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Environmental, economic and political pressures have driven the interest towards the search of sustainable feedstock for biofuel production. At present, macroalgae (green, brown and red marine seaweed) is getting growing consideration as an alternative resource for sustainable biomass to produce biofuels, biochemical and food. The unique chemical composition and wide variation in the availability create various opportunities and also challenges for bio-based energy production. Recently, numerous studies have taken place in the exploitation of seaweed as carbon sources for the bioethanol production. Thus, this paper attempts to highlight the characteristics, processing techniques and potential applications of the seaweed. The present review also focuses on recent innovative approaches for the sustainable production of bioenergy from seaweed.

The increasing energy demand and more stringent legislation for engine pollutant emissions with the use of carbon-neutral fuels have forced to use alcohol. ABE, a combination of acetone, butanol, and ethanol, is a potentially fuel that can be produced from waste biomass via fermentation. Recently, this fuel has attracted researchers’ attention due to its better performance and less emission as a diesel blend when compared to ethanol. First, this article addresses past and recent research conducted in the field of biofuel (ABE) production from lignocellulosic materials. Second, the development in ABE production efficiency is reviewed and various methods of improving ABE production are presented. ABE from lignocellulosic materials (a green energy re- source) can be improved through metabolic engineering of the fermenting yeast (Clostridia) and/or pre-treat- ment techniques. Furthermore, the application of ethanol, butanol and ABE as biofuel blends is compared and summarised considering three aspects (1) combustion characteristics; (2) as an additive blend of diesel fuel in compression engines; and (3) as an additive blend of gasoline in spark ignition engines related to engine per- formance and emission levels. This study shows that ABE has the potential to become an important second-generation biofuel that can be blended with diesel and gasoline for the following reasons: it is cheaper to produce compared to butanol, it is possible to improve engine performance and it reduces exhaust gas emissions. Moreover, engine power is comparable to diesel, and at the same time ABE releases fewer emissions such as CO and NOx than other fuel blends.

Energy security and global warming concern are the two main driving forces for the global alcohol development that also have the effort to animate the agro-industry. Generally, alcohol and ether fuels are produced from several sources and can be produced locally. Almost all alcohol fuels have similar combustion and ignition characteristics to existing known mineral fuels. Mainly the ether fuels (MTBE and DME) are used as additives at low blending ratio to enhance the octane number and oxygen content of gasoline. The addition of alcohol and ether fuels to gasoline lead to a complete combustion due to the higher oxygen content, thereby leads to increased combustion efficiency and decreased engine emissions. The objectives of this paper are to systematically review the use of alcohols and ethers including butanol, methanol, ethanol, and fusel oil, MTBE, and DME as fuels in SI engine. Also, the current study has investigated the effects of performance (brake torque, brake power, BSFC, effective efficiency, and EGT), emissions (CO, CO2, NOx and HC) and combustion characteristics of SI engine with alcohol and ether. The increase in engine performance could be attained with an increased compression ratio along with the use of alcohol fuels which have a higher-octane value. Furthermore, alcohol and ether burn very cleanly than regular gasoline and produce lesser carbon monoxide (CO) and nitrogen oxide (NOx). On the other hand, the energy value of alcohol and ether fuels is approximately 30% lower than gasoline; thereby the specific fuel consumption (SFC) will increase simultaneously when using alcohol and ether as a fuel. Finally, this paper also discusses the impacts of alcohol on engine vibration, engine noise, and potential to be used as a gasoline octane enhancer. Alcohol can be used as a pure fuel in spark ignition engine, but it requires some modifications to the engine.

