Students break acceleration world record...for electric vehicles.
This isn't close to the record for dragsters; if they can increase the energy density per unit mass there are traction and downforce improvements that can be used to improve this. It's very hard to beat chemical energy like detonating gasoline or nitromethane - you're looking at roughly a factor of 100, with ~40 MJ/kg for gasoline and 0.4 MJ/kg for a lithium ion battery - especially if you're racing through a 15 PSI gas that you can use in your chemical reaction without having to accelerate it onboard.
I suspect that traction control for an electric motor may someday allow electric vehicles to exceed the records held by internal (well, mostly internal) combustion engines. You could keep the tire at exactly the right amount of slip for maximum acceleration, rather than trying to balance centrifugal clutches to get just the right amount of power at the right time.
I wonder what the record is for a vehicle that can pick up electric energy from a tether/rail/overhead wire...though cables that can carry megawatts of energy are probably pretty heavy.
Edit: I think the most interesting category here is the typical friction-propelled, human-carrying vehicle of either chemical or electric power sources. Railguns, rockets, fan cars (using active downforce), and vehicles which engage the ground by rack and pinion are qualitatively different. When the question is accelerating your own mass forwards using the friction developed by your own mass being pulled down by gravity, there's an interesting optimization problem trading off weight and power.
«~40 MJ/kg for gasoline and 0.4 MJ/kg for a lithium ion battery»
That is correct. Out of curiosity, I looked it up and for the Tesla Plaid that's 0.65 MJ/kg (or 181.5 watt·hours per kilogram)
But my follow-up question is: if gasoline has an energy density about 100 times higher (well, 60 times) why are dragsters not even faster? This Stuttgart EV does 0-100 km/h in 1.461 seconds (1.87g), and dragsters do it in 0.8 seconds (3.42g). It sounds like with such a phenomenal energy density, gasoline-powered dragsters should be able to accelerate at much more than 3.42g, maybe 10g, or more. Intuitively this indicates that the bottleneck isn't energy density, but mechanical factors (gears, traction, etc). Therefore if battery energy density can increase just a little more, maybe to 2 or 3 MJ/kg, this may be sufficient for EV to be able to beat dragsters.
Edit: actually just thinking about it for a few minutes, I realize that energy density doesn't matter. An EV like the Tesla Plaid uses less than 1% of its entire battery capacity to do one acceleration from 0-100 km/h. So the battery could be reduced to 1% of its size and it would still perform one acceleration at the same speed. So dreamcompiler is right. It's not energy density, but power output that matters.
Edit #2: The Plaid has a power output of 352 watt/kg (761 kW / curb weight of 2162 kg), while the Stuttgart EV has an output of 1241 watt/kg (180 kW / curb weight of 145 kg), so about 3.5 times more.
Compared to electric motors, internal combustion engines provide relatively little torque, over a relatively narrow range of RPM. An typical electric motor can apply its maximum torque, constantly, from zero RPM to its normal RPM.
A gas engine just cannot do that. At low RPM it has little torque and power. At high RPM, you can't really transfer that full power with a transmission in the lowest gear, because now it's too much torque. (Stripped gears and/or snapped belts were pretty common before computer-controlled automatic transmissions.)
Battery capacity does matter, a bit indirectly; you're limited in how much current the pack can supply or recharge with. All batteries have recommended charge/discharge rates based on C, the capacity in Amp-hours. A lot of NiMH batteries are around C/3 or C/4, for example.
Much progress has been made in raising Li-Ion "C" rates, which is why we now have cell phones that can charge at 20W or more. Graphene batteries are starting to get common in RC battery packs and appear to be the next significant jump.
TLDR: no you can't just put a really small pack in big enough to do one run, unless it's a specially designed pack with a very high discharge rate...in which case it might have worse energy density, and you might be back where you started (but with less total energy storage.)
Also, minor point of order: dragsters don't use gasoline, they use nitromethane. And the limitations are material science; you need an engine with internals, and a frame, and wheels, and tires, that can all withstand enough force without being destroyed...in a sport where every bit of weight slows you down.
There's a limit to how much you can shrink the battery. Max current goes down proportionately as well. You could certainly stress the cells beyond their operational envelope a bit to set a record, but even then there's going to be a hard ceiling, and it's presumably an I^2 situation rather than linear. The optimal battery size for a single acceleration is probably smaller than 100% of the production battery, but it's probably not much smaller.
> you're looking at roughly a factor of 100, with ~40 MJ/kg for gasoline and 0.4 MJ/kg for a lithium ion battery
If you only care about acceleration, energy density doesn't matter very much. What matters is power: The rate at which you can move energy from the storage medium to the wheels. In that respect a capacitor-powered dragster could probably smoke a top fuel dragster, even though the energy density of capacitors is pretty lousy. No idea if anybody has tried to build a full-size capacitor-powered dragster. Or if any human would be brave enough to drive one.
Having investigated some of these questions with respect to quadcopters and micro-mouse 'bots, the power density (both in mass and volume) of capacitors is pretty terrible. Whether you're talking about aluminum electrolytic traditional capacitors or double-layer supercapacitors, they're inferior in most cases to a lipo. That's especially true if you're open to high-discharge 50C or 75C lipos, which can dump their entire energy capacity in ~60 seconds.
