柴油、天然气双燃料发动机的燃烧特性分析

研究了柴油,天然气双燃料发动机的燃烧特性,并着重分析了引燃柴油供给系统参数对双燃料发支持性的影响。以试验为基础,首先简要比较了柴油,天然气双燃料发动机与柴油机的燃烧特性,并对比了负荷对双燃料发动机燃烧特性的影响。然后分析了最小循环喷油量,引燃柴油量,引燃油喷射压力,喷嘴参数及供油提前角等引燃柴油供给系统参数对最高爆发压力,燃烧放热率,着火开始时间、累积燃烧放热率等柴油,天然气双燃料发动机燃烧特性的     

柴油/天然气双燃料发动机柴油燃烧策略的研究

基于自主研发的第三代并行式柴油/天然气双燃料发动机电控系统,利用FIRE软件建立柴油/天然气双燃料发动机柴油喷射系统的多次喷射模型。同时,通过进气压力控制过量空气系数,实现柴油/天然气双燃料发动机稀薄燃烧方式。针对高负荷工况,研究了多次喷射策略和稀薄燃烧方式对双燃料发动机最大压力升高率及NOx排放的影响。结果表明:发动机工作在高负荷及柴油替代率为80%时,采用双燃料稀薄燃烧方式能使NOx排放降低,但最大压力升高率仍可能超过安全临界值1MPa/(°)。采用合适的预喷射量与预喷射时刻能降低最大压力升高率。通过多次喷射和稀薄燃烧方式相结合的燃烧策略对缸内燃烧方式进行组织,可以实现双燃料发动机高替代率燃烧,并使高负荷时NOx排放达到或者低于国Ⅴ标准限值。     

船用直喷式天然气发动机喷射策略的优化

利用CONVERGE软件基于L23/30DF型船用天然气发动机建立了双天然气喷嘴、双引燃柴油喷嘴的直喷天然气发动机的缸内燃烧过程的CFD计算模型,计算了不同的柴油和天然气喷射时刻和间隔下发动机缸内燃烧和排放过程。结果表明:引燃柴油的喷射时刻及其与天然气喷射时刻的间隔,对直喷式天然气发动机燃烧和排放性能有重要影响。当喷射时刻为-25℃A时,发动机具有较高的缸内爆发压力和良好的排放性能。在引燃柴油和天然气喷射间隔为16℃A时,可获得最高的缸内爆发压力,此时soot排放降低了22%。     

柴油/天然气双燃料发动机数值优化

利用CONVERGE搭建了柴油/天然气双燃料发动机三维数值模拟平台,在大负荷工况下研究了压缩比和不同喷油策略对发动机燃烧性能的影响.研究结果表明,相同条件下,降低压缩比到14.8能够有效降低最大压升率,从而有助于进一步增大天然气的替代比例.采用单次喷射策略时,通过提高喷射压力并提前柴油直喷时刻,在最大压升率限值内,能在...     

柴油/天然气双燃料发动机循环变动的试验研究

本文通过对一台进气歧管处喷射天然气的柴油引燃发动机缸内最大燃烧压力的试验研究,获得了不同循环进气量下双燃料发动机的最大燃烧压力循环变动率的变化情况,同时与纯柴油模式下的最大燃烧压力循环变动率进行了比较,分析了双燃料发动机最大燃烧循环变动产生的原因,对今后试验具有一定的指导性作用。     

引燃柴油对中速双燃料发动机燃烧与排放的影响

采用SAGE详细化学反应机理燃烧模型,加入液滴破裂、蒸发、碰撞以及碰壁子模型,建立了ACD320DF船用中速双燃料发动机缸内及进排气道的三维仿真模型。在气体模式下对不同引燃柴油喷射策略下的缸内燃烧特性进行数值模拟分析。分析表明:引燃柴油的喷油时刻与喷油量对发动机的燃烧及排放有重要影响。根据发动机工况合理调整微引燃柴油的喷射策略,则能得到较好的燃烧和排放性能。     

