Autofield Blog

Lightening Up CNG Systems


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17. July 2012

If you take a conventional Honda Civic DX with its 1.8-liter engine and put it on a scale, you’ll find that it weighs 2,672 lb.

If you take a Civic Natural Gas with its 1.8-liter engine and put it on a scale, you’ll find that it weighs a heftier 2,848 lb.

 

2012 Honda Civic Natural Gas

 

Given that there are no obvious differences—it isn’t as if there is lots of content in one vs. the other—we wondered why this weight disparity exists. We speculated that it had more than a little something to do with the compressed natural gas (CNG) system.

So, enquiring minds and all that, we asked Honda.

And learned, “From the outside the engines look the same, but the CNG version has unique Honda-designed fuel injectors, hardened valve faces and valve seats, heavier duty connection rods, pistons and crankshaft ( to take the increased compression ratio and heat from burning CNG).

“The added weight is indeed a result of the CNG system including the heavier fuel tank, fuel pressure regulator and fuel filter.”

The proliferation of CNG vehicles is going to be predicated on several factors. One, of course, is an increase in the number of fueling stations. Another is weight reduction: reducing vehicle mass means that it takes less energy to move it.

And one of the areas that needs to be addressed is the CNG tank. Like gasoline tanks, they have to contain the fuel and they have to have little in the way of permeability. But unlike gasoline tanks, the CNG tanks are dealing with, as the name says, gas under compression.

Apparently there are four types of tank. Full steel. Steel/composite. Aluminum/composite. And a plastic liner with either a glass-fiber or carbon-fiber wrapping.

A CNG cylinder provider, GASTANK Sweden AB, has developed a 32-liter capacity tank, the Gastank 32. While the naming may not be particularly clever, the tank itself is as it has an inner liner made with an engineering plastic, Akulon Fuel Lock from DSM, and an outer made with HiPer-tex glass fiber from 3B.

CNG composite tank

According to Kurt Berglund, president, GASTANK Sweden AB, “Well recognized independent consulting Powertech Labs Inc. Canada did not detect any loss of gas via permeation in our newly developed Gastank 32. . . . This unprecedented result makes our lightweight, zero permeation composite CNG tanks a benchmark within the composite cylinder manufacturing industry.”

Reportedly, the new tank is approximately 70% lighter than a steel tank and less expensive than a carbon fiber/plastic tank.

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