First attempt at start and meltdown. Ahh

[ripcrow]

Deisel guy I'm not sure I follow correctly. The shaft is the same size from the gt 30 to a gt 35 it's only the turbine that is different. I plan to use the same gt 30 comp. I have seen comp wheels for the gt30 advertised for up to 70psi so I'm hoping to get the standard comp to run then later on try the 70psi comp for extra performance.
Engine whisperer I don't think buying another turbo is cheaper. Housings on eBay start at $140 and Chinese turbines from $129 when I can get a genuine garrett turbine gt35 for $150 and get my housing machined for $150 and know what I've got. The turbo itself was brand new so I hope with a better match in size I should get a good engine for the cost. The best turbos I can get second hand are all around the $400 and most likely require a rebuild. While my Chinese replica gt30 cost $300 if I put 300 into it I still got a cheap garrett I think.

[dieselguy86]

The shaft where the bearings ride are the same starting at the gt25 all the way up to gt35. But the part of the shaft where the compressor slides on changes. To fit a gt2871 compressor wheel onto a gt35 turbine i had to ream the hole. Also garrett has been known to make the same mm compressor wheel in 2 different versions. The 60mm compressor wheel on a gt2560 is not the same wheel as the 60mm compressor wheel used on a gt2860. The 2860's wheel is taller and able to process more air even though its diameters measure the same as the 2560. I know your dealing with a gt30/35, but theres some wheels that crossover in this size as well.

[ripcrow]

Ok diesel guy thanks. From my research the shaft size for the comp is the same between the gt30 and the gt35. I'm using the gt30 comp do you see a problem with doing so.

[enginewhisperer]

I was talking second hand diesel turbos

[ripcrow]

Yeh I realise that engine whisperer and I couldn't find any that were cheap enough. Got my eye on a large one with a 100 mm inducer approx but I just got to wait to get my hands on it.

[ripcrow]

Got a new turbine and shaft and housing is being machined. The seller tells me it is a p trim turbine. What does he mean. Also tells me it is back cut which I don't understand.

[racket]

If its backcut then the exducer has been "clipped" or ground back to increase the outflow angle which means the flow area has been increased compared to an unclipped/backcut wheel

[ripcrow]

Thanks racket. What should that mean for performance. Also I realise my lpg fuel ring was built wrong. I had my holes pointing towards the centre of the flame tube which would have made a fuel rich mix down the centre of the flame tube. I'm thinking of creating a space at the top of the flame tube. Just a air space that distributes a flow of air from behind the fuel inlets. Theory is to use a lot of small holes to inject air flow and assist the fuel mix and combustion.

[racket]

It should be OK

[ripcrow]

New flame tube built. Any opinions on the flame output. m.youtube.com/watch?v=QKkxwJ1kTyU

[racket]

For an "atmospheric" test you need to have the same temperature exiting the flametube as you would in a running engine for it to be in any way representative of what might happen when installed on the engine.

Currently it looks like theres too much fuel and the exit temps would be above your running temps , you need to have flame up in the primary zone only , so stick a thermocouple on the flametube outlet and reduce the fuel back until you have ~900 C coming out .

Cheers
John

[ripcrow]

Cutting the fuel back still has the flame exiting the tube just a neat little flame the length of the tube. Could drilling extra large holes in the primary zone fix this.

[finiteparts]

Hi ripcrow,

The reason for running an atmospheric test is to determine roughly the stability characteristics of the combustor and if the combustion is occuring roughly in the right areas. If it doesn't work in an atmospheric test, it will likely not work at engine conditions.

Ideally, as John said, the flame should be anchored down in the primary zone over almost point that you can operate it with a leaf blower.

As a refresher, the basic operating principle of a three zone combustor is to have the bulk of the combustion completed within the primary zone. Your secondary jets provide extra air to help complete the slower reactions such as burning out any remaining carbon monoxide into carbon dioxide. Finally, the dilution jets provide the extra air needed to cool the bulk combustor flow down to a temperature that won't melt the turbine.

