Inspired by the battery powered aviation thread : https://boards.straightdope.com/t/fuel-economics-of-battery-powered-airplanes/
What do the aviation experts on the board think about ammonia powered jet engines ? And the claims presented here (it seems Rolls Royce has a collaboration with them) :
It also looks like Raytheon is working on it :
https://www.rtx.com/News/2020/12/09/ammonia-could-fuel-the-future-of-sustainable-flight
Wouldn’t biofuels be zero net emissions, and a lot easier?
Maybe we can discuss biofuels in a separate thread ? I was hoping to get some answers on Ammonia.
Well, your title doesn’t indicate that. If you want the discussion to be that narrow, you may consider asking a moderator to tweak the title.
The title says " Zero carbon emissions aircraft with minimum changes to current engines" - It doesn’t say NET Zero carbon emissions aircraft
The links provided in the OP are also NOT for NET Zero carbon emissions aircraft
Mods - please change the title to Zero (not NET) carbon emissions aircraft with minimum changes to current engines
You can’t ask the mods to do something just by adding a post. Mods don’t read every post on the entire board.
Flag your OP post (three dots to show “More” then Flag) and request the title change.
Note that hydrogen can be used as jet fuel and meets your zero-emissions criterion; in fact the Airbus ZEROe project is investigating exactly that. As early as 1988, the Soviet Tu-155 tri-jet was experimentally powered with hydrogen. If you just want to discuss ammonia, you should say so.
https://www.airbus.com/innovation/zero-emission/hydrogen/zeroe.html
Wouldn’t ammonia result in nitrogen byproducts? Diesel cars emit nitrous oxides (NO and NO2) due to the heat and compression of the combustion cycle. I have trouble imagining the turbojet being cleaner. the issue I assume (IANAChemist) is whether the “cracking” process truly separates all the ammonia into hydrogen and nitrogen, or whether some goes through the engine as ammonia?
Nitrous oxides present their own interesting environmental/medical problems, especially if this implies the area around airports will be high concentrations.
However, given the difficulties of storing hydrogen in bulk, this may be a passable compromise. But ammonia evaporates at -33C (-28F) so presumably the tanks would hold the fuel under a decent pressure. Were most jet liners built to hold appreciably pressurized fuel?
Also consider that whether hydrogen or ammonia, having the aircraft sit in a take-off waiting queue for an hour or more in the hot sun with a super-cooled fuel while fully fueled may be more problematic that with ordinary jet fuel. Even venting pressure with ammonia may create a hazardous environment.
(None of this makes it impossible to use - just that any fuel comes with its own problems.)
The energy density of ammonia is about half that of conventional jet fuel, so an ammonia powered plane will have much less range than an equivalent plane powered with aviation fuel. Not a complete deal breaker, but definitely an issue.
Thanks for the directions and done.
Thats what this post is about, Ammonia is just the carrier of hydrogen - because it is easy to liquefy ammonia and it has no carbon. Hydrogen is easily obtained from ammonia through a catalytic process :
Pasting from the link provided in the OP
Doesn’t the process to create NH[sub]3[/sub] rely heavily on natural gas?
Tanks of Ammonia are commonly shipped on roads as fertilizer - in fact many farmers have ammonia tanks on their farm.
Terminals keep ammonia at -28F 15psi, while the transport / farmer tanks are at 265psi at ambient temperature (like propane).
Ammonia is hazardous though, and needs a lot of safe handling.
Yes - you can make it from Hydrogen, which is in turn derived from natural gas.
You can also make it from Hydrogen, which is in turn derived from electrolyzing water. The power for electrolysis comes from wind / solar. There is no hydrocarbons involved
OK, but it’s quite a stretch to suggest that liquid (L) H2 and (L)NH3 imply the same technology. All three of the ZEROe initiatives are solely based on aircraft carrying liquid hydrogen, which has technical challenges but has three times the energy density by mass of Jet A-1, and well over six times the energy density of (L)NH3. The whole infrastructure inside and outside the aircraft is completely different.
A potential showstopper is accident safety and leak safety. A thousand gallons of released ammonia is a seriots hazard. And everyone who works on the fuel system and infrastructure would be dealing with some pretty hazardous stuff.
Agreed. However, it is routine in the United States for farmers to have Ammonia Nurse Tanks.
Ammonia Nurse Tanks are usually 1000 gal or 1500 gal and the regulations are fairly mature around them
Like this https://www.michigan.gov/documents/msp/Fries_350309_7.pdf or Nurse Tank Anatomy | Minnesota Department of Agriculture