Modified expansion engine?

[Steamchick]

Check the thermal capacity of steam versus air for he simple answer to why steam is better than air. The factor-in some effect for the latent heat of vaporisation of steam, as it condenses to "wet" steam - assuming it was introduced to the engine as "dry" steam, or "superheated".. The no time steam acts like a "perfect gas" is when no condensation takes place. Air can be dry and act like a perfect gas, but without a drier is really a mixture of a lot of air, with a tiny amount of steam (the humidity). So the mathematicians work on equations for perfect gases, but Engineers have to work with an imperfect real world...
Please do the calculations, as it will help you understand what is happening. Compare the "work" between a cylinder of perfect gas expanding and the same pressures for steam at your planned design inputs. It is only when you do the calcs yourself, that you will really start to understand the differences between an air-design and a steam design. But you need to decide if the engine will just "idle" at shows, or do some real work. E.g. drive a boat, wagon, or generator?
Designing just for an exhaust sound is something new to me...
Incidentally, I run a small twin expansion engine on the bench at shows for the Sunderland Model Engineers. Idling "On air", the engine runs effectively as a single. I can't detect any effect of the second expansion cylinder. But when I run on steam, because of the larger energy input, the engine runs as a single for 5 or 10 minutes or so until the temperature rises in the second cylinder, when suddenly the engine will change exhaust, and accelerates as the expansion cylinder starts working.
So first think of what you really want to achieve and why - write it down, then keep a log-book of progress and when any ideas change and why, and enjoy making and dislaying the models you want.
Enjoy!
K

 

[Steamchick]

Sorry about some words and grammar, as I am constantly battling with my spell-checker! It changes words and predicts a different statement often, as I type!
K

 

[teeleevs]

Sorry about some words and grammar, as I am constantly battling with my spell-checker! It changes words and predicts a different statement often, as I type!
K

Solution, watch the line above the keyboard and tap the correct word each time, that will stop its pranks. Ted from down under

 

[Steamchick]

Thanks Ted, I correct every second or third word... but missed a couple of words on this one! I think there is some sort of delay when I am on my tablet, as things are much easier when I use a proper PC. The Tablet seems to think about every word, and sometimes takes all the letters I type but splits the word into pieces. And often if a word begins (E.g.) with a "th" it will make it "the" without my behest and then the rest of the word is translated into gobble-de-gook! How to I tame the "stupid" thing? - This PC has taken my typing with just 2 typos that it prompted me to correct, but the tablet just isn't as friendly. "Technology"! - Designed by a moron I think! - Sorry I am venting my spleen again....

 

[Steamchick]

Forgot to mention - the tablet rejects almost every technical word like "engine"!

 

[L98fiero]

Forgot to mention - the tablet rejects almost every technical word like "engine"!

Just turn off the spellchecker, if your spelling and grammar is better than the spellchecker, why use it at all?

 

[Richard Hed]

Thanks Ted, I correct every second or third word... but missed a couple of words on this one! I think there is some sort of delay when I am on my tablet, as things are much easier when I use a proper PC. The Tablet seems to think about every word, and sometimes takes all the letters I type but splits the word into pieces. And often if a word begins (E.g.) with a "th" it will make it "the" without my behest and then the rest of the word is translated into gobble-de-gook! How to I tame the "stupid" thing? - This PC has taken my typing with just 2 typos that it prompted me to correct, but the tablet just isn't as friendly. "Technology"! - Designed by a moron I think! - Sorry I am venting my spleen again....

Spell it how it sounds and forget about the f**king rules! the only problem this presents is the difference between a few words like: Their there they're and your you're. some times we need to be clear on words that sound the same but has different meanings. the ruels? they are awful offal!

 

[Steamchick]

Sorry, too many years of being a pedant. Language is a root tool of Engineering. My Engineering pedantry makes me want to "do the right thing every time". - I was taught that the "wrong way" and short-cuts often lead to disasters, though can get good results. The reason that the Americans use "Fire" to shoot guns and launch nuclear missiles can lead to confusion with "Fire" - when the chip-pan goes up in flames in the galley. The English use the phrase "shoot" for the former, and "Fire" for the latter case... "get the bastard" is an engineering term for "please pass the coarse-cut file", not "shoot him off his horse" or "please bring the Manager here". I like Engineering and correct language, but the spell-checker is a short-form dictionary with many technical terms missing... And I still think it is only on the Tablet that I have a problem? - I bought it in the USA... - maybe that is significant? I understand they don't speak English, but use the English language for their own "American" language. Though I am always a little perturbed at the use of "American" to describe the USA exclusively, forgetting the South American nations, original North Americans, Canada, the Central American countries, and even Hawaiians!
Enough said.
I still apologise for my Typos, grammatical errors and spelling mistakes because I read the keyboard, not the screen. Oh, to be perfect....

 

[Ken I]

"England and America are two countries separated by the same language" George Bernard Shaw

Not to mention threads, wire gauges, inches vs millimetres, fractions vs decimals, souder vs solder, Bouy (Boo eee ?) etc. etc.

