Progress in the production and application of n-butanol as a biofuel

Butanol is a very competitive renewable biofuel for use in internal combustion engines given its many advantages. In this review, the properties of butanol are compared with the conventional gasoline, diesel fuel, and some widely used biofuels, i.e. methanol, ethanol, biodiesel. The comparison of fuel properties indicates that n-butanol has the potential to overcome the drawbacks brought by low-carbon alcohols or biodiesel. Then, the development of butanol production is reviewed and various methods for increasing fermentative butanol production are introduced in detailed, i.e. metabolic engineering of the Clostridia, advanced fermentation technique. The most costive part of the fermentation is the substrate, so methods involved in renewed substrates are also mentioned. Next, the applications of butanol as a biofuel are summarized from three aspects: (1) fundamental combustion experiments in some well-defined burning reactors; (2) a substitute for gasoline in spark ignition engine; (3) a substitute for diesel fuel in compression ignition engine. These studies demonstrate that butanol, as a potential second generation biofuel, is a better alternative for the gasoline or diesel fuel, from the viewpoints of combustion characteristics, engine performance, and exhaust emissions. However, butanol has not been intensively studied when compared to ethanol or biodiesel, for which considerable numbers of reports are available. Finally, some challenges and future research directions are outlined in the last section of this review.     

Comprehensive study of biodiesel fuel for HSDI engines in conventional and low temperature combustion conditions

In this research, an experimental investigation has been performed to give insight into the potential of biodiesel as an alternative fuel for High Speed Direct Injection (HSDI) diesel engines. The scope of this work has been broadened by comparing the combustion characteristics of diesel and biodiesel fuels in a wide range of engine loads and EGR conditions, including the high EGR rates expected for future diesel engines operating in the low temperature combustion (LTC) regime.The experimental work has been carried out in a single-cylinder engine running alternatively with diesel and biodiesel fuels. Conventional diesel fuel and neat biodiesel have been compared in terms of their combustion performance through a new methodology designed for isolating the actual effects of each fuel on diesel combustion, aside from their intrinsic differences in chemical composition.The analysis of the results has been sequentially divided into two progressive and complementary steps. Initially, the overall combustion performance of each fuel has been critically evaluated based on a set of parameters used as tracers of the combustion quality, such as the combustion duration or the indicated efficiency. With the knowledge obtained from this previous overview, the analysis focuses on the detailed influence of biodiesel on the different diesel combustion stages known ignition delay, premixed combustion and mixing controlled combustion, considering also the impact on CO and UHC pollutant emissions.The results of this research explain why the biodiesel fuel accelerates the diesel combustion process in all engine loads and EGR rates, even in those corresponding with LTC conditions, increasing its possibilities as alternative fuel for future DI diesel engines.     

The impacts of compression ratio on the performance and emissions of ice powered by oxygenated fuels: A review

Energy sources are becoming a governmental issue, with cost and stable supply as the main concern. Oxygenated fuels production is cheap, simple and eco-friendly, as a well as can be produced locally, cutting down on transportation fuel costs. Oxygenated fuels are used directly in an engine as a pure fuel, or they can be blended with fossil fuel. The most common fuels that are conceded under oxygenated fuels are ethanol, methanol, butanol Dimethyl Ether (DME), Ethyl tert-butyl ether (ETBE), Methyl tert-butyl ether (MTBE) and biodiesel that have attracted the attention of researchers. Due to the higher heat of vaporization, high octane rating, high flammability temperature, and single boiling point, the oxygenated fuels have a positive impact on the engine performance, combustion, and emissions by allowing the increase of the compression ratio. Oxygenated fuels also have a considerable oxygen content that causes clean combustion. The aim of this paper was to systematically review the impact of compression ratio (CR) on the performance, combustion and emissions of internal combustion engines (ICE) that are operated with oxygenated fuels that could potentially replace petroleum-based fuels or to improve the fuel properties. The higher octane rating of oxygenated fuels can endure higher compression ratios before an engine starts knocking, thus giving an engine the ability to deliver more power efficiently and economically. One of the more significant findings to emerge from this review study was the slight increases or decreases in power when oxygenated fuel was used at the original CR in ICE engines. Also, CO, HC, and NOx emissions decreased while the fuel consumption (FC) increased. However, at higher CR, the engine performance increased and fuel consumption decreased for both SI and CI engines. It was seen the NOx, CO and CO₂ emissions of oxygenated fuels decreased with the increasing CR in the SI engine, but the HC increased. Meanwhile, in CI engine, the HC, CO and NOx decreased as the CR increased with biodiesel fuel.     

