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MG Midget and Sprite Technical - Did anyone know this was out there?




http://www.youtube.com/watch?v=ow5cGV7bXCw
Steven Devine

It's interesting early on in the video that 25% is the holy grail of efficiency for piston gasoline engines, I remember that was the number in the 60's, I wonder if diesels are still at 41% ? Good knowledgable video. Aviation has given up on the piston and there are small turbines we could get under the hood just can't figure out the exhaust plumbing !!
Bob Ketcham

I've heard more recently it's considered a 1/3, 1/3, 1/3 split.

So 1/3 down the exhaust, 1/3 into the cooling and a 1/3 into actual power.

Clearly the 1/3 into actual power then has transmission loses removed from that.


Rover has already built turbine powered cars….

http://www.4wdonline.com/Rover/GasTurbines.html
Malc Gilliver

Another useful refinement that since been introduced, is available from Specsavers. Pity there weren't around back then. LOL.

Lawrence Slater

Thanks

Im going to watch that tonight

Prop
Prop and the Blackhole Midget

Gasoline engine efficiency is still somewhere around 23%, though some engines do a little better than that, and diesel around 40% as noted. All of David's good analysis in that video has got me into a similar state of mind, so I tried comparing some technologies recently very much in the news:

An interesting comparison is to take the energy content of diesel and gasoline fuel x that efficiency, and then compare those to CNG, which is so very cheap in the US (and with improved transportation technology, gradually becoming cheaper elsewhere as well). Using 57 liters of each (15 US gallons):

Gasoline, @ 1950mJ x 0.23 = 450miles range (roughly, using reported data averaged from similarly sized vehicles/engines)
Diesel, @ 2130mJ x 0.4 = 852 miles range
CNG, @ 513mJ x 0.31 = 160 miles range

Although an ICE running CNG is more efficient, the drastically reduced energy content / liter gives an almost "electric car" sort of range. Usually, this means the storage tanks are made much larger (using up much of the boot) to compensate.

Electric, @ 125mJ x 0.9 = 113miles range (assuming Li Ion batteries)

Electric motors are supremely efficient at converting electricity to work, but their batteries are super heavy and large, and don't store much energy, so they get the smallest range. The upside is their battery packs can be made very flat so they can be stored under the floor, actually improving handling and crash performance (due to the low CG) in an ironic twist.

Now, here's the funny thing:

Compare the energy density of each medium (mJ/Liter), and you can pretty easily see the differences,
Gas = 34.2
Diesel = 37.3
CNG = 9
LiIon = 2.2
H2 = 5.6 (this thrown in for good measure, as it is right on the horizon)

Now, compare a
Nissan Leaf battery, at 294kg, and 24kwh of energy, or approximately 88kBTU,
to a single gallon of gasoline, at 3kg and 120kBTU.

You get 1.5x the energy in the single gallon of gas (sorry, still using US gallons here).
But, the electric motor is super efficient, like 4x as efficient, so does that compensate for the low energy density of the battery?
Unfortunately, no, because the single (US) gallon of gasoline has 40x the energy density, by weight.

Batteries will continue to improve, but we'll see if a convertible chemical process can ever get anywhere near what you get from combustion.


Hydrogen, while more than 2x the specific energy/weight of the other options (143 mJ/kg vs gasoline at 46.4, Diesel at 46.2, CNG at 53.6 or electric at ~0.5mJ/kg), it has a very low volumetric energy density (< 1/4, at 5.6 mJ/L vs. gasoline at 34.2), and because it is such a small molecule (the smallest there is), the storage tanks tend to leak unless kept below -260C (liquid, or slush), so the tanks tend to be super heavy than, say, a CNG tank. If you can produce H2 on the go, you can avoid that issue. There is a lot of work on that going on these days.

What I love about reading Vizard's stuff is how he gathers the data together to support his statements/conclusions, and then does a pretty decent job of putting them into context.


Norm :)
Norm Kerr

This thread was discussed between 17/03/2014 and 18/03/2014

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