火花点火天然气发动机工作过程的数值模拟

近年来,由于能源和环保的要求,火花点火天然气发动机以高效、低污染燃烧的优点正在迅速发展。为了分析和研究这种发动机的运行特性,预测多种参数变化对性能的影响,将零维模型应用于气体燃料发动机燃烧过程中。试验表明,模型的计算值和试验值具有很好的一致性。模拟计算弥补了实验测试中的不足,可以从更深层次地认识气体燃料发动机的运行特性和规律。     

氢-汽油双燃料发动机性能试验研究

介绍一种氢—汽油双燃料发动机，这种双燃料发动机装有余热制氢装置，可用甲醇制取氢并燃用氢与汽油混合燃料。作者对余热制氢装置及氢—汽油双燃料发动机的各项性能进行试验研究。试验结果表明，装有余热制氢装置的氢—汽油双燃料发动机功率和扭矩有所提高，外特性和负荷特性燃油消耗率下降5．3％一7．5％；怠速排放中CO和HC均有所减少。     

AVL BOOST软件在生物质气体发动机性能计算上的应用

AVL BOOST软件是进行发动机循环和进排气系统计算，建立发动机模型的专用程序，一般用于汽油、柴油等液体燃料和天然气、氢等睢组分气体燃料发动机的性能计算。文章将该程序用于多组分低热值生物质燃气发动机，建立数学模型，进行了发动机性能计算，并与试验数据进行对比。结果表明，模拟值与试验值能较好吻合，从而验证了该工作模型的正确性，验证了AVL BOOST软件运用于生物质气体发动机整机和零部件的优化设计的可行性。     

氢燃料发动机燃烧过程模拟与分析

在分析氢作为内燃机燃料特性的基础上,针对氢气与空气的混合与燃烧过程的空间分布特性比汽油均匀的特点,提出并建立了单区模型对氢燃料发动机燃烧过程进行模拟与分析.结果显示,缸内压力与放热率的计算值与试验值相对误差在3%以内,曲线形态吻合度较高.较好地反映出实际的燃烧情况.表明采用单区模型进行氢燃料发动机燃烧过程的模拟与分析能够保证较高的准确性,进一步分析了点火提前角、当量比对燃烧过程的影响,结果表明它们对燃烧过程有较大影响.因此,控制点火提前角、当量比是调整与改善氢发动机性能的重要手段.     

基于径向基函数网络的氢发动机性能建模

建立了氢发动机动力性、经济性及排放特性与发动机运转参数间的径向基函数网络模型,通过对建立的径向基函数网络进行训练和测试,模型能准确地预测氢发动机的输出特性,计算与试验结果的对比研究表明,最大相对误差小于2.8%。     

点火提前角对氢发动机性能的影响及智能控制技术

进行了进气管喷射的氢发动机点火提前角对发动机性能影响的研究，试验指出了点火提前角对氢发动机动力性，经济性和排放性能有较大影响。建立了模糊神经网络控制系统对点火提前角进行优化控制，建立了一个改进的模糊神经网络系统代替传统的试验方法来求解氢发动机的最佳点火提前角(MAP)。仿真和试验结果的对比研究给出该方法具有较高的运行精度。     

氢燃料发动机的应用

叙述了氢燃料发动机的特点，结构和工作原理，以及氢燃料的储存及燃烧特性。给出了一些氢燃料发动机的排放试验数据，并与使用其它燃料时进行了比较。主要从发动机的新能源和排放污染等方面，探讨推广氢燃料发动机的必要性及其应用可行性。     

基于AVL_BOOST的氢发动机燃烧特性和性能分析

基于AVL发动机专用数值模拟软件BOOST,建立了单缸直喷氢发动机模型.模拟结果和实验结果的对比表明,所建BOOST模型具有较高的可信度.通过改变发动机的主要结构参数和运转参数,研究氢发动机的燃烧特性以及它们对氢发动机动力性和经济性的影响.     

车用发动机燃用天然气掺氢燃料的性能计算分析与研究

为了研究天然气掺氢发动机的燃烧特性,从模拟试验的角度运用大型发动机软件建立了6缸火花点火天然气掺氢发动机的虚拟样机,并经过试验验证该模型基本准确.通过仿真计算得出,天然气发动机在掺入氢气之后,提高了燃烧速度,明显拓宽了发动机的稀燃极限.在掺入氢气30 %(体积百分比)时,发动机的综合性能指标较好;提高压缩比,指示热效率得到提高.     

