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Old 05-05-2013, 10:18 PM   #21 (permalink)
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Originally Posted by Occasionally6 View Post
I think that the gas Sky-Active (sp?) engines also run compression ratios around 14:1. Oddly enough, I have seen several sources that suggest that is close to the optimum ratio for efficiency before the losses start to outweigh the gains with higher ratios.
At higher compressions there are higher "pumping losses".

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Old 05-09-2013, 12:05 AM   #22 (permalink)
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At higher compressions there are higher "pumping losses".
In diesels?
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Old 05-09-2013, 11:13 PM   #23 (permalink)
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Not much FE savings with start stop

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Originally Posted by euromodder View Post
Many people shut off the autostart function though.

In the NEDC autostart is allowed, but in real life you'll never see the big gains it gets on NEDC - which has numerous phases at standstill.
These were introduced to simulate traffic: accelerate, brake, wait, ...
I just saw some real test data today from a tier 2 supplier. When running EPA city cycle, they only saw 3% max FE bump with start stop. So unless manufacturers are do some testing in a big city that maybe will show a more significant and marketable gain, and allowed to publish results on window stickers or marketing, I definitely now see why Mazda and others will not bring their start stop systems to USA.
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Old 05-10-2013, 08:23 AM   #24 (permalink)
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Originally Posted by WesternStarSCR View Post
I just saw some real test data today from a tier 2 supplier. When running EPA city cycle, they only saw 3% max FE bump with start stop. So unless manufacturers are do some testing in a big city that maybe will show a more significant and marketable gain, and allowed to publish results on window stickers or marketing, I definitely now see why Mazda and others will not bring their start stop systems to USA.
That also highlights a downside the EPA window stickers. If the manufacturers make changes that do affect real-world FE, but don't show up in the EPA test cycles, for all practical purposes it's as if it never happened.
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Old 05-10-2013, 09:05 AM   #25 (permalink)
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In diesels?
Yes. I've heard as high as 17:1 for a SI engine. I saw it as a footnote for the DOE testing on Ethanol/Methanol in a modified VW diesel engine. That particular engine had a 19:1 static compression ratio.
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Old 05-10-2013, 11:00 AM   #26 (permalink)
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Will the regen cycle on the Skyactiv-D cause it to get horrible fuel economy when it's in regen?
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Old 05-10-2013, 11:41 AM   #27 (permalink)
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Will the regen cycle on the Skyactiv-D cause it to get horrible fuel economy when it's in regen?
I can't image any way around it. Regen cycles require exhaust heat--that means the fuel energy goes into exhaust heat rather than the drivetrain.
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Old 05-10-2013, 12:30 PM   #28 (permalink)
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I can't image any way around it. Regen cycles require exhaust heat--that means the fuel energy goes into exhaust heat rather than the drivetrain.
Dave,

Do you think Mazda is mostly treating the regen cycle like that of the pre DEF (EPA 07) trucks prior to EPA 10 (just using rich fuel and heat since they do not use DEF)?

I wonder if regen cycle is included in EPA test cycle numbers for FE or not.

I know it was a big deal when Detroit Diesel got their FE back up in 2010 and 2013, after the EPA 07 hit they took for having to run high temp regens.
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Old 05-10-2013, 02:49 PM   #29 (permalink)
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Originally Posted by WesternStarSCR View Post
Dave,

Do you think Mazda is mostly treating the regen cycle like that of the pre DEF (EPA 07) trucks prior to EPA 10 (just using rich fuel and heat since they do not use DEF)?
DEF/SCR useage doesn't directly have anything to do with DPF regen cycles. DEF/SCR is for NOx, DPF is for smoke/particulate.

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I wonder if regen cycle is included in EPA test cycle numbers for FE or not.
No, it's not included. The EPA test is fairly short, and DPF regens typically only happen every few hours.
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Old 05-10-2013, 08:47 PM   #30 (permalink)
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Quote:
Originally Posted by WesternStarSCR View Post
Dave,

Do you think Mazda is mostly treating the regen cycle like that of the pre DEF (EPA 07) trucks prior to EPA 10 (just using rich fuel and heat since they do not use DEF)?

I wonder if regen cycle is included in EPA test cycle numbers for FE or not.

I know it was a big deal when Detroit Diesel got their FE back up in 2010 and 2013, after the EPA 07 hit they took for having to run high temp regens.
The FE increase of the SCR engines had little to do with regen cycles. EPA07-09 require in-cylinder NOx control, using ridiculous amounts of EGR and retarded timing, causing poor efficiency. Because EPA10+ engines take care of most NOx with aftertreatment (SCR), EGR flow can be reduced and timing/fuelling tuned for much better FE. Regen cycles did not change a whole lot for EPA10.

Aftertreatment fuel usage in the Cruze will depend largely on duty cycle. Low load city driving will require more aftertreatment fuel. Mostly highway usage will require much less aftertreatment fuel because of naturally higher engine out exh temps.

Typically in on-highway truck applications, overall aftertreatment fuel usage is only a couple percent of total fuel usage.

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