Modeling HCCI combustion of biofuels: A review

The ever increasing energy demands coupled with the limited availability of fossil fuels and the detrimental environmental effects resulting from their use, has guided research toward seeking alternative fuels to gradually substitute conventional ones. Among these, biofuels have received increasing attention due to their attractive features of being renewable in nature and reducing the net CO₂ emissions. Biofuels have been used in conventional diesel and gasoline engines either as neat fuels or as supplements.Fortunately, a relatively new combustion concept for internal combustion engines, namely homogeneous charge compression ignition (HCCI) combustion, has been evolved in parallel to the biofuel research. HCCI combustion seems to be able to take advantage of the diverse properties of biofuels, since in this combustion mode ignition is not externally instigated, but relies on the compression and subsequent autoignition of a fuel-air mixture. This fact allows the utilization of different fuels or blends thereof, in order to regulate the ignition point and provide adequate operation under diverse operating conditions.This study provides an overview of existing simulation models for the simulation of biofueled HCCI combustion. Simulation models aid and supplement the experimental research conducted on HCCI combustion, providing a fundamental insight into the physicochemical parameters affecting performance and emissions formation. The simulation models include single-zone models, multi-zone models, probability based models, and multi-dimensional models in order of complexity. The vast majority of these models implement chemical kinetics to simulate the combustion process, not only due to the inherent dependence of HCCI combustion on the physicochemical properties of the fuel, but also due to the sometimes complex chemical structure of the biofuels, which include esters, ethers and alcohols. The reaction paths for these homologous series are quite different from the conventional hydrocarbons used to simulate conventional fuels, and provide the ground for current and future research work.     

Performance of biodiesel/higher alcohols blends in a diesel engine

Alcohols extensively used in internal combustion engines are important renewable and sustainable energy resources from environmental and economical perspectives. Besides, bio production of alcohols decreases consumption of fossil‐based fuels. Although there are many studies with regards to the use of lower alcohols such as methanol and ethanol in internal combustion engines, there are a limited number of investigations with higher alcohols. Higher alcohols such as propanol, n‐butanol, and 1‐pentanol are part of the next generation of biofuels, given they provide better fuel properties than lower alcohols. Biodiesel–higher alcohol blends can be used in diesel engines without any engine modification but need to be tested under various engine conditions with long periods in order to evaluate their impacts on engine performance and environmental pollutants. The objective of this study was to evaluate the effect of using propanol, n‐butanol, and 1‐pentanol in waste oil methyl ester (B100) on engine performance and exhaust emissions of a diesel engine running at different loads (0, 3, 6, and 9 kW) with a fixed engine speed (1800 rpm). Test fuel blends were prepared by adding propanol, n‐butanol, and 1‐pentanol (10 vol.%) into waste oil methyl ester to achieve blends of B90Pr10, B90nB10, and B90Pn10, respectively. According to engine performance and exhaust emissions results, the addition of propanol, n‐butanol, and 1‐pentanol to B100 had the effect of increasing brake specific fuel consumption and exhaust gas temperatures. The brake thermal efficiency (BTE) decreased for B90Pr10 and B90nB10, while B90Pn10 showed a slight increase in BTE as compared with B100. When compared with B100, B90Pr10, B90nB10, and B90Pn10 decreased carbon monoxide emissions at lower loads while it increased slightly at 9 kW load. The decrement in oxides of nitrogen emission was observed at whole loads for B90Pr10, B90nB10, and B90Pn10 compared with B100. When considering all loads, B90Pn10 presented the best mean hydrocarbon emission with a reduction of 45.41%. Copyright © 2016 John Wiley & Sons, Ltd.     

