Notices
Everything Diesel Discuss R/C Diesel engines here.

Diesel tuned pipe ?

Old 11-17-2010, 04:49 AM
  #1  
vandamned
Junior Member
Thread Starter
 
Join Date: Nov 2010
Location: BirminghamWest Midlands, UNITED KINGDOM
Posts: 4
Likes: 0
Received 0 Likes on 0 Posts
Default Diesel tuned pipe ?



Hi , i was wondering , can a two stroke diesel benefit from a tuned exhaust pipe ?

I'm working on designing my own 1.8cc diesel and I can't find data on tuned pipe dimensions, allI found was nitro and gasoline.
Also , have you got any tips on estimating max rpm , max power and egt ?(i've got all dimensions and timing diagram sorted andI can give you a pretty accurate weight for moving parts as soon as i decide on what materials I'll be using)

Also , since it has the exhaust port on its side , i was thinking of bending the exhaust pipe towards the back and placing the tuned pipe after the elbow. Is this going to affect the efficiency of the tuned pipe ?

Old 11-17-2010, 07:15 AM
  #2  
qazimoto
My Feedback: (1)
 
Join Date: Sep 2005
Location: Central Coast NSW, AUSTRALIA
Posts: 1,452
Received 9 Likes on 9 Posts
Default RE: Diesel tuned pipe ?

ORIGINAL: vandamned



Hi , i was wondering , can a two stroke diesel benefit from a tuned exhaust pipe ?

I'm working on designing my own 1.8cc diesel and I can't find data on tuned pipe dimensions, all I found was nitro and gasoline.
Also , have you got any tips on estimating max rpm , max power and egt ?(i've got all dimensions and timing diagram sorted and I can give you a pretty accurate weight for moving parts as soon as i decide on what materials I'll be using)

Also , since it has the exhaust port on its side , i was thinking of bending the exhaust pipe towards the back and placing the tuned pipe after the elbow. Is this going to affect the efficiency of the tuned pipe ?

Sounds like raw meat for the cyber theorists.

A practical working tuned pipe on a model diesel engine seems to be elusive to date. The world's best performing model diesels, those in F2C control line racers have never used them successfully. The intensity of competition is such that someone must have come up with the idea and tried it out. Perhaps the need to balance both airspeed and fuel economy was a problem. My observations of glows with pipes suggest that as they come on the pipe economy disappears. Otherwise no one really has a serious competition class for outright speed alone with model diesels. The glows always have had a much higher specific output, particularly F2A 2.5cc speed glows. They have a particularly narrow power band at very high rpm and run no nitro.

I once read a suggestion that practical problems with diesels maintaining an optimum compression setting on and off the pipe is a major issue. This doesn't mean that it's impossible, but the effort may not be worth the results.

However I believe that the old ETA 15 diesel team race motor (rear intake, radial exhaust) from the 1960's could be fitted with a tuned length intake venturi to increase economy. The idea didn't seem to have been much of a success.

Several very successful glow engines with side exhausts have been used with tuned pipes. They used a system similar to the one you suggest. I might have a pic of one fitted to a Super Tigre G15 somewhere. Edit: The pics below come from an article by the late George Aldrich published in the 1968-69 Aeromodeller Annual.

How were you intending to use your 1.8cc diesel, I mean for what purpose?


Ray
Old 11-17-2010, 08:55 AM
  #3  
soarrich
My Feedback: (98)
 
soarrich's Avatar
 
Join Date: Feb 2002
Location: The Villages, Florida NJ
Posts: 4,677
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diesel tuned pipe ?

I have a PAW 55 that I put a 5" rubber extention tube on the stock muffler and was shocked when I picked up 400rpm on a 7x4 wood prop.
Old 11-17-2010, 11:58 AM
  #4  
gkamysz
Senior Member
My Feedback: (19)
 
gkamysz's Avatar
 
Join Date: Jun 2003
Location: Crystal Lake, IL
Posts: 3,397
Likes: 0
Received 1 Like on 1 Post
Default RE: Diesel tuned pipe ?