If you only need a few milliseconds of 'zap', yeah, a capacitor bank is great. It's the only option if you need to do that more than a couple hundred times in the life of the battery; a chemical battery will wear out but a capacitor can last for millions or billions of charge/discharge cycles.
But even a time as short as 1.461 seconds is probably on the far side of the inflection point where capacitors make sense.
Also remember that an ultracapacitor is about as far in behavior from a physicist's ideal plate capacitor as you can get - they're not linear, they have highly significant internal series resistance...
> Or if any human would be brave enough to drive one.
From the perspective of being that close to being fried, or with respect to the acceleration?
To be honest though, I still think it’s amazing that people casually handle extremely flammable and volatile hydrocarbons whenever they visit the gas station. The safety ecosystem is very well tuned, albeit after a hundred+ years of accidents and research.
Well, dragsters are laughably slow to accelerate if we're just talking about "acceleration world record" without qualifiers. (Assuming that "acceleration" here means "acceleration of a ground vehicle with a human driver" is just as arbitrary as "…of an electric ground vehicle…", after all. Actual acceleration world records of macroscopic objects are in the 10,000s of gs…)
>cables that can carry megawatts of energy are probably pretty heavy
Required cable thickness (and thus weight) is proportional to current, not voltage. Conductors to carry megawatts of electricity could be fairly light as long as the voltage is extremely high and the amperage relatively low.
And magnetic force is a function of current, and magnetic force is what drives wheels. Technically you are correct, but thick cables are actually needed to do lots of translation from electricity to movement.
Let's say you can control voltage, cross section area A.
Now, you want a constant power across a load P = V * I.
Your net resistance R is C + D * L / A where C and D are constants and L is your cable length.
I is proportional go V * A / (C * A + E) where E is also a constant.
So your load power is proportional V^2* C * A / (C * A + E) which is proportional to V^2 * A / (A + F) where F is also a constant.
With a large "enough" A, this is effectively V^2. With a small A, this is V^2 * g where g is A / F. So the smaller the area you have the more power you are wasting (roughly equal to V^2 * (1-g) which is heat in the wires).
So the smaller area you have, the less efficient your power delivery. And juicing up your source power is a lot more expensive than juicing up your source voltage.
I think probably the fastest accelerating ever car with a driver was the Vanishing Point drag racer which did 0-60 in about 0.25 secs using a peroxide rocket. Not very practical for everyday transport though https://youtu.be/7QC6tymIvKA?t=209
The differences are massive between road-going (on an asphalt surface, ~1 friction coefficient), drag racing type (on a drag strip, which has massively more grip, ~4) and rocket driven (no friction at all, just the thrust/mass ratio) vehicles. It should be clear they are in totally different classes and advances in any of those classes are exciting and worth mentioning, I feel.
Elon Musk at some point tweeted about the idea of an "air rocket" for the cars. But air is too light to give a lot of momentum. What would really work well for acceleration is a water rocket with an electric pump. Water mist is harmless beyond a short distance, as long as it's properly dispersed.
To make a 1000 kg car accelerate at 4 gee or 40 m/s^2, you need 40000 N of force. A water rocket engine with 200 m/s exhaust velocity can deliver that with 200 kg/s of mass flow. Since your target velocity is only 28 m/s, you only need reaction mass for 0.7 seconds, or 140 kg or 140 L of water. That's one feed barrel.
The back of the envelope kinetic energy of the water jet is only 3 million joules or less than a kilowatt hour. But the power is 4 megawatts. Pumps also have startup acceleration cavitation issues, so it'd need to start gradually etc.
One could maybe do it with a lot of small independent systems in parallel: a ultra high C rate lithium iron battery connected via a transistor to a pump. Each has its own water pouch and nozzle. If you can achieve 400 N of thrust with one pumping 2 kg/s, then having 100 of them in a 10x10 grid would work. The transistors would be controlled centrally.
A more boring alternative is, like in a real bottle rocket, also here, a compressed air tank half filled with water, a much more straightforward source of pressure energy.
As a visceral experience, there are few things that top a Top Fuel drag race. They're really something worth experiencing at least once personally. You really just have to be there.
There are some things that audio recordings simply cannot capture. Top Fuel is one of them. When I go, I wear ear muffs that are made for target shooting.
The pulses are so loud it is like being punched in the chest. Sometimes the engines explode which is also fun as the smoking parts fly around.
Once, the Top Fuel driver had the silly thing in reverse. The christmas tree turned green, and he launched backwards. He had lightning reflexes, chopping the power incredibly fast. The thing still flew back nearly 100 feet, and if it had continued would have climbed up the grandstand behind it.
I never, ever, ever stand in front or in back of a dragster when its engine is running. I also do not stand radially to the engine (when they blow, the parts fly out radially).
Other than that, it is great fun to go to a race in person. It's the only motor sport left where the attendees can go into the pits and watch the mechanics at work. Watching a team rebuild a V8 engine in minutes is amazing. Then they'll fire it up to test it. Blipping the throttle produces shock waves that you can see hitting the bystanders.
The barely restrained violence of those machines is just crazy mad fun you'll never get from watching it on TV.
