喷油时刻及压力对直喷式汽油机低速早燃的影响

通过一台单缸增压直喷汽油机,对比了低速早燃和正常燃烧的循环特征、压力振荡强度和振荡频率,开展了不同喷油时刻和不同喷油压力对低速早燃频次及强度影响的试验.结果表明:低速早燃由于自燃时刻不同可以引发普通爆震和超级爆震,超级爆震发生时可能伴随有超声速的冲击波或爆轰波产生.推迟喷油时刻,低速早燃频次呈现先增加后降低的趋势.喷油时刻由300°,CA BTDC推迟到240°,CA BTDC时,低速早燃和超级爆震频次分别降低了96.0%,和88.2%,,超级爆震强度也显著降低.喷油压力从6,MPa提高到12,MPa会导致低速早燃频次增加,继续提高喷油压力,低速早燃和超级爆震频次均有所降低.喷油时刻及压力的改变会导致气缸壁机油稀释和碳烟颗粒物排放发生变化,因而推测上述两种物质均有可能导致低速早燃发生.     

增压直喷乙醇-汽油发动机超级爆震模拟

采用在压缩行程上止点前向燃烧室内直接喷入一定量机油液滴,模拟了悬浮在燃烧室内的机油液滴引燃可燃混合气诱发低速早燃(LSPI)现象的过程.试验验证了选用的计算模型及计算方法的可行性后,数值模拟了不同低速运转条件下、不同乙醇掺混比(体积分数)的乙醇-汽油混合燃料时,小缸径增压直喷发动机燃烧室内由机油液滴引发的低速早燃现象以及后续的超级爆震过程.结果表明:乙醇掺混比分别为10%和20%(E10、E20)时,发动机缸内依次发生了超级爆震燃烧;当乙醇掺混比为30%(E30)时,即使发生了早燃现象(1 200 r/min)并导致随后的爆震燃烧,但压力升高幅度明显降低,此时没有发生超级爆震燃烧;随着发动机转速提高(1 600 r/min),使用E30燃料时发动机缸内也仅发生了早燃现象,而没有发生爆震燃烧;当乙醇掺混比高于50%(E50)后,不同工况条件下发动机缸内已经没有低速早燃现象.使用乙醇-汽油混合燃料的小缸径增压直喷发动机在超级爆震发生前一定有低速早燃现象发生,但低速早燃现象不一定导致超级爆震过程.     

增压缸内直喷汽油机早燃及超级爆震试验研究

在一台增压缸内直喷汽油机上,对影响早燃及超级爆震发生频率与强度的各种因素进行了台架试验研究。研究结果表明:提高燃油挥发性,升高机油和冷却液温度,推迟进、排气门正时,增大点火提前角,提前或推迟喷油定时及使用高的喷油压力能够有效减少早燃及超级爆震。     

稀薄燃烧汽油机爆震特性

研究目的是确定稀薄燃烧对于汽油机爆震倾向的影响,为稀燃发动机中增压的应用提供参考依据.试验在一台模拟增压的汽油机上进行,试验时通过改变燃料的辛烷值,直到出现轻微爆震的方法来确定发动机的爆震特性.结果表明,稀薄燃烧对于汽油机爆震的影响,根据关注目标的不同而有所差异:保持进气量不变,汽油机的爆震倾向会随着空燃比的增加而减小;输出功率保持不变,发动机的爆震倾向会随着空燃比的增加而略有增大.因此,为保证稀燃汽油机的动力输出而采用增压进气会使得发动机的爆震倾向增加,应用中需要同时采用其他技术措施抑制爆震的发生.     

不同燃烧模式的爆震特性及爆震强度评价方法

基于一台配备了全可变气门机构的单缸四冲程发动机开展了不同燃烧模式的燃烧和压力震荡特性研究,包括均质充量压燃(homogeneous charge compression ignition,HCCI)、汽油压燃(gasoline compression ignition,GCI)、湍流射流点火(turbulent jet ignition,TJI)和火花点火(spark ignition,SI)。研究结果表明:不同燃烧模式具有不同的统计学特征,其中HCCI、GCI和TJI的爆震强度分布较为集中,不易出现偶发的高爆震强度的燃烧循环;SI爆震的分布较为离散,通常具有较高的最大值和99%分位数,高爆震强度燃烧循环的偶发性较强;而低速早燃工况则是具有极高的爆震强度最大值和很低的99%分位数。此外,对于爆震工况的评价方面,对传统的算数平均值法和爆震循环占有率法进行了改进,提出了加权平均值法和破坏性循环均值法两种改进的爆震评价方法。二者在HCCI、GCI、TJI和SI爆震判定的准确性和适应性上相比改进前有了很大的提升;但对于低速早燃工况,破坏性循环均值法无法准确识别出其破坏性,加权平均值法具有非常好的准确性。     

