【作者】 梁昱；

【导师】 罗福强；

【作者基本信息】 江苏大学 ， 动力机械及工程， 2007， 博士

【摘要】 内燃机燃料的主要来源为石油和天然气,化石能源渐趋枯竭,温室效应导致全球灾难性气候频繁发生,环境污染日益严重。因此,寻找新的内燃机能源迫在眉睫。生物质能作为可储存和运输的可再生能源,其高效转换和洁净利用日益受到全世界的重视。本文简述了内燃机的能源现状和发展趋势;综述了生物质能源的现状,双燃料发动机技术和双燃料发动机燃烧模拟的进展以及生物质气化技术的发展和研究现状。在前人研究的基础上对生物制气-柴油双燃料发动机的应用技术和理论模型进行了较为深入的探讨,为生物质能源在双燃料发动机上的利用及发展方向提供了的依据。采用自行设计的下吸式气化炉,以农林废弃的生物质为原料产生生物制气,并经过冷却滤清后,将洁净的常温生物制气通入由ZH1115直喷式柴油机改装而成的双燃料发动机。针对可燃生物制气的存在使进入气缸中的空气比相同排量柴油机少,有可能使发动机由于空气不足而使燃料不能充分燃烧,发动机动力性、经济性下降,分析了生物制气的成份及性能,推导了气体-柴油双燃料发动机与柴油机相比的动力性变化计算公式并与试验结果吻合较好。分别进行了纯柴油和双燃料运行时的试验研究。对比分析了柴油机和生物制气-柴油双燃料发动机的万有特性、燃烧特性和比排放特性。分析了负荷、转速、供油提前角等参数对柴油机及双燃料发动机燃烧过程的影响。结果表明:双燃料发动机的燃烧始点落后于柴油机;除低速大负荷外,最高燃烧压力、最大燃烧压力升高率均低于柴油机,最高燃烧压力与最大燃烧压力升高率对应相位均滞后于柴油机;双燃料发动机的后燃较为严重。双燃料发动机的NO_x排放量远比柴油机低。以引燃油喷雾混合、燃烧化学反应机理、湍流运动和燃烧计算、NO_x预测模型、初始及边界条件设定和计算网格划分为主要内容,探讨并建立了生物制气-柴油双燃料发动机的三维燃烧模型。引燃油喷雾混合模拟中,采用离散相液滴模型模拟引燃油液滴的运动;实心圆锥体(solid cone)射流源和Rosin-Rammler分布来描述引燃油的喷射,并采用多段射流源的方法贴近实际的喷油规律;Wave Breakup模型模拟引燃油液滴的破碎:O’Rourke随机碰撞模型模拟液滴的碰撞,并考虑了液滴与壁面碰撞的反弹和粘附;采用Hardcnburg和Hase提出的公式计算滞燃期。湍流运动采用RNG(Renormalization Group Theory)κ-ε方程模拟,并采用壁面函数对壁面湍流进行修正。燃烧计算中,将层流有限速率模型与涡耗散模型进行结合来计算净反应速率;采用单步反应来描述柴油的燃烧;生物制气,则分别采用简化机理和一氧化碳、氢气、甲烷各自的单步反应来处理。NO_x预测模型中,包含了热力型NO_x、瞬发型NO_x和燃料型NO_x的形成,并采用概率密度函数(PDF)方法进行计算。初始条件尽量采用试验中获得的数据,以便获得较好的模拟结果。网格模型中,由于喷油嘴为均布四孔喷嘴,因此只建立缸内四分之一几何空间模型,结合周期性边界,可减小计算时间;用六面体和楔形单元进行网格划分,结合网格刚体运动和网格层铺实现动态网格模拟。通过模拟结果与试验结果的对比表明:本文建立的三维燃烧模型可以较好的模拟柴油机和生物制气-柴油双燃料发动机的燃烧过程,预测发动机的各项性能参数。在此基础上,利用三维燃烧模型,预测分析了不同引燃油量、不同生物制气成份和不同进气量等参数对双燃料发动机燃烧过程的影响。结果表明:引燃油量减小,燃烧始点延迟,最高燃烧压力降低,最高燃烧压力对应转角滞后,后燃增加,NO_x的排放量降低。生物制气的热值越高,缸内最高燃烧压力越大,平均温度也越高,同时NO_x排放量也越大。更多还原

