Non-conventional or alternative fuels.
Keywords: alternative fuels, fuel, alternative, oil, pollution, pollution control, environment
CNG (natural gas fuel)
The use of CNG and compressed gaseous state under 200 bars is already a proven technology solution with over 500 000 vehicles are affected worldwide. On dedicated and optimized engines, CNG provides significant advantages that offset more expensive energy supply. Driveability, acceleration performance, recovery, the maximum speed is very satisfactory.
Energy efficiency projects about 10% that of gasoline engines (except gasoline lean burn engines such as those recently proposed by Japanese manufacturers), but does not reach that of a diesel engine with direct injection. Engine Emission CNG consist almost entirely of methane, thus low toxicity.
Methane is however an important greenhouse gas. But if one considers the greenhouse gas emissions throughout the chain of use, CNG brings gains of about 20 25% compared to the petrol sector and to 10
15% compared to diesel.
The main handicap of CNG storage concerns the very penalizing in terms of weight and bulk. New materials such as composite resins and glass or carbon fibers currently under study, expected to divide by four the weight of constant capacity tank.
CNG is seen as an alternative fuel whose penetration is certain that no one can currently assess its magnitude. It should be realized first in urban uses (including buses) where pollution is worrying.
Many studies have been conducted in 1970 years on the development of fuels containing at 85 100% methanol, designated by the M85 acronyms, or M90 M100 depending on their composition.
Currently, this theme has lost much of its appeal. Methanol is inherently toxic effect and it provides very little benefit in terms of atmospheric pollution. In particular, the risk of ground-level ozone are little changed for the vehicles adopting M85 or M100.
Methanol is maintained indirectly on the fuel market as a basis for intervening in the synthesis of MTBE. This ether is an excellent component of species, prized for its high octane, its perfect compatibility with hydrocarbons and
benefits it can provide to reduce air pollution.
Today, concentrations of MTBE in 5 10% are very common in gasoline. However, problems arise related to low biodegradability of MTBE.
Ethanol is potentially a good quality fuel could fuel type engines ignition. It can be used pure or mixed in small proportion (up to 20%) in a conventional gasoline. In the first case, the engine must be adapted to this specific use (modification of the power system and higher compression ratio); in the
second case, the ethanol-gasoline mixture is completely unmarked and interchangeable in the distribution network with strictly petroleum products.
Yet even that Brazil was committed to a proactive policy in favor of fuel ethanol industry, reviewing its strategy. The reasons for this reversal in Brazil and slow economic takeoff in the world, take a few technical obstacles without being prohibitive, causing reluctance of oil and car industries.
The ethanol-gasoline blends are less stable in the presence of water, more volatile and sometimes more corrosive than the exclusively oil products.
Therefore, like methanol, the fuel ethanol industry is preferentially directed towards the production of ETBE from ethanol and isobutene.
The EU regulation sets a maximum level of 15% (volume) of ETBE in gasoline, about 7% (weight)
of ethanol. This legislative framework therefore leaves sufficient space for the penetration of ethanol in significant levels on the fuel market.
vegetable oil derivatives
Although diesel engines can operate with crude vegetable oils, this path does not appear realistic to have become high-performance vehicles. However, processing of vegetable oils methyl esters offers considerable advantages technically.
The methyl esters of vegetable oils have physicochemical properties similar to those of diesel oil in which it is perfectly miscible. The types of oilseeds are concerned mainly rapeseed and sunflower. Agronomic data are the following: it is
possible to get to 30 35 quintals / year of rapeseed per hectare, of 1,2 1,4 to tons of methyl esters per hectare per year.
On the regulatory front, a decree authorizes, France, the unmarked distribution of rapeseed methyl ester to 5% mixture in diesel.
Ultimately, the energy balance of biofuels production chains are favorable. The ratio of the energy contained in the biofuel and one that was necessary to produce it, is always greater than 1. But from an economic point of view, with the current costs of access to crude oil and non fiscal incentives, biofuels are not competitive.
Finally, the findings of studies on the contribution of biofuels in terms of impact on air pollution are very nuanced. Depending on the type of pollutant considered, fuels
vegetable may prove beneficial sometimes slightly, sometimes slightly unfavorable. With the exception of protection against the greenhouse effect to which the use of biofuels certainly brings a noticeable improvement.
Synthetic fuels are gasolines and traditional diesel fuels, but from other raw materials as oil, mainly coal and natural gas.
The corresponding processes use heavy and expensive technologies. They are to produce, in an intermediate step, the synthesis gas (CO and H2), from which two routes are possible: the direct production of hydrocarbons by the Fischer-Tropsch technology or based on methanol that will then processed into gasoline.
The performance of these sectors is a major handicap between 35 and 55% for the Fischer-Tropsch process of species depending on the characteristics of the raw material and finished product quality requirements; between 60 and 65% for the synthetic fuel industry via methanol 1986 developed by Mobil in New Zealand. These low yields are associated with significant emissions CO2.
Therefore, the significant production of synthetic fuels is conditioned by high oil prices (at least 30 $ / bbl) and by strong demand in no pollutants.
In the medium term, it is for hydrogen to manage a predicted shortage. -intensive refining units (hydrodésulfurations, hydrotreating and hydroconversions)
will multiply to improve the quality of oil products and to adapt to the growing demand oriented towards light products.
Outside the reforming rapidly reach its limits, the production of hydrogen may be considered by methane steam reforming, by residues or by electrolysis oxyvapogazéification. The first two paths lead to self-consumption and emissions of major CO2. The way of electrolysis would require renewed investment in nuclear and acceptance by the general public of this
technology and its risks.
If one subtracts arbitrarily these questions of availability of raw material, the use of hydrogen as a vehicle fuel is still facing great difficulties: the storage in the vehicle is a true technological bottleneck.
If we assume, moreover, that storage in vehicles is technically resolved and basic safety conditions are met, two options are then possible: hydrogen can first be used pure or mixed with CNG in engines specifically designed for this type of fuel. The engine returns are then limited by the laws of thermodynamics and NOx emissions are inevitable. Secondly, the hydrogen can be consumed in the fuel cells.
But technology development problems became apparent. The electrodes are made of precious metals (platinum and palladium) and power density is low. Despite recent commitments
large industrial vehicles to develop fuel cells, this pathway does not seem to compete more conventional converters pollution but to almost zero destined for a great future.
Tensions are predictable on the hydrogen market and fuel pathway is very prospective. It is certain that the use of hydrogen to improve the qualities of traditional fuels long time remain the most effective way technically and economically.
Therefore, the fuel cell and the hydrogen combustion engine do not seem likely to lead in the medium term.