火花点火天然气掺氢发动机结合EGR时的循环变动规律

在火花点火式天然气掺氢发动机上,开展天然气掺氢结合EGR时发动机循环变动的试验研究,分析了不同EGR率和掺氢比时发动机燃烧循环变动规律.结果表明,对于给定的燃料,随EGR率的增加,缸内最高压力和最大压力升高率下降,循环变动增加,缸内最高压力和最大压力升高率与其对应的曲轴转角之间的相关性减弱.平均指示压力下降且分布趋于分...     

车用发动机燃用天然气掺氢燃料的性能计算分析与研究

为了研究天然气掺氢发动机的燃烧特性,从模拟试验的角度运用大型发动机软件建立了6缸火花点火天然气掺氢发动机的虚拟样机,并经过试验验证该模型基本准确.通过仿真计算得出,天然气发动机在掺入氢气之后,提高了燃烧速度,明显拓宽了发动机的稀燃极限.在掺入氢气30 %(体积百分比)时,发动机的综合性能指标较好;提高压缩比,指示热效率得到提高.     

氢燃料发动机燃烧过程模拟与分析

在分析氢作为内燃机燃料特性的基础上,针对氢气与空气的混合与燃烧过程的空间分布特性比汽油均匀的特点,提出并建立了单区模型对氢燃料发动机燃烧过程进行模拟与分析.结果显示,缸内压力与放热率的计算值与试验值相对误差在3%以内,曲线形态吻合度较高.较好地反映出实际的燃烧情况.表明采用单区模型进行氢燃料发动机燃烧过程的模拟与分析能够保证较高的准确性,进一步分析了点火提前角、当量比对燃烧过程的影响,结果表明它们对燃烧过程有较大影响.因此,控制点火提前角、当量比是调整与改善氢发动机性能的重要手段.     

预燃室式天然气掺氢发动机燃烧及排放模拟

为探索掺氢对预燃室式大功率中速天然气发动机燃烧和排放的影响,采用计算流体动力学耦合化学动力学方法,在一台6ACD320型天然气发动机上,对氢气体积分数为0~30%的天然气-氢气混合燃料的燃烧过程进行了数值模拟.结果表明:在天然气中掺氢促使缸内产生了更多的O、OH等活性自由基,从而加速了缸内火焰传播,发动机的指示燃气消耗率下降、指示热效率提高,CO、THC和非甲烷碳氢化合物(NHMC)排放下降,NOx排放上升.对于预燃室式发动机,掺氢增加缸内火焰传播速率的效应主要体现在燃烧过程的后半段,而前半段燃烧过程中,预燃室射流对缸内混合气的湍流激扰效应对缸内湍流燃烧速率起着主导性的作用.综合比较,采用10%的掺氢比对发动机性能和排放较为有利.     

点燃式HCNG发动机一维数值模拟研究

利用AVL BOOST软件建立天然气掺氢(HCNG)发动机的整机工作过程一维模拟模型,通过与试验结果对比,证明了模型的适用性和准确性.并对HCNG发动机进行了一系列的变参数分析研究,主要变化参数包括体积掺氢比、负荷、压缩比及配气相位.模拟计算结果表明:提高掺氢比和负荷可提高缸内燃烧温度,使传热损失和NOx排放增加;提高压缩比有利发动机的动力性和经济性;进气迟闭角和排气提前角相位对发动机的动力性和经济性有较大影响.     

沼气掺氢发动机燃烧稳定性试验

在一台单缸火花点火发动机上开展了燃用不同组分配比的沼气模拟气体的掺氢混合气的燃烧稳定性试验研究.研究结果表明:在15%～35%的掺氢比范嗣内,随着混合气中掺氢比的增加,发动机循环变动变小,燃烧稳定性提高.掺氢导致平均指示压力的循环变动系数减小,燃烧放热率加快,火焰发展期缩短.其中35%掺氢比的混合气比15%掺氢比的混合...     

