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Ask HN: If electricity was $1 per barrel could we see an electric jet engine?

5 points by mentos 11y ago

Really curious to know if the economic incentive was there if the engineering could fill the demand for all commercial flights?

sjs382 11y ago
How much electricity is in a barrel?
- apryldelancey 11y ago
  That's exactly what I thought.
  - claysmithr 11y ago
    1.21 gigawatts
- legitster 11y ago
  According to Wolfram Alpha, 6.11 Gigajoules
gusmd 11y ago
Not sure If I understand your question, but my understanding is that we don't yet have the means to store energy in such a dense manner as to able to power a jet engine. Energy density of aircraft fuel is much higher than any battery available.
flubert 11y ago
Here's a starting point for you in your investigations into electrical propelled airplanes: https://www.nasa.gov/centers/armstrong/Features/leaptech.html https://www.nasa.gov/centers/armstrong/Features/leaptech.htm...
petra 11y ago
Not an expert, just the result of a Google search:Fuel has roughly 100x better energy density than lithium-ion batteries(both in weight and in volume), and batteries improve pretty slowly. Before take-off , the weight of fuel is 25-47% of the aircraft's weight. And since the propulsive efficiency of a jet engine is relatively high(rough search gives 45%-80%) an electric engine doesn't buy much here. So this isn't really a question of money, but basic limits.
- flubert 11y ago
  You may also be interested in aluminum-air batteries, which have better than 10 times the specific energy density compared to lithium ion chemistries. The downside is that they aren't rechargable, but that may not matter for flights (they are recyclable though). https://en.wikipedia.org/wiki/Aluminium%E2%80%93air_battery https://en.wikipedia.org/wiki/Aluminium%E2%80%93air_battery
ksherlock 11y ago
With a piston-prop or turbo-prop airplane, the engine rotates the propeller so it's easy enough to use an electric engine for that. Jet engine thrust comes from the exhaust gas. How do you replace that with electricity? compressing air (pulse jets)? generate plasma?
- chris_va 11y ago
  Not entirely. Modern jet turbines have ~12:1 bypass ratios, meaning the exhaust is mostly just turning a fan, pushing 11 times the amount of air as goes into combustion.
staunch 11y ago
> "Given that practical lithium-ion batteries were capable of achieving energy-densities of 113Wh/kg in 1994, 202Wh/kg in 2004, and are now capable of approximately 300Wh/kg, it’s reasonable to assume that they will hit 400Wh/kg in the coming decade." -Elon Musk http://www.aviation.com/general-aviation/elon-musk-toying-designs-electric-jet/ http://www.aviation.com/general-aviation/elon-musk-toying-de...
deleted 11y ago
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5 points by mentos 11y ago

Really curious to know if the economic incentive was there if the engineering could fill the demand for all commercial flights?

sjs382 11y ago

How much electricity is in a barrel?

apryldelancey 11y ago
That's exactly what I thought.
- claysmithr 11y ago
  1.21 gigawatts
legitster 11y ago
According to Wolfram Alpha, 6.11 Gigajoules

gusmd 11y ago

Not sure If I understand your question, but my understanding is that we don't yet have the means to store energy in such a dense manner as to able to power a jet engine. Energy density of aircraft fuel is much higher than any battery available.

flubert 11y ago

Here's a starting point for you in your investigations into electrical propelled airplanes: https://www.nasa.gov/centers/armstrong/Features/leaptech.html https://www.nasa.gov/centers/armstrong/Features/leaptech.htm...

petra 11y ago

Not an expert, just the result of a Google search:Fuel has roughly 100x better energy density than lithium-ion batteries(both in weight and in volume), and batteries improve pretty slowly. Before take-off , the weight of fuel is 25-47% of the aircraft's weight. And since the propulsive efficiency of a jet engine is relatively high(rough search gives 45%-80%) an electric engine doesn't buy much here. So this isn't really a question of money, but basic limits.

flubert 11y ago
You may also be interested in aluminum-air batteries, which have better than 10 times the specific energy density compared to lithium ion chemistries. The downside is that they aren't rechargable, but that may not matter for flights (they are recyclable though). https://en.wikipedia.org/wiki/Aluminium%E2%80%93air_battery https://en.wikipedia.org/wiki/Aluminium%E2%80%93air_battery

ksherlock 11y ago

With a piston-prop or turbo-prop airplane, the engine rotates the propeller so it's easy enough to use an electric engine for that. Jet engine thrust comes from the exhaust gas. How do you replace that with electricity? compressing air (pulse jets)? generate plasma?

chris_va 11y ago
Not entirely. Modern jet turbines have ~12:1 bypass ratios, meaning the exhaust is mostly just turning a fan, pushing 11 times the amount of air as goes into combustion.

staunch 11y ago

> "Given that practical lithium-ion batteries were capable of achieving energy-densities of 113Wh/kg in 1994, 202Wh/kg in 2004, and are now capable of approximately 300Wh/kg, it’s reasonable to assume that they will hit 400Wh/kg in the coming decade." -Elon Musk http://www.aviation.com/general-aviation/elon-musk-toying-designs-electric-jet/ http://www.aviation.com/general-aviation/elon-musk-toying-de...

deleted 11y ago

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