High EGT vs normal CHT and TIT

[Stetson20]

Any thoughts from the community? I'm showing EGT approx 200 deg higher than CHT and 100 deg hotter than TIT. My A&P suggests switching probes to see if the discrepancy moves with the probe.

Pic attached.

[kortopates]

Was the EGT normal before going to high power? if not it won't be a probe issue.
More likely it could be an ignition or mixture in the form of partially blocked injector. But can eliminate either on picture.
Share your data from Savvy here.

But since you say normal CHT, a blocked injector would raise CHT while ignition would lower CHT.

[Stetson20]

Paul,

I just recently got the airplane back from panel upgrade and have not gotten on the Savvy program yet. This is literally taken on my 2nd flight in the plane since new panel and just-installed engine monitor. Making the call to Savvy Monday. I have Garmin Pilot, but still trying to figure out how to sync the program to my GI-275.

Unfortunately I didn't have the presence of mind to take more pics at different power settings. I was doing an orientation flight, learning the autopilot, gps and engine monitor systems..

Roy Millwood

[Shadrach]

Dead plug would be my first guess. Nothing wrong with doing it in cruise mag check to verify everything is firing provided you don’t have squeamish passengers on board.  It may not show up in a mag check on the ground. I’ve had plugs that fire fine at run up power but drop out on takeoff, or in cruise

[A64Pilot]

44 minutes ago, Shadrach said:

Dead plug would be my first guess. Nothing wrong with doing it in cruise mag check to verify everything is firing provided you don’t have squeamish passengers on board.  It may not show up in a mag check on the ground. I’ve had plugs that fire fine at run up power but drop out on takeoff, or in cruise

Or clogged injector, but a mag check will certainly find a dead plug.

The higher the cylinder pressure the harder for a plug to fire, same of course with the ignition system.

Look under compression pressure for the explanation.

https://www.denso.com/global/en/products-and-services/automotive-service-parts-and-accessories/plug/basic/spark/condition.html

[carusoam]

Way cool!

We get to see a GI275 engine monitor in action!

 

kind of odd that the CHT doesn’t show a higher or lower value… to match with the usual challenges…

A blocked fuel injector usually stands out in a gami spread… as that cylinder will peak early…

A dead plug will definitely bump the EGT up noticeably, but usually has a small sympathetic drop in CHT…

 

Roy,

if able…

upload the data to Savvy,

press the share button

post link here…

 

you have some really sharp eyes following this thread.

 

and others that may be interested seeing the GI engine monitor in action!

Seeing the run-up data and inflight mag test will be interesting…

Best regards,

-a-

[Stetson20]

44 minutes ago, carusoam said:

Way cool!

We get to see a GI275 engine monitor in action!

 

kind of odd that the CHT doesn’t show a higher or lower value… to match with the usual challenges…

A blocked fuel injector usually stands out in a gami spread… as that cylinder will peak early…

A dead plug will definitely bump the EGT up noticeably, but usually has a small sympathetic drop in CHT…

 

Roy,

if able…

upload the data to Savvy,

press the share button

post link here…

 

you have some really sharp eyes following this thread.

 

and others that may be interested seeing the GI engine monitor in action!

Seeing the run-up data and inflight mag test will be interesting…

Best regards,

-a-

Tomorrow I'm taking it up again. I will attempt to connect the GI-275 to Garmin Pilot. I have the Garmin Pilot subscription, and hope to be able to download the data after the flight.

Edit- I don't have the Savvy subscription yet. It's on my "to do" list. Now moved up in priority. I'll call them Monday.

[Shadrach]

1 hour ago, A64Pilot said:

Or clogged injector, but a mag check will certainly find a dead plug.

The higher the cylinder pressure the harder for a plug to fire, same of course with the ignition system.

Look under compression pressure for the explanation.

https://www.denso.com/global/en/products-and-services/automotive-service-parts-and-accessories/plug/basic/spark/condition.html

Which is why the “1700rpm run up” mag check only finds the worst of the worst. 

[carusoam]

1 hour ago, Stetson20 said:

Tomorrow I'm taking it up again. I will attempt to connect the GI-275 to Garmin Pilot. I have the Garmin Pilot subscription, and hope to be able to download the data after the flight.

Edit- I don't have the Savvy subscription yet. It's on my "to do" list. Now moved up in priority. I'll call them Monday.

No subscription required…

To upload the data and see graphs…

 

Subscription gets you to the next more important level…. Serious eyes looking at your data…

See how far you can get.

I bumped into challenges just getting the data out of the box the first time…

 

Best regards,

-a-

[Stetson20]

Yesterday I was able to get the GI-275 to link to my iPad and Garmin Pilot. Didn't go fly. Today we have a cold front with low ceilings and icing over most of Michigan. I will have Savvy data available on my next flight (crossing my fingers) once the weather improves.

