01-05-2017 08:57 PM
Have you taken screen shots from all tabs of both engine monitoring systems and compared ALL the parameters at a given load? Your system seems to provide you a lot of good data, so it may help you determine the differences.
Are these lean burn engines? I'm assuming so based on info you have provided.
An old rule of thumb, for every 1 degree increase in inlet manifold temp, you can expect an increase in exhaust port temp of about 10 degrees (works pretty much the same in F or C)
I ran into a similar situation on a CAT 3516 many years ago, problem had been around for a long time, operator lived with it until one year the summer temperatures came up pretty high, the end of a long story is that the engine had the wrong turbo cartridges from factory install.
On wastegate adjustment, I would hope Waukesha would have a published procedure, however sometimes you have to come up with something more definate yourself. Many years ago I worked in an area that was way ahead of pretty much everyone else on emissions, so at times we had to work a bit outside the box, this bench test procedure came to me from an old AirResearch tech (company who actually makes most wastegates, or at least did back then)
Setup a "good" engine to perform as desired,ideally at full rated load at all specified parameters the throttle should be 70-80% open. Run the engine at 25, 50, 75 and 100% load and record the boost pressure (pressure to wastegate sensing).
Stop the engine and let it cool, remove a "good" wastegate. Connect a test air pressure supply with an adjustable regulator and good gauge. At 0 PSI (or KPa or whatever units you want to work with) measure the projection of the valve from the body of the wastegate, I used a depth micrometer. Take additional measurements as you apply air pressure at the values you recorded from the "good" engine. Ideally the air pressure applied that equaled boost at 25% load did NOT cause the valve to move, valve should move freely and smoothly at remaining pressure test points. The measurement values at the test pressures will become your "specs". Now take the wastegates from your "suspect" engine and perform the same tests, ideally you should be able to adjust the wastegates to behave in the same manner as the ones from your "good" engine. You also need to make sure that both sets of wastegates have the same number of altitude spacers in them (large spacers between the housing and the cover) On some wastegates you will still find shims under the springs, even on ones with adjustment screws. If the wastegates on your engines do have adjustment screws make sure the caps seal properly after adjusting.
For many years I ran into a number of engines with wastegates not working properly due to early life damage from poor startup and tuning procedures, if a wasteagte gets too hot it can get damaged and not perform as expected, causing all kinds of strange problems, at least in my experience.
Your backpressure issue is a valid concern I think and should be investigated further to determine why the large difference from the other unit.
01-05-2017 06:06 AM
First of all, thanks for your help. I will try to answer each question separately:
Verify ignition timing, both global and by cylinder if you have electronic ignition: The timing varies little but, at the day of the test, it was in 25.25, as you can see in the picture below. The other engine in the same site, that works in a good condition of exhaust temperature, registered 23.25.
Are the correct spark plugs installed? All spark plugs are Waukesha's original. We usually prefer buying from the factory just to avoid problems in the field. Besides that, we change the plugs considering predictive information given by the ESM controller, based on the voltage level supplied by the ignition system (Spark Reference #).
Measure exhaust emissions with a good quality analyzer, while you likely don't have the same issues with exhaust emissions in your country like we do in the US, it is still a VERY valuable tool in determining engine condition and state of tune. It would be benefical to take data from a "good" engine to use for comparison. Assure that NOx and CO readings are within expcted ranges at the specified exhaust oxygen level. This is the next step that I'm planning to do. We have three exhaust emission analyzers and I will use one of them in the next time that I will be in the plant. My strategy is just register the measuring of 2 or 3 good engines and, after that, compare to the Genset-B in Piúma station.
Verify the operation of the the device actually measuring the temperature(s), I find in many sites where the temperature probe, wiring or connections may cause an error in the reading, while most of the time these type problems result in lower readings they can also cause higher than expected readings. Yeah, it could be a mismeasurement condition. However, we have two different sensors, one for each bank (it is a V-12 engine) and probably they are not registering wrongly at the same time. Maybe we could have something wrong inside the ESM controller. Furthermore we noticed that the turbochargers are working "redier" than usual, indicating that probably the overtemperature is for real.
You should also find it helpful to sit down and document this engine's history as much as you can. Has this site always had a problem? Did it start after a major service or repair? Are there any environmental factors, such as altitude or extreme temperature or humidity issues that be affecting the units operation? Well, I have already done that. It seems that this engine in particular has been working in a higher step of temperature for a long time. Because of that, I asked to remove the flame arrester in the exhaust pipeline, since I measured a 12"H2O backpressured in the field @ 70% load and documents from Waukesha said that the maximum backpressure for this load should be 12"H2O. After the removal, we measured again and we found just 1"H2O and the temperature decreased 10°C but it is still so high and because of that, I believe that the installation worsened the condition but was not the root cause of the failure. The other engine has a 7,5"H2O in the same load condition. The engine now is close to 20.000h of operation and we are planning to do the top end overhaul. But I believe that the problem is greater than that.
