I mean… If you have enough lemons and sodium bicarbonate to generate a large enough exothermic reaction between the citric acid in the lemons and the baking soda, maybe? But it generates such a small amount of heat when making one of those kindergarten volcano science experiments so you’d probably need a lot before it was hot enough to combust, if it even got hotter with more materials reacting.

Aperture might have ideas I don’t, though. Ask Cave Johnson.