天然气发动机混合气形成与燃烧特点及性能评述

本文根据天然气发动机混合气的形成特点,把天然气发动机分为预混合燃烧型和非均质扩散燃烧型,并分析了这两种天然气发动机的技术特点、燃烧特点与排放等性能。本文重点介绍了实现非均质扩散燃烧的不同型式高压缸内直喷天然气发动机技术及其性能特点,最后提出非均质扩散燃烧天然气发动机技术需要研究的相关问题。     

天然气发动机神经网络控制策略及试验研究

天然气发动机本身具有低排放的特点,所以不需要由排放参数反馈修正发动机的空燃比,减少了控制的反馈系统。传统的混合器式天然气发动机无法高精度地控制发动机的空燃比,采用神经网络控制理论对天然气发动机的空燃比实施控制,使其空燃比始终保持在理论空燃比高精度的状态,提高了天然气发动机的性能。以175F天然气发动机为例,试验结果表明:采用神经网络控制的天然气发动机的性能高于混合器式天然气发动机。     

燃气喷射阀的控制对发动机性能的影响

清洁高效是当前能源领域的主要关注指标,天然气发动机采用低排放的天然气作为燃料,迅速成为发动机行业的新宠。以ACD320DF发动机为对象,针对多点歧管喷射的燃气发动机的性能开展研究,探究喷射阀的开启时刻和持续时间的差异对发动机主要性能的影响。结果表明:通过对ACD320DF发动机整机性能的仿真分析,得到发动机燃气进气总量、缸压、燃气消耗随喷射正时及喷射脉宽的变化规律,最后通过试验进一步验证该规律,可以用于天然气发动机气阀正时设计、试验标定优化的参考。     

天然气发动机,新型绿色动力

天然气作为重要的能源和优质的发动机代用燃料,在21世纪将得到广泛的利用。分析了影响我国燃气汽车发展的基本因素,以及车用天然气发动机的特点和关键技术,还简要介绍了上柴客车用CNG发动机及其应用实例。     

天然气发动机的研究现状

天然气能降低发动机的有害物排放,是一种比较理想的发动机代用燃料。稀燃天然气发动机具有较高的热效率和较低的NOx排放。均质充量压缩着火(HCCI)燃烧也是提高稀燃天然气发动机热效率的方法之一,并有很低的NOx排放。本文综述了稀燃天然气发动机和HCCI天然气发动机的研究进展,尤其是燃烧室形状、点火系统、充量分层、加氢等对天然气发动机性能的影响及天然气HCCI发动机的燃烧与排放特点。     

氢能作为内燃机替代燃料的研究综述与分析

储存有限性与使用过程中对环境的影响是化石能源的两个主要问题。内燃机消耗大量的汽油、柴油和天然气等化石能源,亟待研发其替代品。本文回顾了替代能源的研究现状,综述了氢的物性及其对发动机性能的影响,概述了氢发动机与汽油发动机性能的比较结果。在氢的储存、影响氢发动机热效率的主要因素等方面提出了作者的看法,并指出氢燃料的全面评价应包括其制备过程的能耗和污染。     

小型天然气发电机组控制系统硬件设计

天然气作为一种高效、安全、储量丰富的清洁能源现已进入了人们的视野。由于分布式发电具有体积小、移动方便、成本低等特点,因此对用于分布式发电的小型天然气发电机组的研究具有重要的经济意义和社会效益。本文以小型气体燃料发电机组发动机为研究对象,深入分析研究了小型气体燃料发电机组发动机的运行特点,根据目前国内小型天然气发电机组控制过程中存在的点火控制模块和速度调节模块分离的现象,设计了包括发动机的点火控制模块和速度调节模块在内的小型气体燃料发电机组发动机的电控系统,完成了控制系统的硬件设计和调试试验。     

SC6HT天然气发动机的研发与应用

介绍了SC6HT单燃料天然气发动机燃烧系统、进气系统、燃气供给系统、点火系统的设计及技术特点,简述了性能优化结果及开发中解决的问题。市场应用表明,SC6HT天然气发动机性能优异,完全能够满足城市公交客车的使用要求。     

世界能源状况及车用天然气发动机技术发展

介绍了国内外能源状况以及天然气汽车的发展现状及趋势,分析了国内外车用天然气发动机的技术应用及面临的问题,提出我国车用天然气发动机的技术发展方向。     

T10V120F型天然气发动机的研制

T10V120F型天然气发动机是以捷克TRTRA公司生产的T3-929型柴油机为原型机开发的新一代风冷式天然气发动机。该机设计指标先进,性能可靠,采用预混合式进气系统和专为天然气发动机设计的数字点火系统,点火能量大,点火可靠。其强制式空气冷却方式,彻底解决了水冷发动机的漏水、结垢、使用环境受到限制等缺点。本文重点介绍了T10V120F型天然气发动机的主要性能指标、技术关键和结构特点及试验结果。     

