Are there any known atmospheres that would support traditional combustion engines?

Magic Octopus Urn 06/12/2018 at 18:37. 4 answers, 2.589 views
atmosphere combustion

If we landed a traditional automobile on the moon, the combustion engine would lack oxygen, and, for obvious reasons, would not function. I'm wondering if a planet terrestrial body exists where we would not have to rethink our main method of terrestrial locomotion (being combustion engines).

I would like the answers to focus mainly on atmosphere compositions, not thermal-based problems or other such interference like "the planet is water, there's no surface to drive on". I really am interested what atmospheres would support a combustion engine, if any; any the potential problems with the ones that do (E.G. too much CO2 in atmosphere, would only function at 50% efficiency).

This is not a "should/could we use combustion engines on rovers" question, it's more of a... have we discovered any planets that would support it?

Is there significant information on Trappist to know if any of the planets A-G could support traditional ICE's?

4 Answers

Russell Borogove 06/12/2018 at 18:58.

The short answer is no -- an internal combustion engine needs to pull oxygen from the air to operate, and no solid bodies in the solar system have that kind of atmosphere.

Venus' atmosphere is mostly carbon dioxide with a small amount of nitrogen; neither of those is combustible.

Mars, similarly, has a mostly inert atmosphere; there's a trace of oxygen but it works out to about 1/20000 of the partial pressure of oxygen found on Earth -- probably not enough to run a combustion engine.

Titan is an interesting case; there's no oxygen to speak of, but hydrocarbons make up a couple percent of the atmosphere. You could carry a tank of oxidizer -- liquid oxygen or NTO -- in a vehicle and burn it with atmospheric methane, the opposite arrangement to how a terrestrial ICE works. To get a reasonable amount of power, you'd probably have to run very oxygen-rich, which would make for a fairly corrosive exhaust, so you'd need to choose your materials carefully -- you couldn't adapt an existing car engine to it or anything.

As Evan Steinbrenner notes, there are likely to be many planets in other solar systems with an Earthlike nitrogen-oxygen gas mix, where ICEs would work just fine. We don't currently have a good idea how common such atmospheres are, however.

Evan Steinbrenner 06/12/2018 at 19:05.

In our solar system? No. None of the other planets would support a standard ICE from earth.

In other systems? We think we've found some other earth like planets which are in the habitable zone which should support ICE's but no one has visited them yet and we lack the ability to directly measure the relevant characteristics.

Beyond that statistics would seem to say that with the number of stars out there and the numbers of planets orbiting them that there are bound to be some that are close enough to earth that they would support an ICE but currently confirming that is beyond our capabilities let alone actually getting to them.

Also note that ICE's are a really poor option for locomotion unless the other exoplanets also happen to have fossil fuel deposits that could be extracted. Otherwise batteries + solar or nuclear is probably a far better option for locomotion.

matt_black 06/13/2018 at 14:54.

It seems unlikely in principle

Standard combustion engines rely on burning fuel in an oxidiser taken from the atmosphere. On earth we have an atmosphere which is about one fifth oxygen which does a good job in engines.

We haven't yet observed any planets anywhere with a large supply of oxygen in their atmosphere. And there is a good reason for that. Oxygen is reactive. Things in an oxygen atmosphere burn or oxidise quickly (in fact the specific level of oxygen in earth's atmosphere may be a balance between enough to keep living creatures alive but not so much that fires burn every land dwelling plant every time anything catches fire). So any atmosphere with oxygen in it needs a continuous source of oxygen to keep up the concentration.

Oxygen on earth is a product of life. If there were no life, there would be no continuous supply of oxygen and the concentration would drop until there wasn't enough to support a combustion engine (or fires). Before photosynthesis, earth did not have significant oxygen in the atmosphere (and when photosynthesis became common, geology changed radically with large deposits of, for example, iron oxides suddenly appearing).

So, unless we find a planet that supports photosynthesising life, we are unlikely to find one that supports combustion engines.

Of course other oxidisers are available. But the same objection applies: if they are decent enough oxidisers to support combustion, they will not have a long lifetime in any environment on a geological timescale as they will react with their environment oxidising it and depleting the amount in the atmosphere. So unless you can propose some mechanism to continuously replenish the atmosphere with oxygen (or an alternative) you won't find atmospheres that support combustion. It seem likely that the question has the same answer as "is there any extraterrestrial life". IF we find that we are also likely to find atmospheres that will support engines (and vice versa: if we find atmospheres that support engines, we have found life). But we haven't, yet.

Anthony X 06/15/2018 at 23:39.

Internal combustion is a practical (if undesirable) power source on Earth because there are easy-to-carry, easy-to-store fuels such as gasoline and diesel that can easily be pumped and metered into an engine and reacted with abundant atmospheric oxygen to heat an abundant working fluid (mostly atmospheric nitrogen) to produce mechanical power.

OK, carry your own oxygen and burn with the methane on Titan, sure, but oxygen is hard to store in quantity - you'd be unlikely to attain the sort of energy density with a hypothetical Titan vehicle that we can get here on Earth with gasoline or diesel fueled vehicles.

As stated in other answers, it is, in any event, unlikely you would find naturally occurring chemical reactants in abundance, ready to harvest in any sort of powerplant, on any world unless there was some sort of biological process at work dumping excess energy from some other source (like radiation from a host star) into chemical separation.

Everywhere we have been able to look so far (admittedly only within our own solar system), we find chemical soups on various worlds, but no neatly separated stores of reactants like we have on Earth. Even here we see phenomena like forest fires, triggered by lightning, increasing global entropy combining wood and oxygen to make water vapour, carbon dioxide, and ash. It's just that there's so darn much photosynthetic life that what gets spontaneously consumed by fire is promptly replaced.

The key point is: no celestial body examined to-date has an "exploitable" atmosphere like we have on Earth. As soon as we find one, chances are, we will have found extraterrestrial life.

FWIW: Internal combustion engines are relatively inefficient devices for converting stored energy into mechanical power - at best, only about half the available chemical energy is converted into useful work; the rest ends up as waste heat. They are only practical because of the energy density of the fuel source, power density of ICEs, and the economics of both the devices and the fuels. If you start making chemical substitutions, the economics and practicality can go away, and other options can become more favorable, like fuel cell electric or battery electric.

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