OPOC柴油机喷油提前角对燃烧性能的影响

利用AVL FIRE软件对该型样机不同喷油提前角进行模拟计算,对比分析不同喷油提前角下空气利用率、燃烧累积放热量、缸内压力以及指示功率、燃油消耗率的变化情况。结果显示,喷油提前角通过影响滞燃期的燃气混合情况来影响燃烧性能,随着喷油提前角的增大,滞燃期内可燃混合气增多,燃烧放热更集中在360~385℃A完成,热效率高,最大爆发压力增大。对于该型柴油机来说,由于爆发压力的上限要求160 MPa,喷油提前角不得大于47℃A。     

直喷式柴油机燃用生物柴油的燃烧特性

在一台直喷式增压柴油机上进行了生物柴油、柴油及其掺混油B20、B50的性能试验,通过测量喷油器针阀升程、喷油压力和气缸压力曲线,对放热率、滞燃期等燃烧特性参数进行了分析,以研究生物柴油对发动机燃烧性能的影响。试验结果表明,在相同工况下,随着掺混油中生物柴油比例的增加,喷油始点逐渐提前,喷油延迟角逐渐变大,喷油压力和喷油持续期有所增加;滞燃期逐渐缩短,在大负荷尤为明显;预混合放热峰值逐渐降低,而扩散燃烧放热峰值逐渐增大;缸内最高燃烧压力提高,其对应的曲轴转角也逐渐提前。燃用生物柴油后发动机的热效率有所提高,在中等负荷时尤为明显。     

F-T柴油对直喷式柴油机燃烧和排放的影响

在两种不同供油提前角下研究了燃用F-T柴油对直喷式柴油机燃烧和排放特性的影响,结果表明:发动机不做任何调整时,与0号柴油相比,燃用F-T柴油的滞燃期较短,预混燃烧放热峰值较低,扩散燃烧放热峰值较高,最高燃烧压力和最大压力升高率较低,燃油消耗率和热效率都得到了改善,HC、CO、NOx和碳烟排放同时降低。当供油提前角推迟3℃A时,燃用F-T柴油燃烧持续期明显缩短,预混燃烧放热峰值、最高燃烧压力和最大压力升高率进一步降低,扩散燃烧放热峰值略有升高,燃油消耗率变化不大,NOx排放进一步降低, HC、CO和碳烟略有增加,其中HC排放与原柴油机相当,而CO和碳烟仍远低于原柴油机。     

改装直喷式柴油机中生物柴油喷雾燃烧过程试验研究

利用可视化装置,分析比较了直喷式柴油机燃用生物柴油与常规柴油的喷雾燃烧过程.研究结果表明:生物柴油的喷油时刻较早,着火时刻提前,着火滞燃期缩短,在早期预混燃烧阶段的燃烧速度大于柴油,而在扩散燃烧阶段的燃烧速度比柴油低.通过分析燃料性质、转速和喷油压力这3种因素对生物柴油燃料喷雾燃烧过程的影响,从而得出影响规律为:混合燃料喷油始点、着火时刻均有所提前,滞燃期变短,B5混合燃料的最高燃烧压力最高且出现稍早;生物柴油在高转速工况时的燃烧速度大,且最高燃烧压力也略高;随着喷油压力的提高,滞燃期缩短,燃烧持续期相应缩短,最高燃烧压力升高.     

喷油提前角对柴油机燃烧特性的影响分析

应用三维流体数值分析软件AVL FIRE,建立了柴油机燃烧计算模型,研究了喷油提前角对压力、温度、速度场和放热率的影响及对NO_x和炭烟生成的影响。仿真结果表明,随着喷油提前角的增大,缸内最高燃烧压力和温度不断升高,燃烧初期的放热速率比较高,放热规律相对集中,NO_x生成增加,炭烟生成减少。该研究对柴油机喷油参数的优化,具有理论指导意义。     

推迟供油提前角对生物柴油发动机燃烧和排放性能的影响

在直喷式增压柴油机上进行了供油提前角对生物柴油发动机动力性、经济性和排放性能影响的研究。试验结果表明:与柴油相比,推迟供油提前角后生物柴油的动力性下降,燃油经济性恶化,NO_x和烟度排放均有不同程度的降低。推迟供油提前角对生物柴油的喷油压力和滞燃期影响不大,但喷油始点和燃烧始点均迟于柴油。与柴油相比,推迟供油提前角后最高气缸压力下降,放热峰值出现时刻提前,指示热效率降低。燃烧始点与NO_x排放的相关性最大,喷油始点和放热峰值出现时刻也与NO_x排放呈弱相关性。     

