IO 360 M1B FF at T/O full power

[DanH]

Originally Posted by RV10inOz

....the spread from around full rich to say 75-100 ROP was in the order of a Delta thetaPP of 5 degrees....

So, would it be fair to say that increasing fuel flow in the full rich but not-quite-rich-enough case would only retard thetaPP maybe two degrees at most? Interesting, but not unexpected. As you say, the school chart is pretty close; it says thetaPP response to mixture change is minimal on the rich side of peak, as compared to a significant response on the lean side.

I'd suggest other factors are more likely to be the root of the temperature reduction with mixture richness. Here's a chart from Taylor's "Internal Combustion.." The c and d curves are from NACA data circa start of WWII, mean combustion gas temperature at two measurement points. They're from two different papers, at different times. At the top I've translated F/Fc into more conventional labels.

It would appear that moving from stoichiometric to best power to full rich (15:1, 12.5:1, and 10.7:1) makes a very large difference in heat load applied to the head.

[RV10inOz]

So, would it be fair to say that increasing fuel flow in the full rich but not-quite-rich-enough case would only retard thetaPP maybe two degrees at most?

Dan, unless I am misunderstanding your statement, I suggest that in the case of where a mixture is ideal full rich at takeoff power and reduced back say 10%, this has a more significant effect than the next 10% getting leaner. As for two degrees at the most, well that is not insignificant if that is what you are suggesting.

In other words, the last extra dose is what matters the most. To start splitting the numbers up it was something like this, roughly, from full rich to

As luck would have it, so you are pretty lucky, George Braly sent me some data from fuels testing this morning. And what do you know? x100

The exact question you are asking has its answer hidden within! Now I am under NDA's so I cant publish it here but the data I can take from this confirms what I have said previously. This is from certification testing and can be relied on. The data collection was for completely different and unrelated purposes and the answers yielded are a serendipity of this.

The recent Avstar and Precision FCU's have had under-flows around 15%, and the data points I have of ThetaPP are tabled below which reflect this range. These are averaged over a few runs and cylinder to cylinder variation is to be expected and also from one sample to the next can be a bit of variation, so please anyone reading tis, these are fuzzy numbers that vary by the milliseconds (about 20 times a second) so be careful how you read this.

This is comparing full rich to FR-10% and FR-20% of flow and the % of ThetaPP compared to the previous position.

CYLINDER Delta TPP-10% Delta TPP-20%
C1 >> 88.45 >> 92.50
C2 >> 85.00 >> ----
C3 >> 89.40 >> 95.25
C4 >> 90.55 >> 97.30
C5* >> 97.85* >> 99.10*
C6 >> 92.70 >> 95.50

* this cylinder has an anomaly that could easily be explained by the pressure sensors and the fact this one has been deliberately subjected to a lot of abuse. In any case it shows a similar trend, but beware the raw data.

Interesting parameters here are the EGT values at each point represent a full rich, 1250-1320dF range using a standard 8.5:1 compression ratio engine. Assume this to be about 250-300dF ROP mark. The -10% flow figure was yielding around 70-75dF higher, so about 225-175dF ROP, and the -20% flow was about 150dF higher or about 150-100dF ROP. The ThetaPP shift overall was around the 2.5 to 3 degree range, a little less than the observations I made during less than ideal examples to extract data. Remember this stuff bounces around all the time so no hard numbers, fuzzy averages. Mid you these are not leaned off as much either, so lower changes of TPP are to be expected.

Interesting that if you compare this fresh data from the dyno today, the indicators I have been using to determine who has enough flow and who does not is validated. The concerning thing is that for as long as any of us can remember, Lycomings have flowed well, and TCM not. Now TCM publically declare a bit more would be nice, and Lycoming are shipping variations. Who the heck would know??

I hope that has been as fun for everyone as it was me in collating and delivering the data.

Last point, the thermal transfer is affected by the boundary layer, the higher the pressure, the smaller the layer, the more transfer.

[DanH]

Originally Posted by RV10inOz

..I suggest that in the case of where a mixture is ideal full rich at takeoff power and reduced back say 10%, this has a more significant effect than the next 10% getting leaner.

Tend to agree, but remember, here we're considering the why.

As for two degrees at the most, well that is not insignificant if that is what you are suggesting.

I am suggesting the insignificant shift in thetaPP is not enough to be the sole casual factor underlying the cylinder head temperature drop in the region richer than Lycoming's published minimum fuel flow.

Yes, that particular 10% richer does indeed have more effect...due to several combined factors, one being reduction of mean combustion gas temperature.

This is comparing full rich to FR-10% and FR-20% of flow and the % of ThetaPP compared to the previous position.

