Injected Diesel 56cc 2 Stroke, Will it ever work?"

[Lloyd-ss]

Aha!
Found the article I was looking for...!
k2
https://oldmachinepress.com/2013/01/02/inside-the-cylinder-of-a-diesel-engine-by-harry-ricardo/

Ah, some of those British engineers were brilliant, and prolific. Thanks for those references. And it seriously is amazing how prolific some of the best of the best were. One new idea after the last, with many completely changing the course of prior technology. Zora Duntov was one in the United States. He designed the first Small Block Chevy V8 engine in about 1953. Arguably, the first "modern OHV V8." It started out as a 265 cubic inch and eventually grew to 400 cuin. And the basic design is still in use today. There were so many millions of them produced that they became the engine of choice for hot rodders, for many years. The main reasons being that 1)there were so many of them in existence that they were cheap, 2)after-market manufacturers jumped on the band wagon and made all sorts of hop-up equipment that was affordable, and probably most importantly, 3)Duntov's design was so good that almost no changes needed to be made to the basic design, which led to, 4)a very broad family of engines with very amazing amount of parts interchangeability, which means, cheap aftermarket parts. Genius!

With that said, yes, I think I am more or less finished with the reinventing the wheel stage, but I will probably have a relapse.....soon. Given that the basic concept of the model I am building is the Detroit Diesel 2 stroke (another amazing family of engines), and now that I have the Roots blower and the Unit injector built, probably trying to scale the model to the basic Detroit Diesel design (including the combustion chamber design) will be a reasonable approach. Physically, the injector ended up being larger than I had hoped, so the basic scale of the blower might not be visually correct, but I hope it is.

And I also realize that if the model is, lets say, 1/4th scale, that the piston area is 1/16th, and the cylinder volume is 1/64th, and that the stiffness of the crank pin is 1/256th??? So, if the engine power is proportional to the cylinder volume, i.e., 1/64 the power, does that mean the crank pin will end up being only 1/4th as strong/stiff as it really needs to be? So the crank pin will really need to built to 1/2.8 scale to the original? That is, 2.8 being the 4th root of 64? So as to keep the stiffness of the crank pin in proportion to the power? Or, because the crank pin is also 1/4th as long, and stiffness changes with the cube of the length, will doing a simple 1/4th scale of the crank be ok. Or maybe I am overthinking it, but maybe not. Ha ha, I was just going to say that this is rhetorical question and I need to figure it out myself first, but there I go re-inventing the wheel again. But the journey is more fun than the destination.

I know there are some older threads about the complexities of scaling engines, so I better dive into those first.

Lloyd

 

[Roger B]

It is interesting to think in the other directions and compare the dimensions of a big ship diesel engine (conventional not crosshead) or railway traction diesel engine with a 2L automotive diesel. The proportions are much the same.

 

[Nerd1000]

For my diesel I put together a large and incredibly convoluted spreadsheet that estimates a lot of the critical values e.g. bearing loads, stresses on the conrod, cooling water flow demand, valve sizing etc. Sometimes I use FEM analysis in my CAD software to validate a part design, but I'm not an engineer (well I am a genetic one, but DNA is different from diesel engines) so I'm sure I miss things a first year engineering student would know about. So some trial and error is involved in the design process.

 

[Steamchick]

Hi Lloyd. Re scaling. You are absolutely correct! Scale the bore and stroke then se those to re design the crank (journals) to be strong enough and stiff enough to do the job.
My first lesson in this way a basal wood and tissue glider. Kit made at 27 in wingspan, I doubled all the sizes - when it had so much lift from the wing it would only fly extremely slowly (in still air), with 2 lbs of ballast to stabilise it against the huge lift from the "wrong" aerofoils...
Since then I have had to learn the Engineering of scale!
When you do the calcs for stress and stiffness, you'll be able to relax with your design.
Cheers,
K2

 

[Lloyd-ss]

For my diesel I put together a large and incredibly convoluted spreadsheet that estimates a lot of the critical values e.g. bearing loads, stresses on the conrod, cooling water flow demand, valve sizing etc. Sometimes I use FEM analysis in my CAD software to validate a part design, but I'm not an engineer (well I am a genetic one, but DNA is different from diesel engines) so I'm sure I miss things a first year engineering student would know about. So some trial and error is involved in the design process.

