Request - Injector designs

[Roger B]

Ruben sent me a message asking for details of my latest needle style injector and an early design of helix pump. I will post them directly in this thread in case anyone else is interested.

First the new needle injector:

This was designed to overcome some of the manufacturing problems with the first series of needle injectors, especially the deep hole in the brass nozzle and the long needle. There are still some challenge with this design, a deep 1mm hole that must intersect with the 1.2mm fuel entry and keeping the body and the nozzle concentric.



The body is a piece of 10mm square black bar. The top end was drilled and tapped M8 for the spring adjusting screw. This thread also allows the body to be mounted on an M8 threaded mandrel for turning the other end.

The end of the body was turned to 8mm and the fuel inlet was made and silver soldered on using a short 1mm steel pin to keep it in place. The long 1mm fuel passage was drilled to the correct depth and the hole in the fuel inlet was extended to meet it. The body was fitted back on the mandrel and centered to turn the 7mm locating land and to cut the M8 x 0.5 thread.

The bore for the needle takes some practice. I made a number of trials with different speeds, different drill sizes and various reaming techniques to obtain an accurate and parallel bore with no bell mouthing. The required diameter depends on how the needle is made. I used 1.5mm diameter silver steel which when hardened and lapped ends up around 1.48mm so that was my target diameter. The diameter after reaming needs to be around 1.46mm to allow for lapping. I use a 1.35mm drill and a 1.45mm reamer in a floating reamer holder. The bore was lapped with an Acro needle lap and 1 micron diamond paste. The bores are checked with a set of pin gauges from 1.45 to 1.50mm.

The tip of the needle was turned to 60° and the required length was turned down to 1mm. The needle was then hardened and the working length was lapped to 1.48mm with a homemade brass lap and 1 micron diamond paste.

The nozzle was turned to size externally and parted off. It was then mounted in a 5mm collet and drilled 1.5mm to the required depth. The 90° seating was cut with a homemade D bit. I am using a 60° needle and a 90° seating to get a line contact seating. The 0.2 mm orifice was drilled using a 0.2 mm twist drill fixed into a 1.5mm diameter brass rod.



The nozzle was then fixed to the body with the clamping nut (the 7mm diameter locating land in the nut should be bored so it is accurate and parallel) and needle was lapped to the seating once again with one micron diamond paste. Finally the needle was cut to length and it all went into the ultrasonic bath for cleaning.

I am not a draughtman, I use CAD as an electronic back of an envelope but hopefully all the relevant dimensions are there. I have uploaded the .DWG as well as a .JPG The scallops out of the sides of the body are not essential, they were clearance for the injector fixing nuts on my four stroke diesel.

 

[ruben]

Ruben sent me a message asking for details of my latest needle style injector and an early design of helix pump. I will post them directly in this thread in case anyone else is interested.

First the new needle injector:

This was designed to overcome some of the manufacturing problems with the first series of needle injectors, especially the deep hole in the brass nozzle and the long needle. There are still some challenge with this design, a deep 1mm hole that must intersect with the 1.2mm fuel entry and keeping the body and the nozzle concentric.



The body is a piece of 10mm square black bar. The top end was drilled and tapped M8 for the spring adjusting screw. This thread also allows the body to be mounted on an M8 threaded mandrel for turning the other end.

The end of the body was turned to 8mm and the fuel inlet was made and silver soldered on using a short 1mm steel pin to keep it in place. The long 1mm fuel passage was drilled to the correct depth and the hole in the fuel inlet was extended to meet it. The body was fitted back on the mandrel and centered to turn the 7mm locating land and to cut the M8 x 0.5 thread.

The bore for the needle takes some practice. I made a number of trials with different speeds, different drill sizes and various reaming techniques to obtain an accurate and parallel bore with no bell mouthing. The required diameter depends on how the needle is made. I used 1.5mm diameter silver steel which when hardened and lapped ends up around 1.48mm so that was my target diameter. The diameter after reaming needs to be around 1.46mm to allow for lapping. I use a 1.35mm drill and a 1.45mm reamer in a floating reamer holder. The bore was lapped with an Acro needle lap and 1 micron diamond paste. The bores are checked with a set of pin gauges from 1.45 to 1.50mm.

The tip of the needle was turned to 60° and the required length was turned down to 1mm. The needle was then hardened and the working length was lapped to 1.48mm with a homemade brass lap and 1 micron diamond paste.

The nozzle was turned to size externally and parted off. It was then mounted in a 5mm collet and drilled 1.5mm to the required depth. The 90° seating was cut with a homemade D bit. I am using a 60° needle and a 90° seating to get a line contact seating. The 0.2 mm orifice was drilled using a 0.2 mm twist drill fixed into a 1.5mm diameter brass rod.



The nozzle was then fixed to the body with the clamping nut (the 7mm diameter locating land in the nut should be bored so it is accurate and parallel) and needle was lapped to the seating once again with one micron diamond paste. Finally the needle was cut to length and it all went into the ultrasonic bath for cleaning.