LPG/柴油双燃料发动机压缩比优化研究

采用燃料复合供给方式 ,在单缸直喷式柴油机上进行了LPG/柴油双燃料发动机压缩比的优化试验研究 ,对比分析了使用纯柴油和LPG/柴油双燃料的燃烧特性 ,着重研究分析了双燃料发动机在不同压缩比下的最高燃烧压力、最大压力升高率、压力循环波动及燃烧放热率 ,并以此为依据优选了双燃料发动机的压缩比。试验结果表明 :降低压缩比后 ,双燃料发动机的最高燃烧压力及最大压力升高率均有较大降低 ,同时压力循环波动变小 ,但滞燃期、燃烧持续期都会有所增加。经过优化 ,压缩比确定为 14.5时 ,ZH110 5W柴油机改燃LPG/柴油双燃料后在高负荷工况下无严重爆震现象 ,压力循环波动较小 ,且经济性较好 ,热效率损失不大     

柴油/天然气发动机燃烧系统协同优化方法

采用KIVA-3V软件耦合多目标遗传优化算法NSGA-3,开展了柴油/天然气双燃料发动机的引燃柴油喷射参数、运行参数和燃烧室结构参数的协同优化研究.将湍流火焰速度封闭模型(TFSC)与PaSR燃烧模型耦合,建立柴油/天然气双燃料发动机复合燃烧模型.结果表明:复合燃烧模型能较好地模拟柴油/天然气发动机的燃烧过程;采用KIVA3V-NSGA3程序进行了双燃料发动机运行参数、喷射参数等多目标参数的协同优化;多目标参数优化结果的数据对比分析揭示了设计参数对目标参数的影响规律;涡流比和喷射参数的变化会对燃烧室内温度、NOx和CH4的分布产生较大影响.     

PODE_n-天然气双燃料的燃烧和排放特性研究

天然气双燃料模式与火花点火模式相比,可以获得更高的热效率,但存在小负荷工况下总碳氢化合物(THC)、CO排放较高,大负荷工况下燃烧粗暴、天然气替代率不足等问题.聚甲氧基二甲醚(PODE_n)是一种高十六烷值、高含氧质量分数的煤基燃料,笔者尝试用其替代柴油引燃天然气,以改善柴油引燃天然气燃烧不完全的问题.结果表明:PODE_n引燃天然气可以使THC、CO排放明显降低,获得较高的热效率,同时可以获得较低的颗粒物(PM)和NO_x排放,证明PODE_n是一种更加适用于天然气双燃料燃烧模式的引燃燃料.     

引燃柴油供给系统对双燃料发动机性能的影响

以实验为基础,研究了引燃柴油量、供油提前角、喷油器参数、针阀开启压力等引燃柴油供给系统参数对柴油／天然气双燃料发动机的燃烧特性、动力性、经济性、排放性等的影响。通过对试验结果的比较与分析,提出了改善双燃料发动机引燃柴油供给系统参数的措施。     

高压直喷点燃式发动机燃用航空煤油掺混乙醇对燃烧性能优化的试验研究

为提高航空煤油在点燃式发动机中的燃烧热效率,改善发动机爆震及拓宽发动机负荷范围,以3号航空煤油(RP3)为基础燃料,以乙醇为辅助燃料,基于一台单缸水冷、压缩比可调、四冲程点燃式发动机结合高压共轨缸内直喷技术,开展了不同负荷、不同乙醇和航空煤油掺混比、不同喷射压力、不同喷射时刻下航空煤油燃烧特性的试验研究。结果表明,在压缩比为7的条件下,由于爆震的限制,发动机负荷仅能达到原机的72.0%。而乙醇具有较强的抑制爆震的能力,随着乙醇在航空煤油中掺混比例的增加,发动机负荷区间不断拓展,当乙醇的掺混比为10%时发动机可实现全负荷工作。继续增大乙醇的掺混比例,可进一步提升功率并降低油耗。为探究喷油时刻对动力性、经济性的影响,试验测定了5种喷油时刻对燃烧性能的影响。当喷油时刻为压缩上止点前300°时,发动机具有较好的动力性;当喷油时刻为上止点前360°时,发动机具有较好的经济性。     

A coupling dynamics and thermodynamics study of diesel pilot-ignition injection effect on hydrogen combustion of a linear engine

