For the combustion of petrol, usually spark ignition engines are used. These are internal combustion engines where the fuel-air mixture is ignited with a spark. These engines differ to compression-ignition engines, where the heat and pressure from compression alone ignites the mixture. Spark-ignition engines can be either two- stroke or four-stroke. A four- stroke spark-ignition engine is an Otto cycle engine. Originally the fuel of sparkignition engines is mixed outside the cylinders, as opposed to compression-ignition engines where the fuel is mixed inside the cylinders. However spark-ignition engines are increasingly being designed with direct injection, eliminating this distinction.
Generally all spark ignition engines can run with bioethanol as well. If 10 to 25% ethanol is mixed with gasoline, typically no engine modifications are needed. Many modern cars can run on these mixtures very reliably. But, the higher the ethanol component of blended petrol becomes, the lower is its suitability for standard car engines. This is due to certain characteristics of bioethanol [1-2].
Extensive international experience demonstrates that, in general, E10 blends do not require engine tuning or vehicle modifications. And since most of the materials that have been used by the motor industry over the last two decades are E10 compatible, substitution of parts is not usually required. However, because European Union fuel quality regulations have limited the ethanol content to 5 % (E5) or less, automakers have typically restricted the warranty coverage of vehicles sold in the EU to this level. This limit is currently discussed to be increased up to a 10 % limit.
In Brazil, all brands of automotive gasoline contain anhydrous ethanol in the range of 20-25 % (E20-E25). Foreign vehicles have been adapted by using ethanol-compatible materials in the fuel system and by tuning the engines for a mid-range point, usually at the 22 % ethanol level (E22). This customization has resulted in good drivability and performance, with fuel consumption comparable to gasoline operation.
For using fuels that are higher blended with ethanol (E20-E100) conventional engines have to be refitted with more efforts. This is due to the characteristics of ethanol to dissolve certain rubber and plastic materials. Further, engines running with high blends of ethanol have to be refitted as pure ethanol has a much higher octane rating (116 AKI, 129 RON) than ordinary petrol. Therefore changes to the compression ratio and spark timing are needed to obtain maximum benefits. To refit an engine which will be fueled with pure ethanol, larger carburetor jets, which are about 30-40% larger by area, have to be installed. Additionally, below temperatures of 13 °C, ethanol engines also need a cold-starting system to maximize combustion and minimize uncombusted nonvaporized ethanol. Depending on the particular customization requirements, refitting costs may run from a few euros for substitution of fuel lines to more than €500 if the fuel-supply system is fully upgraded (fuel lines, tank, pump, filter, etc) [3-4].
As an example, in Brazil some vehicles are exclusively running with pure ethanol. They are equipped with ethanol compatible materials and with on-board electronic engine management systems, which can adjust engine operation to ethanol fuelled conditions.
Recently an increasing number of vehicles are manufactured with engines which can run on any petrol/bioethanol ratio from 0% ethanol up to 85% ethanol. Sensors of these flexible fuel vehicles (E85 FFV) can automatically detect the type of the fuel and adapt engine running. They adjust the air/fuel ratio and the ignition timing to compensate the different octane levels of the fuel in the engine cylinders. The main reason to limit ethanol content to 85 % is to enhance volatility conditions for cold start, particularly in cold climates. Therefore the technology does not need any cold start ancillary system.
Worldwide, in February 2006, there were an estimated six million E85 FFVs on the road (WWI 2006). In Europe FFVs are used especially in Sweden, but also in other countries, e.g. in Germany or the United Kingdom, these vehicles are introduced. Pioneers in the European market are the manufacturers Ford and Saab.
As opposed to Europe, in Brazil so called E100 FFVs were introduced in 2003. This variant of the E85 FFV technology is capable to operate either within the E20/E25 range, exclusively with hydrous ethanol (E100), or with any blend between E20/E25 and E100. The ethanol sensors used in the E85 versions are replaced in this technology by an advanced software component in the engine’s electronic control unit. This uses inputs from conventional oxygen sensors in the exhaust system (lambda sensors) and self-calibrates the engine to fuel requirements. This technology has proved feasible in Brazil in large part because the warm climate allows blending of hydrous ethanol to E20/E25 without the risk of phase separation. E100 FFVs have become a sales phenomenon since their introduction in the Brazilian marketplace, in part because E100 is significantly less expensive than E20/E25 in much of the country (WWI 2006).
