LARGER QUESTION:  It is obvious to me that a LOT of heat was generated to melt the rubber plugs on BOTH sides of the rotor.  Does anyone care to venture a guess as to why that rotor was so much hotter than the other?  The EGTs were within a few degrees most of the time.  I will double check the oil jet that cools the rotor tomorrow.

The three piece seals are more trouble prone than the two piece. I would go to two piece 3MM Tracy seals. The recut of the grooves to 3MM will remove any wear problems.

 

It looks to me like a detonation episode. However the look of the pieces should be more granular as in a stress fracture, unless the engine ran for some time after the failure. Once the compression goes down the detonation problem becomes less likely to re-occur and looking at gages will show nothing.

 

 The rear housing runs hotter all of the time. Detonation is charge temperature dependant. This is very hard to do in a NA engine unless the coolant temp has been very high. This is also what happens when all of the air is not removed (very hard to do) an engine.

 

In turbo engines with the boost up it is common. Boosted engines change compression ratios and displacement all of the time.

 

Failures in the rear housing are far more common at high power settings including failed dowel tubes once over 450 HP. The housings are twisting in the opposite direction from the crank. And detonation helped along from the temp difference in the housings.

 

If you have two or more plugs in any engine you have filled in one of the blocks in the quiz on how can I make this pig detonate.

 

An ignition event that occurs after the planned (timed) ignition and remote from the first plug firing. So if there are two plugs, and they both fire at the same time, then there will be a flame front collision every time, that is of little note. My opinion is that the bigger the spread between leading and trailing the worse it is.

 

 If the rotor housing is overheated and the oil temp is high (rotor face temps controlled by oil temp) then the stage is set for an event. Detonation will occur remote from the first plug to fire and usually closer to an apex seal. By the time the overheated mixture is compressed into the corner over a seal and it goes off before the flame front can get to it, it is not the smooth slow  flame front like burning a thin layer of leaves on the ground. It is a shotgun blast.

The Lambda sensor can hear it. You can hear it. You dads pickup truck did it all the time.

That tinkling sound going uphill in top gear. it can shatter an apex seal like glass.

 

Note that Ken disables his trailing ignition during his nitrous shot. Why, do you ask?

 

To eliminate detonation.

 

I am distressed by reports of high coolant temps and oil temps on climb out going unchecked and being done with regularity.

 

If you run across the freeway often enough, eventually you will be killed. It is so easy to avoid.

 

Intake the coolest air possible. Maintain acceptable operating temps, oil and coolant.

 

Tune climb power to rich of best power. Why does a O-550 use 23 GPH to take off and climb out, and then lean to 12 GPH for cruise at the same RPM? Fuel cooling and lower flame front speed, and lower CHTs.  

 

In a boosted street engine, the controller snatches away ignition advance with each Lambda hit. Is there a clue here?  

 

The highest heat is right at the best power setting. (just rich of peak EGT). So if it hurts when you do that.....don't do that. Make the transition from climb mixture, richer than best power, to cruise mixture, leaner than 50 degrees lean of peak power, quickly, so as not to spend many RPM at (or even near) best power. Or have one controller for takeoff and climb and the other for cruise.

 

Since intake air temp is the culprit, perhaps insulated the intake runners is in order. Or a blast tube blowing on them. Intake air temp includes heat of compression in the chamber. That is why boosted engines are more likely to detonate. That is also why they have an inter-cooler to remove heat from the intake air. That is also why they inject water at high boost numbers. Or water and alcohol in big radials at military power.

 

High compression rotors? more likely than lower compression rotors. (because the heat of compression is higher)

 

Ignition advance later (less likely) ignition advance sooner (more likely). Note that the controller takes out advance when the Lambda sensor hears detonation.

 

Adjust advance to show some percentage of RPM below max for any situation. A 13B makes more power right up to 39-40 degrees of advance, but it adds a ton of extra heat along with a small amount of extra power. But power it does make, and if you just watch for more RPM as you advance the timing, you will tune for way too much advance, and more heat than you can dispose of. 

 

Keep in mind that flame front speed in feet per second has a time function. So?

 

Unless there is one of those emergencies where real short engine life is not going to be a factor, roll in that throttle slowly. Detonation is more likely at high load lower RPM, than at high load high RPM.

(remember dads pickup) The propeller is always in top gear.

 

 

We raced for years on 20-22 degrees total and made good power up to 9,000 RPM. That is on crap for gas. On 100LL you can go well above that in a 13B, maybe 26-28 degrees. If you get a dose of car gas with alcohol in it, remember that for any situation it is leaner than 100% gasoline.  

 

I have fried more than a few of these. It got too expensive after a while so I quit doing it.

 

Lynn E. Hanover