Effect of ignition timing and hydrogen fraction on combustion and emission characteristics of natural gas direct-injection engine

An experimental study on the combustion and emission characteristics of a direct-injection spark-ignited engine fueled with natural gas/hydrogen blends under various ignition timings was conducted. The results show that ignition timing has a significant influence on engine performance, combustion and emissions. The interval between the end of fuel injection and ignition timing is a very important parameter for direct-injection natural gas engines. The turbulent flow in the combustion chamber generated by the fuel jet remains high and relative strong mixture stratification is introduced when decreasing the angle interval between the end of fuel injection and ignition timing giving fast burning rates and high thermal efficiencies. The maximum cylinder gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate increase with the advancing of ignition timing. However, these parameters do not vary much with hydrogen addition under specific ignition timing indicating that a small hydrogen fraction addition of less than 20% in the present experiment has little influence on combustion parameters under specific ignition timing. The exhaust HC emission decreases while the exhaust CO₂ concentration increases with the advancing of ignition timing. In the lean combustion condition, the exhaust CO does not vary much with ignition timing. At the same ignition timing, the exhaust HC decreases with hydrogen addition while the exhaust CO and CO₂ do not vary much with hydrogen addition. The exhaust NOx increases with the advancing of ignition timing and the behavior tends to be more obvious at large ignition advance angle. The brake mean effective pressure and the effective thermal efficiency of natural gas/hydrogen mixture combustion increase compared with those of natural gas combustion when the hydrogen fraction is over 10%. __________ Translated from Transactions of CSICE, 2006, 24(5): 394–401 [译自:内燃机学报]     

直喷式柴油机燃烧过程模拟与分析(二)

利用IIVA-Ⅱ程序模拟计算直喷式柴油机燃用柴油时缸内的燃烧过程，如混合气形成过程、缸内温度场、主要有害物质NOx的生成浓度分布等。通过对直喷式柴油机燃用柴油时燃烧过程的模拟计算与分析，对模拟燃用绿色能源-二甲醚的燃烧过程提出了一些建议。     

Experimental study on heat and exergy balance of a dual-fuel combined injection engine with hydrogen and gasoline

In this paper, a dual-fuel engine test rig with gasoline injected in the intake port and gasoline (or hydrogen) injected directly into the cylinder is built up; therefore, two injection models are realized. One is port fuel injection + gasoline direct injection (PFI + GDI), the other is port fuel injection + hydrogen direct injection (PFI + HDI). And the effects of two injection models on heat and exergy balance are investigated experimentally. The results show that, from the perspective of the first law of thermodynamics (heat balance), no matter what the injection mode is, the heat proportion of cooling water is the largest, the exhaust heat ratio and brake power are the second, which two are roughly equivalent, and the uncounted loss is the least. In PFI + GDI mode, the local mixture is too dense due to the increase of mixing ratio, which leads to insufficient combustion and a slight decrease of brake power ratio. However, due to the special characteristics of hydrogen, the increase of direct injection ratio improves the brake power ratio in PFI + HDI mode. Moreover, because of the short quenching distance of hydrogen, the cooling loss rises up with the increase of hydrogen ratio. The engine speed and load also have great impacts on heat distribution, but on account of the different physical and chemical properties between gasoline and hydrogen, resulting in varying degrees of impact and trends. On the basis of the second law of thermodynamics (exergy balance), it is found that no matter what injection mode is, the ratio of exergy destruction is always the highest, accounting for half of the total fuel energy, and the exhaust exergy ratio is lower than the brake power ratio. However, the proportion of exergy contained in cooling water is the smallest, which is quite different from the result of the first law of thermodynamics. The influences of several factors on engine energy balance are analyzed, and the differences and similarities between heat balance and exergy balance are compared. The two analytical methods are interrelated and complementary, and the purpose is to find a reasonable and comprehensive energy balance analysis method for internal combustion engine.     