F2C rules essentially exclude the use of a tuned pipe without being explicit.
Old 11-17-2010, 03:03 PM
  #5  
Mr Cox
 
Mr Cox's Avatar
 
Join Date: Jul 2007
Location: Karlstad, SWEDEN
Posts: 3,791
Likes: 0
Received 2 Likes on 2 Posts
Default RE: Diesel tuned pipe ?


ORIGINAL: soarrich

I have a PAW 55 that I put a 5'' rubber extention tube on the stock muffler and was shocked when I picked up 400rpm on a 7x4 wood prop.
Is that compared to open exhaust or compared to only the exhaust diverter?
Old 11-17-2010, 05:15 PM
  #6  
soarrich
My Feedback: (98)
 
soarrich's Avatar
 
Join Date: Feb 2002
Location: The Villages, Florida NJ
Posts: 4,677
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diesel tuned pipe ?


ORIGINAL: Mr Cox


ORIGINAL: soarrich

I have a PAW 55 that I put a 5'' rubber extention tube on the stock muffler and was shocked when I picked up 400rpm on a 7x4 wood prop.
Is that compared to open exhaust or compared to only the exhaust diverter?
That was using the stock muffler,(exhaust diverter?). I put the 5" extention on it so the exhaust would clear my test stand the sound was a little more mellow and the power went up,
Old 11-17-2010, 05:21 PM
  #7  
Recycled Flyer
Senior Member
 
Join Date: Oct 2009
Location: SydneyNew South wales, AUSTRALIA
Posts: 1,346
Likes: 0
Received 4 Likes on 4 Posts
Default RE: Diesel tuned pipe ?

The fact that you can find no data is telling.

The problem as I see it is that tuned pipes use a returning 'pressure' wave to scavenge out the cylinder all the way down to the crankcase volume.

As Locktite says this 'pressure' wave interferes with the high compressions existing within the engine.

I too have read reports stating unlooked for benefits with just simple straight exhaust tubes but they all were very critical on the length and probably work on harmonics much like a trombone does.

There is much theory on divergent cone tuned pipes ( if this is what you really mean here) being used for power enhancement, so good luck with it!
Old 11-17-2010, 06:26 PM
  #8  
makoman1860
My Feedback: (1)
 
Join Date: May 2008
Location: Oshkosh, WI
Posts: 109
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diesel tuned pipe ?

Another key aspect is that unlike a glow or ignition engine, the "diesel" engines use up more of their expansive energy before exhaust opening, so there is much less available energy to generate a good signal in the pipe. So the benefit might not outweight the increased weight of the powerplant.
Old 11-17-2010, 07:27 PM
  #9  
vandamned
Junior Member
Thread Starter
 
Join Date: Nov 2010
Location: BirminghamWest Midlands, UNITED KINGDOM
Posts: 4
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diesel tuned pipe ?

Well the design started as a second year uni project, but on the way i got hooked up with these tiny two strokes so now i'm actually planing on building one myself (hopefully i'll get acces to the uni's 5 axis machine). My goal is to have an engine as performant as possible for its displacement while maintaining a decent reliability. The problem is that the engine was designed with ease of manufacture in mind but now it's performance i'm really looking after, so any power enhancing tips are more than welcome.

Right now i'm looking at redesigning the crankshaft to a proper one with bearings at each end and adding a glow plug in the crankcase , right where the transfer passages start (no way of adding it closer to the combustion chamber because of the compression screw and contra piston assembly) I'll also modify the ports to improve gas flow, i can upload some CADs tomorrow so you could give me some advice on it. I was also thinking of adding compression rings to the piston , but i'm not quite sure what will happen when those rings slide across the ports.

Also, is there any specific CFD software you could recommend for this type of aplication? It's about time i start learning how to use some of those...


Anyway , as i said i am really looking forward to any tips and keep in mind that i'm quite new to this so don't be too harsh on me.


Oh , and one other thing i have on my mind... Is there a way you can make a two stroke benefit from acoustic supercharging , at trasfer port level perhaps ?
Old 11-17-2010, 10:46 PM
  #10  
makoman1860
My Feedback: (1)
 
Join Date: May 2008
Location: Oshkosh, WI
Posts: 109
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diesel tuned pipe ?