I've been to Santa Pod in the UK a few times and the Top Fuel cars are in a league of their own, you really do know when they are running. Others have mentioned about the noise which is something very hard to describe in words.
You can walk around the pits and watch the crews doing a partial strip down of the engine for each run, although it's fundamentally basic V8 pushrod technology, it's far more than that.
There is a video [1] with a few slow motion clips of the preparation and running of a Top Fuel car. One poster mentioned a cameraman who stood between two cars, you can clearly see why that wasn't a good idea!!
Looking at how the tyres deform, not just at launch 2:00 but also at 2:50 it looks like they are a real limitation in acceleration. To help them off the line the launch area is really sticky, shoes melt into the 'tarmac'.
The 0-60 time, as with many really fast cars, doesn't tell the whole story of using their 10,000BHP to get to about 330MPH in about 4.5 seconds.
It's something I think you really need to go and see.
I went for the first time couple of weeks ago. Standing right by the starting line, when the top fuel funny cars take off, they get engulfed in a bubble of blurriness, caused by the burning nitro, coupled with the tremendous rumbling which causes your eyes to shake, it’s impossible to get a clear view of the cars on takeoff. It’s insane.
yeah the real "all I hear is ringing" experience can't be beaten.
I've been to two Top Fuel drag races and I left feeling like I was surrounded by people who have just enough sophistication to know that they like to play with fire whenever possible.
they are not like that, of course, but they were definitely caught up in the visceral feeling of watching a race and I was caught up in the idea that I'd never be able to hear again.
Yep, it very quickly becomes a question of what exactly you're trying to test. If you take energy and power density out of the equation by allowing unrestricted access to external fixed energy delivery infrastructure, the only thing left to test is traction management (assuming you're not allowing things like adhesive tires, cog rails, active downforce, etc.). If you do start to allow those post-traction things, you are as the stage where you might as well build a railgun.
1. You need a _lot_ of insulation at 50kV
2. I'm no expert but I very much doubt you could run a motor at anything approaching that voltage. Current electric cars, for example, run c400V as the main motor supply. So there would need to be voltage conversion, which adds weight and bulk.
> Students break acceleration world record...for electric vehicles.
...that made the effort to submit to Guinness. In racing, established racing orgs are where racing records matter. 0-60 just isn't relevant in drag racing. Any optimum 1/4 mile run under 7s doesn't spend nearly as long as these students did dawdling along under 60 mph. NEDRA record 1/4 mile runs have been under 7 seconds for at least 10 years.
The current fastest run ticked off 0-60 mph in under a second. The 60 foot time was over a second. That means they ticked off 0-60 mph in significantly less than 60 feet (~18m). Submitting that 0-60 time to Guinness would require lots of work and time, and wouldn't be relevant to competing or their sponsors.
So, this Guinness record is still easy pickings, as these things go. I'd bet nothing more than moving this run to proper sticky drag strip pavement instead of that grotty old runway would scrub off a tenth or two. Then better drag tires, drag optimized suspension, maybe all wheel drive, gearing optimization, weight reduction, weight placement optimization... and sooner or later Guinness is going to stop taking 0-60 mph submissions for safety reasons.
This said my understanding is thermal efficiency in a typical engine is around 20%, and in an electric motor it’s in the 90% range. Holding traction aside I would have assumed the power is considerably more important than energy density, and energy density plays a bigger role in distance, no?
After 500 hours of Kerbal space program I’m a bit of an expert in these things.
Well there are two kinds of energy density measures, energy-unit/volume-unit and energy-unit/weight-unit. For distance, it can be (usually is?) the energy/volume that is the limiting factor, but for acceleration, it is the energy/weight as weight is the other balancing factor, besides power, of your acceleration equation.
Is it really the motor that is the limiting factor at this point? I would guess it is far more about getting the force onto the road. So tires, spoilers, etc.
> especially if you're racing through a 15 PSI gas that you can use in your chemical reaction without having to accelerate it onboard.
Are there any wild designs that actually use the air in an electric powered design? Cooling is obvious, but could I just convert the electric energy to heat (100% efficient) and run the air through a heated mesh, ramjet style? :-)
To answer my own question: this is basically the concept behind nuclear ramjets (e.g. https://en.wikipedia.org/wiki/Project_Pluto). "Going nuclear" solves the energy density problem here ... the same thing with LiIon batteries would just not work (equally well).
It doesn't matter that fossil fuels are energy denser, it's much harder and less efficient to convert fossil fuel into mechanical rotation by setting it alight than it is to turn electrical power into mechanical rotation.
Electric will always win out simply because it's battery->motor. That's it. Apparently the top fuel dragster can do 0-60 in 0.8 seconds and it looks like its biggest advantage is all the downforce it gets from exhaust gasses and airfoil. I'm thinking this is more a difference in the formats of the vehicles; no point making an electric dragster or f1 when the battery won't last the whole race/series.
Batteries are heavy af though, you're right in the disadvantage there. Perhaps the inefficiency of exploding fuel doesn't matter in the face of just how freaking heavy batteries end up being.
Not sure this applies here Top Fuel engines are nearly burning a liquid rather than a gas. And yes I know you can't really compress a liquid. The typical ratio is 1.7 pounds of air to burn 1 pound of Nitromethane. It burns slower than gasoline tho. And normal gas engine runs in the vicinity of 14.5:1 air to fuel.