Linear hydrogen engine is a new type of energy conversion device to supports variable compression ratio operation for clean emission. However, the new hydrogen engine using conventional spark ignition shows slow combustion speed and low thermal efficiency. This study makes a preliminary assessment to discuss the application of diesel pilot-ignition technology in linear hydrogen engine aiming to accelerate combustion and improve efficiency. A new coupling model between dynamics and thermodynamics is proposed and then iteratively calculated to give insight the interrelationship of combustion and motion in a diesel pilot-ignited linear hydrogen engine, while the effect of injection position on the hydrogen engine combustion is also investigated to make clear the feasibility of combustion optimization. The results indicate that the linear hydrogen engine is speeded by properly advancing the injection to promote combustion, and it has a positive effect on in-cylinder gas temperature, pressure and pressure rise rate, unless the injection is too early which results in higher NO emissions and aggravate the working intensity of the engine. In addition, the closer the fuel injection is to the top dead center, the incomplete combustion of hydrogen and diesel in the cylinder, the decrease of engine fuel economy and the increase of soot emissions. There is an optimal thermal efficiency of 40.7% for the LHE when it operates in the 0.8 mm injection position condition.     

高压共轨系统在柴油转子发动机上的应用研究

针对高压共轨燃油喷射系统在柴油转子发动机上的应用，对直接喷射层状充气式柴油转子机的相关燃油及燃烧系统进行了专门设计，开发了新一代的集高压共轨燃油喷射控制等功能于一体的电子控制单元，进行了初步的运行试验。着重讨论了主、引双喷油器结构结合高压共轨燃油喷射系统在柴油转子发动机上的应用策略和实现方法。当前原理样机可以在高达6000r／min下平稳运行，4000r／min时单缸功率达到30kW。试验表明：通过高压共轨燃油喷射系统结合合理布置的主、引双喷油器、高能点火装置及专用ECU的综合应用，是进一步发挥和提高低压缩比柴油转子发动机众多优点的一个有效的途径。     

Numerical Investigation of the Effect of Hydrogen Enrichment on an Opposed-Piston Compression Ignition Diesel Engine

High power-to-weight and fuel efficiency are bounded with opposed-piston compression ignition(OPCI) engine, which makes it ideal in certain applications. In the present study, a dynamic three-dimensional CFD model was established to numerically investigate the combustion process and emission formation of a model OPCI engine with hydrogen enrichment. The simulation results indicated that a small amount of hydrogen was efficient to improve the indicated power owing to the increased in-cylinder pressure. Hydrogen tended to increase the ignition delay of diesel fuel due to both dilution and chemical effect. The burning rate of diesel fuel was apparently accelerated when mixing with hydrogen and premixed combustion became dominated. NO_x increased sharply while soot was sufficiently suppressed due to the increase of in-cylinder temperature. Preliminary modifications on diesel injection strategy including injection timing and injection pressure were conducted. It was notable that excessive delayed injection timing could reduce NO_x emission but deteriorate the indicated power which was mainly attributed to the evident decline of hydrogen combustion efficiency. This side effect could be mitigated by increasing the diesel injection pressure. Appropriate delay of injection coupled with high injection pressure was suggested to deal with trade-offs among NO_x, soot and engine power.     

基于喷油策略和阿特金森循环的汽油压燃 发动机高负荷性能优化研究

基于单缸机开展了多次喷射和阿特金森循环对汽油压燃(gasoline compression ignition,GCI)发动机性能影响的试验研究,试验分别研究了单次喷射、两次喷射及两次喷射结合阿特金森循环对GCI中高负荷性能的影响。结果表明,单次喷射中喷油压力、喷油时刻和喷油量对GCI燃烧有显著的影响,提高喷射压力可提高发动机的平均指示压力,降低循环波动,但喷油压力过高会导致燃烧对喷油时刻变化异常敏感,使燃烧难以正常进行;喷油量增加可提高发动机的平均指示压力,但过高的喷油量会导致不完全燃烧的燃油量增加,热效率下降。在两次喷射中,主喷时刻对燃烧起着决定性的影响。主喷时刻提前,发动机动力性有所提升,但压升率也随之增加;主喷时刻推迟,发动机动力性相应降低,同时循环波动增加。增加预喷量有利于发动机性能的提升,但预喷量过大会导致燃烧可控性降低。阿特金森循环能明显提升GCI热效率,其主要原因是减少了压缩行程的压缩负功,同时燃烧并未恶化,膨胀做功并未降低。     

