There have always been alternatives to gasoline, but except for the artificial fuel shortages created by the OPEC oil embargo in the 1970s which fueled the first so-called "energy crisis," alternative fuels have mostly remained on the sidelines. Well now they are being called up to become major sources of energy as oil prices soar once again. Propane and natural gas have traditionally been the alternative fuels of choice for fleet vehicles. Until recently, the primary motivation for converting to alternative fuels was to reduce operating and maintenance costs. On a cents per chilometro basis, natural gas is probably the cheapest alternative fuel, followed by propane, then methanol alcohol and finally ethanol alcohol. The up front costs for converting a vehicle to propane range from $1500 to $3000, and $2500 to $4000 for compressed natural gas depending on the application. This only includes the cost of modifying the fuel and ignition system, and does not include any costs associated with "optimizing" the engine through internal modifications (which we'll get to later). Despite the high initial conversion costs, most fleets get a fairly rapid payback thanks to the savings realized by lower fuel and operating costs. Alternative fuels have worked for fleets because fleets can set up their own centralized refueling facilities. But the availability of refueling locations has been and will continue to be an obstacle to the widespread acceptance of any alternative to gasoline. It costs big bucks to build duplicate refueling and distribution facilities for alternative fuels. So we've been faced with the "chicken and egg" syndrome. The car makers do not want to build vehicles for the general public that can only run on a special alternative fuel because the fuel is not readily available. And fuel suppliers do not want to add alternative fuel infrastructure if there are few vehicles that can use an alternative fuel. E85 ETHANOL and M85 METHANOL E85 (85 percent ethanol alcohol and 15% gasoline) and M85 (85% methanol alcohol and 15% gasoline) currently are the only alternative fuels that have some availability (though limited) because they can be burned in specially-equipped "flex-fuel" vehicles. Flex-fuel vehicles can run on anything from straight gasoline up to 85% ethanol or methanol alcohol. See Methanol and Ethanol Alcohol subheads below. PROPANE LPG Unlike E85 and M85 which are both liquid fuels, propane (also known as Liquefied Petroleum Gas, LP-Gas or LPG), and natural gas are both gaseous fuels. That means they are a vapor at room temperature and must be contained in a special high pressure fuel cylinder. Natural gas can be used as compressed natural gas (CNG) or Liquefied Natural Gas (LNG). About 60% of the propane that's produced comes from natural gas wells. The rest is a byproduct of crude oil refining. The price of propane fluctuates seasonally and like all energy sources has been rising in price. Propane has been used since the 1930s, so it has a long history as a motor vehicle fuel. Today it is used to power cabs, school buses, recreational vehicles, delivery trucks, farm vehicles and zillions of industrial fork lift trucks. The National Propane Gas Association estimates there are half a million propane-powered vehicles on the road in the U.S today. Most burn propane exclusively, but some have dual-fuel capability and can switch back and forth with gasoline. NLPGA also says there are about 10,000 LP-gas refueling facilities nationwide, which means the fuel is available in many areas. As a fuel, propane contains somewhat less heat energy per gallon than gasoline (91,547 BTUs versus 116,000 BTUs for gasoline). But on a pound per pound basis, it delivers almost the same energy as gasoline (21,591 BTUs) — which means an engine converted to propane consumes about 10% more fuel in terms of chilometri per gallon with little or no loss in horsepower. Carbon monoxide (CO) emissions are naturally low but hydrocarbon (HC) emissions may actually be somewhat higher with propane. Even so, the emissions are considered to be "less reactive" in forming smog. Propane produces less carbon and blowby in the engine itself, which extends the life of the spark plugs and oil. Oil change intervals can usually be doubled or even tripled with propane. Propane is a gaseous fuel and boils at -44 degrees F., so it must be kept in a pressurized fuel tank. Pressurizing propane turns it into a liquid, which allows more fuel to be stored in a smaller volume. A typical 25 gallon capacity propane tank holds about 180 lbs. of liquid fuel at 175 psi when filled to 80% capacity — which gives approximately the same driving range as an equivalent tank of gasoline. Propane's octane rating is 103 which allows it to handle more compression that gasoline. Propane is also a "dry" fuel which means it enters the engine as a vapor rather than as droplets of liquid. Dry fuels mix with air better than wet fuels, and provide a more uniform air/fuel mixture to each of