从29^thCIMAC大会看船用中高速发动机整机开发趋势

基于29届CIMAC大会交流内容,分析了船用中高速发动机整机开发趋势。分析表明:当前整机开发关注的重点是降低排放和提高综合能效;LNG气体机及双燃料机成为整机开发趋势;两级增压可变配气正时成为越来越多主机厂的技术选择。在LNG气体机及双燃料机的开发上,欧美的研究重点是整机的瞬态性能及闭环控制等;日韩的研究重点则侧重于减少燃烧室死区,优化缸内燃烧,提高效率等;而我国船用气体机研究尚处于起步阶段,整机的可靠性有待进一步验证及改进提高。     

Current status and future projections of LNG demand and supplies: A global prospective

An unceasing growth of gas consumption in domestic households, industry, and power plants has gradually turned natural gas into a major source of energy. Main drivers in this development are the technical and economic advantages of natural gas. It is a clean, versatile, and easily controllable fuel. On this basis, natural gas is often considered the form of energy that will be the “bridging fuel” to a sustainable energy system, sometime after 2050. Unlike other main sources of energy, such as oil and coal, gas is not traded on an actual world market. This paper provides an overview on demand and supplies of natural gas (LNG) in the past as a function of gas prices, gas technology (gas sweetening, liquefaction, shipping and re-gasification), and gas market and how they have changed recently. It also discusses the likely developments in global LNG demand for the period to the year 2030.     

中国发展液化天然气面临的机遇和挑战

世界天然气消费量在一次能源结构中已占到24%,预计10年后将上升到35%,成为第三大能源。北美洲、欧洲主要是买方市场,中南美洲、中东和非洲主要是卖方市场,而亚太地区既是主要的进口市场,也是LNG出口的主要来源地区之一。未来10年全球LNG供应将持续趋紧,印度和中国将成为LNG消费的新兴市场。中国发展LNG必须注意资源接替和持续供应,基础设施、设备的建设和扩建,投资主体多元化,天然气市场培育和市场监管等问题。     

Design and Optimization of a Full-Generation System for Marine LNG Cold Energy Cascade Utilization

This paper took a 100,000 DWT LNG fuel powered ship as the research object.Based on the idea of"temperature matching,cascade utilization"and combined with the application conditions of the ship,a horizontal three-level nested Rankine cycle full-generation system which combined the high-temperature waste heat of the main engine flue gas with the low-temperature cold energy of LNG was proposed in this paper.Furthermore,based on the analysis and selection of the parameters which had high sensitivity to the system performance,the parameters of the proposed system were optimized by using the genetic algorithm.After optimization,the exergy efficiency of the marine LNG gasification cold energy cascade utilization power generation system can reach 48.06%,and the thermal efficiency can reach 35.56%.In addition,this paper took LNG net power generation as the performance index,and compared it with the typical LNG cold energy utilization power generation system in this field.The results showed that the unit mass flow LNG power generation of the system proposed in this paper was the largest,reaching 457.41 k W.     

Novel cogeneration power system with liquefied natural gas (LNG) cryogenic exergy utilization

We propose a new cogeneration power system with two energy sources of fuel chemical energy and liquefied natural gas (LNG) cryogenic energy, and two outputs of electrical power and cooling power. Due to the advanced integration of system and cascade utilization of LNG cryogenic energy, the system has excellent energy saving: chemical energy of fuel and LNG cryogenic energy are saved by 7.5–12.2% and 13.2–14.3%, respectively. As CO₂ is selected as working fluid and oxygen as fuel oxidizer, CO₂ is easily recovered as a liquid with LNG vaporization. In this paper, the typical recuperative Rankine cycle and the corresponding cogeneration system are described and a detailed thermodynamic analysis is carried out to reveal the principle of the cycle and system. Furthermore, the influence of key parameters on performance is discussed. Considering the engineering application, the technical advantages and concerns are pointed out.     

Utilization of the cryogenic exergy of LNG by a mirror gas-turbine

In the course of worldwide efforts to suppress global warming, the saving of energy becomes more important. Recently, LNG (liquefied natural gas) terminals in our country have received more than 50 million tons of LNG per year. Therefore, the utilization of the cryogenic exergy in connection with the regasification of LNG gains more and more importance. The aim of this paper is the recovery of the energy consumed in liquefaction using the MGT (mirror gas-turbine), which is a new kind of combined cycle of a conventional gas-turbine worked as a topping cycle and TG (inverted Brayton cycle) as a bottoming cycle. The optimum characteristics have been calculated and it is shown that this cycle is superior to the current-use gasification systems in employing seawater heat in terms of thermal efficiency and specific output. In the present cycle, the cold LNG is used to cool the exhaust gas from a turbine of a TG, and then the exergy of the liquefied natural gas is transformed, with a very high efficiency, to electric energy. The main feature of this new concept is the removal of an evaporation system using seawater.     

