10-23-2015 12:33 AM
The default settings for all the gains (governor, wastegate, and choke) is 100, as the engine ships from the factory. If you raise the number, you make that particular setting more active in the correction process; if you lower the number less active in the correction process.
I have never had success using the factory default of 100 for the governor settings. I usually find that the governor gain setting has to be between 40 and 45, the compensation should be between 40 and 45 and the stability can be between 35 to 50. These are usually good starting points for me and then sometimes these numbers need to be tweaked a bit, depending on how the engine reacts. If it seems to be a little sluggish picking up the load, then the number might need to be raised. You just have to find what the engine likes in these number ranges. That has worked for me if there is no mechanical problem. The hydrax system pressure must be steady and set at 210 psi. If this pressure is not steady it could indicate a problem with the hydrax relief valve of the hydrax pump. The hydrax oil should not be dark; you should be able to see through it. If it is dark, the hydrax pump is leaking engine oil into the hydrax system and it is getting dirty. The servo valves on the actuators don't like dirty oil.
Usually, the choke and the wastegate work okay with these default settings. Occasionally, the wastegate needs to be adjusted downward.
10-22-2015 10:41 PM
The Governor gain sounds like it would be our issue. Our RPM only swings when engine load is light (under 60% or so) and the main recyle valve (Natural Gas Gathering Compressor) is bypassing. Once the recycle valve is closed and the engine is loaded down, the swinging generally will smooth out on its own. The main issue is getting the compressor loaded as we have Automated recycle valves and the main panel has to see 900 RPM from the driver for a specified length of time before it will close it. When the RPM is swinging heavily, it will dip below the 900 RPM limit on the murphy panel and it will not load. This is the point that we have "caught" the RPM manually and it will then load.
I will take a look at the Governor gains on different units and see if they are the same. Can you explain what to expect from adjusting the gain in either direction?
Thanks for any and all information!
10-22-2015 10:30 PM
G3600 speed swings can be caused by several things. The two most common causes is that the governor dynamic settings (gain, compensation, and stability) are not adjusted correctly for the site operating conditions.
Occasionally, I find that the dynamic settings of the wastegate can also cause speed swings. I find this to be the cause of engine speed swings. Many techs keep chasing the fuel linkage, actuator, etc. and can't seem to get the speed to stabilize. If the wastegate settings are the cause of the speed swings, you can usually watch the wastegate linkage and see the linkage move in time with the speed swing. This will usually be a slow speed swing when the engine is loaded. I mentioned this in one of the responses earlier in this thread. It won't affect the speed stability until you get a fairly good load on the engine. That has been my experience.
An actuator solenoid valve can cause speed irregularities but the observed action varies with the issue of the solenoid valve on the actuator. I think that the speed irregularity will be inconsistent as I have seen. This is down on the list as a cause of speed swings in my experience.
Of course, it is important that the engine be tuned to the procedure set forth in the version 11 or later of the Systems Operation, Testing and Adjusting. Previous versions do not have the full correct procedure.
And don't forget the suction controller if there is one on the compressor. A slight swing in the compressor suction controller can cause the same engine speed swings and nothing you do to the engine will solve this issue. You have to stabilize the controller action.
10-22-2015 08:07 PM
i am interested in this topic as well. we have a fleet of about 70 G3606's and a bunch of them have this swinging idle issue. We do fine loose rod ends that sometimes fixes the problem and other times, valve adjustments have made a difference. Also, when it is a unit that normally does this, if you use an adjustable wrench on the fuel linkage, you can "catch" the surge and if you hold it smooth for just a little bit ( you can hear the turbo speed slow down) it will almost always smooth out. This isn't a solution but the info might help both of us to figure out what is happening.
10-13-2015 03:05 PM
The unit swings at start up until you load it. When they load it it the load indicator will gor from 50 to 100% and then settle at 90%. the fuel acuator linkage has been inspected and rod ends replaced along with a new wastgate and linkage ends. The gain, compensation and stability are 10, 20, 120 per CAT Mechanic. The fuel supply is set @48# on a Fisher 99. It has been rebuilt and maintains 48#. We have tuned it in PC CAl several times. Adjusted burn times, and set BTU to 960. The suction header does not have a controller, it is a slam valve. I will send you the configuration to your email. Thanks for your time and help
10-13-2015 02:30 PM
Does the rpm swing under load or with no load? How much load does the engine have on it when it is loaded?
Is there any wear in the fuel actuator linkage? This can cause the rpm to swing.
Is there any wear in the wastegate linkage? This can also cause the rpm to swing under load. Also the wastegate dynamic settings are important. The default for the gain, compensation and stability is 100. If this is where the settings are, you might try reducing these settings to 10 or 20 lower.
Is the fuel supply pressure to the engine steady? It should be steady within +/- 0.25 psi.
When is the last time the engine was tuned in PC CAL?
Does the gas compressor have a suction controller on the suction pipe? Is the suction controller steady or does it swing also?
Can you send me a copy of the configuration screen? And I would like to see the current fuel analysis. Use my email email@example.com. What is the engine serial number?
10-13-2015 01:22 PM
unit are only two year old, about 12,000 hours check all you told me before and still swing, dose better between 900 and 1000 rpm, onces you drop below 900
it start swing. we move it 10 rpm at a time any more then that it start swing
10-09-2015 07:34 PM
I also have another thought if your engine has a lot of hours on it. If the aftercooler is dirty on the air side, when the engine changes operation like changing speed or load, it will sometimes get upset like this if the aftercooler core is plugged. There should be only 1 psi pressure differential across the core on the air side. If the pressure differential gets to be as much as 3.5 or 4 psi, this can cause performance issues of instability.