As a fuel, compressed natural gas (CNG) is one of the most common gases used in alternative-fueled vehicles in commercial transportation and related industries.  Many of the forklifts on the docks that service trains and big trucks run on CNG as do many work trucks and maintenance vehicles in fleets.  Several companies, including Caterpillar and Kenworth, offer vehicle models that run on CNG for medium- and heavy-duty applications.

Most natural gas comes as either a byproduct of drilling for petroleum (CNG is considered a petroleum fuel), venting as the oil comes out of the ground, or is drilled for directly on its own.  It’s easy to extract, contain, and use because it’s lighter than air and spills and other hazards are not a problem.  It is highly combustible and easily burned and is much cleaner than most liquid fuels in its emissions.

How CNG is Stored and Used

Natural gas is methane (CH4) and is usually compressed to 2900-3600psi in cylinders to become CNG.  Because it is similar to gasoline in combustion energy production, CNG is often used as a gasoline alternative or replacement in vehicles that have been fitted to use it.  It is also often added as an injection into diesel engines to boost the octane and burn levels, producing more power.

Advantages and Disadvantages of CNG

Most of the engines that burn CNG are specially made to do so, though gasoline engines can be refitted to handle natural gas.  Because it burns at lower temperatures than gasoline fumes, CNG puts out fewer NOx emissions, reducing greenhouse and ozone (smog) emissions compared to gasoline or diesel.

The largest drawback to CNG is its larger required storage volume compared to most liquid fuels.  Most vehicles built to run on CNG take this into consideration, however, so it becomes less of an issue with factory-built CNG models.  Work is being done to resolve the space storage issue with what is called absorbed storage, where special materials can “sponge” the natural gas into a storage container, eliminating the need to compress it.

Another advantage of CNG burning is that it does not contain most of the heavy deposits and metals that foul most gasoline and diesel engines over time.  Lead, benzene, and others are non-existent in CNG and so fouling of spark plugs, cylinders, and other components does not happen.  This leads to longer service life, less maintenance, and lower costs over time.

Where CNG is Used

CNG is used in a variety of vehicles from passenger cars to locomotives.  Any fuel-injected gasoline engine can be converted to natural gas power relatively inexpensively.  The majority of the vehicles running on CNG, however, are built to do so from the start.

In states like California and Utah, government operated or subsidized fueling stations are available widely and offer CNG at about 1/3 the price of gasoline.  Many home hookups are available for those who own CNG cars and most industrial applications will have filling stations on-site.

In heavy applications, CNG is most often used in medium-duty and heavy-duty, local haul delivery and work vehicles.  Heavy machinery and on-site construction vehicles also often use natural gas as their fuel.  Because it is cleaner burning, CNG is popular in mining and other close-quarters applications as well.

The Future of CNG

Compressed natural gas is likely to continue to be popular as its lower cost and lower emissions become mainstays for adoption.  More and more applications are being found for CNG vehicles every year.  Heavy hauling and trucking are seeing more and more natural gas applications added.  Companies are offering after-market truck accessories such as alternative power units (APU) and other fittings that run on CNG.

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