Let's be fair on the high-mileage EVs

[trebuchet03]

Originally Posted by dcb

I have to say to this point that I've been assuming a simple bomb calorimeter type measurement of the BTU of gasoline. I am struggling to understand how using an intermediate value makes any sense though. If the engine (or powerplant) releases hot gasses (or even liquid that is slightly above room temperature) it is releasing energy that it might otherwise be using.

One doesn't get to apply a handicap because the discharge happens to be in gaseous state, I don't get that at all.

I think Ernie isn't explaining it quite right (I understand because I already know what he's talking about, but I can see it being very confusing)... I am happy, however, that low heat is being brought in

Firstly,
In the microscopic sense of thermo efficiency - low heat isn't a handicap. On the macroscopic level, it is because low heat ignores the inherent problem with the process itself.

High heat versus low heat comes down to the energy in water. Simply put, high heat assumes water after a combustion event is in liquid form whereas low heat takes water to be in steam. While this seems kinda crazy, water's latent heat of vaporization is the culprit for the difference.

This is why Ernie keeps mentioning "gasses."

I normally don't do this because sometimes the book is difficult to understand but...
Fundamentals of Engineering Thermodynamics by M. Moran, H. Shapiro

The heating value of a fuel is a positive number equal to the magnitude of the enthalpy of combustion. Two heating values are recognized by name: the higher heating value(HHV) and the lower heating value (LHV). The higher heating value is obtained when all the water formed by combustion is a liquid; the lower heating value is obtained when all the water formed by combustion is a vapor. The higher heating value exceeds the lower heating value by the energy that would be required to vaporize the liquid formed. Values for the HHV and LHV also depend on weather the fuel is a liquid or a gas. Heating value data for several hydrocarbons are provided in tables A-25

It then goes on to show how to calculate the enthalpy of combustion, which is not exactly trivial. One finds low heat by taking high heat and subtracting the latent heat energy required to vaporize water (something EV components need not worry about ).

Here's the rub (and where your point comes in, dcb) - high heat is the gross, low heat is net. We can't stop water from vaporizing, it will take that energy, so the only available thermal energy to extract mechanical work is the energy available in low heat.



Ignoring the high heat value of combustible fuels is like ignoring the charger efficiency of an electric vehicle. Yes, the motor might be 90% efficiency - but that doesn't mean 90% of the energy put in gets converted to useful work It's not very truthful to ignore everything except the motor...

[theunchosen]

Treb I have that textbook.

I like it, but I had forgotten that it had HCs in the tables.

Our rub is not that it matters between high heat and low heat. Our only issue is that your engine is given this much energy but it can only usefully extract this much. IF we count up all the little pieces of energy that come out the other side its the same as went in, but the point is electric fuel delivery systems and electric engines are more efficient by far than HC fuel delivery systems and ICE engines.

What is worth mentioning is that even a Carnot cycle would be less capable than an EV(cycle and chains included, or not). So if the absolute most efficient heat engine with absolutely no irreversibilities cannot compete, no real engine is even worth talking about. A real engine if its lucky will get 50% of what the ideal theoreticaly will get.

[jamesqf]

Originally Posted by theunchosen

Thats kind of disingenuous though. For a real comparison you would have to compare an SUV EV and an SUV ICE, or an EV insight and an ICE insight.

Not disingenuous, because that's exactly the comparison I want. We have an objective: to get me from A to B using least amount of energy/producing least amount of CO2. The question is whether a reasonably small & efficient gas-powered car does better at this than a full electric SUV getting its electricity from the grid.

Of course, if I have the option of using a small, efficient EV, that's obviously going to beat both of those, but until Aptera starts selling around here that option's not available.

[jamesqf]

Originally Posted by theunchosen

What is worth mentioning is that even a Carnot cycle would be less capable than an EV...

But about 70% (taking an average of the US grid) of the electricity that charges the EV is produced by fossil-fuel burning heat engines, so what matters is (efficiency of large power plant * electric transmission & charging loss factor) vs (lower efficiency of small IC engine * cost of transporting gasoline).

[theunchosen]

Originally Posted by jamesqf

But about 70% (taking an average of the US grid) of the electricity that charges the EV is produced by fossil-fuel burning heat engines, so what matters is (efficiency of large power plant * electric transmission & charging loss factor) vs (lower efficiency of small IC engine * cost of transporting gasoline).

