【作者】 代乾；

【导师】 姚春德；

【作者基本信息】 天津大学 ， 动力机械及工程， 2013， 博士

【摘要】 化石燃料的日益枯竭以及越来越严峻的环境问题是内燃机界的巨大挑战。寻找合适的替代燃料已成为研究热点，乙醇作为最有希望的可再生生物质燃料来源广泛，但是，乙醇具有较高的辛烷值，不易压燃，难以直接用于压燃式的柴油机。将柴油与乙醇二元燃料进行组合燃烧的模式，具有一定的经济性和环保性。然而对于此种燃烧的本质尚不清晰。因此本文对于这种燃烧模式分别进行了发动机台架实验、定容燃烧弹实验和低压层流预混火焰实验，并对二元燃料燃烧进行了化学反应动力学机理分析，在此基础上提出了二元燃料骨架机理，并进行了验证。利用定容燃烧弹研究了柴油在乙醇-空气混合气热氛围的着火特性。研究表明乙醇延长了柴油的滞燃期和火焰浮起长度。随着初始温度的升高，柴油滞燃期变短。在本研究发动机台架实验中也发现乙醇有延长柴油滞燃期的现象。利用发动机台架实验研究乙醇与柴油掺烧对污染物排放影响。研究结果发现，乙醇对于NOx和碳烟的生成也有很大的抑制作用，但是HC和非常规排放乙醛较原机有较大幅度上升。利用低压层流预混火焰结合同步辐射真空紫外光电离质谱技术，对理论当量比下乙醇掺混正庚烷火焰和浓混合气条件下乙醇掺混表征柴油进行了实验研究。结果表明，乙醇的加入对正庚烷和表征柴油的氧化裂解速率并没有实质影响，对于醛类物质，尤其是乙醛的摩尔分数上升有显著的促进作用。乙醇可以显著降低表征柴油中碳烟前驱体PAH的摩尔分数。利用商用软件CHEMKIN进行了柴油参比燃料正庚烷和乙醇混合燃料的机理分析。由计算结果可知，正庚烷低温冷焰反应及负温度系数区的时间均被延长，从而导致总反应延迟。通过反应路径和物质转化率分析得知，两种燃料的相互作用是靠自由基池为中介完成的，OH·和HO2·是池中最重要的自由基。乙醇的加入在低温下将活跃的OH·转化为相对不活跃的H2O2，对正庚烷第一步脱氢表现出强烈的抑制，对整个燃料的氧化进程表现出抑制作用，此即乙醇抑制正庚烷低温氧化的主要原因。在以上分析的基础上，建立了正庚烷乙醇二元燃料骨架机理。该机理包含50步反应和41种物质。并与详细机理在自燃和HCCI发动机缸内燃烧进行了对比验证，结果表明，该机理与详细机理具有较高的一致性。更多还原

【Abstract】 The increasing depletion of fossil fuels and increasingly severe environmentalproblems is the great challenge for the internal combustion engine industry. Lookingfor a suitable alternative fuel has become a research hotspot. Ethanol as one of themost promising renewable bio-fuel has been used as alternative fuels worldwide sinceit could been blended with gasoline. Due to ethanol’s high octane number,diesel/ethanol dual fuel, rather than pure ethanol could be used in conventional dieselengine to maintain or even reduce emission and fuel consumption. However, thenature of such dual fuel compound combustion has not been clearly understood. Tofurther investigate such combustion characteristic, experiments on engine bench,constant volume bomb and low pressure laminar premixed flame were carried out,numerical simulations are also performed with detailed chemical kinetics mechanisms.A skeletal mechanism model is proposed and validated based on experimental results.The constant volume bomb is used to investigate into the ignition characteristicsof diesel under atmosphere of ethanol-air mixture. Introduction of ethanol extends theignition delays and flame left length. As the initial temperature increases, the dieselignition delay becomes shorter. Such ignition delay could also be found on the realengine used in this study.For emissions characteristics during the engine bench test show that ethanolsubstantially suppress the production of NOx and soot. However, emissions of HC,especially aldehyde, illustrate a considerable increase under dual fuel combustionmode.Mole fractions of combustion intermediates of the dual fuel flames are measuredby low pressure laminar premixed flame combined with synchrotron vacuumultraviolet photoionization mass spectrometry. Experimental results show that theintroduction of ethanol has no substantive effect on the dissociation and oxidation ofdiesel (n-heptane) whereas it does greatly increase the mole fractions of aldehydes,especially acetaldehyde. In addition, ethanol significantly reduce the mole fraction ofPAH which are generally regarded as soot precursor. Chemical kinetics simulation of the oxidation of n-heptane as for diesel referencefuel and n-heptane/ethanol blends is carried out based on CHEMKIN softwarerespectively. Calculation results show that both cool-flame reaction at lowtemperature and negative temperature coefficient of n-heptane region are extended,resulting in a delay of overall reaction process. Further analysis of reaction path andproduction rate indicate that the interaction of between the two fuel molecule proceedvia the free radical pool in which the OH·and HO2·is the most important free radicals.Addition of ethanol at low temperature, converses OH· into relatively inactive ofH2O2, thus inhibits the first step H+abstraction of n-heptane, resulting in an inhibitionof the entire fuel oxidation process.A skeletal mechanism model of the oxidation of n-heptane and ethanol isproposed on the basis of the analysis above. The model includes50reactions and41species. Predictions of the model are validated with detailed mechanism on ignitionand testing data from a HCCI engine. The results show that the skeletal model yieldshigh consistency compared with detailed mechanism.更多还原