This is a question for the chemists amongst us, Countrypaul maybe.
Here is the way to do it when running on derv;
How to calculate the CO2 emission from the fuel consumption?
Diesel:
1 liter of diesel weighs 835 grammes. Diesel consist for 86,2% of carbon, or 720 grammes of carbon per liter diesel. In order to combust this carbon to CO2, 1920 grammes of oxygen is needed. The sum is then 720 + 1920 = 2640 grammes of CO2/liter diesel.
An average consumption of 5 liters/100 km then corresponds to 5 l x 2640 g/l / 100 (per km) = 132 g CO2/km.
Anyone know the calculation for biodiesel?
Edit- I've just found this calculator and it gives a 76.4% reduction in CO2 when running on bio- seems a lot!
http://biodiesel.org/using-biodiesel/handling-use/emissions-calculator
