Multidimensional CFD simulation of syngas combustion in a micro-pilot-ignited dual-fuel engine using a constructed chemical kinetics mechanism

A multidimensional computational fluid dynamics (CFD) simulation of a constructed syngas chemical kinetic mechanism was performed to evaluate the combustion of syngas in a supercharged dual-fuel engine for various syngas initial compositions under lean conditions. The modelled results were validated by comparing predictions against corresponding experimental data for a supercharged dual-fuel engine. The predicted and measured in-cylinder pressure, temperature, and rate of heat release (ROHR) data were in good agreement. The effect of the hydrogen peroxide chain-propagation reaction on the progress of combustion under supercharged conditions was examined for different types of syngas using various initial H₂ concentrations. The effect of the main syngas kinetic mechanism reactions on the combustion progress was analysed in terms of their contribution to the total heat of the reaction. The best results compared with experimental data were obtained in the range of equivalence ratios below about 0.8 for all types of syngas considered in this paper. As the equivalence ratio increased above 0.8, the results deviated from the experiment data. The spatial distribution of the in-cylinder temperature and OH^∗ within this equivalence-ratio range showed the completeness of the combustion. The present CFD model captured the overall combustion process well and could be further developed into a useful tool for syngas-engine combustion simulations.     

进气管结构对天然气发动机废气再循环率均匀性的影响

针对某国Ⅵ天然气发动机各缸燃烧一致性差异过大的问题,利用计算流体力学(CFD)软件STAR-CCM+对该发动机的进气管路开展废气再循环(exhaust gas recirculation,EGR)率均匀性分析,发现第1缸～第3缸的EGR率高于第4缸～第6缸,1 200r/min全负荷工况EGR率相对偏差为-29.9%～34.2%。分析表明,EGR的引出方式为第1缸～第3缸单侧取气,导致EGR进气入口存在较大波动,是造成各缸EGR率分配不均的主要原因。从降低管路内EGR废气波动的角度提出了两种进气管路优化方案,使EGR废气在进入稳压腔之前得到了充分混合,各缸EGR率均匀性得到明显提高,EGR率相对偏差在±5%以内。     

预燃室通道直径和形状对低速天然气双燃料发动机爆震的影响

基于三维数值仿真模拟研究了预燃室与主燃室之间通道直径及扩口型和缩口型等通道形状对发动机爆震的影响。研究结果表明:在爆震工况下,预燃室的通道直径越小则火焰射流冲击所引起的压力差越小,从而降低火焰面放热进一步产生的压力差增强效果,最终降低爆震强度。扩口型预燃室通道会减小初始压力差的强度,但是会产生火焰射流持续喷向主燃室的现象,该现象会持续增加压力差的强度,最终提高爆震强度。相反,缩口型预燃室通道可以减少这一现象的发生从而减轻爆震强度。     

基于GT-suite的0483天然气发动机凸轮型线设计及配气性能模拟开发

基于高次方多项式凸轮型线设计原理及方法,采用VT-design模块对0483天然气发动机凸轮型线进行全新设计。在此凸轮型线的基础上,对整个配气机构运动学、动力学进行模拟;采用GT-power模块对整机性能进行一维模拟,得出缸压及充气效率等参数。试验验证表明:模拟结果和试验结果偏差较小;模拟的可靠度较高,且具有成本低、开发周期短、效果好等特点。     

GP210稀燃天然气发动机缸内流动与燃烧模拟分析

基于流动、传热、化学反应及湍流燃烧分析,对GP210稀燃天然气发动机进行了三维流动与燃烧模拟计算。模拟计算结果和试验数据的比较显示:二者偏差在5%以内,表明模拟计算较准确可靠。对模拟计算结果进行分析,提出了该机型缸内气体流动及燃烧的优化方向,为后续提高效率、降低排放提供了理论依据。     

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0、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...     

Hydrogen production from thermal decomposition of ammonia-contaminated acid gas using a detailed reaction mechanism

