Three-Dimensional Models Variations in a Lean for Analyzing the Cyclic Burn CNG Engine

Three-dimensional models, consisting of the flame kernel formation model, flame kernel development model and natural gas single step reaction model, are used to analyze the contribution of cyclic equivalence ratio variations to cyclic variations in the compressed natural gas （CNG） lean burn spark ignition engine. Computational results including the contributions of equivalence ratio cyclic variations to each combustion stage and effects of engine speed to the extent of combustion variations are discussed. It is concluded that the equivalence ratio variations affect mostly the main stage of combustion and hardly influence initial kernel development stage.     

甲烷/空气预混合气在定容燃烧室内的燃烧试验

为研究进气温度、进气压力、当量燃烧比、射流引燃、压燃(自燃)等对甲烷燃烧的影响,以提高点燃式天然气发动机的性能,在定容燃烧室(CVCC)内进行甲烷/空气预混合气的燃烧试验,通过火焰高速摄影和气体压力测量等手段,获取试验结果并进行分析.试验发现,在燃烧室内安装带通孔的横隔板后,有利于加快火焰传播速度、提高燃烧峰值压力和燃烧的稳定性,在某些试验条件下,下燃烧室会出现混合气压燃(自燃)现象.     

火花点火发动机运行参数对其循环变动的影响——建模和仿真

基于循环间变动的排气温度建立了一个发动机循环变动模型. 在这个模型中,第n个循环的排气温度作为模型的输入,通过定压进气过程、绝热压缩过程、定容燃烧过程、绝热膨胀过程、定容放热过程和定压排气过程来近似汽缸内的热力学过程,最后得出第n+1个循环的排气温度. 由于把发动机运行参数,如转速、点火角、计量比、进气压力和进气温度等加入该模型,可定量地估计这些参数对发动机循环变动的影响. 因为循环间排气温度的波动反映了循环变动程度,对排气温度影响最敏感的参数最可能被用于循环变动控制. 模型仿真结果表明,对于接近化学计量比的混合气,循环变动不明显,对于稀薄混合气,在部分负荷和较大点火角的情况下,循环变动以混沌或分岔的形式出现.     

燃烧室形状对天然气发动机缸内流动和燃烧过程的影响

结合4102低排放天然气发动机的开发,应用FIRE软件对4102发动机原燃烧室和2种新的燃烧室设计方案(楔形和弧形燃烧室)进行了建模和仿真计算,对比分析了燃烧室形状对缸内流动和燃烧过程的影响。结果表明,弧形燃烧室效果最好,与原燃烧室相比,在点火时火花塞附近气流速度低,初期火焰核心稳定,火焰传播速度快,燃烧持续期短,缸内最高压力比原始燃烧室提高12.7%,有利于提高天然气发动机性能。     

基于超声雾化的柴油/汽油混合燃料液滴群燃烧特性

利用超声雾化多液滴制备系统,制成了柴油/汽油混合燃料多液滴群,其中液滴直径、液滴浓度、液滴速度等参数均可独立调节,以模拟内燃机缸内喷雾的实际流动及其与空气的混合状态。将该多液滴群引入可控活化热氛围燃烧器中,并对其稳定燃烧后的燃烧特性进行了研究。结果表明:改变混合燃料掺混比、燃料进给速度、空气流量等参数后,多液滴群自燃火焰形状随之发生显著改变,随着燃料中柴油所占比例的增大,火焰起升高度增加,火焰宽度减小;燃料进给速度和空气流量的改变,影响了混合燃料的燃空当量比及中央射流出口速度,进而影响到燃料的燃烧特性。     

二级环流对双级贫预混火焰熄火边界的影响

为改善预混火焰的燃烧稳定性,提出双级贫预混燃烧的火焰组织思路,对预混气流进行不同当量比的径向分级,使其能在较低当量比时稳定燃烧.以一定流动条件下直管射流火焰和双级贫预混火焰的中心气流所能达到的最小稳燃当量比作为熄火边界,实验测量并分析火焰不同组织方式和环流条件变化对熄火边界的影响.结果表明:布置在射流火焰外围的环流对火焰根部附近的浓度和速度分布有一定影响;双级贫预混火焰的二级预混环流能够通过减弱外界环境气氛对锋面前预混气的稀释作用而拓宽火焰的熄火边界;环流的预混当量比是影响火焰熄火边界的关键.与均一当量比的直管射流火焰相比,双级贫预混火焰能够在更低的当量比条件下稳定燃烧,对工业上控制NOx排放有着重要的意义.     

