Bio-ethanol as a Transport Fuel?
The following article by Emily Rudkin presents the results from work on the possibility of using bio-ethanol as a transport fuel and the implications for New Zealand.
Ethanol is a simple alkyl alcohol that can be used as a transport fuel in spark ignition engines. It has high octane levels and can be either blended into petrol and used in unmodified vehicles, or run as 100 percent ethanol in a converted engine. Ethanol can be a renewable fuel if it is produced from agricultural biomass, i.e. bio-ethanol.
Bio-ethanol is probably the most cost-effective renewable transport fuel, and as such the Energy Efficiency and Conservation Authority (EECA) commissioned a study into the implications of its introduction to New Zealand. The information from this report has assisted in refining the Government's preferred target for renewable energy, as stated in the National Energy Efficiency and Conservation Strategy. The renewable energy target is structured around a sector approach, one of which is transport fuels.
The main considerations with the introduction of bio-ethanol into New Zealand include the cost and source of the ethanol, distribution of the fuel, performance of vehicles, and safety and environmental issues.
Ethanol for transport fuels is most commonly produced from sugar crops by fermentation and distillation. The most effective crops that can be used to produce ethanol in New Zealand are maize and sugar beet. Ethanol can also be produced from woody biomass but at a significantly greater cost. Currently New Zealand produces ethanol from whey, a by-product in the dairy industry.
Generally blends of up to 10 percent ethanol in petrol (E10) can be used in modern vehicles without any appreciable changes in performance. Studies in the 1980s identified that there is potential to produce enough maize and sugar beet to replace all petrol in New Zealand with an E10 blend many times over, although this would require substantial changes to farming patterns.
There are well established procedures for mixing, distributing and storing ethanol and ethanol blends. Ethanol is readily miscible in water, so all ethanol (and ethanol blend) distribution and storage systems must be kept "dry". The addition of ethanol to conventional petrol is likely to take the resulting blend outside the petrol specification due to increased fuel volatility, so that a specially tailored hydrocarbon blend stock would likely be required. Some countries allow "splash blending" where ethanol is blended with conventional petrol during truck loading. This is permitted by a waiver on the fuel specifications. The best locations for blending ethanol with petrol are likely to be at the regional bulk storage terminals or at the refinery. Blending equipment and further storage and dispensers would be required.
Engines running on 10 percent ethanol blends will have a slight increase in volumetric fuel consumption due to the lower energy content of ethanol compared with petrol. Although energy efficiency should be similar for blends and petrol, energy efficiency gains of about 1 percent have been reported, particularly in older vehicles due to the leaning effect of ethanol. Driveability may be impaired in older vehicles, although altering the fuel settings can restore this. A small number of older vehicles may be susceptible to paint and fuel systems materials, degradation. Generally the health and safety aspects of ethanol and ethanol blends are similar to petrol.
Exhaust emissions from modern vehicles do not differ significantly when using ethanol blends. In older vehicles, without catalysts and fully functional emission control systems, ethanol may result in reduced emissions of carbon monoxide, slight reductions in hydrocarbons and slight increases in NOx. They do however result in significantly increased engine aldehyde emissions, although these are largely destroyed by exhaust catalysts.
The rationale for assessing the potential of bio-ethanol is largely due to climate change benefits. As bio-ethanol is renewable, CO2 emitted during combustion is taken up in the biomass feedstock. However as energy is consumed during the manufacture of ethanol, it is not completely carbon neutral. CO2 emitted during manufacture is between 30 percent and 90 percent of the CO2 emitted during combustion of ethanol, depending on the process technologies. On this basis, and assuming a slight improvement in efficiency, an E10 blend results in net CO2 savings of between 1.5 percent and 5.5 percent compared with petrol.
There are two well established programmes overseas using bio-ethanol blends. In Brazil, blends of 22 percent ethanol are required, with vehicles specifically designed to use this fuel. In the USA, ethanol may be splash blended into petrol to a concentration of 10 percent. More recently
European countries allow up to 5 percent ethanol in petrol. Australia has an active programme supporting bio-ethanol where currently splash blending into specification grade petrol is permitted.
Full details of the study will be available as a supporting document to the Renewable Energy consultation on the EECA website www.eeca.govt.nz.
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Emily Rudkin Emily is a mechanical engineer with five years' experience in the renewables industry in both the United Kingdom and New Zealand. She has a Master's degree in Renewable Energy and the Environment from Reading University, UK. Emily is currently employed in Wellington by the Energy Efficiency and Conservation Authority (EECA), the government entity encouraging, promoting and supporting energy efficiency, energy conservation and the use of renewable sources of energy. She is committed to seeing renewable energy become New Zealand's mainstream energy source. |
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