I think many of us that have designed and built diesels would be more than happy to help. As for the tuning in the transfers, short answer is no. If you havent seen Rons website, check out www.modelenginenews.org for some historical information, and darn good information at that.
Old 11-17-2010, 11:18 PM
  #11  
mylamo
Senior Member
My Feedback: (1)
 
Join Date: Sep 2003
Location: Mission, TX
Posts: 521
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diesel tuned pipe ?

I thought it would be interesting to try on
my MVVS 2.5 with the factory tuned muffler.
My patience wore thin. Somewhere in the
vicinity of 15000 RPM the pipe begins to resonate
and a setting eludes me. Perhaps with the
proper fuel and star alignment one may
obtain useful results, but not me.
Ralph
Old 11-17-2010, 11:31 PM
  #12  
Recycled Flyer
Senior Member
 
Join Date: Oct 2009
Location: SydneyNew South wales, AUSTRALIA
Posts: 1,346
Likes: 0
Received 4 Likes on 4 Posts
Default RE: Diesel tuned pipe ?

And that is only with a quarter wave tuned pipe - just try it with a full wave one, good luck!
Old 11-17-2010, 11:54 PM
  #13  
DeviousDave
Senior Member
 
Join Date: Feb 2007
Location: , MI
Posts: 1,781
Likes: 0
Received 1 Like on 1 Post
Default RE: Diesel tuned pipe ?


ORIGINAL: mylamo

I thought it would be interesting to try on
my MVVS 2.5 with the factory tuned muffler.
My patience wore thin. Somewhere in the
vicinity of 15000 RPM the pipe begins to resonate
and a setting eludes me. Perhaps with the
proper fuel and star alignment one may
obtain useful results, but not me.
Ralph

I haven't run my MVVS 15's, but considering that the .15 DFSR is a Ducted Fan motor you are likely seeing the start of the motor coming onto the pipe. I know that all kinds of wierd crap happens in a gasoline two stroke motor at this point of operation and has made fuel injecting them extremely difficult. 15k is too much load for this motor..

I think you will see better results with less load. Ducted fan motors need to rev, while an MVVS can be browbeat into swinging 8-10" props, you really should be shooting for 21k+ rpm if the motor is to be used as designed.
Old 11-18-2010, 03:26 AM
  #14  
Lou Crane
 
Join Date: May 2006
Location: Sierra Vista, AZ
Posts: 713
Likes: 0
Received 6 Likes on 5 Posts
Default RE: Diesel tuned pipe ?

Van and all...

Check Gordon Jennings' 2-Stroke Tuner's Handbook, available somewhere on-line...

His formula for resonant pipe exhaust systems was developed for gasoline-burner, motorcycle-size range 2-cycle engines. Gasoline also has considerable remaining pressure when the exhaust port(s) open. Jennings' presumptions on gas temperatures at exhaust opens are for gasoline engines, and with some adjustment also work for methanol fueled engines.

If it is the lower residual pressure at exhaust-opens that changes things for our kerosene-base diesel fuels, it is a very significant change. Anecdotal experience: in a series of tests I ran for a friend, one trial was with a tuned pipe on a DDD converted OS 46FX (predecessor to the AX). The pipe was commercially available and reputed very successful for glow fuel operation.

Running on DDD's excellent ABC blend, which did very well with standard OEM muffler, the converted engine made 'funny' noises, and soon after starting, spat gooey globs of dark, tar-like thick exhaust juice. This, at comp and needle settings which ran clean, light-honey colored exhaust oil w/standard muffler! Varying settings did not find any good, clean run conditions with the pipe.

It - tuned-pipe operation with a converted or designed-as diesel - probably can be done, but it will need a different approach. The point about the mixture and timing (i.e., comp) setting changes needed for resonant- and non-resonant-exhaust conditions may make it VERY critical, and narrow in RPM tolerance.

Hope to hear of a solution on this!
Old 11-18-2010, 04:00 AM
  #15  
HWM77
Member
 
Join Date: Jun 2010
Location: coffs harbourn.s.w, AUSTRALIA
Posts: 72
Likes: 0
Received 1 Like on 1 Post
Default RE: Diesel tuned pipe ?

