Engine Design basic questions

[kf2qd]

I would recommend starting with a 2 stroke, fewer parts, and run it on glow fuel, or model airplane fuel. You get to play with fits and different design ideas. I have posted here somewhere a .60 CI 2 stroke that is a nice first project.

 

[Bentwings]

Hi Andrew, On setting the eccentric for a steam engine, you should not go far wrong when set 15 degrees ahead of BDC for exhaust valves just opening... or inlet just opening at TDC? - I have used both as a starting point then tweaked to optimise depending on use of the engine.
Of course, a lot depends upon the geometry of inlet and exhaust opening and closing times, arrangement of eccentric linkage, etc. - Which is why there are so many different geometries of valve gear, Joy, Stephensons, Walschearts, etc...
The Steam equivalent of the piston ported "valve-less" 2-stroke IC engine would always be the Oscillating engine, - which can be made without worrying about valve timings. Just drill ports accurately according to "the book".
N.B. Joining engines in series, as suggested by our old friend Bentwings, can cause some strange effects in flexible couplings by different cylinders getting a bit ahead or behind others, and setting-up some terrible (destructive?) torsional vibrations.... When a resonance occurs they fight each other until the coupling is over-stressed and fails. Far better to have torsionally rigid couplings with "perfect" alignment.

I suggest you do as "a majority" of modellers have done.... Make a small steam engine - and make it run and power something. This will prove your skills at making things like pistons and bores that fit properly, crank-shafts that are not misaligned, valves that seal, bearings that do not rattle or seize, etc.
Then you can use the proven skills to make small IC engines. Start with a piston ported 2 stroke to prove you can make a runner with good compression.
A half-inch to 1 inch bore and stroke is a reasonable starter model - steam or 2-stroke IC - before you get too ambitious and go smaller or bigger! (I started with a 1/2" bore and 3/4" stroke V-twin steam oscillator - because the kit was cheap. Learned a lot!).
Then think about 4-stroke IC valves and valve gears! Modelling is an education in precision manufacture, so always use the best tools and materials you have or can afford.
And always ENJOY the hobby. We all make mistakes - then discuss solutions or lessons learned on this website. A good way to learn is from mistakes - hopefully others' mistakes, not your own.
K2

I have a threaded blocker that is micro adjustable that I can accurately measure the piston TDC and BDC

Then I can measure the exact eccentric position . I managed to get one engine to run on pretty low air pressure , about 30 psi. Steam having more expansion ability could cause this to change I YHINK. The hard part is getting the port location as it is completely enclosed soni have to use a deep method the piston Orr pistons fit pretty snug so by carefully turning the flywheel an listening I can hear the ports start to open or close once I get some relationship I should be able to duplicate it across the engine 2. I also have a “ joining flywheel with longer hub so I can have a more ridged connection. I also have several beam couplings that are pretty flexible so I may use these . I have half a dozen stepper motors I planned as generators forvthe steamer to drive plus some LED lights so the little steamer has a Job”. My whole project has gotten out of hand as I now have 6 model steam turbines set up to drive “ scale” dynamos I’ll have a” desk top power company”. May need more LED” lights my ultra low noise compressor works hard to keep up with the turbines . I have different couplings available as well as some gear belts and spring belts. For speed reducers. The turbines spin at 5400 rpm but are pretty weak so I had planned on a 3:1 reduction this would speed them to increase the drive torque to the dynamos they put out about 12 volts so I still need better speed control for the turbines . I’m thinking of needle valves maybe a gang of small ball valves . The turbines have a Mickey mouse air or steam connector so I’m in process of making a better one for the application. Always something I guess

 

[Bentwings]

Hi Andrew, On setting the eccentric for a steam engine, you should not go far wrong when set 15 degrees ahead of BDC for exhaust valves just opening... or inlet just opening at TDC? - I have used both as a starting point then tweaked to optimise depending on use of the engine.
Of course, a lot depends upon the geometry of inlet and exhaust opening and closing times, arrangement of eccentric linkage, etc. - Which is why there are so many different geometries of valve gear, Joy, Stephensons, Walschearts, etc...
The Steam equivalent of the piston ported "valve-less" 2-stroke IC engine would always be the Oscillating engine, - which can be made without worrying about valve timings. Just drill ports accurately according to "the book".
N.B. Joining engines in series, as suggested by our old friend Bentwings, can cause some strange effects in flexible couplings by different cylinders getting a bit ahead or behind others, and setting-up some terrible (destructive?) torsional vibrations.... When a resonance occurs they fight each other until the coupling is over-stressed and fails. Far better to have torsionally rigid couplings with "perfect" alignment.