不同点火提前角时HCNG发动机的燃烧与排放特性

在一台火花点火天然气发动机上开展了在不同点火提前角下燃用不同体积掺氢比(O%～50%)的天然气掺氢燃料(HCNG)的试验研究,进行热效率、燃烧放热率、循环变动及排放特性的分析.结果表明:与原天然气发动机相比,HCNG发动机的最大扭矩点火提前角(MB了)减小,MBT时指示热效率变化不大;点火提前角增大时,火焰发展期增长,最大压力变动率减小,快速燃烧期和平均指示压力变动率先减小后增大;在相同点火提前角时,以上4个参数均随掺氢比的增加而减小.N0x、CO排放浓度随掺氢比增加而增大,CH4排放則相反.     

天然气发动机掺氢燃烧的探讨

根据氢气、天然气和天然气掺氢燃烧的一些特性，结合世界各国对天然气掺氢燃烧在发动机上应用的研究状况。探讨天然气发动机掺氢燃烧应用的前途和可行性。     

火花点火发动机燃用天然气掺氢混合燃料循环变动研究

在火花点火天然气发动机上开展了不同掺氢比天然气掺氢混合燃料(氢气在混合燃料中的体积分数为0%、12%、23%、30%和40%)循环变动的试验研究,试验工况点对应于发动机中低负荷.分析了掺混氢气对天然气发动机循环变动的影响.研究结果表明:在稀燃条件下,随着掺氧比的增加,缸内最高压力、最大压力升高率以及平均指示压力均增加.随着掺氢比增加,缸内最高压力与其对应的曲轴转角之间和最大压力升高率与其对应的曲轴转角之间的相关性更强.在化学计量比或浓燃时,掺混氢气可以维持平均指示压力的循环变动系数在较低的水平.在稀燃时,平均指示压力的循环变动系数随掺氢比增加而降低.平均指示压力的循环变动系数达到10%所对应的过量空气系数随掺氢比增加而增加,表明天然气掺混氢气扩展了天然气发动机的稳定稀燃极限.     

不同掺氢比的HCNG燃料对天然气发动机怠速性能影响研究

为了研究在天然气中掺入不同体积比氢气对发动机怠速性能的影响,针对一台6缸天然气发动机开展了不同体积掺氢比的氢气/天然气混合燃料(HCNG)的怠速性能试验研究.试验证实掺氢后热效率提高,要达到相同的怠速转速可减少怠速旁通阀开度;在怠速情况下,掺氢使CH4、CO、NMHC排放下降,Nox排放上升,可通过点火提前角推迟来有效降低怠速Nox排放;在天然气中掺入适量氢气后有利于改善发动机怠速燃烧,从而增加怠速稳定性.在怠速条件下,掺氢后CO、CH4排放随转速升高先减小后增加;怠速转速升高,怠速稳定性变好.在天然气中掺入适量氢气后,发动机热效率提高,经济性改善.     

Zero-dimensional single zone engine modeling of an SI engine fuelled with methane and methane-hydrogen blend using single and double Wiebe Function: A comparative study

Combustion modeling plays a key role in an engine simulation to predict in-cylinder pressure development and engine performance with a high level accuracy. Wiebe function, representing mass fraction burned (MFB) as a function of crank angle position, is widely used to predict the combustion process. The work presents a predictive zero-dimensional (Zero-D) single zone engine modeling of an SI engine fuelled with methane and methane-hydrogen blend. In this work, the single and double forms of Wiebe function were used to estimate the combustion process in the modeling. For this purpose, the single and double-Wiebe functions' parameters were calculated using the least squares method by fitting to the MFB curves calculated from experimental pressure data. These Wiebe functions were, then, introduced to the Zero-D single zone engine model developed for the methane and methane-hydrogen blend fueled SI engine to obtain in-cylinder pressure development and gross indicated mean effective pressure (GIMEP) for the engine performance prediction. The results show that the model with double-Wiebe Function fit better than that with single-Wiebe function. In addition, the fitted double-Wiebe function has a significant improvement in the GIMEP prediction for methane-hydrogen blend fueled SI engine modeling rather than the methane-fueled modeling.     