The increase in the production of acid gas consisting of H₂S, CO₂, and associated impurities such as ammonia and hydrocarbons from oil and gas plants and gasification facilities has stimulated the interest in the development of alternative means of acid gas utilization to produce hydrogen and sulfur, simultaneously. The present literature lacks a detailed reaction mechanism that can reliably predict the thermal destruction of NH₃ and its blend with H₂S and CO₂ to facilitate process optimization and commercialization. In this paper, a detailed mechanism of NH₃ pyrolysis is developed and is merged with the reactions of NH₃ oxidation and H₂S/CO₂ thermal decomposition from our previous works. The mechanism is validated successfully using different sets of experimental data on the pyrolysis and oxidation of NH₃, H₂S, and CO₂. The proposed mechanism predicts the experimental data on NH₃ pyrolysis remarkably better than the existing mechanisms in the literature. The mechanism is used to investigate the effects of NH₃ concentration (0–20%) and reactor temperature (1000–1800 K) on the thermal decomposition of H₂S and CO₂. A synergistic effect is observed in the simultaneous decomposition of NH₃ and CO₂, i.e., NH₃ conversion is improved in the presence of CO₂ and the decomposition CO₂ to CO is enhanced in the presence of NH₃. The presence of H₂S suppressed NH₃ conversion, while the conversion of H₂S remained unchanged with increasing NH₃ concentration at temperature below 1400 K due to the low conversion of NH₃ (up to 18%). At temperature above 1400 K, NH₃ conversion increased rapidly and it triggered a decrease in H₂S conversion as well as the yields of H₂ and S₂. The major reactions involved in the decomposition of H₂S, CO₂, and NH₃ and the production of major products such as H₂, S₂, and CO are identified. The detailed reaction mechanism can facilitate the design and optimization of acid gas thermal decomposition to produce hydrogen and sulfur, simultaneously.     

高涡流比对低速双燃料船舶发动机天然气/空气混合及燃烧性能的影响

以X92DF超大缸径低速二冲程双燃料船用发动机为研究对象,基于三维数值计算分析了天然气和空气混合过程及燃烧特性,并研究了扫气和燃烧过程中缸内涡流强度对混合质量和火焰传播的影响。结果表明：由于上止点前缸内天然气和空气的混合气浓度分布不均,造成局部高浓度区域出现燃烧异常现象,导致缸内压力振荡幅度增大。通过分析不同涡流强度对缸内天然气/空气的混合质量的影响可以得出,随着扫气过程中涡流强度的增大,上止点前缸内天然气高浓度区域面积明显减小,表明天然气和空气的混合质量得到明显提高。同时,随着缸内涡流比的增加,加快了预燃室射流火焰在主燃烧室内的传播速度和缸内天然气的燃烧速度。进一步研究得出缸内混合质量的提高可以有效地避免局部异常燃烧现象和降低压力振荡。最后,提出一种改善缸内混合质量和减小压力振荡的策略,为液态天然气在船机上的普及提供了一定了理论基础。     

米勒循环协同废气再循环对高压直喷天然气船机的影响研究

基于CONVERGE建立了高压直喷(high-pressure direct injection,HPDI)天然气低速船机三维仿真模型,并基于该模型研究了米勒循环和废气再循环(exhaust gas recirculation,EGR)对发动机燃烧特性及污染物排放的影响规律,探究了米勒循环耦合EGR路线满足TierⅢ排放法规的可行性。研究结果表明,单独使用30%EGR率可满足TierⅢ排放标准,但指示油耗和碳烟排放增加显著;应用米勒循环降低NOx排放的潜力低于EGR;过大的排气门晚关角度会增大压气机工作负荷,且降低等量NO_x排放情况下油耗牺牲较大;采用25%EGR率耦合小程度米勒循环(排气门关闭时刻推迟5°曲轴转角)并适当提前天然气喷射正时(提前2°曲轴转角),可在指示油耗仅增加1.58%的前提下降低77%的NO_x排放,是满足TierⅢ排放法规可行的技术路线。     

高压缩比射流点火天然气发动机燃烧及排放特性

采用一维仿真,预测并分析了压缩比对射流点火天然气发动机烧特性规律,进一步结合台架试验研究了高压缩比下采用不同稀释策略时射流点火天然气发动机的燃烧及排放特性.结果表明:压缩比提升至17.0时,燃烧初期放热迅速,滞燃期缩短,燃烧持续期显著增加;采用纯空气稀释时,燃烧效率提高,热效率提升小于1％;CO、NOx排放增加,HC排...     

湍流射流点火对天然气发动机燃烧特性影响的试验研究

湍流射流点火（Turbulent Jet Ignition,TJI）是一种有效的燃烧增强技术,可提供更高的点火能量,使发动机稳定着火,且可以提高燃烧压力和燃烧速率,缩短燃烧持续期,是实现发动机稀薄燃烧的有效手段。基于一台带有预燃室的点燃式单缸试验机,开展了TJI模式下天然气发动机性能的试验研究。首先,研究了不同过量空气系数下TJI对天然气发动机动力性能、排放性能及燃烧特性的影响,并与火花塞点火（Spark Ignition,SI）模式进行对比;其次,在稀燃条件下分别探究了进气增压和预燃室喷氢对天然气发动机动力性、经济性及燃烧过程的优化作用。结果表明：TJI的使用可有效拓展天然气发动机的稀燃极限,且燃烧滞燃期和燃烧持续期均更短,放热率更高;过量空气系数1.5为甲烷TJI最佳稀燃工况,此时燃油消耗率最低,且可实现氮氧化物近零排放;此外,采用进气增压的方式可以提高TJI发动机在高负荷下的经济性;TJI模式下,相较于预燃室喷甲烷,预燃室喷氢气可进一步缩短滞燃期和燃烧持续期,提高放热率,达到提升TJI性能的效果。     