So when we look at the video and see the flame out the back end, we could have several issues going on. The first one that John touched on was over-fueling. Since you reduced the fuel and saw no change, then we need to move to the next one.

The next potential issue is like you touched on...airflow. If the primary zone air fuel ratio is to far away from the ideal air-fuel ratio (AFR), which for propane is 15.571 (based on mass), then you won't be able to complete the reaction in the primary zone. Propane has some very wide stability limits, so it is usually very forgiving. If you could send a picture of your combustor, we may be able to spot something. What size holes doe you have for your primary zone currently?

Moving to the next potential issue...let's assume you have the right AFR in the primary zone...you can still have issues due to an inability of the flame to find a good anchoring point. Turbulent flame speeds for propane are only like 12 ft/s and the airflow through your combustor may be upwards of 100 ft/s, so if the reaction layer doesn't have some sort of anchoring zone, it will just get blow out the back.

Anchoring zones are often done with swirlers or flow blockages (gutters) that set up a recirculation that brings the reacting layers back around to meet the fresh air/fuel that is coming in. This gives a constant ignition of the incoming mix and the very low static pressure core set up by the swirl provides a very slow center flow that the reaction can sit in. With this, the fuel has to be introduced to the air such that it also makes it to this anchoring point...what doe your injector look like?

If the reaction can't stabilize in the PZ, then it often hangs on the outlet, just like yours is doing in the video. But, if you don't have enough air in the PZ or are over-fueling, then it also hangs on the outlet where it is suddenly getting sufficient oxygen to complete the reaction...so there is no real smoking gun...it could be any of these or a combination.

I designed a combustor for my undergrad senior design project which ran on kerosene, but I made a five hole fuel injector to test out the combustor on propane. In the video you can see that the propane injected just downstream of a small swirler reacts quickly and during the majority of the operation, is completely burned within the PZ...with the operation being fairly stable over a wide range of AFRs. Here is a link to the video...

www.youtube.com/watch?v=0wyI5NnM3fg

As you can see, when I push too much fuel, the reaction starts to move backward and when I get way to much fuel, it will burn outside the combustor exit where it can find sufficient oxygen to complete the reactions. Similarly, at the end of the video, you can see that I set the fuel to a lower flow rate and start to increase airflow till the primary zone AFR falls below the lean stability limit and blows out...this is call lean blowout (LBO).

I know the welding and the drilled holes, with their burrs glowing, look like crap, but it was completed and tested with the semester project timeframe and my teams adviser was quite happy with it...so it served it's purpose. Plus, all I had was a Harbor Freight stick welder...which is not great for sheet metal!

Hopefully that helped and if you post some pictures, we can give you better feedback.

Good luck!

Chris

[finiteparts]

Hi again,

Here is a neat video of some reacting CFD that really shows the recirculation in the PZ well...if you watch, you can see that the cool primary jets are helping to "feed" that toroidial vortex (think of a donut shaped ring vortex...or a smoke ring) which forms in the PZ. The swirler creates a low pressure core that causes the flow to turn around and go back towards the fuel injector in a recirculating bubble...this ignites the incoming mixture and the process continues. Note how most of the reaction is done before the secondary jets come in...the bulk stream is being cooled from there...

www.youtube.com/watch?v=Mim33CvQTUQ

Also notice that the jets coming in are bent over...the small jets at the front in the conical dome barely penetrate at all, while the larger dilution jets go into the flow almost halfway through...this is because of momentum. Larger jets carry more momentum and can get into the bulk flow farther before being turned to go with the flow. This is why you always try to make the dilution jets as large as possible, while maintaining the area required to meet the liner pressure drop and keeping the pattern factor out of the combustor as even as possible.

Enjoy!

Chris

[racket]

Hi Rodney

Too much swirl from your tangential delivery tube ,............ I don't like tangential delivery tubes , they can create a situation where the flame is only in the core .

Whats your fuel injector look like ??

Cheers
John