Compressed natural gas vehicles: How they work

Natural gas vehicles aren't new, nor are they radically different than conventional vehicles.

Honda has been building them in the United States for the past 14 years, and there are aftermarket conversions -- including bi-fuel systems that rely on gasoline or diesel as a backup -- for almost any application.

Diesel engine manufacturer Cummins has recently brought natural gas technology to the heavy-duty market with a CNG version of its 9-liter diesel engine used in trucks.

With the exception of sturdier pistons and valves, CNG engines work much like conventional internal combustion versions, though the cleaner-burning fuel requires much less emissions equipment than diesel.

They get similar mileage (measuring in terms of BTUs, a standard for comparing the amount of energy contained in fuel), although they deliver slightly less power.

The most noticeable difference is fuel storage, as highly compressed or chilled gas requires bigger and stronger tanks than gas or diesel.

In Honda's Civic NG, the aluminum-lined carbon-fiber tank takes up about half the trunk space.

The rounded cylindrical shape is designed to minimize pressure points for the gas, which is stored at up to 3,600 pounds per square inch, unlike gasoline tanks, which can be configured to fit under the car.

Some heavy-duty trucks use liquefied natural gas -- chilled to -260 degrees -- because it takes up less space.

Despite the high pressure, natural gas vehicles are considered no more dangerous than conventional models.

Honda Motorwerks owner Chris Schneider points to stress tests in which natural gas tanks sustain direct gunshots and vertical drops that simulate a rear-end collision at 60 mph. The tank, he said, is stronger than any part of the vehicle. And in the event of a puncture, the gas rapidly escapes into the air, unlike gas or diesel fuel that puddles on the ground.

Tanks are filled with a nozzle that couples to the tank like an air hose, and commercial pumps operate much like conventional gasoline dispensers, filling in about the same time and shutting off when the tank is full.

(c)2012 the La Crosse Tribune (La Crosse, Wis.)

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Tags: business, auto, energy, wisconsin