Gas tank fill-up in globally minimum time: Theory and application to hydrogen

The process of filling-up high-pressure gas storage vessels consists of a gas source tank, an isenthalpic (Joule–Thomson or J–T) valve, a cooling system, and a gas storage vessel. These units are assumed to be thermally insulated. The fill-up process is formulated as a minimum time optimal control problem. Despite the nonlinear nature of the aforementioned optimal control problem, its global solution is obtained analytically. A novel transformation technique is employed, to decompose the problem into a process simulation problem independent of time, and a simpler minimum time control problem that only depends on the final molar density value and the maximum allowable feed mass flowrate. The feasibility of the fill-up is uniquely determined by the process simulation problem, and upon fill-up feasibility, the minimum time control problem is then globally solved. Two fill-up case studies, involving two different system configurations are analyzed. In Case 1, the fill-up process has a constant molar enthalpy feed, and no cooling system. Case 2 considers a fill-up process with a constant temperature feed, delivered by an efficient cooling system. It was demonstrated that the optimal control strategy to achieve minimum fill-up time is to have the mass flowrate at its maximum allowable value during the entire duration of the fill-up. The presented problem formulation is general and can be applied to the fill-up of other gases, such as compressed natural gas.     

Analysis of engine characteristics and emissions fueled by in-situ mixing of small amount of hydrogen in CNG

The performance and emission of a CNG-DI and spark-ignition engine when a small amount of hydrogen is added to the CNG using in-situ mixing is studied. The injection timing was set to 300° BTDC, the air--fuel ratio was kept at stoichiometric, and the ignition timing was adjusted to obtain the maximum brake torque. The experiments were performed at 2000, 3000, and 4000 rpm of engine speeds with each operating at WOT conditions. The introduction of a small amount of hydrogen had improved the engine performance, Brake Specific Energy Consumption (BSEC), and cylinder pressures as well as emissions at low engine speed.     

Self-ignition of hydrogen releases through electrostatic discharge induced by entrained particulates

The potential for particulates entrained in hydrogen releases to generate electrostatic charge and induce electrostatic discharge ignitions was investigated. A series of tests were performed in which hydrogen was released through a 3.175-mm diameter orifice from an initial pressure of 140 bar. Electrostatic field sensors were used to characterize the electrification of known quantities of iron oxide particulates deliberately entrained in the release. The ignition experiments focused on using charged particulates to induce spark discharges from isolated conductors and corona discharges. A total of 12 ignition events were observed. The results show that electrification of entrained particulates is a viable self-ignition mechanism of hydrogen releases.     

Life-cycle assessment of diesel, natural gas and hydrogen fuel cell bus transportation systems

The Sustainable Transport Energy Programme (STEP) is an initiative of the Government of Western Australia, to explore hydrogen fuel cell technology as an alternative to the existing diesel and natural gas public transit infrastructure in Perth. This project includes three buses manufactured by DaimlerChrysler with Ballard fuel cell power sources operating in regular service alongside the existing natural gas and diesel bus fleets. The life-cycle assessment (LCA) of the fuel cell bus trial in Perth determines the overall environmental footprint and energy demand by studying all phases of the complete transportation system, including the hydrogen infrastructure, bus manufacturing, operation, and end-of-life disposal. The LCAs of the existing diesel and natural gas transportation systems are developed in parallel. The findings show that the trial is competitive with the diesel and natural gas bus systems in terms of global warming potential and eutrophication. Emissions that contribute to acidification and photochemical ozone are greater for the fuel cell buses. Scenario analysis quantifies the improvements that can be expected in future generations of fuel cell vehicles and shows that a reduction of greater than 50% is achievable in the greenhouse gas, photochemical ozone creation and primary energy demand impact categories.     

Measured effects of filling time and initial mass on the temperature distribution within a hydrogen cylinder during refuelling

We have measured the effects of the initial mass and the total fill time on the temperature rise and the temperature distribution within a compressed hydrogen cylinder during refuelling.     

压缩天然气缸内直喷发动机的现状及发展趋势

天然气作为车用发动机的一种重要的"清洁燃料"日益受到人们的重视,天然气汽车在国内外均获得了较快的发展.本文简述了清洁代用燃料天然气的优缺点,以及直喷发动机的优点和目前的技术难点.最后分析了将两者相结合的天然气缸内直喷技术的特点以及国内外的研究现状和发展趋势.     

