Bioethanol uses ethanol derived from crops (specifically the starch or sugar abundant in a number of food crop varieties), which could offer both economic and environmental benefits. It can combine with gasoline in any concentration and although capabilities vary, around 10 percent bioethanol will work without undue effect on current engines. The ongoing research will likely raise that figure considerably.
Unfortunately, bioethanol doesn’t yet have the same fuel economy as conventional gasoline, especially at higher concentrations. It’s reported that 85 percent ethanol mixes can reduce fuel economy by 25 percent compared to conventional fuel. At lower concentrations, CO2 emissions are also less affected.
Shell reports it is working with Canadian concern, Iogen corporation, on an ethanol derived from straw — cellulose ethanol. A demonstration plant for the fuel opened in 2004 and commercial production is scheduled for 2009. This biofuel can be used as a blend in conventional vehicles and an economic study in Germany showed it should be cost competitive.
Then there is biodiesel — a blend of diesel and bio-esters (a chemical interaction between vegetable oil and an alcohol). The extent to which this can be used on unmodified engines is still in debate and as a result engine warranties extend from 5 to 30 biodiesel mixes. Fuel specifications in Europe currently allow 5 percent blends but some manufacturers claim this can be safely improved upon.
Biodiesel is more expensive than the normal variety although as with all biofuels this should change once economies of scale come into play.
Also as with other biofuels, lower engine wear and reduced emissions are an added bonus. Biofuel usage would mean less ‘coking’ and thus a cleaner engine. And in general, the new fuels are chemically compatible with all fuel system materials, such as seals and joints and make use of existing distribution systems.
Nevertheless, at ground level, electric and Compressed Natural Gas (CNG) vehicles still hold sway in terms of alternative fuel. Swissport, for example, is utilizing electric equipment at several locations, a strategy which, George Hogan, senior vice president of ground handling sales in the Americas reports has worked well.
Hogan says electric vehicle usage has not increased substantially but many airports are moving in this direction with common support infrastructure. One problem is the cost of a unit. “This is based on the higher initial cost plus a need to install chargers/electric, which do not exist at most US airports currently,” says Hogan. ”Also, while units are good for short distance towing at the terminal they do not do well long distance or in snow conditions.”
Many airports around the world are improving infrastructure to handle electric ground fleets but as with biofuels, widespread acceptance has yet to catch on. Manchester Airport in the UK, for example, has a comprehensive environmental program yet reports only that a fleet of new low-emission airside buses have been purchased and trials undertaken of just two Liquefied Petroleum Gas (LPG) vehicles as well as a single electric one.
LPG is a mixture of hydrocarbon gases and, as with CNG, is used by a small percentage of ground support vehicles. CNG is a gasoline substitute made by compressing methane. Both have their advantages environmentally although safety issues have been raised.
It seems that while work continues on alternative fuels, it is only when they become commercially abundant that a true market assessment can be made. But the criteria that any fuel has to meet are exacting, not least of which is the business demands of price and availability.