天然气组分变化对内燃机燃烧及排放特性的影响

根据我国天然气组分变化的情况,研究了天然气组分变化时,燃料的低热值、理论空燃比和燃烧热的变化,由计算、试验结果讨论了在过量空气系数为1时火焰绝热温度、CO2、CO和NOx排放特性随H／C比的变化,并分析了天然气中的乙烷、丙烷、丁烷、N2、CO2和H2含量的变化对华白数和燃烧势的影响．同时将分析的结果与我国的汽车用压缩天然气标准中的技术要求进行了对比,发现了一些有趣的现象．     

掺氢汽油机燃烧过程的准维模型构建

为研究不同工况下掺氢汽油机燃烧特性,构建并验证了用于计算掺氢汽油机缸内燃烧过程的准维模型.模型基于理想气体状态方程、质量守恒方程、热力学第一定律,建立双区热力学微分方程组,通过湍流卷吸模型确定燃烧放热率,通过掺氢汽油层流火焰速率关联式反映掺氢对混合气火焰特征的影响规律,并利用MATLAB数值分析软件完成方程组的求解过程.结合内燃机台架试验,对不同掺氢体积分数、混合气当量比、进气道压力条件下模型的准确性进行了验证.对比结果表明,该模型能准确地反映不同运行条件下掺氢汽油机的燃烧特性.     

Characteristic of rich-mixture ignition kernel driven by nanosecond repetitive pulsed discharge

Plasma-assisted ignition is a promising technology to improve engine performance. Nanosecond repetitive pulsed discharge is widely used in plasma-assisted ignition owing to its chemical activations and thermal and hydrodynamic expansions. However, the influence of ultrafast heating and hydrodynamic effects on the development of the rich-mixture ignition kernel is largely unknown. The present study aims to illustrate these effects using electrical and schlieren measurement. The number and the frequency of discharge pulses are exactly controlled to establish the relationship among the discharge energy, frequency, and rich-mixture ignition-kernel characteristics. The evolution of the ignition kernel in the early stage is mainly dominated by the discharge energy and frequency, i.e., a greater energy and a higher frequency yield a larger ignition kernel. Moreover, the influence of both the energy and frequency on the ignition kernel gradually disappears as the ignition kernel develops. According to the experimental data and theoretical analysis, the calculated laminar burning velocity is 0.319 m/s with a Markstein length of 13.43±0.11 cm when the voltage is 5.9 k V, the frequency is 3 k Hz, and the equivalence ratio is 1.3. This result indicates that the rich-mixture flame is stable in the early stage of ignition.     

Combustion Characteristics of a Single Cylinder Spark Ignition Engine Fueled with Coal Mine Methane

An experimental investigation was conducted on combustion characteristics of a single cylinder spark ignition engine fueled with coal-mine methane (CMM). The CMM was simulated by the compressed nature gas (CNG)/nitrogen blend fuels. The cylinder pressure was measured. The maximum heat release ratio, the flame development duration and the main combustion duration were analyzed with the nitrogen volume fraction in the blends changing from 0% to 35%. The results indicate that the maximum cylinder pressure, the maximum rate of pressure, the flame development duration and the main combustion duration increase and the maximum rate of heat release decreases with increasing nitrogen fraction. When the level of nitrogen volume fraction in coal-mine methane is lower than 20%, the combustion process of engine is stable. But with the level of nitrogen volume fraction over 30%, the cycle to cycle combustion variation is large, especially under low load condition.     