Did any of y'all notice what's wrong/weird/different on my display? Most of my time is flying turbine engines (military/airline) so I didn't notice the discrepancy, but a very experienced GA/freight/corporate friend went up with me and noticed it right off the bat- my MP and Prop RPM indicators are swapped! That's also on my list to address when I take my plane back to the avionics shop when the weather cooperates...

[kortopates]

1 hour ago, Stetson20 said:

my MP and Prop RPM indicators are swapped!

In their order? That should be a config setting.

You should be able to download all your stored flight data by connecting a USB memory stick to the USB port, which should be hanging below the panel somewhere if you haven't seen it yet. 

[Stetson20]

I'll look for the USB port. Yes, the MP and Prop RPM are flip flopped from the actual controls (not a big deal, but distracting).

I agree it's probably a config setting. I need a GPU so I can sit in the plane and fiddle with the new equipment without worrying about running my batteries down! Along with the air compressor, shop tools, and 1000s of other support equipment and materials I should have!

[Fly Boomer]

On 10/15/2022 at 1:50 PM, A64Pilot said:

mag check will certainly find a dead plug.

Depends on your definition of "dead."  Sometimes okay up to a certain ICP, but not happy when higher.

[Fly Boomer]

10 hours ago, Stetson20 said:

experienced GA/freight/corporate friend went up with me and noticed it right off the bat- my MP and Prop RPM indicators are swapped!

That's funny.  Half the pictures of the EDM JPI series I have seen are also reversed.  Some show the conventional order, so I suspect it's an option with Garmin as well.

[Stetson20]

On 10/17/2022 at 7:56 PM, Fly Boomer said:

Depends on your definition of "dead."  Sometimes okay up to a certain ICP, but not happy when higher.

ICP? Not familiar with that acronym.

[Fly Boomer]

1 hour ago, Stetson20 said:

ICP? Not familiar with that acronym.

Internal Cylinder Pressure.  It’s the measurement that the GAMI guys were able to get in real time by using tricked-out spark plugs.  That’s how they were able to show that the engine manufacturers’ favorite mixture recommendation, 50 dF ROP, is very close to the highest ICP possible — not healthy for your engine.  That’s one reason to run LOP because it retards timing a little to shift max ICP away from TDC, and slows the flame front so the combustion event is less a TDC “explosion”, and more an after-TDC “push”.

[Jim F]

On 10/15/2022 at 9:37 AM, Stetson20 said:

Any thoughts from the community? I'm showing EGT approx 200 deg higher than CHT and 100 deg hotter than TIT. My A&P suggests switching probes to see if the discrepancy moves with the probe.

Pic attached.

You still have the protective installation plastic on the display.  Your display will look much clearer when removed.

[Stetson20]

Took a snapshot enroute KRDG to home base… going to upload the data to Savvy later tonight.

[A64Pilot]

On 10/20/2022 at 6:19 AM, Fly Boomer said:

Internal Cylinder Pressure.  It’s the measurement that the GAMI guys were able to get in real time by using tricked-out spark plugs.  That’s how they were able to show that the engine manufacturers’ favorite mixture recommendation, 50 dF ROP, is very close to the highest ICP possible — not healthy for your engine.  That’s one reason to run LOP because it retards timing a little to shift max ICP away from TDC, and slows the flame front so the combustion event is less a TDC “explosion”, and more an after-TDC “push”.

Internal cylinder pressures have been monitored since well before WWII.

Horsepower and CHT closely follow pressures.

It’s very simple and more accurate to move the pressure peak around with timing, but it’s not usually done as it reduces power.

I was wrong, cylinder pressures have been measured since 1796

https://www.fs.isy.liu.se/en/Publications/Articles/IFACWC_17_LE_AT.pdf

Spark plugs have been used to measure internal cylinder pressure at least since Henry Ford did it with the Model-T, they didn’t use piezo crystals to measure pressure, they were direct to the cylinder, thise same plugs could be used to prime early engines to help with hand starting by putting fuel directly in the cylinder. 

https://www.mtfca.com/discus/messages/179374/231606.html?1314245899

 

[Fly Boomer]

44 minutes ago, A64Pilot said:

Internal cylinder pressures have been monitored since well before WWII.

Horsepower and CHT closely follow pressures.

It’s very simple and more accurate to move the pressure peak around with timing, but it’s not usually done as it reduces power.

I was wrong, cylinder pressures have been measured since 1796

https://www.fs.isy.liu.se/en/Publications/Articles/IFACWC_17_LE_AT.pdf

Spark plugs have been used to measure internal cylinder pressure at least since Henry Ford did it with the Model-T, they didn’t use piezo crystals to measure pressure, they were direct to the cylinder, thise same plugs could be used to prime early engines to help with hand starting by putting fuel directly in the cylinder. 

https://www.mtfca.com/discus/messages/179374/231606.html?1314245899

 

Regarding the 1796 reference, I thought Watt was the steam engine guy?  Also, the second reference shows plugs with priming cups.  Didn't read the whole thing.

[A64Pilot]

He was but apparently also played with ICE as the article speaks to combustion. I just Googled first measurement of cylinder pressure or something, never saw the article before

The point is a WHOLE lot of what’s being marketed as new isn’t, people have been running LOP for 100 years or longer. The only thing new is the name.

This is from the POH of the P-40, a 1930’s design for extending range, it puts it LOP

Its the primer cups that were modified to measure pressure, but Google didn’t find any pressure measuring Model-T plugs, if any exist still, I bet they are really rare.

There is even a very simple system that monitors current to fire the plugs, as the difficulty to fire a plug goes up with pressure a pretty accurate pressure measurement can be inferred by measuring current. Modern ignitions often spark the plug for a significant duration.

Even the Ford Model-T sparks the plug for about 15 degrees of rotation, that’s not new either.

NOTES ON MIXTURE CONTROL

The engine ls fitted with a Bendix-Stromberg carburettor Instead of the usual two-position mixture control, as fitted to British engines. the mixture control has the following 4 main positions:

FULL RICH: In this position there is no automatic compensation for altitude and temperature

AUTOMATIC RICH: This is the position for the richest mixture which is automatically maintained by the compensating device.

AUTOMATIC LEAN: This is the normd position for weak mixture. The automatic device maintains the mixture at this setting also.

IDLE CUT OFF: For stopping the engine and while priming during engine starting operations.

Furthermore, the mixture strength can be progressively weakened by moving the lever from the AUTOMATIC HIGH position towards the IDLE CUT-OFF position, the weakening being effective also in the region beyond the AUTOMATIC LEAN position up to the point where the IDLE CUT-OFF operates (at the extreme end of the travel). At any point in this range the automatic compensating device is in operation.

Although placing the mixture control in the AUTOMATIC LEAN position gives a considerable reduction in fuel consumption, it is possible to obtain a consumption of about 5% lower by adjusting the mixture control as follows:

1. Obtain the desired engine cruising conditions

2. Change the airscrew control from AUTOMATIC to MANUAL. In this position the airscrew becomes effectively a fixed pitch airscrew

3. Set the mixture control to the position determined by weakening the mixture until a drop of 40 to 50 R.P.M. is indicated. The position may possibly be between AUTOMATIC LEAN and IDLE CUT OFF

4. Return the airscrew control to AUTOMATIC

If changes in altitude or cruising conditions are made, this setting should be checked by repeating the above operations.

 

 

 

[A64Pilot]

It’s often thought that Lindbergh taught LOP ops to the P-38 guys in the Pacific, he didn’t that was in the POH.

‘What he taught was low rpm / high manifold pressure (oversquare) which reduces internal friction somewhat, doesn’t make as much difference as LOP but helps and I’m sure over water running low on fuel you’ll take any help even if it’s small.

‘But finally, yes the flame front proceeds slower LOP and reduces peak pressures, and it’s probably the biggest reason HP goes down so much LOP, and many will increase timing to get that peak pressure back and recover some of the HP that LOP costs, of course this reduces their detonation margin when operating high power ROP. TANSTAAFL.

[Fly Boomer]

32 minutes ago, A64Pilot said:

There is even a very simple system that monitors current to fire the plugs, as the difficulty to fire a plug goes up with pressure a pretty accurate pressure measurement can be inferred by measuring current. Modern ignitions often spark the plug for a significant duration

That would be cool.  I know I have had plugs that worked okay at lower power, but pooped out when the engine was pushed.

[A64Pilot]

9 minutes ago, Fly Boomer said:

That would be cool.  I know I have had plugs that worked okay at lower power, but pooped out when the engine was pushed.

Here you go. But yes since the beginning I guess ignition “busting up” under high loads has been an issue. I wouldn’t expect to see it in aircraft though, but ICE while a mature technology, hasn’t reached a dead end, there are still advances. I personally see Mazda’s spark ignition, gasoline Diesel as a big achievement.

https://www.researchgate.net/publication/256463297_Estimation_of_In-Cylinder_Pressure_Using_Spark_Plug_Discharge_Current_Measurements

Oh, finally having peak pressures occur right at or very slightly past TDC and high peak pressures is not considered a bad thing, lowering pressures is not a good thing, high pressure is striven for and why automobiles from 70 years ago have had both vacuum and mechanical advance on their ignition systems, to keep that pressure as high as possible and close to TDC in order to keep HP and efficiency up. Higher RPM you have to lead ignition as the flame front spread speed is constant, and you advance timing at low loads because the engine will tolerate it.

Neither is used in aircraft as our RPM band is very narrow and our low load time is very short.

[A64Pilot]

17 minutes ago, Fly Boomer said:

That would be cool.  I know I have had plugs that worked okay at lower power, but pooped out when the engine was pushed.

Oh, and I believe that was exactly Shadracks point about 1700 RPM mag checks not being very effective, to effectively test an ignition system it has to be tested under a load.

I don’t mean to be putting words in his mouth and apologize if I’m wrong