含氧燃料对内燃机燃烧和排放性能的影响

列举醇类、醚类、酯类、生物柴油等及其作为含氧燃料添加剂与汽、柴油混合的混合燃料性能，介绍部分纯质含氧燃料及其混合燃料对内燃机燃烧和排放的影响。研究表明，醇类燃料及其与汽油的混合燃料能够降低点燃式发动机的HC和CO排放，使发动机的动力性和经济性提高；二甲醚燃料、柴油与DMC或ADMM等的混合燃料对降低压燃式发动机的微粒排放具有显著的作用。含氧化合物混入燃油中有利于降低内燃机中HC，CO等物质的排放。     

Analysis of performance parameters of an ethanol fueled spark ignition engine operating with hydrogen enrichment

Concerns with the environment and energy security have increased interest in phasing out fossil fuels in the automotive industry, as it transitions from conventional internal combustion engines (ICE) to electric and fuel cell powertrains. During this transition, ethanol is of particular interest as a renewable fuel option in ICE, despite drawbacks compared to gasoline. Adding hydrogen to ethanol could remedy the disadvantages associated with ethanol, while maintaining the benefits of using renewable fuels. There is a gap in the literature of both experimental and numerical studies considering hydrogen addition in turbocharged ethanol engines. Therefore, this paper presents an experimental and numerical study of a turbocharged ethanol engine operating with hydrogen enrichment at stoichiometric conditions under boosted conditions. It was concluded that hydrogen addition allowed spark ignition engines to achieve lower brake specific energy consumption, better performance, and lower emissions. Thus, after proper calibration, a simulation model was created and shown to be a suitable tool to predict engine performance of a spark ignition engine operating with hydrogen enrichment and reduce the overall number of experimental tests needed to tune engines operating with this fuel blend. Finally, some operating strategies are recommended based on these findings.     

Experimental investigations of a four-stroke single cylinder direct injection diesel engine operated on dual fuel mode with producer gas as inducted fuel and Honge oil and its methyl ester (HOME) as injected fuels

In order to meet the energy requirements, there has been growing interest in alternative fuels like biodiesels, methyl alcohol, ethyl alcohol, biogas, hydrogen and producer gas to provide a suitable diesel oil substitute for internal combustion engines. Vegetable oils present a very promising alternative to diesel oil since they are renewable and have similar properties. Vegetable oils offer almost the same power output with slightly lower thermal efficiency when used in diesel engine [Srivastava A, Prasad R. Triglycerides-based diesel fuels. Renew Sustain Energy Rev 2000;4:111–33. [1]; Vellguth G. Performance of vegetable oils and their monoesters as fuels for diesel engines. SAE 831358, 1983. [2]; Demirbas A. Biodiesel production from vegetable oils via catalytic and non-catalytic supercritical methanol transesterification methods. Int J Prog Energy Combust Sci 2005;31:466–87. [3]; Jajoo BN, Keoti RS. Evaluation of vegetable oils as supplementary fuels for diesel engines. In: Proceedings of the XV national conference on IC engines and combustion, Anna University Chennai, 1997. [4]; Altin R, Cetinkaya S, Yucesu HS. The potential of using vegetable oil fuels as fuel for diesel engines. Int J Energy Convers Manage 2000;42:529–38, 248. [5]; Gajendra Babu MK, Chandan Kumar Das LM. Experimental investigations on a Karanja oil methyl ester fuelled DI diesel engine. SAE 2006-01-0238, 2006. [6]; Agarwal D, Kumar Agarwal A. Performance and emission characteristics of a Jatropha oil (preheated and blends) in a direct injection compression ignition engine. Int J Appl Therm Eng 2007;27:2314–23. [7]]. Research in this direction with edible oils have yielded encouraging results, but their use as fuel for diesel engine has limited applications due to higher domestic requirement [Scholl Kyle W, Sorenson Spencer C. Combustion Analysis of soyabean oil methyl ester in a direct injection diesel engine. SAE 930934, 1993. [8]; Nwafor OMI. Effect of advanced injection timing on the performance of rapeseed oil in diesel engines. Int J Renew Energy 2000;21:433–44. [9]; Nwafor OMI. The effect of elevated fuel inlet temperature on performance of diesel engine running on neat vegetable oil at constant speed conditions. Renew Energy 2003;28:171–81. [10]]. In view of this, Honge oil (Pongamia Pinnata Linn) being non-edible oil could be regarded as an alternative fuel for CI engine applications. The viscosity of Honge oil is reduced by transesterification process to obtain Honge oil methyl ester (HOME).Gasification is a process in which solid biomass is converted into a mixture of combustible gases, which complete their combustion in an IC engine. Hence, producer gas can act as a promising alternative fuel, especially for diesel engines by substituting considerable amount of diesel fuels. Downdraft moving bed gasifiers coupled with IC engine are a good choice for moderate quantities of available biomass, up to 500 kW of electric power. Hence, bioderived gas and vegetable liquids appear more attractive in view of their friendly environmental nature. Since vegetable oils produce higher smoke emissions, dual fuel operation could be adopted for improving their performance.     

