Brettus Turbo install thread
#276
Registered
The whole charge is not uniform; there is a higher concentration of fuel and air by the trailing plug (richer mixture) due to the sweeping motion of the rotor; then as the flame propagates out toward the leading plug - this takes a long time in our chamber - heat and pressure are pushing out to this leaner mixture (faster hotter burn); it will not be a smooth flame front consuming everything. Most likely the heat and pressure will cause the mixture in the leading area to explode uncontrollably = detonation.
#281
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I was hoping you wouldn't say that. Third opinion anyone?
#283
Illudium Q-36 Space Moderator
iTrader: (1)
Firstly, I thought the trailing plug only firing was a suggested possibility. Are you now saying that it was definitely happening? Secondly, this is about detonation, not about the rotor turning backwards (which to some extend has a tendency to happen anytime the timing is BTDC)
I was hoping you wouldn't say that. Third opinion anyone?
I was hoping you wouldn't say that. Third opinion anyone?
#285
Firstly, I thought the trailing plug only firing was a suggested possibility. Are you now saying that it was definitely happening? Secondly, this is about detonation, not about the rotor turning backwards (which to some extend has a tendency to happen anytime the timing is BTDC)
?
?
#288
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#289
Illudium Q-36 Space Moderator
iTrader: (1)
Finally, the long, narrow shape of the combustion chamber means the flame front has a long way to travel, and sometimes it doesn't make it all the way to the ends. Partially because the motion of the rotor sweeps all the condensed fuel to the back of the combustion chamber, there tends to be a pocket of fuel-rich gases near the trailing apex seal. This pocket of unburned gas turns into a spurt of HCs as it gets pumped out the exhaust. The side exhaust port helps tremendously here, for the simple reason that it closes before the trailing end of the rotor gets there. The pocket of fuel-rich gases simply get swept around into the next intake stroke for a second chance at complete combustion. In the aforementioned research engine, moving the exhaust port to the side cut hydrocarbon emissions by 35 to 50 percent!
It turns out that even in a well-balanced charge of fuel and air, there are highly localized "pockets" of varying mixtures at the "local level." By "local level" you should think of a bunch of little fuel molecules huddling together "over here" and "over there" in different places inside the cylinder as the piston is rising up towards top dead center and starting down. Some of these pockets may be so lean (or so rich) that they won't burn at all, some may be in the combustible range, and some may be perfectly mixed, "ready to go," so to speak.
1. We have nice cool induction air and fuel entering a cylinder;
2. The cylinder happens to have very hot walls. Those hot walls cause some of that nice cool induction air to start to heat up. And it doesn't all happen uniformly.
3. Further, shortly after the sparks go off, we have a couple of flame fronts, giving off lots of infrared heat, adding to the continuing heat load being absorbed by some of those little remote pockets of fuel and air that are waiting for the flame front to arrive and consume them;
4. The unburned mixture is experiencing a very rapid increase in pressure, because of two things: A) The piston is rising rapidly during the compression stroke; and B) the flame front combustion products are creating a huge increase in released energy and resulting bulk gas pressure, all of which is neatly measured on the pressure traces you see in the accompanying graphics.
5. At least some of those little "local pockets" of unburned combustion mixtures have exactly the right mixture of fuel and air to be just a hair-trigger away from exploding.
6. And … if the fuel is the wrong octane, or the spark advance was set too soon, or the manifold pressure was too high, or the cylinder head temperature was too high ... then one or more of those little "local pockets" of unburned fuel do just that ... they "explode."
If you want to know more - buy the book I mentioned earlier.
And for a Rotary with a misfire on the leading coils - the front HALF of the combustion chamber = Number 5.....
Last edited by Kane; 12-09-2008 at 12:58 AM.
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rob babicki (06-16-2021)
#290
Registered
Hey Kane - good on you man - seriously. Thanks for that reference on how the fuel can be concentrated near the trailing end of the chamber (albeit as a condensate). However still not obvious to me about that whole trailing plug issue. It's those cheap 'nose bleed' seats.
#291
Banned
iTrader: (3)
All these bits about pockets and detonation are interesting and important.
However, with a leading plug failure, that is not the issue.
Its all about the direction of the flame front and the relative motion of the rotor and leverage.
We fire the trailing some 15º after the leading in crank rotation, but think how many degrees in rotor motion the trailing is ahead of the leading.
However, with a leading plug failure, that is not the issue.
Its all about the direction of the flame front and the relative motion of the rotor and leverage.
We fire the trailing some 15º after the leading in crank rotation, but think how many degrees in rotor motion the trailing is ahead of the leading.
#292
Should have motor back tomorrow night and install over the weekend .
Yushi is going to sell me his blue injectors - I think they should go in the secondary position due to the high boost at low ish rpms from the turbo .
In the Greddy fix thread they talk about using them in the P2 position . What is the latest thinking on this ?
Yushi is going to sell me his blue injectors - I think they should go in the secondary position due to the high boost at low ish rpms from the turbo .
In the Greddy fix thread they talk about using them in the P2 position . What is the latest thinking on this ?
#293
Illudium Q-36 Space Moderator
iTrader: (1)
Should have motor back tomorrow night and install over the weekend .
Yushi is going to sell me his blue injectors - I think they should go in the secondary position due to the high boost at low ish rpms from the turbo .
In the Greddy fix thread they talk about using them in the P2 position . What is the latest thinking on this ?
Yushi is going to sell me his blue injectors - I think they should go in the secondary position due to the high boost at low ish rpms from the turbo .
In the Greddy fix thread they talk about using them in the P2 position . What is the latest thinking on this ?
With a Flash tuner or standalone you should be fine.
May be a few rich spots as they come online depending on latency.
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rob babicki (06-16-2021)
#297
Administrator
iTrader: (7)
quick turnaround on that engine!
#298
Finally Boosted!!!!!!!
My Secondary valve is set to open at about 2000rpm. I know because I can hear it click open and closed on a cold start when the RPMs are coming down.
#300
Banned
iTrader: (3)
This shouldn't really matter with the AP or the Interceptor as you can set the secondary valve to open at an earlier RPM, right? What would be the problem with putting larger injectors in these slots if the valve is set to open at an earlier rpm?
My Secondary valve is set to open at about 2000rpm. I know because I can hear it click open and closed on a cold start when the RPMs are coming down.
My Secondary valve is set to open at about 2000rpm. I know because I can hear it click open and closed on a cold start when the RPMs are coming down.
The onset of the injectors is tied to load, not RPM, so it is always possible to have the secondaries spraying where there is no forward moving air on applications that do not employ an alternate SSV opening schedule.