R Leo,

Early Diesel engines did input compressed air with the fuel possibly because they did not know how to build a high pressure fuel injections that would atomize the fuel. The compressed air was used to help atomize the fuel to make the engine more efficient.

But I agree with you that the injection of the fuel in the animation is incorrect. It should show that the fuel is injected slightly BTDC and then show orange color in the cylinder for the entire power stroke.

P E H