煤直接液化柴油燃烧反应机理研究

Direct coal liquefaction diesel (DCLD) has been put into mass production firstly and recently as a new alternative fuel for diesel in China. Because of its different hydrocarbon groups composition, combustion, physical and chemical properties from petro-diesel, the project systematically studies the combustion mechanism of its surrogates。Considering feasibility, simplicity, similarity and practicability, bicyclo-alkane and its mixture with other alkanes are specially-chosen as the surrogates. Based on reaction sorting, a detailed kinetic mechanism construction principle for single-constituent surrogate is proposed. The combustion mechanism consists of core mechanism and step-expanded mechanism. The effect of temperature on reaction rate is uncovered. In view of inter-fuel repeatable reactions and surplus reactions as well as typical characteristics representation for pure constituent, a methodology for constructing detailed kinetic mechanism for multi-constituent surrogates is also given. To overcome the analytical locality of conventional CSP（computational singular perturbation）, an integral CSP algorithm is put forward for reducing comprehensive mechanism with hi-fidelity. Shock tube experiments and others are performed to verify the comprehensive mechanisms. Skeletal mechanisms are derived with Directed Relation Graph and global mechanisms using integral CSP. 3D combustion simulation model is created for engine operation with fuel property prediction model, fuel evaporation model and turbulence-reaction interaction model.The global mechanisms are then employed to simulate in-cylinder combustion. Finally, on an electrical controlled diesel engine, the ignition, combustion and emissions of DCLD are investigated with global mechanisms validated in an intensely unstable complex combustion environment. The effects of injector structure, injection parameter and operation condition on ignition and combustion are researched. The study provides a theoretical support for controllable clean and high-efficiency LT combustion.

煤直接液化柴油DCLD最近在我国率先成熟、大批量生产。针对其迥异于石化柴油的烃族组成、理化和燃烧特性，本项目系统研究其替代物燃烧反应机理。据可行性、简易性、相似性、实用性，选择环烷烃及其与其它烃类（如链烷烃）的混合物作替代物。提出单组分燃料详细机理构建策略，燃烧机理由核心机理和阶梯式扩展机理构成。揭示反应速率受温度的影响机制。考虑燃料间重复反应、剩余反应、纯燃料燃烧典型特征再现等，提出并实施多组分燃料详细机理构建策略。针对传统计算奇异摄动CSP方法仅能局部分析的缺陷，提出积分CSP高保真度机理简化原理和算法。用激波管等试验验证详细机理。用多步直接关系图法得框架机理，用积分CSP得全局简化机理。构建发动机燃烧模拟计算平台，添加燃料特性预测模型，改进燃料蒸发模型，添加湍流与化学反应相互作用模型，用简化机理3D数值模拟DCLD发动机缸内过程。在电控柴油机上研究DCLD着火、燃烧与排放，及喷油器结构参数、喷射控制参数、运转工况的影响规律。在缸内强烈瞬变复杂环境下，检验全局简化机理的有效性。本研究为柴油机可控清洁高效低温燃烧技术的发展提供依据。

煤直接液化柴油DDCL是我国率先成熟并大批量生产的一种柴油替代燃料。本研究据DDCL的烃类组成结合当前各烃类氧化研究基础确定了煤直接液化柴油单组分替代物为十氢萘，两组分替代物为十氢萘和正十二烷，两者的摩尔比以实际燃油的十六烷值、低热值、C/H比、密度为目标最终确定为0.797:0.203。.据烃类氧化的典型路径编写了详细机理构建程序，在环己烷核心机理的基础上分别构建了十氢萘和正十二烷的详细机理，合并后的详细机理有434种组分和1876步反应，该机理总体上能准确预测燃料在激波管中的着火延时以及射流搅拌反应器中大部分组分的浓度。.利用直接关系图法考虑尽可能广的工况范围对详细机理进行了初步简化，按阈值0.15删除了97种组分得到框架机理。在计算奇异扰动算法的基础上加入物质浓度、物质净生成速率和放热率作为权重因子提出了积分CSP算法，用该算法进一步简化了框架机理，得到了324种组分和318步反应的全局简化机理。.建立了电控共轨四缸增压柴油机试验台，测试了DDCL在发动机中的着火、燃烧、排放等性能。研究表明：随着主喷时刻推迟，滞燃期先缩短后延长，最大压升率降低；NOX排放明显降低，碳烟和CO排放先上升后下降，当量燃料消耗率升高。预喷策略可降低DDCL最大压升率，但随预喷时刻提前，最大压升率升高；预喷策略可显著降低NOX排放，且存在特定的预喷时刻，提前或推迟预喷NOX排放都会降低；预喷策略增加了碳烟排放，且碳烟排放随预喷时刻的提前而降低。喷射压力升高，最大压升率上升；NOX排放升高，碳烟、CO和当量燃料消耗率降低。.采用简化机理模拟了各工况下DDCL的发动机试验，结果表明：针对不同主喷时刻、预喷时刻、喷射压力、EGR率模拟的缸内压力与放热率曲线均与试验结果吻合较好；NOX预测值与实验值较为接近，预测的碳烟生成变化趋势与试验一致，预测的CO趋势与试验相符；总体而言，该简化机理在模拟DDCL的燃烧与排放方面是可靠的。