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Natural Gas For Long-Haul Trucks: Which Version Makes More Sense?

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Natural Gas-powered Kenworth truck (Image: Flickr user TruckPR)

Natural Gas-powered Kenworth truck (Image: Flickr user TruckPR)

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LNG or CNG? If that just looks like a jumble of letters to you, we're talking about liquefied natural gas and compressed natural gas--and so is the trucking industry.

Natural gas has, to a degree, been overlooked in the passenger vehicle industry while companies look towards electrification (in varying degrees) or biofuels to cut down on oil usage.

But in trucking, where fill-up cost is all-important and the energy density of a fossil fuel is highly important for covering great distances, LNG and CNG are a hot topic.

The two fuels are slightly different, reports Navigant Research, but offer similar benefits.

LNG, liquefied natural gas, is largely composed of methane, cooled and condensed to liquid form to make it easier to transport--it's around one six-hundredth the volume as a liquid as it is in its natural gaseous state.

CNG or compressed natural gas is similar in chemistry--once again, largely methane--compressed to a volume around one percent that of its natural state.

ALSO READ: Natural Gas As Vehicle Fuel: Why Trucks Make More Sense Than Cars

Unsurprisingly, this means it isn't as dense as LNG and not as easy to transport by road--instead, it's usually piped in to a retailer.

LNG's extra compression also gives it higher volumetric energy density than CNG, which is where its benefit to trucks comes in--in theory, you can go further on a similarly-sized tank of LNG than you can on CNG.

In practice, that isn't quite the case. In the real world, range is pretty similar, and LNG has a few significant disadvantages. It's more expensive than CNG and trucks that actually use it cost more than CNG trucks too.

That means the incremental cost payback of LNG trucks is at least double that of CNG trucks. If you're a haulage firm squeezing every penny, those figures don't look great.

2013 Chevrolet Silverado 2500 HD bi-fuel (natural gas & gasoline) pickup truck

2013 Chevrolet Silverado 2500 HD bi-fuel (natural gas & gasoline) pickup truck

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Due to LNG's similarity to oil-based products in infrastructure--i.e. produced in a central location and driven to retailers--it's also more capital-intensive as a whole.

Forbes notes another problem: It's hard to keep LNG cooled to the temperatures it requires to remain a liquid. So it evaporates. And that means methane--a powerful greenhouse gas--readily evaporates into the atmosphere from LNG vehicles.

LNG does offer a few more benefits, in that it's suitable for particularly long-haul trucks--that greater energy density per volume means a large tank can mean infrequent fill-ups, and filling up itself is quicker with its liquid form than it is to fill a CNG tank with gas.

Navigant's research also suggests that worldwide, investment in LNG infrastructure is slightly outpacing that of CNG.

MORE: Do Electric And Natural-Gas Cars Compete Against Each Other?

In contrast, sales of CNG trucks are hugely outpacing that of LNG trucks, and are expected to do so for decades to come.

It's also worth noting that CNG is more popular in the passenger car market--Honda, Ford, GM and RAM all offer CNG vehicles of various descriptions, and companies like Audi are exploring the concept abroad too--Audi's A3 g-tron uses natural gas called 'e-gas' produced synthetically via wind power.

CNG is also popular in countries with high natural gas reserves, like Brazil. Dozens of vehicles in the South American markets are available with natural gas variants.

Cost considerations would likely dictate the LNG or CNG choice for trucking firms.

But even if they don't, the popularity of CNG, its wider availability and higher growth rate suggest it might be the better long-term solution regardless.

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