Effects of H_2/CO/CH_4 syngas composition variation on the NO_x and CO emission characteristics in a partially-premixed gas turbine combustor

This paper reports the effects of variations in the fuel composition of H_2/CO/CH_4 syngas on the characteristics of NO_x and CO emissions in a partially-premixed gas turbine combustor. Combustion tests were conducted on a full range of fuel compositions by varying each component gas from 0% to 100% at heat inputs of 40 and 50 k Wth. Flame temperature, combustor liner temperature, ignition delay time, and flame structure were investigated computationally and experimentally to judge whether they are significant indicators of NO_x and CO formation. The characteristics of and reasons for NO_x and CO emissions were investigated by analyzing the emission mechanisms and relationships among fuel property, equivalence ratio, flame temperature, liner temperature, flame shape. The flame structures were investigated using the following flame visualization methods:(1) time-averaged OH* chemiluminescence and its Abel-deconvolution;(2) direct photography; and(3) instantaneous OH-PLIF. The flame structures were greatly changed by the fuel composition and heat input, and they were subjected to key affecting parameters of the temperatures of the flames and the liners. NO_x and CO emissions also largely varied according to fuel composition and heat input, showing neither linearly nor exponentially clear proportional trends toward the syngas compositions because of the singular conditions. For example, only the 100% CO flame at low load emitted lots of CO, whereas complete combustion was observed in other cases. However, the qualitative observations showed that the root causes of NO_x emission behaviors were flame temperature and flame structure, which were directly related to the residence time in the flame. Various sets of practical test results were obtained, and these results could contribute to the optimal selection of the fuel-feeding condition when fuel is changed from natural gas to syngas in order to minimize NO_x and CO emissions with stable combustion.     

臭氧对甲烷/空气层流火焰传播速度影响规律

为提高气体机稀薄燃烧时的燃烧性能,解决天然气发动机在稀薄燃烧情况下点火能量高以及火焰传播速度慢的问题,利用强氧化性的臭氧对燃料进行改质,进而提高天然气燃烧性能。通过Chemkin软件研究臭氧添加对甲烷层流火焰传播速度的影响,并对臭氧助燃的化学机理进行数值分析。试验结果表明:添加臭氧后,层流火焰传播速度增加,在稀薄混合气条件下增加量更明显。在不同温度及压力条件下,掺加臭氧均能增加层流火焰传播速度,最大可增加36%。分析表明:掺加臭氧能明显提升自由基及中间产物的生成量,进而提高甲烷层流火焰传播速度。     

甲烷HCCI燃烧反应机理简化与分析

通过分析系统温度变化与主要中间产物生成率,以敏感度分析为基础对GRI-MECH3.0机理进行简化,最后得出一个包含25种组分、36个反应的简化机理。此简化机理适用于天然气HCCI模式燃烧着火相位研究,与详细机理在着火点预测上吻合良好。经验证,在较广的初始压力、温度、转速、压缩比、空燃比变动范围内可以保证与详细机理相近的精度。同时在简化过程中梳理出着火延迟期的关键反应。     

Numerical and experimental investigation on emission performance of a fuel staged combustor

The low NOx emission technology has become an important feature of advanced aviation engine.A wide range of applications attempt to take advantage of the fact that staged combustion under lean-premixed-prevaporized(LPP)conditions can significantly cut down emission and improve combustion efficiency.This paper proposes a scheme with fuel centrally staged and multi-point injection.The mixing of fuel and air is improved,and the flame temperature is relative low in combustion zone,minimizing the formation of nitrogen oxides(NOx),especially thermal NOx.In terms of the field distribution of equivalence ratio and temperature obtained from Computational Fluid Dynamics(CFD),a chemical reactor network(CRN),including several different ideal reactor,namely perfectly stirred reactor(PSR)and plug flow reactor(PFR),is constructed to simulate the combustion process and predict pollution emission.The influences of the pilot equivalence ratio and percentage of pilot/main fuel on NOx and carbon monoxide(CO)emission were investigated by CRN model.The effects of the pilot fuel and primary fuel on pollution emission were investigated experimentally.Finally,the effects of pilot equivalence ratio and pilot fuel proportion on NOx emission were discussed in detail by comparing predict of CRN and experimental results.     

