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 coalmine 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.

Gas film/regenerative composite cooling characteristics of the liquid oxygen/liquid methane (LOX/LCH4) rocket engine

The thermal protection of rocket engines is a crucial aspect of rocket engine design.In this paper,the gas film/regenerative composite cooling of the liquid oxygen/liquid methane(LOX/LCH4)rocket engine thrust chamber was investigated.A gas film/regenerative composite cooling model was developed based on the Grisson gas film cooling efficiency formula and the one-dimensional regenerative cooling model.The accuracy of the model was validated through experiments conducted on a 6 kg/s level gas film/regenerative composite cooling thrust chamber.Additionally,key parameters related to heat transfer performance were calculated.The results demonstrate that the model is sufficiently accurate to be used as a preliminary design tool.The temperature rise error of the coolant,when compared with the experimental results,was found to be less than 10%.Although the pressure drop error is relatively large,the calculated results still provide valuable guidance for heat transfer analysis.In addition,the performance of composite cooling is observed to be superior to regenerative cooling.Increasing the gas film flow rate results in higher cooling efficiency and a lower gas-side wall temperature.Furthermore,the position at which the gas film is introduced greatly impacts the cooling performance.The optimal introduction position for the gas film is determined when the film is introduced from a single row of holes.This optimal introduction position results in a more uniform wall temperature distribution and reduces the peak temperature.Lastly,it is observed that a double row of holes,when compared to a single row of holes,enhances the cooling effect in the superposition area of the gas film and further lowers the gas-side wall temperature.These results provide a basis for the design of gas film/regenerative composite cooling systems.

Technical Innovation of LH2/LOX Rocket Engines in China

This paper provides a detailed introduction to and analysis of the course of China's technological innovation in liquid hydrogen/liquid oxygen(LH2/LOX)rocket engines from a historical point of view.It starts with the investigation of LH2/LOX rocket engines by relevant departments of the Chinese Academy of Sciences in the 1960s and their preliminary achievements.Then,the policy decision concerning LH2/LOX engine development,the project approval of the Long March-3(Chang Zheng-3,CZ-3)rocket,and the process of developing LH2/LOX engines are analyzed in detail,followed by an introduction to and summary of the development situation and technical innovation characteristics of China's LH2/LOX engines as they grew from 4 tons to 8 tons,and finally to 50 tons.Finally,the paper briefly analyzes the innovation experience connected with China's LH2/LOX engines.

Mechanical property and permeability of raw coal containing methane under unloading confining pressure

Based on domestic-developed triaxial servo-controlled seepage equipment for thermal-hydrologicalmechanical coupling of coal containing methane,an experimental study was carried out to investigate mechanical property and gas permeability of raw coal,under the situation of conventional triaxial compression and unloading confining pressure tests in different gas pressure conditions.Triaxial unloading confining pressure process was reducing confining pressure while increasing axial pressure.The research results show that,compared with the peak intensity of conventional triaxial loading,the ultimate strength of coal samples of triaxial unloading confining pressure was lower,deformation under loading was far less than unloading,dilation caused by unloading was more obvious than loading.The change trend of volumetric strain would embody change of gas permeability of coal,the permeability first reduced along with volumetric strain increase,and then raised with volume strain decrease,furthermore,the change trends of permeability of coal before and after destruction were different in the stage of decreasing volume strain due to the effect of gas pressure.When gas pressure was greater,the effective confining pressure was smaller,and the radial deformation produced by unloading was greater.When the unloading failed confining pressure difference was smaller,coal would be easier to get unstable failure.

Kinetic models of natural gas combustion in an internal combustion engine

In this study, combustion of methane was simulated using four kinetic models of methane in CHEMKIN 4.1.1 for 0-D closed internal combustion （IC） engine reactor. Two detailed （GRIMECH3.0 ＆ UBC MECH2.0） and two reduced （One step ＆ Four steps） models were examined for various IC engine designs. The detailed models （GRIMECH3.0, ＆ UBC MECH2.0） and 4-step models successfully predicted the combustion while global model was unable to predict any combustion reaction. This study illustrated that the detailed model showed good concordances in the prediction of chamber pressure, temperature and major combustion species profiles. The detailed models also exhibited the capabilities to predict the pollutants formation in an IC engine while the reduced schemes showed failure in the prediction of pollutants emissions. Although, there are discrepancies among the profiles of four considered model, the detailed models （GRIMECH3.0 ＆ UBC MECH2.0） produced the acceptable agreement in the species prediction and formation of pollutants.

