We are going to do a small experiment on liquid combustion. We have some diesel fuel in this bottle, that we are going to pour a little into a bowl.

Fuels have different combustion or ignition temperatures. The lowest temperature at which this happens, that is, when there is fuel vapor above the liquid surface that allows combustion, we call it the flash point.

There are fuels like gasoline where this flash point is very low, around -40º Celsius, which means that gasoline is always flammable.

However, diesel fuel ignites at a much higher temperature, around 70ºCelsius, which means that it doesn’t ignite at room temperature. We can see that when we light a match and put it inside the diesel bowl, the match doesn’t ignite the liquid fuel.

So how can we burn diesel fuel at room temperature?

We can try a different way:

We will put some diesel fuel inside this bottle spray, the same fuel that did not ignite in the bowl, close it, and light a alcohol lamp as a source of ignition.

Now, when diesel fuel is spread in tiny drops it will easily ignite and burn at room temperature.