柴油机燃用F-T柴油与0号柴油混合燃料的燃烧特性

根据实测的喷油器针阀升程和示功图,开展了直喷式柴油机燃用F-T柴油与0号柴油混合燃料时燃烧特性的研究．试验用燃料为0号柴油、含25%和50%F-T柴油的混合燃料以及100%F-T柴油．结果表明,在相同工况下,随着混合燃料中F-T柴油比例的增加,喷油延迟角增大,而喷油持续期变化不大．滞燃期随着F-T柴油比例的增加而缩短,其中当F-T柴油的比例由0增至25%时,滞燃期缩短最为明显,此后进一步增加F-T柴油的比例,滞燃期缩短幅度减小．随着混合燃料中F-T柴油比例的增加,预混燃烧放热峰值降低,扩散燃烧放热峰值增大,燃烧持续期略有延长,缸内最高燃烧压力和气体最高平均温度降低,最大压力升高率显著下降,发动机的燃烧噪音和机械损失减小,有效燃油消耗率和有效热效率得到改善．     

柴油机预混合燃烧滞燃期的试验

滞燃期是柴油机预混合燃烧当中一个极为重要的参数.在电控共轨柴油机上进行了EGR率、喷油始点、喷油压力、负荷、转速和进气温度等单一参数对预混合燃烧滞燃期的试验研究.结果表明,名义过量空气系数能够帮助解释各试验参数对柴油机预混合燃烧滞燃期的影响.混合气的温度、压力和混合气中O2浓度影响柴油机预混合燃烧的滞燃期.提高进气温度...     

喷油定时对汽/柴油混合燃料燃烧影响的可视化研究

通过一台光学发动机,利用高速摄影技术,对纯柴油和汽油体积掺混比为60%汽/柴油混合燃料(G 60)在不同喷油定时下进行了燃烧特性试验.结果表明:G 0和G 60燃料均呈单峰放热规律;与纯柴油相比,G 60燃料最高燃烧压力pmax对喷油定时变化更为敏感.随着喷油定时提前,纯柴油和G 60燃料的滞燃期呈线性增大,着火时刻逐渐提前,着火点分布于视窗边沿,G 60燃烧图像中高亮火焰面积逐渐减少,柴油扩散燃烧比例降低,累计放热量为5%(CA 5)至累计放热量为50%(CA 50)对应燃烧持续期逐渐缩短.相对于柴油,G 60燃料滞燃期延长,着火时刻滞后,在稀燃状况下,CA 5至CA 50的燃烧持续期延长.     

柴油机瞬变工况下某些喷油及性能参数变化的研究

本文建立了柴油机瞬变工况喷油及燃烧过程瞬态参数的测量分析系统,研究了柴油机转速及负荷突变过程中喷油及燃烧过程瞬态参数的连续变化情况.结果表明,在开始加速时喷油提前角增大,喷油持续期及滞燃期延长,使得最大压力升高率急剧增加.在转速及负荷突变过程中,喷油及燃烧过程均呈波动状变化.     

Effect of advanced injection timing on the performance of rapeseed oil in diesel engines

Combustion studies on both diesel fuel and vegetable oil fuels, with the standard and advanced injection timing, were carried out using the same engine and test procedures so that comparative assessments may be made. The diesel engine principle demands self-ignition of the fuel as it is injected at some degrees before top dead centre (BTDC) into the hot compressed cylinder gas. Longer delays between injection and ignition lead to unacceptable rates of pressure rise with the result of diesel knock because too much fuel is ready to take part in premixed combustion. Alternative fuels have been noted to exhibit longer delay periods and slower burning rate especially at low load operating conditions hence resulting in late combustion in the expansion stroke. Advanced injection timing is expected to compensate these effects. The engine has standard injection timing of 30°C BTDC. The injection was first advanced by 5.5°C given injection timing of 35.5°C BTDC. The engine performance was very erratic on this timing. The injection was then advanced by 3.5°C and the effects are presented in this paper. The engine performance was smooth especially at low load levels. The ignition delay was reduced through advanced injection but tended to incur a slight increase in fuel consumption. Moderate advanced injection timing is recommended for low speed operations.     

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.     

