Pros and cons of alternative fuels

It takes 17 trees 30 years to absorb the amount of carbon dioxide a medium-sized, gas-driven car emits annually. Research is being done to find viable fuel alternatives. Here are some of the advantages and disadvantages of alternative fuels.

• Made from any fat or oil, this fuel runs in conventional diesel engines without modification.
• It reduces carbon monoxide (a greenhouse gas) by 33 per cent and black smoke by 26 per cent.
• Biodiesel dates back to the early 20th century, but it's still virtually unobtainable commercially in certain parts of the world.
• This may change as world demand for oil continues to grow, making biodiesel more price-competitive.

• Efficient, compared with commercial diesel engines, CNG-burning engines can reduce carbon monoxide emissions by 90 per cent and particulate matter by 50 per cent.
• It is already used by some urban buses.
• Made up of 95 per cent methane, CNG reduces greenhouse emissions by about 30 to 40 per cent for cars.
• Having your car converted to CNG is expensive, and only a small number of refuelling stations stock it.

• New batteries are lighter, longer lasting and less toxic than conventional batteries – and can be charged either by being refilled or plugged into a charger.
• Electricity is generally better for the environment than gas, as it can be produced en masse by turbines at a power station more efficiently than gas can be turned into energy in thousands of separate car engines.
• Conventional batteries tend to be bulky and slow to recharge.
• Electric cars generally have lower top speeds because they are smaller vehicles, designed for urban, rather than highway, use.

• Derived from agricultural crops, and added to gasoline.
• The carbon dioxide released by burning the ethanol is offset by the carbon dioxide absorbed from the atmosphere by the crops before harvesting.
• It has less energy than gas, so motorists must buy 3.5 per cent more E10 fuel (see below) to travel the same distance.
• Ethanol releases higher levels of benzene into groundwater than conventional fuel.
• Using ethanol/gasoline blends may cause starting difficulties, engine knock and other problems.

• A type of alcohol made from agricultural crops, ethanol has been proposed as an eco-friendly alternative fuel, and a 10 per cent blend.
• E10, has been approved for use in new cars by most car manufacturers.
• Ethanol does have some green credentials: when burned as a fuel, its only by-products are water and carbon dioxide, and the latter is offset by carbon dioxide emitted by the crops.
• However, growing and transporting the crops and manufacturing the ethanol require significant amounts of fossil fuel energy.
• Indeed, studies have shown that the use of E10 is likely to reduce vehicle greenhouse emissions by just one to five per cent.
• Moreover, the different chemical properties of E10 relative to conventional fuel result in higher levels of groundwater pollution by benzene, a known carcinogen.

• PG is a mixture of propane and butane (the same mix that fuels suburban barbecues).
• It has been used in transport for more than 60 years and is popular with taxi firms.
• Compared with gas or diesel, it cuts greenhouse gas emissions by about 10 per cent.
• LPG consumption on the open road can be up to 30 per cent higher than that for gas, although in the city it is only 10 to 20 per cent higher.
• Not all service stations stock LPG.
• Also, an LPG tank can take up a lot of trunk space.
• Taxi drivers report LPG doesn't always give the same acceleration as gas.