Experimental study on characteristics of pore water conversion during methane hydrates formation in unsaturated sand

Understanding the pore water conversion characteristics during hydrate formation in porous media is important to study the accumulation mechanism of marine gas hydrate.In this study,low-field NMR was used to study the pore water conversion characteristics during methane hydrate formation in unsaturated sand samples.Results show that the signal intensity of T_(2) distribution isn’t affected by sediment type and pore pressure,but is affected by temperature.The increase in the pressure of hydrogen-containing gas can cause the increase in the signal intensity of T_(2) distribution.The heterogeneity of pore structure is aggravated due to the hydrate formation in porous media.The water conversion rate fluctuates during the hydrate formation.The sand size affects the water conversion ratio and rate by affecting the specific surface of sand in unsaturated porous media.For the fine sand sample,the large specific surface causes a large gas-water contact area resulting in a higher water conversion rate,but causes a large water-sand contact area resulting in a low water conversion ratio(C_(w)=96.2%).The clay can reduce the water conversion rate and ratio,especially montmorillonite(C_(w)=95.8%).The crystal layer of montmorillonite affects the pore water conversion characteristics by hindering the conversion of interlayer water.

Formation mechanism,experimental method,and property characterization of graindisplacing methane hydrates in marine sediment:A review

Grain-displacing hydrate deposits exist at many marine sites,which constitute an important part of methane hydrate resources worldwide.Attributed to the difficulties in acquiring field data and synthesizing experimental samples,the formation and property characterization of grain-displacing hydrate remains less understood and characterized than the pore-filling hydrate in current literature.This study reviews the formation mechanisms of grain-displacing hydrate from the perspective of geological accumulation and microscale sedimentary property.The experimental methods of synthesizing grain-displacing hydrate in the laboratory and the current knowledge on the property of grain-displacing hydrate sediment are also introduced.Shortcomings in current theories and suggestions for future study are proposed.The work is hoped to provide valuable insights for the research into the hydrate accumulation,geophysics,and hydrate exploitation targeted at the grain-displacing hydrate in the marine sediments.

The experimental study on combustion characteristics and emissions of a CMM fueled engine

In this paper, an experimental study on combustion characteristics and emissions of a single cylinder spark ignition engine fueled with coal-mine methane （CMM） is investigated under various loads. CMM is simulated by the compressed nature gas（ CNG）/nitrogen blend fuels. Based on experiment results, it is shown that under 0% - 35% nitrogen volume fraction in CNG/nitrogen blends, the maximum cylinder pressure, the maximum rate of pressure rise and the rate of heat release decrease, the flame propagation period increases, the center of heat release curve is closed to the top dead centre （TDC）markedly with the increase of nitrogen volume fraction. Meanwhile, the hydrocarbon （HC）, CO emissions increase, the NOx emission decreases apparently with the increase of nitrogen volume fraction.

Identification of functionally active aerobic methanotrophs and their methane oxidation potential in sediments from the Shenhu Area,South China Sea

Large amounts of gas hydrate are distributed in the northern slope of the South China Sea,which is a potential threat of methane leakage.Aerobic methane oxidation by methanotrophs,significant methane biotransformation that occurs in sediment surface and water column,can effectively reduce atmospheric emission of hydrate-decomposed methane.To identify active aerobic methanotrophs and their methane oxidation potential in sediments from the Shenhu Area in the South China Sea,multi-day enrichment incubations were conducted in this study.The results show that the methane oxidation rates in the studied sediments were 2.03‒2.36μmol/gdw/d,which were higher than those obtained by sediment incubations from other areas in marine ecosystems.Thus the authors suspect that the methane oxidation potential of methanotrophs was relatively higher in sediments from the Shenhu Area.After the incubations family Methylococcaea(type I methanotrophs)mainly consisted of genus Methylobacter and Methylococcaea_Other were predominant with an increased proportion of 70.3%,whereas Methylocaldum decreased simultaneously in the incubated sediments.Collectively,this study may help to gain a better understanding of the methane biotransformation in the Shenhu Area.

Jet Plasma-Chemical Reactor for the Conversion of Methane: the Use of Clustering

The research results of processes proceeding in supersonic jets of light hydrocarbons, activated by an electron beam are presented. It is shown, that condensation suppressed at activation by electrons in the initial stage of condensation. The developed condensation conditions mode leads to increasing of a part of heavy corpuscles in activated stream and not only owing to stimulation of condensation but because of formation of heavy hydrocarbonic molecules.