 

[Steamchick]

I think you could include gallons in the list of diverse and strange differences between our 2 great nations?
A curiosity: When driving, it seems that the "strong hand" should retain control of the Steering, while the "lesser" (Left-hand in 80% of the population) should manage function such as changing gear, etc.
When inventing a "horseless carriage", the driver was situated where the Stagecoach or Surrey driver would, sit, as opposed to the "shotgun" or "girlfriend".... or whatever. Never having driven a Horse carriage, I don't know which hand controls the whip, and which steers.... by the reigns? - So maybe that's how we developed a difference between driving on the left - or right - of the vehicle, or road? I think Mr Renault started the gme, so who is "right"? - At the start of the 20th century, the English preferred to be different to the French... so maybe that's how it started? We remember Gustave Eiffel, but not Designer Benjamin Baker, Consulting Engineer John Fowler and Building Contractor William Arrol, who built the Forth Bridge. ...?

 

[Richard Hed]

"England and America are two countries separated by the same language" George Bernard Shaw

Not to mention threads, wire gauges, inches vs millimetres, fractions vs decimals, souder vs solder, Bouy (Boo eee ?) etc. etc.

I thimk I would take a lift down to the lorry.

 

[Richard Hed]

Sorry, too many years of being a pedant. Language is a root tool of Engineering. My Engineering pedantry makes me want to "do the right thing every time". - I was taught that the "wrong way" and short-cuts often lead to disasters, though can get good results. The reason that the Americans use "Fire" to shoot guns and launch nuclear missiles can lead to confusion with "Fire" - when the chip-pan goes up in flames in the galley. The English use the phrase "shoot" for the former, and "Fire" for the latter case... "get the bastard" is an engineering term for "please pass the coarse-cut file", not "shoot him off his horse" or "please bring the Manager here". I like Engineering and correct language, but the spell-checker is a short-form dictionary with many technical terms missing... And I still think it is only on the Tablet that I have a problem? - I bought it in the USA... - maybe that is significant? I understand they don't speak English, but use the English language for their own "American" language. Though I am always a little perturbed at the use of "American" to describe the USA exclusively, forgetting the South American nations, original North Americans, Canada, the Central American countries, and even Hawaiians!
Enough said.
I still apologise for my Typos, grammatical errors and spelling mistakes because I read the keyboard, not the screen. Oh, to be perfect....

I insist, as an American, that you British don't know how to speak English! (This is a long standing joke between us Americans and my Brit friends since I probably have to explain this.)

 

[Bruce T]

"England and America are two countries separated by the same language" George Bernard Shaw

Not to mention threads, wire gauges, inches vs millimetres, fractions vs decimals, souder vs solder, Bouy (Boo eee ?) etc. etc.

As an American I only wish the Brits would learn to properly pronounce AL u Min eum. LOL.

 

[Ken I]

Bruce - I worked for a US company that was taken over by the Aluminium conglomerate Alusuisse - who promptly issued a directive to it's newly acquired US workers on the correct spelling and pronunciation of Aluminium - It wasn't well received.

Regards - Ken

 

[RonW]

I insist, as an American, that you British don't know how to speak English! (This is a long standing joke between us Americans and my Brit friends since I probably have to explain this.)

You mean the only nation who can screw up the english language worse than the Brits is the Yanks.
RonW

 

[peterl95124]

Rudy,

1) (repeating what has already been said) check out johnsmachines.com/catagory/triple-expansion-miniature-steam-engine as his runs fine on both air and steam.

2) what I've read about triple expansion engines so far is that the valve timing for each cylinder is adjusted as though it were a single, but it seems to me that the objective should be to make it so that the exhaust timing of the higher pressure cylinder coincides with the intake timing of the lower pressure cylinder that it feeds into.

i've brought this question up in a variety of forums but have never gotten any decent feedback. I have a casting kit for the Bolton Triple so in the "fullness of time" (its pretty far down the todo list at the moment) will do the experiments myself.

best,
Peter.

 

[Steamchick]

I have a Twin expansion engine - timing is simple - the cylinders are timed 180 degrees apart, so when one cylinder opens the exhaust valve the other opens the inlet valve - and closing is simultaneous as well. On air it runs as a single - it seems to have no effect on the second cylinder - but on steam after 5 minutes or so of running the second cylinder starts to get sufficient "hot" steam so it starts to drive and there is a significant increase of idle speed. (Changing from a vapour/water pump to engine mode doing real work with the steam.). I imagine a triple will just follow the same logic? Each cylinder needs to open the exhaust valves as "normal" timing, so the receiving cylinder must open the inlet valve onto the appropriate cylinder at the same time. I can't see how it would work otherwise, on a common crank.
There is a built-in inefficiency of expansion engines that steam exhausting from a higher pressure cylinder expands to the volume of the lower pressure cylinder without doing any work (Half the energy is lost if volumes are 1:2). but the advantage is that the remaining energy of the steam can give up temperature and pressure in driving the next piston. I suspect that even when my twin is initially running and still warming to the steam there will be some energy extraction from the residual steam from the HP cylinder.
But always remember to have ALL the cylinder cocks open while the engine is warming, only closing (progressively, HP to LP) as each cylinder "cleans-up" and blows to minimal water in the cylinder-cock exhaust. The LP cylinder takes a lot longer for this to happen than the HP. If you don't carefully manage the cylinder drainage, you risk an Hydraulic Lock - and possible damage to bearings and rods. You really don't want to damage the precisely made bearings and have a shortened life before you have a "knocker" that is embarrassing to show running. (Perhaps that is why so many engines are polished and pretty ornaments and are never seen running?).
K