IslandManFree-piston engines normally produce what in effect is compressed air mixed with exhaust. On a conventional two-stroke diesel only part of the total power output is expended in compressing air, the rest of the power being used to turn the crankshaft. In a free-piston compressor all of the power appears as compressed gas.
I worry that saying it this way is going to confuse the non-technical posters. (Not that what I'm going to say won't do worse!)
Most of the 'commercialized' free-piston engines were not used as 'air compressors' (the original use on submarines in the '30s); the air in the bounce chambers being used primarily as the 'return spring' to make the free-piston cycle work properly, and as scavenge air for a two-stroke cycle that does not use separate mechanical compression for that purpose (e.g. the Roots blowers on non-turbo EMDs).
In general, gas for use in a turbine wants to have low oxygen content and relatively low turbine inlet temperature. Only very circumstantially would there be any 'compressed air' in the combustion exhaust. All the free-piston proposals I have seen, and this includes what I have seen of the FG9 derivative as well as the GM automotive developments, used only the combustion gas from the 'power' side of the opposed pistons to drive the turbine.
The major issue with proper free-piston designs (and I believe this includes the Pescara designs) was noise -- interestingly, the major problem being intake noise from the required volume of ambient air in the sheet-metal ductwork directing it from intake filtration into the engine. (See the marine conversion in the mid-Fifties for more detail on the specific issues.)
In my opinion, it has become practical to coordinate the stroke and frequency of multiple-opposed-piston sets to reduce both the objectional 'timbre' and the acoustic power spectrum of the ambient noise. Whether that will, at some point, open up the use of free-piston/turbine power for some aspect of rail service will be interesting to watch.
Firelock76 Well, isn't that interesting. That Q1 looks so grim and "all-business" it makes me think Oliver Cromwell must have been on the design team. However, I'm sure it more than got the job done!
Well, isn't that interesting.
That Q1 looks so grim and "all-business" it makes me think Oliver Cromwell must have been on the design team.
However, I'm sure it more than got the job done!
Firelock76 Anyway you look at it that Kitson-Still hybrid was just too damn ugly to live! Yuck! A Stanier Pacific it ain't!
Anyway you look at it that Kitson-Still hybrid was just too damn ugly to live! Yuck!
A Stanier Pacific it ain't!
It's pretty, but not as pretty as this loco:
https://www.flickr.com/photos/43057478@N05/6156846048/
(Class Q1 built for the (UK) Southern Railway during WW II - it was a 'no-frills' loco designed to simplify manufacturing and reduce materials demand. No beauty but it was powerful for its weight and an effective freight loco.)
M636C IslandMan Thanks for the info. It is possible to produce compressed air by means of a free-piston diesel engine and then use this to power a turbine. The article below describes prototype locomotives based on this: http://utahrails.net/up/fg9.php Free-piston engines have a high power-to-weight ratio and few moving parts. As an alternative to producing compressed air it is possible to use them in linear alternators to produce AC electricity. Toyota announced a free-piston linear generator in 2014 to complement batteries in hybrid automobiles. If diesel free-piston generators started to be mass-produced with suitable power outputs (for example for defense applications or for standby gensets) it might become practical to use them for locomotives. The FG9 used the Free Piston exhaust, rather than simply compressed air to power the turbine, as indicated in the equipment layout at the link. EMD used electric transmission, but a 1951 (or so) Renault locomotive in France used direct drive from the turbine, possible since the gas generator was independent. It would have been significantly cheaper and somewhat lighter with direct drive. The Renault had four axles against five for the EMD. Peter
IslandMan Thanks for the info. It is possible to produce compressed air by means of a free-piston diesel engine and then use this to power a turbine. The article below describes prototype locomotives based on this: http://utahrails.net/up/fg9.php Free-piston engines have a high power-to-weight ratio and few moving parts. As an alternative to producing compressed air it is possible to use them in linear alternators to produce AC electricity. Toyota announced a free-piston linear generator in 2014 to complement batteries in hybrid automobiles. If diesel free-piston generators started to be mass-produced with suitable power outputs (for example for defense applications or for standby gensets) it might become practical to use them for locomotives.
Thanks for the info.
It is possible to produce compressed air by means of a free-piston diesel engine and then use this to power a turbine. The article below describes prototype locomotives based on this:
http://utahrails.net/up/fg9.php
Free-piston engines have a high power-to-weight ratio and few moving parts. As an alternative to producing compressed air it is possible to use them in linear alternators to produce AC electricity. Toyota announced a free-piston linear generator in 2014 to complement batteries in hybrid automobiles. If diesel free-piston generators started to be mass-produced with suitable power outputs (for example for defense applications or for standby gensets) it might become practical to use them for locomotives.
The FG9 used the Free Piston exhaust, rather than simply compressed air to power the turbine, as indicated in the equipment layout at the link.
EMD used electric transmission, but a 1951 (or so) Renault locomotive in France used direct drive from the turbine, possible since the gas generator was independent.
It would have been significantly cheaper and somewhat lighter with direct drive. The Renault had four axles against five for the EMD.
Peter
You're right about the FG9. I was using 'air' too indiscriminately. Free-piston engines normally produce what in effect is compressed air mixed with exhaust. On a conventional two-stroke diesel only part of the total power output is expended in compressing air, the rest of the power being used to turn the crankshaft. In a free-piston compressor all of the power appears as compressed gas.