Effect of endogenous hydrogen utilization on improved methane production in an integrated microbial electrolysis cell and anaerobic digestion： Employing catalyzed stainless steel mesh cathode

Improving the production of methane, while maintaining a significant level of process stability, is the main challenge in the anaerobic digestion process. Recently, microbial electrolysis cell(MEC) has become a promising method for CO_2 reduction produced during anaerobic digestion(AD) and leads to minimize the cost of biogas upgrading technology. In this study, the MEC-AD coupled reactor was used to generate and utilize the endogenous hydrogen by employing biocompatible electrodeposited cobalt-phosphate as catalysts to improve the performance of stainless steel mesh and carbon cloth electrodes. In addition, the modified version of ADM1 model(ADM1 da) was used to simulate the process. The result indicated that the MEC-AD coupled reactor can improve the CH_4 yield and production rate significantly. The CH_4 yield was enhanced with an average of 48% higher than the control. The CH_4 production rate was also increased 1.65 times due to the utilization of endogenous hydrogen.The specific yield, flow rate, content of CH_4, and p H value were the variables that the model was best at predicting(with indexes of agreement: 0.960/0.941, 0.682/0.696, 0.881/0.865, and 0.764/0.743) of the process with SSmeshes 80/SS-meshes 200, respectively. Employing the catalyzed SS mesh cathode, in the MEC-AD coupled reactor, could be an effective approach to generate and facilitate the utilization of endogenous hydrogen in anaerobic digestion of CH_4 production technology, which is a promising and feasible method to scale up to the industrial level.

新疆煤层气大规模高效勘探开发关键技术领域研究进展与突破方向

新疆煤层气资源量7.5万亿m^(3)(2000 m以浅),已施工煤层气井450口,年产气量达到0.8亿m^(3),新疆维吾尔自治区提出了2025年实现煤层气产量25亿m^(3)的目标,煤层气大规模高效开发成为紧迫的重大需求。从煤层气富集模式与选区技术、“甜点”预测探测技术、加速滚动开发与快速增储上产策略、地质适配性开发技术、煤层气与煤炭、油气协同开发技术5个关键技术领域,系统梳理了新疆煤层气勘探开发已取得的主要研究进展,分析提出了可能突破方向。研究表明:新疆煤储层具有多-厚煤层普遍、低阶煤发育、急倾斜煤层多见、煤体变形与构造控制显著、水文条件和露头条件复杂,和三“低”(含气量低、甲烷体积分数低、含气饱和度低)五“高”(高含气强度、高孔隙度、高地应力变化、高储层压力变化、高渗透率变化)的含气性及物性等煤层气地质独特性;煤层气成因与富集模式具有多样性,包括生物成因气、热成因气或生物-热复合成因及其相应富集模式,生物成因气藏或生物成因气贡献普遍;煤层气分布赋存规律呈现前陆盆地、山间盆地显著差异性;创新形成基于“两”分开(浅部与深部,低阶煤与中高阶煤)“两”结合(地质评价与工程评价,多元数据)的科学评价与基于“机器学习+三维地质建模”的精准选区技术是第1个突破方向。深部煤层气/煤系气“甜点”发育区域主要为盆内坳陷的凸起、盆内隆起的凹陷、盆缘斜坡,高产井位多为构造高点,发育层位为割理裂隙发育的原生结构煤层或孔裂隙发育的煤系砂砾岩储层;基于“地球物理+岩石物理+岩石力学地层新方法”和“地质甜点+工程甜点新理念”的深部煤层气/煤系气“甜点”预测探测技术是第2个突破方向。低风险、短周期、高效率、多批次工程部署是加速滚动开发的基本原则;中浅部煤层气快速增储上产技术策略是在优选新区块布井建井、对老区块煤层气井进行增产改造;深部煤层气快速增储上产技术策略是在大型盆地缓坡深部和盆内凸起“甜点”区优先部署开发;科学加速滚动开发与高效快速增储上产的工程部署方法与技术策略是第3个突破方向。在井网井型差异性优化部署、低储层伤害钻井固井、高可靠性录井测井试井、多井型高效分段压裂、低套压-控压排采管控等工程技术取得重要进展;发展构建新疆煤层气大规模高效勘探开发地质适配性技术体系是第4个突破方向。开展先采气后采煤、煤层气与煤共采、煤层气与原位富油煤共采,推动中浅部煤层气与煤炭协同勘探开发;开展煤系叠合型气藏开发、煤层气与煤系气共探共采、煤系全油气系统勘探开发,推动深部煤层气与油气协同勘探开发,已有关注和探索;煤层气与煤、油气共探共采是第5个突破方向。成果试图为新疆煤层气大规模高效勘探开发提供技术支持和工程决策参考。

