Diesel fuel itself will burn but you really can't call it flammable. When you add gasoline to it, the flammability greatly increases with the amount of gasoline you add.
Gasoline engine is an internal combustion engine where a diesel is an internal compression engine. Gasoline is highly flammable and explodes when an electrical spark is applied to it where diesel explodes when it is put under pressure
a
Class "B"
Mix diesel in a gasoline engine and it will stall or run very poorly depending on how much you mixed in. Mix gasoline in a diesel engine and you will have engine damage.
Class B
a
It will not run or if it is mixed with gasoline it will not run correctly and smoke depending on how much diesel was added.
It's much more efficient (higher BTU rating in diesel than in unleaded gasoline), and it's much less flammable.
Actually, Diesel is not flammable, it is combustible. The difference is the flash point. Diesel does not flash until 143 degrees Fahrenheit. Anything between 100 and 200 is combustible; less than 100 is flammable. Compare it to "gasoline" which has a flash point of -42 F (I think).
Gasoline is very flammable.
Class "B"
Oxygen is required for fire, but it is not itself "flammable". The elements of hydrogen and helium, while flammable, are present in such minute quantities that they are to diffuse in our atmosphere to ignite. Imagine put a thimble of gasoline some how absorbed in a gallon of water. Gasoline is flammable, but mixed in the water is not going to light.