Lou,i think you are on the money,bigest problem is when the resonant cycle starts the extra charge will send the engine into an over compressed state,back off the comp and it will come off the pipe,i think it can be done,its a good talking point,like tuning reed valves!!
Old 11-18-2010, 09:03 AM
  #16  
vandamned
Junior Member
Thread Starter
 
Join Date: Nov 2010
Location: BirminghamWest Midlands, UNITED KINGDOM
Posts: 4
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diesel tuned pipe ?



Can anyone give me an approximate value of EGT?
I've just found that java pipe app and i need the EGTto estimate tuned pipe dimensions. After that I'll try using CFD to finely tune it.

And why won't improving flow around ports work ? I'm keeping the same area and timing , it's just the edges of the passages I'm trying to get rid of.
Also is a square window better than a round one for top end power? Providing I'm maintaining the same port area ofc.

Edit:

Finished designing the pipe using an EGTof 450K and the total length is 36.1 cm !!! My engine look like a rat wih a spear in it now

Old 11-18-2010, 10:29 AM
  #17  
gkamysz
Senior Member
My Feedback: (19)
 
gkamysz's Avatar
 
Join Date: Jun 2003
Location: Crystal Lake, IL
Posts: 3,397
Likes: 0
Received 1 Like on 1 Post
Default RE: Diesel tuned pipe ?

I did run an MVVS 2.5 with a pipe on it may years ago. Before I knew much about engines or cared to look into the details of consumption and power output. It did tune OK, but there was a compromise between full throttle settings and part throttle. Looking at this engine now with significant black soot in the crankcase and a worn out rod, it was not happy.
Old 11-18-2010, 03:58 PM
  #18  
Recycled Flyer
Senior Member
 
Join Date: Oct 2009
Location: SydneyNew South wales, AUSTRALIA
Posts: 1,346
Likes: 0
Received 4 Likes on 4 Posts
Default RE: Diesel tuned pipe ?

Seems to me that the returning wave of a tuned pipe would recycle the heavy particles that diesels just love to pump out.

But I have seen an extractor effect on diesels with a straight length of pipe done successfully, it gained about 500rpm but only when the entire length of straight aluminium tube was very warm.

That the best I have witnessed to date.
Old 11-18-2010, 11:43 PM
  #19  
Lou Crane
 
Join Date: May 2006
Location: Sierra Vista, AZ
Posts: 713
Likes: 0
Received 6 Likes on 5 Posts
Default RE: Diesel tuned pipe ?

Perhaps we are all overlooking the basic reason that tuned-pipes work so well with methanol-based fuels?

(NB: Jennings' excellent reference book includes the concept that "off" the pipe, the engines had little to no useful advantage. ...that, in effect, for ultimate power, a great number of 'gears' could keep a human-carrying motorcycle's engine RPM in the band where a positive gain was available. We can't do that with our models, whether RC or CL Pattern, or any other use...)

Methanol can burn productively at a/f ratio from about 3:1 (by weight) to 25 or 30 to one - if you don't mind temps that will weld the sleeve to the piston. Kerosene (USA for paraffin?) is like gasoline: it works best - and only - within a much narrower a/f ratio - say, 15:1 to 18:1. Needling becomes more critical! Methanol-based fuels can better 'survive' over(-lean or -rich) conditions long enough to allow us to find a mixture setting to match the 'needs.'

For F2C (FAI CL Team Race) performance, except that FAI rules inexplicitly - but effectively - disallow it, a pipe system could most likely limit takeoff and acceleration performance 'boost,' once max economy and power are dialed for the 'long' stretches between pit stops and takeoffs. Leaving unanswered the unknown - whether a diesel engine so set WOULD start and resume full piped effect...

We get a usable output from 'standard' model diesels, which (high performance special-purpose 'specials' aside) seem happiest around their Torque Peak RPMs. The output 'curve' is favorable: In-flight RPM settles where the needed thrust matches the models' drag total for the conditions. The engine, if needed, can exceed those conditions, at that RPM, on that prop, date, temperature, barometer. Mixture and compression setting restrain further RPM increase. Further load - as in abrupt CLPA corners - drags RPM down -slightly - closer to max torque RPM - which limits RPM drop and applies the greater torque to regaining 'cruise' RPM and load conditions.

