# Regen cycles in gassers?



## Taxman (Aug 10, 2017)

I was reading old threads, and saw mention of the fact that the only reason to run a DI injector with the exhaust valves open was to heat up the catalyst. (much like the diesels dump fuel out the exhaust to incinerate the soot in the DPF)

Do our LE2s do that?
Is that why my MPG sucks for the first 10-12 miles in cold weather, the computer is dumping excess fuel into my engine for the purpose of blowing it out the exhaust? Is that contributing to oil dilution?


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## Fireworks234 (Jan 4, 2018)

That would explain why my fuel economy is terrible on my drive to work and back but good any time I leave town.


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## Snipesy (Dec 7, 2015)

Fuel isn’t injected with the exhaust open. Period. Not in diesels. Not in gasses. I’m not sure where that idea comes from. That’s not how post injection works.

Yes there is a warm up procedure for basically all modern gas engines. It changes the tuning to make things less efficient and hotter, but does not “spray fuel” into the exhaust. Diesels also do this but you can do more with EGR and a higher flash point.


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## Fireworks234 (Jan 4, 2018)

Snipesy said:


> Fuel isn’t injected with the exhaust open. Period. Not in diesels. Not in gasses. I’m not sure where that idea comes from. That’s not how post injection works.
> 
> Yes there is a warm up procedure for basically all modern gas engines. It changes the tuning to make things less efficient and hotter, but does not “spray fuel” into the exhaust. Diesels also do this but you can do more with EGR and a higher flash point.


I'll be honest I didn't think it was spraying fuel in the exhaust but during the warm-up I do feel like it's killing my fuel economy and not just because the engine is less efficient when cold. My point was more about the duration of time of the warmup period being ten miles vs just until coolant temp is up to normal.


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## WillL84 (Aug 5, 2019)

Well engines naturally run way more rich when it's cold, it's just a necessity. They'll lean as the engine warms but then if you have cold air coming in then the cold air has more oxygen which requires more fuel to burn properly. Cars make more power in the winter but use more fuel, that's just the way it is


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## Merc6 (Jun 8, 2013)

Open loop vs closed loop. Some tuners for other cars can change when it happens based on petal position for power vs FE. You also have to take into account winterized fuel in areas where you see...winter.


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## Taxman (Aug 10, 2017)

Mine goes closed loop within 1/2 mile. I hit the freeway at 7 miles, MPG picks up long before the freeway in summer, 3-6 miles after entering the freeway in winter.


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## MP81 (Jul 20, 2015)

It's just because it's cold out. Colder air = denser, meaning more fuel is required to maintain the designated AFR. Winter-blend fuel has less energy/volume, therefore _even more_ fuel is required to accomplish this goal. And then they do run slightly richer to heat the cat up to be more efficient, correct - just not via a separate injector.


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## Barry Allen (Apr 18, 2018)

Snipesy said:


> Fuel isn’t injected with the exhaust open. Period. Not in diesels.


It is. This is how modern diesel engines regenerate (burn the soot out of) the particulate filter. Extra fuel is injected during the exhaust stroke and is burned in the catalyst.

This happens in diesel engines that do not have a dedicated fuel injector in the exhaust stream.


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## MRO1791 (Sep 2, 2016)

Barry Allen said:


> It is. This is how modern diesel engines regenerate (burn the soot out of) the particulate filter. Extra fuel is injected during the exhaust stroke and is burned in the catalyst.
> 
> This happens in diesel engines that do not have a dedicated fuel injector in the exhaust stream.


I believe only some of the 6.6L Duramax diesels did the injector in the exhaust (and that to avoid fuel dilution issues into the oil), but most diesels do post injection in the combustion chamber that goes out with the exhaust stroke to drive a regen, and keep DPF temps up (not only during regen from what I've observed). 

That said, definitely not a factor to the OP and gassers.. for gas engines it's a combination of open loop (rich when cold) and winter fuel with higher ethanol blend (which is less energy/volume), and both lower MPG, and most when cold. It's also true that gas emissions are set up for rapid warm up of the catalyst, because the majority of gas engine emissions are at cold start, the sooner it gets up to temp, the lower the tailpipe emissions, and you can bet that will trump low MPG concerns on a cold engine as far as EPA is concerned.


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## Barry Allen (Apr 18, 2018)

MRO1791 said:


> winter fuel with higher ethanol blend


Winter gasoline blends typically have lower ethanol blends due to the lower vapor pressure of alcohol. 

E85 fuel blends used to be lowered to E70 during winter because of cold start problems, and now the EPA has allowed E85 to be as low as E51. My cousin has a Ford Ranger with the Vulcan engine that he exclusively fuels with E85 and I can remember it having horrible starting problems in really cold weather. It's somewhat better now but still has problems, I think because the engine is aging. A couple years ago he installed a block heater to make things much easier (he parks outside, so no warm garage).

