Model Diesel: 32mm bore, 38mm stroke, indirect injection

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Are you planning to make a compression tester? There is quite a difference between what feels like a lot of compression and enough to reach ignition temperature ~30 bar plus.
 
Are you planning to make a compression tester? There is quite a difference between what feels like a lot of compression and enough to reach ignition temperature ~30 bar plus.
I have a small engine compression tester, but I would need to make some kind of funky adaptor to allow it to connect up to the injector hole.

I think my next mission is the rockers and pushrods. I've been a bit indecisive on this matter, and actually designed two options
1714344508338.png

1714344665495.png


Which option do people like more? I see pros and cons to each. The second option might also be altered to omit the side supports and just use the pillar in the middle.
 
I would remove the centre pillar from the second option and just support from the sides. This would give you more space if you have to modify the injector design (which my experience suggests will be the case).
 
I don't often have time to do machine work during the week, but the 3d printer is at my apartment so I can sometimes print a part. I just did the rear gear cover, from carbon fiber filled nylon 6.

I think this is the best part I've ever printed from this material, must have finally got the settings just right. The cover is also the housing for the centrifugal governor which accounts for the funky shape.
 

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After some trials, tribulations and a redesign, here are the rockers fitted along with the pushrods.
20240511_150944.jpg

I like this system of rocker pedestals and trunnions, it turned out very nicely and I'd certainly use it again. I would however beef up the middle of the rocker a bit, I managed to squash one in the vise and had to remake it.

It's not so obvious in the photo, but I also made the copper head gasket. It seals well, and at present the only obvious leak is the valves. I'll have to re-lap them. Even with a substantial leak from the valves the compression pressure is considerable, the engine is very difficult to turn past TDC by hand. This of course raises the question of how I'm going to start it, as it is also a struggle for my electric drill.

In terms of major assemblies I only have the injection pump and governor left to go. Plus a few odds and ends. Very exciting and I can't wait for the next time I've got some free time for machining :)
 
After some trials, tribulations and a redesign, here are the rockers fitted along with the pushrods.View attachment 156112
I like this system of rocker pedestals and trunnions, it turned out very nicely and I'd certainly use it again. I would however beef up the middle of the rocker a bit, I managed to squash one in the vise and had to remake it.

It's not so obvious in the photo, but I also made the copper head gasket. It seals well, and at present the only obvious leak is the valves. I'll have to re-lap them. Even with a substantial leak from the valves the compression pressure is considerable, the engine is very difficult to turn past TDC by hand. This of course raises the question of how I'm going to start it, as it is also a struggle for my electric drill.

In terms of major assemblies I only have the injection pump and governor left to go. Plus a few odds and ends. Very exciting and I can't wait for the next time I've got some free time for machining :)
Buy a bigger drill?

But seriously:
Can you set up a movable shim on your exaust valve to be a decompression set up. Then once the flywheel has some speed you could drop the valve?
 
After some trials, tribulations and a redesign, here are the rockers fitted along with the pushrods.View attachment 156112
I like this system of rocker pedestals and trunnions, it turned out very nicely and I'd certainly use it again. I would however beef up the middle of the rocker a bit, I managed to squash one in the vise and had to remake it.

It's not so obvious in the photo, but I also made the copper head gasket. It seals well, and at present the only obvious leak is the valves. I'll have to re-lap them. Even with a substantial leak from the valves the compression pressure is considerable, the engine is very difficult to turn past TDC by hand. This of course raises the question of how I'm going to start it, as it is also a struggle for my electric drill.

In terms of major assemblies I only have the injection pump and governor left to go. Plus a few odds and ends. Very exciting and I can't wait for the next time I've got some free time for machining :)
Buy a bigger drill?

Can you set up a movable shim on your exaust valve to be a decompression valve to let you spool it up freely?
 
View attachment 156112


It's not so obvious in the photo, but I also made the copper head gasket. It seals well, and at present the only obvious leak is the valves. I'll have to re-lap them. Even with a substantial leak from the valves the compression pressure is considerable, the engine is very difficult to turn past TDC by hand. This of course raises the question of how I'm going to start it, as it is also a struggle for my electric drill.
"the engine is very difficult to turn past TDC by hand" 👍👍
Only when you build will you know how it is
 
I spent today doing some odds and ends parts of the engine project. The crankcase has been drilled and tapped for mounting brackets so I can bolt it to a base, I made a new washer for the timing gears, put the nylon cap on the front end of the cam, and made a starter dog and driver. After re-lapping the valves yet again, they are finally sealing well enough that the rings are now the main leak. An aside here, they still leaked despite the lapping compound having made a dull ring all round the seat. I ended up checking by putting a thin coat of prussian blue on the valves and turning them in their seats. I also sealed the two crankcase halves together with RTV.

