Diesel engines work in a Diesel Cycle, which consists in heating air by adiabatic compression and later adding fuel that will be ignited by the heat inside the chamber. Considering this is a constant pressure cycle, in order to achieve that pressure in a cylinder that displaces an specific volume per cycle, you need to have all the air possible. This means diesel engine always intake all the air possible. What determines the power output of the combustion will always be the amount of fuel injected.

Gasoline engines work in a Otto Cycle, which is a constant volume cycle. This means that the power output will be determined by the volume of air/fuel mixture compressed by the piston.

Proof of this is that in Diesel engines, you control fuel delivery with the accelerator. There's no paddle in the intake, which means all the air volume possible enter the engine on every cycle. In gasoline engines, you have a paddle in the intake, which allows you to control the volume of air entering the engine through the accelerator.

Just a piece of knowledge, as simple as I can remember it...

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1982 W123 300D NA Euro, 300K Miles, 4-speed manual, 3.46 rear diff, early W126 front brakes, Penta rims with 205/60R15 FH900's, custom fitted (by me) audio system, more to come into the money pit... Soon to be installed: Bilstein HD, R107 front discs and 4-piston calipers, HD Suspension springs, wagon front swaybar.