# 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 CO_{2}, 1920 grammes of oxygen is needed. The sum is then 720 + 1920 = 2640 grammes of CO_{2}/liter diesel.

An average consumption of 5 liters/100 km then corresponds to 5 l x 2640 g/l / 100 (per km) = 132 g CO_{2}/km.

**Petrol:**

1 liter of petrol weighs 750 grammes. Petrol consists for 87% of carbon, or 652 grammes of carbon per liter of petrol. In order to combust this carbon to CO_{2}, 1740 grammes of oxygen is needed. The sum is then 652 + 1740 = 2392 grammes of CO_{2}/liter of petrol.

An average consumption of 5 liters/100 km then corresponds to 5 l x 2392 g/l / 100 (per km) = 120 g CO_{2}/km.

**LPG:**

1 liter of LPG weighs 550 grammes. LPG consists for 82,5% of carbon, or 454 grammes of carbon per liter of LPG. In order to combust this carbon to CO_{2}, 1211 grammes of oxygen is needed. The sum is then 454 + 1211 = 1665 grammes of CO_{2}/liter of LPG.

An average consumption of 5 liters / 100 km then corresponds to 5 l x 1665 g/l / 100 (per km) = 83 g of CO_{2}/km.

**CNG:**

CNG is a gaseous fuel (natural gas), stored under high pressure. Consequently, the consumption can be expressed in Nm3/100km, but also in kg/100km. Nm3 stands for a cubic meter under normal conditions (1 atm and 0 â”¬â–‘ C). Consumption of natural gas vehicles is, however, most often expressed in kg/100km.

Different types of natural gas are available in Belgium, roughly divided into two categories: low and high calorific gas (L- and H-gas). CO2 emissions differ between both categories, and strongly depends on the composition and origin of the gas. The calculations below are therefore merely indicative. The public CNG stations in Belgium mainly offer low calorific gas. You will see that the CO2 emissions per kg of H-gas is higher than that of L-gas. H-gas, however, contains more energy, so you will need less kg of gas per 100 km, which ensures that, at least in theory, the average CO2 emissions from CNG vehicles is independent of the gas type used.

Low-calorific:

1 kg of L-gas consists for 61,4% of carbon, or 614 grammes of carbon per kg of L-gas. In order to combust this carbon to CO2, 1638 grammes of oxygen is needed. The sum is then 614 + 1638 = 2252 grammes of CO2/kg of L-gas.

An average consumption of 5 kg / 100 km then corresponds to 5 kg x 2252 g/kg = 113 g CO2/km.

High-calorific:

1 kg of H-gas consists for 72,7% of carbon, or 727 grammes of carbon per kg of H-gas. In order to combust this carbon to CO2, 1939 grammes of oxygen is needed. The sum is then 727 + 1939 = 2666 grammes of CO2/kg of H-gas.

An average consumption of 4,2 kg / 100 km then corresponds to 4,2 kg x 2666 g/kg = 112 g of CO2/km.