Application potential of vegetable oils as alternative to diesel fuels in compression ignition engines: A review

Vegetable oils have been identified as the promising alternative source to replace fossil based fuel in the compression ignition (CI) engine. It is renewable and possesses characteristics that is similar to that of the diesel. Biodiesel, transesterifiedform of vegetable oil (VO), is now being commercially used in CI engines. However, biodiesel production from VO involves use of alcohols and chemicals which results the need of skilled labor and investment for its production. In view of this, many studies are also being carried out on the direct use of VO in the engine. The direct use of VO oil in engine is as good as that of the diesel. The superior quality of diesel however makes it better performance in engine as compared to the vegetable oil. Preheating and blending of VO are found to be the most common solution to overcome its inferior properties. The use of preheated and blended VO is found to improve the engine overall performance. This paper is focused exclusively on the one-to-one basis of study pertaining to the effect of neat, preheated and blended vegetable oils on diesel engine performance and emission through supplementation of illustrative figures from the various experimental studies.     

Biogas as a potential renewable energy source: A Ghanaian case study

The associated harmful environmental, health and social effects with the use of traditional biomass and fossil fuel has enhanced the growing interest in the search for alternate cleaner source of energy globally. Ghana, a developing country depends heavy on woodfuel as a source of fuel contributing about 72% of the primary energy supply with crude oil and hydro making up the rest. Biogas generation has simply been seen as a by-product of anaerobic digestion of organic waste. Having proven to be a practicable and promising technology, it has been very successful and a very reliable and clean source of energy when proper management programmes are followed. There are vast biomass resources including organic waste in Ghana that have the potential for use as feedstock for biogas production to reduce the over reliance of woodfuel and fossil fuel, and to help reduce the it would reduce greenhouse gas emissions which may be affecting climate change. Ghana having the technical potential of constructing about 278,000 biogas plants, only a little over 100 biogas plants has so far been established. This paper presents the energy situation and the status of the biogas technology and utilization in Ghana. It also presents the potential benefits, prospects and challenges of the biogas technology.     

Flexibility as a source of value in the production of alternative fuels: The ethanol case

There is typically a high degree of flexibility associated with the production of alternative fuels due to the ability to source from different input raw materials or to produce different output products based on market conditions. In this paper, we consider the particular example of ethanol and seek to quantify the incremental value from flexibility in its production from sugarcane in Brazil. We accomplish this by first jointly modeling the stochastic processes for the prices of the two relevant commodities, sugar (a food commodity) and ethanol (an energy commodity) in discrete time as a bivariate lattice. This framework allows us to value the option to switch output products based on the respective price signals of the two commodities. However, unlike the usual assumption of geometric Brownian motion stochastic processes, we use the more realistic case of mean reverting commodity price processes. We estimate the parameters for these processes by applying a regression-based procedure to empirical sugar and ethanol data collected during a period from 1998 through 2008. Our results show that the option to switch outputs has significant value, even under the assumption of mean reverting prices, which has implications for both producers and policy-makers alike.     

Combustion of droplets of liquid fuels: A review

A review is presented of recent developments of the combustion of single droplets with the object of stimulating discussion and future work in the field. Among the areas covered are the combustion of stationary and moving droplets in an oxidising atmosphere, the combustion of monopropellants, the influence of high pressures and the ignition of droplets. The application of droplet theories to the modelling of various combustion systems is also outlined.     

Life cycle evaluation of hydrogen and other potential fuels for aircrafts

In the present study, hydrogen and some other alternative fuels (such as ammonia, methanol, ethanol, liquefied natural gas) are considered for aviation applications under a comprehensive life cycle assessment study and are evaluated comparatively with the conventional kerosene based jet fuel for various impact categories. Therefore, this study is performed with a well-to-wake approach to evaluate the overall life cycle of an aircraft running on these conventional and alternative fuels. Both conventional and renewable fuel routes are considered for the production of ammonia and hydrogen fuels. Although there are modifications required to fulfill the aviation fuel specifications for such alternative fuels, the long term viability and environmental sustainability make them attractive solutions for the future of aviation industry. This study uses a life cycle assessment of an average aircraft utilizing various alternative aviation fuels to determine the relative environmental impact of each life cycle phase. The life cycle phases included in the analyses are as follows: (i) production, operation and maintenance of the aircraft, (ii) construction, maintenance and disposal of the airport, (iii) production, transportation and utilization of the aviation fuel in the aircraft. The results show that hydrogen and liquefied natural gas represent more environmentally benign alternatives although fuel costs are higher compared to ammonia, jet fuel and methanol. The total GHG emissions from hydropower based ammonia and hydrogen are calculated to be about 0.24 kg CO₂ eq. per traveled tonne-km and 0.03 kg CO₂ eq. per traveled tonne-km, respectively. Renewable based ammonia and hydrogen fueled aircrafts can further decrease the overall environmental impact in many categories allowing a brighter future for aviation industry.     

