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I'm not sure if I'm reading the details on flammability limits and air/fuel ratios correctly, but it seems to me that it wouldn't ignite. For gasoline, the stoichiometric air/fuel (mass air/mass fuel) ratio is 14.7. The lower flammability limit is 1.6% (volume fuel/volume air). Density of air is 1.225 kg/m^3 and of gasoline is 719.7 kg/m^3. So the lowest air/fuel ratio capable of igniting would be:

Mass air/mass fuel = density air/density fuel x 1/0.016 = 0.106

In other words, it seems the lowest air/fuel ratio to ignite is 1:9.4, which is way richer than the stoichiometric ratio 14.7:1. Am I reading this right?

Esteban
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  • I suspect this question would be better addressed in the chemistry stack exchange. But my two cents, ignition for lean mixtures may just raise the necessary activation energy required for the reaction to go. For exact stoichiometric ratio I would expect the least activation energy. There are probably other constraints, limitations such as initial temperature and pressure of the mix. – docscience Mar 27 '17 at 23:59

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The lower flammability limit of 1.6% is the percent by volume of gasoline vapour in air. So when calculating the molar ratio in the air you need to use the density of the gasoline vapour not the density of liquid gasoline.

John Rennie
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