes are challenged by the demanding needs of fast ignition at high speed and high altitudes. Two Ph.D. students and one undergraduate student in Applied Engineering Physics will be trained in this project. Selected math and science talented high school students from a local high school will also be involved in this project. A small-scale Research Station for Plasma and Combustion studies will be established to attract undergraduate students for summer research; and it will be open for tours to high school students and K-12 science teachers during a series of annual outreach events in the local community. The proposed research will enhance research infrastructure in clean energy and laser diagnostics and control in the southeast.