I am not a draughtman, I use CAD as an electronic back of an envelope but hopefully all the relevant dimensions are there. I have uploaded the .DWG as well as a .JPG The scallops out of the sides of the body are not essential, they were clearance for the injector fixing nuts on my four stroke diesel.View attachment 159898

Thank you for the plans and help

 

[Roger B]

Helix controlled injection pump:

My first injection pump was used for manifold injection on a petrol engine so a variable stroke controlled by a wedge was adequate. For the diesel trials a more defined start of injection was required so I decided to go for a helix controlled jerk pump.



I had already resolved lapping the pump bore in the variable stroke pump using a similar technique to that used for the injector. The first plungers were made from hardened and lapped 2mm diameter silver steel but after a problem with a tri lobar piece I now use commercial hardened and lapped pin gauges. As the silver steel ended up at around 1.98mm this is the bore size I have been using.

The body is once again made from 10mm square black bar. The bore axis is not in the centre of the bar so it needs to be set up in the 4 jaw independent chuck. The 5mm diameter for the control gear is turned first, followed by the pump bore. Initially I made it all 1.98mm but for later versions the first 6mm was opened out to 2.2mm diameter. The bore was drilled 1.85 mm and reamed 1.95 mm using a floating reamer holder. It was not lapped until the 1mm diameter inlet port was drilled.

The body was then turned round and held in a collet by the 5 mm diameter section so the delivery valve seating could be cut with a 4.5 mm end mill and the M5 x 0.5 thread for delivery valve body tapped. I initially made the seating by tapping a 3 mm ss ball with a hammer and brass drift but I found I got better results using a 3mm diamond charged ball lap after the pump bore had been lapped. The delivery valve bodies were initially made from modified commercial unions but later they were turned from brass bar.

The plunger is made from a 1.98mm diameter pin gauge. The helix is cut to a 4mm pitch in the lathe using a Proxxon mini tool with a grinding disc. I cut both ends of the pin gauge when the lathe is set up for this to have a spare if necessary. The grinder needs to be set at 32° and I cut to a depth of 0.5mm in 0.05mm steps. The plunger is then cut to length with the Proxxon grinder and the end is annealed to allow an M2 thread to be cut.

The control gear is 20T MOD 0.5 meshing with a length of MOD 0.5 rack. There is a rectangular recess cut in the face of the gear to engage with a rectangular piece threaded and Loctited onto the end of the plunger. The gear is wide enough so that it stays engaged for the full 3mm stroke.

I am not a draughtman, I use CAD as an electronic back of an envelope but hopefully all the relevant dimensions are there. I have uploaded the drawing as .DWG and .JPG. There are also a couple additional pictures.

 

[xander janssen]

Here is a schematic on how understand that Mr. Hansen controls amount of diesel injected and start of the injection. All deduced from his YouTube movies. Both amount and timing are coupled but it seems to work for a low and fixed RPM engine. For a high RPM engine that needs to rev up and down very quickly (like a real car engine), it will most likely not work.

The wedge is moved in and out between the pusher and the pump piston to control the amount of fuel.

The Pusher is moved in and out by an eccentric in the axle of the lever.

 

[Roger B]

To complement this thread I have posted about my injector test pump here:

https://www.homemodelenginemachinist.com/threads/fuel-injector-test-pump.36893/

 

[ruben]

Ruben sent me a message asking for details of my latest needle style injector and an early design of helix pump. I will post them directly in this thread in case anyone else is interested.

First the new needle injector:

This was designed to overcome some of the manufacturing problems with the first series of needle injectors, especially the deep hole in the brass nozzle and the long needle. There are still some challenge with this design, a deep 1mm hole that must intersect with the 1.2mm fuel entry and keeping the body and the nozzle concentric.



The body is a piece of 10mm square black bar. The top end was drilled and tapped M8 for the spring adjusting screw. This thread also allows the body to be mounted on an M8 threaded mandrel for turning the other end.

The end of the body was turned to 8mm and the fuel inlet was made and silver soldered on using a short 1mm steel pin to keep it in place. The long 1mm fuel passage was drilled to the correct depth and the hole in the fuel inlet was extended to meet it. The body was fitted back on the mandrel and centered to turn the 7mm locating land and to cut the M8 x 0.5 thread.

The bore for the needle takes some practice. I made a number of trials with different speeds, different drill sizes and various reaming techniques to obtain an accurate and parallel bore with no bell mouthing. The required diameter depends on how the needle is made. I used 1.5mm diameter silver steel which when hardened and lapped ends up around 1.48mm so that was my target diameter. The diameter after reaming needs to be around 1.46mm to allow for lapping. I use a 1.35mm drill and a 1.45mm reamer in a floating reamer holder. The bore was lapped with an Acro needle lap and 1 micron diamond paste. The bores are checked with a set of pin gauges from 1.45 to 1.50mm.

