氢燃料发动机性能参数的研究

针对氢作为发动机燃料的优越性以及氢燃料发动机的特点、技术发展趋势进行了简要概括,并在此基础上,结合实验研究,对压缩比、当量比、过量空气系数对氢燃料发动机性能的影响进行了分析研究.     

EGR和过量空气系数协同控制改善甲醇发动机部分负荷性能

通过一台柴油机改装的高压缩比(17.5)进气道喷射点燃式甲醇发动机,研究了废气再循环(EGR)和过量空气系数协同控制对甲醇发动机部分负荷经济性和排放性能的影响.结果表明:负荷越小,协同调节范围越宽,节油潜能越大,在1,400,r/min、50%,负荷时,甲醇消耗率降低幅值最大可达13.1%,,25%,负荷时甲醇消耗率最大可降低26.6%,;EGR率小于20%,或过量空气系数小于1.4时,协同控制对缸压峰值的影响较明显;当过量空气系数大于1.4后,甲醇发动机燃烧持续期急剧增加,循环变动迅速变大;与无外部EGR、过量空气系数为1相比较,合理利用EGR和过量空气系数协同控制,可以保证HC、CO排放值增幅不大且能有效降低NOx,甚至实现NOx的"零"排放.     

过量空气系数对HCCI汽油机燃烧特性的影响

在一台Ricardo Hydra单缸四气门汽油机上,利用气门重叠负角方法实现了均质充量压缩着火(HCCI)燃烧,并通过试验研究了过量空气系数对HCCI汽油机燃烧特性的影响.研究结果表明,在相同的转速和气门相位角下,随着过量空气系数的增加,平均指示压力减小,缸内残余废气率也减小,但燃油消耗率的变化趋势与转速有关.在大多数工况下,过量空气系数为1.05时,HCCI发动机的着火时刻最早,燃烧持续期最短.过量空气系数对循环波动的影响与转速和气门相位角有关.随着转速的增加,循环波动增大.     

火花点火发动机燃用天然气掺氢混合燃料循环变动研究

在火花点火天然气发动机上开展了不同掺氢比天然气掺氢混合燃料(氢气在混合燃料中的体积分数为0%、12%、23%、30%和40%)循环变动的试验研究,试验工况点对应于发动机中低负荷.分析了掺混氢气对天然气发动机循环变动的影响.研究结果表明:在稀燃条件下,随着掺氧比的增加,缸内最高压力、最大压力升高率以及平均指示压力均增加.随着掺氢比增加,缸内最高压力与其对应的曲轴转角之间和最大压力升高率与其对应的曲轴转角之间的相关性更强.在化学计量比或浓燃时,掺混氢气可以维持平均指示压力的循环变动系数在较低的水平.在稀燃时,平均指示压力的循环变动系数随掺氢比增加而降低.平均指示压力的循环变动系数达到10%所对应的过量空气系数随掺氢比增加而增加,表明天然气掺混氢气扩展了天然气发动机的稳定稀燃极限.     

汽油机燃用乙醇／汽油混合燃料的研究进展

总结了目前在汽油机上已经开展的有关乙醇/汽油混合燃料的试验研究,主要包括:燃用乙醇/汽油混合燃料对发动机的动力性、燃油经济性和排放性能的影响;催化转化器、过量空气系数(φat)以及压缩比和点火时刻对燃用乙醇/汽油混合燃料时发动机的燃烧和排放特性的影响.最后对其发展和研究方向做出展望.     

乙醇混氢发动机怠速性能的试验

利用进气混氢来改善乙醇发动机的怠速性能.试验在加装了电控氢气喷射系统的4缸点燃式内燃机上进行,在怠速条件下,逐渐增加氢气的喷射脉宽,研究混氢对乙醇发动机怠速性能的影响.在各种混氢分数下,减小乙醇喷射脉宽,使混氢前后的混合气始终保持在理论过量空气系数附近.结果表明,随混氢分数的增加,发动机热效率提高,燃料燃烧速度加快,循环变动降低,混氢后发动机HC排放降低但NOx略有升高,CO随混氢分数的增加先降低而后又有所升高.进气混氢有利于降低乙醇发动机的乙醛排放,当混氢能量分数由0%提高至13.84%时,乙醛排放降低约37.4%.     

过量空气系数对柴油机低速烟度的影响研究

为了研究发动机在低速时,过量空气系数与烟度的关系,选择了1 000,1 200,1 400 r/min三个转速,调整三个转速下外特性点的过量空气系数,测试不同过量空气系数时的发动机性能和烟度,根据烟度和性能的需求去确认各转速下合理的过量空气系数值,这对于发动机性能开发试验具有一定的指导意义。     

低压缸内直喷CNG发动机燃烧特性的影响因素

自主研发了低压缸内直喷压缩天燃气(CNG)发动机,研究了过量空气系数、喷气时刻、点火能量、点火时刻等 对发动机燃烧特性的影响.结果表明,喷气时刻对低压缸内直喷CNG发动机的燃烧性能有很大影响,对于给定的工况,发动机存在一个最佳喷气提前角;提高点火能量有助于改善CNG发动机的燃烧过程,增大点火提前角,可以在一定程度上弥补由于天然气燃料火焰传播速度慢所导致的热效率下降,从而改善发动机缸内的燃烧过程,使其功率增加,燃气消耗率降低.     

电控顺序喷射CNG发动机过量空气系数研究

分析了影响电控顺序喷射压缩天然气（CNG）发动机最佳过量空气系数（Фat）的主要因素。建立了CNG发动机试验台架，进行了过量空气系数对发动机经济性、动力性和排放性影响的试验。试验结果表明：过量空气系数对于CNG发动机经济性的影响非常明显，经济性最好时的过量空气系数大于NOx排放量最大时对应的过量空气系数，HC排放随着过量空气系数增大而增大，CO排放在过量空气系数为1．2到1．4之间时急剧下降，排气温度随过量空气系数增大而下降。该发动机的过量空气系数在1．5左右时其综合排放性能和经济性最佳。     

小型发动机燃用汽油、乙醇和LPG燃料的排放对比

对125mL发动机燃用汽油、乙醇和液化石油气(LPG)时的过量空气系数和点火提前角与排放性能之间的关系进行了试验研究．指出了影响这三种燃料发动机排放性能的敏感参数的合理取值范围．通过对比试验，验证了发动机燃烧乙醇可降低NOx排放浓度．发动机燃烧LPG时，低HC排放的空燃比范围比其它两种发动机空燃比范围广．研究结果可为小型汽油、乙醇和LPG发动机参数匹配提供参考。     

基于神经网络的柴油机性能建模

提出了正交试验法与神经网络相结合，建立柴油机动力性、经济性及排放特性与柴油机运转参数间神经网络模型的方法，研究了转速、供油量、VGT开度和过量空气系数变化对柴油机性能的影响，用复相关系数检验模型的泛化能力，确定模型的权值矩阵。研究表明该方法可行并可较好地预测柴油机的性能。     

含水乙醇在内燃机的应用研究

在摩托车发动机和车用柴油机上进行了含水乙醇的使用研究，当含水乙醇用于汽油机时，它是直接与汽油混合后使用而未对发动机进行任何改造；而当含水乙醇用于柴油机时则在柴油机的进气系统上安装含水乙醇的喷射系统，含水乙醇喷入进气歧管后蒸发并与进入的空气混合，然后在进气过程中进入气缸。试验结果显示，发动机的动力性都没有受到影响，燃料的能耗率都有所降低，柴油进气预混含水乙醇可大量降低其炭烟排放但导致HC和CO排放的增加；含水乙醇与汽油混合燃烧可降低其CO排放而可能导致NOx排放的增加。综合比较的结果，汽油机中应用含水乙醇比在柴油机中有更大的优势。     

带有可变喷嘴涡轮增压系统的天然气发动机试验研究

在CA4G22E发动机的基础上开发出了一台多点顺序喷射的天然气发动机。该发动机采用了增压中冷技术及可变喷嘴涡轮增压技术。试验结果表明，采用增压中冷技术争可变喷嘴涡轮技术可以提高发动机的进气量，优化发动机在全工况范围内与增压器的匹配，大幅度提高发动机的动力性与经济性。     

Experimental study of a single-cylinder engine fueled with natural gas–hydrogen mixtures

The objective of this study is to evaluate the power, efficiency and emissions of an electronic-controlled single-cylinder engine fueled with pure natural gas and natural gas–hydrogen blends, respectively. Replacing the nature gas with hydrogen/methane blend fuels was found to have a significant influence on engine performance. The effects of excess air ratio and spark timing were discussed. The results show that under certain engine conditions the maximum cylinder gas pressure, maximum heat release rate increased with the increase of hydrogen fraction. The increase of hydrogen fraction in the blends contributed to the increase of NO_x and the decrease of HC and CO. The brake specific fuel consumption decreased with the increase of hydrogen fraction. Using HCNG at relatively leaner fuel–air mixtures and retarded spark timing totally improved the engine emissions without incurring the performance penalty.     

