Idling or turning off the engine? 3

[pietro82]

Hi all,

I am aware that idling is fuel inefficient and a waste of fuel, but I guess that it is not always convenient to turn the engine off, since the turning on requires more energy than idling. So, I think that for long periods, turning the engine off is more fuel efficient than idling, but not for very short periods. Is there any study or paper that reports when it is more efficient to idle than turning off the engine?
Thank you so much.

Best regards,

Pietro

 

[GregLocock]

I agree entirely.

Cheers

Greg Locock


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[VEBill]

Reportedly, some Stop-Start vehicles have Integrated Starter Generators (ISG) which would seem to address many of these concerns.

Furthermore, when combined with electric hybrid drive, then of course the ICE Stop-Start concept becomes nearly transparent.

 

[3DDave]

I mentioned that the result could be seen in higher initial component cost. Looking at ISGs I believe that I am correct.

https://www.youtube.com/watch?v=YnLcP2fpEQ4

 

[dgallup]

Some vehicles like the RAM 1500 with 5.7l Hemi use a 48 volt mild hybrid system for the start-stop. So a conventional 12 V starter engages the flywheel for a cold start but after that the belt driven motor/generator re-starts the engine and adds 130 ft-lbs of torque to the bottom of the powerband. It does not increase peak torque because it's no longer active when the engine is turning at higher speeds. It handles charging both the 12 V battery and the 48 V lithium battery during decel. So you are definitely paying $1450 more for the system but it's completely optional.

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[SuperSalad]

malbeare,
How would oil flow while the engine is not running reduce wear? If this pump primed the oil lines immediately before starting, that might have some effect, by getting the oil circulating that little bit quicker. A dry start really isn't a thing though. There's always some amount of oil film on parts and it should be adequate to protect until the flow gets to where it needs to be.

Andrew H.

http://www.mototribology.com

 

[CWB1]

Prelube pumps do exist for engines in harsh environmental conditions and those picking up load quickly upon starting but the automotive cycle is fairly gentle and conditions rarely extreme in most markets.

 

[VEBill]

...higher initial component cost. Looking at ISGs...

Governments regulate tailpipe CO2 emissions, but they don't regulate embodied resources (such as "$1450" worth of optional ISG to save a wee bit of energy, with potentially dubious Eco-ROI).

 

[gruntguru]

ISG's and their mild hybrid role do a lot more and save a lot more fuel than the mere "stop start" function.

je suis charlie

 

[SomptingGuy]

Indeed, adding an ISG and a mild hybrid system to a gasoline-engined vehicle can tangibly improve the economy (albeit with high initial cost). But so can switching to a simple diesel engine.

Steve

 

[enginesrus]

I'm curious is there data on the longevity of start stop engines? Both CI and SI. How much start enrichment is applied?
Cat converter heat loss and HC emissions? I've heard of cases of cars starting when unoccupied, though that could be more of a remote start system fault.

 

[BrianPetersen]

In an engine stop-start situation, there are no more cold starts than without it ... stop-start only operates with a warm engine. So, there is no enrichment on start-up. Generally there is a mathematical temperature model of some sort in the ECU, so the catalyst works immediately (the internal parts of catalysts stay hot for quite a while when there is no flow through them). Indeed, there can be issues with people forgetting to turn the car off, thus leading to surprise engine restarts, because it was never actually switched off. Keyless pushbutton starting takes the blame for that one.

 

[dgallup]

SomptingGuy - It seems like "simple diesel engine" is an oxymoron these days with cats, particulate filters and DEF. Diesel seems to be on the decline and possibly on the way out for light duty. A number of inner city areas are banning them completely.

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[waross]

That was my first though as well, dgallup.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[SomptingGuy]

I agree dgallup. Who'd buy a new small diesel car these days? My last one (2004) was only Euro 3 and it had expensive bits on it that broke. Interestingly (and back to the initial topic), it was on its third starter motor when I got rid of it.

Steve

 

[RodRico]

I'm going to say the mere fact that so many automakers incorporate start-stop tells me there's some small gain to it. That being said, they don't really have to add anything to the engine to make it work, so it wouldn't take much of a gain to motivate them to incorporate it.

 

[RodRico]

I wouldn't count diesel out just yet. It's always held low market share in the US, but it still represents a significant share of sales in Europe. It's declining in popularity there, but industry analysts expect it to plateau soon. A key factor in this is that much of US oil is light crude preferred by gasoline refiners while diesel as opposed to the heavy crude preferred by diesel refiners. This is why diesel costs so much more than regular gasoline these days in the US... why go diesel when it's improved efficiency is offset by increased fuel cost at the pump?

 

[dgallup]

Interesting that diesel sales in Spain are still above 50%. Any idea why?

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[LionelHutz]

"How much start enrichment is applied?" - on new engines there is almost none, even on a cold start. The manufacturers have the EFI systems very well refined.

 

[GregLocock]

In many jurisdictions farmers and home furnaces access a substance that is remarkably diesel like but on which no or little excise is payable.

It may be that in less policed jurisdictions that diesels have an economic benefit to the owner not available to their gasoline burning competitors.

Cheers

Greg Locock


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[pietro82]

I have read that idling is detrimental for the engine life. Why?