As the piston rises during the compression stroke, the temperature and pressure of the air-fuel mixture increase significantly. Under these conditions, the oxygen and fuel molecules react, resulting in combustion. However, nitrogen, being relatively inert, does not participate directly in the combustion process. Instead, it serves as a diluent, absorbing heat energy and reducing the peak temperatures reached during combustion.
During the expansion stroke, as the hot gases expand and push the piston down, the nitrogen continues to play its role as a diluent, moderating the rate of pressure rise and temperature increase. It also acts as a cushion, preventing the rapid transfer of heat to the engine's components.
Overall, the presence of nitrogen in the internal combustion engine serves several purposes:
1. Dilution and temperature moderation: Nitrogen absorbs heat during the combustion process, helping to control the temperature and pressure within the engine.
2. Reduced pollutant emissions: By diluting the fuel-air mixture, nitrogen helps reduce the formation of nitrogen oxides (NOx), which are harmful air pollutants.
3. Improved fuel efficiency: The presence of nitrogen in the mixture lowers the specific heat ratio, which results in more efficient fuel combustion and improved fuel economy.
4. Engine durability: Nitrogen's inert nature prevents it from reacting with the engine's components, reducing wear and tear and contributing to the engine's longevity.
