1. High Combustion Temperature: During the combustion process in an engine, the temperature inside the cylinder can reach several thousand degrees Celsius. These high temperatures cause the nitrogen (N2) and oxygen (O2) molecules in the air to dissociate into their atomic form.
2. Reaction of Nitrogen and Oxygen: At the high temperatures inside the engine, the dissociated nitrogen and oxygen atoms can react to form nitric oxide (NO). This reaction occurs primarily in areas of the combustion chamber where temperatures are highest, such as near the piston and cylinder head.
3. Reaction of NO with Oxygen: Once formed, nitric oxide (NO) can further react with oxygen (O2) to form nitrogen dioxide (NO2). This reaction typically occurs as the exhaust gases cool down after leaving the combustion chamber and entering the exhaust system.
4. Influence of Excess Air: The amount of excess air present in the combustion mixture can also affect NO2 formation. If there is insufficient oxygen (lean mixture), the combustion process may not be complete, leading to the formation of carbon monoxide (CO) and unburned hydrocarbons (HC). These partially oxidized products can react with NO in the exhaust system to produce NO2.
5. Engine Design and Operating Conditions: Engine design and operating conditions, such as fuel injection timing, ignition timing, and air-fuel ratio, can influence the formation of NO2. Proper engine calibration can help optimize combustion and minimize the production of NO2 and other pollutants.
Efforts to reduce NO2 emissions from internal combustion engines typically involve various strategies such as lean burn combustion, exhaust gas recirculation (EGR), catalytic converters, and advanced engine technologies that enhance fuel efficiency and reduce combustion temperatures.