A study of hydrogen fuelled compression ignition engines

The possibility of establishing a hydrogen fuelled compression ignition engine has been investigated experimentally using a conventional swirl chamber diesel engine. Two different attempts are included in this work; one dealing with the compression ignition on an air-aspirated engine system, and another with an engine operating with an argon-oxygen charge. In the former, the effect of preliminary fuelling was clarified in detail. It has been suggested that both pilot injection and fuel leakage from the injector can aid ignition of the hydrogen fuel, bringing about a smooth operation. A discussion is given of the mechanism of stabilizing ignition, from the viewpoint of thermal interactions between the engine cycles. In the latter attempt, a closed-cycle engine system is oriented and has been simulated by supplying a 21% oxygen containing mixture to the test engine. The result has indicated that ignition and engine operation are satisfactory without any ignition aid. A considerable gain has also been proved in thermal efficiency of using the argon mixture. Also, the practical feasibility of a closed-cycle compression ignition engine has been discussed.     

Ignition delay of dual fuel engine operating with methanol ignited by pilot diesel

An investigation on the ignition delay of a dual fuel engine operating with methanol ignited by pilot diesel was conducted on a TY1100 direct-injection diesel engine equipped with an electronic controlled methanol low-pressure injection system. The experimental results show that the polytropic index of compression process of the dual fuel engine decreases linearly while the ignition delay increases with the increase in methanol mass fraction. Compared with the conventional diesel engine, the ignition delay increment of the dual fuel engine is about 1.5° at a methanol mass fraction of 62%, an engine speed of 1600 r/min, and full engine load. With the elevation of the intake charge temperature from 20°C to 40°C and then to 60°C, the ignition delay of the dual fuel engine decreases and is more obvious at high temperature. Moreover, with the increase in engine speed, the ignition delay of the dual fuel engine by time scale (ms) decreases clearly under all engine operating conditions. However, the ignition delay of the dual fuel engine increases remarkably by advancing the delivery timing of pilot diesel, especially at light engine loads.     

基于高压直喷航空煤油点燃式发动机燃烧性能优化的试验研究

为提高航空煤油在点然式发动机中的燃烧热效率,改善发动机爆震及拓宽发动机负荷范围,以3号航空煤油(RP-3)为基础燃料,基于一台单缸水冷、压缩比可调、4冲程点燃式发动机结合高压共轨缸内直喷技术,开展了单双点火、不同负荷、压缩比、喷射压力、喷射时刻和两次喷射策略下航空煤油燃烧特性的试验研究。结果表明,在原机压缩比为10的条件下,将直喷汽油改为直喷航空煤油后,由于航空煤油的抗爆性差、雾化困难、燃烧速率慢等理化特性,发动机的动力性损失约50.0%,油耗增加约60.0%,循环波动也大幅增加;相比于单点火,双点火可使缸内平均有效压力提高,燃烧相位提前,循环波动降低;为了抑制高压缩比下的爆震倾向,可通过降低压缩比来拓宽负荷范围,恢复原机功率。随着压缩比的降低,有效平均压力(BMEP)持续增大,当压缩比为6时,最大转矩可达39.5N·m,功率恢复至原机的88.0%。同时耦合高压及两次喷射策略,随着喷射压力的增大,有效燃油消耗率(BSFC)减小约30.0%,经济性有所提高。相比于单次喷射,采用两次喷射策略可降低油耗,提升缸内有效平均压力,提升燃烧效率,最终可实现发动机燃用航空煤油的性能接近原机水平,最大负荷达原机的90.0%且油耗增加量不超过15.0%。     

基于AVL-BOOST的天然气发动机性能优化仿真

采用AVL-BOOST软件建立了天然气发动机的数学模型,验证了模型的有效性,通过变参数研究,分析了压缩比、点火提前角对发动机动力性和经济性的影响。研究结果表明,随着压缩比的增大,发动机的有效功率和最高爆发压力均呈上升趋势,压缩比在10～13的范围内,最高压力升高率始终在爆震警戒线以下,在点火提前角为27°～36°CA范围内,发动机的有效功率随着点火提前角的增大而增加,同时发动机的燃油经济性得到改善。