正丁醇作为生物燃料在生产和应用方面的进展

作为车用替代燃料,丁醇的热值比乙醇高30%左右,挥发性只有乙醇的1/6左右,吸湿性远小于甲醇、乙醇和丙醇,具有适度的水溶性,腐蚀性低,安全性更高。但丁醇直接应用到发动机上也存在一些问题,如其热值比传统汽油或柴油低,使得燃料消耗量增加;燃烧效率低于甲醇、乙醇;当应用于点燃式发动机时,丁醇较高的黏度将产生潜在的沉积或腐蚀等问题。目前许多研究者将正丁醇作为替代生物燃料进行研究,现有的研究主要是将丁醇与汽油或柴油混合应用在发动机上,或是应用在一些基本的燃烧反应器中。综合各方面的研究成果,正丁醇在混合燃料中体积分数小于20%时,无需调整发动机就可获得与汽油燃料相同的发动机功率;当达到30%时,发动机最大功率开始下降;随着正丁醇体积的增加,燃料消耗量增加。CO、THC、NOx排放的减少或增加取决于具体的发动机、操作条件、丁醇-汽油的混合比等。混合燃料与纯汽油相比,未燃烧醇的排放增加,而且丁醇的比例越高,未燃烧醇的排放越高。     

NOX emissions of compression ignition engines fueled with various biodiesel blends: A review

There are some challenges about NO_X emissions exhausted from diesel engines fueled with biodiesel. Due to increasingly stringent emission regulations, the different methods such as varying the engine operating parameters, treatment with antioxidant additive and blending fuels have been adapted to reduce emissions of biodiesel combustion. One of the effective methods is the combustion of dual or blending fuels. Various fuels such as gasoline, hydrogen, natural gas, biogas, different types of alcohols and also fuel additives have been used to reduce biodiesel disadvantages. This study reviews the potential of the different fuels as an additive in biodiesel fuel in correspond to reduce NO_X emissions. The general reduction of NO_X has been observed with the presence of gasoline, biogas and alcohols in biodiesel blends. The reduction of NO_X in biodiesel-hydrogen, biodiesel-diesel or biodiesel–CNG combustion has not been observed through all engine conditions. Moreover the retarding injection timing, the lower injection pressure, EGR higher than 30% can result in the reduced NO_X emissions. However it seems the decrease in NO_X emissions can be achieved by the use of most fuels in blending with biodiesel under all engine operating conditions, if only the proper injection parameters and blending proportions of fuels are set.     

Combustion chemical kinetics of biodiesel and related compounds (methyl and ethyl esters): Experiments and modeling – Advances and future refinements

The motivation for and challenges in reducing the world's dependence on crude oil while simultaneously improving engine performance through better fuel efficiency and reduced exhaust emissions have led to the emergence of new fuels and combustion devices. Over the past ten years, considerable effort has gone into understanding combustion phenomena in relation to emerging fuel streams entering the market. The present article focuses specifically on one typical emerging transportation fuel dedicated to the diesel engine, biodiesel, with an emphasis on ethyl esters because of recently renewed interest in its use as a completely green biofuel. Based on a review of the research developments over the past ten years in advanced experimental and kinetic modeling related to the oxidation of biodiesel and related components, the main gaps in the field are highlighted to facilitate the convergence toward clean and efficient combustion in diesel engines. After briefly outlining the synergy between “feedstocks – conversion process – biodiesel combustion”, the combustion kinetics of methyl and ethyl biodiesels are reviewed with emphasis on two complementary aspects: mechanism generation based on a detailed chemical kinetic approach that leads to predictive combustion models and experimental combustion devices that generate the data required during the development and validation of the predictive models.     

