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In addition to save GHG emissions, the greatest advantage of ethanol as a fuel for spark ignition (SI) engines is perhaps its high-octane number and the ability to withstand high pressures and temperatures without uncontrolled ignition. As the efficiency of SI engines mainly depends on the compression ratio and high‐octane fuels are particularly suitable for high compression ratios, the use of ethanol in SI engines can offer higher energy efficiency. The result is that the efficiency of engines using E85 blend can be 9% higher than that of gasoline-fuelled engines.
One way to obtain high compression ratio is to configure the engine with a turbocharger (e.g. Lotus Engineering on a Toyota engine). For the Brazilian market, Ford has designed an engine for E93 (7% water), which is also able to run efficiently on E25 (gasohol). When running on E93, in addition to high compression ratio, Ford uses high precision optimized ignition timing and higher coolant temperatures to increase the efficiency. Concerns in using ethanol to fuel vehicles is associated with corrosion in the fuel system and storage facilities.
The most notable compatibility problems identified in fleet tests include: a) degradation of plastic materials and rubber (i.e. soften and swell) caused by the solvent‐like nature of ethanol; b) degradation of metals due to the acidic or galvanic nature of ethanol. Although anhydrous ethanol is only slightly corrosive, its hygroscopic nature makes water contamination unavoidable, with metal corrosion risk increasing significantly in the presence of water contaminants such as sodium chloride and organic acids. Minor problems also include clogging of fuel lines due to ethanol “stripping off” deposits, cold start and increased fuel emissions by evaporation. The above problems are mostly associated with existing vehicles using ethanol blends E10 and beyond. Upgrading this vehicle to the use of blends with up to 20% anhydrous ethanol requires basically substitution of certain plastic parts of the fuel systems.
In the common practice, low-ethanol blends E5 and E10 are already on the market all around the world and have generally shown good compatibility with existing SI engines. For high ethanol blends, Ford and others car makers are already producing flex-fuel vehicles, which can run on ethanol blends from 0 to 85%, with relatively inexpensive engine modifications. In both non‐FFVs and FFVs, corrosion and degradation problems in the fuel system have been solved by using stainless steel substituting for aluminium, magnesium, lead, and brass among other metals. Polyvinyl chloride and some rubber parts have been replaced by materials such as high‐density polyethylene, nylon, and fluorinated plastics such as Teflon.
There is no direct scientific documentation on the engine and fuel systems in Brazilian vehicles running on E100, but by all accounts, the 30-year experience of car manufacturers with hydrous ethanol fuel seems to have eliminated any major compatibility problems through the correct choice of materials. As to the cold‐start problems, current vehicles running on high‐ethanol blends use either dual‐fuel systems (i.e. a small auxiliary tank with a specific volatile fuel for cold starts, that is used in Brazil) or block heaters in combination with lowering the E85 ethanol content to 70% (this approach is used in FFVs in the northern hemisphere in the wintertime). As far as the fuel transport and distribution infrastructure is concerned, low-ethanol blends can be relatively easily handled with the existing infrastructure while for high bio-ethanol blends there may be the need for investment in appropriate facilities and infrastructure.
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