I just saw a breakdown of a crash where the engine shut down, allowing the clutch to stop slipping. That final clamp dumped a huge impulse into the drivetrain and ripped the tires off the wheels. (At least that's the way I understood it).
The clutch slips for about 2/3 of the 1/4 mile. It is a huge factor.
My college motorsports team got to meet with John Force, and someone suggested a flexible rear spoiler for variable downforce. He was quick to note it likely would be faster but would almost certainly get you killed.
its my understanding that the clutch designers are the highest paid crew members. Choosing how the clutch performs is the critical piece to winning, based on track temperatures, weather conditions, engine performance, etc.
> I wonder what the record is for a vehicle that can pick up electric energy from a tether/rail/overhead wire...though cables that can carry megawatts of energy are probably pretty heavy.
I am not sure the end result would be faster, though. You’ll need grip to get up to speed, and starting from a standstill, you won’t get that from aerodynamics. you’ll need mass. Take away the batteries, and you may have to add a similar mass in dead weight (could be used to add a good Faraday cage to protect the driver from mishaps with the electricity supply)
I think what you care about is to have enough power to be at the limit of the grip of (all) your tires. If you are heavier, you need more power to reach at point. If you do have enough power, then it's all about maximizing grip - tires, surface, downforce and so on.
More mass and more power are roughly equivalent to less mass and less power, if the above holds. Maybe even with less mass it's easier, since you can produce significant downforce with smaller wings.
Think like a purpose built dragster. You only need enough energy for 1.5 seconds and that’s as long as the wiring needs to take the current for. I think a purpose built electric dragster might be lighter just because of the parts you don’t need. The motors may reverse the energy weight savings
Great Scott! That’s surprisingly small. In all seriousness though, that’s probably not at useable voltage, you might end up with a 5 ton transformer on the car if you delivered 33kV in such a small cable.
To get anywhere near the the down force required to avoid spinning the tires you need a vertical acceleration vector from something like the propulsion thrusters used in dragsters.
To clarify for anyone unfamiliar - this isn't a manhole cover in the traditional sense. It was a 2000 pound hunk of solid steel. It makes this story much more plausible because a regular manhole cover would blow into a million pieces
I've been a huge fan of drag racing, and the engineering behind it. I've seen the influx of electric cars making their way into the scene but they never seem to be competitive, and that comes down to their top end.
The extreme end of combustion engines, you really got top fuel dragsters. Not much faster land vehicles than those. The flaw with those, they got about 2 uses tops before it needs to be completely gutted and rebuilt, not great as a weekend track car. As well, it's somewhere around $1000/second to drive it.
You can sit more in the middle with people getting 1000hp daily drivers. With dynamic tuning, flex fuel, etc you can get the best of both worlds. As well, DCT AWD transmissions make grip/shifting issues a thing of the past.
However, these middle ground drag cars can still get eaten by a $130k bone stock tesla*. The extra weight, infinite torque, and zero shifting is a real advantage, even if their top end isn't as strong as their ICE counterpart.
I've always dreamed of building a hybrid car with tiny tiny battery packs. Maybe enough charge for 4-5 passes. Enough for a day at the track. But have a fully built high revving ICE. You get the launch in full electric, your ICE can be fully spooled, and ready to switch over automatically. Perhaps the smaller batteries couldn't put out enough power? Who knows.
Once you do this you are sunk due to weight. If you need another torque band, far better to add a second electric motor with a different gear ratio (Tesla already does this) or use something like a DSG with the single motor.
You literally describe the setup in a Prius CVT here. You could run your ICE at peak torque RPM in standstill (all torque would go to the small electric motor/generator). Then you accelerate with all three motors in tandem, all the while keeping your ICE at peak torque over the whole speed range.
The Prius of course is not a track car, so instead you accelerate with just the electric motor and continue to use it until your battery gets low or more power is required. The the ICE is automatically started while driving.
Yes, their top speed is much much faster. But put that same vehicle on a 1/4 mile race track, racing a top fuel dragster. The top fuel dragster produces around 5g's at launch, the top speed cars are very very slow to build up speed. So much so, they usually require a pilot vehicle just to start them, like you trying to start pedaling your bicycle in 5th gear. You'll want a push. It's a different type of racing.
> Not much faster land vehicles than those.
Its a poor choice of words, perhaps 'quick' is a better word?
Nope, your typical Tesla isn't the rocket you describe. Most are quick, but not that quick. I frequently get challenged by wannabes while commuting. I rarely take the bait, but I've yet to have one live up to the hype.
> You can sit more in the middle with people getting 1000hp daily drivers. With dynamic tuning, flex fuel, etc you can get the best of both worlds. As well, DCT AWD transmissions make grip/shifting issues a thing of the past.
> However, these middle ground drag cars can still get eaten by a $100k bone stock tesla
A 1000HP drag car with AWD and a DCT shouldn't "get eaten by" a $100K Tesla (unless you actually meant the $130K Tesla Model S Plaid). Not unless someone is lying about their power numbers or doesn't know how to set up a car.
The Tesla's drag mode is a neat party trick and perfect for singular drag races, but spending 15 minutes preconditioning your battery before you can launch is also kind of ridiculous by ICE car standards.
