Start-Up Gas Turbine Frame 6B on Destilate Mode


Thread Starter


Dear Team,

We have an issue on gas turbine Frame 6B. When we tried to start on distillate mode, we got failure to ignite alarm.

FYI, our Frame 6B is dual fuel and we don't have a problem with gas.
I tried to start with gas till FSNL than changed it to distillate (and everything looks fine).

I checked FQL and Atomizing air pressure everything is okay (atomizing air pressure 6 bars on FSNL).

I checked AA booster compressor (GARDNER DENVER CYCLOBLOWER) driven with diesel starter engine when we started with distillate (we got 1 bar).

I checked the two spark plugs and its looks okay, same with flame detectors, we changed it to new ones.

Many thanks, and i look forward to hearing from you.

Did you get any other Alarm. When were the Fuel Nozzles last maintained? Did the machine ever start on Diesel? If Yes, when was that and has any other work been done since then?

When you try to ignite, does the Exhaust Temp. rise at all before you get loss of flame?
Thank you for your response.

So, we have got failure to ignite alarm only, and the machine was started and working on distillate before. We didn't work on the machine (No MI or HGPI or....).

When we tried to ignite, we didn't get any change of exhaust temperature. And, we can start on gas then change to Diesel ON fsnl WITHOUT any issue.

Thank you.
Hi again.

Check your A.A. P&ID. Please check the two non-return valves in the AA line, one just after the main A.A. compressor and one in the Booster compressor discharge line (I don't have a drawing at the moment so I can't give you Tag numbers.)

This system works automatically to change over from booster to main during start-up, as CPD increases then AA increases until AA pressure is greater than booster and the non-return valve after the main compressor opens. If this non-return valve is stuck partly open, you will have low AA pressure at the point of ignition.

Have someone on stand-by at the liquid Fuel Flow Divider and get them to check nozzle pressures when trying to ignite.

I have checked the non return valve of AA booster compressor, and I found it damaged.

We trying to get a new one for now.

For the pressure nozzle in the flow divider, I have checked it before, when we tried to start on diesel, all the nozzles are okay.

Thank you very much,

I will give a feedback soon as possible.


There have been several issues discussed here in this thread, and failures or problems igniting on liquid fuel have been covered MANY times before in other threads on There is a very good 'Search' feature at the top of every webpage (look for the magnifying glass).

When did your problem start? After a trip from load? After a maintenance outage?

What have you done to try to troubleshoot your problem--and MOST IMPORTANTLY, what were the results of your troubleshooting?

When you attempt to start the turbine on liquid fuel (and I'm presuming it's a GE-design Frame 6B (or Frame 5) heavy duty gas turbine-generator) do you see any change in exhaust temperature? If so, are all the exhaust temperatures relatively even or are some hotter and colder than others?

When you attempt to start the turbine on liquid fuel, if you see a change in exhaust temperature (an increase of some of all exhaust temperatures), do you see any white smoke coming from the exhaust stack shortly after you see the exhaust temperature change? White smoke is an indication of EITHER poor atomization of the liquid fuel or liquid fuel which has collected in low points, including the gas turbine exhaust, from multiple failed starts where liquid fuel flowed but was not ignited and when it gets hot instead of burning (combusting) it just "smolders" and smokes. If you have been trying repeatedly to start on liquid fuel and you are seeing white smoke, or even fuel vapors exiting the stack, that's an indication that liquid fuel has been flowing but has not been properly ignited--and it pooling (collecting) in low points which can lead to an explosion if not properly vented. You might want to CRANK the unit for 30-45 minutes to help remove vapours and reduce and pooled liquid fuel. (Make sure the false start drains are all open and working, for the turbine compartment, and the exhaust.)

Have you stationed two people near the liquid fuel flow divider, one with a clipboard, paper and a pencil or pen and the other who will rotate the manual valve handle around and shout out the pressure readings on the gauge for the other person to write down? (It will help is the handle is placed at the #1 position prior to starting the unit, and the person writing down the pressures has 12 rows numbered and ready for the pressures being shouted out. There will only be 30-60 seconds once fuel starts flowing to record the pressures, but once you see the pressure in the #1 position rise and stabilize you can then start rotating through the other detents (positions) and recording the pressures.

The pressure readings should all be pretty much the same pressure, within about 10% or so of each other. Any reading which is more than 10% higher the average readings or less than 10% lower than the average readings probably indicates some kind of problem with the liquid fuel delivery system (the high-pressure liquid fuel delivery system). Either the liquid fuel check valve is not working correctly (usually indicated by a lower then normal pressure, but if the check valve is plugged with debris of some sort (including algae in the liquid fuel system) the pressure for that combustor could be higher than normal. If there is a problem with a blockage in the liquid fuel nozzle that will usually be indicated by a higher than normal pressure for that nozzle/combustor. If there is a problem with the liquid fuel check valve (some are assemblies which can loosed over time if not properly assembled), that can be indicated by a lower than normal pressure for that nozzle/combustor. If the liquid fuel nozzle internals are worn that would be indicated by a lower than normal pressure for that nozzle/combustor.

