system
Given the following post, respond as if you're commenting on Reddit:
human
Why do two stroke gasoline engines have to use mixed fuel? Why aren't they designed with a separate oil system?

The main problem with two stroke engines is that they do not burn cleanly, thus restricting their use to small applications despite their high power to weight. I do not understand why they must have the fuel be the lubricant instead of having separate oil and fuel like 4 stroke engines.
gpt
Two-stroke engines can have a separate fuel and lubrication systems.  This is common in marine 2-stroke diesel engines. (Marine 2-stroke diesels also aren't small.)

The lubricant-in-fuel thing does make for a simple engine.