Development of glycerol/O2 biofuel cell

Glycerol is an attractive fuel for a fuel cell, because it is non-toxic, non-volatile, non-flammable, has high energy density, and is abundant due to the fact that it is a byproduct of biodiesel production. However, it has not been an effective fuel for low temperature, precious metal catalyzed fuel cells. In this paper, we describe the use of glycerol as a fuel in an enzymatic biofuel cell. An alcohol dehydrogenase and aldehyde dehydrogenase-based bioanode has been developed that oxidizes glycerol, a safe high energy density fuel. Glycerol/O₂ biofuel cells employing these bioanodes have yielded power densities of up to 1.21 mW cm⁻², and have the ability to operate at 98.9% fuel concentrations. Previous biofuel cells could not operate effectively at high fuel concentrations due to the nature of the solid fuel such as sugar or the solvent characteristics of fuels such as lower aliphatic alcohols. The glycerol/O₂ biofuel cell provides improved power densities compared to ethanol biofuel cells due to ability to more completely oxidize the fuel.     

A review of hydrogen as a compression ignition engine fuel

Diesel fuelled engines emit higher levels of carbon dioxide and other harmful air pollutants (such as noxious gases and particulates) per litre of fuel than gasoline engines. This fact, combined with the recent diesel emission scandal and the rumours of more widespread cheating by automotive manufacturers have initiated a long discussion about the future and sustainability of diesel engines.Improving the compression ignition engine is a direct way of going green. Reducing the harmful emissions can be achieved by future developments in the engine technology but also the implementation of alternative fuels. Hydrogen is a renewable, high-efficient and clean fuel that can potentially save the future of diesel-type engines. The evolution of high-efficiency renewable hydrogen production methods is the most important path for the start of a new hydrogen era for the compression ignition engine that can improve its sustainability and maximum efficiency.This paper provides a detailed overview of hydrogen as a fuel for compression ignition engines. A comprehensive review of the past and recent research activities on the topic is documented. The review focuses on the in-cylinder combustion of hydrogen either as a primary fuel or in dual fuel operation. The effects of injection strategies, compression ratio and exhaust gas recirculation on the combustion and emission characteristics of the hydrogen fuelled engine are fully analysed. The main limitations, challenges and perspectives are presented.     

The potential role of hydrogen as a sustainable transportation fuel to combat global warming

Hydrogen is recognized as a key source of the sustainable energy solutions. The transportation sector is known as one of the largest fuel consumers of the global energy market. Hydrogen can become a promising fuel for sustainable transportation by providing clean, reliable, safe, convenient, customer friendly, and affordable energy. In this study, the possibility of hydrogen as the major fuel for transportation systems is investigated comprehensively based on the recent data published in the literature. Due to its several characteristic advantages, such as energy density, abundance, ease of transportation, a wide variety of production methods from clean and renewable fuels with zero or minimal emissions; hydrogen appears to be a great chemical fuel which can potentially replace fossil fuel use in internal combustion engines. In order to take advantage of hydrogen as an internal combustion engine fuel, existing engines should be redesigned to avoid abnormal combustion. Hydrogen use in internal combustion engines could enhance system efficiencies, offer higher power outputs per vehicle, and emit lower amounts of greenhouse gases. Even though hydrogen-powered fuel cells have lower emissions than internal combustion engines, they require additional space and weight and they are generally more expensive. Therefore, the scope of this study is hydrogen-fueled internal combustion engines. It is also highlighted that in order to become a truly sustainable and clean fuel, hydrogen should be produced from renewable energy and material resources with zero or minimal emissions at high efficiencies. In addition, in this study, conventional, hybrid, electric, biofuel, fuel cell, and hydrogen fueled ICE vehicles are comparatively assessed based on their CO₂ and SO₂ emissions, social cost of carbon, energy and exergy efficiencies, fuel consumption, fuel price, and driving range. The results show that when all of these criteria are taken into account, fuel cell vehicles have the highest average performance ranking (4.97/10), followed by hydrogen fueled ICEs (4.81/10) and biofuel vehicles (4.71/10). On the other hand, conventional vehicles have the lowest average performance ranking (1.21/10), followed by electric vehicles (4.24/10) and hybrid vehicles (4.53/10).     

