Nitrogen oxides found in diesel emissions primarily consist of Nitric Oxide (NO) and Nitrogen Dioxide (NO2), which are collectively referred to as NOx.
How Nitrogen Oxides Form in Diesel Engines
The creation of nitrogen oxides inside diesel engines is a direct result of the combustion process. As stated by the reference, "Nitrogen oxide is created inside diesel engines, and it occurs as a result of combustion."
Here's the breakdown of the formation process:
- Combustion Starts: Diesel fuel burns within the engine cylinders.
- Temperature Rises: As combustion occurs, the internal temperature rises significantly.
- Nitrogen and Oxygen React: "This heat is what triggers the nitrogen to break apart from the oxygen molecules that are in the air." At these high temperatures, nitrogen (N2) and oxygen (O2) present in the intake air react to form various nitrogen oxides.
The vast majority of nitrogen oxide initially formed during the high-temperature combustion phase is Nitric Oxide (NO).
Key Nitrogen Oxides in Diesel Exhaust: NOx
While several nitrogen compounds can theoretically exist, the two most significant and prevalent nitrogen oxides emitted by diesel engines are Nitric Oxide (NO) and Nitrogen Dioxide (NO2). The regulatory term NOx is used to represent the sum of these two pollutants.
Understanding NOx Components
- Nitric Oxide (NO): This is the primary nitrogen oxide produced during the high-temperature combustion in the cylinder. It's a colorless, odorless gas.
- Nitrogen Dioxide (NO2): Some NO is converted to NO2 within the exhaust system or after being released into the atmosphere. NO2 is a reddish-brown gas with a pungent odor and is more harmful than NO.
These compounds are significant air pollutants and contribute to issues like smog and acid rain. Controlling NOx emissions is a major focus in modern diesel engine technology and emission standards.
