The problem with the combustion of fuels today is twofold: the carbon emissions of the fuels we burn and the pollutant emissions that result from the way we burn those fuels. These emissions, therefore, are what make combustion technologies, and fuel-based power more generally, incompatible with our climate and clean air ambitions.
If, however, we examine the root of these problems, it becomes apparent that their source is the flame. This means that flameless combustion has the potential to unlock a path to both decarbonising and cleaning up fuel-based power.
Why do we use flames?
We are all likely familiar with fire and flames, whether from a match, a candle, or our kitchen hob. The flame itself is the key to releasing heat which is converted from the chemical energy trapped inside the fuel. That is to say, without a flame the match remains a stick, the wax does not melt, and our food goes uncooked.
The purpose of the flame in combustion technologies is exactly the same. The heat of the flame creates and sustains the environment necessary to release the chemical energy stored in a fuel, now so as to drive a piston, or spin a turbine blade, and ultimately allowing this mechanical power to generate electricity.
Sounds good, what’s the problem?
Problem 1: Flames are hot
It is no surprise that flames are hot. But, what you may not know is actually how hot. In some cases, flames can reach in excess of 2000°C, and it is at these temperatures that the energy inside the fuel is rapidly released, self-sustaining the chemical reaction and keeping the flame burning.
But it is also at these extremely high temperatures, found inside the flame, that create the perfect environment for oxygen and nitrogen from the atmosphere combine to form nitrous oxides (NOx). This is one of the pollutant emissions responsible for as many as 36,000 early death a year in the UK alone.[1]
Problem 2: Flames are localised
A flame concentrates the release of heat from the fuel in a localised area so as to sustain the process for as long as fresh air and fuel are provided. This localisation is the cause of the other types of pollution emissions carbon monoxide (CO) and particulate matter (PM). These pollutants result from when fuel, that is partially combusted, leaves the area of the flame without having been fully converted to carbon dioxide (CO2).[2]
Problem 3: Flames are different for every fuel
To sustain a flame, and continue the release of heat from the fuel, a fine balance of air flow and fuel must be maintained, and this balance differs depending on the fuel used. It’s easier to blow out a candle than it is your kitchen hob.
Engineers must therefore design combustion technologies for each specific fuel, carefully regulating and mixing the cool incoming air and fuel. This is why existing technologies are fuel-specific – think, you cannot put diesel into a petrol car.
This fuel-specificity of existing combustion technologies becomes problematic when you consider the uncertainty in the future fuel market, specifically around the timelines to availability of the net-zero- and zero-carbon fuels required to decarbonise fuel-based power. If technology are fuel specific, businesses that want to decarbonise must stake a bet on the availability of specific alternative fuels, which creates risk and limits adoption.
So, no flame, no problems.
Flameless Combustion is, quite simply, the chemical reaction of combustion without the flame. This process is made possible by our Heat Regenerator which recycles waste heat from the exhaust of the Ceramic Turbine and channels it through the combustion chamber. This incoming air is at 930°C, which is well above the auto-ignition, or spontaneous combustion, temperature of methane, biofuels, and hydrogen. As such, fuel can be simply injected into, and distributed by, the air stream, within which it undergoes the auto-ignition process, increasing the air temperature to 1250°C. By ensuring there are no areas of high fuel-density, no flame is formed.
How does this solve the problem of carbon and pollutant emissions?
In today’s uncertain and evolving fuel landscape, fuel-flexibility is crucial to decarbonising fuel-based power by de-risking the switch to renewable fuels for businesses. By eliminating the flame, we have eliminated the design complexities surrounding the different types of flames from different fuels, meaning our turbine can literally “burn” any net-zero- or zero-carbon fuel.
Equally, without the flame, the temperature in the combustion chamber does not exceed the temperature required for the formation of NOx. It also ensures we have complete combustion of fuels. This means no harmful pollutants are formed.
Fuel-flexible Flameless Combustion, therefore, enables businesses and industries to continue to benefit from the demand-responsive, dispatchable properties of fuel-based power generation, but without the pollutants and carbon emissions typical of diesel and gas generators.
Read more in our "WTF is Flameless Combustion" article on LinkedIn, here.
[1] Public Health England (2018), Associations of long-term average concentrations of nitrogen dioxide with mortality, available from: https://assets.publishing.service.gov.uk/ [2] This only happens with hydrocarbon fuels. It will not happen with hydrogen.
