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 the 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 puzzled him (but this is only basic chemistry ...)
Recall the method
We start from the combustion equation to arrive at the following observation.
The mass of CO2 emissions from an alkane of formula CnH (2n + 2) is 44n and the water vapor emissions are 18 (n + 1). This water will eventually condense a few days later, 2 weeks on average, the 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 assimilated to pure octane, i.e. n = 8. In fact, 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 gasoline consumption to CO2 emissions is 352/114 = 3,09 and that for water 162/114 = 1,42
Knowing that the density of gasoline is 0,74 kg / l and that 1 gram of burnt gasoline releases 3,09 grams of CO2 and 1,42 grams of water, it comes to: 0,74 * 3,09, 2.28 = 2 kg of CO0,74 per liter of gasoline burned and 1,42 * 1,05 = XNUMX kg of water.
In the end, we have emissions of 2,3 kg of CO2 and 1 L of water per liter of gasoline burned. The CO2 + H20 to fuel mass ratio is 3,3 / 0,74 = 4,46!
A liter of diesel (or diesel or fuel oil) that weighs 0,85 kg rejects 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 water H2O rejected per mole of hexadecane burnt 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 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 to: 0,85 * 3,16 = 2,67 , 2 kg of CO0,85 per liter of Diesel burned and 1,35 * 1,15 = XNUMX kg of water.
In the end, we have emissions of 2,7 kg of CO2 per liter of diesel, gas oil or heating oil burned and 1,15 kg of water. The CO2 + H20 to fuel mass ratio is 3,85 / 0,85 = 4,53!
LPG: 1,7 kg of CO2 per liter
LPG is a mixture of butane and propane, ie C4H10 and C3H8. Depending on the tanker, the proportion varies from 40 to 60 of one or 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 about 0.55 kg / l at 15 ° C and that 1 gram of burnt LPG releases 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!
WARNING this value is not directly comparable with that of gasoline because the energy supplied by a liter of LPG is less than that of gasoline or diesel fuel. Indeed; an LPG car will consume 25 to 30% more than gasoline per 100km, which is perfectly logical since LPG weighs 25 to 30% less than gasoline.
With gases, it is important to always think 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 car catalogs that no one ever actually achieves! It is false and untrue to claim that a Diesel vehicle pollutes more than a gasoline 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 the pollution calculation! The longer you keep a vehicle, the less it will pollute because of its manufacturing energy.
Indeed; it is estimated thatit takes between 100 and 000 km to make the purchase of a new vehicle profitable to replace an old one that is still running! It is the calculation of thegray 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:
- Gasoline: 2,28 / 0,74 = 3,08 kg CO2 / kg of gasoline (we find the value: 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 more a fuel has a number of alkane (n), the more it will reject CO2 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 a hydrocarbon!
It should also be noted that each mole of methane will also release 36 grams of water (18 * (n + 1) grams of water per mole) ... ie 2,25 kg of water per kg of natural gas burned!
For each mole of Diesel the value of water produced is 18 * 17 = 306 g / mole or 306/226 = 1,35 kg of water per kg of Diesel or 1,35 * 0.85 = 1,15 L of water by L of Diesel! As much water put, in fact it is synthetic water that was not in nature before, in the "climate cycle" is perhaps not so negligible!
Conclusion: our emissions are heavy, very heavy, and heavier than the fuels themselves!
As you can see, for CO2 when we speak in kg of fossil energy, this plays out like a “pocket handkerchief” and in the end what matters a lot in CO2 emissions are the yields of the devices that burn these fuels. Thus a Diesel engine will pollute less CO2 than a gasoline engine because its efficiency is better by design!
The difference in CO2 when switching from Diesel to methane is only 2,75 / 3,16 = 0,87 ... or 13% less, so it is certainly not natural gas that will save the climate ( yet it is sold by some as such ... must be said that "natural" gas can lead to confusion)!
And finally, the combustion of fossil fuels depletes the atmosphere in oxygen (hence the excess mass of waste!) While enriching it with water!
And the excess water introduced into the "climate system" by the combustion of fossil fuels is perhaps not so trivial for the climate and climate change!
To go further, a few pages on synthetic fuels:
Synthesis of alternative synthetic fuels
Process Laigret, synthetic petroleum from waste
Process synthetic Fischer-Tropsch gasoline (solid fuel to liquid fuel)
Forum of biofuels and alternative fuels