List the factors responsible for formation of Nox during combustion. ?

 

🔥 Factors Responsible for the Formation of NOₓ (Oxides of Nitrogen) During Combustion

NOâ‚“ emissions primarily include nitric oxide (NO) and nitrogen dioxide (NO₂), which are major pollutants formed during the high-temperature combustion of fuels, especially in IC engines.


📌 Key Factors Contributing to NOₓ Formation:

1. 🌡️ High Combustion Temperature

  • NOâ‚“ formation increases exponentially above 2,000 K.

  • At high temperatures, nitrogen (N₂) and oxygen (O₂) from air dissociate and react:

    N2+O22NON_2 + O_2 \rightarrow 2NO

2. ⏱️ Long Residence Time at High Temperatures

  • The longer the gases remain at high temperature, the more NOâ‚“ is produced.

  • This is common in lean mixtures or engines under heavy load.

3. 💨 Excess Oxygen (Lean Mixtures)

  • More oxygen availability supports the reaction between nitrogen and oxygen, forming more NOâ‚“.

  • Lean burn engines are more prone to NOâ‚“ formation.

4. 🔄 High Compression Ratio / Advanced Ignition Timing

  • Leads to faster and hotter combustion, increasing peak temperatures and NOâ‚“ production.

5. ⚙️ Engine Load and Speed

  • Higher load = more fuel burned = higher temperatures → more NOâ‚“.

  • Fast combustion at high speeds can also cause higher NOâ‚“ formation.

6. 🔥 In-cylinder Turbulence

  • Increased turbulence improves combustion efficiency, raising peak temperature and thus NOâ‚“ levels.

7. 🛠️ Injection Pressure and Timing (in CI Engines)

  • Early or high-pressure injection can raise cylinder temperature and pressure, increasing NOâ‚“.


Summary Table:

Factor Effect on NOâ‚“ Formation
High combustion temperature Increases dissociation & NO formation
Long residence time at high temp More time for NOâ‚“ reactions to occur
Excess oxygen (lean mixtures) Supports formation of thermal NO
Advanced ignition/injection timing Increases peak pressure and temperature
High engine load Increases fuel burned and heat release

🧠 Conclusion:

NOâ‚“ formation in engines is primarily driven by temperature, oxygen availability, and combustion timing. Engine design and control strategies (like EGR, retarded ignition timing, or lean-NOx traps) are used to minimize NOâ‚“ emissions.

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