催化燃烧对均质压燃发动机排放影响的数值模拟

通过耦合DETCHEM软件包及CHEMKIN软件包中的SENKIN模块,对活塞顶涂有催化剂的均质压燃(HCCI)发动机的燃烧过程进行了数值计算,建立了多区模型.利用此模型分析了催化燃烧对HCCI发动机缸内温度、热释放速率以及未燃碳氢化合物(UHC)、氮氧化合物(NOx)、一氧化碳(CO)排放的影响,结果表明催化燃烧能降低UHC、CO的排放,但NOx的排放会有所升高.对不同催化剂及混合催化剂对HCCI发动机缸内温度、热释放速率以及UHC、NOx、CO排放的影响进行了探索,结果表明,和金属铂相比,以铑作催化剂时UHC的排放降低,但NOx、CO排放会有所升高;采用500/0Pt-500/0Rh的混合催化剂时,UHC、NOx的排放介于1000/0Pt与1000/0Rh之间,但CO的排放却比采用1000/0Pt与1000/0Rh时都要低.     

汽油转子发动机热力过程数值模拟研究

建立了汽油转子发动机燃烧室内热力过程及一些边界的数学模型,并发展了相应的计算软件。通过数值模拟计算获得了汽油转子发动机燃烧室内气体压力、各区内气体温度随偏心轴转角的变化及各工况下的性能参数,并将数值计算和试验测量结果进行了对比分析。结果表明：本文发展的预测汽油转子发动机热力过程的数学模型正确,计算软件可靠,计算精度满足工程需要,可用作设计研制汽油转子发动机的分析工具。     

催化燃烧对HCCI发动机着火点、燃烧性能及排放的影响

对甲烷在催化剂铑(Rh)表面的反应机理进行了分析。通过修改CHEMKIN软件包中的SENKIN模块,对活塞顶涂有催化剂的HCCI发动机的燃烧过程进行了数值计算,建立了单区、多区模型。利用单区模型分析了催化燃烧对HCCI发动机着火时刻的影响,结果表明在控制HCCI发动机着火时刻方面催化燃烧有其他方式所没有的优势;利用多区模型分析了催化燃烧对HCCI发动机的燃烧性能及HC、CO、NOx排放的影响,结果表明催化燃烧对燃烧效率、着火持续期有较大的影响,同时能降低HC、CO的排放,但会提高NOx的排放。     

Mobile hydraulic power supply: Liquid piston Stirling engine pump

Conventional mobile hydraulic power supplies involve numerous kinematic connections and are limited by the efficiency, noise, and emissions of internal combustion engines. The Stirling cycle possesses numerous benefits such as the ability to operate from any heat source, quiet operation, and high theoretical efficiency. The Stirling engine has seen limited success due to poor heat transfer in the working chambers, difficulty sealing low-molecular weight gases at high pressure, and non-ideal piston displacement profiles. As a solution to these limitations, a liquid piston Stirling engine pump is proposed. The liquid pistons conform to irregular volumes, allowing increased heat transfer through geometry features on the interior of the working chambers. Creating near-isothermal operation eliminates the costly external heat exchangers and increases the engine efficiency through decreasing the engine dead space. The liquid pistons provide a positive gas seal and thermal transport to the working chambers. Controlling the flow of the liquid pistons with valves enables matching the ideal Stirling cycle and creates a direct hydraulic power supply. Using liquid hydrogen as a fuel source allows cooling the compression side of the engine before expanded the fuel into a gas and combusting it to heat the expansion side of the engine. Cooling the compression side not only increases the engine power, but also significantly increases the potential thermal efficiency of the engine. A high efficiency Stirling engine makes energy regeneration through reversing the Stirling cycle practical. When used for regeneration, the captured energy can be stored in thermal batteries, such as a molten salt. The liquid piston Stirling engine pump requires further research in numerous areas such as understanding the behavior of the liquid pistons, modeling and optimization of a full engine pump, and careful selection of materials for the extreme operating temperatures. Addressing these obtainable research quandaries will enable a transformative Stirling engine pump with the potential to excel in numerous applications.     

