Quote:
Originally Posted by moon161
1. Starting a hot engine is real easy, easier still if the car is rolling. Which hits a battery harder? .5 seconds at 200 amps for a starter or a 10 second cycle of 10 amps for a cooling fan?
2. Full authority ECU's (push button start) make this more practical.
3. At idle, gas engines suck the air charge past a nearly closed throttle, doing significant back work. Diesels idle by governing down to idle stop or idle rpm w/ free flowing intake. Stop/start engines gain more w/ gas than diesel.
4. The benefit varies- you would see none on the thruway, but a lot in a traffic jam. Most people live in cities, most urban drivers know sitting in traffic.
5. Stop/start engines would also benefit air quality & reduce heat pollution where it sucks the most (well, due to cars)- next to jammed up urban traffic.
|
your point #5 is the ONLY reason it is done.
200 amperes x 12 volts = 2.4 kW, 2.4 kW for 10 seconds = 7 watt hours. BUT, you have to recharge the battery, between alternator and battery inefficiencies you are up to 30 watt hours.... this can ONLY come from energy that would otherwise be used to propel the car.
A diesel idling at (mb 300d) 0.6 litres an hour = 6.6 kW an hour = 110 watt hours for 1 minute idle.
If you work it out as 20 traffic light stops on a journey, each one for a full minute, you save around 2 kWh, or around a pint and a half of diesel.
but in the real world, your radio is running, your electric cooling fan may still be running, your heater / ac may still be running, and these are all sucking the battery down, so your real comparison is not 30 watt hours vs 110 watt hours per stop, but 60 or 90 watt hours vs 110, plus the increased wear and tear and load on starter, alternator, battery (only so many charge / discharge cycles in any battery) and suddenly it looks crap from an energy viewpoint.
Even emissions it only works if you ONLY measure emissions while waiting at the stop light.... you get MORE emissions on the way to the next stop light recharging the battery.