燃烧室结构对XN2100双燃料发动机性能的影响

对一台XN2100柴油一天然气双燃料发动机采用了三种燃烧室结构进行性能对比试验,并采集示功图,进行燃烧放热规律的计算和分析.结果表明,燃烧室形状和压缩比对双燃料发动机的燃烧压力、压力升高率、燃烧放热率的影响较大,燃烧室适当缩口和压缩比适当增大对双燃料发动机的燃烧过程有利,能够提高天然气的替代率,改善双燃料发动机的性能.     

微燃烧稳定性分析和微细管道燃烧实验研究

为了研究微尺度下的燃烧特性，在考虑散热和熄火距离影响的基础上建立了二维火焰燃烧模型，模型表明在微尺度燃烧中容易发生熄火和吹熄，不容易发生回火.同时在2 mm内径的微细T型管道中通入了氢气和空气的预混气体进行预混燃烧实验，测试了燃烧的火焰温度、流量和燃烧效率的关系.实验结果表明，采用T型管道有利于维持火焰的稳定，不容易被吹熄，但在氢气或空气流量小时容易发生熄火；低流速下，燃烧效率较高，可以完全反应，高流速下，混合气来不及在管道内反应，燃烧效率较低.无论流速的高低，在化学计量比附近燃烧效率较高.     

NOx emission characteristics of hydrogen internal combustion engine

In order to investigate the NOxemission of hydrogen internal combustion engines.A test system for four-cylinder intake port-fuel-injection hydrogen internal combustion engine(H2ICE)is established to study the effect of fuel-air equivalence ratio,ignition advance angle,engine speed and exhaust gas recirculation on NOx emission.Experimental results show that the fuel-air equivalence ratio is the key factor to NOxemission,NOxemission concentration is always higher than 8 000×10-6 when the fuel-air equivalence ratio is larger than 0.8and lower than 500×10-6 when the fuel-air equivalence ratio is smaller than 0.5.The ignition advance angle and engine speed also play important roles on NOxemission formation.EGR is an useful method to reduce NOx emission concentration at large fuel-air equivalence ratio especially when engine speed is low and EGR ratio is high.     

甲烷空气混合气在定容燃烧弹内的射流引燃

提出一种适用于气体燃料燃烧的横隔板式定容燃烧弹系统,在此系统中进行了甲烷空气射流引燃的实验研究.通过对压力曲线及火焰传播纹影图片进行分析,探究孔径、初始压力和当量比等初始条件对射流引燃过程的影响.研究结果表明,一定范围内,增大孔径可以提高甲烷燃烧速率;随着当量比的增加,压力峰值升高并且对应出现时刻提前;在不同当量比和孔径下,初始压力增大,压力峰值随之增加.     

缸内燃烧光电测量的可视化技术

利用光纤传感器对内燃机缸内燃烧进行了探测 ,并与以往常规压力传感器的测量结果进行了比较 ,探索了将光纤传感技术应用于燃烧测量的可行性。利用光强信号可实现同步探测燃烧过程的燃烧时刻、爆震燃烧、循环稳定性、火焰传播及成分分析等多项燃烧特征。图像光纤传感器是未来普及与实现燃烧深层次研究的有效手段。燃烧可视化对燃烧过程测量具有重要意义。     

Numerical investigations on effects of bluff body in flat plate micro thermo photovoltaic combustor with sudden expansion

In order to reveal combustion characteristics of H_2/air mixture in a micro-combustor with and without bluff body, the effects of inlet velocities, equivalence ratios and bluff body's blockage ratios on the temperature field, pressure of the combustor wall, combustion efficiency and blow-off limit were investigated. The numerical results indicate that the sudden expansion plate micro combustor with bluff body could enhance the turbulent disturbance of the mixed gas in the combustion chamber and the combustion condition is improved. Moreover, a low-speed and high temperature recirculation region was formed between the sudden expansion step and the bluff body so that the high and uniform wall temperature(1000 K) could be gotten. As a result, it could strengthen the mixing process, prolong the residence time of gas, control the flame position effectively and widen the operation range by the synergistic effect of the bluff body and steps. When the blockage ratio ranged from 0.3 to 0.6, it could be found that the bluff body could play a stabilizing effect and expand combustion blow burning limit, and combustion efficiency firstly was increased with the inlet velocity and equivalence ratio, and then was decreased.