BeechTalk - BT

Username Protected · **Posted:** 25 Sep 2016, 21:10

Username Protected wrote:

My understanding: EGT is an average of the exhaust gas temperature while the exhaust valve is open and and while it's closed. It is closed most of the time, so this average temperature is much lower than the actual exhaust gasses. TIT measures the combination of exhaust gasses from all six cylinders.

I don't buy that Josh, because the monitor has no way of knowing when the valve is open or closed. It is just a temp probe, the same as the TIT probe which is 12" down stream of the back cylinder. If anything, it should be a bit lower, since the gas has a moment to cool.

Username Protected · **Posted:** 25 Sep 2016, 21:19

Username Protected wrote:

Ok, I'm no turbo guy but how can the air come out the exhaust (egt) at 1520 and go in the turbo (tit) at 1600?

Oh, this is simple: 1520 is for one cylinder, but there are six cylinders, so it's six times 1520, or about 9,000 when they all come together, then it cools back down before getting to the turbo so it's only 1600.

Didn't they learn you math in Waco?

Username Protected · **Posted:** 25 Sep 2016, 21:37

Username Protected wrote:

Ok, I'm no turbo guy but how can the air come out the exhaust (egt) at 1520 and go in the turbo (tit) at 1600?

Oh, this is simple: 1520 is for one cylinder, but there are six cylinders, so it's six times 1520, or about 9,000 when they all come together, then it cools back down before getting to the turbo so it's only 1600.

Didn't they learn you math in Waco?

Username Protected · **Posted:** 25 Sep 2016, 21:41

Username Protected wrote:

I think we're saying the same thing. :scratch:

Each EGT probe is sitting in relatively cool air most of the time, because the exhaust valve is closed. If the EGT probe reads 1500, that value is an average of the typical, say 1400 degree environment with occasional blasts of, say, 1700 degree exhaust gas.

The TIT probe is getting six time more blasts of the 1700 degree exhaust gasses, hence, it reads hotter.

LOL. Sorry Josh, I misunderstood what you were saying, but on the Ram setup, the probe is downstream of the left cylinder bank and only sees those 3 temps. Also, why is it not that way on a Bonanza? On a factory TC, or a TN, the TIT will usually be similar or lower to the EGT's.

Username Protected · **Posted:** 25 Sep 2016, 22:23

Don't know, this is all academic for me. I fly behind a NA engine :thumbdown:

Username Protected · **Posted:** 27 Sep 2016, 08:31

Username Protected wrote:

Ok, I'm no turbo guy but how can the air come out the exhaust (egt) at 1520 and go in the turbo (tit) at 1600?

Oh, this is simple: 1520 is for one cylinder, but there are six cylinders, so it's six times 1520, or about 9,000 when they all come together, then it cools back down before getting to the turbo so it's only 1600.

Didn't they learn you math in Waco?

Username Protected · **Posted:** 27 Sep 2016, 09:02

Username Protected wrote:

My understanding: EGT is an average of the exhaust gas temperature while the exhaust valve is open and and while it's closed. It is closed most of the time, so this average temperature is much lower than the actual exhaust gasses. TIT measures the combination of exhaust gasses from all six cylinders.

I don't buy that Josh, because the monitor has no way of knowing when the valve is open or closed. It is just a temp probe, the same as the TIT probe which is 12" down stream of the back cylinder. If anything, it should be a bit lower, since the gas has a moment to cool.

Username Protected · **Posted:** 27 Sep 2016, 11:35

Username Protected wrote:

Doug,

May I try to simplify?

Imagine the events of two turns of the crankshaft, so we have a complete power cycle on the engine. During 2 turns, each exhaust valve opens once - and thus each EGT probe is hit by one blast of hot exhaust gases from its cylinder. In the same time the TIT probe is hit by how many blasts? Six blasts of hot gasses hit the TIT probe (assuming it reads both banks of cylinders) in two turns of the crank.

In that two turns of the crank - however long it takes - each EGT probe is hit by one blast of hot gas - and the TIT is hit by six. Thus in that time period the TIT probe has only 1/6 of the cooling off period that each EGT has. Thus it is not that the TIT probe is getting hit by hotter gas - but it has less time (by a lot) to cool off between blasts of hot gas. If you doubt that math, go hold your hand 6 inches from a lit stove for one second and then try to hold it for 6 seconds...

