TURBO BOOM, Pic inside, what might have caused this?

[Scotts87LX]

I will have to save some of the other characteristics for burn rates for a little later, time for dinner.   

-Rob

Wow, that must have been some dinner 

[ford-swap]

More just waiting to see if someone still had interest. But yes, it was a good dinner

Expect something fairly shortly.

-Rob

[Scotts87LX]

More just waiting to see if someone still had interest.
Expect something fairly shortly.

-Rob

Yup, I'm still very interested. 

[Bellman Jeff]

More just waiting to see if someone still had interest. But yes, it was a good dinner

Expect something fairly shortly.

-Rob

I'm lurking in the shadows, soaking it all in  ..

[ford-swap]

Ok, so now why does timing requirements (may or may not) change with rpm and VE...

As already stated, the flame speed is very much dependent on the turbulence inside the chamber. If there is more turbulence the flame speed is increased. This is a fact of combustion theory, but how we generate the turbulence is a fluid mechanics problem. The physical interaction between the piston and the cylinder head (squish or quench, though I don't like the term quench in this case) is the process that converts large scale motion in the chamber to small scale turbulence. Image the cylinder at BDC on the intake stroke. Picture the flow inside the cylinder as a tumbling flow (the mixture is doing a barrel roll as it enters from the intake port). So the entire length of the cylinder, there is this tumbling flow. Now, as the piston moves upward, the tumble gets 'squished' as piston removes volume from the chamber. Lets assume there is no loss of momentum through viscous damping. Thus the flow goes from making rolls of 4" tall at BDC, to rolls of 0.4" tall at TDC. If a figure skater is spinning with their arms out, and then pulls them in, they increase in rotational speed from the conservation of momentum. ie big roll spins slowly, smaller roll spins more quickly.

This is what occurs as the piston reaches TDC, it is crunching the large scale motions in the chamber, into smaller, higher frequency motions. We can go into vortex theory and the like, but it gets nasty. Despite the popular misconception, the squish of an engine rarely has great effects on generating turbulence, but it often works much better at converting large scale turbulence into small scale turbulence that is effective at imparting rapid burning of the air/fuel. So what does all of this have to do with rpm? Well, imagine filling up a bucket with a nice slow trickle of water, or with a fast stream of water. The slow trickle has little turbulence in it (low rpm), and the fast jet has considerable turbulence (high rpm). As the rpm increases, the sources of turbulence in an engine go up, and thankfully they are almost linear with engine speed. So if we double the engine speed, we get approximately twice the turbulent kinetic energy, and thus the mixture burns about twice as fast. However, if it doesn't exactly increase linearly, we have some timing curve that doesn't keep the lead angle constant...

The VE dependence on timing comes down to infuential factors and their effect on flame speed. Mixture AFR, EGR level, mixture temperature, and mixture pressure play roles in this. For typical hydrocarbon fuels, the laminar (laminar means with no turbulence) flame speed is a function of AFR. Typically the highest flame speed is obtained with a lambda of 0.8-0.9 (for gasoline this it is an AFR of about 13). This means that the least amount of timing will be required at this mixture, to get the mixture to burn as quickly was we would like. Any richer, or leaner than this, and the flame speed drops off fairly sharply. Since typical light load AFR's tend to be approximately 14.7:1, the timing requirement is going to increase compared to the WOT case, where the desired AFR is ~13.

More coming soon. Discuss 

-Rob

[Don Bailey]

Ok Rob, I'll see your quench and raise you a RPM dependent question.  Why are some chambers designed for high RPM?  And for the double or nothing, want to address wet flow?

[ford-swap]

I'll see what kinda stuff I can come up with.

Still waiting on the 11th?

[Don Bailey]

Yep and its getting ugly quick, send beer.

[Outlaw5.0]

This is usually about 7-10* after TDC for the point at which 50% of the mixture has been consumed.
-Rob

100 percent correct. With the cylinder pressure equipment I use at work, we use the 50 percent burn rate and location of peak pressure to set MBT or MST.