Having done all this, temptation took over and i put the head on and cranked the engine with a more powerful drill in low gear. There was a noticeable smell of burnt oil, and so, optimistic, I sprayed some 'start ya bastard' into the intake port and tried again... a large cloud of white smoke shot out of the exhaust as the valve opened. We've achieved compression ignition! After a few more tries the engine stopped firing after getting a squirt, so I put a bit of oil down the intake and it fired on the next attempt. Seems like we just need the rings to bed in (or to crank faster than 550 rpm). I pulled the head, and here's what I saw on top of the piston:
20240514_154125.jpg


As you can see, there's a burn mark, where the oil on the piston crown got scorched. It's right under the pre-chamber passage, which would be consistent with ignition happening in the pre-chamber and shooting hot gases out towards the piston.

This is all very promising, I'm pretty confident that if we can fire from cold on starter fluid we can probably get it running on diesel. However, the starter dog is a problem.
20240514_154236.jpg

The setscrew securing it to the crankshaft chewed up the flat on the shaft pretty badly. I need a better solution, currently thinking of changing to a clamp style design that grips the shaft by closing up. And of course, we need the injection pump so it can run for more than one revolution.
 
I use a split clamp for my starting dog. I doesn't damage the crankshaft so much and will act as a mechanical fuse if something jams whilst you are cranking with a drill.
Congratulations on the first puffs of smoke 👍 :)
 
I'm making some progress on the injection pump. The body of the pump and the barrel are done and the barrel has been lapped, though I may give it one more go with finer abrasive. I also made a plunger. Both plunger and barrel are of silver steel and hardened by quenching in oil. Worked well for the barrel, but it backfired with the plunger! I tried lapping it today and discovered that it warped from the quench, so I couldn't get it to clean up all the way around before it went undersized.

I'm part way through making a replacement. I think I will forego the heat treatment this time.
 

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Hola a todos,

Después de que Minh-Than construyera su diésel, me interesé en fabricar el mío propio. Desde entonces me he vuelto completamente Nerd y me he hundido en un agujero muy profundo leyendo sobre sistemas de combustión diésel, en particular el trabajo que hizo Sir Harry Ricardo (que debería ser un héroe personal de cualquier fabricante de motores a escala) para conseguir motores diésel pequeños y de alta velocidad. funcionó bien en las décadas de 1920 y 1930. Me gustaría hacer funcionar mi motor con biodiesel o combustible diesel normal y (potencialmente) usarlo para impulsar una carga, por lo que definitivamente necesitamos un buen sistema de combustión para evitar un consumo deficiente de combustible, humo excesivo, etc.

Mi plan para lograr esto es utilizar una cámara de turbulencia. Esto exige una relación de compresión alta: mi diseño está previsto que sea de alrededor de 23:1. Probablemente también necesite precalentar el aire de inducción para el arranque en frío (no puedo colocar una bujía incandescente y un inyector en la cámara de turbulencia de 10 mm de diámetro). Está previsto que el abastecimiento de combustible se realice mediante una bomba tipo Jerk estilo Bosch, que será lubricada por el propio combustible para que podamos tolerar algunas pequeñas fugas más allá del émbolo.

Aquí está el progreso actual en el diseño de las entrañas del motor.

View attachment 139396

Debido a un error en el trabajo de un cliente, ahora poseo una gran cantidad de cojinetes de bronce de manganeso de 20 mm de diámetro interior, por lo que serán los principales. Puede ver el pistón (tres anillos de compresión y un control de aceite) y la biela (bastante convencional) junto con el cigüeñal de alta resistencia y un sustituto para el árbol de levas y los elevadores. Al fondo está la carcasa de la bomba de inyección.