Evaluation mass fraction burned obtained from the ion current signal fuelled with hydrogen/carbon dioxide and natural gas

The mass fraction burned (MFB) of the gas mixture in combustion process as the function of the combustion duration time, reflects the percentage of fuel consumed at the every moment in the combustion process, and is an important factor for analysing of the fuel combustion performance, and it has high engineering value for evaluating engine design parameters and operating performance and for improving the combustion process in-cylinder combustion process. The ion current signal directly originated from the fuel combustion process in the cylinder, and contained much information about the combustion process; the MFB of fuel in combustion process can be obtained based on the correlation between the MFB and ion current signal. In this paper, the ion current method is constructed to calculate the MFB of fuel in combustion process under different initial conditions (initial pressure from 1 bar to 3 bar, equivalence ratio from 0.8 to 1.2, hydrogen mass fraction from 0% to 10%, and CO₂ dilution ratio from 0% to 10%), the method based on the waveform parameters of ion current signal for obtaining the efficiency factor and the form factor of Wiebe function, and further to slove the mass fraction burned of combustion process. The mass fraction burned is obtained through ion current method reduced assumptions error and improved the calculation accuracy compared with the well-known Rassweiler–Withrow method, and the ion current method has an advantage that not requires an high-cost sensor and some rather complex measuring instruments. The ion current method is a simple but powerful calculation model that provide a new technical path for analysing and online obtaining the MFB of fuel in combustion process.     

利用离子信号计算已燃质量分数

在定容燃烧弹中分别用离子信号和压力对已燃质量分数进行了研究,通过对点火电极附近离子信号的研究表明,其信号分别在点火、火焰前锋与后区中存在3个峰值。利用从点火到达火焰前锋与后区两个峰值的时间间隔以及所测量的压力值分别计算了已燃质量分数,其结果表明,两方法所计算出的已燃质量分数比较一致,当相对空燃比等于1时,已燃质量分数曲线较为陡峭;而当其偏离1时,曲线逐渐平坦,并且起始位置也愈加滞后,选取系数为0.98的计算结果表明,当相对空燃比在0.9～1.1附近时,两者计算结果的最大差值小于10%。     

柴油机排气中可溶性有机物排放的特性

通过柴油机台架试验,在一款柴油机上加装氧化型催化转化器(DOC)装置,研究了DOC前/后排气颗粒物中可溶性有机物(SOF)和固相多环芳烃(PAHs)的变化趋势,分析了不同转速和负荷对SOF及PAHs排放的影响以及排气中SOF及PAHs排放在排气过程中的变化规律.结果表明:DOC能明显降低排气中SOF及PAHs排放,SOF最高减排为50.69%,PAHs最高减排为83.28%,同时PAHs的毒性当量最高降低为49.31%.随着柴油机转速增加,燃烧过程后燃增加,排气中SOF及PAHs有增加的趋势,而随负荷的增加,缸内燃烧温度升高,各成分氧化速率加快使得SOF及PAHs排量逐渐降低.随排气输运距离增加,排气组分冷凝现象加重致使SOF及PAHs排量明显升高.     

Double-Wiebe function: An approach for single-zone HCCI engine modeling

Single-zone Wiebe-function HCCI combustion models tend to over-predict the peak cylinder pressure. The over-prediction arises because it is not possible for the standard Wiebe function to fully match both the slower combustion (i.e. the large spread of autoignition times) that occurs in the cooler boundary regions adjacent to the walls and the faster combustion (small spread of autoignition times) in the hot core. The slower combustion by the wall is commonly modeled with a multi-zone approach. The aim of this work was to improve the ability of a single-zone model to predict cylinder pressure without introducing a separate wall zone. This was accomplished by using, within a single zone, a double-Wiebe function combustion model in which most of the fuel burns as usual but a minor fraction (typically 10–20%) burns at a reduced rate. In the present article, cylinder pressure traces predicted by using both standard and double-Wiebe functions are compared to experimental pressure traces obtained from a Ricardo Hydra HCCI engine. The best agreement with the experiments was obtained by using double-Wiebe function approach.     

