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I took the numbers from wikipedia which to my knowledge refer to the raw chemical energy density of the battery without any additional control circuit. The wei

by zaarn 8y ago

I took the numbers from wikipedia which to my knowledge refer to the raw chemical energy density of the battery without any additional control circuit. The weight of a fueltank is not that much. Modern airplanes use the wings for fuel storage, you get the mostly for free. That goes for other storage tanks too, it's largely just reused space. You could replace that with battery space but... >Hopefully someone will one day invent structural batteries where the whole thing is a battery that neither zaps you or boils you to death. A battery that has the same energy density as jet engine fuel will, upon thermal runaway, behave similar to jet fuel being set on fire. That is the cruel reality of fuels. The chemical reactions happening in jet fuel are immensely more exotherm than batteries. Batteries need to put out their chemical energy into electricity without being exotherm (ideally) but that is inherently less efficient. And as mentioned in another comment, batteries have an inherent and unfixable flaw; they do not get lighter when used. A ~2700 Ton battery will weigh 2700 Tons on takeoff and 2700 Tons during landing. 19 Tons of Fuel weigh 19 Tons on takeoff and maybe a couple hundred kilos during landing. Not having to bring all the fuel all the way saves a lot of energy. >the actual energy density would not have to be in the same league as highly explosive hydrocarbons. As mentioned above, if your battery has the same energy density as highly explosive hydrocarbons, it's mostly going to behave like highly explosive hydrocarbons once it goes into runaway. The reason for that is rather simple; there is no battery material (that I'm aware of) that provides high density without also being able to release the same energy via method of rapid unplanned combustion. >I know nothing about engineering and why batteries have to be ultra bulky For an airplane, every kilogram matters immensely. Jet fuel is energy dense and thusly you can safe a lot of fuel. On a modern plane fuel is also saved wherever possible, ie by riding jet streams, by reducing high thrust sitations, etc. Batteries have to be bulky for several reasons; any LiIon battery needs to have the charger hooked up to every battery cell. If you don't do that you run into a potentially detonating battery cell ones it is overcharged (which will happen if you don't balance cells) On top of that, battery chemistry is largely very simple. Take an oxidizer and a reductant (oxidizers don't need to contain oxygen here). The properties must be such that during oxidation they give of electric charge. Ideally the reaction is auto-reversable by applying a current to the battery. This process must run very cool and slow when using up electricity but the reality of the matter is that it doesn't. It'll always run a bit hot. If it gets too hot, it will almost always result in the battery switching from electric to combusting once it reaches the exothermic threshold (ie, the temperature at which the reaction becomes fully self-sustaining). Batteries WANT to be discharged. Every battery on this planet is longing to be discharged instantly in a big hot explosion. There is an energy difference that needs to be released. If your battery has the same energy density as jet fuel, this reaction wants to happen even harder than already and if it goes nuclear it'll behave like jet fuel. Except worse because lithium-fires are hard to extinguish if not impossible unless you can cool it fast enough (which is impossible once it reaches a certain size) --- The sad reality is; Petrol fuels won't be going away. They are energy dense. They are relatively easy to combust with good efficiency. They can be stored relatively easily and safely. Same for transport. Batteries don't offer these advantages because there is an inherent tradeoff. We do have other alternatives. Alternative fuels with similar energy density, like Cryogenic HydroOxy or Methane. The burnoff from these is not as bad depending on what you do.

