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Diffusion Air Purpose in DLN2.6
Purpose of Diffusion Air in DLN2.6

Greetings all.

I have been wondering about the purpose of diffusion air in DLN2.6. Is it used before transferring into premix mode? Is it used for Gas Turbine Purging? Diffusion air has a manifold which is distributed to all Cans. Diffusion air is clearly taking from CPD. The connection of the diffusion air is on the Can End Cover just as PM1, 2 and 3. I don't remember the diffusion air is being monitored on Mark 6.

Thank you in advance.

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What do the Operation Manual sections on the fuel systems and combustion system say the diffusion air is for?

I believe GE has published a lot of documents describing DLN combustion systems, many of which are freely available on the World Wide Web, that provide very good--if brief-- descriptions and explanations.

In most GE-design F-class heavy duty gas turbines with DLN combustion systems, diffusion air flow is neither monitored nor controlled by the gas turbine control system.


Unfortunately, there is no mention of diffusion air in the operation manual. Also I asked the GE consulting office in my plant, and they seem have no information about it.

what puzzles me is that when you look at the cutaway of the fuel nozzle of DLN2.6, you will see five passages (premix gas, diffusion gas, atomizing air, water injection, and liquid fuel). there is no passage for the diffusion air.

I have read more than one patent (like patent US 5259184) about DLN2 and what I understood is that during gas operation [low loads], diffusion gas will mix with air coming for the atomizing air passage (I believe it is called purge air when running on gas with lower pressure ratio). So the air fed to the combustor during diffusion gas operation is from the atomizing air passage. Diffusion air purpose still not clear as I don't see how it will get to the combustion liner since there is no passage for it inside the fuel nozzle.


Can you post the P&IDs for Gas Fuel and Atomizing Air to a websharing site?

In my recollection, diffusion refers to diffusion flame, which is the bright orange flame which emits UV, as opposed to premix combustion which doesn't emit any UV. There must always be a small diffusion flame (or multiple small diffusion flames), sometimes referred to as pilot flame(s) in order to keep the temperature high enough to sustain premix combustion--and to burn CO (Carbo Monox).

It's been many years since I studied DLN, and there have been many changes to the technology since then (2.0, 2.6, 2.6e, 2.6e+, etc.). Again, GE has published many documents about DLN combustion (GE publications usually are identified with GEH- followed by for or five digits and sometimes a single alpha character (which identifies the revision of the document). They can generally be found on the World Wide Web by searching for portions of the title; the search results should indicate the location is some GE website or webpage. I think GER-3620 has some information about different DLN combustion technologies. And one must always remember when dealing with any GE-design heavy duty gas turbine that GE Belfort has responsibility for (9F-class units fall into this category), they modify proven technology and needlessly complicate simple (and even complicated) things. Which makes life very interesting at times. And they do not document or explain their "improvements."