氢发动机排气污染及NOx排放优化控制

研究了在汽油中加入氢气后混合燃料发动机的排放特性,给出了氢汽油混合燃料可以全面改善汽油机的废气排放,然后进行了高压喷射型氢发动机的两个主要运转参数(点火提前角和喷氢提前角)对NOx排放影响的研究。试验表明点火提前角、喷氢提前角对NOx排放量有很大影响。在建立以点火提前角、喷氢提前角、喷氢量为控制变量,以动力性或经济性为性能指标泛函,且排放不超标等为约束条件的氢发动机最优控制模型的基础上,提出了分别以径向基(RBF)网络、模糊神经网络(FNN)求解最优控制模型的新方法,进行了仿真计算和试验数据的对比研究。研究结果给出了两种网络均可以成功取代传统MAP而满足要求。其中以模糊神经网络所用时间较短。     

Influence of operating parameters on performance and emissions for a compression-ignition engine fueled by hydrogen/diesel mixtures

Hydrocarbon exhaust emissions are mainly recognized as a consequent of carbon-based fuel combustion in compression ignition (CI) engines. Alternative fuels can be coupled with hydrocarbon fuels to control the pollutant emissions and improve the engine performance. In this study, different parameters that influence the engine performance and emissions are illustrated with more details. This numerical work was carried out on a dual-fuel CI engine to study its performance and emission characteristics at different hydrogen energy ratios. The simulation model was run with diesel as injected fuel and hydrogen, along with air, as inducted fuel. Three-dimensional CFD software for numerical simulations was implemented to simulate the direct-injection CI engine. A reduced-reaction mechanism for n-heptane was considered in this work instead of diesel. The Hiroyasu-Nagel model was presented to examine the rate of soot formation inside the cylinder. This work investigates the effect of hydrogen variation on output efficiency, ignition delay, and emissions. More hydrogen present inside the engine cylinder led to lower soot emissions, higher thermal efficiency, and higher NO_x emissions. Ignition timing delayed as the hydrogen rate increased, due to a delay in OH radical formation. Strategies such as an exhaust gas recirculation (EGR) method and diesel injection timing were considered as well, due to their potential effects on the engine outputs. The relationship among the engine outputs and the operation conditions were also considered.     

Hydrogen as an additive to methane for spark ignition engine applications

The performance of a gas fuelled spark ignition engine is enhanced when relatively small amounts of hydrogen are present with methane. This improvement in performance, which is especially pronounced at operational equivalence ratios that are much leaner than the stoichiometric value, can be attributed largely to the faster and cleaner burning characteristics of hydrogen in comparison to methane. Through analytical simulation of engine performance, the addition of hydrogen is considered through its production in situ on board the engine by electrolysis of water with the necessary energy supplied from engine power. It is shown that when the work energy required for the production of hydrogen by electrolysis is taken into account, the range of viable operation of such an engine is very narrow. This would render the whole concept of in situ hydrogen production through water electrolysis uneconomical in conjunction with engine operation, even though the presence of additional oxygen produced with the hydrogen tends, in principle, to improve engine performance beyond that observed with hydrogen addition. © 1999 International Association for Hydrogen Energy.     

1D thermo-fluid dynamic modelling of an S.I. single-cylinder H2 engine with cryogenic port injection

This paper describes the numerical and experimental research work carried out on a single-cylinder spark-ignition research engine with cryogenic port injection of gaseous hydrogen. A 1D thermo-fluid dynamic simulation code for the simulation of a hydrogen fuelled S.I. engine has been developed; in particular, a quasi-D multi-zone combustion model has been enhanced to predict the burning rate of a homogeneous mixture of hydrogen and air, on the basis of an extended database for laminar burning velocities. Moreover, a 1D simulation of the unsteady flows in the whole intake and exhaust systems coupled to the engine has been addressed, considering the transport of chemical species to account for the port injection of hydrogen at very low temperature (cryogenic conditions). The working fluid is treated as a mixture of ideal gases, including para-hydrogen, with specific heats depending on the gas temperature and the mole fractions. A validation of the simulation model is shown in the paper, comparing the computed results with the experimental data of in-cylinder pressures, cylinder NO emissions and intake and exhaust instantaneous pressure pulses at different locations, for naturally aspirated engine conditions.     