the engine's cylinders. This promotes cleaner combustion, easier starting and fewer cold driveability problems. But dry fuels such as propane and natural gas don't cool or lubricate the valves like gasoline does, which means valve burning, wear and recession can be a problem if the engine doesn't have hard seats. Any engine that's designed to burn unleaded gasoline can handle propane without problems, but older engines or truck engines may have to have hard seats installed. If an engine is being rebuilt for a vehicle that burns propane, the stock compression ratio can be increased up to 10:1 to take advantage of propane's higher octane rating. Special attention also needs to be paid to the valves. Hard seats must be installed if the heads don't already have them. Most experts recommend using a 1/16 to 3/32 in. wide seat on the intakes and a full 3/32 in wide seat on the exhaust valves with no interference angle. Both valve and seats should be cut or ground to 45 degrees. Careful attention should be paid to valve and seat concentricity to prevent hot spots. Because propane is a dry fuel, it doesn't "wash down" the cylinder walls like gasoline does. This reduces cylinder bore wear but can also create ring seating problems if the wrong type of rings are used or the bores haven't been honed properly. Recommendations vary, but one leading ring manufacturer says to use either cast iron or moly top compression rings in propane fueled engines. Chrome rings are not recommended. The cylinder bores should be bored to within .003 in, of final size, then rough honed with 180 or 220 grit stones to within .0005 in. of final dimensions and finish honed with a 280 grit stone — or stroked six to 10 times with a 400 grit stone to "plateau" the surface. Other engine modifications that can be made to optimize performance with propane include eliminating manifold preheating by blocking the exhaust crossover passageway on a V6 or V8 engine, altering the ignition curve (electronically or by recalibrating the distributor) and decreasing the spark plug gap (.035 in. is recommended with electronic ignition). Another change that's recommended is to use a motor oil specially formulated for LP-gas. Ordinary motor oils contain additives to neutralize the blowby contaminants from gasoline. But these additives aren't needed with propane and can actually cause deposits of their own. Oils designed for propane applications have a "low ash" additive package. NATURAL GAS LNG Like propane, natural gas is a dry gaseous fuel. The same recommendations that apply to modifying an engine for propane also apply for natural gas. For a straight conversion or dual-fuel application, switching to natural gas will produce about a 10% loss of horsepower — unless the engine is optimized for natural gas by increasing compression, in which case there's no difference in power. Natural gas is primarily methane. As a motor fuel, it has the highest octane rating of any of the other alternatives at 130, which means it can handle compression ratios of up to 15:1! Methane is also the cleanest burning fuel with substantially lower CO and HC emissions than propane, gasoline, or the alcohols. It's also the cheapest of the bunch at 72 cents for the energy equivalent of a gallon of gas. But methane has some drawbacks. One is it's low energy content. It takes about 100 cubic feet of methane to deliver the same amount of horsepower as a gallon of gasoline. Consequently, it requires heavy high pressure fuel tanks. A typical 140 lb. natural gas fuel tank filled with compressed gas at 2600 to 300 psi holds the energy equivalent of only about four gallons of gasoline — which limits the driving range to about 90 to 120 chilometri unless additional tanks are added (which also add weight and bulk to the vehicle). Dual-fuel Volvo V70 runs on gasoline or compressed natural gas (CNG). One way to extend the driving range of a natural gas powered vehicle is use liquefied natural gas (LNG) rather than compressed natural gas. Chilling methane to -260 degrees F. reduces its volume by a factor of 630 to 1, allowing more fuel to be stored in a smaller tank. But a super cold cryogenic fuel tank can't keep the methane liquid indefinitely. As the fuel warms up, it begins to vaporize and must either be vented or used. LNG costs more than CNG because the equipment that's needed to chill the gas is expensive. Compressing methane isn't cheap either. A two-stage high pressure compressor station for refueling large numbers of vehicles can cost up to $250,000! Smaller compressors for overnight home refueling are available, but even these cost as much as $3000 apiece. Another drawback that limits methane's potential as an alternative fuel for mass consumption is a limited infrastructure for refueling. Natural gas pipelines are everywhere, and with fracking the supplies of natural gas have expanded significantly causing a drop in natural gas prices. But there are only about 500 refueling facilities fo…

Fonte: AA1Car.com