I don't have credible, measured RPM shifts for glow and diesel 'reponses' for these load-change effects, but a farily certain understanding that a system in dynamic equilibrium will respond to a change in load by changing one of the several power-producing elements. In our CL or RC pattern flight requirements, settled RPM between figures results from prop, fuel and setting conditions. Our engines increased RPMs ONLY to where drag in those conditions is nullified by prop thrust applied to the model.

Quickly apply a pitch (or any other axis) maneuver loading, and - before the engine could respond to a throttle correction - the asociated drag incereases. With no thrust change - at that critical point - the model must slow in response to the increased drag. (Hence I visualize a momentary slowing, followed by - if it occurs - an increased prop contribution towards restoring the intermediate - least loaded - conditions.)

Engine RPM is pulled closer to it's Torque Peak value, which both reduces RPM loss and provides more 'twisting-effort' (positive torque curve slope below peak) to regain any lost RPM.

Yes, exhaust gas temperature is part of the problem. So, also, is the cooling along any resonant length... Anyone want to tackle that? Methanol-based fuels give us latitude to try to find an answer.Othper, more critical fuel-based solutions do not.

Kept within the native limits, our diesels do a fine job; why go outsde that 'realm' for what suits anothe approach?
Old 11-19-2010, 08:43 AM
  #20  
vandamned
Junior Member
Thread Starter
 
Join Date: Nov 2010
Location: BirminghamWest Midlands, UNITED KINGDOM
Posts: 4
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diesel tuned pipe ?

All right , this is how the engine with the tuned pipe on looks like... highly unpractical i would say


Old 11-19-2010, 09:50 AM
  #21  
Mr Cox
 
Mr Cox's Avatar
 
Join Date: Jul 2007
Location: Karlstad, SWEDEN
Posts: 3,791
Likes: 0
Received 2 Likes on 2 Posts
Default RE: Diesel tuned pipe ?

What is the scale in that figure?
Appart from the diameter, which looks a little small to me, it doesn't look any more unpractical than any of the pipes that I have for small glow engines.
The real test would be to take a glow engine, timed for a pipe, and try it on diesel with and without a tuned pipe. Anyone fancy sacrifysing their Cox Conquest?
Old 11-19-2010, 10:13 AM
  #22  
gkamysz
Senior Member
My Feedback: (19)
 
gkamysz's Avatar
 
Join Date: Jun 2003
Location: Crystal Lake, IL
Posts: 3,397
Likes: 0
Received 1 Like on 1 Post
Default RE: Diesel tuned pipe ?

Lou, have you seen any published data supporting the likelihood of a glow engine supporting running methanol leaner than stoich? I have serious doubts that it's even possible. Besides, anyone needling the engine would certainly notice the power drop after going lean of stoich. It is my opinion that glow engine damage occurs when ignition advances due to lean(not necessarily lean of stoich) conditions and associated problems arise. I've not had the opportunity to measure myself, but I also think that most if not all glow engines run quite rich of stoich, even at peak RPM. As for gasoline, best power is often quoted at 12.5:1 A/F again using a rich mixture to prevent knock. A gasoline engine will run much richer than that. Model diesels rich. I've actually made some measurements in this regard, but airflow was estimated. And they will also run very rich. In and HCCI engine like glow of model diesel, air fuel ratio is a compromise and always rich.

There have been glow to diesel conversions of ducted fan installations with pipes and it seems without issue. Putting a pipe on a designed as diesel engine with a short exhaust duration will yield little gain. I don't play with two strokes much anymore to have any interest in spending time on it. I might make a new rod for my MVVS 2.5 and take some measurements.

Vandamed, While I can't see the details of your porting there is probably much more to be gained there, than in adding a pipe to an engine design that isn't optimized. For instance a Cyclon 1.5cc diesel will make over 0.4HP at 22kRPM open exhaust.