RAS

That makes perfect sense,but the part I cannot wrap my head around is why this does not occur in a factory TC or TN Bonanza.
They have a probe at the turbo, while the Ram isnt even a real TIT. It is simply a probe 12" downstream of the left bank before the Y pipe. Would the real TIT, in theory, not produce a higher indicated temp than one only reading 3 cylinders?

Username Protected · **Posted:** 27 Sep 2016, 12:47

Username Protected wrote:

Doug,

May I try to simplify?

Imagine the events of two turns of the crankshaft, so we have a complete power cycle on the engine. During 2 turns, each exhaust valve opens once - and thus each EGT probe is hit by one blast of hot exhaust gases from its cylinder. In the same time the TIT probe is hit by how many blasts? Six blasts of hot gasses hit the TIT probe (assuming it reads both banks of cylinders) in two turns of the crank.

In that two turns of the crank - however long it takes - each EGT probe is hit by one blast of hot gas - and the TIT is hit by six. Thus in that time period the TIT probe has only 1/6 of the cooling off period that each EGT has. Thus it is not that the TIT probe is getting hit by hotter gas - but it has less time (by a lot) to cool off between blasts of hot gas. If you doubt that math, go hold your hand 6 inches from a lit stove for one second and then try to hold it for 6 seconds...

RAS

That makes perfect sense,but the part I cannot wrap my head around is why this does not occur in a factory TC or TN Bonanza.
They have a probe at the turbo, while the Ram isnt even a real TIT. It is simply a probe 12" downstream of the left bank before the Y pipe. Would the real TIT, in theory, not produce a higher indicated temp than one only reading 3 cylinders?

Username Protected · **Posted:** 27 Sep 2016, 13:21

Quote:

the monitor has no way of knowing when the valve is open or closed.

It is not the monitor but the probe itself. Imagine you are standing in a door way when it is real cold and windy outside. You are nice and warm. Someone opens the door and an icy blast hits you. The door stays open for a while. Then the door closes and the process repeats. What will the temperature of the change in you pocket be after a while?

The valve opens and a blast of very hot gas heats the probe. The valve closes and the blast stops. The probe cools off a bit. The process repeats. The probe faces the hot blast 1,200 times per minute (at 2400 RPM), 20 times per second but most of the time the valve is closed and the probe is cooling off.

The gasses go to the collector where there is always one cylinder providing heat even if the other 4 or 6 are not.

Username Protected · **Posted:** 27 Sep 2016, 23:18

I know you all are right but how many times does a single EGT probe get hit with this blast of air over a one minute cycle at 2400rpm?

Username Protected · **Posted:** 28 Sep 2016, 01:11

Quote:

I know you all are right but how many times does a single EGT probe get hit with this blast of air over a one minute cycle at 2400rpm?

At 2400 rpm there are 1200 intake strokes, 1200 compression strokes, 1200 power strokes and 1200 exhaust strokes. Therefore the probe is blasted with exhaust gas 1200 times per minute or 20 times per second. As it is a 4 stroke engine the probe is not being blasted with exhaust gas roughly 75% of the time (not being blasted during the intake, nor compression nor power stroke.

Username Protected · **Posted:** 28 Sep 2016, 10:43

1200 times a second seems pretty constant to me but I am just a simple man... :peace:

Username Protected · **Posted:** 28 Sep 2016, 11:18

Username Protected wrote:

1200 times a second seems pretty constant to me but I am just a simple man... :peace:

That would be 1200 times per minute.

You might be simpler than you thought.

Username Protected · **Posted:** 28 Sep 2016, 13:53

Username Protected wrote:

I have been experimenting with LOP operations in the 340. Normal cruise is 30/2300 and 18.5gph. This will yield 190-195 ktas in the summer, faster when cool.
LOP is: 33/2300 and 14gph yielding 188-193ktas, so I am saving 9 gallons per hour and only losing 3-4knots! The best part is the CHT's are down, but I still have issues with #2 and #4 on both sides. ROP they are running 390 and LOP they are maybe 5 deg cooler.
All the others are 320-350deg. I think a baffle tweak will help. I cannot for the life of me reconcile the TIT temps in my head, as they are 50-100 deg higher than the average of the EGTs :scratch:

. George has tried to explain it, but I just don't get it. I'll post a couple of pics.

Doug,

IF you can leave your plane with our shop for a few days, we might be able to fix # 2 in a definitive way. There is a Q&D fix, but I would rather take the time and do it right. There are some other 340s that would also benefit.

George

Guess its time