The effect of engine speed and cylinder-to-cylinder variations on backfire in a hydrogen-fueled internal combustion engine

The port-injection-type hydrogen engine is advantaged in that hydrogen gas is injected into the intake pipe through a low-pressure fuel injector, and the mixing period with air is sufficient to produce uniform mixing, improving the thermal efficiency. A drawback is that the flame backfires in the intake manifold, reducing the engine output because the amount of intake air is reduced, owing to the large volume of hydrogen. Here, the backfire mechanism as a part of the development of full-load output capability is investigated, and a 2.4-liter reciprocating gasoline engine is modified to a hydrogen engine with a hydrogen supply system. To secure the stability and output performance of the hydrogen engine, the excess air ratio was controlled with a universal engine control unit.The torque, excess air ratio, hydrogen fuel, and intake air flow rate changes in time were compared under low- and high-engine speed conditions with a wide-open throttle. The excess air ratio depends on the change in the fuel amount when the throttle is completely opened, and excess air ratio increase leads to fuel/air-mixture dilution by the surplus air in the cylinder. As the engine speed increases, the maximum torque decreases because the excess air ratio continues to increase due to the occurrence of the backfire. The exhaust gas temperature also increases, except at an engine speed of 6000 rpm. Furthermore, the increase in exhaust gas temperature affects the backfire occurrence. At 2000 rpm, under low-speed and wide-open throttle conditions, backfire first occurs in the No. 4 cylinder because the mixture is heated by the relatively high port temperature. In contrast, at 6000 rpm, under high-speed and wide-open throttle conditions, the backfire starts at the No. 2 cylinder first because of a higher exhaust gas temperature, resulting in a lower excess air ratio in cylinders 2 and 3, located at the center of the engine.     

Emission and engine performance analysis of a diesel engine using hydrogen enriched pomegranate seed oil biodiesel

The aim of this study is to determine the availability of pomegranate seed oil biodiesel (POB) as an alternative fuel in diesel engines and evaluate engine performance and emission characteristics of pure hydrogen enriched POB using diesel engine. For this purpose, the intake manifold of the test engine was modified and hydrogen enriched intake air was supplied throughout the experiments. Physical properties of POB and its blend with diesel fuel were also determined. The results showed that measured physical properties of POB are comparable with diesel fuel. According to engine performance experiments, although POB utilization has slight undesirable effects on some engine performance parameters such as brake power output and specific fuel consumption, it can be used as alternative fuel in diesel engines, by this way CO emission can be improved. Finally, hydrogen enrichment experiments indicated that pure hydrogen addition causes a slight improvement in both engine performance and exhaust emissions.     

不同排量小型四冲程通用汽油机的排放控制策略

过量空气系数是影响小型通用汽油机动力、经济、排放性能和运转稳定性的关键因素之一.从排放性能出发,不同排量的小型四冲程汽油机对过量空气系数的要求是不一样的.以排放控制为重点,并且能兼顾其他性能的过量空气系数与小型四冲程通用汽油机的优化匹配是本文研究的重点.通过试验研究和理论分析,探讨不同排量的小型四冲程通用汽油机的排放控制策略.     

有叶普通涡轮增压器与发动机稳态匹配模型的建立、验证与模拟

建立了在稳态工况下有叶普通涡轮增压器和发动机匹配的数学模型，讨论了建模中的几个关键问题。在此基础上，利用Simulink建立了有叶固定截面涡轮增压器与发动机匹配的模拟模型，并通过发动机与涡轮增压器的匹配试验对模拟模型进行了验证，结果表明模型是正确的，并互具有较高的准确性。最后，通过模拟给出了不同发动机工况下的增压压比、过量空气系数、涡轮膨胀比、增压器转速等变化情况，得出了一些有关涡轮增压器与发动机匹配的结论。     

天然气成分对发动机性能及排放影响的试验研究

在同一台发动机上通过燃用属于同类别的两地天然气的对比试验，研究了天然气（CNG）成分对发动机性能及排放的影响。试验结果表明：天然气成分的差异导致发动机的空燃比发生变化，是造成发动机性能与排放产生较大变化的主要原因，而控制发动机空燃比在较小范围变化，可以减少天然气成分对发动机性能及排放的影响。     

Generating efficiency and emissions of a spark-ignition gas engine generator fuelled with biogas–hydrogen blends

We investigated the generating efficiency and pollutant emissions of a four-stroke spark-ignition gas engine generator operating on biogas–hydrogen blends of varying excess air ratios and hydrogen concentrations. Experiments were carried out at a constant engine speed of 1200 rpm and a constant electric power output of 10 kW. The experimental results showed that the peak values of generating efficiency, maximum cylinder pressure, and NO_x emissions were elevated at an excess air ratio of around 1.2 as the hydrogen concentration was increased. CO₂ emissions decreased as the excess air ratio and hydrogen concentration increased, due to lean-burn conditions and hydrogen combustion. An efficiency per NO_x emissions ratio (EPN) was defined to consider the relationship between the generating efficiency and NO_x emissions. A maximum EPN value of 0.7502 was obtained with a hydrogen concentration of 15%, for an excess air ratio of 2.0. At this EPN value, the NO_x and CO₂ emissions were 39 ppm and 1678.32 g/kWh, respectively, and the generating efficiency was 29.26%. These results demonstrated that the addition of hydrogen to biogas enabled the effective generation of electricity using a gas engine generator through lean-burn combustion.