EGT/Thermocouple handling

[msoultan]

I've been doing a lot of research on EGT and I had some thoughts. First, though, I thought I'd provide my setup so you have an idea what I'm working with. I have an aircooled VW bus and it has 4 CHTs and 4 EGTs that are being brought into the MS3 via Jean's IOX. For the most part everything seems to be working great. I'm using the Generic Sensor inputs for the CHTs (CAN ADC09-12) and now I'm bringing in the EGTs through the EGT/Thermocouple settings (CAN ADC13-16).

I was looking at the EGT settings page and I noticed that there are various actions for excessive EGT temps and after some further readings, I'm thinking that those settings might not really be valid. According to this page (http://www.ls1tech.com/forums/advanced- ... 101-a.html), detonation will cause the EGTs to drop, not go up, which honestly was a surprise to me. I'm wondering if those EGT temp settings are really even useful. Again, I'm no expert in EGT, but that article seemed pretty enlightening and I wanted to hear some thoughts on this.

That said, I think the warning system on the EGT page is very applicable to CHT. When the engine gets hot and gets closer to pre-ignition/detonation conditions, the CHT goes up, so it would be great if there were some means to use that page for CHT as well, maybe with its own warning/handling system? Or I guess I could use that page for CHT instead of EGT, but the labels would be confusing.

That brings me to my last issue, would it be possible to make some adjustments so that the thermocouple settings were more CHT friendly? It would be great if the CHT values would get datalogged as CHT01 instead of Sensor 01. I know aircooled engines are the minority, but you have all done a great job in accommodating the aircooled folks with other temp settings throughout and I wanted to see if we could bring in the measurements somewhere like the EGT page along with warning so that engine conditions can be adjusted should a high-temp condition be reached.

Thanks,
Mike

[msoultan]

And for those of you that don't want to read the whole article, here's the section on EGT temps:

The other technique is a little more subtle but usable if attention is paid to EGT (Exhaust Gas Temperature). Detonation will actually cause EGTs to drop. This behavior has fooled a lot of people because they will watch the EGT and think that it is in a low enough range to be safe, the only reason it is low is because the engine is detonating.

The only way you know what is actually happening is to be very familiar with your specific engine EGT readings as calibrations and probe locations vary. If, for example, you normally run 1500 degrees at a given MAP setting and you suddenly see 1125 after picking up a fresh load of fuel you should be alert to possible or incipient detonation. Any drop from normal EGT should be reason for concern. Using the "Tin Ear" during the early test stage and watching the EGT very carefully, other than just plain listening with your ear without any augmentation, is the only way to identify detonation.

It looks like the same article was published here as well:

http://www.streetrodstuff.com/Articles/ ... etonation/

Really interesting stuff!!

[msoultan]

I found another article on this:

http://www.vansairforce.com/community/s ... php?t=7827

This article slightly contradicts the one I included in the previous posts in that it says pre-ignition causes a drop in EGT, whereas the other articles says it's detonation that causes the EGT drop, but they both agree that there is a significant drop in EGTs when you're getting close to these engine-destoring conditions:

That leads us to pre-ignition. Pre-ignition is the initiation of the flame front BEFORE the planned spark ignition event. It is a normal flame front, just started too soon. As opposed to detonation where EGT is little changed, pre-ignition results in rapidly falling EGTs and rapidly rising CHTs. The Peak Internal Cylinder Pressures can get very high, very quickly and this can destroy an engine in seconds.

So it's looking like the current EGT settings page would be better suited for CHT and another EGT settings page that has a temp-drop threshold would work better for out-of-range EGT handling.

[jsmcortina]

EGT safety has tripped on my with a lean nitrous setting.

Why do you think it was designed for det prevention?

James

[msoultan]

EGT safety has tripped on my with a lean nitrous setting.

Why do you think it was designed for det prevention?

Sorry.. I was kinda making an assumption that you were trying to avoid pre-ignition/detonation as that seems like it's the real engine killer, so I apologize for this assumption. I just installed the EGTs on my engine so I'm learning about all of this stuff and it's really interesting how it all works. I did just read somewhere that EGTs weren't really a good indicator of the head/cylinder temps (compared to CHT), but it is a good indicator of pre-igntion/detonation conditions... but I forgot where I found that... looking...

[msoultan]

It was in this article:

http://www.avweb.com/news/pelican/194452-1.html

That I found this:

The fact is, EGT is not a good reflection of combustion temperature at all. It is more an indication of when the combustion occurs relative to top dead center or valve opening. In fact, if you lean enough, to something around 150ºF LOP, just before combustion ceases entirely, the EGT will rise briefly, as the very slowly-burning combustion event continues until the exhaust valve starts to open! This little oddity drove us nuts when we first saw it. (As an aside, diesel engines have very high peak pressures and temperatures, but tend to have lower EGTs than spark-fired engines.)

It's towards the bottom under the "EGT Isn't The End of the (Combustion) Story" heading.

[racingmini_mtl]

EGTs are an indirect indicator of AFR. And since they are less expensive than WBO2 controller you can have one per cylinder, check that you have the same temperature in each cylinder and trim the fuel accordingly. But as I said, this is an indirect indicator and EGT is also affected by timing and detonation. So you can't rely on it blindly.

Jean

[msoultan]

Yeah.. I was hoping to use it when I got my independent injector setup going so that I could adjust the fuel trim to each cylinder. So far everything seems to be working, but now it's understanding how to use the numbers. After all of this reading that I've been doing, I'm learning that it isn't nearly as straightforward as CHT, as I had thought it would be... really neat stuff!