What are the CO2 emissions depending on the fuel you use: gasoline, diesel (oil) or LPG? In kg of CO2 per liter of fuel
This page is the practical application and summary of the page alkane combustion equations, H2O and CO2
We invite the reader to read this page to know the precise method and combustion equations used. He may also ask questions about the forum energies, especially if these figures leave him perplexed (but it is only basic chemistry…)
Recall the method
We start from the combustion equation to arrive at the following observation.
The mass of CO2 emissions of an alkane of formula CnH (2n + 2) is 44n and the releases of water vapor of 18 (n + 1). This water will eventually condense a few days later, 2 weeks on average, CO2 has a lifespan in the Earth's atmosphere of about 120 years.
We have studied the case of the most common fuel 3 and natural gas:
- Diesel or fuel oil
- LPG or LPG
One liter of gasoline that weighs 0,74 kg emits 2,3 kg of CO2 and 1 kg of water
Chemically, gasoline can be compared to pure octane, i.e. n = 8. In reality, there are dozens of different molecules in gasoline, including additives, but it can be likened to octane.
- The molar mass of octane is 12 * 8 + 1 * (2 * 8 + 2) = 114 grams / mole
- The mass of CO2 released per mole of octane burned is 44 * 8 = 352 g
- The mass of H2O water released per mole of octane burned is 18 (8 + 1) = 162 g
- The ratio of fuel consumption to CO2 emissions is 352/114 = 3,09 and that for water 162/114 = 1,42
Knowing that the density of petrol is 0,74 kg / l and that 1 gram of burned petrol rejects 3,09 grams of CO2 and 1,42 grams of water, it comes: 0,74 * 3,09, 2.28 = 2 kg of CO0,74 per liter of fuel burned and 1,42 * 1,05 = XNUMX kg of water.
In the end we have releases of 2,3 kg of CO2 and 1 L of water per liter of gasoline burned. The ratio CO2 + H20O to fuel mass is 3,3 / 0,74 = 4,46!
A liter of diesel (or diesel or fuel oil) that weighs 0,85 kg emits 2,6 kg of CO2 and 1,15 kg of water
Chemically, diesel, diesel oil or heating oil can be assimilated to pure hexadecane, ie n = 16.
- The molar mass of hexadecane is 12 * 16 + 1 * (2 * 16 + 2) = 226 grams / mole.
- The mass of CO2 released per mole of hexadecane consumed is 44 * 16 = 704 g
- The mass of H2O water discharged per mole of hexadecane burned is 18 (16 + 1) = 306 g
- The ratio of diesel consumption to CO2 emissions is 704/226 = 3,16 and that of water is 306/226 = 1,35
Knowing that the density of the diesel is 0,85 kg / l and that 1 gram of burnt diesel rejects 3,16 grams of CO2 and 1,35 grams of water, it comes: 0,85 * 3,16 = 2,67 , 2 kg of CO0,85 per liter of burnt Diesel and 1,35 * 1,15 = XNUMX kg of water.
In the end we have releases of 2,7 kg of CO2 per liter of diesel, diesel or heating oil burned and 1,15 kg of water. The CO2 + H20O ratio over fuel mass is 3,85 / 0,85 = 4,53!
LPG: 1,7 kg of CO2 per liter
LPG is a mixture of butane and propane, C4H10 and C3H8. Depending on the tanker, the proportion varies from 40 to 60 for one or the other of the components.
We will retain an average value of 50 / 50 or 3,5 n = medium.
The mass of CO2 released per mole of octane consumed is: 44 * 3,5 = 154 g.
The LPG consumption ratio on CO2 releases is 154 / 51 = 3,02
Knowing that the density of LPG 50/50 is approximately 0.55 kg / l at 15 ° C and that 1 gram of burned LPG rejects 3,02 grams of CO2, it comes: 0.55 * 3,02 = 1.66 kg of CO2 per liter of LPG burned.
Or 1,7 kg of CO2 per liter of LPG, the mass ratio of CO2 to mass of fuel is 1,66 / 0.55 = 3! LPG is therefore still a major emitter of CO2!
CAUTION this value is not directly comparable with that of petrol because the energy supplied by one liter of LPG is less than that of petrol or diesel fuel. Indeed; an LPG car will consume 25 to 30% more compared to petrol per 100km which is perfectly logical since LPG weighs 25 to 30% less than petrol.
With gases, it is important to always reason in mass and not in volume…. Even for liquefied gases!
Releases of CO2 for 100 km by car Essence or Diesel?
Let's move on to practice: how much does your petrol car reject? How much does your Diesel car reject?
- Petrol car
- : if your petrol car consumes 6,0L / 100 km then it rejects 6,0 * 2,3 =
13,8 kg of CO2 for 100 km is 138 g / km
- Diesel car
- : if your diesel car consumes 5,0L / 100 km then it rejects 5,0 * 2,6 =
13 kg of CO2 for 100 km is 130 g / km
We use here real numbers, not the idealistic figures from the car catalogs that nobody ever actually reaches! It is false and untrue to claim that a Diesel vehicle pollutes more than a petrol vehicle, on the contrary the Diesel engine is advantageous for limiting CO2 emissions and the greenhouse effect because its efficiency is better. In addition, it should be noted that a Diesel vehicle has a longer lifespan which must be taken into account in calculating pollution! The longer you keep a vehicle, the less it will pollute due to its manufacturing energy.
Indeed; it is estimated thatit takes between 100 and 000 km to make profitable the purchase of a new vehicle to replace an old one still running! This is the calculation ofgray energy of making a car.
Discharges of CO2 per kilogram of fuel burned
The differences are much less obvious when we speak in kg of fuel, so we get:
- Petrol: 2,28 / 0,74 = 3,08 kg CO2 / kg of petrol (the value is found: 3,09)
- Diesel: 2,67 / 0,85 = 3,14 kg CO2 / kg diesel (we find the value: 3,16)
- LPG: 1,66 / 0,55 = 3,02 kg CO2 / kg LPG (we find the value: 3,02)
The higher a fuel has an alkane number (n), the more CO2 it will release per kg… logical!
The cleanest fossil fuel is natural gas CH4, methane, which will reject it:
The mass of CO2 released per mole of octane consumed is: 44 * 1 = 44 g.
The ratio of methane consumption to CO2 releases is 44 / 16 = 2,75 g
1 kg of methane releases 2,75 kg of CO2! And, sorry for the defenders of "clean" gas, but we will not find better as hydrocarbon!
It will also be noted that each mole of methane will also reject 36 grams of water (18 * (n + 1) grams of water per mole) ... or 2,25 kg of water per kg of burnt natural gas!
For each mole of Diesel the value of water produced is 18 * 17 = 306 g / mole, i.e. 306/226 = 1,35 kg of water per kg of Diesel, i.e. 1,35 * 0.85 = 1,15 L of water by L of Diesel! So much water put, in fact it is synthetic water which was not in nature before, in the "climate cycle" is perhaps not so negligible!