Analysis of the liquefaction process of exhaust gases from an underwater engine

In operating underwater engines, such as in exploring submarines, the dumping of the exhaust gas out of the engine requires a large portion of the total power, frequently amounting to 25–30% of the power generated. This can be solved by liquefying the exhaust gas and storing it. In the present study, two liquefaction systems are simulated to enhance the overall efficiency; one is a closed cycle diesel cycle and the other is a closed cycle liquefied natural gas (LNG) engine. LNG was chosen as a fuel not only because it is economical but also because its cold energy can be utilized within the liquefaction system. Since a mixture of oxygen and carbon dioxide is used as an oxidizer, liquefying carbon dioxide is the major concern in this study. To further improve this system, the intercooling of the compressor is devised. The power consumed for the liquefaction system is examined in terms of the related properties, including pressure and temperature of the carbon dioxide vessel as a function of the mass fraction of the exhaust gas that enters the compressor. The present study shows that much gain in the power and reduction of the vessel pressure could be achieved in the case of the closed cycle LNG engine. The compression power was remarkably low, typically only 6.3% for the closed cycle diesel engine and 3.4% for the closed cycle LNG engine, respectively, of net engine power. For practically, a design–purpose map of the operating parameters of the liquefaction systems is also presented.     

Experimental investigation of varying composition of HCNG on performance and combustion characteristics of a SI engine

With rapid depletion of petroleum resources, researchers are investigating alternate fuels to meet global transportation energy demand. Gaseous fuels such as compressed natural gas (CNG) and hydrogen are of special interest because of their cleaner combustion characteristics compared to liquid petroleum based fossil fuels. However both these gaseous fuels have some technical issues when they are used as stand-alone alternate fuel in conventional spark ignition (SI) engines. CNG suffers from lower energy density and narrow flammability range whereas backfiring tendency is highly pronounced in hydrogen fueled engines. Hydrogen enriched compressed natural gas (HCNG) mixtures are observed to be good alternative to these individual fuels since these mixtures do not pose the issues experienced by the constituent fuels i.e. CNG and hydrogen. In this study, experiments were conducted in a spark ignited gas engine using various compositions of HCNG mixtures having 0, 10, 20, 30, 50, 70 and 100% (v/v) hydrogen fraction. The performance and combustion characteristics of these test fuels were compared with that of baseline CNG, in order to find an optimum HCNG mixture composition for a single cylinder gas engine. Results obtained showed that 30HCNG mixture delivered superior engine performance compared to other HCNG mixtures and baseline CNG, which is in sharp contrast to 15HCNG being advocated globally.     

LNG运输船气体管理系统设计

对液化天然气(liquefied natural gas,LNG)运输船气体管理系统开展设计研究。分析表明:在不同船舶工况下,气体管理系统可通过透气桅放气、气体燃烧单元(gas combustion unit,GCU)燃烧、再液化、喷淋、再气化等方式将LNG运输船货舱舱压控制在安全范围内;能够在货舱蒸发气(boil off gas,BOG)量充足或者不足的情况下对主机/发电机组进行燃气供给。在船舶实际运行过程中协调采用多种气体处理模式可保障LNG运输船安全稳定运行。     

Thermodynamic analysis of combustion and pollutants formation in a wood-gas spark-ignited heavy-duty engine

Awareness of limitations of petroleum based liquid fuels as for example used in spark-ignited heavy-duty engines for power generation, has led engineers to propose various solutions such as the use of alternative/renewable energy sources. Wood-gas is an alternative gaseous fuel generated from the gasification of wood, which could be used as a full supplement fuel in conventional heavy-duty spark-ignited engines fuelled with natural gas. Previous related research studies have shown that the main disadvantage of the wood-gas combustion is its negative impact on brake engine efficiency compared to the normal natural gas operation, while NO and CO emissions are also increased. Compression ratio and spark timing are some of the engine parameters, which influence significantly the combustion mechanism inside the combustion chamber of a wood-gas powered spark-ignited engine. In order to examine the effect of these parameters on the performance and exhaust emissions of a heavy-duty, turbocharged, spark-ignited engine fuelled with wood-gas, a theoretical investigation is conducted in this work by using a numerical simulation. The results concern engine performance characteristics, NO and CO emissions for various engine operating conditions (i.e. air to fuel excess ratios), by using a comprehensive two-zone phenomenological model. The predictive ability of the thermodynamic model was tested against experimental measurements, which were obtained from the operation of a multi-cylinder, four-stroke, turbocharged, spark-ignited engine fuelled with wood-gas fuel at various loads. The experimental results are found to be in good agreement with the respective computed ones obtained from the simulation model. The main objective of the comparative assessment shown in the present work is to record and comparatively evaluate the relative impact of each one of the above mentioned parameters (compression ratio and spark timing) on the engine performance characteristics and emitted pollutants. Furthermore, an effort is made to determine the optimum combinations between these parameters, since at high engine load conditions their simultaneous increase may lead in undesirable results concerning the engine performance characteristics. The conclusions from the present investigation are valuable for the use of wood-gas as a full supplement energy source in conventional, natural gas fuelled, heavy-duty, spark-ignited engines used for electric power generation.