Laser Absorption Measurements of Hydroperoxy-Related Reactions in Shock Tubes at Intermediate Temperatures

中温激波管中氢过氧基反应的激光吸收测量氢/氧氧化是当今燃烧中最重要的系统之一。这导致了对高温(1200K以上)下H2/O2化学的极其准确的描述。然而，在中温(约800-1200K)下，许多重要化学反应的速率系数是不确定的，特别是那些涉及过氧化氢自由基HO2和过氧化氢过氧化氢的化学反应。在均质充气压燃式发动机(HCCI)等氢动力发动机中，H_2O_2动力学可以控制化学成分，并且对于描述发动机爆震和柴油点火是至关重要的。还需要了解过氧化氢化学，以此作为解决过氧基(RO2)化学这一更大问题的基础，这一化学问题在碳氢化合物的中温氧化中很重要。迫切需要新的测量方法来改进这些过程的化学模型和计算机模拟。烷烃是汽油、煤油和柴油等所有碳氢燃料的重要组成部分。在燃烧过程中，这些烷烃(如正庚烷和异辛烷)分解为烷基自由基。随后，这些烷基自由基会被氧化或进一步分解。氧化和分解的这两条烷基路径及其相对速率决定了燃烧系统随后的行为。这些反应的性质导致了中温区氧化机理的改变，导致了烃类氧化过程中的负温度系数(NTC)行为。对烷基氧化机理的全面了解在燃烧化学、自燃、发动机爆震、大气化学和自由基反应化学中具有重要意义。在这些体系中，将利用激波管中的紫外激光吸收来定量测量瞬时自由基，包括OH、HO2和烷基过氧基。根据这些对物种浓度的时间历史的测量，将确定几个关键碳氢化合物燃烧反应的反应速率。具体的反应包括：H_2O_2·OH+OH；H+H_2O_2·HO_2+H_2；C_2H_5+O_2·HO_2+C_2H_4；C_3H_7+O_2·HO_2+C_3H_6。这些反应被认为是造成中温(800-1200K)燃烧模型不确定性的主要因素。关键的贡献将是测量本身，落在一个关键的温度区域，测量压力从1到100个大气压，以及一种新的215 nm深紫外激光吸收诊断方法。这项研究将提供一个机会，培训一代工程科学家现代燃烧动力学和最先进的激光诊断和激波管技术。利用现有数据库通过网络公开传播这些数据，将为公众、学生、教师和政府工作人员提供必要的信息，以批判性地了解燃烧过程。当今美国人面临的重要问题之一是燃烧过程中产生的温室气体以及随之而来的全球变暖影响，因此迫切需要研究燃烧的基本原理。

Laser Absorption Measurements of Hydroperoxyl-Related Reactions in Shock Tubes at Intermediate TemperaturesR. K. Hanson, Stanford UniversityPublic AbstractHydrogen/oxygen oxidation is one of the most important systems in combustion today. This has led to the development of an extremely accurate description of H2/O2 chemistry at high temperatures (above 1200 K). However, at intermediate temperatures (from about 800 to 1200 K) the rate coefficients of many important chemical reactions are uncertain, particularly those involving HO2, the hydroperoxyl radical, and H2O2, hydrogen peroxide. H2O2 kinetics can dominate the chemistry in hydrogen-powered engines, such as homogenous charge compression ignition engines (HCCI), and are critical to describing engine knock and diesel ignition. An understanding of H2O2 chemistry is also needed as a basis for attacking the larger problem of peroxy-radical (RO2) chemistry important in oxidation at intermediate temperatures of hydrocarbons. New measurements with smaller uncertainties of the rate coefficients in the H2O2 system at intermediate temperatures are urgently needed to improve chemical models and computer simulations of these processes.Alkanes are important components of all hydrocarbon fuels such as gasoline, kerosene and diesel. During combustion, these alkanes (such as n-heptane and iso-octane) decompose into alkyl radicals. Subsequently these alkyl radicals are either oxidized or further decompose. These two alkyl pathways of oxidation and decomposition, and their relative rates, dictate the subsequent behavior of the combustion system. The properties of these reactions cause a change in the oxidation mechanism in the intermediate temperature regime which results in the "negative temperature coefficient" (NTC) behavior in hydrocarbon oxidation. Complete understanding of the alkyl oxidation mechanism has implications in combustion chemistry, auto-ignition, engine knock, atmospheric chemistry and radical reaction chemistry.Quantitative measurements of transient radicals, including OH, HO2 and alkyl-peroxy-radicals, will be made in these systems using UV laser absorption in shock tubes. From these measurements of time histories for species concentrations, reaction rates will be determined for several critical hydrocarbon combustion reactions. Specific reactions of interest include: H2O2 OH + OH; H + H2O2 HO2 + H2; C2H5 +O2 HO2 + C2H4; C3H7 +O2 HO2 + C3H6. These reactions have been identified as major contributors to the uncertainty in the modeling of intermediate temperature (800-1200 K) combustion. Key contributions will be the measurements themselves, falling in a key temperature region and measured at pressures from 1 to 100 atm, and a new 215nm deep-UV laser-absorption diagnostic method.This research will provide an opportunity to train a generation of engineering scientists in modern combustion kinetics and state-of-the-art laser diagnostic and shock tube techniques. Public dissemination of this data through the web using current databases will provide the public, students, teachers and government workers with the information needed to critically understand combustion processes. With one of the important problems facing Americans today being generation of greenhouse gases from combustion processes and the subsequent effect of global warming, research on combustion fundamentals is critically needed.