I love spreadsheets,too, and also use them to excess. But I have a couple of them that I use for high pressure tube calculations and internal ballistics for airguns that I have been tweaking for almost 10 years. Pathetic, nah.

I misinterpreted (I think) your statement about being a genetic engineer. I thought you meant that the "engineering gene" in your DNA was strong, and you could not resist the force. That is fine,too.

 

[Lloyd-ss]

Injector Volume Test

The flame test was pretty dramatic, especially at max output from the injector, but I had not tested the actual flow rate.
Here is the set-up I made for flow testing. It is driven with a toothed belt by a really slick sewing machine servo motor that I got on ebay for about $100, including the controller. You can set all sorts of things like rotation direction, top speed, ramp-up rate, etc. I have already made a prony brake for it to check the output torque and was amazed that it held its target RPM even as I increased the load on the prony brake. It didn't loose its RPM until it hit close to 1/2 HP.

But, back to the flow testing. Earlier in the thread we calculated about 5 or 6 cubic mm of fuel per stroke at max power. In the picture of the test set up you can see that injector squirts into a piece of clear vinyl tubing with 3/8" I.D.. That is a volume of 71 cubic mm's per mm of depth. The motor was set at 500RPM and I just ran it, with a stop watch going, till about 5 or 10mm depth of fuel had squirted into the tube. Then, calculated the actual number of strokes and figured out the actual volume of fuel per stroke in cubic mm's. Here are the results.

500 RPM volume test, with control lever adjusted each time.
Lever set to approx 10 degrees off no-flow = 3 cubic mm/stroke
Lever set to approx 30 degrees off no-flow = 6 cubic mm/stroke
Lever set to approx 70 degrees off no-flow = 35 cubic mm/stroke

I didn't test at a higher RPM because the volume of excess fuel was pretty obvious.

That's a serious over-kill at the 70 degree setting and explains the dramatic flames at max setting in the flame test video. Looks like I need to modify the ramp on the pump plunger in the injector. I already did that once, but now I see how it needs to be fixed. Probably also need to modify the cam, also. The starting point seems to be ok, but the overall stroke is much too long. The cam mod will be easy, too.
Lloyd

 

[Lloyd-ss]

I modified the helix (flattened the angle) on the pump plunger, modified the cam to shorten the length of the pump stroke, and re-made an internal spacer to eliminate some dead volume on the output side of the pump plunger.
The output of the injector at 500 RPM will now go from a minimum of 1.7 cubic mm per stroke to 5.7 cubic mm per stroke, as the pump shaft is rotated through 45 degrees by the control arm. I am more satisfied than I was, but I am not sure how to get the fuel to shut off totally, or if that is even possible with the style of pump I have.
1.7 cubic mm still seems like a lot of fuel for a 56 cc diesel to idle with. The minimum stroke volume of fuel was 3 cubic mm per stroke before the modification, so definitely an improvement.
Lloyd

 

[Roger B]

I couldn't wait any longer. Its a pretty day, perfect for a flame test.
No idea what it proves, but yes, it was fun.

View attachment 144911

My experience has been that if you can ignite the atomised fuel with a small flame it will ignite in the engine. If it is too much of a jet it will not ignite. This is an extreme example with just a 0.35mm hole. All it would do was cover my lighter in oil.

 

[Lloyd-ss]

There was a wonderful, long discussion thread about needle bearings and other aspects of this diesel model build, but I will try and bring the discussion back to this thread. Thank you.

This build is of a single cylinder "interpretation" of a Detroit Diesel 2 stroke, 1-71. I am having a hard time finding a manual specifically for the 1-71 (single cyl, 71 cubic inch), but have them for the 2-71, which is different from the 3-71 thru the 6-71.
Anyway, here are some pics of the 2-71 that hopefully will help clarify what this icon looks like.