CYLINDER Delta TPP-10% Delta TPP-20%
C1 >> 88.45 >> 92.50
C2 >> 85.00 >> ----
C3 >> 89.40 >> 95.25
C4 >> 90.55 >> 97.30
C5* >> 97.85* >> 99.10*
C6 >> 92.70 >> 95.50

Percentage reduction of thetaPP is a bit obscure...heaven forbid we should see the actual peak pressure point in degrees ATDC. However, if we accept the curves on the school chart as accurate (blue curve, full rich peak at 16 degrees ATDC), then full rich less 20% flow only moves the point of peak pressure 10%, or 1.6 degrees.

(Throw out high and low, average the other four values = 90.275%, making the shift 9.725% of 16)

BTW, the column labels are switched.

[RV10inOz]

No the column labels are correct.

The -10% column id full rich flow x0.9 and the second column is FR flow x0.8, and as I have said the first reduction of fuel flow moves Theta PP more than the next ..... think about it for a minute.

[DanH]

Originally Posted by RV10inOz

No the column labels are correct. The -10% column id full rich flow x0.9 and the second column is FR flow x0.8, and as I have said the first reduction of fuel flow moves Theta PP more than the next ..... think about it for a minute.

The -20 column is expressed as a percentage of the -10 column? Please excuse me....lets recompute.

Again drop the high and low, average the rest, assume 16 degrees @ full rich per the school chart. The first 10% flow reduction moves peak pressure 1.6 degrees and the second moves it an additional 0.7.

Conversely, if a particular setup is 10% leaner than your ideal full rich, adding that additional fuel only retards the point of peak pressure 1.6 degrees, perhaps 2 degrees if it was 15% too lean?

Your previous statement was 2.5 to 3 degrees for 20%. Works for me. Shall we consider it quantified?

[DanH]

I'll take that as a yes, so returning to discussion...

Originally Posted by RV10inOz

..I suggest that in the case of where a mixture is ideal full rich at takeoff power and reduced back say 10%, this has a more significant effect than the next 10% getting leaner.

Agreed; the data is clear. Could you quantify the above ideal full rich in terms of A:F, F/A, or F/Fc please?

[Relentless]

Originally Posted by Airhead

I am trying to find what is the anticipated fuel flow (or range) for an IO 360 M1B (Van's) with C/S hartzell and Precision FI. Full throttle / full rich during take off and initial climb near sea level. Thanks

Airhead,

Hey I checked with the braintrust here at Titan Engines concerning your question and this is what I found:

"Measured fuel flow for the same engine, same prop, under near sea level conditions. 16 -18 GPH."

Hope that helps.

[RV10inOz]

Relentless, 16-18 is a BIG range, have the TITAN folk measured the Internal Cylinder Pressures on the Dyno at 16GPH at full rated power?

It sounds like 16-18 is a throw away line, a rough statement, even if it is just within a manufacturers range, and I bet they would much prefer the 17.5 range if they set it up and saw the data.

It is a bit like saying spark plug gaps 0.016 - 0.028", when really they should be 0.016 - 0.018" if you get what I mean.

Until you see the data, everything else is just an opinion.

[DanH]

I bet they would much prefer the 17.5 range if they set it up and saw the data.

Please tell us why...and show us the data so we don't mistake it for opinion.

[RV10inOz]

No, I get sick of going over the same thing and I have trouble deciding whether to waste more time on this or not. Plenty of data been provided already, all of which is all in harmony with the physics, which you seem to accept.

....when the FCU is set up properly by those who have the data and spec's which I do not have readily at hand is why you expect to get around 17.5GPH.

As for data.......I have seen enough of late with one IO360 and one IO540 (stock engines) in the last two weeks alone, who have had ridiculous take off CHT's and low fuel flows yet when the FCU is sent to a qualified repair shop and corrected everything data wise reflects what it should. Data enough. This validates the correct flows set up with the correct data, yields the expected result. The repair stations have it, 99% of pilots would not understand it if they saw it anyway, you would and most would not, but I still do not have it at hand and not going to spoon feed it to you. Go ask a good servo overhaul shop for the manuals, they do cost a few thousand dollars to purchase.

Bear in mind also, the BSFC if you want a unit of measure varies from some engines to others, i.e IO550 Vs TNIO550, both 300HP, so printing a specific here could be the misleading thing to do. But you can calculate that just as easily as I can. I bet for an IO360/540 it is around 0.57-0.58 which is the right range. For a TIO540J2BD it is 0.68-0.72 and say a TSIO 520 is 0.66-0.68 so it is horses for courses.

Bottom line if your CHT's are high and your fuel flow is way too low, fix it.

EOM