增压缸内直喷汽油机抑制预燃试验

预燃是增压缸内直喷汽油机上与普通爆震不同的异常燃烧模式,通过阐述预燃的特征,对比分析了预燃与常规爆震和正常燃烧的基本不同.通过初步分析预燃产生机理,指出了可能抑制预燃的主要手段,试验研究了冷却水温度、点火角、进气相位等对预燃的影响.试验结果表明,降低冷却水温度,优化进气相位,可以一定程度抑制预燃;提前点火角,发生轻微常规爆震,但未出现预燃     

增压直喷汽油发动机早燃现象改善的研究

低速大负荷早燃现象是制约增压直喷汽油发动机低速性能提升的主要因素之一,早燃易导致发动机火花塞烧蚀、活塞熔顶等质量问题,所以在发动机设计开发过程中必须对早燃问题加以优化改善。阐述了早燃产生的机理,更换不同机油、改变压缩比以及空燃比进行试验,结果表明：更换机油以及改变空燃比能够降低早燃频次,改变压缩比对早燃无影响。     

增压直喷汽油机超级爆震现象与初步试验

在增压缸内直喷汽油机上发现了与普通爆震不同的异常燃烧模式——超级爆震,阐述了超级爆震的特征,对比分析了超级爆震与常规爆震和正常燃烧的基本不同．发生超级爆震时,最大爆压达到正常燃烧的2倍以上,并且通过推迟点火角不能抑制超级爆震的发生．在此基础上,初步研究了冷却水温度、进气温度、进气相位和过量空气系数等对超级爆震的影响．试...     

增压直喷汽油机喷油策略对低速早燃的影响研究

试验研究了喷油策略对增压直喷汽油机低速早燃的影响。研究结果表明:低速早燃现象在发动机正常运行过程中随机且非连续的发生,发生时最高燃烧压力显著上升并引发强烈的爆震;空燃比加浓(过量空气系数0.75~0.90)可以显著地降低低速早燃的发生频率;单次喷射的喷油开始时刻过于提前(330~300°CA BTDC)或者推后(250~210°CA BTDC)都将增大低速早燃的发生频率;采用高的喷油压力(15MPa)对于低速早燃的发生频率具有抑制的趋势;当第一次喷油开始时刻较为提前(330~300°CA BTDC)时,相比单次喷射策略,二次喷射策略能够较明显地降低低速早燃的发生频率。     

直喷增压汽油机扫气条件下喷油策略对超级爆震的影响

在缸内直喷汽油机上,将扫气和两次喷射相结合,研究在扫气条件下燃油策略对超级爆震抑制作用及对发动机经济性和排放性的影响。试验中制定了一种考虑发动机实际运行工况的超级爆震的试验测试程序。在不同喷油策略下发动机超级爆震工况点的试验结果表明:采用一次喷射策略,不同的燃油喷射角对性能影响很大,燃油喷射角过于提前,会产生油束与活塞顶面碰壁现象,推迟燃油喷射角可以降低碳烟排放。采用两次喷射相对一次喷射,碳烟排放可更进一步降低,输出转矩变化不大。两次喷射中二喷油起始角对超级爆震十分敏感。采用两次晚喷的分层模式会增大超级爆震频次,采用两次早喷的均质模式能减少超级爆震频次。     

Research on optimal control to resolve the contradictions between restricting abnormal combustion and improving power output in hydrogen fueled engines

In this paper, based on experiment result in a hydrogen fueled engine, pre-ignition and transforming process from pre-ignition to backfire of the hydrogen fueled engine was analyzed. Moreover, mechanism of pre-ignition and backfire of hydrogen fueled engines was studied by analyzing chain reaction. The analysis shows that the temperature, pressure and rate of pressure rise have great influence on pre-ignition and backfire. And based on thermodynamic relations of heat release rate, both pre-ignition and backfire were also analyzed. Finally, optimization control model which has multi-variables, multi-objectives and multi-constraints was established. And the simulation was carried out through the genetic algorithm. Results have shown that the excess air ratio and ignition advance angle can be adjusted by weighted coefficients to optimize the power output and restrict the abnormal combustion. Thus, a useful method is shown to resolve the contradictions between restricting the abnormal combustion and improving hydrogen fueled engine’s power output.     

