Engine efficiency

[NeilBlanchard]

Lower weight is better when you have to stop and go a lot, or have a lot of hills. But once you get moving, kinetic energy allows you to partially regain some of that invested energy. If you use a regenerative alternator to slow the car, then you can gain a little more.

Aerodynamic drag loss is *always* a *total* loss. It is about 50% of the total load at about 30-35mph, and it is 75% of the load at >65mph.

You may have missed the related part of my blog post:

So the lowest MPGe of an electric drive; the AMP'd Sky was 86.7MPGe (Tango was 86.8), while the best of a car with an internal combustion is the Edison2 #97 at 101.4. (Actually, the FVT has a ICE powered generator onboard, but did not need it *at all* in the X-Prize. It would be great to see how the eVaro does for MPGe in charging mode!) The hybrids all were all below the 67MPGe -- except the WWU at 92.5 (and the FVT).

The average of the 12 vehicles using electric drive MPGe (I'm including the FVT in this) was 134.7MPGe
The average of the 6 hybrids (not including the FVT) was 61.26MPGe (Please note, these are all parallel hybrids?)
The average of the 5 internal combustion drive cars was 82.92MPGe

The X-Prize results table does not include weights, but I daresay that the average weight of the internal combustion cars was lowest (the Edison2 and Spira are all much lighter!).

The best aero drag is on the X-Tracer, followed by a very close group including the Aptera, Edison2, Li-ion.

Those four critical things are; from most important to least important (as I am interpreting the Knockout results):

* Drivetrain Efficiency
* Aerodynamic Drag
* Weight
* Rolling Efficiency

Now we have the Edison2 VLC Electric that with a DC drivetrain and about 220 additional pounds (830 vs 1040) -- and additional ~26%, the efficiency went from 110MPGe up to 245MPGe. They are looking at a AC drivetrain which should improve it another 20% at least.

Also, the 2,900 pound Illuminati Motor Works 7 gets 207MPGe on the EPA Combined test:

http://illuminatimotorworks.org/blog/?p=292

This is ~3.5X heavier and the aerodynamic drag is 0.23 vs 0.164 if I recall correctly. The drivetrain efficiency is at the top of the list.

[drmiller100]

Ummm, No.

There are two primary factors affecting how much horsepower it takes to move down the road. Rolling resistance, and Wind resistance.

Rolling resistance can be calculated within 10 percent if you merely know the weight of the vehicle - the rolling resistance is turned to heat and lost, and the rolling resistance is linear in relation to weight.

Heavier is ALWAYS bad except in a windstorm.

[drmiller100]

>>>It is about 50% of the total load at about 30-35mph, and it is 75% of the load at >65mph.

Answer this for me please - Given your numbers, what is the other 50 percent of the "load" at 30 to 35mph???

[NeilBlanchard]

If weight is always worse, then how does the Jacobs Honda (on the EM home page) more than double it's FE with ~33% more weight? How does the Edison2 VLCe more than double the efficiency of the VLC with ~25% more weight?

At lower speeds rolling resistance is the majority of the load. Above a threshold that depends on the CdA of the car, the aerodynamic drag becomes the majority of the drag.

Speed X weight = kinetic energy. So, once you accelerate the weight, you can coast. With lower aero drag, you can coast farther with a given weight.

Aerodynamic drag trumps weight, because aero drag is a total loss, and because at most speeds aero drag swamps all other losses combined.

Edit: I do think that with the significantly lower efficiency of IC engines, that weight is closer to aerodynamic drag; but aero still is more important. The Spira4u (X-Prize vehicle) weighed about 485 pounds, while the Edison2 was about 830 pounds, the Edison2 was more efficient.

The Illuminati 7 at 3,100 pounds is about 2X more efficient than either one. When you are wasting 80% of the energy under acceleration, it matters a lot more than if you are wasting only 20%.

[euromodder]

Originally Posted by NeilBlanchard

Speed X weight = kinetic energy. So, once you accelerate the weight, you can coast.

Sure, but you usually won't always regain all of that energy in a coastdown.

Weight definitely is an issue.
Some electric bikes go over 100km on a tiny battery.
Some far heavier EVs are hard pressed to go that distance at all.

[NeilBlanchard]

I'm not saying that you can regain even a majority of the kinetic energy in an IC engined vehicle. But you can reclaim *some* of it it any vehicle.

All four factors are interrelated. But the relative order of importance is still:

* Drivetrain Efficiency
* Aerodynamic Drag
* Weight
* Rolling Efficiency

...for almost all vehicles in most typical situations. It is interesting too, that ICE's "like" a constant load best (fixed speed on flat ground) while an EV does very well with stop and go, because there is no idling, they are still quite efficient at low RPM's under high load, and regenerative braking is possible.

