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Old 10-22-2019, 12:16 PM   #11 (permalink)
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This touches on something I would love to see. What could be done as far as ICE efficiency if all the other rules and preconceptions were tossed. Like a 2 stroke, lean burn, diesel. I don't think the major players even play with things like this because they know the emissions make them a non starter. Never mind that sure it may pollute twice as much per gallon but if it travels 3 times as much per gallon isn't that actually better?

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Old 10-22-2019, 12:51 PM   #12 (permalink)
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Quote:
Originally Posted by Hersbird View Post
This touches on something I would love to see. What could be done as far as ICE efficiency if all the other rules and preconceptions were tossed. Like a 2 stroke, lean burn, diesel. I don't think the major players even play with things like this because they know the emissions make them a non starter. Never mind that sure it may pollute twice as much per gallon but if it travels 3 times as much per gallon isn't that actually better?
3x increase in efficiency isn't possible, and the emissions would be much more than 3x.

Anyhow, if we could build more efficient engines that pollute more, we'd just end up with more powerful cars that get about the same MPG, since people will almost always choose more power instead of more efficiency.
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Old 10-23-2019, 11:12 PM   #13 (permalink)
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Lean burn works a little bit better than cooled EGR, but there's ways around it. The Skyactiv-X I think can run at a lambda of 2.2 with significant EGR dilution which means around 70% of the gas in the cylinder is not being burned. To get there, it needs a supercharger or the mix wouldn't burn. For Euro 6 and whatever the next CARB standard is, it probably will need urea injection to pass.

IIRC with VW's SFI, they were able to run at lambda >3 by using the central direct injector to inject fuel into the piston bowl at the last moment. Much simpler than what Mazda came up with, but has the NOx problem AND a particulate matter problem (which I guess can be solved with a particulate filter), and I'm guessing it leaves more unburned fuel making it less efficient.

Another way to get very lean burn without HCCI is Mahle "jet ignition" as they use on the Mercedes F1 cars, or injecting diesel to ignite a homogeneous gasoline mix, both proven to produce very high thermal efficiency.

Slightly worse would be multi-point laser ignition, or using multiple spark plugs. Actually, the Chevy small block has only 2 valves per head, so theoretically there's plenty of space for more spark plugs.
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Old 10-24-2019, 01:59 PM   #14 (permalink)
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I could see it. The prius is only slightly more aerodynamic that the corvette with similar frontal area. Per Stanford the car reaches ~36% peak thermal efficiency at 2000 rpm. (think air pump n chart g/kWh).
If you could do it similar to the prius, boats, or airplanes, and have it tuned to have max efficiency at a x speed you could really take advantage of it.
Also, an interesting note about afr per NASA from 1930 ish on airplanes:

"with gasoline as a fuel, maximum power is obtained with fuel-air mixtures from 0.07 to 0.08 pound of fuel per pound of air; (3) nearly minimum specific fuel consumption is secured by decreasing the fuel content of the charge until the power is 95 per cent of its maximum value. Presumably this information is of most direct value to the carburetor engineer."

https://ntrs.nasa.gov/archive/nasa/c...9930091255.pdf

So basically tune the car to run at 2000 rpm at 70 mph at around 75-92% load and then lean it out.

I'd probably add that its centered from 1500-2000 RPM at almost the same efficiency.

I had a guy stay in my airbnb recently and he showed me his gm hp tuners on his laptop. From what I saw with that and it showing VE tables, and BSFC at each value I honestly think its doable. Also, you could then just delete the cats and delete the cat enrichment warmup process.
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Old 10-24-2019, 06:35 PM   #15 (permalink)
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I have heard that just plain direct injection is going to probably need DEF and a catalyst in the near future. This is why Fiat didn't go with direct injection on the Chrysler 3.6 V6 refresh that happened in 2018 I think.
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Old 10-25-2019, 03:06 AM   #16 (permalink)
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Quote:
Originally Posted by Hersbird View Post
I have heard that just plain direct injection is going to probably need DEF and a catalyst in the near future.
You only need DEF for NOx reduction if the engine runs lean. It's hard to imagine most car companies being okay with adding that cost.

What is true is that plain direct injection will probably require a particulate filter in the future, because stratified injection is so useful. Notably, Toyota used to use the side "fan spray" injector that only ran on the intake stroke, but has now switched to piezoelectric injectors that can spray multiple times (can spray at the end of the compression stroke to create a stratified charge).
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Old 10-25-2019, 10:09 AM   #17 (permalink)
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Originally Posted by serialk11r View Post
You only need DEF for NOx reduction if the engine runs lean. It's hard to imagine most car companies being okay with adding that cost.

What is true is that plain direct injection will probably require a particulate filter in the future, because stratified injection is so useful. Notably, Toyota used to use the side "fan spray" injector that only ran on the intake stroke, but has now switched to piezoelectric injectors that can spray multiple times (can spray at the end of the compression stroke to create a stratified charge).
How does the filter clean itself? I know you add fuel but I thought the purpose of a fluid was to make that process faster and more efficient.
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Old 10-25-2019, 10:50 AM   #18 (permalink)
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It basically uses the exhaust heat to catalyze the unburnt fuel "clumps" in the "DPf". Problem is the temp for this to occur is above typical aluminium melting points, so they add fuel somewhere. In a diesel you have masses of extra O2, I would think they add air somewhere in a gasser.
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Old 10-25-2019, 11:53 PM   #19 (permalink)
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Quote:
Originally Posted by Piotrsko View Post
I could be wrong, but Afaik, you need a DEF/ad blue assisted catalyst for nox.
If a gasser reaches the point of requiring SCR, I'd rather resort to a Diesel swap anyway...


Quote:
Originally Posted by Hersbird View Post
I have heard that just plain direct injection is going to probably need DEF and a catalyst in the near future.
In some cases it already requires. Every version of the 4th-gen Mercedes-Benz A-Class is now fitted with a particulate filter, including the gasser ones...

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Old 10-26-2019, 02:59 AM   #20 (permalink)
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Do gassers suffer unburnt fuel causing particulate pollution? I thought that was only a problem for diesels.

I wonder if there's a way to utilize the electric portion of a hybrid drive-train to keep super efficient engine designs in their regulation compliant pollution zones? For instance if it's heavy loads that cause it to fall out of compliance, just eliminate heavy loads and compensate with electricity for the short duration of accelerating or climbing a hill.

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