超声振动在矿山煤岩致裂中的研究进展与展望

为了推动超声振动致裂煤岩体技术的发展,提高矿山煤层气增产及硬岩掘进的效率,回顾了超声波技术的发展历程,综述了超声振动在致裂煤岩体方面的应用现状与研究进展,明确了超声振动在煤岩致裂领域存在的关键阻碍性技术难题及发展趋势。(1)总结了传统技术在矿山煤层气增产和硬岩掘进领域存在的技术问题,介绍了超声波技术的独特优势及应用领域,阐述了超声波发生器和超声波换能器的发展阶段及相应性能;(2)归结了超声振动煤层气促解增渗装置及流程,分析了超声振动煤层气促解增产现状,阐明了超声空化效应、机械振动效应、热效应作用下煤层气降压、加速、位能及动能增加进而促进其解吸增渗的机制;(3)归纳了超声振动破岩装置及流程,阐述了超声振动破碎硬岩的进展,揭示了超声振动产生的机械振动效应与热效应作用下疲劳损伤、微裂纹亚临界扩展、矿物颗粒不均匀热膨胀或矿物相变、岩石物理力学特性劣化导致硬岩破碎的内在机理;(4)针对超声波发生器、换能器及超声振动在矿山致裂煤岩体中的局限度,对未来超声振动致裂煤岩体在现场高效应用的研究重点提出了4点建议:高性能防爆型超声波发生器和换能器的研发,超声振动促解增渗机理的深入分析及管线技术框架设计,多功能及多场耦合室内超声振动致裂煤岩体设备研制与试验,井下抗干扰超声振动设备的研发应用。

膨胀循环氢氧发动机火炬点火系统方案研究

针对膨胀循环氢氧发动机多次点火需求,开展了火炬式电点火系统方案论证和仿真研究,明确了较为合理的低压火炬式电点火系统方案,并完成整机级试验验证。结果表明,氢主阀打开瞬间点火室混合比波动较大,可能造成结构烧蚀;从氢涡轮前引气氢、氧泵后引液氧的方案烧蚀风险较小,但对发动机起动和稳态特性有一定影响。试验验证了仿真分析结果,实现了中国液体火箭发动机首次低压火炬式电点火起动,初步表明点火系统方案可行。

不同NaOH预处理浓度和预处理时间对麦秆常温厌氧发酵效率的影响

在确保NaOH对小麦秸秆预处理效果的前提下,通过适当延长预处理时间可减少NaOH用量,进而降低二次污染风险,为小麦秸秆的户用沼气生产提供理论依据。采用自行设计的厌氧发酵装置,研究不同NaOH预处理质量分数和预处理时间对小麦秸秆常温(20℃)厌氧发酵效率的影响。结果显示,在小麦秸秆常温厌氧发酵时,NaOH质量分数为3%时的预处理效果优于质量分数为0和6%的预处理效果;在预处理7~28 d时,纤维素、半纤维素和木质素的脱除率分别为3.66%~8.07%、43.08%~46.43%和47.88%~51.44%;发酵时的初始pH值为8.36~8.47,108~113 d发酵基本完成,累积产甲烷1 565.80~1 833.16 mL,干物质累积产甲烷体积为97.86~114.57 mL/g,产甲烷速率为13.86~16.97 mL/d,甲烷体积分数为50%~58%的持续时间为57~72 d。通过响应面模型试验得到最优预处理条件为:NaOH质量分数为4.36%,预处理时间为12.44 d。该条件下干物质甲烷产量的实测值为113.76 mL/g,与预测值接近,相对误差小于5%,表明模型有效。综合判断,在小麦秸秆常温(20℃)厌氧发酵时,利用质量分数为4.36%(以秸秆干重计)的NaOH对秸秆进行预处理切实可行。

沁水盆地南部煤层气地质工程一体化关键技术

沁水盆地南部煤层气资源丰富,但地质、工程条件复杂,樊庄成熟工艺技术推广邻区适应性较差,煤层气规模效益开发面临严峻挑战。为了解决沁水盆地南部煤层气“井位部署难度大、钻井周期长、裸眼井井眼易垮塌、单井产量低”等问题,开展了地质工程一体化技术攻关,形成了“三性”煤储层评价、可控水平井钻完井、分段压裂及疏导式排采等多项关键技术,并开展现场试验与推广。研究结果表明:通过地质与工程有机结合,实现了地质模型为工程技术优化提供技术支撑,工程实践不断校正地质模型,施工精度提高;水平井煤层钻遇率95%,单井钻井复杂平均减少40%,产能到位率达90%,单井平均日产量超过8000 m^(3)。