催化燃烧对均质压燃发动机燃烧特性影响的数值模拟

通过运用DETCHEM软件包,对甲烷在催化剂Rh表面的详细反应机理进行了分析,结果表明数值模拟结果与实验数据相当吻合;通过耦合DETCHEM软件包及CHEMKIN软件包中的SENKIN模块,对活塞顶涂有催化剂铑的均质压燃(HCCI)发动机的燃烧过程进行了数值计算,建立了单区和多区模型．利用单区模型分析了催化燃烧对HCCI发动机着火时刻的影响,同时讨论了催化燃烧对燃烧过程中主要化学组分浓度变化的影响,结果表明催化燃烧会使HCCI发动机着火时刻提前;利用多区模型分析了催化燃烧对HCCI发动机的未燃碳氢化合物(UHC)、氮氧化合物(NOx)排放的影响,结果表明催化燃烧能降低UHC的排放,但会提高NOx的排放．     

活塞头部形貌对汽油机爆震敏感性影响研究

基于台架试验和完整工作循环数值模拟,开展了汽油机活塞头部形貌特征对爆震的敏感性研究。以台架试验数据为基准校正了汽油机性能仿真模型,通过开展压缩比为9～16区间的外特性仿真模拟,得出压缩比为12时外特性最优。在压缩比为12的3 500r/min全负荷工况,采用化学反应动力学离子分析法,通过数值模拟分析3类基于活塞头部形貌方案的燃烧室,得出具有点火驻涡区域、气门避障区域、驻涡与避障区域之间的连通区域、后部连通区域的SABCD方案抗爆性最优,并指出活塞头部形貌特征中的连通区域对爆震敏感性具有显著影响。通过对方案SABCD的连通区域关键参数进行优化得出,当区域连通宽度和连通台阶高度均为4mm时爆震敏感性最低。研究结果表明,通过对活塞头部形貌特征的合理设计,能实现提升汽油机压缩比的同时有效抑制燃烧室对爆震的敏感性。     

高滚流Atkinson循环燃烧系统研究

为进一步提高发动机热效率,提出高滚流Atkinson循环燃烧系统概念。其特征是采用高滚流气道和活塞组合,配合Atkinson循环和废气再循环(EGR)技术,提高缸内的滚流和湍流水平,加快燃烧速度,同时降低汽油机爆震倾向。利用GT-Power和AVL FIRE软件针对某型汽油机进行了一维整机工作过程和三维计算流体动力学(CFD)模拟分析。结果表明:高滚流气道有利于促进缸内滚流运动,滚流比由原机的0.5提高到2.6;配合高滚流活塞后,使进气过程中产生的缸内初始滚流和压缩过程中的滚流维持作用都比原机有所增强,湍动能水平提升6.3%,瞬时放热率与原机相比平均提高15%;在此基础上,采用进气门晚关的方式实现Atkinson循环,并增加EGR系统,降低高压缩比带来的爆震倾向,比油耗在整个万有特性中均呈下降趋势,最低比油耗区明显变大,最低比油耗相比原机下降11.3g/(kW·h)。     

Optimal ratios of the piston speeds for a finite speed irreversible Carnot heat engine cycle

The performance of an irreversible Carnot heat engine cycle is analysed and optimized by using the theory of finite time thermodynamics based on Agrawal's [2009. A finite speed Curzon-Ahlborn engine. European Journal of Physics, 30 (3), 587–592] model of finite piston speed on the four branches and Petrescu et al.’s [2002b. Optimization of the irreversible Carnot cycle engine for maximum efficiency and maximum power through use of finite speed thermodynamic analysis. In: Proceedings of ECOS’2002, 3–5 July, Berlin, Germany, Vol. II, 1361–1368] model of a Carnot cycle engine with the finite rate of heat transfer, heat leakage from heat source to heat sink and irreversibilities caused by finite speed, friction and throttling through the valves. The finite piston speeds on the four branches are further assumed to be different, which is different from the model of constant speed of the piston on the four branches. Expressions of power output and thermal efficiency of the cycle are derived for a fixed cycle period and internal entropy generation rate. Numerical examples show that the curve of power output versus thermal efficiency is loop shaped, and there exist optimal finite piston speeds on the four branches which lead to the maximum power output and maximum thermal efficiency, respectively. The effects of the heat leakage coefficient and internal entropy generation rate on the optimal finite piston speed ratios are discussed.     

