OT: Hybrid cars

[Nadav Har'El]

On Tue, Sep 17, 2013, Oleg Goldshmidt wrote about "Re: OT: Hybrid cars":
> speed and everything is a bliss. As you watch km/l the number keeps
> climbing up because for a while the computer still remembers that you
> used to burn fuel at traffic lights without moving forward, but with
> time it will gradually forget it. At some point it will more or less
> stabilize, assuming that you have enough of the highway to drive at a

This is not how the fuel consumption guage worked on any of the cars I
had... It's always a momentary measurement - I can see 0 (when the
engine is shut down on an hybrid car), put the pedal to the metal - and
jump to 20L / 100km in an instant. It's not a running average (at least,
not an average of more than a few seconds).

In addition to the momentary fuel consumption, you also get in many cars
some fuel consumption average over a long period - The Prius gives you
a monthly average, in most other cars you can reset the averaging period
yourself (so you can measure an average over 5km, or 5000km, as you
wish).

> out to a large extent by the averaging (details in note [2] below). If
> you do it a couple of times at 80km/h and a couple of times at 100km/h
> and notice a difference the result will not be "scientific" but you will
> get a basic idea which cruising speed is more economical.

When I drive at constant speed on the highway, I see different momentary
fuel consumption all the time: It depends on the road slope (even very
small road slope), small acceleration (if I accelerate from 100 to 105
without even meaning it), the outside heat (the air conditioner also
takes fuel), etc. It's really hard to get any meaningful measurement
without averaging over long periods.

Moreover, in a hybrid car, it's possible that the car will use less fuel
over 5 minutes because it uses up the battery, and then use more fuel
over the next 5 minutes, because it recharges the battery. There's no
way you can tell this is happening unless you average over longer
periods.


-- 
Nadav Har'El                        |     Tuesday, Sep 17 2013, 13 Tishri 5774
nyh at math.technion.ac.il             |-----------------------------------------
Phone +972-523-790466, ICQ 13349191 |Topologist, n.: A person who cannot tell
http://nadav.harel.org.il           |a doughnut from a coffee mug.