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Dimethyl ether and other oxygenated fuels for low-emission diesel engine combustion.

机译：二甲醚和其他含氧燃料，用于低排放柴油机燃烧。

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Two classes of oxygenated compounds, ethers and glycols, have been identified as possible alternative fuels for Diesel engine combustion. These compounds offer the possibility for significantly lower Diesel engine emissions and improved driveability for two reasons: (1) because they are oxygenated, they appear to produce almost no smoke or particulate matter when burned in a Diesel engine, and (2) they have excellent autoignition quality. Excellent autoignition quality, defined as having short autoignition delay times, leads to improved cold start performance, lower combustion noise, and lower levels of NOx. The fact that the fuels produce almost no smoke also offers the possibility to use increased levels of exhaust gas recirculation in order to further lower NOx emissions. Finally, all of these synthetic Diesel engine fuels can be produced from natural gas, coal, biomass, or other hydrocarbons feedstocks making them viable replacements for traditional, crude oil-derived fuels.; Experiments were performed in a unique apparatus, the externally heated constant volume combustion apparatus (CVCA-II) designed specifically to study the pyrolysis and autoignition of fuels. For pyrolysis, the fuels were injected into an inert volume of helium, and extractive samples were taken to measure product yields. For autoignition, the fuels were injected into a heated, high pressure volume of oxidizing gas (usually air). Autoigntion delay times were measured based on the time-pressure history of the gases in the CVCA-II.; A chemical kinetic mechanism consisting of 44 species and 148 reversible reactions was developed to describe the autoignition, oxidation, and pyrolysis of methane, methanol, diemethyl ether, and dimethoxy methane. For some species, thermodynamic properties were estimated using a program developed by the author. Hydrogen abstraction reactions were estimated based on principles of analogy with other known reactions. Uni-molecular decomposition reactions, assumed to be at the high pressure limit, were estimated using transition state theory. For dimethyl ether and dimethoxy methane, sensitivity analysis showed that at lower temperatures ({dollar}<{dollar}800 K) peroxide chemistry plays an important role in determining the rate of autoignition, while at higher temperatures ({dollar}>{dollar}1000 K) uni-molecular decomposition and hydrogen abstraction control the rate of autoigntion. At intermediate temperatures (800-1000K), a negative temperature coefficient (NTC) behavior was observed. For methanol and methane, peroxide chemistry did not play a role in the autoignition delay times calculated for temperatures between 700 K and 1100 K, and no NTC behavior was observed.; A multi-zone adiabatic mixing approach was used to model the non-homogeneous autoigntion of a fuel injected into a hot quiescent environment. The model assumes that fuel and air are present in zones of varying stoichiometry. Because of the heat transfer required to vaporize and heat the fuel, the zones vary in temperature which is a function of stoichiometry. A trade-off exists between the leaner-hotter zones and the cooler-richer zones, with autoignition occurring at an optimum point of stoichiometry and temperature. The model predicts the autoigntion delay times of methane, methanol, DME, and DMM measured in the experiments. The model also describes the physical and chemical effects of methane mixed homogeneously with the oxidizing gas before injection of ignition fuel. Finally, the autoignition delay times of fuel mixtures such as methane and methanol blended with dimethyl ether and dimethoxy methane were studied to examine the use of oxygenated fuels as autoignition improvers.
机译：已经确定了两类含氧化合物，醚和乙二醇，是柴油机燃烧的可能替代燃料。这些化合物提供了显着降低柴油发动机排放和改善驾驶性能的可能性，其原因有两个：（1）因为它们被氧化，在柴油发动机中燃烧时几乎不产生烟尘或颗粒物，（2）它们具有优异的自燃质量。出色的自燃质量（定义为具有较短的自燃延迟时间）可改善冷启动性能，降低燃烧噪声并降低NOx含量。燃料几乎不产生烟雾的事实也提供了使用增加水平的废气再循环以进一步降低NOx排放的可能性。最后，所有这些合成柴油发动机燃料都可以由天然气，煤炭，生物质或其他碳氢化合物原料生产，使其成为传统原油衍生燃料的可行替代品。实验是在一种独特的设备上进行的，该设备是专门设计用于研究燃料的热解和自燃的外部加热的恒定容积燃烧设备（CVCA-II）。为了进行热解，将燃料注入惰性体积的氦气中，并提取样品以测量产品收率。为了自动点火，将燃料注入加热的高压体积的氧化气体（通常是空气）中。自燃延迟时间是根据CVCA-II中气体的时间-压力历史记录来测量的。建立了由44个物种和148个可逆反应组成的化学动力学机制，以描述甲烷，甲醇，二甲基醚和二甲氧基甲烷的自燃，氧化和热解。对于某些物种，使用作者开发的程序估算了热力学性质。氢提取反应是根据与其他已知反应的类比原理估算的。使用过渡态理论估算了假定处于高压极限的单分子分解反应。对于二甲醚和二甲氧基甲烷，敏感性分析表明，在较低温度下（{dollar} <{dollar} 800 K），过氧化物化学在决定自燃速率方面起着重要作用，而在较高温度下（{dollar}> {dollar} 1000 K）单分子分解和氢提取控制自燃速率。在中间温度（800-1000K）下，观察到负温度系数（NTC）行为。对于甲醇和甲烷，过氧化物化学在计算700 K至1100 K温度之间的自燃延迟时间中不起作用，并且未观察到NTC行为。使用多区域绝热混合方法对注入热静态环境中的燃料的非均匀自燃进行建模。该模型假设化学计量比不同的区域中存在燃料和空气。由于蒸发和加热燃料所需的热传递，区域的温度变化是化学计量的函数。在较热的区域和较冷的区域之间存在权衡，自燃发生在化学计量比和温度的最佳点。该模型可预测实验中测得的甲烷，甲醇，DME和DMM的自燃延迟时间。该模型还描述了在注入点火燃料之前，甲烷与氧化气体均匀混合的物理和化学作用。最后，研究了混合有二甲醚和二甲氧基甲烷的甲烷和甲醇等燃料混合物的自燃延迟时间，以研究含氧燃料作为自燃改进剂的用途。

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