skitown
Member
Except, of course, Bosch's version probably uses pure diesel NOx.
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Space X Option Package
- Thread starter McManX
- Start date
dhanson865
Well-Known Member
Space X has been working on new rocket engines that use methane instead of the standard kerosene-based rocket fuel, so I suppose that technology could find it's way to cars, but it would really go against their zero emission goals. I'm more inclined to think they would use water heated by electricity.... assuming this is not all in jest. It would essentially be a vape car.
Elon specifically says compressed air and he is serious.
the question "Actually, so this doesn't imply any carbonhydrates being used for propulsion on a roadster right? Because, imo that would be a disappointment on any Tesla." Gets this response from Elon
then the question "what about the noise?" gets the answer
The reply "No, he is using them for energy storage, he is using them for a supercar to assist with brakes, turns, and speed, they are cold air thrusters." gets Elon to say
The response "Wait. You were serious?" gets Elon to say
Man that is wild! Okay, I stand corrected. There really is going to be such an option on the new Roadster.
Writing the software to control such a system in a road car is going to be challenging.
Writing the software to control such a system in a road car is going to be challenging.
The question that needs to be answered is the price for the SpaceX option, and whether or not it is included in the Founders model.
Uncle Paul
Well-Known Member
I was thinking he was going to install not a flame thrower nozzles. Again, not for us in Urban areas : )
Seems I was wrong about the combustive fuel, but before that, right about the cold gas thrusters. What he meant about going "a lot further" remains to be seen, but all the tweets since then suggests they're not going a lot further.
I've been thinking about it, and I think they'll go with a higher volume lower pressure tank than what I've been thinking. This simplisfies refilling the tank. If they go for a 200 liter 200 bar tank, tank capacity will be:
PV / RT = (20 MPa x 0.2 m^3) / (8.3144598 x 293K) = 1642 mol
1642 x 28.97 grams/mol = 47.57 kg
And stored energy will be:
20 MPa x 0.2 m^3 x ln (0.1 MPa / 20 MPa) + (20 MPa - 0.1 MPa) x 0.2 m^3 = -17,2 MJ = - 4.8 kWh
If they store 47.57 kg of air, each thruster is 2000N and Isp is 60s, that means they can fire a single thruster for 14 seconds without running the pump. If each thruster is 1000N and Isp is 60, they can fire a single thruster for 28 seconds. I think 1000-2000N per thruster is about what they need to make a meaningful difference.
With 4.8 kWh of energy stored in the tank, and assuming a 70% efficiency for the compressor, it would take 1 hour to refill the tank with a 7 kW compressor. With a 50 kW compressor, it would take 8 minutes. With a 100 kW compressor, 4 minutes. Or put differently, if you have a 2000N burst for 1 second, it will take 35 seconds to refill the tank, with a 50 kW compressor. 18 seconds with a 100 kW compressor.
My guess is that 100 kW power levels are what's needed to be able to run the car indefinitely, without depleting the tank. And even then you need to be careful with how much you're using it.
I've been thinking about it, and I think they'll go with a higher volume lower pressure tank than what I've been thinking. This simplisfies refilling the tank. If they go for a 200 liter 200 bar tank, tank capacity will be:
PV / RT = (20 MPa x 0.2 m^3) / (8.3144598 x 293K) = 1642 mol
1642 x 28.97 grams/mol = 47.57 kg
And stored energy will be:
20 MPa x 0.2 m^3 x ln (0.1 MPa / 20 MPa) + (20 MPa - 0.1 MPa) x 0.2 m^3 = -17,2 MJ = - 4.8 kWh
If they store 47.57 kg of air, each thruster is 2000N and Isp is 60s, that means they can fire a single thruster for 14 seconds without running the pump. If each thruster is 1000N and Isp is 60, they can fire a single thruster for 28 seconds. I think 1000-2000N per thruster is about what they need to make a meaningful difference.
With 4.8 kWh of energy stored in the tank, and assuming a 70% efficiency for the compressor, it would take 1 hour to refill the tank with a 7 kW compressor. With a 50 kW compressor, it would take 8 minutes. With a 100 kW compressor, 4 minutes. Or put differently, if you have a 2000N burst for 1 second, it will take 35 seconds to refill the tank, with a 50 kW compressor. 18 seconds with a 100 kW compressor.
My guess is that 100 kW power levels are what's needed to be able to run the car indefinitely, without depleting the tank. And even then you need to be careful with how much you're using it.
Kant.Ing
Member
So you got a few key things
- air intake where you got to mind drag and downforce
- compressing air efficiently and doing thermal management
- size of the pump and tank
- having flexibility in how the air is released, direction and flow
- impact of air jets on the air going over the car
Air intake, we'll have to see how they balance drag and downforce and if they aim to create substantial downforce even at low speeds
How efficient they compress it and how they do thermal management remains to be seen.
A big tank is heavy and requires substantial mechanical volume but they could keep the jets on for longer and how fast the pressure drops is a major factor. A big pump makes sense too.
