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Old 05-03-2021, 06:53 AM   #21 (permalink)
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We're kind of veering off topic since none of this is stuff is realistic DIY mods, but IIRC a problem with stratified charge is that the leaner areas don't burn well and the fuel there is sort of wasted. A higher energy ignition system, preferably that ignites the cylinder at multiple points, that can ignite a more homogeneous lean mixture is optimal.

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Old 05-03-2021, 08:21 AM   #22 (permalink)
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Quote:
Originally Posted by serialk11r View Post
We're kind of veering off topic since none of this is stuff is realistic DIY mods, but IIRC a problem with stratified charge is that the leaner areas don't burn well and the fuel there is sort of wasted. A higher energy ignition system, preferably that ignites the cylinder at multiple points, that can ignite a more homogeneous lean mixture is optimal.
The early Civic Hybrid used two spark plugs per cylinder for this reason, but oddly, the Insight (Honda's highest thermally efficient engine until the Clarity) did not.

~

I imagine that, past a just slightly lean, learn burn isn't providing more complete combustion of fuel, but is instead only reducing pumping losses by increasing load? Or are there other reasons it improves efficiency?
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Old 05-03-2021, 10:32 AM   #23 (permalink)
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I'm now testing with the catless headers.

- worse fuel economy
- little bit more power from 1500rpm to limiter, most difference is on the midrange; peak torque and after 6000rpm. Also more sharper throttle response while driving
- quiet, but only because the catalytic converter header was cracked, or actually in 2 pieces.

Why the worse fuel economy: probably because egr effect is not present the same way.
More power is not really a good deal for fuel economy, but I have an idea that I'm going to try if I can recover the fuel economy.

About 2 months ago I tried different, mostly intake cam timing at part throttle.
When I went way more advanced, at some point the engine started missfiring badly and had to retard ignition timing quite a lot.

It may have been because of too much egr effect, and did not like more ignition timing at all.
Before missfiring it was able to keep the speed as low as 6L/100km reading, when usually it's 8L or more when driving straight road (I use same road for testing) at 100km/h.

That _might_ work better with the better flowing catless headers. Don't know untill trying and testing.
Quote:
problem with stratified charge is that the leaner areas don't burn well and the fuel there is sort of wasted. A higher energy ignition system, preferably that ignites the cylinder at multiple points, that can ignite a more homogeneous lean mixture is optimal.
Maybe sort of "controlled" pre-ignition could solve this problem?
Something like spark-assisted compression ignition.

Ethanol could work better than gasoline.
Atleast with gasoline the engine would probably melt spark plug quickly.
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Old 05-03-2021, 11:34 AM   #24 (permalink)
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Quote:
Originally Posted by serialk11r View Post
We're kind of veering off topic since none of this is stuff is realistic DIY mods, but IIRC a problem with stratified charge is that the leaner areas don't burn well and the fuel there is sort of wasted. A higher energy ignition system, preferably that ignites the cylinder at multiple points, that can ignite a more homogeneous lean mixture is optimal.
Super lean is going to create areas that don't burn well one way or another. The stratisfied charge actually helps because the rich area creates a hot quick flame in one part of the cylinder that helps ignite the adjacent lean pockets.

Also some crazy efficient lean burning concept engines use the rich area to jet out into the lean areas by putting it in a sort of precombustion chamber with small holes that shoot jets of flames into the combustion chamber.

Some also do away with the stratisfied charge and use just a precombustion chamber that does the same thing I wonder if it would be feasible to make a spark plug replacement with all this. Basically you'd have a metal (or ceramic) that doesn't accept much heat (Tungsten?) then have a hole going down to several small holes at the "tip". Back where the sparkplug cable connects is where you'd have the spark plug inside the tube inside a pocket. When air and fuel is compressed into the "hollow spark plug" and ignites on the pocket on the end the flame would shoot down the tube and out the small holes and jet around inside the combustion chamber.