[ford-swap]

Bill (?),

Who's stuff do you guys use? We have A&D (formerly MTS Powertrain) CAS, along with Adapt and Atlas. I write my own stuff anyway, all I use the equipment for is crankangle (0.1deg) datalogging.

As far as I know everybody uses CA50 (point at which 50% of the mass fraction in the cylinder is burned) to determine combustion phasing.

-Rob

[Outlaw5.0]

Bill (?),

Who's stuff do you guys use? We have A&D (formerly MTS Powertrain) CAS, along with Adapt and Atlas. I write my own stuff anyway, all I use the equipment for is crankangle (0.1deg) datalogging.

As far as I know everybody uses CA50 (point at which 50% of the mass fraction in the cylinder is burned) to determine combustion phasing.

-Rob

I use mainly the DSP ACAP, although we do use CASS also, just not as much. I use the EACA50, CA50 and so. I look at the peaks, and average of the peaks. Low #'s are good for sorting out issues. Max power is seen at 5.0-7.0 50 percent burn on the post process report depending on rpm, load, and cam placement(Variable cam timing).

[ford-swap]

Gonna be in town during SAE this year? I have to present a paper there this year. Anyone up for beers? 

[Outlaw5.0]

Sure.

[Bellman Jeff]

 Despite the popular misconception, the squish of an engine rarely has great effects on generating turbulence, but it often works much better at converting large scale turbulence into small scale turbulence that is effective at imparting rapid burning of the air/fuel.

-Rob

I'm going to have to chew on that one for a while.. Cause over the last 20 years,  I've been sold on the concept of squish forcing the mixture to the center of the combustion chamber at supersonic speed, as being a great creator of turbulence..

Not trying to get off track.. But how is it that too large of a squish clearence, can make an engine more prone to detonation.. Even with less compression..

[Don Bailey]

Gonna be in town during SAE this year? I have to present a paper there this year. Anyone up for beers? 

You are presenting?  I haven't been to the congress in some time, hmmm better check my status.

[Selder]

Your picture isn't really clear enough or large enough to too much detail but it is possible to have wheel failures such as that without excessive EGT or foreign object damage (FOD). Blade can fail from high cycle fatigue and cause damage similar to what is seen on your wheel. To do this you would have to be operating the turbo in a overspeed condition. Unfortunately in the aftermarket workd of turbochargers there is rarely any attention paid to compressor or turbine speed limits. The compressor is at least easier to predict because we typically have a compressor map to look at. The turbine is worse since rarely does anyone even look at one (if they're even available for most wheels). It's possible to spec a turbo with a compressor wheel that is capable of say 130kRPM but the turbine wheel is only goo to 110kRPM. Yet if the turbo is matched by the compressor and that match dictates 110kRPM turbo speeds you can very easily fail the turbine and not even know why.

I'm not saying that this is what nescessarily what happened but it is a possibility if you can't find any FOD and you are confident in your tune.

Steve

[ford-swap]

I'm going to have to chew on that one for a while.. Cause over the last 20 years,  I've been sold on the concept of squish forcing the mixture to the center of the combustion chamber at supersonic speed, as being a great creator of turbulence..

Not trying to get off track.. But how is it that too large of a squish clearence, can make an engine more prone to detonation.. Even with less compression..

A close squish clearance is still key to good performance, just the mechanism is often not what people think. For a large number of applications, the squish jets come too late in the cycle to have significant effects on the combustion. However, they do make good surfaces for this crunching of turbulence that I have talked about. Again, every application/cylinder is different. Look how little timing most pent roof 4valve/cyl stuff needs, and very little if any squish surfaces.

You are presenting?  I haven't been to the congress in some time, hmmm better check my status.

Come on down  Three names on the paper, and I have a feeling it's going to be me doing the presenting. If stuff goes well I might be in Chicago for another SAE conference in October I believe.

[BottleFed70]

I think I'm going to have to re-read some of these posts to absorbe all of this.  Great info!

So while I have the experts here.  What do you think of this guy and his combustion chamber grooves stuff?
http://somender-singh.com/content/view/7/49/

[Don Bailey]

Up to this point the focus has been largely on chamber shape.  I think its time one start to address piston design.  The CUP boys have tested all the designs.  What's interesting is to see how certain shapes change the mixture motion and why that was beneficial at certain RPM ranges.

