EGT at engine startup

Something that's puzzling me: From what i've learned so far, when a turbine engine is started, EGT spikes the moment the fuel ignites or shortly thereafter and as the engine spools up, EGT goes down due to more cool air being forced around or through the combustion chamber, mixing with the hot gas and cooling it somewhat (therefore the need to monitor EGT closely at startup to shutoff in the case of a hot start). However, in Black Shark EGT rises gradually with RPM at startup and does not 'spike'. Is this a limitation of the simulator or do the real TV3 engines show the same "behaviour" (and if yes, for what reason)?

Something that's puzzling me: From what i've learned so far, when a turbine engine is started, EGT spikes the moment the fuel ignites or shortly thereafter and as the engine spools up, EGT goes down due to more cool air being forced around or through the combustion chamber, mixing with the hot gas and cooling it somewhat (therefore the need to monitor EGT closely at startup to shutoff in the case of a hot start). However, in Black Shark EGT rises gradually with RPM at startup. Is this a limitation of the simulator or do the real TV3 engines show the same "behaviour" (and if yes, for what reason)?

I can't tell you about the helicopter engine in the KA-50, but as a mechanic on jet aircraft, EGT could spike during start ( not always do) because during initial ignition, there is not enough airflow yet to maintain proper temperature. A lot of modern jet engine have very specific airflow required to maintain normal operational temps. In normal operation it should increase gradually. Ripid rise or increase in EGT could and are often used as indicator for malfunctions like hot start, hung start or stagnation.

There could be a malfunction and fuel may be schedule at a faster rate than the turbine (A.K.A. compressor) can move the air, creating a hot start/fire overheating components and creating a possibility for an explosion or a melt through.

Also there is, stalls or stagnation of air, The flow of air to or going true the turbine may get out of sink, creating a overpressure or vacuum area.

There could be a hung start, where the RPM of the compressor stop increasing due to a malfunction.

'Spike' was maybe too hard a word to describe what i mean, i was just talking about the normal rise in EGT at startup and the subsequent falloff when the engine spools up. I know about these overtemp situations you mentioned, but i was wondering why the simulated TV3 shows just a linear EGT rise with RPM and not an initial rise and afterwards a stabilisation.

Oh I see what you mean ... like on this video you can see it well

You can see EGT (A.K.A. FTIT on the F-16) drop at 1:13 bottom gauge.

I do not know, maybe helicopter engines, with the extra set of turbines run hotter. The KA-50 engine in the game do run pretty hot in my opinion, but I sure they are normal in RL. At any rate I see what you mean now , maybe we can get some cool info.

This is how the TV3's actually start, they don't spike and then cool down. On the other hand, the APU *does* spike and then cool down slightly during a normal start, which it does not do in the game (it also has a very smooth EGT rise in-game).

EDIT: I should revise my statement on the APU...in my experience, it *usually* spikes to around 700 then drops back down to somewhere in the 600 range, but not all of our APUs do that. Some run very cool and have a smoother EGT rise during start, but in my case it's the exception rather than the rule.

Thanks Alpha

Oh I see what you mean ... like on this video you can see it well

You can see EGT (A.K.A. FTIT on the F-16) drop at 1:13 bottom gauge.

Exactly!

This is how the TV3's actually start, they don't spike and then cool down. On the other hand, the APU *does* spike and then cool down slightly during a normal start, which it does not do in the game (it also has a very smooth EGT rise in-game).

Interesting! Any insight on why it does not spike? AFAIK (i'm no proffessional like you guys are) the spiking behaviour at startup is pretty common to turbine engines in general because the compressor does not supply enough air to mix with the hot exhaust gases from the combustion chamber.

Sorry, guys...

No need to be, i was just curious, my intent was not to complain :)

Well, to be quite honest.

...when it's things as detailed as that that we find to "complain" about... You guys over at ED can congratulate yourselves on a job well done. Most sims, old and new, wouldn't be able to receive such criticism simply because they don't even attempt to simulate with anything near that level of detail. :P

...when it's things as detailed as that that we find to "complain" about... You guys over at ED can congratulate yourselves on a job well done. Most sims, old and new, wouldn't be able to receive such criticism simply because they don't even attempt to simulate with anything near that level of detail. :P

Well, I did implement engine temperature spiking when starting the turbines in EECH :p But of course DCS har much better system modeling in almost every other respect.

Well, did you implement it in table manner or through actual simulation, though?

Well, did you implement it in table manner or through actual simulation, though?

It was simulated in the way that temperature increased more rapidly at first because low RPM meant there was little airflow and hence little cooling. Then when the RPM picked up there would be more airflow.

Exactly!

 

 

 

Interesting! Any insight on why it does not spike? AFAIK (i'm no proffessional like you guys are) the spiking behaviour at startup is pretty common to turbine engines in general because the compressor does not supply enough air to mix with the hot exhaust gases from the combustion chamber.

On turboshafts, *no* air is mixed with the exhaust gasses. That is, there is *no* bypass like you have with jet engines, so no air from the compressor is used to cool anything, it all goes to the combustion chamber (well, not entirely accurate, but suffice to say that no air in the compressor is bypassed around the combustion section for the purpose of cooling).

On turboshafts, *no* air is mixed with the exhaust gasses. That is, there is *no* bypass like you have with jet engines, so no air from the compressor is used to cool anything, it all goes to the combustion chamber (well, not entirely accurate, but suffice to say that no air in the compressor is bypassed around the combustion section for the purpose of cooling).

I guess i express myself way too inexact. :)

Ok, i know that there's no bypass on a turboshaft, but what i think i meant :) was, when the compressor rpm is still low and the mixture ignites, doesn't the combustion actually reach way further towards the turbines than when there's more air being supplied to the combustion? In my simple mind that would cause EGT (or TIT to be exact) to be higher (at same fuel flow). Or am i mistaken somewhere? Great info in this thread btw :thumbup:

By the way in the BS engine model one the most hard work is to adjust these devices.

Control Systems can be a bitch, tell me about it :)

Hey, got back home yesterday and had a first try on 1.0.1. I have to say that i really love what you did with the temp gauges of engines and APU. They feel even more real now! big :thumbup: