Origin of pollutants from tailpipes emissions
The operation of a car engine is based on the combustion of fuel. All fossil fuels contain carbon (C) and hydrogen (H) and are ideally combusted as follows:
HC+O2=> CO2+ H2OH
The better the combustion process, the more fuel burns according to the ideal reaction. In reality, many other reactions occur, releasing all kinds of gases and substances:
- PM (particulate matter): unburned or incompletely burned fuel residues or contaminants in the fuel can be solid or liquid. These form the so-called fine dust. High concentrations of particulate matter in the air stimulate infections and respiratory diseases and lead to cancer. Fuel quality plays an important role in reducing PM emissions from cars.
- NOx (nitrogen oxides): the oxygen used for combustion comes from the ambient air. The air also contains nitrogen (N2), and at high temperatures (such as in a combustion engine), nitrogen reacts with oxygen in the air to form NOx. Too high NOx concentrations lead to respiratory diseases and contribute to the formation of ozone and acid rain, and a limited extent to the greenhouse effect.
- SO2 (sulphur dioxide): small amounts of sulphur are usually present in the fuel. That sulfur also reacts with oxygen and forms SO2. Too high concentrations of SO2 cause respiratory infections, worsen heart disease and contribute to the formation of acid rain. The quality of the fuel is a determining factor here.
- CO (carbon monoxide): CO is formed when insufficient oxygen is present during combustion instead of CO2. CO is toxic to humans and can lead to health problems at sufficiently high concentrations.
- HC (hydrocarbons): too little oxygen, temperature or time can result in part of the fuel not being burned or burned incompletely. In that case, residues of hydrocarbon compounds remain in the exhaust gases (in gaseous form). Depending on the substance and the concentration, hydrocarbons can affect human health and contribute to ozone formation or the greenhouse effect.
Since all these gases and substances arise from undesirable reactions, improving the combustion process (so that as much fuel as possible is burned according to the ideal reaction) is an efficient way to reduce their emissions. As a result, not only are fewer unwanted substances created but more energy is also released to drive the engine so that less fuel is used to deliver the same power.