Experimental investigation of the performance and exhaust emissions of a swirl chamber diesel engine using JP-8 aviation fuel

An experimental study is conducted to evaluate the use of JP-8 aviation fuel as a full substitute for diesel fuel in a Ricardo E-6 high-speed naturally-aspirated four-stroke experimental engine having a swirl combustion chamber. The study covers a wide range of engine load and speed operating conditions, comprising measurements of cylinder pressure diagrams, high-pressure fuel pipe pressures, exhaust gas temperatures, fuel consumptions, exhaust smokiness and exhaust gas emissions (nitrogen oxides, unburned hydrocarbons and carbon monoxide). Processing of the measurements provides important performance parameters such as maximum combustion pressure, dynamic injection timing, ignition delay, combustion irregularity and knocking tendency. The differences in the measured performance and exhaust emission parameters are determined for engine operation with JP-8 fuel, against baseline engine operation using diesel fuel. The study shows that the exhaust emission levels are not much different for operation with the two fuels. On the contrary, operation with JP-8 fuel increases combustion pressures, combustion intensity and irregularity. This is caused mainly by high pressure fluctuations present in the fuel injection system due to the different physical properties of JP-8 fuel (compared to diesel fuel), which totally change the injection characteristics. Retardation of the static injection timing is one means of improving this situation, while using the same fuel injection equipment. © 1997 John Wiley & Sons, Ltd.     

天然气发动机在不同喷射和点火时刻下的性能优化研究

为解决改装的天然气发动机动力性比原柴油机低,燃料消耗率比原柴油机高的问题,对影响燃烧时刻的喷射提前角与点火提前角这两个重要参数进行模拟实验,研究其对发动机的缸内压力与功率、燃气消耗率的影响,并根据研究结果进行优化设计。结果表明,对于缸内直喷天然气发动机,适当增大喷气提前角和选择恰当的点火提前角能在较经济的情况下提高发动机的动力性;发动机转速增加,点火提前角和喷射提前角也应提前,保证燃料的充分混合和最大化做功能力;在所有转速下,天然气发动机的功率都能恢复到原柴油机的水平。     

辛烷值对均质压燃发动机燃烧特性和性能的影响

通过不同比例的正庚烷和异辛烷混合得到不同辛烷值的混合燃料，在一台单缸直喷式柴油机上研究燃料辛烷值对均质压燃发动机燃烧特性、性能和排放特性的影响．研究结果表明，燃料辛烷值增加，着火始点推迟，燃烧反应速率降低，缸内爆发压力降低．燃料辛烷值增高，均质压燃向大负荷工况拓宽，燃料辛烷值较高时，存在极限转速，辛烷值增加，极限转速降低．对于每一工况，存在一个最佳经济性的燃料辛烷值，负荷增大，最佳辛烷值增高；随着燃料辛烷值增高，发动机NO、HC和CO排放增加，尤其是HC排放增加更为明显．对于均质压燃发动机，低负荷工况适合燃用低辛烷值燃料，高负荷工况适合燃用高辛烷值燃料。     

天然气/柴油双燃料发动机燃料喷射及着火特性

基于计算流体动力学(CFD)软件CONVERGE模拟了缸内高压直喷式柴油微引燃液化天然气(LNG)发动机的燃料喷射混合以及着火过程,校核和验证了湍流模型对模拟结果的影响,分析了天然气喷射正时、天然气喷射持续期及柴油与天然气射流中心轴线的夹角对缸内柴油和天然气射流发展、混合和着火的影响.结果表明:Smagorinsky大...     

Effect of advanced injection timing on emission characteristics of diesel engine running on natural gas

There has been a growing concern on the emission of greenhouse gases into the atmosphere, whose consequence is global warming. The sources of greenhouse gases have been identified, of which the major contributor is the combustion of fossil fuel. Researchers have intensified efforts towards identifying greener alternative fuel substitutes for the present fossil fuel. Natural gas is now being investigated as potential alternative fuel for diesel engines. Natural gas appears more attractive due to its high octane number and perhaps, due to its environmental friendly nature. The test results showed that alternative fuels exhibit longer ignition delay, with slow burning rates. Longer delays will lead to unacceptable rates of pressure rise with the result of diesel knock. This work examines the effect of advanced injection timing on the emission characteristics of dual-fuel engine. The engine has standard injection timing of 30° BTDC. The injection was first advanced by 5.5° and given injection timing of 35.5° BTDC. The engine performance was erratic on this timing. The injection was then advanced by 3.5°. The engine performance was smooth on this timing especially at low loading conditions. The ignition delay was reduced through advanced injection timing but tended to incur a slight increase in fuel consumption. The CO and CO₂ emissions were reduced through advanced injection timing.     

生物制气-柴油双燃料发动机放热规律试验研究

采用气化炉热解气化各种农林废弃的生物质,产生可燃生物制气,用作为以柴油引燃的双燃料发动机的主要燃料。测量生物制气-柴油双燃料发动机气缸压力,计算分析放热规律。双燃料发动机与燃用纯柴油时的发动机相比,燃烧始点延迟,最大燃烧压力降低,最大放热率和排气温度增加,后燃较严重。负荷增大时,双燃料发动机燃烧始点提前,最大燃烧放热率增高,最高燃烧温度升高,后燃较严重。供油提前角提前时,后燃减小,燃烧过程明显改善。     

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.