Theodores 8y ago
Airlines do want to save fuel but the reality is that there are some easy wins that have not been tackled. Before take-off the taxi journey to the runway is under jet power when you could have a more efficient tow truck to take the plane there. Concorde was the worst, B52s excepted, 2 tonnes of fuel just to get from the departure lounge to the runway. Then there is the final approach. The Space Shuttle was somewhat brick shaped but they could glide that down from space to land on a runway. Obviously the safety of fare paying planet trashers coming back from their cheap flight is paramount and the peace of those living under the flight path matters not, however, planes could land space shuttle style, gliding in with no fuel being burnt. After 3000 miles of journey this ten miles of coasting might be rounding error, but what if you could catch the jet stream and, rather than take an hour off the journey time, coast as much as possible? If the external costs of cheap flights had to be paid for then I am sure these options would become as standard as 'stop start' is with today's automobiles. Regarding batteries destined to explode, there are ceramic batteries that do not spontaneously combust, imagine if parts of your car/plane/bicycle used such materials, e.g. if the boot liner or bumpers were made of such a lower density battery but doubled up with functionality? It can't be ruled out as possible.
- zaarn 8y ago
  I checked the ceramic batteries but all I found was replacing electrolyte with ceramic materials. This won't solve all the problems, only some that occur due to physical damage. Since the wikipedia energy density is to my knowledge based on raw chemical performance, there would be no change as ceramics would only allow you to pack existing battery packs more densely. And we're still talking about 2700 tons of battery to carry with the plane. Even if you improved the performance of a battery by an order of magnitude overnight, you'd still perform significantly worse than petrol fuel. Regarding the taxi fuel; that includes other fuel consumption like the APU burning until engine start and 2 tonnes would be the standard usage for larger airports, smaller ones have 1 ton. Also consider that I calculated pure flight performance, if you'd use electric engines to taxi then you'd need an even bigger battery that you can't shed. Taxing by a tow truck is possible but likely too slow (you have to pull an entire airplane). Regarding landing; Spaceshuttles are hardly comparable to normal airplanes. The Spaceshuttle when landing goes a lot faster than most airplanes can safely do at that altitude and requires all brakes and a parachute to slow down on an extra long runway. Airplanes already minimize fuel consumption when there is no engine really needed but for landing a normal airplane you need the engines 999 out of 1000 times.

by zaarn 8y ago

Theodores 8y ago

Airlines do want to save fuel but the reality is that there are some easy wins that have not been tackled. Before take-off the taxi journey to the runway is under jet power when you could have a more efficient tow truck to take the plane there. Concorde was the worst, B52s excepted, 2 tonnes of fuel just to get from the departure lounge to the runway. Then there is the final approach. The Space Shuttle was somewhat brick shaped but they could glide that down from space to land on a runway. Obviously the safety of fare paying planet trashers coming back from their cheap flight is paramount and the peace of those living under the flight path matters not, however, planes could land space shuttle style, gliding in with no fuel being burnt. After 3000 miles of journey this ten miles of coasting might be rounding error, but what if you could catch the jet stream and, rather than take an hour off the journey time, coast as much as possible? If the external costs of cheap flights had to be paid for then I am sure these options would become as standard as 'stop start' is with today's automobiles. Regarding batteries destined to explode, there are ceramic batteries that do not spontaneously combust, imagine if parts of your car/plane/bicycle used such materials, e.g. if the boot liner or bumpers were made of such a lower density battery but doubled up with functionality? It can't be ruled out as possible.

zaarn 8y ago
I checked the ceramic batteries but all I found was replacing electrolyte with ceramic materials. This won't solve all the problems, only some that occur due to physical damage. Since the wikipedia energy density is to my knowledge based on raw chemical performance, there would be no change as ceramics would only allow you to pack existing battery packs more densely. And we're still talking about 2700 tons of battery to carry with the plane. Even if you improved the performance of a battery by an order of magnitude overnight, you'd still perform significantly worse than petrol fuel. Regarding the taxi fuel; that includes other fuel consumption like the APU burning until engine start and 2 tonnes would be the standard usage for larger airports, smaller ones have 1 ton. Also consider that I calculated pure flight performance, if you'd use electric engines to taxi then you'd need an even bigger battery that you can't shed. Taxing by a tow truck is possible but likely too slow (you have to pull an entire airplane). Regarding landing; Spaceshuttles are hardly comparable to normal airplanes. The Spaceshuttle when landing goes a lot faster than most airplanes can safely do at that altitude and requires all brakes and a parachute to slow down on an extra long runway. Airplanes already minimize fuel consumption when there is no engine really needed but for landing a normal airplane you need the engines 999 out of 1000 times.