Aviation matters are regulated by a different part of the DOT than automobiles. The FAA wasn't always part of the DOT but it became part of it in 1967 when the DOT was formed. The Federal Aviation Administration sets the safety standards for the aerospace industry throughout the whole range of operation. Its goal has always been to make the industry more safe. Aviation fuel is just a small part of what they regulate and is exempted from all other laws regarding motor fuels in the US. There are diesel engines certified now but they run on Jet A turbine fuel.
Some STCs (supplemental type certificates) were developed to run older aircraft engines on Mogas but they require testing of it before use. The Mogas also has to meet specification for vapor pressure. This was an effort to drop the octane rating for fuel back to nearer the older 80/87 level for older lower compression engines. After some problems with this practice Lycoming issued a service instruction (latest revision SI-1070AA. Folks can look at this document on line from Lycoming engines and it gives a person an idea of how careful they should be when running Mogas. Even the STC documents give folks an idea about testing for ethanol in the fuel and how to find the good stuff. Ethanol is not recommended unless it is in at least 91 octane Mogas and no more than 1% by volume. Folks have to be careful about vapor pressure too. It's critical at altitude and vapor lock up there would be no fun. Winter Mogas fuel blend is the one to worry about most. They set the volatility way up for winter fuel and it's not controlled all that well. After all this, the STC documents still recommend running a tank full of 100LL every 75-hours just to lube the valves a bit or Avgas can be blended with Mogas. It' seems to be getting harder for folks to get fuel to meet the STC specs these days but it's still out there if you know where to look.
https://www.autofuelstc.com/