Diesel fuel certainly is combustable when sprayed from an injector, but not a much as gasoline. Gasoline vapor can be readily ignited with a spark, but not diesel fuel or oil. It takes the high compression pressure (and consequent high combustion chamber heat) of a diesel engine to ignite diesel fuel. Thus even if a gasoline engine had a high pressure, diesel type injector it would not be able to readily ignite diesel fuel with a spark plug. That's why you never see a spark ignition engine running on diesel fuel.Once any combustible liquid is sprayed out of a diesel engine fuel injector at a high pressure its about as combustible as gasoline vapors!
You make a good point. Certainly I didn't mean to say that atomized diesel fuel won't ignite, just that it didn't seem to ignite very well at room temperature in a spark-ignited, internal combustion engine.Actually diesel fuel mist will ignite with a spark at room temperature.
The old (and still often used) fuel oil furnaces are routinely set up to run on diesel fuel and they are spraying room temp diesel fuel across a spark gap that easily ignites it. Many of the more modern oil furnaces shut off the spark gap a few seconds after the fuel is ignited and the fine spray holds a self sustaining flame.
By adding an air source (bubble atomization principle) to the fuel spray coming out of the nozzle thicker fluids like used motor oil will in fact ignite quite easily and can also still hold a self sustaining flame as well. Used oil burner systems typically work this way.
Its why I still suggest the added precautions with any atomized fuel mists. They may not flash ignite as easily as gasoline vapor but still they can ignite rather easily with far less ignition source energy than most think.
Either way you get a big hot flash thats at minimum rather surprising for a result.
If the OP manages to fire a fuel injector with 1600 Bars pressure on it there will be an incredibly fine mist produced that will ignite very easily.