In recent years, alternative fuel studies have been conducted thoroughly by researchers through their experimental work. Depletion of fossil fuel raised the attention of researchers to investigate renewable energy sources such as biodiesel and alcohol. There is a lack of literature review study on the viability of alcohol acting as additive in biodiesel-diesel fuel blends. Thus, this review paper studies on the effects of various alcohol additives in biodiesel-diesel fuel blends on combustion behaviour, performance and emission characteristics of diesel engines. The physicochemical properties of alcohol and biodiesel are rigorously discussed, in which they are the main factors in determining the quality of the blended fuel. The aim of this paper is to identify the potential of alcohol fuel as an additive in the blended biodiesel and diesel fuel in correspond to the type of alcohol, blending ratio and engine operation conditions. Wide range of results from previous research studies with different types of compression-ignition engine, different engine operation conditions and varieties of alcohol-biodiesel-diesel fuel blending ratios were collected in this literature review study. Combustion behaviour such as coefficient of variations (COV), in-cylinder pressure, ignition delay, heat release rate and combustion duration are presented. Low cetane number and high latent heat of vaporization of alcohol cause a longer ignition delay, produce higher rate of heat release and lower in-cylinder pressure when compared with that of diesel fuel. Low density and viscosity of alcohol improve the spray characteristics and enhance air-fuel mixing process. In terms of engine performance analysis, the presence of oxygen in alcohol fuel promotes a more complete combustion; hence, resulting in an increase of thermal efficiency. In turn, emissions of carbon monoxide (CO), hydrocarbon (HC) and particulate matter (PM) are decreasing.

Current estimates for world cotton production are about 25 million tonnes and accounting for 50 million tons of biomass waste. The options for utilising cotton biomass wastes include composting, gasification, pyrolysis, fermentation (ethanol), anaerobic digestion and direct incineration. Solid cotton gin waste cannot be directly reused on-farm due to farm hygiene risks. Composting either on-farm or at the gin is an accepted method for pathogen disinfection and pesticide degradation, although this option may face the problem of small market demand and possible disease concerns. On the other hand, on-farm cotton residues are fundamental for minimising losses in soil carbon, organic carbon content and surface protection. Converting these wastes to energy using various treatments such as gasification, pyrolysis and anaerobic digestion minimises the land required for processing, and the energy produced may offset the much higher capital costs involved. The scope of this study is to examine the size of cotton industry in Australia and the associated by-products produced. The strengths, weaknesses, opportunities and threats of different options for utilising cotton wastes throughout processing were examined. The technical, environmental and economic aspects of each waste management option have formed the basis of our conclusions and recommendations. It seems that pyrolysis of cotton stalks is a good option due to the potential revenue of $104 million dollars. Using cotton gin trash (CGT) for ethanol production is another option, and the average production would be around 33–47 million litres of ethanol for the entire industry. The revenue from this process can be $33–47 million ($1/L). Cotton stalk provides the highest burning efficiency and longest burn time compared to corn stover and soybean residues. The potential amount of energy produced from burning cotton stalks can be around 24.8 PJ which is equivalent to $97 million worth of coal.

This paper introduces the resource, status and prospect of solar energy in Iran briefly. Among renewable energy sources, Iran has a high solar energy potential. The widespread deployment of solar energy is promising due to recent advancements in solar energy technologies. Therefore, many investors inside and outside the country are interested to invest in solar energy development. Iran’s total area is around 1600,000 km 2 or 1.6×10 12 m 2 with about 300 clear sunny days in a year and an average 2200 kW-h solar radiation per square meter. Considering only 1% of the total area with 10% system efficiency for solar energy harness, about 9 million MW h of energy can be obtained in a day. The government’s goal on 2012 was to install 53,000 MW capacity plants for electricity generation. To reach this goal, it was assumed that the new gas-fired plants along with the hydroelectric and nuclear power generating plants could be financed by independent power producers including those of foreign investment. Based on the fifth 5 year Socio-economic and Cultural Development Plan, the private sector was expected to have a share of at least 270 MW in renewable energy development. The existing small capacity solar energy plants are in Shiraz, Semnan, Taleghan, Yazd, Tehran and Khorasan. Based on the specified available solar trough technology, solar area, average solar hours and average solar direct irradiation, the technical potential of solar electricity was estimated to be 14.7 TWe. Under the current energy policies, the combined solar, wind and geothermal power plants are economically viable. These huge RES’s potential can be realized assuming the availability of technology, investment capital, human expertise and the other resources along with a long-term driven renewable energy policy. Due to high growth rate of electricity demand in Iran, the nominal installed capacity has increased by 8.9% per annum during 2001–2007. In the reference scenario, the share of RES in total installed electricity capacity is expected to be about 2% in 2030. It is expected that the cumulative RES installed capacity will reach 2.8 GW in 2030. This requires more than 2800 million US dollar investment during 2010–2030.