HCCI发动机多区燃烧模型的比较研究

多区模型作为现阶段均质压燃（HCCI）发动机高效准确的数值模型得到了世界范围的广泛关注。讨论了不同子模型对多区模型预测性能的影响。以实验为基准,比较了多区模型中区间划分、缸壁传热模型、区间热量交换模型、区间质量交换模型和边界层模型对HCCI发动机燃烧和排放模拟结果的影响,全部计算均基于异辛烷的详细化学动力学机理。结果表明：在区间划分时对温度较低的区域细化可以提高排放的计算效果,而对高温区域的细化对计算结果影响不大;改进的Woschni传热模型更准确地模拟了缸壁的传热过程;区间的质量和热量交换对计算结果影响显著,特别是质量交换模型的加入使CO排放的预测与实验值更为接近;而边界层厚度模型对整个结果影响不大。     

液压自由活塞发动机活塞运动规律自适应特性的研究

在一台液压自由活塞发动机(HFPE)样机上进行了活塞运动规率的试验。研究表明:活塞的运动规律对于燃烧相位和累积放热量的变动具有自适应性;随着燃烧相位的提前或累积放热量的增大,活塞换向提前,最大升程和压缩比降低;这种自适应性可有效避免均质压燃过程中的爆震与后燃现象,保证缸内最高压力、最大放热速率的稳定,减少指示功的损失。     

直喷式柴油机缸内热辐射多区(多维)模型的研究

以准维现象学多区喷雾燃烧模型和碳粒生成预测了模型为基础,建立了缸内空间辐射多区（多维）模型,并以Ｇ４１３５直喷式柴油机为研究对象,用蒙特卡洛（Ｍｏｎｔｅ－Ｃａｒｌｏ）法计算和分析了燃烧室壁面辐射热量的分布,结果表明,热流量分布规律和数值与柴油机缸内燃烧过程,有关试验结果相符。     

Effect of variable stroke on fuel combustion and heat release of a free piston linear hydrogen engine

Variable stroke (or compression ratio) has been expected as a potential technology for optimizing engine combustion all the time. The free piston motion of linear engines introduced by its unconstrained dynamics is well suited for this expectation. This paper introduces a numerical analysis to explore the effects of variable stroke operation on the combustion and heat release of a linear hydrogen engine (LHE). A system model which couples zero-dimensional dynamics, multi-dimensional combustion, and one-dimensional gas exchange is established and verified experimentally to predict the combustion of the LHE, and then a series of simulations are performed over a range of motion stroke from 62 mm to 72 mm in 2 mm interval to evaluate its effect on LHE combustion. Results indicates that short stroke operation of the LHE shows obvious advantages in thermal efficiency and high peak combustion pressure, although the completion level of hydrogen combustion is slightly poor. Fast combustion, large heat release, and low level of post-combustion effect can be obtained by neither lengthening nor shortening from the certain stroke length of 68 mm, while serious NO emission is indicated. Long-stroke operation makes the LHE clean, although it induces slow engine speed, low thermal efficiency and output power.     

