Generally speaking diesels usually use a glow plug simply for primary ignition & warm up - once the temps reach the appropriate level compression & heat alone serve to ignite the fuel/air mix, If I
remember correctly lol, the Lohmann (and some others) had variable compression settings to assist in maximum performance & ignition, perhaps not needing even a glow plug *shrug*
Although not true diesels (mixed fuels, kerosene, ether, castor etc), some model aircraft engines operate on this same principal, a battery is hooked to a glow plug & once ignited it's removed - leaving no (functioning) electrical components at all, I believe the Lommann used a paraffin mix and not (modern) diesel fuel... I don't really know for sure as I've no experience w/one. Unfortunately model "diesel" fuel is prohibitively expensive, sad as there's some "giant" scale engines that would otherwise be viable candidates for MBs... mebbe... depending on level of determination & insanity ofc;
Tartan 50cc twin (no longer in production)
TARTAN 77 TWIN ENGINE. AWESOME CONDITION. NO RESERVE (07/13/2009)...
There's been some experimentation amongst the model airplane guys, some research into true diesel conversions & even biodiesel... but I've not found anything I could consider "conclusive" and viable... but on the other hand I'm not a model airplane guy & I've not actually talked to anyone or even seen converted engines - it's got potential tho... perhaps someone with some actual modeling experience might chime in?
Diesels have never seemed particularly popular in the States, our infrastructure defo favoring gasoline - I'm constantly surprised that with today's fuel prices that we've not seen a rise in popularity in small diesel engines as they're relatively commonplace in other countries *shrug* We've some ofc, but we seem to mostly use 'em for large trucks and heavy equipment.
There's a buncha fascinating info here: Diesel engine
including 2 & 4 stroke, turbo & superchargers and ofc some history