Diesel economy, and math.
 

A litre of diesel is the energy equivalent of approximately 11 kWh.

If you get 25 mpg that means it "costs" you 440 watt hours to go one mile.

Chances are, the lion's share of this is going to go on a mixture of;

1. rolling resistance
2. aerodynamic resistance
3. acceleration

#1 is affected by good maintenance, and custom options such as wide or narrow tyres.

#2 is affected by vehicle speed, not much else you can do to change it.

#3 is affected by vehicle weight, and jackrabbit starts.

Once you own a vehicle, there isn't much you can do about air drag coefficients, or vehicle weight, they are pretty much fixed.

Once you own a vehicle, you CAN make a huge difference to actual air drag by keeping the speed down, 60 mph or less, you can also make a huge difference by driving smooooooth and steady and reading the road ahead.

Once you own a vehicle you can minimise rolling resistance by maintaining the vehicle running gear well, and fitting narrow tyres.

You can boost your economy by 30% doing these things.

Making SIGNIFICANT changes is fuel economy can only be done with a NEW vehicle.

It needs to be very low drag, which means low.
It needs to be VERY light, think 750 kg kerbside weight.
It needs to be SLOW, think 0-60 of 15 second and a top speed of 70 mph

Do this and you can get a 100 mpg diesel car.

Or go from 440 watt hours per mile travelled to 150 watt hours per mile travelled.

But you absolutely CANNOT do it with a vehicle built like a modern car, steel body, glass windows, leather seats, 2,800 kg kerbside weight, fat tyres, 125 mph top speed, etc.

In the end, it is all going to come down to cost.

Here in the UK one kWh cost around 13 pence, that's around 20 cents, doesn't matter how you buy it, as electric, as diesel, as natural gas.

The amount of kWh that your weekly wage can afford is going to decide what kind of economy your vehicle runs.

You are absolutely correct; and when the cost of a kW-hr of energy doubles or triples some of those changes are likely to be implemented in production vehicles.

I disagree. Most of that energy is lost in heat, ie exhuast gas. Also, radiator cooling. Heat is energy. Energy is not created nor destroyed, just transformed.
Electricity can be very effiecient. I think some electrical motors get 80 to 90% effiecient. You do have loses by transmitting electricity over power lines. You also loose when you transform from one voltage to another.
Tom

Interesting read. I enjoyed it.
Here's my take on the plug-in vehicle thing. I haven't done any calculations but the thought process is as follows:
In a conventional IC engine you take a fuel which has chemical energy and transform it into heat energy which you then transform into mechanical energy. Each of these steps involves a loss of energy which is quantified as efficiency.
In a plug-in vehicle you take a fuel and extract it's chemical energy to produce heat energy to produce mechanical energy to produce electricity which is transported through several step-down transformers to your house. You then convert that to chemical energy by charging a battery which is used to drive a motor thereby converting it to mechanical energy. Each of these steps also involves a loss of energy. One could infer that a greater number of energy changes would involve a greater loss of overall efficiency.
However, the scale of power generation (and the vast array of heat-recovery features in these plants) makes it quite efficient and the heat losses in an IC engine make it quite inefficient. Also, from the first post, the desire to have it all in one package (speed, comfort, safety, convenience) tends to reduce the efficiency of that package.
I don't know the answer but it's interesting to think about. I do think that if we eliminated all drive-up windows (my pet peeve) and built a feature into cars that minimized the time you could idle them it would save a bunch of fuel. And the bottom line is we are going to have to be better stewards of energy as the population grows and the planet does not.
Thoughts?

From what I read many of the new cars will turn the engine off each time you come to a stop of some minimum interval of time. When you hit the gas again, the motor comes back to life - even in gas engines. It is hard for me to understand how so much energy can be wasted at stop lights that this is an efficient answer. Doesn't this strategy play havoc with the starter wear and maybe the battery? Are the overall savings justified?

You have clearly never put your hands on a 75 kW / 100 BHP electric motor, or control electronics, or any DC battery bank (of any variety) producing that sort of power....

80% overall system efficiency is a laboratory dream.

It is what is claimed for brushless motors. Cobalt motors at claimed at above 80%.
Tom

I think his point was that automotive ICEs are closer to 15% while stationary power plants can convert thermal to electrical energy at closer to 40%.

Also, depends on what cycle the ICE power plant is in. At Highway speeds, they do well against electric power or Hybrids. Deisel is more effieceint that gasoline, but gasoline has made strides. Also MB and others are messing with Atuodeisel (??). Basically a deisel engine designed to run on gasoline. I think the main savingins is in emmisions add ons.
Tom

Agreed, I'm just using round numbers. It is difficult to talk about cost per unit energy only, it depends on the form of energy.

meh, might as well claim that my hydraulic transmission is 95% efficient, it is meaningless unless you take the system as a whole, that means....

1. MEAN efficiency of electric motor, likely to be around 50% for any motor with a peak efficiency of 80%
2. MEAN efficiency of control circuitry, usually around 85%
3. MEAN efficiency of battery on discharge cycle, 50% if you are lucky.

Resulting on an overall efficiency of 21.25%

You STILL have issues with aerodynamic drag and rolling resistance.

You ALSO have the downside of the mass of batteries you are toting around, which weigh the same discharged as fully charged, with an energy density of approx 150 watt hours per kilogramme... you get...

4 kilogrammes of battery per mile travelled, so a 100 mile range = 400 kilogrammes of battery.

while the diesel car will do 100 miles on 4 kg of diesel.

100 kg is 7.5% of the weight of a small/average vehicle kerb weight, which therefore represents 7.5% of rolling resistance, which, due to the nature of the battery, IS ALWAYS THERE.

THAT is precisely my point, if you do the actual math and actual engineering, it doesn't, all that matters is the cost of the energy per kWh.

What you are missing is the fact that the energy cost increases as it is converted to a more useable form. A pile of coal containing 1 kW-hr of energy is much less valuable than 1 kW-hr of electricity delivered to your house; it will take more than 2 kW-hr of "coal energy" to make 1 kW-hr of "electrical energy" after a very expensive conversion process. That is what you a paying for; energy delivered in a usable form.

True. I think think electic vehicles are in their infancy. If/when lithium batteries become viable, then the weight paragram might change. Although different, I fly RC airplanes. 10 years ago, electrics were a niche market. Now, every Hobby shop, Walmart, K-Mart etc. has them. The performance, cost/weight of batteries, everything has changed.
I'm not saying diesel is dead (I hope not, it keep shoes on my feet). Presently, I don't see the cost as being practical. Niether was ABS, or air bags originally. I do agree that the accounting of mpg might and probably is deceptive on these vehilces, ie Chevy Volt type.
Also, I'd rather put my hand on an eletric motor, than the exhuast of an ICE motor. HEat loss is every loss. Check out semi adiabatic motors.
Tom

bzzzzzzzzt

compare like for like, ice exhaust vs leccy motor windings.