>unless you actually meant the $130K Tesla Model S Plaid
Rounding error to $100k. Yes I'm referring to the Plaid. People have taken those cars and gutted the interiors on them, and demolished drag races.
> spending 15 minutes preconditioning your battery before you can launch is also kind of ridiculous by ICE car standards.
It's far from rare to see people setting up an array of box fans, and bags of ice around their engines to cool it off between passes. Many high high powered cars won't even have full size radiators.
For the amount of spaces he put in front of his link slowing me down on my way to YouTube, I could have watched the car accelerate to 100 two or three times.
That's an average acceleration around 2g. This seems beyond the limits of tires and friction. Do aerodynamic down forces kick in fast enough to make more force usable against the road at these relatively low speeds? Do the tires have more than static friction going for them (say, fine scale interlocking with the pavement)?
Drag racers can do 3gs, but that's at higher average speed.
Aero might play in a tiny way at the 40-60 MPH space, not meaningfully enough.
As for tires, no actually you can go much further than this. The big detail is wear and heat caused by tire softness and pressure. Road car tires can't enable 0-100KPH much faster than 1.9s or so purely because they can't be so soft as crusing on the highway would cause excess wear(practicality), heat (Danger), and friction(Range).
Drag Racers can accelerate way faster, 0-60MPH in .8s.
The aero packages for these vehicles create a pretty significant amount of downforce at relatively low speeds - for example, our car last season produced ~140 lbs of downforce at 35 mph.
Edit - A lot of that comes from the rear wing though, which the green team didnt run for this particular event.
Although the other comments are correct about the 30mph optimization for the aero package, this car uses active underbody aero (aka, fans) to create additional downforce even when at a standstill. See the recent runs of the Speirling at Goodwood festival of speed to see a purpose built "fan car" in action.
Interestingly, this setup wouldn't be allowed due to rules in Formula SAE in the US but is legal in the german competition cause those teams are just built different.
Edit - Quick plug! If anyone is interested in supporting FSAE and the awesome engineering that goes into these cars, I am a member of the San Jose State team and our aero team is in need of HPC access to run their CFD simulations. My email is in my profile. Cheers.
These formula student/fsae cars have aero packages which tend to be designed around 30mph average track speeds, so they will get contribution from that, especially in the latter half of the run. Even so, the tire friction involves both physical interlocking due to deformation and chemical adhesion.
You can see the tire warmers in the video being removed in addition to their approach burnout which imparts additional heat into the tires, so that the tires more effectively stick to the ground.
For all of the questions about why they don't compete with dragster techniques, the student race series they participate in has very strict regulations regarding vehicle layout which forces them to be more of an autocross car, these kinds of (heavily couched) records being produced are really somewhat incidental.
> That's an average acceleration around 2g. This seems beyond the limits of tires and friction.
Tires don't only rely on friction but also on mechanical grip (the road and the tire are not perfectly smooth surfaces, they interlock) and chemical grip (just like glue). The last two also scale with surface area as opposed to friction. So you get two common misbeliefs about tires from school physics: that you can't go over 1g and it doesn't matter how large the contact patch is. Both false in practice.
That's what I wondered too specially that front wing can't really be helping during the initial acceleration if majority of the power is coming from the real wheels, however, they can be helpful for slowing down under control.
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This isn't close to the record for dragsters; if they can increase the energy density per unit mass there are traction and downforce improvements that can be used to improve this. It's very hard to beat chemical energy like detonating gasoline or nitromethane - you're looking at roughly a factor of 100, with ~40 MJ/kg for gasoline and 0.4 MJ/kg for a lithium ion battery - especially if you're racing through a 15 PSI gas that you can use in your chemical reaction without having to accelerate it onboard.
I suspect that traction control for an electric motor may someday allow electric vehicles to exceed the records held by internal (well, mostly internal) combustion engines. You could keep the tire at exactly the right amount of slip for maximum acceleration, rather than trying to balance centrifugal clutches to get just the right amount of power at the right time.
I wonder what the record is for a vehicle that can pick up electric energy from a tether/rail/overhead wire...though cables that can carry megawatts of energy are probably pretty heavy.
Edit: I think the most interesting category here is the typical friction-propelled, human-carrying vehicle of either chemical or electric power sources. Railguns, rockets, fan cars (using active downforce), and vehicles which engage the ground by rack and pinion are qualitatively different. When the question is accelerating your own mass forwards using the friction developed by your own mass being pulled down by gravity, there's an interesting optimization problem trading off weight and power.
That is correct. Out of curiosity, I looked it up and for the Tesla Plaid that's 0.65 MJ/kg (or 181.5 watt·hours per kilogram)
But my follow-up question is: if gasoline has an energy density about 100 times higher (well, 60 times) why are dragsters not even faster? This Stuttgart EV does 0-100 km/h in 1.461 seconds (1.87g), and dragsters do it in 0.8 seconds (3.42g). It sounds like with such a phenomenal energy density, gasoline-powered dragsters should be able to accelerate at much more than 3.42g, maybe 10g, or more. Intuitively this indicates that the bottleneck isn't energy density, but mechanical factors (gears, traction, etc). Therefore if battery energy density can increase just a little more, maybe to 2 or 3 MJ/kg, this may be sufficient for EV to be able to beat dragsters.