低热值燃气-柴油双燃料发动机动力性能计算

推导了低热值燃气-柴油双燃料发动机动力性能计算公式,并对由单缸、四冲程、水冷、直喷式柴油机改装的生物制气-柴油双燃料发动机的动力性能进行了计算分析。结果表明：双燃料发动机能够达到原柴油机的动力水平;其动力性能随引燃油量的减小而降低;在新鲜空气充足的前提下,供给更多的燃气,双燃料发动机的动力性能增强;燃气替代率有一最大值,超过该值后,随替代率增大,动力性能急剧下降;燃气低热值越高,替代率便可越大。计算得出的生物制气-柴油双燃料发动机在标定点和最大转矩点的最大生物制气替代率和对应的燃气进气比,与试验结果相吻合。     

LY12V140型天然气发动机模拟计算及性能分析

应用AVL-BOOST软件对LY12V140型天然气发动机建立工作过程计算模型,计算模拟配气定时、点火正时、压缩比、增压比、进气温度等参数对发动机燃烧过程和性能的影响,找出这些参数最佳的取值范围,从而为发动机的参数优化匹配奠定理论基础,减少开发过程中的人力、物力和财力的消耗。     

双燃料低速船机火焰发展和污染物生成机理

基于计算流体力学平台CONVERGE以及MATLAB后处理程序,通过数值仿真的方法,研究了船用柴油-天然气双燃料发动机预燃室内外的着火燃烧过程和火焰发展机制.此外,研究了双燃料发动机有害污染物氮氧化物(NOx)和碳氢(HC)生成及迁移过程.结果表明:整个燃烧过程分为三个阶段,首先,在预燃室内的流动和进气作用下,近通孔处...     

Ammonia chemistry in oxy-fuel combustion of methane

The oxidation of NH₃ during oxy-fuel combustion of methane, i.e., at high [CO₂], has been studied in a flow reactor. The experiments covered stoichiometries ranging from fuel rich to very fuel lean and temperatures from 973 to 1773 K. The results have been interpreted in terms of an updated detailed chemical kinetic model. A high CO₂ level enhanced formation of NO under reducing conditions while it inhibited NO under stoichiometric and lean conditions. The detailed chemical kinetic model captured fairly well all the experimental trends. According to the present study, the enhanced CO concentrations and alteration in the amount and partitioning of O/H radicals, rather than direct reactions between N-radicals and CO₂, are responsible for the effect of a high CO₂ concentration on ammonia conversion. When CO₂ is present as a bulk gas, formation of NO is facilitated by the increased OH/H ratio. Besides, the high CO levels enhance HNCO formation through NH₂+CO. However, reactions NH₂+O to form HNO and NH₂+H to form NH are inhibited due to the reduced concentration of O and H radicals. Instead reactions of NH₂ with species from the hydrocarbon/methylamine pool preserve reactive nitrogen as reduced species. These reactions reduce the NH₂ availability to form NO by other pathways like via HNO or NH and increase the probability of forming N₂ instead of NO.     

燃气预喷对高压直喷天然气船机的影响研究

针对高压直喷(HPDI)天然气双燃料低速船机的燃料喷射系统,研究了不同的天然气预喷策略对发动机燃烧特性及性能的影响,探究了适用于低速船机燃烧系统的天然气喷气规律。利用计算流体力学(CFD)软件Converge建立了HPDI天然气双燃料的单缸机仿真模型,与试验数据进行标定后,计算得到了不同预喷间隔及预喷比例下发动机燃烧性能和排放数据。分析计算结果表明,预喷策略的采用影响了燃烧过程中预混燃烧的比例,从而影响了燃烧放热相位及燃烧等容度。预喷比例相比预喷间隔对燃烧过程的影响更显著,后者在较大预喷比例下才会明显影响缸内燃烧放热过程。合理优化预喷策略可控制预混燃烧程度,从而同时改善NOx排放和油耗。不同的预喷策略使得缸内碳烟分布区域不同;与无预喷算例相比,采用预喷策略的算例最终碳烟排放量偏高。