【Abstract】 Up to the present, petroleum and nature gas are still the main sources of fuel for the internal-combustion engine. However, the reserves of petroleum and nature gas are reducing sharply. Moreover, greenhouse effect results in the frequent appearance of global catastrophic climate and the situation of environment are getting serious. So to searching a new substitute of energy for the engine is urgent. Biomass energy is considered as the reproducible energy that can be stored and transported, and its high efficiency of conversion and low pollution are more and more significant. The present situation and development trend of internal-combustion engine are briefly discussed. The developments of biomass energy, the technology and combustion modeling of dual fuel engine and the technology of biomass gasification are summarized. The re-equip technology and theory model of the dual fuel engine are developed on the basis research of predecessors. The foundation for the utilizing and development trend of biomass energy sources is given.Biogas is made from agricultural and forestry residues by a negative pressure downdraft gasifier. It is utilized as main fuel in a biogas-diesel dual fuel engine that is refitted from the ZH1115 direct injection diesel engine after being cooled and filtrated. The power and economic performances of a gas-diesel dual fuel engine may be worse because its air volume in cylinder is less than the diesel engine with the same displacement volume due to the volume of gas fuel in cylinder. The components and their performances data of biogas are analyzed. The calculation formula of power performance of the gas-diesel dual fuel engine is deduced. The calculated results are fitted in with the experimental ones. The tests at different loads and speeds are carried out for the diesel engine and the dual fuel engine. The mapping characteristics, combustion characteristics and specific emission characteristics of the diesel engine and the dual fuel engine are compared and analyzed. The effects of parameters such as load, engine speed and fuel supply advance angle on combustion process are studied. The results show that compared with diesel engine, the ignition time of dual fuel engine delays, maximum combustion pressure and maximum combustion pressure rise rate are lower and their corresponding phases are later, after combustion period is longer except at low speed and large load. The NO_x emission of dual fuel engine is lower remarkably than diesel engine.Based on the pilot fuel spray and mix, combustion chemical reaction kinetic, turbulent flow, combustion calculation theory, NO_x formation model, initial and boundary conditions and mesh creation, a three dimension combustion model of biogas-diesel dual fuel engine has been established. In the pilot fuel spray and mix model, discrete phase liquid droplets model has been used to simulate the movement of pilot fuel liquid droplets. Multi-injection solid cone injector source and Rosin-Rammler distribution have been used to distribute fuel injection. The breakup of pilot fuel liquid droplets has been simulated by Wave Breakup model. Ignition delay has been calculated by the formula deduced by Hardenburg and Hase. Turbulent flow has been simulated by Renormalization Group Theory （RNG）κ-εformula and near-wall region turbulent flow has been amended by wall functions. In combustion calculation, net production rate has been gained based on combining the laminar finite-rate model and the eddy dissipation model. Diesel combustion has been described by single step reaction, and biogas combustion by simplified chemistry mechanism and single step reaction of CO, H₂ and CH₄. In NO_x estimating model, thermal NO_x formation, prompt NO_x formation and fuel NO_x formation have been calculated by probability density function （PDF）. In order to get more reasonable results, initial conditions are set to testing data. In calculating mesh, periodic boundary has been adopted. Because the injector has four even collocation nozzle holes, in order to save calculation time, only a quarter geometry model has been considered. Mesh creation has been carried out with hexahedral and cuneiform cell. The mesh regions swept out by the moving surfaces has been represented by dynamic layering zones.By comparing the computer simulation results with the experiment ones, it is shown that the three-dimension combustion model can be used to simulate the combustion process of diesel engine and biogas-diesel dual fuel engine and to evaluate performance parameters of the two engines. Then, the effects of main parameters such as the quantity of pilot fuel, the biogas component and quantity on the combustion process of dual fuel engine have been researched. The results show that with the quantity of pilot fuel decreasing, ignition time delays, maximum combustion pressure becomes lower, the corresponding phase gets later, the after burning is heavier and NO_x emission reduces. The higher the heat value of biogas is, the higher the maximum combustion pressure and the average temperature are, and the worse the NO_x emission is.更多还原