Development of online control system for elimination of backfire in a hydrogen fuelled spark ignition engine

Backfire is one of the major technical issues in a port injection type hydrogen fuelled spark ignition engine. It is an abnormal combustion phenomenon (pre-ignition) that takes place in combustion chamber and intake manifold during suction stroke. The flame propagates toward the upstream of the intake manifold from combustion chamber during backfire and thus can damage the intake and fuel supply systems of the engine, and stall the engine operation. The main cause of backfire could be the presence of any hot spot, lubricating oil particle's traces (HC and CO due to evaporation of the oil) and hot residual exhaust gas present in the combustion chamber during suction stroke which could act as an ignition source for fresh incoming charge. Monitoring the temperatures of the lubricating oil and exhaust gas during engine operation can reduce the probability of backfire. This was achieved by developing an electronic device which delays the injection timing of hydrogen fuel with the inputs of engine oil temperature (T_{lube oil}) and exhaust gas temperature (T_exh). It was observed from the experimental results that the threshold values of T_{lube oil} and T_exh were 85 °C and 540 °C respectively beyond which backfire occurred at equivalence ratio (φ) of 0.82. The developed device works based on the algorithm that retards the hydrogen injection to 40 ⁰aTDC whenever the temperatures (T_{lube oil} and T_exh) reached to the above mentioned values and thus the backfire was controlled. Delaying injection of hydrogen increased the time period at which only air is inducted during the early part of the suction stroke, this allows cooling of the available hot spots in the combustion chamber, hence the probability of backfire would be reduced.     

Optimization control of hydrogen engine ignition system based on ACO-BP

With the development of new energy, hydrogen fuel engines have become a research boom in the automotive field. But there are abnormal problems such as backfire and pre-ignition during the combustion of hydrogen engines. This paper is based on the Ant Colony Optimization-Back Propagation (ACO-BP) algorithm to study the influence of different speed and load conditions on the ignition advance angle, so as to optimize the control of the hydrogen engine. The experimental system is established on a hydrogen engine converted from a 492Q gasoline engine. The prediction of the optimal ignition advance angle was obtained through experiments, and the optimal ignition MAP diagram of the hydrogen engine is constructed. The optimal ignition advance angle under different working conditions can effectively avoid the occurrence of hydrogen engine pre-ignition. The accuracy reaches 0.0018209 when the training reaches 14 times, the fitness between the actual value and the predicted value of ACO-BP training is 0.99921, the verification accuracy reaches 0.99913, and the test accuracy reaches 0.99932. Compared with the three optimization methods, the convergence speed and error accuracy of ACO-BP are significantly better than the BP neural networks and Genetic Algorithm-Back Propagation (GA-BP). This method realized the model of the nonlinear mapping model from hydrogen engine speed and load to optimal ignition advance angle, which is of great significance for solving the problem of abnormal combustion in hydrogen engine.     

Performance of a stationary diesel engine using vapourized ethanol as supplementary fuel

The modification and testing of a compression ignition engine using diesel and vapourized ethanol as fuel has been carried out. Tests on the engine fuelled with diesel only were made, and the performance evaluated to form a basis for comparison for those of ethanol–diesel dual fuelling.

Modifications were made in the introduction of the ethanol and air. A carburettor was used to vapourize aqueous ethanol into the engine. The effect of preheating the intake ethanol–air mixture was also investigated. Performance was evaluated in terms of engine horsepower, brake specific fuel consumption, brake thermal efficiency, the exhaust gas temperature, lubricating oil temperature and exhaust emissions. The vapourized ethanol partially reduced diesel fuel consumption but also increased total fuel delivery. Vapourization increased power output, thermal efficiency and exhaust emissions but lowered exhaust temperature and lubricating oil temperatures.     

YZ485ZLQ柴油机润滑系统性能与主油道压力特性试验

采用台架试验方法,进行YZ485ZLQ柴油机润滑系统的整体性能和主油道的压力特性试验,探讨在YZ485QB柴油机基础上改进的YZ485ZLQ柴油机润滑系统性能。结果表明,YZ485ZLQ柴油机润滑系统性能良好,满足使用要求。转速变化对主油道压力的影响明显,润滑油温度变化对主油道压力的影响次之并呈现较强的非线性关系,负荷变化对主油道压力的影响最小。随着柴油机转速的增加,润滑系统中主油道的压力不断增加,最后趋于稳定值;随着柴油机负荷和润滑油的温度增加,主油道的润滑油压力下降。     

