Will We Have a 100-mpg Car Soon?

[Dan McNeil]

Bandidoz said:

The drawdown of electric charge should not even be considered to be part of the MPG.

Rubbish.

Like people before you on this thread, you appear confused by the term MPG; you also appear confused by the difference between hybrid (gasoline/electric) and plug-in (gasoline/grid-charged) vehicles.

MPG = amount of fuel (petrol, in this case) used over a measured journey (measured in miles). MPG can be measured over a single journey, or multiple journeys (as an average). But, at the end of the day, MPG is MPG, i.e. fuel used over a measured distance of units.

Unlike plug-ins, hybrid vehicles don't take power from the grid. Hybrid vehicles simply charge a battery during the normal act of driving; the battery is then used to exclusively move the car over short distances at low speeds (without needing the gasoline engine at all), or intermittently at high speeds (in tandem with the gasoline engine).

This is achieved in two basic ways, by: 1) the battery is charged while the gasoline motor is running and 2), the battery is charged when the car is braked and/or when the car is decelerating (this works particularly well on motorways). In addition, when the throttle on a hybrid vehicle is released, the gasoline engine cuts out and the battery is charged.

The bottom line is that over a measured distance, a hybrid vehicle is (for a percentage of that distance) using means other than its gasoline engine for propulsion, and that this alternative means of propulsion is powered by a) the normal use of the gasoline engine and b) the recouping and storage of kinetic energy.

Therefore, the MPG of a hybrid vehicle must take into account the amount of fuel used over a measured distance.

Trust this is clear.

Regards,
Dan.

[clv101]

clv101 said:

I don't understand this. 100mpg is almost twice 55mpg. How does a different battery pack manage to get almost twice the work out of the same fuel? The engine is the same, the duty cycle can be improved a bit, but I wouldn't have thought anywhere near a doubling.

The standard battery and electric motor can run the car for around 3 miles without using the gasoline motor, after which the battery has run down, causing the gasoline motor to start up to recharge the battery. The lithium battery can power the car for around 30 miles without using the gasoline motor. The clue is in the term MPG ...the car is basically travelling more miles without using gasoline, hence increased MPG.

The drawdown of electric charge should not even be considered to be part of the MPG. Otherwise you could suggest that it has infinite MPG if you just do a 100m trip down the road; which is clearly ridiculous.


I suppose the impact a different battery pack could have is that it may weigh a lot less than the standard model?

It's fine to talk about MPG as long as we remember to think about it in terms of miles per energy. If it's a plug-in we can still work out a comparable MPG figure by equating the primary energy in the lump of coal with the primary energy in the litre of petrol (or even crude, but that opens a can of worms!).

[Bandidoz]

you also appear confused by the difference between hybrid (gasoline/electric) and plug-in (gasoline/grid-charged) vehicles.

Well Dan, when you say things such as....

The lithium battery can power the car for around 30 miles without using the gasoline motor. The clue is in the term MPG ...the car is basically travelling more miles without using gasoline, hence increased MPG.

...you are implying that the vehicle is being charged from the grid - hence my comment (because a non-plug-in hybrid would have had to have burnt petroleum to have gained the initial charge - so not "without using the gasoline motor"). Otherwise a larger capacity battery would make no difference to MPG since the charging cycle would be longer, and you may actually reduce MPG since the time between charges would be longer (there is some degree of self-discharge in batteries) and the overall weight carried is larger.

I think we both agree that the MPG is what would be needed to run the vehicle continuously from its petroleum-based mechanism. The fact that the car can sometimes be driven for 30 miles without firing up the petrol engine is completely irrelevant.

[fifthcolumn]

What's retarded about this debate is people are insisting on arguing about the efficiency of the vehicle rather than
DOES IT USE MUCH LESS PETROL?

Frakken idiots.

[welshgreen]

Well if an engine is more efficient of course it will use less fuel!