活塞运动规律对点燃式HFPE燃烧过程影响的仿真研究

使用仿真软件Converge,建立了点燃式液压自由活塞发动机(HFPE)的三维仿真模型。为了解决HFPE的爆震问题,提升其热效率,研究了不同活塞运动规律对HFPE的燃烧过程、爆震倾向与热功转换效率的影响。结果表明:火花点燃式HFPE的爆震燃烧发生在活塞边缘的末端混合气区域,是由若干个爆震核快速扩展而成,与曲柄连杆式火花点燃发动机爆震的发生地点和机理相同;通过改变活塞的运动规律,使活塞上行速度加快,在上止点附近停留时间变短,可以明显减小发动机的爆震倾向与爆震强度。利用优化的活塞运动规律,加上高达14的高压缩比,可以在一定程度上提升发动机的热功指示效率。     

Study of the steady and transient temperature field and heat flow in the combustion chamber components of a medium speed diesel engine using finite element analyses

The present work describes the development of a model for the calculation of the temperature field and heat flow in the combustion chamber components of internal combustion piston engines, which occur both under steady and transient engine operating conditions. Two and three-dimensional finite-element analyses were implemented for the representation of the complex geometry metal components (piston, liner and cylinder head). The model is applied for the piston and liner of a medium speed diesel engine, for which relevant experimental data exist in the literature. Special care is given for accurately specifying the thermal boundary conditions (temperatures and heat transfer coefficients). Gas side boundary conditions are calculated using a thermodynamic cycle simulation code, including spatial variation of the gas side heat transfer coefficient. Coolant sides (water on the external liner surface and oil on the piston undercrown surface) boundary conditions are calculated using correlations pertaining to real engine conditions. Also an effort is made to model the piston-ring belt-liner complex thermal paths using equivalent thermal circuits. A satisfactory degree of agreement is found between theoretical predictions and experimental measurements, revealing that the finite-element methods presented are successful in formulating this kind of problem, giving accurate results with reasonable computational cost. The utilization of the model reveals very clearly the essential role of engine operating transients (sudden changes in speed and/or load) in the generation of sharp temperature excursions in the metal components until a new steady state is reached. The phenomenon should be taken into account for correct engine design and safe operation (i.e. the avoidance of high local stresses).     

基于传热系数反求法的船用柴油机组合活塞热分析

建立了柴油机组合活塞的2D有限元模型,并利用传热系数反求法对该模型进行热分析。在仿真分析中,将活塞头部外表面传热系数定义为设计参数,实测温度与仿真温度的差值定义为目标函数。通过仿真计算得到了活塞头部外表面传热系数的分布,并利用反求法得到的传热系数对有限元模型进行热分析,仿真结果与实测温度吻合;传热系数反求法收敛迅速,可以有效用于活塞及其他内燃机零部件的温度分布和热负荷分析。     

双对置二冲程柴油机性能分析方法探讨

双对置二冲程发动机内外连杆的特殊结构决定了内外活塞的运动规律不同于传统发动机。基于等容积变化率原理,并对比传统结构形式发动机性能分析方法,探讨BOOST软件用于双对置二冲程发动机性能分析的方法及其可行性。研究表明:该方法可行;由于双对置二冲程发动机活塞运动规律的差异,使得P-V图更趋于丰满,有利于提高热效率,但同时最高燃烧温度随之升高,热负荷增加。     

Thermodynamic Analysis and Comparison of Performances of Air Standard Atkinson,Otto, and Diesel Cycles with Heat Transfer Considerations

This paper focuses on the overall performances of Otto, Atkinson, and Diesel air standard cycles. This study compares performance of these cycles with regard to parameters such as variable specific heat ratio, heat transfer loss, frictional loss, and internal irreversibility based on finite‐time thermodynamics. The relationship between thermal efficiency and compression ratio, and between power output and compression ratio of these cycles are obtained by numerical examples. In this study, it is assumed that during the combustion process, the heat transfer occurs only through the cylinder wall. The heat transfer is affected by the average temperature of both the cylinder wall and the working fluid. The results show that for each cycle, with the increase of the compression ratio in the specific mean piston speed, power output and thermal efficiency first increase and after reaching their maximum value, start to decrease. The results also indicate that maximum power output and maximum thermal efficiency of an Atkinson cycle could be higher than the values of these parameters in Diesel cycle and Otto cycle in the same operating conditions. The maximum power output and the maximum thermal efficiency of the Otto cycle have the lowest value among studied cycles. By increasing the mean piston speed, power output and thermal efficiency of Atkinson, Diesel, and Otto cycles start to decrease. The results of this study provide guidance for the performance analysis and show the improvement areas of practical Otto, Atkinson, and Diesel engines.     