The utilization of hydrogen in hydrogen/diesel dual fuel engine

A hydrogen fueled internal combustion engine has great advantages on exhaust emissions including carbon dioxide (CO₂) emission in comparison with a conventional engine fueling fossil fuel. In addition, if it is compared with a hydrogen fuel cell, the hydrogen engine has some advantages on price, power density, and required purity of hydrogen. Therefore, they expect that hydrogen will be utilized for several applications, especially for a combined heat and power (CHP) system which currently uses diesel or natural gas as a fuel.A final goal of this study is to develop combustion technologies of hydrogen in an internal combustion engine with high efficiency and clean emission. This study especially focuses on a diesel dual fuel (DDF) combustion technology. The DDF combustion technology uses two different fuels. One of them is diesel fuel, and the other one is hydrogen in this study. Because the DDF engine is not customized for hydrogen which has significant flammability, it is concerned that serious problems occur in the hydrogen DDF engine such as abnormal combustion, worse emission and thermal efficiency.In this study, a single cylinder diesel engine is used with gas injectors at an intake port to evaluate performance swung the hydrogen DDF engine with changing conditions of amount of hydrogen injected, engine speed, and engine loads. The engine experiments show that the hydrogen DDF operation could achieve higher thermal efficiency than a conventional diesel operation at relatively high engine load conditions. However, it is also shown that pre-ignition with relatively high input energy fraction of hydrogen occurred before diesel fuel injection and its ignition. Therefore, such abnormal combustion limited amount of hydrogen injected. Fire-deck temperature was measured to investigate causal relationship between fire-deck temperature and occurrence of pre-ignition with changing operative conditions of the hydrogen DDF engine.     

Conversion of a commercial spark ignition engine to run on hydrogen: Performance comparison using hydrogen and gasoline

The modifications performed to convert the spark ignition gasoline-fueled internal combustion engine of a Volkswagen Polo 1.4 to run with hydrogen are described. The car is representative of small vehicles widely used for both city and interurban traffic. Main changes included the inlet manifold, gas injectors, oil radiator and the electronic management unit. Injection and ignition advance timing maps were developed for lean mixtures with values of the air to hydrogen equivalence ratio (λ) between 1.6 and 3. The established engine control parameters allowed the safe operation of the hydrogen-fueled engine (H₂ICE) free of knock, backfire and pre-ignition as well with reasonably low NO_x emissions. The H₂ICE reached best brake torque of 63 Nm at 3800 rpm and maximum brake power of 32 kW at 5000 rpm. In general, the brake thermal efficiency of the H₂ICE is greater than that of gasoline-fueled engine except for the H₂ICE working at very lean conditions (λ = 2.5) and high speeds (above 4000 rpm). A significant effect of the spark advance on the NO_x emissions has been found, specially for relatively rich mixtures (λ < 2). Small changes of spark advance with respect to the optimum value for maximum brake torque give rise to an increase of pollutant emissions. It has been estimated that the hydrogen-fueled Volkswagen Polo could reach a maximum speed of 140 km/h with the adapted engine. Moreover, there is enough reserve of power for the vehicle moving on typical urban routes and routes with slopes up to 10%.     

润滑油性质对汽油机排放标准的影响

用试验数据说明汽油机润滑油的性能和质量与排放、节能的关系,分析国内外汽油机润滑油的现状和发展趋势,提出了今后我国汽油机润滑油的发展方向。     

Analysis of ignition delay by taking Di-tertiary-butyl peroxide as an additive in a dual fuel diesel engine using hydrogen as a secondary fuel

Ignition delay (ID) is one of the important parameters that make influenced on the combustion process inside the cylinder. This ignition delay affects not only the performances but also the noise and emissions of the engine. In this regards the experiments were conducted on single cylinder 4–stroke compression ignition research diesel engine, power 3.50 kW at constant speed 1500 rpm Kirloskar model TV1 with base fuel as diesel and hydrogen as secondary fuel with and without Di-tertiary-butyl-peroxide (DTBP). Experiments were conducted to measure the ignition delay of the dual fuel diesel (DFD) engine at different load conditions and substitution of diesel by hydrogen with or without DTBP and then it was compared with predicted ID given by Hardenberg-Hase equation and modified Hardenberg-Hase equation.The experimental values of ignition delay were compared with theoretical ignition delay which was predicted on the basis of Hardenberg-Hase equation by considering mean cylinder temperature, pressure, activation energy and cetane number and variations are found in between 6.60% and 21.22%. While, the Hardenberg-Hase equation was modified (by considering variation in activation energy) for DFD engine working on diesel as primary fuel and hydrogen as secondary fuel shows variations 1.20%–11.96%. Furthermore, with DTBP it gives variation up to 18.01%. It was found that ID decreases with increase in percentage of DTBP and hydrogen in air-fuel mixture. This might be due to the cetane improver nature of DTBP, pre-ignition reaction rate and energy release rate of hydrogen fuel. The polytropic index get increased by addition of (Di-tert butyl peroxide) DTBP. Similarly, 5% Di tertiary butyl peroxide reduces Ignition delay.