Would a 1:18 mixture still be within the workable ignition range?

• A. Yes
• B. No
• C. Only with catalyst
• D. Not defined

Answer: (A)

Flammability limits define the workable ignition range: a fuel–air mixture must lie between the lower and upper flammability limits to ignite. If the mixture is too lean (not enough fuel) or too rich (too much fuel), a flame cannot be sustained.

A 1:18 fuel-to-air ratio places the mixture toward the lean side, but for many fuels this composition still falls within the flammable range. With an appropriate ignition source, combustion can occur under normal conditions, so it would be considered ignitable.

Catalysts aren’t part of the ignition-range concept; they can affect reaction rates but aren’t required for ignition to be possible within the flammable limits. While exact numbers depend on the specific fuel, temperature, and pressure, this ratio typically remains within the workable ignition range, so ignition is possible.