It has a really high compression ratio which aids in using all the energy of the injected fuel, and we know that a diesel engine runs and accelerates by adding or taking away fuel and no regulation of air. The rest is pretty basic physics from there on.
diesel engine heats up when you add fuel to it, the more fuel the more heat it generates - thats why on turbo diesels, the pump first dumps some fuel into the engine and subsequentially heat into the turbo, which then spools up - the pump then increases fuel to use this advantage - the downside is excessive heat which is being used as increased torque at the time of acceleration. As soon as it backs off - the engine cools off.
Same reason when you remove the thermostat in a diesel and let it idle - it wont even heat up to normal temperature after a day of idling.
