Merlyn Waste Gate for 231

[LANCECASPER]

@Jeff Shapiro may be able to help with that

[hubcap]

12 hours ago, Crawfish said:

Reviving an old thread for a quick question!

I was told that just the Merlyn UDC will help lower CDT due to more efficient Turbo operations, has anyone seen this in real world operations? (obviously an intercooler is the best way to lower CDT) 

 

Thank you! 

Austin 

I don't believe the Merlyn has much if any effect on the CDT. The temperature of the air coming out of the turbocharger is significantly cooled by the intercooler which improves the efficiency of the engine and I believe it also reduces the likelihood of detonation. @jlunseth is the most knowledgeable guy I know on the 231. Perhaps he will chime in soon.

I added the Merlyn to my aircraft and it definitely helps with bootstrapping and critical altitude.

[Crawfish]

@hubcap that’s what my understanding of the wastegate did, but a couple mechs said it could help with the CDT  as well. 
 

I couldn’t wrap my head around their reasoning of how it would lower CDT, because the compressor still had to compress the air thereby heating it up. 

Edited October 10, 2023 by Crawfish
Clarity

[jlunseth]

Wow is this an old thread! People still have the same questions ten years later.

Crawfish I don’t really have an answer for you that is based on testing, but I would venture to say that whether the Merlin helps with CDT is speculative and not likely to be significant. It helps to understand the difference between a turbocharger and a supercharger. Different people in the combustion field will use these words differently, but it has generally become accepted to use turbocharger to describe a turbine operated compressor (hence the “turbo”) and supercharger to refer to a mechanically driven compressor (gear or belt drive). It would not be possible to put your hand on the case of an operating turbocharger because it is cherry red. Most of the heat comes from the 1500+ dF heat in the collected exhaust that is used to drive the turbo. Since the turbo is a unit, quite a bit of the heat that goes into Compressor Discharge Temperature comes from the heat of the exhaust gases. There are no exhaust gases going on in a supercharger, but you would still not want to put your hand on the case of one. It would be too hot. But not hot like a turbocharger gets. I have seen superchargers in full power operation and the casing is made can be made of aluminum, not steel like the turbo must be. 

What’s the point? There is no doubt that the act of compressing air increases its temperature, but the contribution of the exhaust gases that heat the turbo are a major contributor and the TIT is what it is, the Merlin does not have much to do with it. The heat that warms a supercharger is mostly from the act of compressing the air, but in the turbocharger the effect of compression is much smaller than the effect of the exhaust gases.

As for the contribution the work done to compress the induction air has to the CDT, If you are compressing air from 20” to 30” as you would at 12000 (approximately), the gas laws say that the increase in temperature due to compression alone is the same regardless of how the compression is done. 

[Crawfish]

@jlunseth thank you for the awesome explanation! I’ve read lots of your posts regarding 231 operations and it’s been a wealth of knowledge. I’m sure everyone appreciates the time and effort you put into your posts! 

[jlunseth]

Thanks. The time and effort was really years ago, about a decade, trying to figure out how turbocharging works. I went to the GAMI seminar, had conversations with the GAMI people, esp. Walter Atkinson, asked Mooney, was involved myself with a supercharger company, read a lot. Credit should go to those terrific groundbreaking experts who taught us all a different way of running our engines. The neat thing is that in the early 2000s when I first bought my aircraft the TSIO360 had a poor reputation, runs hot, high maintenance costs, early top overhauls, etc. I had problems like that the first year or two and decided I had to learn to run the engine. More recently, since we pilots have collectively learned how to run the engine better, I am hearing how tough and durable that “little” 360 is. I replaced mine at 22 years and 2300 hours. My A&P has another customer whose 360 is over that. Although operation is more manual than other engines, it is a pretty good “little” engine. Knock on wood.

Edited October 10, 2023 by jlunseth

[T. Peterson]

2 hours ago, jlunseth said:

Wow is this an old thread! People still have the same questions ten years later.

Crawfish I don’t really have an answer for you that is based on testing, but I would venture to say that whether the Merlin helps with CDT is speculative and not likely to be significant. It helps to understand the difference between a turbocharger and a supercharger. Different people in the combustion field will use these words differently, but it has generally become accepted to use turbocharger to describe a turbine operated compressor (hence the “turbo”) and supercharger to refer to a mechanically driven compressor (gear or belt drive). It would not be possible to put your hand on the case of an operating turbocharger because it is cherry red. Most of the heat comes from the 1500+ dF heat in the collected exhaust that is used to drive the turbo. Since the turbo is a unit, quite a bit of the heat that goes into Compressor Discharge Temperature comes from the heat of the exhaust gases. There are no exhaust gases going on in a supercharger, but you would still not want to put your hand on the case of one. It would be too hot. But not hot like a turbocharger gets. I have seen superchargers in full power operation and the casing is made can be made of aluminum, not steel like the turbo must be. 

What’s the point? There is no doubt that the act of compressing air increases its temperature, but the contribution of the exhaust gases that heat the turbo are a major contributor and the TIT is what it is, the Merlin does not have much to do with it. The heat that warms a supercharger is mostly from the act of compressing the air, but in the turbocharger the effect of compression is much smaller than the effect of the exhaust gases.

As for the contribution the work done to compress the induction air has to the CDT, If you are compressing air from 20” to 30” as you would at 12000 (approximately), the gas laws say that the increase in temperature due to compression alone is the same regardless of how the compression is done. 

Looks like 10 years later folks are coming back to the 231 guru! Thank you for your long history of insightful contributions.

[Red Leader]

On 10/10/2023 at 4:12 PM, jlunseth said:

Although operation is more manual than other engines, it is a pretty good “little” engine. Knock on wood.

And very fuel efficient - At altitude, speeds are in excess of 180+ Kts at a little over 11gph.