Encyclopedia of Renewable Energy. James G. Speight
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economy. Energy efficiency is the percentage of the fuel’s thermal energy that is delivered as engine output, and biodiesel has shown no significant effect on the energy efficiency of any test engine. Volumetric efficiency, a measure that is more familiar to most vehicle users, is usually expressed as miles traveled per gallon of fuel (or kilometers per liter of fuel).
Approximately 11% of the weight of B100 is oxygen. The presence of oxygen in biodiesel improves combustion and therefore reduces hydrocarbon, carbon monoxide, and particulate emissions; but oxygenated fuels also tend to increase nitrogen oxide emissions. Engine tests have confirmed the expected increases and decreases of each exhaust component from engines without emission controls.
Areas of concern and interest are for the biofuels industry to have in place a good- quality control protocol for the measurement of bioalcohols, to avoid metal corrosion from water and acid corrosion (due to weak and strong acids and inorganic chlorides in solution). Also of importance are the limits set on phosphorous content (less than 5.0 mg/L in ethanol) to prevent engine catalyst deterioration, and copper content (less than 0.1 mg/kg), along with a sulfur content less than 10 mg/kg.
Up to a 10% blend level, the performance of bioethanol-blended petrol is similar to ordinary gasoline At higher levels however, some engines may begin to exhibit problems, for example, stumbling under slight acceleration. The fuel also has more aggressive properties at higher concentrations of bioethanol which increases the possibility of deterioration of some components. Gasoline must be volatile enough to move from the carburetor or injectors into the cylinders and to vaporize prior to combustion. However, it can’t be so volatile that it vaporizes and boils in the injectors, carburetor, fuel lines, or fuel pump, which could prevent it from being metered correctly. Also, if gasoline is too volatile, moiré evaporates into the air adding to environmental problems. There are a number of volatility specifications to ensure suppliers get this balancing act right. Adding bioethanol to gasoline as low-level blends increases the volatility of the blended fuel.
The Engine Fuel Specifications Regulations specify volatility measures for bioethanol-blended gasoline and gasoline. The limits for blends are similar to those for gasoline so as to ensure no changes in vehicles are required. Bioethanol introduces more oxygen into the fuel. In vehicles with simple fuel metering systems such as carburetors, this causes the mixture to become leaner which is advantageous for fuel economy and for lowering some types of exhaust emissions. However, it may cause some engines to stumble if they are already tuned reasonably lean. If a vehicle stumbles on bioethanol-blended gasoline, re-tuning should solve the problem. A vehicle tuned correctly for use on ordinary gasoline would normally not exhibit problems when using bioethanol blends.
The factors of availability, price, and independence of manufacturer, health benefits, engine improvements, and political implications must all be carefully weighed and assessed, before educated decisions can be made by the powers that be. It is hoped however, that despite some of the obvious setbacks of biofuel production, that it is still viewed as a step in the right direction, and emerging technologies and innovative ideas will encourage improvements in what is undoubtedly, the future of fuel.
Biofuels – Third Generation
Third-generation biofuels (also called advanced biofuels) seek to improve the feedstock, rather than improving the fuel-making process.
Designing oilier crops, for example, could greatly boost yield. Scientists have designed poplar trees with lower lignin content to make them easier to process. Researchers have already mapped the genomes of sorghum and corn, which may allow genetic agronomists to tweak the genes controlling oil production.
Algae fuel, also called oilgae or third-generation biofuel, is a biofuel from algae, which are low-input, high-yield feedstocks that can produce biofuels. Algae can produce up to 30 times more energy per acre than land crops such as soybeans. With the higher prices of fossil fuels, there is much interest in algaculture (farming algae).
One advantage of many biofuels over most other fuel types is that they are biodegradable, and so relatively harmless to the environment if spilled. Algae fuel still has its difficulties though, for instance, to produce algae fuels, it must be mixed uniformly, which, if done by agitation, could affect biomass growth. Algae, such as Botryococcus braunii and Chlorella vulgaris, are relatively easy to grow, but the algal oil is difficult to extract. Macroalgae (seaweed) also have a great potential for bioethanol and biogas production.
Recently, the term fourth-generation biofuels has arisen and is coming into popular use. Fourth-generation technology combines genetically optimized feedstocks, which are designed to capture large amounts of carbon, with genomically-synthesized microbes, which are made to efficiently make fuels. The key to the process is the capture and sequester of carbon dioxide, a process that renders fourth-generation biofuels a carbon negative source of fuel. However, the weak link is carbon capture and sequestration technology, which continues to challenge industry.
See also: Biofuels – First Generation, Biofuels – Second Generation
Biofuels – Use
Biomass has the potential to supply a considerable portion of the energy needs of the world, but the conversion of biomass to energy is carried out in an unsustainable manner that there are many negative environmental consequences. If biomass is to supply a greater proportion of the energy needs in the future, the challenge will be to produce biomass and to convert and use it without harming the natural environment. Technologies and processes exist which, if used correctly, make biomass-based fuels less harmful to the environment than fossil fuels. Applying these technologies and processes on a site-specific basis in order to minimize negative environmental impacts is a prerequisite for sustainable use of biomass energy in the future.
Biodiesel and bioethanol are widely used in automobiles and freight vehicles. For example, in Germany, most diesel fuel on sale at gas stations contains a few percent biodiesel, and many gas stations also sell 100% biodiesel. Some supermarket chains in the UK have switched to running their freight fleets on 50% biodiesel, and often include biofuels in the vehicle fuels they sell to consumers, and an increasing number of service stations are selling biodiesel blends (typically with 5% biodiesel).
In Europe, research is being undertaken into the use of biodiesel as domestic heating oil. A blend of 20% biodiesel with 80% kerosene (B20) has been tested successfully to power modern high efficiency condensing oil boilers. Boilers needed a preheat burner to prevent nozzle blockages and maintain clean combustion. Blends with a higher proportion of biodiesel were found to be less satisfactory, owing to the greater viscosity of biodiesel than conventional fuels when stored in fuel tanks outside the building at typical (non-arctic) winter temperatures.
See also: Biodiesel, Biofuels, Ethanol, Methanol.
Biogas
Biogas, which is also known as biomethane, landfill gas, swamp gas, and digester gas, is a collection of gases (largely methane and carbon dioxide) produced by the anaerobic degradation of biomass (non-fossil organic matter) by various bacteria (Table B-11).
Thus, biogas is a combustible gas derived from decomposing biological waste under anaerobic conditions. Biogas typically refers to a biofuel gas produced by anaerobic digestion or fermentation of organic matter including manure, sewage sludge, municipal solid waste, biodegradable waste, or any other biodegradable feedstock, under anaerobic conditions. Depending on where it is produced, biogas is also called swamp gas, marsh gas, landfill gas, and digester gas (Table B-9).
Table B-11 The composition of gas from various carbonaceous fuels.
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