膨润土粉体对管网甲烷爆炸的抑制特性及抑爆机理

为了探寻高效的抑爆剂,有效降低甲烷爆炸事故发生率,最大限度地降低事故损失,利用自主搭建的爆炸管网测试系统进行了膨润土粉体抑爆试验。将爆炸超压峰值、爆炸威力指数和爆炸火焰首次到达管网两出口的时刻作为表征抑制剂抑爆性能的参数,探究了不同粒径膨润土粉体对管网甲烷爆炸的抑制性能,利用热解特性分析和分子动力学仿真探究了膨润土粉体的物理和化学抑爆机理。结果表明,粒径为>27~33μm的膨润土粉体对于管网甲烷爆炸的抑制性能最佳。膨润土粉体的物理抑爆机理为通过热解吸收反应热来实现抑爆目的;其化学抑爆机理为膨润土分子能够有效消耗反应体系中的自由电子和活性自由基,减缓甲烷链式反应速率。研究结论可为提高甲烷运输的安全性、有效降低灾害风险提供理论参考。

磷酸二氢铵对甲烷爆炸火焰结构影响的抑爆试验研究

本研究旨在探讨磷酸二氢铵对甲烷/空气爆炸火焰传播和结构的直观影响。基于能量守恒和化学动力学原理,在60L定容燃烧弹中进行甲烷抑爆试验,利用纹影技术获取爆炸火焰传播图像并进行分析。试验结果表明,磷酸二氢铵对爆炸火焰有减弱作用,并且随着其浓度增加,火焰传播速度下降显著,火焰半径缩小,在接近最佳甲烷气体爆炸浓度时,效果更加明显。其中,150 g/m 3磷酸二氢铵抑制9.5%、8.0%浓度甲烷爆炸体现出高效性。此外,磷酸二氢铵使甲烷爆炸反应时间延长,表现为流场中自发光时间的显著增加。从热力学角度来看,磷酸二氢铵的分解吸热效应降低了火焰温度,不仅减缓火焰传播速度,也导致火焰边界呈现出片状和变薄的特征。这种现象在甲烷浓度为11%时表现得尤为突出,进一步证实了磷酸二氢铵作为抑爆添加剂的潜在效能。

鄂尔多斯盆地神府区块深部煤层气体积压裂实践与认识

鄂尔多斯盆地东缘神府深煤层大气田探明地质储量超千亿方,实现该地区深部煤层气高效开发对保障国家能源供应具有重要意义。但是,由于深煤层地质环境复杂,具有高地应力、中高温度、特低渗透、强非均质性、割理/裂隙发育等特点,导致现有中浅煤层压裂改造技术难以完全适用于深煤层,其施工规模与参数仍处于探索阶段。为了探究与深煤层地质条件相适应的增产改造技术,以鄂尔多斯盆地神府区块为地质背景,以深煤层大规模体积压裂为工程实践,围绕“极限动用+均衡扩展+有效支撑”的设计理念,提出“少段多簇适度密切割+等孔径深穿透限流射孔+复合液造缝(高黏液体破岩+低黏液体造复杂缝)+大排量高强度加砂+前置酸液降低破裂压力+多粒径组合支撑剂”为核心的体积压裂技术,并引入地质−工程−智能一体化压后评估方法,通过压裂−产能双重智能拟合校正,精细刻画了储层改造体积(SRV)和气体泄流体积(DRV),预测了不同压裂规模及井型条件下的最终可采储量EUR。最后,通过统计神府区块深煤层压裂井地质、工程和产量特征数据,采用随机森林算法量化分析了影响深部煤层气产能的主控因素。实践结果表明:采用上述大规模体积压裂技术,已投产的直/定向井最高日产气量超过1×10^(4) m^(3),水平井最高日产气量超过2×10^(4 )m^(3),说明深煤层可压性良好、开发潜力巨大;深部煤层气峰值产气量的主要影响因素为:煤层含气量、煤层厚度和加砂强度;累积产气量的主要影响因素为:煤层含气量、加砂强度和总砂量。

LOX/LCH_4变推力发动机技术初步研究

对国内外变推力发动机和LOX/LCH4发动机的研究进展进行了总结,在此基础上,提出了一种LOX/LCH4变推力发动机系统方案。在深入分析的基础上,对此方案进行了功率平衡和推力室传热计算,结果表明该系统方案完全能够实现10:1推力变比。LOX/LCH4变推力发动机可以广泛应用于多种运载器和航天器中,对我国探月及后续的载人登月工程均可以提供技术支持,对LOX/LCH4发动机的技术发展和未来的载人登陆火星等任务都具有深远影响。