A critical review: Application of methanol as a fuel for internal combustion engines and effects of blending methanol with diesel/biodiesel/ethanol on performance,emission, and combustion characteristics of engines

This article presents a comprehensive overview of methanol as a potential oxygenated fuel for internal combustion engines. Here two approaches have been examined to evaluate the utilization of methanol, namely blending with diesel/biodiesel/methanol and premixing with intake air or fumigation. In conventional compression ignition engines, up to 95% and 25% diesel can be replaced by methanol through fumigation and blending, respectively. Higher latent heat of vaporization of alcohol led to lower peak in-cylinder pressure and NO_x; however, it negatively affects thermal efficiency and hydrocarbon and carbon monoxide emissions. Fumigation of alcohol requires modifications in the existing engine, whereas blending needed surfactants or additives to produce stable alcohol–diesel blends. High injection pressure and late direct injection, methanol–diesel blends have shown lower emissions and proved their potential as a suitable replacement for ethanol–diesel blends from the components durability perspective.     

相同氧含量醇类混合燃料燃烧和排放特性差异研究

对一台4缸发动机燃用相同氧浓度的不同醇类混合燃料进行了试验研究,以对比不同三元燃料柴油机在相同转速不同负荷情况下的燃烧特性和常规排放的差异。试验结果表明:甲醇混合燃料在醇类混合燃料中获得最高的燃烧压力,而丁醇混合燃料的热释放率最高。与普通柴油相比,戊醇混合燃料在不同混合物中具有相对最佳的CO和未燃碳氢排放,甲醇混合燃料可获得最优的氮氧化物排放;乙醇混合燃料减小颗粒物效果明显,最大可以减少22.4%～55.6%的颗粒物数量浓度和3.4%～12.8%的颗粒物粒径,其中乙醇混合燃料的核态颗粒物和聚集态颗粒物排放量也最低,戊醇混合燃料达到最高(除高负荷外)。     

Future fuels and mixture preparation methods for spark ignition automobile engines

Research in the automobile industry focuses on studies of spark ignition automobile engines especially of stratified charge engines, lean combustion concepts, engines fueled by alcohol/gasoline blends, alcohol engines, and engines with on-board gas generators fueled by a variety of liquid fuels. The goal of this work is the development of low-emission, high fuel-economy and high performance power systems for the early 1990s. The implementation of this objective makes it necessary for more information on future fuel characteristics. In addition proper mixture preparation methods must be applied to find solutions to specific problems such as NO_x formation and aldehyde emission, while maintaining good fuel economy and high engine efficiency. The goal of this paper is to discuss the most attractive approaches for improved preparation and distribution of the fuel-air mixture with respect to future fuels such as alcohol/gasoline blends and other alcohol fuels.     

Determination of ecological efficiency in internal combustion engines: The use of biodiesel

This paper evaluates and quantifies the environmental impact from the use of some renewable fuels and fossils fuels in internal combustion engines. The following fuels are evaluated: gasoline blended with anhydrous ethyl alcohol (anhydrous ethanol), conventional diesel fuel, biodiesel in pure form and blended with diesel fuel, and natural gas. For the case of biodiesel, its complete life cycle and the closed carbon cycle (photosynthesis) were considered. The ecological efficiency concept depends on the environmental impact caused by CO₂, SO₂, NO_x and particulate material (PM) emissions. The exhaust gases from internal combustion engines, in the case of the gasoline (blended with alcohol), biodiesel and biodiesel blended with conventional diesel, are the less polluting; on the other hand, the most polluting are those related to conventional diesel. They can cause serious problems to the environment because of their dangerous components for the human, animal and vegetable life. The resultant pollution of each one of the mentioned fuels are analyzed, considering separately CO₂, SO₂, NO_x and particulate material (PM) emissions. As conclusion, it is possible to calculate an environmental factor that represents, qualitatively and quantitative, the emissions in internal combustion engines that are mostly used in urban transport. Biodiesel in pure form (B100) and blended with conventional diesel as fuel for engines pollute less than conventional diesel fuel. The ecological efficiency for pure biodiesel (B100) is 86.75%; for biodiesel blended with conventional diesel fuel (B20, 20% biodiesel and 80% diesel), it is 78.79%. Finally, the ecological efficiency for conventional diesel, when used in engines, is 77.34%; for gasoline, it is 82.52%, and for natural gas, it is 91.95%. All these figures considered a thermal efficiency of 30% for the internal combustion engine.     