A model of particulate and species formation applied to laminar, nonpremixed flames for three aliphatic-hydrocarbon fuels

A detailed kinetic mechanism is developed that includes aromatic growth and particulate formation. The model includes reaction pathways leading to the formation of nanosized particles and their coagulation and growth to larger soot particles using a sectional approach for the particle phase. It is tested against literature data of species concentrations and particulate measurements in nonpremixed laminar flames of methane, ethylene, and butene. Reasonably good predictions of gas and particle-phase concentrations and particle sizes are obtained without any change to the kinetic scheme for the different fuels. The model predicts the low concentration of particulates in the methane flame (about 0.5 ppm) and the higher concentration of soot in the ethylene and butene flames (near 10 ppm). Model predictions show that in the methane flame small precursor particles dominate the particulate loading, whereas soot is the major component in ethylene and butene flames, in accordance with the experimental data. The driving factors in the model responsible for the quite different soot predictions in the ethylene and butene flames compared with the methane flame are benzene and acetylene concentrations, which are higher in the ethylene and butene flames. Soot loadings in the ethylene flame are sensitive to the acetylene soot growth reaction, whereas particle inception rates are linked to benzene in the model. A coagulation model is used to obtain collision efficiencies for some of the particle reactions, and tests show that the modeled results are not particularly sensitive to coagulation at the rates used in our model. Soot oxidation rates are not high enough to correctly predict burnout, and this aspect of the model needs further attention.     

压缩天然气汽车火灾危险性分析、预防及救援措施

主要阐述压缩天然气汽车（以下简称CNG汽车）发生事故的原因,并提出CNG汽车安全预防措施及救援处理方法。     

压缩天然气内燃机的应用

本文介绍了压缩天然气的特性及其在国内外应用状况提出了在内燃机上应用压缩天然气应注意的问题及相应的技术措施     

我国西南地区车用替代能源发展战略的思考

评述了车用替代燃料现状,根据我国西南地区的能源分布特点,压缩天然气（CNG）,煤制甲烷和生物质注化燃料显然更适合本地区车用替代燃料,它们具有资源丰富,供给稳定,空气污染少等优点,可以充分利用本地的能源资源,在发展车用替代燃料时,政府应发挥应有作用。     

Numerical simulation of hydrogen combustion process in rotary engine with laser ignition system

In this paper the combustion and ignition process in the hydrogen-fueled peripheral-ported rotary engine with single and dual laser ignition systems was studied numerically. The computational method was established for the process simulation including interaction between turbulence and chemical reactions. The detailed chemical kinetic model of hydrogen combustion was used. It was shown that the ignition and combustion process in the H₂-fueled rotary engine is highly transient with specific distortion and stretching of the combustion front in the combustion chamber due to complex motion of the rotor relative to the engine housing. The single and dual laser ignition systems were simulated to compare the ignition efficiency and the rate of hydrogen burning out. The evaluation of pressure in the combustion chamber was performed and compared with the experimental data obtained for the rotary engine fueled by natural gas. It was shown that the H₂-fueled rotary engine with the dual laser ignition system has potential application in alternative automotive industry due to high efficiency and near-zero carbon-based emission.     

Effect of hydrogen addition on early flame growth of lean burn natural gas–air mixtures

Effect of hydrogen addition on early flame growth of lean burn natural gas–air mixtures was investigated experimentally and numerically. The flame propagating photos of premixed combustion and direct-injection combustion was obtained by using a constant volume vessel and schlieren photographic technique. The pressure derived initial combustion durations were also obtained at different hydrogen fractions (from 0% to 40% in volumetric fraction) at overall equivalence ratio of 0.6 and 0.8, respectively. The laminar premixed methane–hydrogen–air flames were calculated with PREMIX code of CHEMKIN II program with GRI 3.0 mechanism. The results showed that the initial combustion process of lean burn natural gas–air mixtures was enhanced as hydrogen is added to natural gas in the case of both premixed combustion and direct-injection combustion. This phenomenon is more obvious at leaner mixture condition near the lean limit of natural gas. The mole fractions of OH and O are increased with the increase of hydrogen fraction and the position of maximum OH and O mole fractions move closing to the unburned mixture side. A monotonic correlation between initial combustion duration with the reciprocal maximum OH mole fraction in the flames is observed. The enhancement of the spark ignition of natural gas with hydrogen addition can be ascribed to the increase of OH and O mole fractions in the flames.     

Lessons learned from the installation and operation of Northern California's first 70-MPa hydrogen fueling station

A hydrogen dispensing facility capable of providing rapid 70-MPa vehicle fills became operational in May 2011 as the first such hydrogen dispensing facility in Northern California. The facility is operated by the University of California – Berkeley in support of fuel cell vehicle research with automakers, regional and state agencies, and industrial groups. In addition to storing and dispensing high-pressure hydrogen fuel, the station also incorporates a number of key advances in hydrogen refueling system capabilities, including novel fuel pre-cooling, fuel storage, and system safety systems. Key lessons learned from the construction and initial operation of the station include: 1) extensive initial planning is essential for smooth project development; 2) permitting is a key step and early engagement with local officials is critical; 3) extensive safety reviews may be required; 4) site work should be conducted with careful planning and execution; 5) methodical system commissioning is a key step in the project development process; 6) careful station maintenance and operational planning is critical for minimization of station downtime; and 7) station upkeep and utility expenses can be considerable.     

Research on the application technique of the natural gas engine with direct injection

Based on the analysis of the advantages of the Natural Gas Engine with Direct Injection （NGEDI） and the state of the art of the research in this area, the authors point out that, the NGEDI with high pressure is one potential selection and will have a good application prospects. Through investigation experiment and simulation results, the key techniques are put foreword for deployment of the NGEDI and some solutions are given.