不同简化机理对高压直喷天然气船机燃烧和排放影响研究

基于三维CFD仿真软件模拟了高压直喷天然气船机的燃烧过程,探讨了四种不同简化程度机理对燃烧和排放的影响规律。结果表明：四种机理均能很好的预测高压直喷天然气船机在不同喷射时刻下的缸压和放热率。四个机理预测的燃烧相位和最高爆发压力随喷射时刻提前或推迟变化趋势一致;预测的不同燃烧相位的温度、当量比和NO_x分布存在较小差异。但35步机理和27步机理预测的碳烟排放比334步机理和250步机理高。整体上,受船机大尺度计算资源高限制,耦合简化的35步和27步机理的CFD模型预测的燃烧参数最大误差小于4.3%,预测的NO_x排放最大误差小于12.0%,能够满足船机工程开发需求。     

气相色谱分析啤酒中风味成分最简单的方法--直接进样法

啤酒样品由于不能完全气化,给啤酒的气相色谱分析带来一定困难。该文采用直接进样法分析啤酒中的主要风味成分,取得了良好的效果。     

高压喷射的高速直喷柴油机混合气形成及燃烧过程

为了有效组织燃烧室内气流特性,改进了车用缩口直喷高速柴油机燃烧室结构,并在此基础上基于CFD商用软件FIRE对匹配不同轨压的喷雾特性时燃烧室内气液混合流的速度场、浓度场和温度场的动态分布特性进行了仿真计算分析。研究了高速直喷柴油机的混合气形成规律,并通过试验研究了这种混合气形成特性对燃烧过程及排放特性的影响。结果表明:通过对缩口直喷燃烧室内气流特性和轨压的优化匹配,可以有效地控制燃烧过程的滞燃期、预混合燃烧比例和扩散燃烧过程,从而控制高温燃烧持续期,在保证经济性的前提下,可以有效地降低NOx和烟度排放。     

Development of a simplified n-heptane/methane model for high-pressure direct-injection natural gas marine engines

High-pressure direct-injection (HPDI) of natu- ral gas is one of the most promising solutions for future ship engines, in which the combustion process is mainly controlled by the chemical kinetics. However, the employment of detailed chemical models for the multi-dimensional combustion simulation is significantly expensive due to the large scale of the marine engine. In the present paper, a reduced n-heptane/methane model consisting of 35-step reactions was constructed using multiple reduction approaches. Then this model was further reduced to include only 27 reactions by utilizing the HyChem (Hybrid Chemistry) method. An overall good agreement with the experimentally measured ignition delay data of both n-heptane and methane for these two reduced models was achieved and reasonable predictions for the measured laminar flame speeds were obtained for the 35-step model. But the 27-step model cannot predict the laminar flame speed very well. In addition, these two reduced models were both able to reproduce the experimentally measured in-cylinder pressure and heat release rate profiles for a HPDI natural gas marine engine, the highest error of predicted combustion phase being 6.5%. However, the engine-out CO emission was over-predicted and the highest error of predicted NO_x emission was less than 12.9%. The predicted distributions of temperature and equivalence ratio by the 35-step and 27-step models are similar to those of the 334-step model. However, the predicted distributions of OH and CH₂O are significantly different from those of the 334-step model. In short, the reduced chemical kinetic models developed provide a high-efficient and dependable method to simulate the characteristics of combustion and emissions in HPDI natural gas marine engines.     

单燃料天然气发动机缸内直喷技术研究

将175F汽油机改造为一台单燃料缸内直喷天然气发动机,并设计了以80C196KC单片机为微处理器的控制系统,探讨了控制电路设计、控制参数匹配及控制策略制定等问题.通过发动机台架试验,检验了控制系统设计及控制方法的有效性,其结果是满意的.用准维双区燃烧模型,以理论计算和实验相结合的方法对燃烧特性进行了研究,揭示天然气燃烧特性,理解燃烧机理,分析了各种结构参数、运行参数对发动机性能的影响,预测发动机参数变化后各性能参数的变化规律,减少试验工作量,为发动机研制开发提供指导.     

生物柴油应用研究

在一台小型直喷单缸柴油机上进行了黄连木生物柴油和麻风树生物柴油的性能和排放试验,探讨了传统柴油机燃用生物柴油的可行性以及生物燃料对柴油机性能和排放的影响。试验结果表明,采用生物柴油后燃油消耗率略高于0^#柴油,但CO,HC,NOx排放均有一定程度的降低,并能有效降低碳烟排放,在大负荷时效果尤为显著。     

基于MATLAB/SIMULINK的柴油转子发动机性能模拟研究

在理论分析的基础上选择了数学模型,基于MATLAB/SLMULINK建立了仿真模型.并利用DZ270双缸柴油转子发动机的实验数据进行校准,通过仿真计算比较,三种工况下缸内压力的预测值和试验值的平均误差均在2%以内,满足工程应用要求;本模型易用于其它机型的仿真.