Edit: actually just thinking about it for a few minutes, I realize that energy density doesn't matter. An EV like the Tesla Plaid uses less than 1% of its entire battery capacity to do one acceleration from 0-100 km/h. So the battery could be reduced to 1% of its size and it would still perform one acceleration at the same speed. So dreamcompiler is right. It's not energy density, but power output that matters.
Edit #2: The Plaid has a power output of 352 watt/kg (761 kW / curb weight of 2162 kg), while the Stuttgart EV has an output of 1241 watt/kg (180 kW / curb weight of 145 kg), so about 3.5 times more.
A gas engine just cannot do that. At low RPM it has little torque and power. At high RPM, you can't really transfer that full power with a transmission in the lowest gear, because now it's too much torque. (Stripped gears and/or snapped belts were pretty common before computer-controlled automatic transmissions.)
This (idealized) chart may help explain: https://www.researchgate.net/profile/Ronghui-Zhang-2/publica...
Much progress has been made in raising Li-Ion "C" rates, which is why we now have cell phones that can charge at 20W or more. Graphene batteries are starting to get common in RC battery packs and appear to be the next significant jump.
TLDR: no you can't just put a really small pack in big enough to do one run, unless it's a specially designed pack with a very high discharge rate...in which case it might have worse energy density, and you might be back where you started (but with less total energy storage.)
Also, minor point of order: dragsters don't use gasoline, they use nitromethane. And the limitations are material science; you need an engine with internals, and a frame, and wheels, and tires, that can all withstand enough force without being destroyed...in a sport where every bit of weight slows you down.
The grip is limited. You would probably need to pull a wire or have gear mesh rail to accelerate "much more".
Normal tires provide a grip of about 0.8 newton per newton normal force. If you look at a drag racing wheel in slowmo the deformation is insane.
Because the limitating factor stops being the power, and becomes the grip to the road.
This is like asking if Usain Bolt can run a 9.5s 100m why is a cheetah that can run 6.1s not that much faster
If you only care about acceleration, energy density doesn't matter very much. What matters is power: The rate at which you can move energy from the storage medium to the wheels. In that respect a capacitor-powered dragster could probably smoke a top fuel dragster, even though the energy density of capacitors is pretty lousy. No idea if anybody has tried to build a full-size capacitor-powered dragster. Or if any human would be brave enough to drive one.
If you only need a few milliseconds of 'zap', yeah, a capacitor bank is great. It's the only option if you need to do that more than a couple hundred times in the life of the battery; a chemical battery will wear out but a capacitor can last for millions or billions of charge/discharge cycles.
But even a time as short as 1.461 seconds is probably on the far side of the inflection point where capacitors make sense.
If you like, run through the options on Digikey:
https://www.digikey.com/en/products/filter/electric-double-l...
ex:
https://www.eaton.com/content/dam/eaton/products/electronic-...
Also remember that an ultracapacitor is about as far in behavior from a physicist's ideal plate capacitor as you can get - they're not linear, they have highly significant internal series resistance...
From the perspective of being that close to being fried, or with respect to the acceleration?
To be honest though, I still think it’s amazing that people casually handle extremely flammable and volatile hydrocarbons whenever they visit the gas station. The safety ecosystem is very well tuned, albeit after a hundred+ years of accidents and research.
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Required cable thickness (and thus weight) is proportional to current, not voltage. Conductors to carry megawatts of electricity could be fairly light as long as the voltage is extremely high and the amperage relatively low.
Let's say you can control voltage, cross section area A.
Now, you want a constant power across a load P = V * I.
Your net resistance R is C + D * L / A where C and D are constants and L is your cable length.
I is proportional go V * A / (C * A + E) where E is also a constant.
So your load power is proportional V^2* C * A / (C * A + E) which is proportional to V^2 * A / (A + F) where F is also a constant.
With a large "enough" A, this is effectively V^2. With a small A, this is V^2 * g where g is A / F. So the smaller the area you have the more power you are wasting (roughly equal to V^2 * (1-g) which is heat in the wires).
So the smaller area you have, the less efficient your power delivery. And juicing up your source power is a lot more expensive than juicing up your source voltage.
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To make a 1000 kg car accelerate at 4 gee or 40 m/s^2, you need 40000 N of force. A water rocket engine with 200 m/s exhaust velocity can deliver that with 200 kg/s of mass flow. Since your target velocity is only 28 m/s, you only need reaction mass for 0.7 seconds, or 140 kg or 140 L of water. That's one feed barrel.
The back of the envelope kinetic energy of the water jet is only 3 million joules or less than a kilowatt hour. But the power is 4 megawatts. Pumps also have startup acceleration cavitation issues, so it'd need to start gradually etc.
One could maybe do it with a lot of small independent systems in parallel: a ultra high C rate lithium iron battery connected via a transistor to a pump. Each has its own water pouch and nozzle. If you can achieve 400 N of thrust with one pumping 2 kg/s, then having 100 of them in a 10x10 grid would work. The transistors would be controlled centrally.
A more boring alternative is, like in a real bottle rocket, also here, a compressed air tank half filled with water, a much more straightforward source of pressure energy.
The pulses are so loud it is like being punched in the chest. Sometimes the engines explode which is also fun as the smoking parts fly around.
