Makes a lot of sense tbh. C and O have roughly the same atomic weight, and CO2 is about a third C (from the fuel). The fuel of course has a bunch of H but by ma

Makes a lot of sense tbh. C and O have roughly the same atomic weight, and CO2 is about a third C (from the fuel). The fuel of course has a bunch of H but by mass that's only a small fraction. So a given mass of fuel turns into roughly three times as much CO2. With petrol being a bit lighter than water (which is 1 kg/l) the 2.3 kg CO2 per liter is right around the "factor 3" estimate.