Greg
Old 11-19-2010, 10:14 AM
  #23  
gkamysz
Senior Member
My Feedback: (19)
 
gkamysz's Avatar
 
Join Date: Jun 2003
Location: Crystal Lake, IL
Posts: 3,397
Likes: 0
Received 1 Like on 1 Post
Default RE: Diesel tuned pipe ?


ORIGINAL: Mr Cox
Anyone fancy sacrifysing their Cox Conquest?
Hmmmmm......
Old 11-20-2010, 02:40 PM
  #24  
Lou Crane
 
Join Date: May 2006
Location: Sierra Vista, AZ
Posts: 713
Likes: 0
Received 6 Likes on 5 Posts
Default RE: Diesel tuned pipe ?

Greg,

I agree, it is unlikely that a methanol-based fuel will ever go leaner than stoich (I like that contraction of a difficult-to-type word! Thanks!). Probably also that a methanol-based fuel will never APPROACH stoich! One of the few references I came across a decade or two ago was an SAE paper comparing flame front propagation speeds for - mostly - gasoline and diesel fuel types. I seem to recall this addressed "conventionally" lubricated engines - you know: oil pans, pumps, galleries, filters. IOW, no oil mixed into the combustion package... I don't subscribe to SAE papers, just came across this one associated with a project I was involved with.

IOW, it was more likely for their tests to approach stoich, because there was no oil fraction cooling and damping the combustion process. As I recall, the paper cited finite flame propagation speeds for the fuels of primary interest, and "the propagation velocity of methanol* was too rapid to measure." !! (* - I am not positive they referenced methanol, or simply "alcohol" fuel, which is, generally, methanol or the slightly fussier, but slightly hotter, ethanol.)

In our model engines, 2- or 4-cycle, we blend oil and nitro in the liquid eventually presented for combustion. The SAE tests did not. The damping effects of a non-combustible fraction, and the skewing of the combustion process by the nitro which "brings its own oxygen" in a sense, makes the SAE paper even less directly applicable for us.

Further, chilling from vaporizing methanol is an important part of our total cooling process. An excess of methanol passing through the combustion chamber, then, appears necessary for that purpose.

So, particularly for us, the extreme speed of combustion of lean methanol, unbuffered by other vaporized or atomized materials could VERY quickly get VERY expensive - pre-ignition as hard as in a hydro-locked diesel? Richer mixes allow the methanol itself to damp the process... I don't know if SAE has done further studies since the rise of methanol or ethanol-blended (for which I'll use (m)ethanol to simplify typing.) automotive fuels. E-85, in the USA, is government subsidized to disguise the much higher cost of (m)ethanol as a fuel. And, given its lower heat yield under best practical conditions than gasoline, MORE of a (m)ethanol fuel must be burned for comparable power.

Commercial, large-engine gasoline fuels are tailored with considerable subtlety to meet the Octane Rating standards. "Proper" diesel fuels seem less finicky, except with an eye to preventing pollutants and corrosives. Compression heat and timed, fine spray seem to be very tolerant. Combustion chamber design for both types has much to do with things, and has also evolved subtly.

Opinion: "unbuffered" (oil, etc.) lean methanol combustion could "burn" more explosively, far more quickly, than our machinery could tolerate. Even if it were strong enough, using glow ignition means having a floating ignition point. With an engine heated quite high, that could even be destructively before TDC.
Old 11-21-2010, 02:16 PM
  #25  
gkamysz
Senior Member
My Feedback: (19)
 
gkamysz's Avatar
 
Join Date: Jun 2003
Location: Crystal Lake, IL
Posts: 3,397
Likes: 0
Received 1 Like on 1 Post
Default RE: Diesel tuned pipe ?

Lou, I'm not sure what you're getting at in the last post. It quite common to run 8-10° more advance in a spark ignition engine burning methanol as compared to gasoline. This indicates a longer combustion duration. Oil in the fuel does little to reduce combustion temperatures. Methanol's octane rating is very high and usually knock is not a problem, certainly not in a engine with a compression ratio of ~7:1

I've experience tremendous knock with kerosene(no ether), even very rich. It's complicated issue.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.