Calculate the Excess air %, if the stoichiometric A/F ratio = 6.4 and actual A/F ratio = 18.6.

To calculate the Excess air %, you need to follow these steps:

1. First, understand that the Excess air % is the amount of air in a combustion process that is supplied beyond the theoretical air required for complete combustion. It is calculated using the formula:

   Excess air % = ((Actual A/F ratio - Stoichiometric A/F ratio) / Stoichiometric A/F ratio) * 100

2. Substitute the given values into the formula:

   Excess air % = ((18.6 - 6.4) / 6.4) * 100

3. Perform the subtraction in the numerator:

   Excess air % = (12.2 / 6.4) * 100

4. Perform the division:

   Excess air % = 1.90625 * 100

5. Multiply by 100 to get the percentage:

   Excess air % = 190.625%

So, the Excess air % is 190.625%.