Burning fossil fuels in internal combustion engines impacts on the environment in several ways, the principal of which are as follows:
- Gases are emitted which are residues of the air drawn in by the engine. The most significant of these, nitrogen and oxygen, are completely benign.
- Further gases and vapours are produced as the products of complete combustion. In this category we have water (harmless !) and carbon dioxide which, whilst not toxic, is known to be a greenhouse gas implicated in global warming.
- Toxic gases, liquids and solids are also emitted, which we class as ‘primary pollutants’. Generally, these are the products of partial combustion.
The following table summarises the main constituents of exhaust gas, as it enters the atmosphere:
| Residues of intake air | Products of complete combustion | Primary pollutants |
| Oxygen | Carbon dioxide | Carbon monoxide |
| Nitrogen | Water | Unburnt hydrocarbons |
| Oxides of nitrogen | ||
| Particulate matter |
Once the exhaust gas leaves the engine, some of the primary pollutants may react with each other or with substances already present in the atmosphere to create what are known as ‘secondary pollutants’. Examples of secondary pollutants include ozone, acid rain and photochemical smog.
At Blackthorn, our expertise is in exhaust gas aftertreatment, the aim of which is to reduce primary pollutants. The four most important of these are:
