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Liquefied Natural Gas (LNG) Part I

Liquefied natural gas for vehicles comes from the same sources as compressed natural gas (CNG), or for that matter as the gas that cooks your dinner. Unlike liquefied petroleum gas (LPG), which is changed from a vapour to a liquid at room temperature by application of pressure, LNG has to be cooled to very low temperatures in order to cause it to liquefy; this makes it hard (though not impossible) to transport via tanker, and it is usually liquefied at the dispensing station.

As with CNG, LNG can benefits from decades of infrastructure development because of heavy domestic, industrial, and utility use of natural gas. But LNG is somewhat behind CNG in retail availability, because of the added complexity of a cryogenic (ultra-cold) liquefying station compared to a compressor station. However, in USA and some other developing countries, here are projects being undertaken to construct enough refueling stations along major trucking highways to allow LNG-powered long-haul trucks to replace diesels along some routes. Also, individual local delivery fleets are building their own stations for central refueling so that they don't have to worry about publicly-available facilities.

Advantages

LNG has all the emissions advantages I bragged about for CNG. In addition, the liquefaction process amounts to a distillation, so the fuel is essentially pure methane (CNG can contain up to 12 percent of heavier molecules, like ethane and propane etc.), which prevents variations in fuel quality. Also, LNG is a somewhat less bulky and heavy way to store natural gas than as CNG in high-pressure tanks.

Disadvantages

Though LNG tanks are less bulky and heavy CNG tanks, they are still more to than tanks for liquid fuels like petrol, diesel, or alcohol. They are also more complex and expensive because they have to insulate the fuels very well in order to prevent it from warming up and boiling off too fast. Even with modern, rocket-science (literally!) insulation materials and techniques, a LNG tank will begin venting fuel if left to sit for several days, so the fuel is best used in high-duty-cycle applications like delivery trucks.

Methanol (M85)

Methanol is typically made from natural gas; though it is possible to produce it by fermenting biomass (this is why it is sometimes called "wood alcohol"), this is not economically competitive yet. Because it is easier to transport natural gas to a distant market by converting it to methanol, which is a liquid at ordinary temperatures and pressures, than by chilling and liquefying it or by building a long pipeline, some petroleum-exporting countries are looking at exporting their "waste" natural gas (which they currently "flare off" in huge flames visible from the Space Shuttle!) by converting it to methanol; however, most of the natural gas that goes into methanol in the United States and few other countries is still domestically produced. For reasons to be explained below, most fuel methanol in this country is sold as a blend of 85% methanol with 15% unleaded premium petrol, whence "M85".

Advantages

M85 is perhaps the most "transparent" alternative fuel to the user, i.e., it is the least distinguishable from petrol in how you buy and use it, which should ease acceptance. The fuel system of a car or truck only needs to be slightly changed (somewhat different materials, bigger fuel injectors, and a fuel composition sensor) in order for it to run on M85, and recently automakers have been offering M85 vehicles at no extra cost over their petrol counterparts (or even for slightly less money). And perhaps best of all, M85 vehicles being sold these days are flex-fuel vehicles in USA, which means that any mixture of M85 and petrol in the fuel tank can be used by the engine; a fuel-composition sensor tells the engine computer what percentage of methanol is in the fuel, and it adjusts the injectors and ignition accordingly. Thus an M85 vehicle is a petrol vehicle if M85 is not available, but you can top it off with M85 whenever you get back into an area where it can be found, and you don't have to carry (and pay for!) two separate fuel systems to do this.

Disadvantages

Methanol is more corrosive than petrol; this is why you need to change some of the materials in the fuel-handling systems of both the vehicle and the refueling station to materials that can withstand attack by the fuel. Special oil additives are necessary in order to protect the engine. Also, because the mixture of air to