The problem would be it would likely only work at high loads as low loads wouldn't be able to compress fuel and air far enough up the tube to reach the part where the spark is created. But that could be fixed by using a second spark plug.

Quote:
Originally Posted by Juho View Post
... probably because egr effect is not present the same way.
...It may have been because of too much egr effect...
I wonder if you're going for a lean burn engine, why not hook the EGR circuit to the intake air filter? The excess air is basically inert like EGR in a lean burning engine anyway. You'd get the EGR effect performancewise while still having enough oxygen to burn up the fuel.
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Old 05-03-2021, 01:45 PM   #25 (permalink)
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I would if there was an actual egr valve.

What I meant by egr effect was just the catalytic converter headers that are made on purpose to flow very bad and exhaust cam timing goes retarted.

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Last edited by Juho; 05-03-2021 at 02:29 PM..
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Old 05-03-2021, 02:27 PM   #26 (permalink)
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One thing to keep in mind about the whole exhaust restriction thing is that it increases exponentially with flow. So what could cause a considerable restriction at high RPMs is likely not going to change a thing at low RPMs.
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Old 05-04-2021, 01:52 AM   #27 (permalink)
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Quote:
Originally Posted by Ecky View Post
The early Civic Hybrid used two spark plugs per cylinder for this reason, but oddly, the Insight (Honda's highest thermally efficient engine until the Clarity) did not.
I remember the early Honda fit resorted to dual-spark in the 1.4L 8-valve engine, while the 1.5L 16-valve one didn't.
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Old 05-04-2021, 12:19 PM   #28 (permalink)
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I don't generally like to just dump links, but I found this researcher's papers to be interesting reads:

https://www.researchgate.net/profile/Fanhua-Ma

Also a good write-up on a Miata forum:

https://forum.miata.net/vb/showthread.php?t=676260

This was also on topic:

https://www.semanticscholar.org/pape...756a975ffd5f1d

I think what I'm going to do is make a window of ~1.25 lambda from 1000-2000rpm 0-500mbar manifold pressure, tapering to 1.07 lambda up to 600mbar, 1.0 lambda from 600-800 mbar, then go progressively rich at higher loads.

Reading through the above links, what I'm gathering is that in these regions, I can expect to need only 2-3 extra ignition timing for every 10% leaner I run - so at, say, 1.25 lambda 1500rpm 400mbar, I'll have an extra 6-7 degrees of ignition advance.

I don't have any flat roads nearby or access to a load dyno, so I'm basically shooting in the dark with my timing numbers.
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Old 05-04-2021, 02:09 PM   #29 (permalink)
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Quote:
Originally Posted by Ecky View Post

I think what I'm going to do is make a window of ~1.25 lambda from 1000-2000rpm 0-500mbar manifold pressure, tapering to 1.07 lambda up to 600mbar, 1.0 lambda from 600-800 mbar, then go progressively rich at higher loads.

Reading through the above links, what I'm gathering is that in these regions, I can expect to need only 2-3 extra ignition timing for every 10% leaner I run - so at, say, 1.25 lambda 1500rpm 400mbar, I'll have an extra 6-7 degrees of ignition advance.

I don't have any flat roads nearby or access to a load dyno, so I'm basically shooting in the dark with my timing numbers.
That sounds like the right ballpark, but I wonder if you want to run lean at minimum load, the engine might misfire there. The biggest gain from lean burn happens at medium load anyways, since your throttle loss reduction is proportional to load and lambda - 1.
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Old 05-04-2021, 03:13 PM   #30 (permalink)
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Quote:
Originally Posted by serialk11r View Post
That sounds like the right ballpark, but I wonder if you want to run lean at minimum load, the engine might misfire there. The biggest gain from lean burn happens at medium load anyways, since your throttle loss reduction is proportional to load and lambda - 1.
I cruise down the highway at barely more than idle vacuum levels.


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