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Aviation industry tries to go green

phys.org

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Re: Aviation industry tries to go green

#21

Post by nradov »

mtreis86 wrote: post #13
nradov wrote: post #5

There are a number of other initiatives underway to reduce greenhouse gas emissions from commercial aviation. Synthetic kerosene can be manufactured using power and heat from renewable energy sources. Electric motors can be used for taxiing so that the turbines only have to be started immediately before takeoff. The electromagnetic catapults used on the latest Navy aircraft carriers can be scaled up to launch redesig…

Shutting turbine engines down and starting them up is when most of the routine wear happens, it may actually be cheaper and greener to use the fuel.

The number of engine cycles would be the same. The only difference is that the pilots would wait to start the turbines until nearly ready to take off, and then shut down the turbines immediately after landing.

Re: Aviation industry tries to go green

#22

Post by redis_mlc »

mtreis86 wrote: post #13
nradov wrote: post #5

There are a number of other initiatives underway to reduce greenhouse gas emissions from commercial aviation. Synthetic kerosene can be manufactured using power and heat from renewable energy sources. Electric motors can be used for taxiing so that the turbines only have to be started immediately before takeoff. The electromagnetic catapults used on the latest Navy aircraft carriers can be scaled up to launch redesig…

Shutting turbine engines down and starting them up is when most of the routine wear happens, it may actually be cheaper and greener to use the fuel.

That's correct, each start is considered to be an engine cycle, same as doing a trip.

The parts in jet engines almost all have cycle limits, so it's a big deal.

You'll notice that skydive operators reposition their Cessna Caravans using a tug - they never turn on and taxi around without a load.

Re: Aviation industry tries to go green

#24

Post by danaliv »

Ididntdothis wrote: post #14
cgrealy wrote: post #8

The big win would obviously be electric aircraft, but I doubt we'll see that in my lifetime (barring a massive breakthrough in battery technology). The problem is even the best batteries have a much lower energy density compared with traditional fuels. Also, a battery that weighs 100kg when full weighs pretty much 100kg when empty. Real Engineering did a pretty good video on the topic https://www.youtube.com/watch?v=…

I think hydrogen would be a candidate but then you have to deal with cooling.

The problem with hydrogen is that it has a lot of mass-specific energy but its density sucks. Jet-A has something like 35,000 MJ/m^3 while liquid hydrogen is a measly 8500.

Re: Aviation industry tries to go green

#25

Post by newnewpdro »

WalterBright wrote: post #17
newnewpdro wrote: post #15

Earlier quoted context omitted.

I couldn't find mention of anything else aviation-related in the per-tank pages, and the Maybach WWII engines page [0] doesn't speak to it either. Do you have any good references we can check out? [0] https://en.wikipedia.org/wiki/List_of_WWII_Maybach_engines

I have a few hundred books on WW2, it's possible I'm mis-remembering it. I am ashamed :-(

No worries, I was just curious to read about it.

Re: Aviation industry tries to go green

#27

Post by jcampbell1 »

animalnewbie wrote: post #26

Serious question, pardon my ignorance. How much is the per capita fuel consumption compared to a petrol car? Small steps are good too but I sincerely hope we can spend that effort in safety and perhaps speed. Societies progress as distances get shorter.

Airlines get about 40-60 passenger miles per gallon. Not sure if that answers your question.

Re: Aviation industry tries to go green

#28

Post by Ididntdothis »

danaliv wrote: post #24
Ididntdothis wrote: post #14

Earlier quoted context omitted.

I think hydrogen would be a candidate but then you have to deal with cooling.

The problem with hydrogen is that it has a lot of mass-specific energy but its density sucks. Jet-A has something like 35,000 MJ/m^3 while liquid hydrogen is a measly 8500.

Interesting! I didn't think about volume. Is that why the Saturn V first stage also used kerosene?

Re: Aviation industry tries to go green

#29

Post by imsofuture »

WalterBright wrote: post #19
chrisseaton wrote: post #6

Earlier quoted context omitted.

> Electric motors can be used for taxiing so that the turbines only have to be started immediately before takeoff. I thought that this was pointless because the engines needed that time during taxiing to warm up properly anyway? If you moved them to the runway electrically they'd then just need to sit there burning fuel for five minutes to warm up. Naval jet fighters, which launch through steam or electronically and…

I know that for piston engine aircraft, it is critical that the engine be properly warmed up before takeoff. Otherwise, the engine would likely stall shortly after liftoff, leading inevitably to a crash. This is a common cause of accidents. I don't know specifically about jet engines, but as the engine is designed to run while hot, and metal expands when hot, I'd be quite surprised if it wasn't necessary to warm them…

I know that for piston engine aircraft, it is critical that the engine be properly warmed up before takeoff. Otherwise, the engine would likely stall shortly after liftoff, leading inevitably to a crash. This is a common cause of accidents.

This is not true. Engine start to takeoff is usually at least a few minutes, but there is no critical temperature factor for the engine (barring extreme heat or cold).

It's a lot like a car, you don't want to overly stress by flooring it when cold, before oil is circulating comfortable -- but running for 10s of seconds is plenty to get going.

Re: Aviation industry tries to go green

#30

Post by animalnewbie »

jcampbell1 wrote: post #27
animalnewbie wrote: post #26

Serious question, pardon my ignorance. How much is the per capita fuel consumption compared to a petrol car? Small steps are good too but I sincerely hope we can spend that effort in safety and perhaps speed. Societies progress as distances get shorter.

Airlines get about 40-60 passenger miles per gallon. Not sure if that answers your question.

It does exactly. Thank you. This is 4 times that of a singly occupied car. Probably more effort should go towards car pooling. And maybe electric scooters.
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