La mayor parte del trabajo que he hecho hasta ahora fue en la culata. El diseño de admisión de contraflujo debería ayudar a mantener el calor en la carga para una combustión suave y fomentar la turbulencia en el cilindro para ayudar a la segunda fase de combustión fuera de la cámara de turbulencia.
View attachment 139397

La cámara de turbulencia está formada por una cavidad semiesférica en el cabezal y un inserto de acero inoxidable correspondiente que forma la parte inferior de la cámara e incluye un puerto tangencial que la conecta al cilindro. El Inyector es del tipo pivote con apertura hacia el interior:
View attachment 139398
El conector de púas en la parte superior es un drenaje para el combustible que escapa a través de la aguja hacia la parte superior del inyector. La aguja sella el orificio a través de un anillo de pistón de Delrin y, como los anillos tienen un espacio, siempre habrá alguna fuga.

¡Espero que todos estén interesados en el inicio de este gran proyecto! Queda mucho más trabajo de diseño por hacer, junto con la creación de prototipos de componentes del sistema de combustible, etc., antes de iniciar la construcción del motor. Deséame suerte.

-Nerd
Hola buenas tardes

Me podrías mandar los planos del inyector

Gracias
 
Es un problema interesante saber qué sucede cuando el combustible se inyecta en aire a alta presión (y por lo tanto de alta densidad). Mis experimentos iniciales con inyectores de aguja con varios orificios de 0,2 mm a 0,5 mm parecieron producir una buena atomización, pero no tuvieron éxito cuando se instalaron en el motor diésel de 2 tiempos. El flujo de aire/remolino era obviamente diferente al del cuatro tiempos actual.



El diseño de mi inyector de aguja necesitará modificaciones significativas para adaptarse a la culata de cuatro tiempos.

View attachment 143138

Hola podría mandarme los planos del inyector de aguja

Gracias
 
I'm making some progress on the injection pump. The body of the pump and the barrel are done and the barrel has been lapped, though I may give it one more go with finer abrasive. I also made a plunger. Both plunger and barrel are of silver steel and hardened by quenching in oil. Worked well for the barrel, but it backfired with the plunger! I tried lapping it today and discovered that it warped from the quench, so I couldn't get it to clean up all the way around before it went undersized.

I'm part way through making a replacement. I think I will forego the heat treatment this time.
I think it would be better to harden the plunger while it is round and then grind the helix otherwise the unequal sections will distort when hardening. I moved from hardened and lapped silver steel to commercial pin gauges for my plungers.
 
................... snip

Having done all this, temptation took over and i put the head on and cranked the engine with a more powerful drill in low gear. There was a noticeable smell of burnt oil, and so, optimistic, I sprayed some 'start ya bastard' into the intake port and tried again... a large cloud of white smoke shot out of the exhaust as the valve opened. We've achieved compression ignition! .

Nerd, I missed the engine firing party, but want to add my congratulations! 🥧 I brought an apple pie, too.
Your tenacity is admirable and contagious. Well Done !!
Lloyd
 
My understanding of helix plungers is that they need to be rotated(or the pump body) to align the helix for a given discharge volume.

What are you guys, who use helix plungers, using to rotate the plungers?
 
My understanding of helix plungers is that they need to be rotated(or the pump body) to align the helix for a given discharge volume.

What are you guys, who use helix plungers, using to rotate the plungers?
My plunger passes through the middle of a control collar that has a slot cut in it. The plunger is cross drilled for a pin that rides in the slot.
 
My understanding of helix plungers is that they need to be rotated(or the pump body) to align the helix for a given discharge volume.

What are you guys, who use helix plungers, using to rotate the plungers?
@The Ignoble Troll
The GM plungers had a flat ground along the outboard end to make it D shaped. Then a small gear with a matching D hole thru it allowed the plunger to move up and down thru the gear. A rack went cross-axis, and off the center axis, thru the injector body and engaged the gear. Pulling the rack in and out rotated the plunger.

One problem with all of the helix arrangements is that they are easy to twist when not under load. But when they are pumping and under load for the down-stroke, it is like shifting a trans with dogs but no synchronizers: it will only rotate when the load is off for that half cycle. The Detroit Diesels had a hydraulic assist in their governors to move the racks in and out in unison even when in that loaded half of the pump cycle. The ramp angle of the helix can really affect its sensitivity where (in a worst case) any slop in the linkages can cause different amounts of hysteresis and thus inconsistent injection amounts. I find it amazing that they work at all, LOL.
 

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