A couple of things to note:
4.25" bore x 5" stroke
It uses a "unit injector", that is fuel pump, metering, and nozzle all in one unit.
The piston is over 5 " long because of how it needs to keep the inlet ports covered.
The cylinder liner is about 10-3/4" long to accommodate the full travel of the piston.
The conn rod is 10.2" long to be able to swing and miss the bottom of the cyl liner.
The camshaft and balance shaft are mounted lower in the engine than in the 3-71 and larger sizes.
The cam and balance shafts are counter weighted to minimize side-to side vibration.
The roots blower is geared to run overdrive at twice the engine speed.
Note that the blower rotors are similar in diameter to the cyl bore.
The 2-71 weighs 960 lbs, is 41" tall, makes 68HP at 2000rpm. That would make a Honda Civic sit funny.
The model will have an open crankcase and closed loop lubrication with supply and return lines.

Here are 3 thumbnails. Click on them to get up-close and personal with the 2-71. Sorry, no pics for the 1-71.

 

[Lloyd-ss]

Starting on the Cylinder Head

Finally back at it, getting off of dead center.

Here are a couple of pics of the first roughings of the cylinder head for the 2 cycle diesel.
The bore is 39mm, and one of the two 16mm exhaust valves is more or less roughed in. To be able to fit the springs and rockers for the 2 valves and the unit injector onto the top of the head, the valves had to be canted back 10 degrees and to the side 3 degrees. The unit injector will also have to be a few mm off-center in order to fit. The head itself started as a piece of Nitronic 50 stainless steel 2.5" dia x 1.5" tall.
The head still needs to be sculpted to unshroud the 2 valves and grind in proper seats. The Nitronic 50 machines nicely.

I am wary of possible mental burn-out on this project so decided to use a pair of easily available 16mm x 69mm exh valves. Better to take advantage of some time savers than have the project languish in a dusty box. The fact that the head machined so nicely was a real shot in the arm.
Lloyd

 

[minh-thanh]

I am wary of possible mental burn-out on this project so decided to use a pair of easily available 16mm x 69mm exh valves. Better to take advantage of some time savers than have the project languish in a dusty box.
Lloyd

There is still a lot of work to be done, saving time and effort for other things...

 

[peterl95124]

am eagerly following this thread, am doing things in the opposite order, building everything but the fuel injector, waiting to see what works for everyone else first !!!
am hedging my bets by building two, the first will be gas and spark ignition as a risk mitigation fall back contingency plan, and the second will hopefully run on kero and compression ignition.
if you ever decide to go with silver-brazing rather than JBWeld, ask me what the challenges are first, I went through lots of MAPP gas trying to braze a flywheel without having the braze crack on cooling before I finally figured it out.
here's my progress so far, I call it an adventure in silver-brazing, part 2 will be an adventure in direct fuel injection

 

[Lloyd-ss]

.......................... I call it an adventure in silver-brazing, part 2 will be an adventure in direct fuel injection............

Good brazing is quite an art, and difficult to do. The joints look nice and sound, which is certainly most important.
Quite a nice looking engine, and even with a back-up.

 

[peterl95124]

Good brazing is quite an art, and difficult to do. The joints look nice and sound, which is certainly most important.
Quite a nice looking engine, and even with a back-up.

I don't really think of silver-brazing as an art, just something that anyone can learn, you included if you wanted to, TIG welding aluminum on the other hand I've never been able to do, that's an art !

 

[metalmangler]

I don't really think of silver-brazing as an art, just something that anyone can learn, you included if you wanted to, TIG welding aluminum on the other hand I've never been able to do, that's an art !

What's the difference between silver-brazing and silver-soldering (if any) ?

 

[peterl95124]

What's the difference between silver-brazing and silver-soldering (if any) ?

no difference, problem with "silver soldering" is sometimes people confuse it with lead free plumbing solder which is tin with only 1~3 percent silver which isn't very strong nor heat resistant

anyway, silver-soldering/brazing is basically easy, its only an art when you're doing jewelry where you want to use the minimum amount of solder and not get any overflow onto parts of the piece where it would be visibly the wrong color, but for the sort of things us model builders do there's no art to it, just heat with flux and apply silver once it gets red hot

you need 1) mapp-gas with torch on end of hose so you can point it downward (can't do that with typical plumbing propane torch), 2) white flux which goes clear once its melted so you can see what you're doing, 3) 56% and 45% silver solder the 56 is for close fitting joints as it flows like water and 45 is for gaps and fillets as its mushy, 4) a "scratch rod" (a foot long steel/stainless rod pointed at the end and 1/2" tip bent at right angle) for pushing the molten flux around and then the molten silver, 5) some weak acid (vinegar works, as does CLR remover, etc) to dissolve the flux and remove oxide after the part cools, I put the part in a pot, cover it with vinegar, put a lid on it, bring it to a boil on the stove, let cool, part comes out nice and clean