How about the fuel gas? Do you have an analysis? Do you have another engine in the same area running off this particular gas supply? The fuel gas has great quality, since I work in the company that is responsible for the natural gas transport in Brazil and these engines are the prime movers of generator sets installed in compressor stations of natural gas. We get a little of gas that flow in the pipelines and use them to feed the engines. The only different between the gas that are usually used in the residences are related to their odor, since this is put after the transport has been done. As I said, I had other engine installed in the same plant and other 12, which have the same model and sequencial serial number, in different states in Brazil. And here, the installation condition relative of altitude, ambient temperature and natural gas quality dont change in a way that we would have to restrict the standard operation of each equipment.
How about mechanical condition of the engine? How many hours total? How many hours since last overhaul? Have you done a compression test? As I said, the engine is a great condition but it is close to the overhaul, at least considering the number of operation hours (here, for a decision of reliability we overhaul these equipment considering not their predictive condition but just their working hours).
Something that I found out that are really strange is related to the inlet air temperature and manifold pressure that are a little bit higher than usual. It could lead to a problem in the aftercooler or perhaps in the wastegate valve. But in this last case, I have never had a problem on it. Is it difficult to adjust? The wastegate valves installed on the VHP-7044 are, at least visually, the same used in the G3516. Don't you have any literature that could help me in the field?
Thanks again for all your support.
01-04-2017 02:43 PM
I would add some other things, like
Verify ignition timing, both global and by cylinder if you have electronic ignition.
Are the correct spark plugs installed?
Measure exhaust emissions with a good quality analyzer, while you likely don't have the same issues with exhaust emissions in your country like we do in the US, it is still a VERY valuable tool in determining engine condition and state of tune. It would be benefical to take data from a "good" engine to use for comparison. Assure that NOx and CO readings are within expcted ranges at the specified exhaust oxygen level.
Verify the operation of the the device actually measuring the temperature(s), I find in many sites where the temperature probe, wiring or connections may cause an error in the reading, while most of the time these type problems result in lower readings they can also cause higher than expected readings.
You should also find it helpful to sit down and document this engine's history as much as you can. Has this site always had a problem? Did it start after a major service or repair? Are there any environmental factors, such as altitude or extreme temperature or humidity issues that be affecting the units operation?
How about the fuel gas? Do you have an analysis? Do you have another engine in the same area running off this particular gas supply?
How about mechanical condition of the engine? How many hours total? How many hours since last overhaul? Have you done a compression test?
Hope that helps, MikeL
01-04-2017 01:05 PM
First of all, I would like to apologize for sharing a problem that is not related specificaly to a Caterpillar engine, but I didn't find a Waukesha's forum of a good quality like this one here and I really need help from other experienced people.
My name is Flavio and I write from Brazil. I am an electrical engineer with 14 years of experience working with generator sets. I worked in Sotreq, the biggest Caterpillar dealer in Brazil for 7 years, and now I have been working in Petrobras for another 7.
I am responsible for the maintenance of 18 generator sets installed throughout the whole country. One of them, installed in the state of Espírito Santo, has been operating with high exhaust gas temperature. The standard value @ 100% load (1200ekW) should be 639°C, but we have measured 730°C @ 70% load (ekW). Because of that, the ESM (an ECU similar to the Caterpillar's ECM) is calculating wrongly the estimated mechanic power (bhp), and the engine has been shutdowning by high exhaust temperature or mechanic overload.
I would like to discuss what can cause an overtemperature situation in an exhaust system of a natural gas engine (rich fuel). I am leading some actions in order to do a research in the field, and I will list below what I believe that must be checked:
1) Correct WKI (Caterpillar's Methane Number);
2) Correct position of Air Fuel Ratio controllers;
3) Correct adjustment in the carburators;
4) Correct adjustiment of the wastegate valve;
5) High inlet air temperature;
6) High exhaust backpressure;
7) High water temperature in the auxiliary cooling system;
8) Exhaust valve misadjustment (although it is a 0 valve lash, I will list here anyway);
Do you have any other suggestion that could help me to find out what is wrong with this equipment?
Thanks in advance, and sorry again to bring here an off-topic situation.
Flavio Dupim Pires.