Ability to direct air anywhere and at variable flow would be nice but doing the math in real time on how that impacts the air going over the car might be less than practical.
Found a source claiming the Space X COPV can do 350 bar, anyone has any idea about volume for the thing?
@ Yggdrasill
Was thinking that Pa is newton per m3 so why not look at area. at 350 bar a 1cm2 (0.0001m2) nozzle would result in 3500N so that would be a simple max force. If they got 10 of those, that''s 35000N so the equivalent of 3571.4kg and that's before any increase in downforce at air intake and impact of the jets on aero.
There are some other factors to consider and some efficiency losses ofc. How fast that force drops depends on tank size.
If they can adjust the flow at the nozzle and they do want to do that, they can apply less force for just enough. Ofc the 1cm2 nozzle area is arbitrary, it could be a few times larger for more flexibility. Likely the limitation is structural integrity and no idea how they deal with that.
- air intake where you got to mind drag and downforce
- compressing air efficiently and doing thermal management
- size of the pump and tank
- having flexibility in how the air is released, direction and flow
- impact of air jets on the air going over the car
Air intake, we'll have to see how they balance drag and downforce and if they aim to create substantial downforce even at low speeds
How efficient they compress it and how they do thermal management remains to be seen.
A big tank is heavy and requires substantial mechanical volume but they could keep the jets on for longer and how fast the pressure drops is a major factor. A big pump makes sense too.
Ability to direct air anywhere and at variable flow would be nice but doing the math in real time on how that impacts the air going over the car might be less than practical.
Found a source claiming the Space X COPV can do 350 bar, anyone has any idea about volume for the thing?
@ Yggdrasill
Was thinking that Pa is newton per m3 so why not look at area. at 350 bar a 1cm2 (0.0001m2) nozzle would result in 3500N so that would be a simple max force. If they got 10 of those, that''s 35000N so the equivalent of 3571.4kg and that's before any increase in downforce at air intake and impact of the jets on aero.
There are some other factors to consider and some efficiency losses ofc. How fast that force drops depends on tank size.
If they can adjust the flow at the nozzle and they do want to do that, they can apply less force for just enough. Ofc the 1cm2 nozzle area is arbitrary, it could be a few times larger for more flexibility. Likely the limitation is structural integrity and no idea how they deal with that.
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I can see this... A model 3 motor attached to a high pressure pump. That would give you an (up to) 190 kW compressor, no? Also Elon mentioned a while ago that their COPV tanks run at 380 bar (which then survived re-entry!). Maybe more like 70Kg of compressed air, give-or-take at that pressure?
I think people underestimate the effect this could have on performance. Plus I am sure, just for fun, he will allow it to "fly" for a few seconds a few feet off the ground just simply for fun.. This is, after-all, the guy that made the S and X "dance" and just sold 20,000 flamethrowers. Cant wait to see the unveil of the upgrade package!
One question I have.... is at what stage are they at? For him to go public I am willing to bet there is a thrown together prototype that works and proves the theory. But its really ugly right now (nozzles and pipes everywhere) so they wont show it until they work it into the frame and Franz works his magic. Just my theory.
Well, it’s a tweet from Elon. So my answer would be...sort of.But is it a verified fact?
I added Elon’s tweets about the “SpaceX option package” to the pinned post in this forum.
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If the Roadster has 47.57 kg of air and it fires off ten 3500N thrusters, the tanks will be empty in about 0.8 seconds, though. Assuming an Isp of 60, that is.
I think they will more likely go for smaller thrusters, and simply fire them for a longer duration, than go for a bigger thruster. I expect the thrusters will be positioned roughly like this:
So if you want acceleration, you fire 6-9, if you want deceleration, you fire 2 and 3. If you're making a turn to the left and get understeer, you fire 4 and/or 10, and if you get oversteer you fire 1 and/or 5. To drift while making a turn to the left, you could fire 10 and/or 1. You basically have lots of options, but you never fire all the thrusters at the same time.
(Oh, btw, I'm not Franz, if you couldn't tell.
)
Rashomon
Member
Except, of course, Bosch's version probably uses pure diesel NOx.
Bosch’s version uses compressed helium/argon from 4 cold gas generators in production for some airbag application. As explained at the demo event in Germany, this was just a proof-of-concept mule, and a dedicated compressed gas source would be used if this saw production. Also, Bosch passed out earplugs though those of us witnessing the demo were about 40 meters away. I wonder how Tesla is going to deal with the noise issue; 1000N thrusters are not going to be quiet...
I'm not so sure it's just a matter of attaching a big motor to a fan. I think you need several fans, depending on how high in pressure you're going. I know you at least need several fans to get a high vacuum. Each fan has a range of pressure where it does it's job well, and outside that area it's pretty useless.
The compressor is essential. Most 100 kW units I can find online look like they would be quite hard to fit into a car. But at least, reliability can be prioritized quite low. And you could probably also reduce cooling hardware. The compressor would likely only run for a few hours over the life of the car.
