Why didn't WWI and WWII planes and tanks use diesel engines?

by IronRoughneck

From a cursory google search, I have noticed almost all tanks and airplanes used in combat during WWI and WWII had gasoline/petrol engines as opposed to diesel engines.

Both the diesel and four-stroke gasoline engines were invented in the 1890s.

Diesel fuel is easier to refine than gasoline and far less flammable. Does anyone have any idea why militaries used gasoline so much more prevalently in the early to mid 20th century?

Seraph062

Does anyone have any idea why militaries used gasoline so much more prevalently in the early to mid 20th century?

Petrol engines have a few significant advantages:

  1. Diesel engines in the early-mid 20th century were generally incapable of the same power output for a given engine size. This is important in tank design, where increasing the size of your engine can also increase the amount of armor (i.e. weight) you need to carry. It's VERY important in airplane design which is very much an "every pound counts" kind of thing. The only application I'm aware of for aviation diesels in that time frame were airships (zeppelin) and flying boats where the fuel savings and flammability improvements would make up for the extra weight of the engines.
  2. A poorly made gasoline engine will generally be more reliable than a poorly made diesel engine. This is because the higher pressures that the latter experience tend to punish design or manufacturing flaws.

So airplanes end up being a fairly straightforward decision most of the time thanks to the improved power/performance of gasoline engines. The specifics of why each nation made the decisions it made for tank engines is going to come down to factors unique to them.