The workable limits for reliable ignition by spark plug range from as rich as to as lean as?

• A. rich- 1:9 to as lean as 1:18
• B. rich- 1:8 to as lean as 1:15
• C. rich- 1:10 to 1:20
• D. rich- 1:12 to 1:16

Answer: (A)

Ignition depends on keeping the air–fuel mixture within the flammable limits. If the mixture is too rich (too much fuel for the air), the flame can be quenched or fail to propagate, so reliable ignition becomes difficult. If it’s too lean (not enough fuel), there isn’t enough fuel to sustain the flame. For spark-ignition engines, a practical, widely cited workable range is about 1 part fuel to 9 parts air on the rich side to about 1 part fuel to 18 parts air on the lean side. That is why the range from 1:9 to 1:18 best describes the usable ignition window.