If the compressor issue is easily solved, it can make sense to go for higher pressure. While if the compressor is difficult to solve, it's probably best to go for lower pressure and higher volume. I have no idea what SpaceX will be able to do on this area.
@ Yggdrasill
As you point out, the nozzles can't all point fully up or backwards so the max force you get is never 10x max nozzle so they likely want as much per nozzle as possible the limitation being the integrity of the hardware. All can be fired at same time for max downforce/lift.
This is a bit difficult for me as I haven't really done any fluid dynamics since high school and that was a while ago.
I am thinking the air they capture, is gonna be drag, hopefully I am not wrong.
So drag is 1/2 x air density x v^2 x Cd x area
That's energy they spend on going forward and energy they need to capture in the COPV, as much as possible.
If they want to suck air faster, that's extra energy so maybe it is only worth it if they do it to lower pressure under the car to increase downforce.
So they spend energy, they harvest it back and the pump spends.....got 0 idea. Anyway, point being that maybe the pump is not that huge.
The size of the tank, likely the info is out there if they use the same as SpaceX. Musk did mention ultra high pressure tank so i'll assume 350-380 bar as that's what i've seen mentioned.
important edit - the formula is for force, energy is Drag x v
As you point out, the nozzles can't all point fully up or backwards so the max force you get is never 10x max nozzle so they likely want as much per nozzle as possible the limitation being the integrity of the hardware. All can be fired at same time for max downforce/lift.
This is a bit difficult for me as I haven't really done any fluid dynamics since high school and that was a while ago.
I am thinking the air they capture, is gonna be drag, hopefully I am not wrong.
So drag is 1/2 x air density x v^2 x Cd x area
That's energy they spend on going forward and energy they need to capture in the COPV, as much as possible.
If they want to suck air faster, that's extra energy so maybe it is only worth it if they do it to lower pressure under the car to increase downforce.
So they spend energy, they harvest it back and the pump spends.....got 0 idea. Anyway, point being that maybe the pump is not that huge.
The size of the tank, likely the info is out there if they use the same as SpaceX. Musk did mention ultra high pressure tank so i'll assume 350-380 bar as that's what i've seen mentioned.
important edit - the formula is for force, energy is Drag x v
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dhanson865
Well-Known Member
I'm thinking there will be track mode just like there is a launch mode. Thrusters would be emergency use only if not in track mode.
If you enable track mode in downtown expect to get a ticket for noise pollution.
If you enable track mode after 10pm in your neighborhood expect people to figure out where you live and cops to come to your house to issue the citations.
Found an article form 2016 that notes
"Falcon’s COPVs measure around 60 centimeters in diameter, stand 1.5 meters tall and a pressurized to over 350 bar."
http://spaceflight101.com/falcon-9-...-testing-in-falcon-9-explosion-investigation/
A perfect cylinder's volume at those dimensions would be 0.42m3 so let's say 0.35-0.4m3 of air if they use same or similar tank.
For max pressure i've seen 350 and 380 bar mentioned but they could decide to go anywhere bellow that.
This implies they can store up to around 180kg of air, remains to be seen if they go much lower than that.
"Falcon’s COPVs measure around 60 centimeters in diameter, stand 1.5 meters tall and a pressurized to over 350 bar."
http://spaceflight101.com/falcon-9-...-testing-in-falcon-9-explosion-investigation/
A perfect cylinder's volume at those dimensions would be 0.42m3 so let's say 0.35-0.4m3 of air if they use same or similar tank.
For max pressure i've seen 350 and 380 bar mentioned but they could decide to go anywhere bellow that.
This implies they can store up to around 180kg of air, remains to be seen if they go much lower than that.
Olle
Active Member
you may have forgotten ambient air viscosity in your calculations. It occurs we don't need to depend on specific impulse only for a thruster designed for mostly sea level operation. With the right geometry thrusters, you should be able to get the same order of magnitude energy back as you inserted in COPV .If the Roadster has 47.57 kg of air and it fires off ten 3500N thrusters, the tanks will be empty in about 0.8 seconds, though. Assuming an Isp of 60, that is.
I think they will more likely go for smaller thrusters, and simply fire them for a longer duration, than go for a bigger thruster. I expect the thrusters will be positioned roughly like this:
So if you want acceleration, you fire 6-9, if you want deceleration, you fire 2 and 3. If you're making a turn to the left and get understeer, you fire 4 and/or 10, and if you get oversteer you fire 1 and/or 5. To drift while making a turn to the left, you could fire 10 and/or 1. You basically have lots of options, but you never fire all the thrusters at the same time.
(Oh, btw, I'm not Franz, if you couldn't tell.
I'm going out on a limb here; but perhaps you could add little compressors and bypass fans to the thrusters to increase their "grip" of the air, the way a jet has bypass fans to multiply its thrust. Although I don't know if there would be too much inertia to spool up fast enough.
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