Homogeneous charge compression ignition (HCCI) engine uses a relatively new mode of combustion technology. In principle, there is no spark plug or injector to assist the combustion, and the combustion auto-ignites in multiple spots once the mixture has reached its chemical activation energy. The challenges in developing HCCI engines are the difficulties in: controlling the auto-ignition of the mixture and the heat release rate at high load operations, achieving a cold start, meeting emission standards and controlling knock. At low engine speeds, early auto-ignition can occur, possibly leading to knocking, while late auto-ignition at high engine speeds will make HCCI susceptible to misfire. Hydrogen greatly reduces emissions levels but with reduced power. However, when hydrogen is combined with diesel in dual-fuel mode, low NOx, CO and particulate matter (PM) emissions levels can be achieved, and engine efficiency can be increased by 13–16%. Numerical methods are commonly used to predict HCCI engines' performance (i.e. emissions levels, brake thermal efficiency and combustion phasing), which is cost-effective compared to solely relying on experimentation. The multi-zone method promises better simulation results compared to the single-zone model by combining detailed chemical kinetics with simplified 3D modeling so that turbulence and inhomogeneity in the mixture are considered; good agreement between simulations and experiments have been achieved. Specific strategies used in the experimental method (e.g. fuel additives, inlet air heating, inlet air pressurizing, exhaust gas recirculation (EGR) and injection methods), and numerical method (e.g. single-zone and multi-zone models, mixing model, turbulence model and multi-dimensional model), and other issues associated with HCCI engines are discussed in this paper.

Coalbed methane (CBM) or coal seam gas (CSG) as it is known in Australia is becoming an increasingly important source of energy around the world. Many countries such as United States, Canada, Australia and China are investing in the CSG industry. A rise in the cost of conventional natural gas and many other energy resources, along with a decline in these conventional resources and issues such as climate change have encouraged a global interest in alternative sources of energy like CSG. The estimated quantity of CSG worldwide is around 1.4×1014 m3, it is clear that coal seam gas is a significant source of energy. The first section of this paper will discuss the production size of CSG worldwide and the future of the industry. The usage of the coal bed seam for the sequestration of CO2 is also an added benefit. The reduction of CO2 released to the environment may help in the future mitigation of global warming. In addition, the re-injecting of the co-produced CO2 enhances the commercial recovery and production of CSG wells. In the second section, the impact of the CSG industry's by-products on the environment, the freshwater ecosystem and human health are analysed. The second section includes issues associated with the large volume of co-produced water with undesirable composition in the CSG industry. The management of this enormous amount of water requires cost effective technologies and methods. Many methods for dealing with water problems are discussed and analysed in this paper.