Numerical study of heat transfer of hydrogen combustion in noble gases atmosphere in compression ignition engine

The high energy content of hydrogen and zero carbon emission from hydrogen combustion is very important for compression ignition engine development. Hydrogen requires a very high auto-ignition temperature, which encourages replacing nitrogen with noble gases with higher specific heat ratio during compression process. In noble gases-hydrogen combustion, higher combustion temperature potentially leading to a higher heat loss. This paper aims to investigate the effect of hydrogen combustion in various noble gases on heat distribution and heat transfer on the cylinder wall. Converge CFD software was used to simulate a Yanmar NF19SK direct injection compression ignition engine. The local heat flux was measured at different locations of cylinder wall and piston head. The heat transfer of hydrogen combustion in various noble gases at different intake temperatures was studied using the numerical approach. As a result, hydrogen combustion in light noble gases such as helium produces faster combustion progress and higher heat temperature. The hydrogen combustion that experienced detonation, which happened in neon at 340 K and argon at 380 K, recorded a very high local heat flux at the cylinder head and piston due to the rapid combustion, which should be avoided in the engine operation. At a higher intake temperature, the rate of heat transfer on the cylinder wall is increased. In conclusion, helium was found as the best working gas for controlling combustion and heat transfer. Overall, the heat transfer data gained in this paper can be used to construct the future engine hydrogen in noble gases.     

Performance of a single nutating disk engine in the 2 to 500 kW power range

A new type of internal combustion engine with distinct advantages over conventional piston-engines and gas turbines in small power ranges is presented. The engine has analogies with piston engine operation, but like gas turbines it has dedicated spaces and devices for compression, burning and expansion. The engine operates on a modified limited-pressure thermodynamic cycle. The core of the engine is a nutating non-rotating disk, with the center of its hub mounted in the middle of a Z-shaped shaft. The two ends of the shaft rotate, while the disk nutates. The motion of the disk circumference prescribes a portion of a sphere. In the single-disk configuration a portion of the surface area of the disk is used for intake and compression, a portion is used to seal against a center casing, and the remaining portion is used for expansion and exhaust. The compressed air is admitted to an external accumulator, and then into an external combustion chamber before it is admitted to the power side of the disk. The external combustion chamber enables the engine to operate on a variable compression ratio cycle. Variations in cycle temperature ratio and compression ratio during normal operation enable the engine to effectively become a variable-cycle engine, allowing significant flexibility for optimizing efficiency or power output. The thermal efficiency is similar to that of medium sized diesel engines. For the same engine volume and weight this engine produces approximately twice the power of a two-stroke engine and four times the power of a four-stroke engine. The computed sea-level engine performance at design and off-design conditions in the 2 to 500 kW power range is presented.     

Modeling HCCI combustion: Modification of a multi-zone model and comparison to experimental results at varying boost pressure

The present study presents a comparison of the results obtained from a modified HCCI multi-zone model to experimental measurements, at different load and boost pressure conditions. The multi-zone model includes a modified sub-model for the wall heat transfer and accounts for the heat transfer between zones. Gas mixing between cold and hot regions of the combustion chamber, which is of major importance for the emissions formation, is also accounted for throughout compression, combustion and expansion. Combustion is modeled using a reduced set of chemical reactions coupled with a chemical kinetics solver. A refined zone configuration near the combustion chamber wall was used, in order to obtain a high resolution at the emissions formation regions. The pressure traces and emissions of nine experimental cases were compared to the multi-zone model results. In these cases the equivalence ratio and the boost pressure were varied, while maintaining constant engine speed. The results show adequate agreement with the pressure traces. The emissions trends are also adequately captured, with the absolute values presenting some deviation from the experimental cases especially for the HC and CO emissions at the relatively low air-fuel equivalence ratios.