CNG & LNG – What’s the difference and which should you choose?
Trucks run on diesel, everyone knows that.
Or do they?
Natural gas is quickly changing the narrative. Natural gas made up over 10% of 4×2 sales in 2018 and the market for 6x2s is seeing significant growth and genuine competition with Iveco’s 6×2 launch following fast in the footsteps of Volvo’s earlier in the year.
The growth of the market, however, means that there is an increasing amount of people using gas with scarce experience of it. To secure our customers’ operational efficiency and to ensure our customers get the right solution for their business, we want them to be comfortable with, and well-informed, about gas.
Whilst the trucks run just like a diesel, gas has its differences for a start, with gas there are two different types of fuel: LNG and CNG. But trust us, it’s much simpler than it first seems.
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 you get in your home and in the national grid.
LNG means liquefied natural gas. CNG means 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 LNGiss denser and you can, therefore, get more energy on a vehicle than with CNG.
How do we liquefy it?
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.
We don’t liquefy it ourselves – no one does in the UK these days – we collect it, pre-cooled, at the LNG gas terminal at the Isle of Grain, Kent, and deliver it with our own tankers, all of which run on natural gas.
Refuelling is complicated, isn’t it?
There is a prevailing myth that you must wear a spacesuit to refuel with LNG. In fact, the only real hazard is that the pipes get very cold – the fuel is at minus 161°C, after all – so to protect users from cold burns we ask that they 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 pipes coming into contact with moisture in the air. This creates a cloud of water vapour which people mistake for leaking gas. For extra safety, we simply ask that you put safety glasses on.
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.
The other benefit is CNG can be taken from the gas mains, compressed, and then dispensed straight into your truck, there’s no need to move the gas by tanker.
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.