Once, the Top Fuel driver had the silly thing in reverse. The christmas tree turned green, and he launched backwards. He had lightning reflexes, chopping the power incredibly fast. The thing still flew back nearly 100 feet, and if it had continued would have climbed up the grandstand behind it.
I never, ever, ever stand in front or in back of a dragster when its engine is running. I also do not stand radially to the engine (when they blow, the parts fly out radially).
Other than that, it is great fun to go to a race in person. It's the only motor sport left where the attendees can go into the pits and watch the mechanics at work. Watching a team rebuild a V8 engine in minutes is amazing. Then they'll fire it up to test it. Blipping the throttle produces shock waves that you can see hitting the bystanders.
The barely restrained violence of those machines is just crazy mad fun you'll never get from watching it on TV.
You can walk around the pits and watch the crews doing a partial strip down of the engine for each run, although it's fundamentally basic V8 pushrod technology, it's far more than that.
There is a video [1] with a few slow motion clips of the preparation and running of a Top Fuel car. One poster mentioned a cameraman who stood between two cars, you can clearly see why that wasn't a good idea!!
Looking at how the tyres deform, not just at launch 2:00 but also at 2:50 it looks like they are a real limitation in acceleration. To help them off the line the launch area is really sticky, shoes melt into the 'tarmac'.
The 0-60 time, as with many really fast cars, doesn't tell the whole story of using their 10,000BHP to get to about 330MPH in about 4.5 seconds.
It's something I think you really need to go and see.
[1] https://www.youtube.com/watch?v=Lt6iltuxD48
I've been to two Top Fuel drag races and I left feeling like I was surrounded by people who have just enough sophistication to know that they like to play with fire whenever possible.
they are not like that, of course, but they were definitely caught up in the visceral feeling of watching a race and I was caught up in the idea that I'd never be able to hear again.
I do not recommend races, myself.
Getting dangerously close to "car launched by a railgun" territory, hehehe
Not really, high speed train lines do it all the time. They usually operate at 25 kV or 50 kV and often consume a few megawatts per train.
(At 50 kV, one megawatt is only 20 amps, which you can deliver on 12 AWG wire, theoretically.)
1. You need a _lot_ of insulation at 50kV 2. I'm no expert but I very much doubt you could run a motor at anything approaching that voltage. Current electric cars, for example, run c400V as the main motor supply. So there would need to be voltage conversion, which adds weight and bulk.
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...that made the effort to submit to Guinness. In racing, established racing orgs are where racing records matter. 0-60 just isn't relevant in drag racing. Any optimum 1/4 mile run under 7s doesn't spend nearly as long as these students did dawdling along under 60 mph. NEDRA record 1/4 mile runs have been under 7 seconds for at least 10 years.
http://nedra.com/record_holders.html
The current fastest run ticked off 0-60 mph in under a second. The 60 foot time was over a second. That means they ticked off 0-60 mph in significantly less than 60 feet (~18m). Submitting that 0-60 time to Guinness would require lots of work and time, and wouldn't be relevant to competing or their sponsors.
https://insideevs.com/news/447378/video-custom-electric-moto...
So, this Guinness record is still easy pickings, as these things go. I'd bet nothing more than moving this run to proper sticky drag strip pavement instead of that grotty old runway would scrub off a tenth or two. Then better drag tires, drag optimized suspension, maybe all wheel drive, gearing optimization, weight reduction, weight placement optimization... and sooner or later Guinness is going to stop taking 0-60 mph submissions for safety reasons.
After 500 hours of Kerbal space program I’m a bit of an expert in these things.
Are there any wild designs that actually use the air in an electric powered design? Cooling is obvious, but could I just convert the electric energy to heat (100% efficient) and run the air through a heated mesh, ramjet style? :-)
Apparently, electric ramjets for spacecraft propulsion is an active field of research: https://www.sciencedirect.com/science/article/pii/S187770581...
It doesn't matter that fossil fuels are energy denser, it's much harder and less efficient to convert fossil fuel into mechanical rotation by setting it alight than it is to turn electrical power into mechanical rotation.
Electric will always win out simply because it's battery->motor. That's it. Apparently the top fuel dragster can do 0-60 in 0.8 seconds and it looks like its biggest advantage is all the downforce it gets from exhaust gasses and airfoil. I'm thinking this is more a difference in the formats of the vehicles; no point making an electric dragster or f1 when the battery won't last the whole race/series.
Batteries are heavy af though, you're right in the disadvantage there. Perhaps the inefficiency of exploding fuel doesn't matter in the face of just how freaking heavy batteries end up being.
>detonating
Should be deflagrating because the ICE flame is designed to be subsonic.
Clay Millican has an amazing YouTube channel that brings you behind the scenes of an NHRA top fuel team - https://www.youtube.com/channel/UClT3GT7hxLbNnypukfyxelQ/vid...
My college motorsports team got to meet with John Force, and someone suggested a flexible rear spoiler for variable downforce. He was quick to note it likely would be faster but would almost certainly get you killed.
