All those measures are done to keep the RPM low.
They aren't. The fundamental problem with diesels is the slow combustion due to the gradual introduction of the fuel - contrast that with SI where the all the fuel is present at commencement of ignition.
There had been experiments with Diesel which had throttles,
Yes, but not as load control.
there had been diesel with low compression to get to higher RPM.
Cold start capability defines how low the CR can be - unless other strategies are employed (eg, pre-heating devices)
From a chemistry perspective - Diesel burns slower,
Only because of the difficulties associated with introducing the fuel and it finding air to combust with. Try running a SI engine on a fuel with octane rating as low as diesel's and combustion will be uncontrollably fast - spontaneous. We call it detonation.
The oxidation process is slower- the flame front is slower
There is no flame front. Flame fronts are a feature of SI engines not CI. Diesel burns where it find air - 'off the nozzle'. There isn't a prepared homogenous air/fuel mixture for a flame front to traverse.
- there is a physical limitation how fast your can rev it because of those factors. That's why you optimize a Diesel engine to produce most of it's output low and revs - means less parasitic losses from the rotating assembly.
There is no other option for diesel. It cannot turn high rpm because of the combustion restraint and DI is worse than IDI in that regard.
Diesels (CI) and gasoline (SI) engines pick up where the other left off. Eg, CR. The highest usable CR for a SI engine (to avoid detonation) is the lowest CR a CI can cold start with. The leanest mixture a SI can run is circa Lambda = 1.25, the 'richest' a CI can run is with circa 80% air utilisation (which is Lambda = 1.25). A CI will typically make its maximum power between 3500 and 4000 rpm - which is where a SI makes its maximum torque - with maximum power some several thousand rpm higher. For some SI engines, 4000 rpm is idle speed.