Effect of engine parameters and type of gaseous fuel on the performance of dual-fuel gas diesel engines—A critical review

Petroleum resources are finite and, therefore, search for their alternative non-petroleum fuels for internal combustion engines is continuing all over the world. Moreover gases emitted by petroleum fuel driven vehicles have an adverse effect on the environment and human health. There is universal acceptance of the need to reduce such emissions. Towards this, scientists have proposed various solutions for diesel engines, one of which is the use of gaseous fuels as a supplement for liquid diesel fuel. These engines, which use conventional diesel fuel and gaseous fuel, are referred to as ‘dual-fuel engines’. Natural gas and bio-derived gas appear more attractive alternative fuels for dual-fuel engines in view of their friendly environmental nature. In the gas-fumigated dual-fuel engine, the primary fuel is mixed outside the cylinder before it is inducted into the cylinder. A pilot quantity of liquid fuel is injected towards the end of the compression stroke to initiate combustion. When considering a gaseous fuel for use in existing diesel engines, a number of issues which include, the effects of engine operating and design parameters, and type of gaseous fuel, on the performance of the dual-fuel engines, are important. This paper reviews the research on above issues carried out by various scientists in different diesel engines. This paper touches upon performance, combustion and emission characteristics of dual-fuel engines which use natural gas, biogas, producer gas, methane, liquefied petroleum gas, propane, etc. as gaseous fuel. It reveals that ‘dual-fuel concept’ is a promising technique for controlling both NO_x and soot emissions even on existing diesel engine. But, HC, CO emissions and ‘bsfc’ are higher for part load gas diesel engine operations. Thermal efficiency of dual-fuel engines improve either with increased engine speed, or with advanced injection timings, or with increased amount of pilot fuel. The ignition characteristics of the gaseous fuels need more research for a long-term use in a dual-fuel engine. It is found that, the selection of engine operating and design parameters play a vital role in minimizing the performance divergences between an existing diesel engine and a ‘gas diesel engine’.     

我国生物质能源现代化应用前景展望(三)——生物质能源转化技术经济评估

秸秆、动植物油脂、微藻等生物质原料可以生产液体运输燃料,生物燃料的化学成分包括醇、酯、烃三类。燃料乙醇主要替代汽油,受到各国重视,其中纤维素乙醇技术发展较快。脂肪酸甲酯是第一代生物柴油的主要成分,价格主要受油脂原料价格的影响,由于和柴油相容性差,低温流动性不好,将逐渐被加氢生产的第二代生物柴油取代。相比醇、酯等含氧燃料,烃类生物燃料在使用性能上有很多优势。有多条技术路线可以生产烃类燃料,其中油脂加氢制喷气燃料已接近商业应用,热解油加氢可将木质生物质原料中的"木质素"组分转化为生物油,大型快速热解工厂可以和热电联产装置组成联合系统,从而提高工厂综合热效率,降低生物燃料生产成本。因此,快速热解生产汽柴油将成为主要的生物燃料生产路线。生物质与煤共气化技术通过提高气化温度,不仅可以提高生物质气化效率,减少焦油的生成,还可以解决生物质供给的季节性问题,为生物质的高效利用提供了一条新的技术途径。微藻高压液化生产柴油是最具发展潜力的第三代生物燃料技术,我国需要加强微藻养殖及加工技术攻关。