You do get about 2% higher energy content with summer blend gasoline, though. The higher RVP requirements in winter means you lose some of the "heavier" components in gasoline that provide more energy. It's actually very similar to how winter diesel gets thinned out to be closer to #1 diesel than #2 diesel like you'd fuel up with in summer.


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## MRO1791 (Sep 2, 2016)

Barry Allen said:


> Winter gasoline blends typically have lower ethanol blends due to the lower vapor pressure of alcohol.
> 
> E85 fuel blends used to be lowered to E70 during winter because of cold start problems, and now the EPA has allowed E85 to be as low as E51. My cousin has a Ford Ranger with the Vulcan engine that he exclusively fuels with E85 and I can remember it having horrible starting problems in really cold weather. It's somewhat better now but still has problems, I think because the engine is aging. A couple years ago he installed a block heater to make things much easier (he parks outside, so no warm garage).
> 
> You do get about 2% higher energy content with summer blend gasoline, though. The higher RVP requirements in winter means you lose some of the "heavier" components in gasoline that provide more energy. It's actually very similar to how winter diesel gets thinned out to be closer to #1 diesel than #2 diesel like you'd fuel up with in summer.


Interesting, but I was referring to regular unleaded, I don't think any cruze gasser was made for E85, that I know of. Found an interesting article the expands on your point about winter vs. summer, but does not mention ethanol blended into the fuel. https://newsroom.aaa.com/2013/06/what-is-the-difference-between-summer-and-winter-blend-gasoline/


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## MRO1791 (Sep 2, 2016)

Found it. E10 gasoline exceeds RVP in many areas for summer fuel, so in many places they reduce Ethanol blend in the summer, to reduce RVP. That was what I was referring to, for regular unleaded. https://www.caranddriver.com/news/a15339380/the-vapor-rub-summer-versus-winter-gasoline-explained/


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## Barry Allen (Apr 18, 2018)

MRO1791 said:


> Found it. E10 gasoline exceeds RVP in many areas for summer fuel, so in many places they reduce Ethanol blend in the summer, to reduce RVP. That was what I was referring to, for regular unleaded. https://www.caranddriver.com/news/a15339380/the-vapor-rub-summer-versus-winter-gasoline-explained/


That's interesting. I assumed the 10% ethanol was year-round for standard gasoline blends. Now I see lots of pumps selling E15 (usually slightly cheaper) for any cars newer than about 2007. I wonder if those fuel blends change with the seasons.

I know California has very specific fuel blends to the point that all their diesel fuel is 53 cetane, and a lot of Texas requires 48 cetane. I know long-haul truckers that relentlessly complain about CA diesel fuel prices! Now I see their gasoline is specific as well, explaining a lot of the cost difference there.


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## Snipesy (Dec 7, 2015)

Barry Allen said:


> It is. This is how modern diesel engines regenerate (burn the soot out of) the particulate filter. Extra fuel is injected during the exhaust stroke and is burned in the catalyst.
> 
> This happens in diesel engines that do not have a dedicated fuel injector in the exhaust stream.


Really for the average person or tech the details don’t matter. So if that makes sense for you really no reason to change it.

Every modern diesel does post injection shortly after the main injection. I can think of a few issues with doing it later but frankly I don’t even know. It’s just never been done before.

The big thing really comes down to mixing. Optimally it would be nice if fuel and air mixed perfectly and it all just combusted perfectly instantly but that is not the case. The mixture is poor and the combustion process takes a long time as fuel flows around the cylinder. A big objective of pilot injection and a bit of post injection directly deals with this issue. Better mixing, less emissions.


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## Barry Allen (Apr 18, 2018)

Snipesy said:


> The big thing really comes down to mixing. Optimally it would be nice if fuel and air mixed perfectly and it all just combusted perfectly instantly but that is not the case. The mixture is poor and the combustion process takes a long time as fuel flows around the cylinder. A big objective of pilot injection and a bit of post injection directly deals with this issue. Better mixing, less emissions.


Diesel fuel can never truly be mixed perfectly and combusted perfectly. 

Early diesels and into the 1960s with locomotive engines just assumed that you'd be throwing some of the unburned fuel out of the exhaust in the form of soot. These were industrial engines running on a cheap fuel that was essentially a waste product from oil refining.

We've spent the past 20+ years bringing the quality of fuel up to a better specification, and also vastly increasing injection pressure and atomization to get a much finer mist of fuel sprayed into the combustion chamber. Still, the nature of diesel combustion is a diffusion flame that leaves soot as a byproduct. That, and combustion is deliberately tuned to reduce NOx production at the expense of more soot generated.


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