Air breathing engines question

[Malenfant]

(from the Yiarn Cardee Vehicle Catalogue preview)

On worlds where the atmospheric pressure falls below 0.5 atmospheres, rises above 3 atmospheres, or where there is no oxygen in the atmosphere, these engines are of no use.

Why would air-breathing engines not work if the pressure is too high? Do they just get too much oxygen and explode or something?

And realistically, is the issue the oxygen pressure (percentage of O2 in the atmosphere multiplied by the atmospheric pressure) or is it the actually atmospheric pressure? (I realise that Traveller usually doesn't differentiate between the two. I'm just asking out of general curiosity)

 

[JustinThyme]

If it's a gasoline engine, you couldn't get enough fuel to the cylinders without saturating them. In the days when imports were truly imports and not assembled in the states, the first thing needed for that newly arrived Japanese auto was a leaning of the fuel mixture. They were assembled and adjusted to run in a higher air pressure, being on an island. Diesels may require tlc to get them running, but I think they would; but not anywhere like Venus. The same for the closed systems burning compressed fuels like propane.

 

[DaveChase]

There are 3 things that effect the engine when dealing with pressure changes

oxygen to fuel ratio
heat transfer ratio (depends on lots of conditions but thinner atmosphere loses heat faster than thicker
dryness of the air (not always a factor because you can have swamps or deserts at sea level (first very humid, second normally dry)

The details are many, so I only list the few things above that I know and have personally had to deal with

Dave

 

[tjoneslo]

Originally posted by Malenfant:
Why would air-breathing engines not work if the pressure is too high? Do they just get too much oxygen and explode or something?

For the same reason the Traveller rules require special breathing equipment for people at high atmospheric pressures.

And realistically, is the issue the oxygen pressure (percentage of O2 in the atmosphere multiplied by the atmospheric pressure) or is it the actually atmospheric pressure? (I realise that Traveller usually doesn't differentiate between the two. I'm just asking out of general curiosity)

I did it for exactly the reason you state. The T20 rules have no way of distinguishing 02 partial pressure from atmospheric pressure. There are some realistic limits on what the O2 partial pressure can be without getting the atmosphere classified as tainted, exotic or corrosive.

I think 3 Atm is also the upper limit of the pressure defined in the world building section of the T20 book. So I picked something arbitrary.