Yeah, but at least the T-34 worked!
Some still do.
https://www.youtube.com/watch?v=nTrt_qPXmQY
Well I dunno...kind of has an Alco- Westinghouse-Pennsy thing going on, with a little bit of Soviet T-34 thrown in. ...except that middle part with the windows, some streetcar/trolley manufacturer.
Handrails/ steps draping over the cylinders...oh yeah that's safe and acceptable isn't it?
Obviously designed by committee.
If I had one in N scale I would paint her up for the Grand Trunk Western in the green and gold.
Don't ask.
IslandManBefore electric transmission was developed there were also proposals (I don't think it got to the prototype stage) for using compressed air as the transmission medium.
Would you call this a "prototype"? (I would)
You can read more about it here.
Meanwhile, here is an account of early Russian dieselization, including the 1-E-1 type mentioned in Self's article. (Note that Shelest's patent already describes a better approach, which would be developed more exhaustively in the free-piston locomotive proposals and designs after the '30s.)
Note that a bit later the MAN engineers had given up 'direct' compressed-air transmission but had evolved an interesting transition step; see US patent 1887633 A
IslandManI suppose it might be possible in principle to combine recovery of energy in hot exhaust gases with the exhaust cooling and recirculation used to reduce emissions in Tier 4 locomotives.
It is, but a quick review of the thermodynamics involved shows that it's even less useful than energy recovery from the whole mass of diesel exhaust.
Remember that, as with early EMD turbochargers, the 'useful' range comes only at relatively high throttle notch, and the fancy heat-recovery systems and devices produce relatively little meaningful output at lower power. It's highly unlikely that a complete steam-turbine bottoming cycle could be justified for this heat-flux recovery, and I have not seen an ORC version that would justify the cost and complexity -- there appears to be restricted enough space on locomotives for passive EGR cooling, although it might be interesting to see if a properly-chosen ORC circuit could be operated 'in refrigeration' to absorb peak heat in a physically smaller cooler at those comparatively-short transients that proved so troublesome in Tier 4 final testing.
TACs are fun, and represent a useful form of thermoelectric generator that can be (relatively) easily packaged; they can produce relatively high voltage from small thermal differential and, to my knowledge, have little if any problem with overheating, physical aging, etc. within the expected conditions and service life of locomotive components. Whether there is a practical, cost-effective use for the power they generate, however, is another issue entirely.
The principal concern with generators that use 'solar concentrators or biomass combustion' isn't their workability; it's their packaging and maintenance in a locomotive environment. And, of course, the degree to which 'the game is worth the candle'.
I suppose it might be possible in principle to combine recovery of energy in hot exhaust gases with the exhaust cooling and recirculation used to reduce emissions in Tier 4 locomotives.
The problem would be finding a mass-produced power-producing device suitable for marrying-up to a locomotive diesel engine. I doubt if a steam turbine is available in a suitable size. There are potential devices such as thermoelectric generators and Stirling engines but these are at present more of interest to NASA than more Earth-bound organizations! In the future this might change if electric generators capable of using heat from solar concentrators or biomass combustion come onto the market.
Even in the present day, heat recovery is a problem. The Rolls Royce WR21 recuperative gas turbines in the Royal Navy's Type 45 Destroyers have proved less reliable than anticipated, resulting in a demand to increase the auxiliary diesel power to a level where the ship can get by without the turbines if required. The recuperators themselves find it difficult in the heat of the gas turbine exhaust. There appears to be no simple bypass to operate as a normal gas turbine.
My favourite Russian experimental was TP1-1, seen in Self's webpage.
A four cylinder two cab opposed piston steam/diesel 2-10-2 that produced its own gas and condensed its steam.
As Dr Louis A Marre was known to say: "What could possibly go wrong?"
I did say it was an oddity!
Before electric transmission was developed there were also proposals (I don't think it got to the prototype stage) for using compressed air as the transmission medium.
Succeeding mainly in marrying the maintenance intensiveness of the steam locomotive with the higher capital cost and complexity of the diesel engine. For thermodynamic benefits largely accruing only in steady-state operation, and (at the time) requiring some fairly fiddly adjustments to work. These can be achieved in marine practice (cf. the Sharp 'turborecompression' arrangement) or stationary arrangements (Anderson recompression, as tried in the Holcroft-Anderson experimental locomotive on the UK Southern) but absent the kind of operating conditions that, for example, made GPCS workable on the Rio Turbio 2-10-2s for a while the results won't be as good for general railroad service.
The gains from recuperating diesel-exhaust heat in some kind of 'boiler' appear to me to have been terribly overestimated. You should read [Douglas Self's description of the Still system and then follow the two blue links at the bottom to his coverage of the Kitson-Still and Schneider-Still locomotives and the 'teploparovoz' 8000.
The correct use of diesel exhaust would have been in a Franco-Crosti style economizer, but it is still (no pun intended) questionable that meaningful heat recovery for the required capital and maintenance could have been obtained.
An attempt to marry the characteristics of steam propulsion with the fuel economy of the diesel engine:
https://www.lner.info/locos/IC/kitson.php
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