I suggest you do as "a majority" of modellers have done.... Make a small steam engine - and make it run and power something. This will prove your skills at making things like pistons and bores that fit properly, crank-shafts that are not misaligned, valves that seal, bearings that do not rattle or seize, etc.
Then you can use the proven skills to make small IC engines. Start with a piston ported 2 stroke to prove you can make a runner with good compression.
A half-inch to 1 inch bore and stroke is a reasonable starter model - steam or 2-stroke IC - before you get too ambitious and go smaller or bigger! (I started with a 1/2" bore and 3/4" stroke V-twin steam oscillator - because the kit was cheap. Learned a lot!).
Then think about 4-stroke IC valves and valve gears! Modelling is an education in precision manufacture, so always use the best tools and materials you have or can afford.
And always ENJOY the hobby. We all make mistakes - then discuss solutions or lessons learned on this website. A good way to learn is from mistakes - hopefully others' mistakes, not your own.
K2

Thanks I’ll try that tip. I’m gettingvreadyvtonrelocatvtobtenn. Due to better med care and be with family more. They may be able to provide a “ get going “ atmosphere so I can get over this fatigue issue. I’m packing steamer and turbines for the move. I will still have a hobby room. And I don’t really need much more than a desk and some storage area some of the bigger tools like drill press and air compressor will go in my sons work are. Me and kitty don’t take much room . I’ll still have a computer table and maybe a push to teach cad to don maybe even grand daughter. Son and I talked about education and in view of grand daughter interest in looking things up and investigating we think maybe journalism might be a good direction It’s a tough field but we think it might be satisfying . Ultimately it will be her choice to go what direction she wants but we hoped provide the drive to follow through on her choice . The same goes for grandson . As he get older. Both at playing sports and son and I big sports people. We think this gives an edge to kids to excell at what ever they do with internal fortitude .

 

[Aerostar55]

Hi All,

Being a newly minted engineer (as in Diploma not Engineer with a Degree), obviously I have a head full of knowledge and no real world experience.
I am also learning quite a lot including self learning (I have a book and I am not afraid to use it!). The current book I have is about the design of
four stroke engines, so with pen at the ready I was going to use this book to help design a basic One Cylinder petrol (ok, gas for you Americans) four
stroke engine. Nothing fancy, just something that "should" work and has all of the basic bits like cranks and valves and cam shafts etc. For those
interested, the book is "Engineering Fundamentals of the Internal Combustion Engine" by Willard W Pulkrabek. This guy is apparently a Guru and is
better known for his books about Two Stroke engines but I find it easy to read and understand.

I am at the very beginning of this journey. I am going to read the book and work everything out as I go, then draw it and try to build it. One of the
things I need to decide is how big to make it. I want it to be big enough so that it doesn't cost too much to fabricate, but not so small I need a
watchmaker's lathe to do the machining. I also thought that if it was big enough it might serve some useful purpose in the future. One idea in the
back of my mind was that it might be nice to use the base design for other more complex designs later. My thoughts on this were: a One Cylinder
engine should be easy to turn into something like a V-2 (No. NOT some fancy rocket from the 1940s), that in turn could become a V-4 then a V-8.
By now you are probably thinking that innocence and naivity is so sweet. Well - we all started somewhere.

So, some questions.

What is the smallest practical engine that can be built? I don't want to either make my own spark plugs or source ones only available to Pygmy tribes
of the mythical Himalayas of Antarctica. I want to scale it so that I DON'T have to fabricate EVERYTHING.

What is a good size engine that might be of practical use? My thoughts here were that a 5 Litre V8 is common so what about a 0.5 Litre engine?
This would make a single cylinder engine about 25cc or 1.5cu" - is 1/10th scale too small?

The little I have read so far suggests that a "square" engine, or close to it, is practical. What the book does NOT tell me is that Stroke is easy, but is Bore
the DIAMETER of the cylinder so that 25cc = 5 x 5 or is it the ACTUAL area of the cylinder (Pi x 2.5^2) x 5 = 19.63cc when working out the size? The book
has some great definitions but that particular one is ambiguous.

What are general tolerances used in engines like this? Metric please - I can cope with "thous" but I have 10 fingers not 12 so it is easier for a "youngster"
(over 50) from Australia to work it out. 1 thou = 0.0254 mm - just sitting on the edge of the accuracy of "common" machine tools.

Final question. I have been a member here for a while, mainly lurking and reading other people's posts. I did at one stage download some files from
this site but they seem to have disappeared. I know there was a way to do it but there don't seem to be many files in the downloads section, only
posts about the files. I recall downloading some Steam Engine plans some time ago. I notice I can attach file to this post so is it I just didn't dig deep
enough into the Downloads forum? What I would really like to find is a simple car style engine plan to have a good look at. It doesn't have to be a V8
just one with all of the standard bits - cylinders pistons, crank and cam shafts, valves, etc.

Thanks in advance for all of your help.

Cheers

Andrew

Andrew - find a copy of Edgar Westbury's "Model Petrol Engines" you will find it very helpful as well as enjoyable to read for Model Motor heads.

 

[Bentwings]

Andrew - find a copy of Edgar Westbury's "Model Petrol Engines" you will find it very helpful as well as enjoyable to read for Model Motor heads.

I went the other way I started out as machinist then to tool maker maker then mech Eng school for 5-6 years actually longer as I got into deeper physics along the way I did auto mechanics part time so tools and their use became second nature. Surprisingly kids now day don’t know standard tools and are not ver creative it’s nice that you want to develop . I’m sure you will find prey o help here. The hardest part is just what to ask for . Which is what you are doing . 4 strokes are a good place to start a single cylinder square bore , stroke not a bad idea. Some times you can find used yard equipment to just mess with. It’s hard to beat a Briggs and Stratton lawn mower. I’ve had a bunch over the years. They are simple and hard to destroy. I’ve run them on nitromethane , alcohol gas even tried diesel spray oxy acetylene in them a few have come apart violently but fun learning what is strong and not so strong . I did INR have any steam training in schools but learned some just by purchasing build kits. Many can be bought as machine it your self kits too it’s a great way to get knowledge “ on the job”

Good luck to you. Stay around there are lots of good people here.