The "throttle" is effectively the mixture control on a diesel engine.
A diesel has no true throttle like a spark ignition engine (i.e. no restrictor plate in the intake). The intake pipe is fully open all the time and the power is controlled by varying the amount of fuel entering the cylinders. The cylinders take a "full gulp" of air irrespective of power demand.
At low power, therefore, the mixture is very weak. More power is achieved by increasing the amount of fuel injected (richening the mixture). Older systems did this mechanically by increasing the stroke of the fuel pump but modern systems may do it by varying the opening time of the injectors, controlled electronically. The black smoke emitted by some road vehicles on acceleration is a sign of a poorly adjusted fuel system, causing over-fuelling
Diesels work at much higher compression ratios than gas engines (typically 19:1 or higher to ensure ignition takes place) and because the volumetric efficiency is also higher (no throttle acting as a restrictor) the fuel economy is much better. This is also why the low speed torque is very good.
A disadvantage of compression ignition is that it is difficult to advance the ignition timing (because of slower combustion) which means that the engine will not rev as highly as a spark ignition engine, limiting the max power that can be produced. However, the power output can be increased significantly at lower rpm by fitting a turbo-charger which simply shoves more air through the engine at lower rpms, allowing more fuel to be burned. On an aero engine this isn't a great disadvantage at all because the engine is normally required to work in a fairly constant rpm band.
N.b. It is very important to keep a diesel's air filter clean, as the throughput of air is much higher than on the equivalent spark ignition engine. There is no danger of carb ice because there is no carb, all that is required for cold weather is to ensure the intake doesn't get blocked by snow!
Nerd mode off as my brain now hurts....
