Natural gas and hydrogen…a “natural” kinship…when blending together natural gas and hydrogen
Hydrogen blends with natural gas have appeared under different brand names: hythane™, HCNG, hydromethane, for example. They all refer to blends containing a percentage of hydrogen in natural gas from 10% up to 30%.
Why do we blend?
HCNG blends (let’s take this name) represent a practical way to include hydrogen in the transport sector with a ‘low-cost approach’, using the natural gas engine technologies.
So, compared to fuel cells, here we are referring to ‘conventional’ internal combustion engine technologies and not to electric propulsion.
Which are the benefits of hydrogen and methane blends?
Compared with pure natural gas, HCNG blends offer additional CO2 reduction potential.
Due to the Hydrogen-Carbon ratio, a 30% blend offers 11% CO2 emissions reduction on top of the 23% reduction obtained with natural gas (when we compare with Petrol, for example).
This means that, compared to a gasoline car, this blends would reduce tailpipe CO2 emissions by 32%.
Moreover, combustion is ‘boosted’ by hydrogen, achieving a more complete process with fewer pollutant emissions, in particular, unburned hydrocarbons (THC) and carbon monoxide (CO).
How much hydrogen can be blended with natural gas?
Let’s try to explain why usually experiments refer to a maximum content of hydrogen around 30% by volume.
A first limitation is related to the need to “control” the combustion process. Contrary to natural gas, hydrogen offers very low resistance to autoignition.
This parameter, normally translated into conventional fuels with the Octane Number, is fundamental in the attainment and operation of highly efficient engines.
A short technical but intuitive explanation of why we can only blend certain amounts:
Today, highly efficient engines, most of which also turbocharged, require that the mix of air and fuel ‘waits’ for the ignition event (from the spark plug) to start the combustion process at the right moment. But what if combustion is generated inside the combustion chamber before the spark plug event? Then, we would have different propagation waves of different combustion flames.
This is what generates the typical metallic sound, the ‘knocking’. But, above all, can lead very quickly to the destruction of the engine and could be the reason for the pressure and temperature peaks.
It is like an orchestra not waiting for the conductor, with each musician playing by themselves… what a chaos!
A second important reason to limit hydrogen to a certain percentage is because of the lower energy density of the resulting blend. A 30% blend contains approximately 20% less energy than CNG only. This means that the range of your NGV will be reduced by the same proportion.
Is a HCNG the same as a CNG one ?
HCNG blends fit with natural gas technologies, BUT hydrogen can generate corrosion on carbon steel components. Therefore, an attentive analysis of the compatibility of the materials in contact with the blends (especially on the high-pressure part of the storage and feeding system) must be made.
So, is this all there is to it?
Not quite. Because hydrogen affects the characteristic of combustion, HCNG blends require the adaptation of engine calibrations to ensure the best conditions of efficiency and emissions control.
So, unless hydrogen percentages are very low, you wouldn’t be able to just refill and start your engine.
What about the future for this kind of blends?
Discussing all these technical details was important to provide us with an understanding of what the limitations are and why they are there.
But, at the same time, it may seem that it is all too complicated for the future of these hydrogen-methane blends.
In reality, with growing production of hydrogen from renewable energy sources (wind and solar), it is expected that part of the surplus of electricity will be converted into hydrogen and simply injected into the natural gas grid.
Once again, NGVs technologies reveal an incredibly flexible mechanism to match future mobility with a growing role of renewably-produced energy. From biomethane to synthetic methane, from natural gas to hydrogen blends, NGVs are already able to support all this in an easy and affordable way!