Slashdot Mirror
The Flux Capacitor Becomes World's Fastest Street-Legal Electric Car (arstechnica.com)
An anonymous reader writes from a report via Ars Technica: Jonny Smith now has the world's fastest street-legal electric car, called the Flux Capacitor. Previously, the Flux Capacitor was only Europe's fastest street-legal electric vehicle, with a less than 11 second, 1/4-mile time under it's belt. Now it can run the quarter-mile in 9.87 seconds, thanks to the extra 44 cells added to the existing 144-cell Hyperdrive Innovation lithium-ion battery pack. That has boosted the car from 370v to 400v and the range from about 30 miles (48km) to about 50 miles (80km). "The combination of big voltage, amps, and phenomenal grip gave us early ten-second quarter miles, and when we braved the RPM limit of the motors, we managed a nine [second run]," Smith told Ars Technica. "Despite all of this power and speed, the little Enfield still felt smooth, stable, and happy, which is unbelievable given that it was designed to do 40 miles an hour."
112 MPH when crossing the 1/4 mile mark.
The article has a photo of the summary sheet from the drag strip showing all the statistics.
1) EVs do have kinetic energy recovery; it's called regenerative braking.
2) Gasoline vehicles that have them are known as hybrids.
3) All systems, including KERS, have purchase price, mass, and maintenance penalties, which is why they're not universally adopted.
4) The particular approach of flywheel-based kinetic energy storage has good W/kg but poor Wh/kg, W/l, and Wh/l. It has catastrophic failure mechanisms, limited storage time, and tends to offbalance vehicles. Flywheels have been becoming less popular with time in vehicles, not more - being overtaken by electric systems, which are increasingly compact and lightweight vs. their power output.
5) All kinetic energy recovery mechanisms suffer from losses. I haven't looked into the round-trip efficiency of flywheels, but round-trip efficiencies of conventional hybrids are often 40% or less, while for li-ion EVs they're often more like 60-70%. The problem is that you're storing and withdrawing power quickly, which reduces efficiencies, and all losses hit you twice - motor, drivetrain, controller, wiring and battery. Hybrids are hit worse than EVs because the packs are smaller (meaning higher-C charge/discharges) and the packs are generally NiMH, which is less efficient than li-ion.
6) Braking losses are only dominant in city driving. In combined driving they're significantly reduced and in highway driving they're almost an irrelevant fraction of the total. Aero losses dominate at high speeds while rolling losses dominate at low speeds.
7) The biggest energy benefit of a hybrid isn't recapturing braking losses, as most people assume. It's that it lets you operate with a much less powerful engine, without the vehicle feeling underpowered, thus helping the engine stay in its optimum power band (IC engines operate most efficiently when fairly near their maximum torque capability). Hybrid vehicle efficiencies don't drop that much when the hybrid system is broken (losing regenerative braking and stop/start), but they lose responsiveness.
8) Rolling losses, for the most part, come down to your tires; there's a balance between 1) grip, 2) rolling resistance, and 3) price. Choose two. (I could throw in other factors like noise, comfort, wearing, etc, but let's keep it simple)
9) Reducing aero losses comes down to reducing your cross sectional area and your drag coefficient. A reduced cross sectional area means that you can have a long car but not a wide or tall one. Reducing the drag coefficient means breaking with styling choices that people prefer in cars in favour of making it look more like an airplane (see the Aptera as an example of taking it to extremes).
Note that things that look aerodynamic often aren't; many "sleek"-looking race cars actually have high drag coefficients (on purpose - to add downforce). General principles for achieving a low drag coefficient include:
* A relatively blunt, steadily-curved front end. The popular American car style of a massive front end is right out - you want the length on the other end.
* Steady transition to a highly raked windshield (within the limits of strength, weight and visibility.. and construction, as multi-axis bending windscreens are more expensive than single-axis)
* A slowly tapered rear end, down to as small of an area as you can. Tapering can be on two axes (teardrop) or either axis alone (airfoil-shaped)
* If you can't achieve a slow taper at any point due to internal space constraints, truncate it sharpy, ideally with vortex generators; otherwise you'll get flow separation and drag a low pressure wake, which is Very Bad(TM).
* Adjust the vehicle angle to have zero net up or downforce.
* Reduce or eliminate the air intakes on the
Hourglass says she knows a kid in Iowa who grows up to be president.