Abstract
Expanding the use of hydrogen as a zero carbon fuel has some potential implications for air
quality if it is used as a combustion fuel. Using hydrogen to power fuel cells that directly
generate electricity does not create any air pollution at point-of-use. When hydrogen is
burned in engines, boilers, cookers and furnaces the very high temperature of the flames
can split apart nitrogen (N2) in the air leading to the formation of nitrogen oxides (NOx), an
important class of air pollutant. Hydrogen burns with a hotter flame than most fossil fuels
and has the potential to emit more NOx per unit of heat that is generated. On the other hand
burning hydrogen gas instead of hydrocarbon fuels (e.g. gasoline, diesel, or bioderived fuels
such as ethanol) can bring benefits for air quality, producing lower emissions of particulate
matter and eliminating carbon monoxide. Reducing emissions of NOx from the combustion of
hydrogen can be achieved in many situations using existing exhaust aftertreatment
technologies, by lowering the temperature at which the hydrogen is burned and by
optimising the ratio of fuel to air. This can sometimes leads to additional cost and/or a
reduction in energy efficiency. There are few commercially available examples of engines or
boilers that have been specifically designed to burn hydrogen and real-world data on
emissions performance is very limited. To ensure hydrogen fulfils its potential to be a
substantially cleaner fuel from an air quality perspective requires effective NOx emission
controls (both technical and regulatory) to be in place.
quality if it is used as a combustion fuel. Using hydrogen to power fuel cells that directly
generate electricity does not create any air pollution at point-of-use. When hydrogen is
burned in engines, boilers, cookers and furnaces the very high temperature of the flames
can split apart nitrogen (N2) in the air leading to the formation of nitrogen oxides (NOx), an
important class of air pollutant. Hydrogen burns with a hotter flame than most fossil fuels
and has the potential to emit more NOx per unit of heat that is generated. On the other hand
burning hydrogen gas instead of hydrocarbon fuels (e.g. gasoline, diesel, or bioderived fuels
such as ethanol) can bring benefits for air quality, producing lower emissions of particulate
matter and eliminating carbon monoxide. Reducing emissions of NOx from the combustion of
hydrogen can be achieved in many situations using existing exhaust aftertreatment
technologies, by lowering the temperature at which the hydrogen is burned and by
optimising the ratio of fuel to air. This can sometimes leads to additional cost and/or a
reduction in energy efficiency. There are few commercially available examples of engines or
boilers that have been specifically designed to burn hydrogen and real-world data on
emissions performance is very limited. To ensure hydrogen fulfils its potential to be a
substantially cleaner fuel from an air quality perspective requires effective NOx emission
controls (both technical and regulatory) to be in place.
| Original language | English |
|---|---|
| Commissioning body | Department for Environment Food & Rural Affairs (DEFRA) |
| Number of pages | 22 |
| Publication status | Published - 7 Nov 2024 |