How does that work? I'm not very literate in science, but...how does something get used, turned into energy, and yet produce a waste product of greater mass than the input?
If I boil 1kg of water, it isn't going to become 2litres of steam.
No but the water isn't changing into something else and reacting with other elements.
If we assume petrol is pure octane which it is not but it has a high proportion (90-98%) then 1L of petrol is 703g of octane (density of octane)
Octane has a molecular mass of 114.2 g/mol so we have 6.154 moles of octane in 1L of petrol. Each octane molecule is composed of 8 carbon atoms and 18 hydrogen atoms. So that's 49.23 moles of carbon and 110.78 moles of hydrogen.
If complete combustion occurs (which it doesn't) we would get 49.23 moles of CO2 and 55.39 moles of H2O. Converting those back to grams we have 2166g of CO2 and 997g of H2O.
591g of the 2166g of CO2 is actually carbon if we were to do it by weight.
TLDR: 2.3kg CO2 from 1L of petrol is a reasonable approximation.