[Scotts87LX]

So Don, what about that "groove" thingy? I've personally not heard of it. I'm 43 years old and being somewhat "old school" I was always taught to smooth anything that even resembles a sharp edge in a combustion chamber that could be considered a heat riser that could cause detonation. Also, I was also taught that if you "tighten up" the quench area it dramatically reduces the opportunity for detonation by forcing the remaining mixture back toward the plug when the piston reaches TDC.

This is not a "performance" engine, but a decent example: I had a Chris Craft inboard ski boat with a small block chevy and it always pinged unless you reduced the timing to a point were power started to noticably suffer. After years of my adding octane booster (a band aid fix) it finally beat the bearings out of it. When I rebuilt it, I applied a little drag racing knowledge to it and had the block decked to put the piston .002" down in the cylinder and with the .038" thickness of the Fel Pro Gasket (.040 piston to chamber quench area clearance), apparently that was all that was needed to fix the problem. From that point forward, I was able to run 38 degrees total advance on regular gas with no evidence of detonation. The reasaon I would site this as a good example is the fact that a direct drive (straight inboard) boat is about as close to "dyno loading" an engine as you will find in a daily usage vehicle.

Obviously any engine builder worth his salt already knows to do what I did in the boat engine, but I thought since detonation had come up in this dicussion, the example was worth mentioning.

I've never heard of "the groove" and since I'm admittedly NOT a technical expert on the subject of the combustion process, I'm the wrong person so comment on it. However, I'd love to hear Don and Rob's comments/thoughts on it.

Thanks,
Scott Russell

[Don Bailey]

Scott,

When I see unconventional things such as a groove I think there is a larger problem.  While the groove solution may work, and in his application may be the only solution.  I am not disputing his results.  I simply think there was a larger problem that wasn't addressed.  Most of the time wet flow analysis will show you the basic things to clean up.  The SBC chamber in the picture leaves alot to be desired.  I would think moving the runner or changing the chamber shape would be a better option.  Even the OEM's are moving toward enhancing mixture motion and directing the mixture.  Look at the fins or directional devices in modern heads such as the LS1 family of engines.  GM is most certainly attempting to direct the mixture and introduce mixture motion at low RPM.  Which leads me to my previous post about high RPM chambers and low RPM chambers.  Mixture motion changes with RPM.  Swirl and tumble are good for street engines and almost never present in race engines.  Finally, your example of the Chris Craft is a perfect example of an overly conservative approach causing undesired results.  If you put the rings too low bad things happen.

[Robert1320]

Don and Rob,

Thanks guys.  Lots of great information.
Thanks for hangin' out!

Someday I need to buy both of you a couple of adult beverages!
 

[TurboShortBus]

I think I'm going to have to re-read some of these posts to absorbe all of this.  Great info!

So while I have the experts here.  What do you think of this guy and his combustion chamber grooves stuff?
http://somender-singh.com/content/view/7/49/

Let me know when Hendricks engines start showing up at Daytona with grooved chambers...then, I'll know that there's something to it.  However, I'm always leery of "solutions" that seem to be more like snake oil than anything else...just like mid-lift rockers...

Mark

[slowfox]

Don and Rob,

Thanks guys.  Lots of great information.
Thanks for hangin' out!

Someday I need to buy both of you a couple of adult beverages!
 

+2 on that

You guys are great. This type of tech is what keeps me from sleeping at night. I'll be dead tired and can't keep from laying there and cycling theories and ideas through my head. The way I rock myself to sleep LOL.

Thanks
Eric

[Scotts87LX]

Don and Rob,

Thanks guys.  Lots of great information.
Thanks for hangin' out!

Someday I need to buy both of you a couple of adult beverages!
 

   I will 3rd that. As I mentioned in my post "fact or myth" does advancing a cam help get a turbo motor "on the converter" more quickly, I really think you two guys lend a great technical credibility to this site and I think we should all be grateful to have the benefit of your expertise. I know I am.