Here's a breakdown:
Stoichiometric Air-Fuel Ratio:
* This is the ideal ratio where all the fuel is completely burned with no excess air or fuel remaining.
* For gasoline, the stoichiometric ratio is approximately 14.7:1, meaning 14.7 kg of air for every 1 kg of gasoline.
Lean Mixture:
* An air-fuel ratio greater than stoichiometric (e.g., 17:1) is considered a lean mixture.
* This means there's more air than needed for complete combustion.
* Benefits:
* Increased fuel efficiency
* Lower emissions
* Drawbacks:
* Can cause engine knock (pre-ignition)
* Reduced power output
Rich Mixture:
* An air-fuel ratio lower than stoichiometric (e.g., 12:1) is considered a rich mixture.
* This means there's more fuel than needed for complete combustion.
* Benefits:
* Increased power output
* Smoother engine operation
* Drawbacks:
* Reduced fuel efficiency
* Increased emissions
Operating Range:
* Most petrol engines operate in a range of 12:1 to 18:1 under various driving conditions.
* Modern engines use electronic control units (ECUs) to adjust the air-fuel ratio in real-time based on factors like engine speed, load, and temperature.
Factors Affecting Air-Fuel Ratio:
* Engine design: Different engines have different ideal air-fuel ratios.
* Fuel quality: Different types of gasoline have different combustion characteristics.
* Environmental conditions: Air temperature, humidity, and altitude affect the air density.
Key Points:
* The air-fuel ratio is a dynamic variable that constantly changes in a running engine.
* Achieving the optimal air-fuel ratio is essential for maximizing engine performance and minimizing emissions.
* Leaner mixtures are generally preferred for fuel economy, while richer mixtures are needed for power.
Hope this explanation helps!