Automotive engines and fuels: A review of future options

This paper reviews the current status and development potential of automotive heat engines: various types of internal combustion engines, the gas turbine, Stirling and Rankine cycle engines, and compound engine systems. Expected changes in transportation fuels from natural petroleum, and the likely impact of alternative fuels are also examined. Emphasis is placed on the general structure of the issues to be faced in making choices about where to put research and development resources, rather than on technical detail, to provide an overview of this broad area.     

The potential supply of synthetic fuels from Alaskan hydroelectric power and coal

It is proposed to develop and utilize the large potential hydroelectric power resources in Alaska to produce hydrogen by the electrolytic decomposition of water and to combine the hydrogen with the large Alaskan coal reserves to produce synthetic liquid and gaseous fuels. It is estimated that in this manner, as much as 1.8 million bbls/day of gasoline or 6.2 billion SCF/day of substitute natural gas can be produced. The existing and projected Alaskan pipelines would provide the means of transporting the fuels to energy consuming load centers in the U.S. This development would move the U.S. a considerable way towards energy independence as well as employing the natural resources in Alaska in an efficient manner.     

Taxation on vehicle fuels: its impacts on switching to cleaner fuels

Vehicular consumption of fossil fuel contributes over 90% of air pollution in Hong Kong. A key strategy to improve Hong Kong's air quality is to discourage dirty fuels (e.g., leaded petrol and high-sulphur diesel) and to promote the use of clean fuels (e.g., low-sulphur diesel and liquefied petroleum gas (LPG)). This paper presents the empirical evidence on the effectiveness of the Government's clean fuel programs that offer tax subsidy to lower the consumption cost of such fuels. For the cases of unleaded petrol and ultra-low-sulphur diesel, lower fuel duties were offered so that the prices of these fuels were below those of leaded petrol and conventional diesel. Conventional petrol and diesel were phased out. In order to decide on the level of fuel duty concessions required to introduce LPG for taxis and bio-diesel for other vehicles, various Government-run trial programs were introduced to obtain cost estimates of using these alternative cleaner fuels. LPG using vehicles were subsequently exempted from the fuel duty in order to attract taxi and light bus operators to switch to LPG. It is apparent that the higher the subsidy, the faster is the rate at which switching to cleaner fuels takes place.     

On the potential of solar energy conversion into hydrogen and/or other fuels

Solar energy, when used together with water for the production of hydrogen, forms an inexhaustible source of transportable primary energy. Hydrogen is also a potential means of storing solar energy. In this paper the thermodynamic and energetic conditions for the splitting of water are established. The different water decomposition techniques are discussed.Electrolysis. Electrolysis is a proven and convenient way of producing hydrogen. If the very high temperature electrolysis (80–1000°C) development is successful, heat-assisted electrolysis with electric efficiencies of 100% and more looks attractive in connection with thermo-mechanical helio-electricity conversion.Thermal conversion. Highest temperature (≈ 3000°C) direct decomposition (thermolysis) is thermodynamically interesting, but is, for the time being, technologically not feasible. Use of thermochemical cycles is mainly a question of economics and of adaptation to the high temperatures, attainable with solar concentrating devices.Quantum conversion. The thermodynamic potential of light makes quantum conversion highly attractive, requiring much basic research, though.Bioconversion. Biosystems are already operating in nature but with low and lowest efficiencies. With successful R & D to increase efficiencies, bio-energy systems seem to become a convenient way of fuel production.Economics are considered when it seems reasonable to do so, otherwise educated guesses are made as to the economics of the different decomposition techniques and their implications for the possible large-scale hydrogen production by solar energy.Some considerations are made on the influence of large-scale solar power plants on the climate.     