I keep lots of 1/16 diam 56 and 45 solder on hand, plus a bit of 1/32 diam 56 for very small stuff

there are two schools of thought regarding flux, one is only put flux where you want the silver, the other is flux the entire part to keep it from getting so oxidized, I often do the latter but often get silver flowing all over the place, YMMV.

Kozo recommends cutting pieces of silver and laying them on the joint and heating from the back side, this seems to be a beginner technique as it avoids changing from holding the scratch rod to the silver and back, and avoids melting the silver into large blobs before it adheres to the metal, but heating from the back side isn't always possible, so IMHO it is best to learn how to heat it from the front side sooner rather than later. The technique is to get the metal hot enough (bright red) so you can lift the flame and touch the solder to the metal and have it melt by contact, the metal isn't always large enough to hold enough heat to do this so you have to be able to quickly put the silver in the flame and take it back out quickly if it doesn't melt and adhere quickly and get the part a little bit hotter.

other niceties are firebricks to do the work on, and for large pieces firebricks to surround and insulate the piece, and some "heat blankets" (plumbing supplies to keep from setting your house on fire when soldering in place in a wall) also for insulation

OK, didn't mean to highjack Lloyd's excellent thread, but so many questions about silver, I hope he doesn't mind...

 

[Lloyd-ss]

.....................................
OK, didn't mean to highjack Lloyd's excellent thread, but so many questions about silver, I hope he doesn't mind...

Peter, No problem at all. These long threads tend to wander but always end up back on track.
I would like to add another comment about the silver brazing. The only experience I have is with copper brazing and I use a BeCuP5 filler rod, sold as Silvalloy 15. (Berrylium, copper, phosphorous, and 15% silver). Choosing the right alloy (and flux) is important for material compatibility, strength, melting point, gap filling, etc. For example, the BeCuP5 has phosphorous in it which acts as a built-in flux, and has good gapfilling and a wide "melting point", that aids the gap filling properties. Another confusing thing is that all different manufactuers will have their own special names for the same alloy. Practice a lot, LOL.

 

[Lloyd-ss]

More Work On The Head

Here is some more progress. The unit injector will be held in place with a clamp bracket like on the actual DD's. I am glad this portion of the project seems to be moving along faster than the injector part, which almost did me in, LOL.

I need to check the spray pattern to make sure it works with this head design. Valves are sitting a little proud but will hopefully be fine after they are lapped in later on. The 10 degree x 3 degree valve cant is pretty obvious now.

 

[Steamchick]

Excellent work Lloyd, Keep on with the posts.
K2
P.S. To "draw a line" to limit flow of silver solder - for cosmetic reasons, - use a slightly soft pencil. The graphite and clay stop the silver solder from flowing.
And I must concur - ALWAYS use the correct flux for the alloy being used. And DO NOT overheat the flux - Poisonous gases ensue, which need good ventillation or acid-fume burning inside your lungs, and the break-down of the flux with high temperature stops it working as a flux and the joint will be bad.

 

[ajoeiam]

I don't really think of silver-brazing as an art, just something that anyone can learn, you included if you wanted to, TIG welding aluminum on the other hand I've never been able to do, that's an art !

That was the building of techniques that was used in my training.

Brazing - - - steel parts
welding - - - - oxy-acetylene
welding - - - stick (first 6010 then 7018)
welding - - - MIG (MAG) including aluminum
(then comes the Queen (grin!!!)
welding - - - TIG

IMO its all a matter of some decent instruction followed by someone correcting your process for a bit and then LOTS of practice
(the second part really helps things!!!!)

An art - - - - sorta - - - - but its also a craft and I think anyone can learn the craft
(making it to art - - - -dunno - - - - don't think that happens too often - - - - like welding stick by sound - - - - )