Why does my car waste so much energy at idle? What were the engineers thinking?

Question

I've been told a typical 3 litre V-6 uses about 0.36 gallons per hour at idle. I pencil this out real quick and am shocked to learn that that this is a total waste of 15 horsepowers. What were the engineers thinking?

.36 gph

1 h equals 3600 seconds

.36 / 3600 = 36/100 /36 /100 = 1/10000 = 10e-4

so .36 gph equals 1/10000 gal per second.

.0001 gallons equals 13.1 k Joules

.0001 gal/s equals 13.1 kW equals 4/3 * 13.1 horsepower

~ 17 horsepower waste at idle

multiplying by 30% gasoline to mechanical energy conversion

engine efficiency that is still over 5 horse powers of wasted energy.

Why so wasteful?

How much of idle waste does a typical alternator recapture?

Answer 1

The engineers gave each car a starter, and a shut-off option.  It is not their fault people are too stupid to shut the cars off when they are going to be sitting idle for any length of time, then re-started when it is time to drive.  Idling is just plain a waste of fuel.

Answer 2

Stop pretending you didn't buy a piece of crud car.

Also, if I hear an ignition Turning to start back up a car someone shut down at a red light, I will drag you out and beat you.

I promise.  That means all of you.

Answer 3

Because gasoline powered vehicles have little efficiency. Even when decelerating they burn power insufficiently.

Answer 4

That's like running an electric motor with nothing hooked to it. It is ineefficient to like the other guy said, this is why the cars turn on and off. It has just been in this century that we have developed batteries with enough capacity to make an economical vehicle. Its not that the engineers are stupid its just that they know if the make a car that is 98% efficient know body could afford to buy it.