A general mathematical model of solid fuels pyrolysis

The aim of this work is to present and discuss a detailed kinetic model that describes the devolatilization process of solid fuels under pyrolysis conditions. The major reason for this interest in better understanding pyrolysis and combustion of coal, biomasses and solid fuels lies in the increasing concern for the environmental impact of large scale combustion processes. The common chemical and structural aspects of the different fuels are singled out and used as the starting point to define this mathematical model. The formation of light gases and liquid tars is the first step in the pyrolysis process. Particular attention is also devoted to the generality and flexibility of numerical and mathematical methods. Two major critical points are present inside this model: the first is related to the definition of the initial structure of the fuel and the second is constituted by the set of reference kinetic parameters of the different reactions. Several comparisons with experimental data are analysed and the molecular weight distributions of the tar from different coals evolved at different temperatures are also discussed.     

Muskmelon (Cucumis melo) seed oil: A potential non-food oil source for biodiesel production

Methanolysis of muskmelon seed oil was optimized employing RSM (response surface methodology). Four process variables were evaluated at two levels: methanol/oil molar ratio (3:1–12:1), catalyst concentration in relation to oil mass (0.25–1.25 wt % KOH), reaction temperature (25–65 °C) and methanolysis reaction time (20–90 min). Multiple regression analysis was employed to get the quadratic polynomial equation for predicting transesterification using RSM. The result indicated that catalyst concentration and reaction temperature were the important factors that significantly affect the yield of MMOMEs (muskmelon oil methyl esters)/biodiesel. The RSM methodology was used to obtain methyl esters yield (89.5%) were found at following reaction conditions; 5.8:1 methanol-to-oil ratio, 0.79% catalyst concentration, 55 °C reaction temperature and 72.5-min reaction time. There was a linear correlation between observed and predicted values. The biodiesel was analyzed using GC/MS (gas chromatography/mass spectrometry) which indicated four FAMEs (fatty acid methyl esters) (linoleic-, oleic-, palmitic- and stearic acids) as its major components. The FT-IR (fourier transform infraRed) spectrum of MMOMEs was also acquired to ensure the confirmation of methyl esters formation. Fuel properties of MMOMEs were determined and found to satisfy the ASTM D 6751 and EU 14214 specifications.     

Spray properties of alternative fuels: A comparative analysis of biodiesel and diesel

Physical properties of biodiesel play an important role in the injection, atomization and combustion performance. An experiment was carried out to investigate the spray properties of biodiesel. The experimental setup was based on an electronic unit‐pump (EUP) bench, a constant volume chamber and a high‐speed digital camera. The photographs of spray were dealt with by using an image processing procedure. Then the spray tip penetrations and cone angles were obtained and analyzed. The experimental results indicate that the spray tip penetrations and cone angles of biodiesel increase with increasing injection duration. In addition, with decreasing ambient pressure the spray tip penetrations increase while the cone angles decrease. Furthermore, ambient pressure has a stronger effect on the spray properties of biodiesel than injection pressure. On the macroscopically view, the shape of biodiesel spray is similar to that of diesel. The final tip penetrations and cone angles of biodiesel are greater than those of diesel due to its higher viscosity, density and bulk modulus. Copyright © 2008 John Wiley & Sons, Ltd.     

Hydrogen: A clean energy source

In this review, hydrogen has been considered as a “clean” energy source and carrier and discussed in comparison with present day energy sources mainly based on fossil fuels and nuclear energy. In particular, the environmental and safety issues connected with both nuclear power and coal gasification plants, such as those due to nuclear wastes, acid rain and carbon dioxide, have been considered. Conventional as well as advanced methods of hydrogen production have been examined, attention drawn to direct hydrogen production from alternative energy sources, and an overview provided on the state of the art. A brief insight into hydrogen storage and distribution as well as into conversion and utilization concludes the review.     

Demand for transportation fuels in the oecd: A temporal cross-section specification

The determinates of the demand for transportation fuels interest many researchers and policymakers who are considering various energy plans. This paper uses a random coefficient regression approach to estimate the demand for gasoline, diesel fuel and jet fuel. For these three fuels a flow adjustment specification is assumed and for gasoline demand a stock adjustment model is also estimated. Individual European country data are used as the data because these data contain wide variations in the price variables, due to the different tax structures of the individual countries. These data are averaged across countries and time to produce firm estimates of the price and income elasticities of demand. For gasoline demand the estimates obtained from the European data are compared with estimates made by other researchers for the United States.     

