CNG & LNG – What’s the difference and which should you choose?
Trucks run on diesel, everyone knows that.
Or do they?
Biomethane is changing the narrative. Gas truck sales made up around 10-15% of all UK HGV sales in 2021 and the market for 6x2s is seeing significant growth with Scania’s 6×2 following in the footsteps of Volvo’s and Iveco’s.
Whilst the trucks run just like a diesel, there ar some differences. For a start, gas there are two different types of fuel: LNG and CNG. In this article, we’ll try to clarify the differences between the two fuels and we’ll dispel some common myths while we’re at it.
When a gas is not a gas
The first thing to say is that both gases are methane, the same as in domestic homes and in the gas transmission network (otherwise known as the gas grid).
LNG is liquefied natural gas. CNG is compressed natural gas. The key point – and the reason there are two fuels, not one – is that gas has different energy densities in different states. One unit of liquid gas energy takes up 3 times less volume than one unit of compressed gas energy. Simply, this means LNG is denser and you can, therefore, get more energy on a vehicle by using LNG, compared to CNG.
How is it liquefied?
The gas becomes liquid when it falls below -161°C. At this temperature, it also falls to a very low pressure as its volume decreases, to somewhere around 2 to 3 bar, about the same as a can of coke at room temperature. By the time the gas reaches our stations the pressure and temperature will have risen.
Refuelling is complicated, isn’t it?
There is a prevailing myth that you must wear a spacesuit to refuel with LNG. The fuel can be as cold as minus 160°C – so to protect users from cold burns we ask that all users wear cryogenic gloves and eye protection, long sleeves and trousers should also be worn.
The other thing you see when refuelling is a small amount of vapour, caused by freezing piepwork coming into contact with moisture in the air. This creates a cloud of water vapour which can be mistaken for leaking gas.
Other than that the process is tailored to replicate existing models; swipe in, enter mileage data, then fill.
Two fuels for two uses
The range offered by the denser LNG is preferred by many long-haul operators. However, if you’re just doing regional work and don’t need 6×2 tractors or 1000kms range you might decide that CNG is the better option.
The main reason people choose CNG is the simplicity of the refuelling process. It really is easier than diesel – there are no gloves or other equipment to be seen and it’s fully automatic, you just have to attach the nozzle.
But if you want to go up to 44 tonnes and get a reasonable range, LNG will be for you.
Weights and measures
The other thing is, gas, unlike diesel, is sold in kilograms. That’s because the amount of gas energy you’ll get in any given volume will vary depending on the temperature and pressure of the gas at that given point in time. Thus, to ensure we always give you the right amount of gas we offer it by a constant measurement: its mass, measured in kilograms.
The other thing to note is that a kilo of gas has a different amount of energy than a litre of diesel. To get the amount of energy in 1L of diesel you only need 0.72kg of gas.
If you want to know anything else, email us on info@gasrec.co.uk, call us on 01788 822360 or go to our website and click the live chat icon at the bottom right of your screen and you can speak directly to one of our team.