An electrical short to ground.
It would depend on what is burning.
A rubber burning smell and smoke near your two front tires could be the result of sticking calipers. The brake line could also be the cause of the burning smell.
Campfires generally have a distinctive smell that is a combination of burning wood, smoke, and sometimes a hint of pine or other burning vegetation. The smell can be warm, earthy, and nostalgic, and it often evokes feelings of coziness and outdoor adventure.
If you can smell burnt plastic then you could potentially be in danger. Smoke from burning plastic can be harmful to breathe.
The smell was dead bodies being burned to ashes
because the fan belt is burning
An air conditioner should not smell like smoke when turned on (or when turned off). I would have to suspect that the electrical insulation is burning.
If awake you can see the smoke and smell the burning odor. If asleep you rely on your nose and if smoke is inhaled your cough warns you of fire.
Possibly a problem with one of your belts?
pcv system is clogged up.
your car is burning oil.
Wildfires can produce a strong, smoky smell that is often described as acrid, bitter, or resembling burned wood. The smell can be quite overpowering, even from a distance, due to the various chemicals and particles released during the burning process.