True Coal and natural gas make up 70% of US consumption in electricity. It also makes up 70% of the power used to refine gasoline.

mine-coal-transport-plant-grid-charger-battery-motor

mine-coal-transport-plant-well-transport-refinery-transport-pump-ICE.

Yes of course some of the transport in coal to the power plant requires gasoline, but in freight trains its miniscule. They can haul 960,000 cubic feet of coal for 6 gallons a mile. oil transport is only close to that efficient in boats, but it has to travel across a pipeline and then an ocean before it gets to the US. diesel-truck tankers are far less efficient than freight train and coal doesn't have to get shipped first and then transported.

Like I said, if you want to toss in the fuel delivery systems for each, gasoline is going to start at the percentage efficiency EV ends at and then start shaving off lots of %'s.

small gas itself is currently more efficient than anything else, i.e. the Insight running steady state and not engaging the electric IMA.

If you want to build your own by ripping prius batteries out and popping the drive train out of an insight and making it all EV it might be more weight efficient than the hybrid but I can't say.

[dcb]

Originally Posted by trebuchet03

Ignoring the high heat value of combustible fuels is like ignoring the charger efficiency of an electric vehicle.

Thanks for the details Treb. My lightbulb gloweth dimly. So back to the OP, what is "fair". I think I'm with uncho (and others) here in that it doesn't really matter as long as it is consistent and tracked seperately.

Motion to request adding additional kwh field to fuel logs and apply mpg conversions based on 114,000 btu per gallon of gasoline. Users using both electric and gas should be able to enter one or both and note the mileage (plug in hybrid, block heater, cabin heater, alternatorless recharging, etc).

[roflwaffle]

Originally Posted by trebuchet03

Ignoring the high heat value of combustible fuels is like ignoring the charger efficiency of an electric vehicle. Yes, the motor might be 90% efficiency - but that doesn't mean 90% of the energy put in gets converted to useful work It's not very truthful to ignore everything except the motor...

That's true, and at the same time it isn't truthful to ignore or trivialize the energy needed to extract, refine, and transport oil/gasoline. Very few look at well to wheels efficiency, or even mention that with a PV setup or something similar the efficiency of electricity generation is something of a moot point.

[trebuchet03]

Originally Posted by roflwaffle

That's true, and at the same time it isn't truthful to ignore or trivialize the energy needed to extract, refine, and transport oil/gasoline. Very few look at well to wheels efficiency, or even mention that with a PV setup or something similar the efficiency of electricity generation is something of a moot point.

I don't think it is trivial (I think I posted a link to the refinery consumption figures the other day)... But in context of comparing one car to another... It isn't particularly useful - especially when attempting to attract more drivers towards better driving habits.

I'm with dcb's motion Because to what end? Can the next discussion be on a conversion factor for motorcycles because they use less tires and therefore there's less tire manufacturing cost/pollution/recycling? It's not that I don't enjoy the discussion (I do) - it's just that every page adds another nuance in the chain

[NachtRitter]

Originally Posted by dcb

Motion to request adding additional kwh field to fuel logs and apply mpg conversions based on 114,000 btu per gallon of gasoline. Users using both electric and gas should be able to enter one or both and note the mileage (plug in hybrid, block heater, cabin heater, alternatorless recharging, etc).

SECONDED!!

[Ernie Rogers]

There has been a lot of talk about efficiency of production for gasoline and electricity. I thought it might be nice to add some numbers to the discussion.

The numbers I am listing are the percent efficiency, energy in the "fuel" divided by the total energy to produce it, from Greet 1.7 (2005). There may be later values, but I doubt they are much different. ANL gives two sets of numbers, for California, and average for the whole U.S.

WELL-TO-PUMP OR MINE TO PLUG EFFICIENCY

.........................Calif........U.S.
Electricity...........45.9%.....38.1%
Gasoline (RFG).....80.7........80.8
Diesel #2............82.8........82.6

I can look up efficiency for other fuels if people are interested

Ernie Rogers

Originally Posted by roflwaffle

That's true, and at the same time it isn't truthful to ignore or trivialize the energy needed to extract, refine, and transport oil/gasoline. Very few look at well to wheels efficiency, or even mention that with a PV setup or something similar the efficiency of electricity generation is something of a moot point.