Both ICE's and EV's need low aero drag, for slightly different reasons: and ICE has to minimize the load for efficiency, while an EV is limited by range. For weight, as I said before, the EV loses much less under acceleration, and it can coast better (no idling) and it has much greater capacity of regenerative braking.

[gone-ot]

...yes, but aero drag is a squared function, not semi-linear, as rolling load (bearings, tires, mech. friction, etc.) are.

[user removed]

Originally Posted by Old Mechanic

Neil read my post # 52 above with the link to the Chiron free piston engine. I think they are in the neighborhood of 55% thermal efficiency. I also believe that is measured in the produced hydraulic pressure, which eliminates the engine driving a separate pump and the corresponding losses. I would absolutely love to have one of those in my prototype.

They also make a version that is a linear electric generator or alternator (not sure which). It can also run on many different liquid fuels.

Also read the section in the site about the electric hydraulic hybrid, something that I have tried to present for quite some time, incorporating regenerative efficiencies hydraulically that mirror your beliefs that electric motors are substantially more efficient than IC engines.

It will be interesting to see what happens in the next decade as development of batteries and IC engines will progress, probably at a very high rate. I see all vehicle efficiencies doubling in the next decade. It will be quite a show to watch.

regards
Mech

Neil, did you even bother to read the link I suggested in this post.

You claim 20% efficiency for an IC engine when accelerating.
That's a complete falsehood. IC engines are at their most efficient under accelerating.
You claim good efficiency in regeneration for an electric vehicle, then you claim they need no transmission, as well as basically claim they need no maintenance.
All false.
Make legitimate claims and DO the research you need to be educated in the topic when you make claims that are not substantiated by facts, most here know already. To make false claims about poor IC efficiency when the facts do not support your claim just confirms you do not want to make any unbiased comparison, in other words a biased agenda not supported by facts.

Fact. the linked article you seemed to ignore shows 55% efficiency for the Chiron motor.
Fact, an electric motor is less efficient from a dead stop, in some cases lower than the Chiron.
Fact. Even if you have an electric car you still have maintenance. Would you like me to list all the components that still will need replacement.
Fact.
Tires, axles, brakes, differential, shock absorbers, wiper blades, light bulbs, heater, air conditioner, alignment.
Fact. Consumer Reports tested the Leaf and it cost you 15% in electricity lost to charge the battery, that's meter to discharge of the battery, so you should reduce every claim by that amount, instead of evading the fact that I pay for fuel at the pump, and I get 100% of what I pay for, while your electric car only returns 85% of what you pay for.

I can continue for for the sake of some brevity maybe YOU should name the common parts on every vehicle you think do not exist on an electric vehicle.
Fact. A direct drive engine to wheel electric vehicle still needs a differential and its regenerative capability is 30% or less. Hydraulic Hybrids were 78% 5 years ago.

Fact. There is no way you can recover even 30% of decelerative energy in any direct drive electric vehicle, even with a 400 pound battery.
The reason your electric motor is simply not spinning fast enough to generate that kind of energy, and even if it could, that battery can not accept energy at that rate.

regards
Mech

Here are some facts for you Neil.

regards
Mech

[pete c]

I think extra weight can be helpful if your drive includes long not very steep declines where the extra weight keeps you at a high enough speed to avoid being run down. On level ground it will hurt you, although the lengthened P&G cycles may lessen the pain some.

As for rolling losses being a certain percentage of load a 30 mph, that depends quite a bit on weight. When I am on my bicycle at 25 mph on level ground, I am hammering it pretty damn hard. If I am lucky enough to catch the rear bumper of a city bus, I can and have maintained better than 30 mph with damn near no power output because the bus knocks my aero drag down to next to nothing, but, it does zilch for my rolling losses.

A 5000 lb car, doing the same thing will see little difference in throttle inputs.

[pete c]

Originally Posted by drmiller100

you confusing rod length and stroke. different things.

Nope. I understand the differences perfectly.

As rod length increases, side loads decrease. Efficiency improves, cylinder and piston wear decrease. Of course, it does make your engine block taller/heavier and it does increase reciprocating mass. You can get some of that mass back with a less robust piston.

As stroke length increase, side loads increase. This is a bad thing, but, it is the cost of getting greater torque and efficiency gains of a longer stroke.

The concept is a lot simpler to understand with a picture. I'll see if I can dig one up. It certainly made it a lot clearer to me.