Biogas (a promising bioenergy source): A critical review on the potential of biogas as a sustainable energy source for gaseous fuelled spark ignition engines

Increasing demand for energy accompanied by environmental concerns has raised the requirement for limiting the use of fossil fuels in energy generation and transportation applications. Among the green and renewable energy-based solutions, biogas is quite promising since it could be implemented for power generation applications (engines driving generators and pump sets) in rural areas, at domestic and industrial scales with lower capital investment and production cost by using the agricultural crop residues and other domestic biomass sources as raw materials. However, the composition of biogas varies depending on the raw materials, and higher concentration of carbon dioxide in biogas results in combustion variations affecting engine durability. This review focuses on the role of biogas in achieving sustainable development goals with an emphasis on its utilization in gaseous fuelled spark-ignited engines. Recent progress in biogas production and upgradation techniques are also detailed. Challenges related to the stability and characteristics of biogas fuelled spark-ignited engines could be addressed by either modifying the physical parameters of the engine or by enhancing the fuel quality (upgradation to biomethane or blending with hydrogen). A comprehensive review on the effects of these approaches on the performance, combustion, and emission characteristics of biogas-fuelled engines is discussed in detail with a note on engine operating parameters.     

A review on exergy analysis of biomass based fuels

Renewable energy sources can be a good substitute of the fossil fuels which are being terminated fast. Nowadays biomass and biofuels are considered because of their environment friendly characteristics and their ability of supplying much more energy. An alternative means to select the most efficient and convenient biomass, is exergy analysis. The present paper has reviewed the existent surveys on the exergy analysis of different kind of biomass included the woody biomass, herbaceous and agricultural biomass, aquatic biomass, contaminated biomass and industrial biomass. The most common thermochemical processes are investigated and the efficiency of the different process and various kinds of biomass are determined.     

Biomass-derived aviation fuels: Challenges and perspective

The worldwide utilization of fossil energy, including its specific application as transportation fuel, significantly contributes to the continuous increase of the atmospheric CO₂ concentration. Several solutions have been promoted or scheduled to reduce CO₂ emissions. Among these solutions, the development of renewable energy resources, such as bio-fuels, offers important advantages as promoted by several countries and institutions who disclosed their plans to partly or totally use alternative renewable energy sources in the future. For the rapidly growing aviation sector, aviation fuel derived from fossil resources is still the major available energy source. The development of renewable aviation fuel is considered to be a promising future strategy to reduce related CO₂ emissions. The worldwide total aviation fuel consumption by commercial airlines increased from about 260 million m³/year in 2005 to over 340 million m³/year in 2018, and a further annual increase of about 5% is expected till 2050.Worldwide actions have hence been undertaken with respect to bio-aviation fuel production, distribution, and demonstration flying. As a relatively new topic, there are a lot of remaining challenges in technology development, fuel certification and distribution. The production technology, policy and environmental impact of bio-aviation fuel were comprehensively reviewed, including its production by the catalytic conversion of lipids, by the conversion of carbohydrates or lignocellulosic biomass, and by developing bio-refinery concepts for bio-aviation fuel production. The future reduction of CO₂ emissions in the aviation sector requires an improvement of the biomass to aviation fuel production technology through the correct integration of biology, chemical engineering, and energy crops. The paper illustrates this potential integration through reviewing the current research in the production of aviation fuels from biomass, including the complete industrial chain from airplane manufacturer, aviation fuel producer and provider, airline strategies, and ongoing R&D, bearing in mind that major efforts are required to foster the development of the cost-effective production of renewable aviation fuel. The different topics of the Table of contents will be subsequently dealt with.     

Anhydrous ethanol: A renewable source of energy

Anhydrous ethanol is one of the biofuels produced today and it is a subset of renewable energy. It is considered to be an excellent alternative clean-burning fuel to gasoline. Anhydrous ethanol is commercially produced by either catalytic hydration of ethylene or fermentation of biomass. Any biological material that has sugar, starch or cellulose can be used as biomass for producing anhydrous ethanol. Since ethanol–water solution forms a minimum-boiling azeotrope of composition of 89.4 mol% ethanol and 10.6 mol% water at 78.2 °C and standard atmospheric pressure, the dilute ethanol–water solutions produced by fermentation process can be continuously rectified to give at best solutions containing 89.4 mol% ethanol at standard atmospheric pressure. Therefore, special process for removal of the remaining water is required for manufacture of anhydrous ethanol. Various processes for producing anhydrous ethanol have been used/suggested. These include: (i) chemical dehydration process, (ii) dehydration by vacuum distillation process, (iii) azeotropic distillation process, (iv) extractive distillation processes, (v) membrane processes, (vi) adsorption processes and (vii) diffusion distillation process. These processes of manufacturing anhydrous ethanol have been improved continuously due to the increasingly strict requirements for quantity and quality of this product. The literature available on these processes is reviewed. These processes are also compared on the basis of energy requirements.