循环流化床燃烧室密相区燃烧份额计算的数学模型

建立了基于热平衡法、烟气分析法和烟气量法的循环流化床锅炉燃烧室密相区燃烧份额计算数学模型，并分析比较了各种模型的特点。在对1台65t／h油页岩循环流化床锅炉测试的基础上，应用所建立的计算模型对该炉密相区燃烧份额进行了计算。图3参7     

生物柴油掺烧率对非道路用柴油机燃烧循环变动特性的影响

针对非道路用186FA柴油机掺烧生物柴油燃烧循环变动情况,进行了燃用不同生物柴油掺烧率的试验.根据实测示功图对主要燃烧参数进行了循环变动分析.结果表明:随着生物柴油的掺烧,燃烧始点提前,放热率峰值减小;平均指示压力(pmi)、缸内压力峰值(pmax)、放热率峰值循环变动系数(COV)呈减小的趋势,而其对应相位波动比纯柴油大;最大压力升高率在中低负荷时循环变动显著;平均指示压力与缸内压力峰值和放热率峰值都有很好的对应关系.     

分隔室压燃式天然气发动机燃烧过程变参数多维模拟计算

利用详细的化学动力学机理与CFD多维数值模拟计算软件,对分隔室压燃式天然气发动机的着火及燃烧过程进行了变参数模拟研究。研究的参数包括：喷气时刻、进气终了温度、天然气成分。模拟内容有：着火时刻、缸内平均压力、NO质量分数。结果表明,喷气提前使最高温度压力增加,NO排放增加;提高进气终了温度可以改善着火性能;天然气中乙烷含量增加可以改善着火性能,同时使最高温度压力增加,NO排放增加。     

Availability analysis of n-heptane and natural gas blends combustion in HCCI engines

One of the major problems associated with HCCI combustion engine application is lack of direct control for combustion timing. A proposed solution for combustion timing control is using a binary fuel blend in which two fuels with different auto-ignition characteristics are blended at various ratios on a cycle-by-cycle basis.The aim of this research is to investigate the exergy analysis of HCCI combustion when a blended fuel, which consists of n-heptane and natural gas, is used. In order to accomplish this task, a single-zone combustion model has been developed, which performs combustion computations using a complete chemical kinetics mechanism.The study was carried out with different percentages of natural gas in blended fuels and EGR (exhaust gas recirculation) ranging from about 45 to 85 percent and 0 to 40 percent, respectively. The results reveal that, when mass percentage of natural gas increases, exergy destruction is decreased increasing the second-law efficiency. Introducing EGR into the intake charge of dual fuel HCCI engine up to some stage (optimum value) enhances the second-law performance of the engine in spite of a reduction in work.     

Experimental study on combustion characteristics of a spark-ignition engine fueled with natural gas–hydrogen blends combining with EGR

An experimental study on the effect of hydrogen fraction and EGR rate on the combustion characteristics of a spark-ignition engine fueled with natural gas–hydrogen blends was investigated. The results show that flame development duration, rapid combustion duration and total combustion duration are increased with the increase of EGR rate and decreased with the increase of hydrogen fraction in the blends. Hydrogen addition shows larger influence on flame development duration than that on rapid combustion duration. The coefficient of variation of the indicated mean effective pressure increases with the increase of EGR rate. And hydrogen addition into natural gas decreases the coefficient of variation of the indicated mean effective pressure, and this effectiveness becomes more obviously at high EGR rate. Engine fueled with natural gas–hydrogen blends combining with proper EGR rate can realize the stable low temperature combustion in gas engine.