For a one-off design, those cables could be very short. You could even have a very small pantograph (https://en.wikipedia.org/wiki/Pantograph_(transport))
I am not sure the end result would be faster, though. You’ll need grip to get up to speed, and starting from a standstill, you won’t get that from aerodynamics. you’ll need mass. Take away the batteries, and you may have to add a similar mass in dead weight (could be used to add a good Faraday cage to protect the driver from mishaps with the electricity supply)
More mass and more power are roughly equivalent to less mass and less power, if the above holds. Maybe even with less mass it's easier, since you can produce significant downforce with smaller wings.
Gotta love the the mix up SI and imperial units, truly effortless. 15PSI is just one bar, it'd even fit nicer too.
In top fuel events, they're burning roughly 20 kg of fuel per second, so a 200kg engine still doesn't equalize the density of that chemical fuel.
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https://physics.stackexchange.com/questions/488151/could-the...
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The extreme end of combustion engines, you really got top fuel dragsters. Not much faster land vehicles than those. The flaw with those, they got about 2 uses tops before it needs to be completely gutted and rebuilt, not great as a weekend track car. As well, it's somewhere around $1000/second to drive it.
You can sit more in the middle with people getting 1000hp daily drivers. With dynamic tuning, flex fuel, etc you can get the best of both worlds. As well, DCT AWD transmissions make grip/shifting issues a thing of the past.
However, these middle ground drag cars can still get eaten by a $130k bone stock tesla*. The extra weight, infinite torque, and zero shifting is a real advantage, even if their top end isn't as strong as their ICE counterpart.
I've always dreamed of building a hybrid car with tiny tiny battery packs. Maybe enough charge for 4-5 passes. Enough for a day at the track. But have a fully built high revving ICE. You get the launch in full electric, your ICE can be fully spooled, and ready to switch over automatically. Perhaps the smaller batteries couldn't put out enough power? Who knows.
*Plaid
Once you do this you are sunk due to weight. If you need another torque band, far better to add a second electric motor with a different gear ratio (Tesla already does this) or use something like a DSG with the single motor.
The Prius of course is not a track car, so instead you accelerate with just the electric motor and continue to use it until your battery gets low or more power is required. The the ICE is automatically started while driving.
Top fuels top out around 350 mph. The land speed record is 760 (manned, for unmanned it's a rocket sled exceeding mach 8).
The land speed record has been above 350 since 1938: https://en.wikipedia.org/wiki/Railton_Special
There are in fact a fair number of much faster land vehicles.
> Not much faster land vehicles than those.
Its a poor choice of words, perhaps 'quick' is a better word?
Muscle or German?
(Wondering whether the motivator is performance or ideology)
> However, these middle ground drag cars can still get eaten by a $100k bone stock tesla
A 1000HP drag car with AWD and a DCT shouldn't "get eaten by" a $100K Tesla (unless you actually meant the $130K Tesla Model S Plaid). Not unless someone is lying about their power numbers or doesn't know how to set up a car.
The Tesla's drag mode is a neat party trick and perfect for singular drag races, but spending 15 minutes preconditioning your battery before you can launch is also kind of ridiculous by ICE car standards.
Rounding error to $100k. Yes I'm referring to the Plaid. People have taken those cars and gutted the interiors on them, and demolished drag races.
> spending 15 minutes preconditioning your battery before you can launch is also kind of ridiculous by ICE car standards.
It's far from rare to see people setting up an array of box fans, and bags of ice around their engines to cool it off between passes. Many high high powered cars won't even have full size radiators.
https://youtu.be/xjDK0LhKkMs?t=82
For reference, a top-fuel dragster can do 0-100 mph (~ 161 kmh) in about 0.86 seconds, exposing the driver to nearly 5g.
https://jalopnik.com/the-fastest-0-60-time-a-person-could-ac...
http://www.procato.com/convert/
Drag racers can do 3gs, but that's at higher average speed.
As for tires, no actually you can go much further than this. The big detail is wear and heat caused by tire softness and pressure. Road car tires can't enable 0-100KPH much faster than 1.9s or so purely because they can't be so soft as crusing on the highway would cause excess wear(practicality), heat (Danger), and friction(Range).
Drag Racers can accelerate way faster, 0-60MPH in .8s.
Edit - A lot of that comes from the rear wing though, which the green team didnt run for this particular event.
Interestingly, this setup wouldn't be allowed due to rules in Formula SAE in the US but is legal in the german competition cause those teams are just built different.
Edit - Quick plug! If anyone is interested in supporting FSAE and the awesome engineering that goes into these cars, I am a member of the San Jose State team and our aero team is in need of HPC access to run their CFD simulations. My email is in my profile. Cheers.
You can see the tire warmers in the video being removed in addition to their approach burnout which imparts additional heat into the tires, so that the tires more effectively stick to the ground.
For all of the questions about why they don't compete with dragster techniques, the student race series they participate in has very strict regulations regarding vehicle layout which forces them to be more of an autocross car, these kinds of (heavily couched) records being produced are really somewhat incidental.
Tires don't only rely on friction but also on mechanical grip (the road and the tire are not perfectly smooth surfaces, they interlock) and chemical grip (just like glue). The last two also scale with surface area as opposed to friction. So you get two common misbeliefs about tires from school physics: that you can't go over 1g and it doesn't matter how large the contact patch is. Both false in practice.
https://youtu.be/YYjYqWdHZ8w?t=78