CO2 emissions per liter of fuel: petrol, diesel or LPG

What are the CO2 emissions depending on the fuel you use: gasoline, diesel (oil) or LPG? In kg of CO2 per liter of fuel

CO2 exhaust gas and water

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.

With n hydrocarbon index (family of alkanesSee their classification).

We have studied the case of the most common fuel 3 and natural gas:

  • Essence
  • Diesel or fuel oil
  • LPG or LPG
  • Methane

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
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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!

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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
      1. : 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
      1. : 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:

    1. Petrol: 2,28 / 0,74 = 3,08 kg CO2 / kg of petrol (the value is found: 3,09)
    1. Diesel: 2,67 / 0,85 = 3,14 kg CO2 / kg diesel (we find the value: 3,16)
    1. 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!

Conclusion: our emissions are heavy, very heavy, and heavier than the fuels themselves!

As you can see, when it comes to CO2 in kilograms of fossil energy, this is a “pocket handkerchief” and in the end what matters a lot in CO2 emissions is the efficiency of the appliances that burn these fuels. Thus a Diesel engine will pollute less CO2 than a petrol engine because its performance is better by design!

The difference in CO2 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 say that "natural" gas can be confusing)!

And finally the combustion of fossil fuels depletes the atmosphere of 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 may not be so trivial for the climate and climate change!

12 comments on "CO2 emissions per liter of fuel: gasoline, diesel or LPG"

  1. I am happy to read this page which highlights what has been for me for a long time.
    But beyond that, we are not talking about the transformation of crude oil into gasoline, a more complex process than for diesel.
    And if we want to tackle the diesel that pollutes then let's see the side of the ships ... when a real carbon tax on commercial transport that rebalance trade and revive local production. But that would not do the business of multinationals hence their lobbies and our pseudo ecologists who see no more than the tip of their nose ... or their corrupt portfolio.
    And if we pass the vehicles electrically, how many EPR plants will it be necessary to power all these cars?
    Moreover who manufactures batteries ... German and Chinese and in France ... Bolloré? QED. Not to mention recycling ... in progress?
    In short, all this is only foutage mouth of our government who bail out the coffers of the state on our back ... as always since the dawn of time ... we cut heads at a time ...

    1. Some elements of answer to Martineaud, whose answer contains unfortunately several received ideas:

      1 - Normally, one does not transform the crude, one refines it, that is to say one separates the principal constituents. To obtain gasoline is not a priori easier than to get diesel or more difficult, it all depends on the initial composition of the crude, which varies from one oil field to another. If the crude is particularly light, it will not contain diesel fuel - this is typically the case with US parent rock oil (so badly termed shale oil by the media). The heavier the crude oil, the less fuel it will contain and the more it will contain heavy fractions, such as fuel oil (or diesel: it is the same product), or even heavy fuel oil - and the general trend of crude oil production. in the world is that of a heavier, slow and progressive crude extracted.
      When the crude is really too heavy compared to the uses (the extreme cases being the extra-heavy fuel oils, extracted especially in Venezuela, and the bitumens, extracted typically in Alberta, in Canada), the too heavy fractions of this crude must to be (there, for the blow, actually) transformed to lighten them (by hydrogenating them with the hydrogen obtained by cracking methane, or natural gas - which, in passing, is strongly emitter of CO2, since once the carbon and the hydrogen of the methane separated, the carbon is allowed to combine with the oxygen of the air, which forms ... CO2, which is then released into the atmosphere).

      2 - Yes, the heavy fuel oil of ships pollutes more than fuel oil / diesel cars or boilers (to warm themselves at home). But to wait for an international carbon tax is to wait for Saint-Glinglin. If we are not already able to implement one at the national level, how can we believe that one day, such a tax will have a chance of being implemented at the multinational or even the world level? Moreover, it must be remembered that crude oil is a mixture of hydrocarbons, and that heavy fuel oil is a fraction of the same (as is LPG, gasoline, kerosene or fuel oil). If we deprive ourselves of this fraction by refusing to use it, then we deprive ourselves of part of the crude. The boats will therefore consume other fractions of crude (today, there is much talk of them consume fuel oil / gas, or even gas). This will accentuate the pressure on current consumers of these other crude fractions. But it may not be very clever at the moment when the peak of global crude oil production is announced by those who even denied it a few years ago (see, for example, the latest annual report of the International Energy Agency, which now expects that by 2025, global production of all liquid fuels, petroleum and non-petroleum, will be lower from 13 to 34 million barrels per day compared to the expected demand, which today is around 100 million barrels per day and which, according to what the IEA imagines, should be in those waters by 2025, see the analysis of this report in the link in my signature).