Dedicated ethanol vehicles are even more efficient in using pure ethanol due to better combustion characteristics than FFVs which must retain dual-fuel capability. In these engines the compression ratio is increased. According to WWI (2006), the average fuel consumption has been 25 % lower than for equivalent E20/E25 fueled versions. Most experience with this technology is made in Brazil, again. Volkswagen, Fiat, General Motors, and Ford have all produced dedicated ethanol versions for more than 25 years, with full warranty coverage.
Compression ignition engines, also called diesel engines, are internal combustion engines in which the fuel is ignited by high pressure and temperature, rather than by a separate source of ignition, such as a spark plug, as is the case in the spark ignition engine. The German pioneer Rudolf Diesel invented this type of engine in 1892. He also demonstrated that this engine is running with peanut oil, too. Originally, compression ignition engines are designed for being fuelled with diesel. Nevertheless also ethanol can be combusted in these engines, but this application is limited.
For example, since ethanol is difficult to ignite in a compression ignition engine, one option is to blend it with an additive to enhance fuel ignition. Therefore, 5 % of the additive “Beraid” is mixed with 95 % hydrous ethanol. Experiences with approximately 500 urban buses using this fuel mixture for compression ignition engines have been made in Sweden. In October 2007, the first E95 bioethanol bus has been introduced in Brazil (JANSSEN et al. 2007). Also the engine has to be refitted e.g. in that the compression ratio and the volumetric capacity of the fuel pump are increased. The use of material that is compatible to ethanol is a precondition for using ethanol in engines as well.
Another option for using ethanol in standard compression ignition engines is to blend ethanol with diesel. It has been shown that a good compromise in terms of fuel economy, performance, drivability and emissions can be achieved when diesel is blended with about 7 % ethanol (WWI 2006). Other approaches of using ethanol in diesel engines are either to use diesel and ethanol simultaneously by “fumigation” or to convert the diesel engine into a spark ignition engine.
Although the use of bioethanol in fuel cells is not yet commercially viable, technical applications of ethanol in so called direct-ethanol fuel cells (DEFC) is possible. DEFC systems are a subcategory of proton-exchange fuel cells, also known as polymer electrolyte membrane fuel cells (PEMFC). Their distinguishing features to other fuel cells include lower temperature/pressure ranges and a special polymer electrolyte membrane. When bioethanol is applied to these fuel cells, ethanol is not reformed, but fed directly to the fuel cell.
Using bioethanol in DECF applications has several advantages. As it is fed directly into the DEFC, complicated catalytic reforming is not needed. Further, storage of ethanol is much easier than that of hydrogen which is usually used for fuel cells. Storage of liquid ethanol does not need to be done at high pressures, as it is needed for hydrogen, which is a gaseous fuel under normal conditions. Thus, the use of ethanol would overcome both the storage and infrastructure challenge of hydrogen for fuel cell applications. Additionally, the energy density of ethanol far greater than even highly compressed hydrogen.
Besides the use of ethanol in DEFC technologies, vehicles could also be equipped with multi-fuel onboard reformers. These devices could continuously generate hydrogen out of ethanol and would enable vehicles to use a combination of conventional and lower-cost fueling systems. Alternatively, commercial-size multi-fuel reformers could generate hydrogen from biofuels on-site at retail stations, avoiding costly hydrogen distribution infrastructure (WWI 2006 p. 223).
The use of ethanol as transport fuel is growing in Europe during the last few years. Parallel to this development the need for specifications and standards raised on European level.
Since recent times there was no European standard, neither on the utilization of additives in ethanol, nor on ethanol as fuel itself. Consequently the European Commission has inter alia mandated CEN/TC 19 (Comité Européen de Normalisation - Technical Committee 19) to produce a standard on ethanol for blending with petrol. This standard prEN 15376 “Automotive fuels - Ethanol as a blending component for petrol - Requirements and test methods” is currently under approval and will be issued most probably in October 2007. A first draft is already publicly available. Since the Swedish market is the most established ethanol market in the EU, Swedish stakeholders actively participate in the creation of this standard (ATRAX ENERGI 2005). In parallel the European standard for gasoline, EN 228, has been adapted to allow a maximum content of 5 % ethanol.
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