If the unit also runs on gas fuel, there will be some fuel purge lines and at least one "tell-tale leak-off" on the right side of the turbine compartment, underneath the walkway. The leak-off should drain into a "cup" of some sort, so that if there is any liquid flowing out of the tell-tale leak-off it can be spotted. (By the way: There should be no liquid fuel coming out of the tell-tale leak-off.) You can find the tell-tale leak-off(s) on the P&IDs for either the Liquid Fuel System, or the Atomizing Air System or the Liquid Fuel Purge system (again, I'm presuming the unit also burns gas fuel--this may be a bad presumption, and there will be not tell-tale leak-offs if the unit only burns liquid fuel (distillate fuel only).

Atomizing air is VERY important to starting a GE-design heavy duty gas turbine on liquid fuel. There is usually an AC (Alternating Current) motor-driven Boost Atomizing Air Pump to help provide sufficient Atomizing Air flow (the pressure is very low and very difficult to read on most gauges) during starting. If the unit you are working on uses a diesel engine for a starting means the Booster Atomizing Air Compressor may be driven by a belt from the crankshaft pulley of the diesel engine. In any case, as was mentioned previously in this thread, it's important that the check valves in the suction and discharge lines of the Booster Atomizing Air Compressor are free to move and are working properly and are not sticking open or closed or in some mid-stroke position.

As was mentioned, most Atomizing Air pressure gauges on GE-design heavy duty gas turbines are designed to read Atomizing Air pressure when the unit is running at rated speed, and so the gauge is chosen such that it's range makes it easy to read at normal Atomizing Air pressures. Unfortunately, during starting, Atomizing Air pressure is VERY low, often so low that the needle of the pressure gauge barely moves. So, sometimes, it's necessary to find a pressure tap in the AA piping and install a manual valve and a pressure gauge with a low range. By opening the manual isolating valve during starting, it should be easier to read an increase in AA pressure--just remember to close the manual isolation valve so as not to damage the gauge when the unit is accelerating up to rated speed (once your firing problem is resolved).

Also, when you are trying to start the unit on liquid fuel and liquid fuel is flowing to the unit what is the liquid fuel supply pressure to the Liquid Fuel Stop Valve (usually in the Accessory Compartment) doing? It should be stable, and it should be approximately 4 barg (50-60 psig) or so. If the pressure is a little higher or a little lower--but stable and not fluctuating--that's okay. The important thing is that the liquid fuel supply pressure is stable, and not higher than approximately 6 barg (80-85 psig).

A few questions--necessary because we really don't have much information to work with. Atomizing Air pressure (flow) is very important during starting on liquid fuel. It's necessary for atomization of the liquid fuel which is necessary for complete combustion (to help avoid white smoke).

It's also common for the ignitors (spark plugs) to get very wet during starting on liquid fuel, especially if the unit has been unsuccessfully started several times in a row. If the ignitors (plugs) get wet with liquid fuel, they can't develop a strong spark. Also, ignitors need to be checked and maintained over time--they don't last forever. They have replaceable parts which must be checked and replaced if necessary.

The above should give you enough to reply and to do some troubleshooting you might not have already done. When posting to with a problem, you should ALWAYS tell us as much as possible about the problem you are having, AND what troubleshooting you have, and MOST IMPORTANTLY what the results of your troubleshooting were. (By the way, it's not enough to say, "The liquid fuel supply pressure was good." You need to tell us what the liquid fuel supply pressure was recorded to be AND if it was changing, even if by half a barg or just a few psig.

The last thing you need to know is that one of the most common problems for failures to ignite on liquid fuel is air trapped in the liquid fuel lines--anywhere in the liquid fuel lines. A properly installed liquid fuel piping system will have high-point vents, and when having problems like this its important to make sure all the liquid fuel filter canisters/vessels are vented of all air. AND, that if there is a liquid fuel storage tank from which a liquid fuel forwarding pump is taking its suction to send fuel to the turbine, there is usually a strainer on the suction piping of the forwarding pump. Very often these strainers don't have either a differential pressure gauge or a differential pressure switch to warn that the strainer is dirty/clogged and needs to be cleaned.

Please write back with the requested information. We realize English is probably not your primary language, but do your best. We can often read between the lines. And with more information, we can be of more help.