      As long as 10000 km to a product made in a low-wage country will cost less than the same product manufactured here, then international trade will have a bright future. If we want to "rebalance the exchanges", there are not many solutions: either we reduce drastically the wages at home (I doubt that it is socially acceptable, and unfortunately, it is that towards which long pushes international trade), or the cost of transport is high (and that, instituted locally * and * at the borders, it can have several names, including "carbon tax"). Or, we are waiting for everyone to be sorely lacking in oil, but here we too will be in a very serious situation, and the effects of contraction and massive impoverishment will be much more powerful than the stimulating effects of local trade. because, whether we like it or not, oil is the energy of transportation, at home and in the world, and that less oil for everyone means that * all * the physical flows are under strong constraint of contraction. For now, unfortunately it is towards this last path that we are moving fast, and what is emerging is not really beautiful to see. We'd be much better off agreeing to pay ourselves this insurance premium of the carbon tax (that is, an insurance premium against future damage from our current fuel consumption) .

      3 - There are nearly 40 million cars and vans in France. If we were to replace 100% of this fleet with equivalent electric vehicles, we would need only 2 or 3 additional nuclear reactors, because the vehicles would be recharged mainly at night, when, today, the national electricity consumption is experiencing a big "Hole", and where EDF is obliged to "slow down" the production of nuclear power plants that are capable of doing so (roughly half of our nuclear power plants are said to be "controllable", that is, we can adapt the production of the power station at the request of electricity of the moment: you can go to ERDF's Eco2mix site to see for yourself the control of French nuclear power stations day after day). The nightly charging of electric vehicles would then make all nuclear reactors work like daylight, and calculations show that there would not be much electricity left to recharge all electric vehicles (in this case, basically, the equivalent of 2 or 3 additional reactors).

      4 - The batteries manufactured by Bolloré is (fortunately or unfortunately, I do not know) peanuts. Market and life cycle studies of lithium-ion batteries show that it is China that manufactures most of our lithium-ion batteries today. This is not without posing geopolitical problems, by the way (China can quite decide one day to close the tap battery, and it will put us damn in the panade).
      As for the recycling of batteries, technically, it is entirely possible. But as recycling a battery costs more energy (and therefore money) than going to extract, at the other end of the world, raw materials in mines and salars to make a new battery, we do not recycle batteries used. And we risk not to recycle them anytime soon (in any case, massively).
      By the way, I said that I was a strong supporter of electric vehicles but that I came back: in my opinion (but this is only my opinion), we will never have close to 40 million vehicles electric to replace the nearly 40 million thermal vehicles. Because for at least half of our population, these vehicles will always be much too expensive and unaffordable. The public power would do much better to regulate the fuel consumption of the thermal vehicles for sale, so that their consumption is divided by 3 by 2030 (technically cars to 2 L / 100 km, it is already possible; on the other hand, we will have to agree to abandon the 4 × 4 and other "SUV" so greedy, and adopt much narrower vehicles, much lower and much lighter ... and prohibit advertising for fast and powerful cars!) . And to avoid any rebound effect, it will at the same time increase the liter of fuel, so that for the end consumer, the cost per kilometer traveled remains the same.

      5 - Revise his story is very useful: it clearly shows that cutting heads leads nowhere, leaving the field open to anarchy, then to more tyranny. It took nearly 90 years to France to become democratically lasting after cutting the head of his king. And in a tyranny, it becomes impossible to demonstrate publicly, even once, his discontent: arbitrary arrests and assassinations of political opponents become the norm. Is this really what we want for our country?

  2. This is an interesting page. However, I must not confuse the pollution of refineries or power plants, which, being localized can be corrected, with the pollution of the vehicles, which is dependent on it, can not be cleaned up. Gasoline vehicles generate little more CO2 than fuel (25%), but other pollutants are much less toxic and less numerous with gasoline.
    Another remark, we confuse the pollution that intoxicates us with the minor pollution which, slightly polluting the atmosphere, supposedly produces global warming. The earth has experienced many warmings and colds of which we are not interested in the cause. So we can not say that we are at the origin of the warming because we can not say if it is not natural.