Performance and combustion characteristic of CI engine fueled with hydrogen enriched diesel

The combustion of hydrogen–diesel blend fuel was investigated under simulated direct injection (DI) diesel engine conditions. The investigation presented in this paper concerns numerical analysis of neat diesel combustion mode and hydrogen enriched diesel combustion in a compression ignition (CI) engine. The parameters varied in this simulation included: H₂/diesel blend fuel ratio, engine speed, and air/fuel ratio. The study on the simultaneous combustion of hydrogen and diesel fuel was conducted with various hydrogen doses in the range from 0.05% to 50% (by volume) for different engine speed from 1000 – 4000 rpm and air/fuel ratios (A/F) varies from 10 – 80. The results show that, applying hydrogen as an extra fuel, which can be added to diesel fuel in the (CI) engine results in improved engine performance and reduce emissions compared to the case of neat diesel operation because this measure approaches the combustion process to constant volume. Moreover, small amounts of hydrogen when added to a diesel engine shorten the diesel ignition lag and, in this way, decrease the rate of pressure rise which provides better conditions for soft run of the engine. Comparative results are given for various hydrogen/diesel ratio, engine speeds and loads for conventional Diesel and dual fuel operation, revealing the effect of dual fuel combustion on engine performance and exhaust emissions.     

Study on the extension of lean operation limit through hydrogen enrichment in a natural gas spark-ignition engine

An experimental study aimed at investigating the extension of lean operation limit through hydrogen addition in a SI engine was conducted on a six-cylinder throttle body injection natural gas engine. Four levels of hydrogen enhancement were used for comparison purposes: 0%, 10%, 30% and 50% by volume. The effects of various engine operating conditions on engine's lean burn capability were also examined. Test results were then analyzed from a combustion point of view. The results show that engine's lean operation limit could be extended through adding hydrogen and increasing load level (intake manifold pressure). Effect of engine speed on lean operation limit is smaller. At low load level increase in engine speed is beneficial to extending lean operation limit but this is not true at high load level. The effects of engine speed are even weaker when the engine is switched to hydrogen enriched fuelling. Spark timing also influences on lean operation limit and both over-retarded and over-advanced spark timing are not advisable. It is also observed there existed a limiting value imposed on spark-90% MFB burn duration if lean operation limit is not to be exceeded and interestingly, this limiting value was independent on hydrogen enhancement level and engine operating conditions examined in this study.     

Investigations of the discharging of metal hydride beds for hydrogen-gasoline mixture operation of SI-engines

A mathematical simulation model is presented describing the discharge process of metal hydrides. The model is applied to FeTi-single tube and multiple tube beds and the results are compared directly to the results of experimental investigations. Furthermore, the most important engine parameters, with respect to the operation with metal hydride stored hydrogen, were determined for the nonsteady FTP 72-driving cycle. Minimum hydride quantities, necessary to supply the engine with hydrogen during the warm-up phase, were calculated for different starting temperatures and initial hydrogen contents of the bed.     

Effect of hydrogen addition on RCCI combustion of a heavy duty diesel engine fueled with landfill gas and diesel oil

The aim of this study is to investigate the effects of hydrogen addition on RCCI combustion of an engine running on landfill gas and diesel oil. A single cylinder heavy– duty diesel engine is set in operation at 9.4 bar IMEP. A certain amount of diesel fuel per cycle is fed into the engine and hydrogen is added to landfill gas while keeping fixed fuel energy content. The developed simulation results confirm that hydrogen addition which is the most environmental friendly fuel causes the fuel consumption per any cycle to reduce. Also, the peak pressure is increased while the engine load is reduced up to 4%. Landfill gas which is enriched with hydrogen improves the rate of methane dissociation and reduces the combustion duration at the same time the engine operation would not be exposed to diesel knock. Moreover, hydrogen addition to landfill gas would reduce engine emissions considerably.     

VNT可变涡轮增压器与柴油机的匹配研究

根据一款WG增压柴油机原机的基本结构参数和试验数据,匹配一款VNT废气涡轮增压器,建立VNT增压柴油机的GT-Power一维计算模型,并对柴油机外特性工况和ESC工况进行仿真计算研究。分别以动力性和经济性参数为分析指标,对外特性工况和ESC工况的VNT开度进行优化选择。研究表明,开度优化选择后的VNT柴油机与柴油机原机相比,外特性转矩均有较大幅度提高,最大转矩工况的运行范围拓宽,且VNT增压器的转速在整个转速范围内提高,联合运行曲线的高效率范围扩展;ESC工况加权比油耗值下降幅度约为3.8%,且空燃比增大,VNT柴油机经济性获得提升。可以得出结论,VNT可变涡轮增压器与柴油机匹配良好。     

基于Matlab/Simulink的车用增压柴油机建模与仿真

介绍利用数值仿真研究车用增压柴油机瞬态特性的意义，从柴油机的试验数据出发，在平均值模型的基础上，建立车用增压柴油机的动态模型，详细描述了涡轮增压器、柴油机及车用负载模型，并在Matlab／Simulink环境下给出了仿真模型结构框图和在两种瞬态工况下的仿真结果。