9.3 What are the advantages of alcohols and ethers?
Description
This article is from the Gasoline FAQ, by Bruce Hamilton with numerous contributions by others.
9.3 What are the advantages of alcohols and ethers?
This section discusses only the use of high ( >80% ) alcohol or ether fuels.
Alcohol fuels can be made from sources other than imported crude oil, and the
nations that have researched/used alcohol fuels have mainly based their
choice on import substitution. Alcohol fuels can burn more efficiently, and
can reduce photochemically-active emissions. Most vehicle manufacturers
favoured the use of liquid fuels over compressed or liquified gases. The
alcohol fuels have high research octane ratings, but also high sensitivity
and high latent heats [8,27,80,116].
Methanol Ethanol Unleaded Gasoline
RON 106 107 92 - 98
MON 92 89 80 - 90
Heat of Vaporisation (MJ/kg) 1.154 0.913 0.3044
Nett Heating Value (MJ/kg) 19.95 26.68 42 - 44
Vapour Pressure @ 38C (kPa) 31.9 16.0 48 - 108
Flame Temperature ( C ) 1870 1920 2030
Stoich. Flame Speed. ( m/s ) 0.43 - 0.34
Minimum Ignition Energy ( mJ ) 0.14 - 0.29
Lower Flammable Limit ( vol% ) 6.7 3.3 1.3
Upper Flammable Limit ( vol% ) 36.0 19.0 7.1
Autoignition Temperature ( C ) 460 360 260 - 460
Flash Point ( C ) 11 13 -43 - -39
The major advantages are gained when pure fuels ( M100, and E100 ) are used,
as the addition of hydrocarbons to overcome the cold start problems also
significantly reduces, if not totally eliminates, any emission benefits.
Methanol will produce significant amounts of formaldehyde, a suspected
human carcinogen, until the exhaust catalyst reaches operating temperature.
Ethanol produces acetaldehyde. The cold-start problems have been addressed,
and alcohol fuels are technically viable, however with crude oil at
<$30/bbl they are not economically viable, especially as the demand for then
as precursors for gasoline oxygenates has elevated the world prices.
Methanol almost doubled in price during 1994. There have also been trials
of pure MTBE as a fuel, however there are no unique or significant advantages
that would outweigh the poor economic viability [15].
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