The option of using an aero- Diesel engine to be able to run from Jet-A1, which is plentiful at many airports seems to be a good approach, and far preferable to having a heavy, bulky pressure vessel onboard.
Do you have a reference for lower NOx emissions from propane? My understanding is that most NOx is a product of combustion in air (although it can come from impurities in the fuel).
As for SOx, natural gas can contain H2S which produces these, is it normally significantly less for propane?
I wonder how hard it would be to adapt a plane to run on propane? You'd need to find somewhere to keep a cylindrical tank (so not the wings) and ideally you'd need a liquid-cooled engine so the coolant could heat the gas vapouriser. You'd get 115 octane fuel, and no CO / HC / NOx / SOx or other nasties in the exhaust, just CO2 and water.
Ammonia combustion directly produces NOx, so I am skeptical about using it in jet as such. It may require decomposing it to N2 and H2 before injection.
You're correct: methane would not work well as a replacement for conventional aviation fuel both for the reason you mention (weight of storage system) as well as the lower energy density per unit volume: 35 MJ/L for jet fuel vs. 9 MJ/L for compressed natural gas at 3600 PSI. (https://en.wikipedia.org/wiki/Energy_density)
Heavy vehicles use diesel, ships use fuel oil, jets use jet fuel. What industry are you thinking of that would use amounts of gasoline comparable to all light vehicle traffic? I'm honestly curious but doubtful.
The ratio is only referring to sulfur. I'm fairly sure the high octane required for jet fuel would prohibit most sulfur emissions. Additionally, the weight sensitivity would be an added incentive to reduce any unused components, such as sulfur.
> Avgas is a specialized fuel used to power piston engine aircraft
The vast majority of airplanes in operation - be it per passenger numbers or cargo tonnes - aren't piston engined but turboprops, turbofans and turbojets.
It sounds like ars was trying to suggest that the fuel we currently use is very similar to that aircraft use (ie. if you can synthesize oil you kill two birds with one stone)
The cetane number and the flash point is a little different, but to simplify, diesel is Jet-A with additives, mainly for lubrication. You can put jet fuel in a diesel truck and it'll work fine, the military often mixes it in to avoid two separate fuel supplies. The same thing can be done with piston aircraft (100LL vs auto gas)
Also, I can only imagine the use of a biomass mix will increase. Last year the USAF was saying it was roughly 10x the cost, but that's dropping with production scale while oil obviously is only going up.
You seem to be an expert on this topic. I wouldn't expect them to have the exact same characteristics. Kerosene as it is used in aviation today is distilled from crude oil extracted from the ground. This is synthesized gas that is then refined. My question is how much of NOx and particulate emission is from impurities and what the differences are between the synthetic and conventional kerosene.
Is there a way to make a kerosene with less NOx and particulate emission that simply isn't practical today? Since we need to ramp up renewable energy sources to synthesize this fuel can that economy of scale justify some currently impractical process?
The way I read the Wikipedia article on NOx [1] it sounds like NOx comes from nitrogen in the fuel. Is it possible to reduce or eliminate this nitrogen and then emit less NOx? I also parse the Wiki article to suggest the nitrogen is from coal and oil based fuels, which the technology in the article is not.
You can have a look at the calculations if you'd like. There's a deceptively high amount of emissions with jet kerosene, even with the planes loaded up.
Gas turbines (which includes jet engines) can potentially use a lot of different fuel sources. For example, the M1 Abrams tank can run off a variety of different fuels. If it’s liquid and burns, it’ll probably work.
Turbofan engines may need to be redesigned to accommodate a different fuel source, but there isn’t any reason you can’t use automotive gasoline to power a jet. It’s just not a good idea because it vaporizes more readily on the ground, has less power per volume, and freezes in the temperatures jet operate in.
Piston engines aren’t as flexible. They don’t inject fuel in a constant stream, they compress and explode it.
Do you have a reference for lower NOx emissions from propane? My understanding is that most NOx is a product of combustion in air (although it can come from impurities in the fuel).
As for SOx, natural gas can contain H2S which produces these, is it normally significantly less for propane?
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