  3. Interesting page, except on the water point, where this article is totally wrong. Even though water vapor is the largest greenhouse gas and indeed our climate system, the atmosphere is already saturated with water, so any excess water vapor condenses into liquid water in a few hours (in our latitudes) to a few days (in the driest parts of the Earth), and is fully recycled in at most a week, in the form of rain. The effect of excess water in the atmosphere on the climate (in terms of "radiative forcing", to be precise) is therefore virtually non-existent. Nothing to do with the CO2 which will remain in the atmosphere 5000 or 10000 years before being naturally purified.

    1. Thank you for the comment.

      a) I always learned that the lifetime of atmospheric CO2 was 120 years ... so far from the 5 to 10 000 years you mention

      b) The article is concerned more with the creation of "fossil" water, hence "ex nihilo", and its placement in the natural water cycle than its presence in the atmosphere (average life of water before condensation: 2 weeks). We can not talk about recycling since it is water that did not exist BEFORE.

      Billions of liters of water are created by burning fossils every day: nothing but oil at 90 million barrels a day is more than 10 billion L of water created from "nothing" a day ... more than 400 million L creates every hour or more of 100 m3 / s just for oil!
      Ok it is weak compared to the atmospheric water and the capacity of evaporation of the oceans but in fine it is not at all that it is so negligible!

      It rains how much on Earth permanently and on average in m3 / s? History to compare?

  4. Hello simple question how can a vehicle produce more than it consumes?

    Let me explain why my car consumes 6l / 100km for 130g./km therefore in my calculation base, 1300g.CO2 / 10km, 13000g.CO2 / 100km, 130000g.CO2 / 1000km.

    130kg / 1000km for 60l consumed knowing that the liter of gas oil = +/- 0.850kg so for 60l = +/- 51kg.

    So how do I consume 51kg of diesel I produce 130kg of CO2?

    1. Hello,

      The calculation is good: 51 kg of diesel will produce 130 kg of CO2. And 130 g / km is consistent with a car that consumes 6L / 100km.

      The answer is in the equations of the article: the extra mass comes from the oxygen of the air. Fuel combustion takes oxygen to transform it into CO2 ... and H2O ...

      There are only carbon and hydrogen atoms that come from fuel.

      The molar masses are as follows:
      C = 12
      O = 18
      H = 1

      So on CO2 of total molar mass 12 + 2 * 18 = 48 g / mol, the mass of O2 is 2 * 18 = 36 g is 36 / 48 = 75%.

      So 75% of the mass of CO2 released by the combustion comes not from the fuel but from the atmosphere (it does not change at all the problem of the warming) ...

      I hope it's clearer.

      Have a good day

  5. It remains an argument in favor of the LPG, apart from the emission of CO2, it is the only fuel derived exclusively from oil. I mean that its manufacture does not affect agricultural production and the increase in the price of food raw materials at the world level, unlike the others that contain an increasing percentage of alcohol or vegetable oil.

  6. Bonjour à tous

    The subject was raised with the commentary on the cracking, but as always we talk about the rejection of CO2 exhaust outlet, but when is it that of then at the pump which represents at least 3/4 of the releases.

    There are other factors:
    - The extraction of crude
    - Transportation of crude / product (crude is not extracted locally)
    - Cracking (see previous comment)
    - Refining and treatments (de-sulfuring, etc.)
    - The distribution

    What I know (source Elf, it dates) the treatment of diesel is very expensive, Elf said it takes just for the de-sulfuring the equivalent of a ton of heavy fuel oil for 1 ton of diesel, also knowing that in this process also uses hydrogen (which is itself very expensive to produce in CO2 equivalent release)

    From what I had read, but unfortunately it is not precise enough or detailed enough, and I would like to have more info on it, than just the values ​​below:
    This would be the equivalent in rejection for:
    - Diesel: 5 liters for 1 liter consumed
    - Gasoline: 4 liters for 1 liter consumed
    - Ethanol: 2,5 liters per 1 liter consumed (deducts what is returned by the plant)
    - Others … ?

    But how are these values ​​calculated, does it take into account the additional components used such as the production of hydrogen?

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