Algae can be converted directly into energy, such as biodiesel, bioethanol and biomethanol and therefore can be a source of renewable energy. There is a growing interest for biodiesel production from algae because of its higher yield non-edible oil production and its fast growth that does not compete for land with food production. About 50% of algae weight is oil that this lipid oil can be used to make biodiesel. Algae is capable of yielding 30 times more oil per acre than the crops currently used in biodiesel production. Processes for biodiesel production from algae-oil are similar to food and non-food crops derived biodiesel processes. Because of disadvantages of fossil fuels, renewable energy sources are getting importance for sustainable energy development and environmental protection. Among the renewable sources, Iran has high biofuel energy potential. The Iranian government is considerable attention to the utilization of renewable energy, especially biofuels. Iran has enough land in order to algae cultivation that does not compete with food production. A salt lake (Lake Orumieh) in Iran's West Azarbaijan province, Maharlu salt lake in Iran's Fars province, Qom salt lake in Iran's Qom province have given rise to a new species of algae for biofuel. Algae are frequent in the shallow-marine lime stones in Zagros Mountains in north of Fars province. Greenish blooms of algae can be seen in the Persian Gulf and Caspian Sea, south and north of Iran respectively. This study presents a brief introduction to the resource, status and prospect of algae as a sustainable energy source for biodiesel production in Iran. The main advantages of using algae for biodiesel production in Iran are described.

Australia is one of those countries that are considered rich and abundant in fossil fuel energy resources. It is important for Australia to regulate the use of conventional energy and attempt replacing these conventional energies with renewable energy (RE) resources. Renewable energy resources in Australia are widely categorised as solar energy, biomass, wave energy and wind energy. By increasing the utilisation of renewable energy resources the national contribution to world wide green house gases (GHG) emissions would be reduced, at the moment approximately 50% of Australia's GHG emissions are contributed from electricity generation [Dicks, AL, Diniz da Costa, JC, Simpson A, McLellan B. Fuel cells, hydrogen and energy supply in Australia. Journal of Power Sources 2004;1:1–12] with a large proportion of the remaining emissions coming from transport and vehicular sectors. As Australia's population, as well as that of the world, continues to grow and live increasingly energy dependant lives, the future of energy supply will grow. This paper investigates the potential of renewable resources in Australia at present and the magnitude of their present and future contributions to the national energy consumption. Conclusions will be drawn from the results of this investigative scan and recommendations will be proposed.

The production of bioethanol from agricultural residues such as wheat, barley, sugar cane, corn and rice in Iran is investigated in this paper. In Iran, agricultural residues are not commonly used for energy application. This paper aims to cover several perspectives on the size of the bioethanol feedstock resource in Iran. Crop residues and sugar cane bagasse are included in feedstock for production of bioethanol. There are approximately 17.86 MT of wasted crops in Iran that can potentially produce 4.91 GL of bioethanol per year. Wheat, sugar cane bagasse, rice, barely and corn are the most favourable bioethanol production source in Iran. Agricultural waste materials can be used for production of bioethanol fuel. Bioethanol can be considered as the optimum alternative fuel for gasoline. Bioethanol is an environmentally friendly fuel and has the potential to provide comparable engine performance results.

The activities in field of renewable energy in Iran are focused on scientific and research aspects, and research part is aimed at reduction of capital required for exploitation of related resources. The second step is to work research results into scientific dimension of this field for practical means, i.e. establishing electricity power plants. Due to recent advancements in wind energy, many investors in the country have become interested in investing in this type of energy. At the moment, projects assuming 130 MW of wind power plants are underway, of which, 25 MW is operational. Based on the planning in the 4th Socioeconomic and Cultural Development Plan (2005–2010), private sector is expected to have a share of at least 270 MW in renewable energies. However, it is the government's duty to take the first step for investment in biomass and solar power plants; private sector may then play its part once the infrastructures to this end are laid out. At the moment, a 250 kW plant is under construction in Shiraz and two more geothermal units with 5 and 50 MW capacities will follow. Moreover, two biomass and solar energy plants, standing at 10 and 17 MW, respectively, are of other upcoming projects. The project of Iran's renewable energy, aims to accelerate the sustainable development of wind energy through investment and removal of barriers. This preparatory project is funded by the global environment facility (GEF) and will provide for a number of international and national consultant missions and studies. Once the studies are concluded, a project to develop 25 MW of wind energy in the Manjil region of Gilan will be prepared. It will be consistent with the national development frameworks and objectives and form part of 100 MW of wind-powered energy, which is expected to be developed under the government's third 5-year national development plan (started 21 March 2000).