The tip of the needle was turned to 60° and the required length was turned down to 1mm. The needle was then hardened and the working length was lapped to 1.48mm with a homemade brass lap and 1 micron diamond paste.

The nozzle was turned to size externally and parted off. It was then mounted in a 5mm collet and drilled 1.5mm to the required depth. The 90° seating was cut with a homemade D bit. I am using a 60° needle and a 90° seating to get a line contact seating. The 0.2 mm orifice was drilled using a 0.2 mm twist drill fixed into a 1.5mm diameter brass rod.



The nozzle was then fixed to the body with the clamping nut (the 7mm diameter locating land in the nut should be bored so it is accurate and parallel) and needle was lapped to the seating once again with one micron diamond paste. Finally the needle was cut to length and it all went into the ultrasonic bath for cleaning.

I am not a draughtman, I use CAD as an electronic back of an envelope but hopefully all the relevant dimensions are there. I have uploaded the .DWG as well as a .JPG The scallops out of the sides of the body are not essential, they were clearance for the injector fixing nuts on my four stroke diesel.View attachment 159898

Roger, what drill bits did you use to make the 0.2mm hole?

This
https://es.aliexpress.com/item/1005...*MTczOTgxNTE3Ni4zMi4xLjE3Mzk4MTUyNDMuNTguMC4w

 

[Roger B]

Roger, what drill bits did you use to make the 0.2mm hole?

This
https://es.aliexpress.com/item/1005007055097407.html?spm=a2g0o.productlist.main.1.2cf4DotrDotrmm&algo_pvid=69dcfe8d-3893-4f0e-a1ba-f5a9b11d38db&algo_exp_id=69dcfe8d-3893-4f0e-a1ba-f5a9b11d38db-0&pdp_ext_f={"order":"67","eval":"1"}&pdp_npi=4@dis!EUR!4.62!0.99!!!34.38!7.40!@210391a017398152446014520e8530!12000039250426020!sea!ES!4621097370!ABX&curPageLogUid=Qoun38CB9VxY&utparam-url=scene:search|query_from:&_gl=1*1ei3rog*_gcl_aw*R0NMLjE3Mzk4MDk4NzUuQ2p3S0NBaUEyY3U5QmhCaEVpd0FmdDZJeEZROTNEakR1aTdlM0JYbFFmN0ItTkVkaDBHMU9HQkNPT0t0OXFHamxOdFNoWEdRX3NyTWVCb0NpNjRRQXZEX0J3RQ..*_gcl_dc*R0NMLjE3Mzk4MDk4NzUuQ2p3S0NBaUEyY3U5QmhCaEVpd0FmdDZJeEZROTNEakR1aTdlM0JYbFFmN0ItTkVkaDBHMU9HQkNPT0t0OXFHamxOdFNoWEdRX3NyTWVCb0NpNjRRQXZEX0J3RQ..*_gcl_au*OTU5MzU4NTA0LjE3MzMzOTY4MTg.*_ga*MzY5MzMyNTg3LjE3MzMzOTY4MTU.*_ga_VED1YSGNC7*MTczOTgxNTE3Ni4zMi4xLjE3Mzk4MTUyNDMuNTguMC4w

Hallo Ruben,

As ever this is complicated. I initially tried cheap ‘hobby’ small drills but they were generally badly ground and did not cut properly. The shank on PCB drills, 3.2 mm (1/8”), is too large for this injector design.

To drill the nozzle hole the drill needs to be supported by a 1.40 – 1.45 mm diameter rod to keep it centered in the nozzle body. I initially used industrial 0.35 mm drills as I had some and it was possible to drill a hole in the end of a piece of brass rod and then Loctite the drill in place. This also worked with a 0.5 mm drill from a Proxxon set.

The first trials with ‘normal’ 0.2 mm drills didn’t work as it was not possible to drill a deep enough hole in the end of the rod. I then purchased some, expensive, 0.2 mm drills with a 1 mm shank with which I could make a nozzle drill although I had to use silver steel to make the support rod as the ~0.2 mm wall thickness in brass was too weak.

Is a 0.2 mm nozzle on a needle injector better than the easier 0.5 mm nozzle? I don’t know. The atomization appears to take place in the anulus between the needle and the nozzle, nozzle bore may just affect the spray cone angle.

 

[ruben]

Hallo Ruben,

As ever this is complicated. I initially tried cheap ‘hobby’ small drills but they were generally badly ground and did not cut properly. The shank on PCB drills, 3.2 mm (1/8”), is too large for this injector design.

To drill the nozzle hole the drill needs to be supported by a 1.40 – 1.45 mm diameter rod to keep it centered in the nozzle body. I initially used industrial 0.35 mm drills as I had some and it was possible to drill a hole in the end of a piece of brass rod and then Loctite the drill in place. This also worked with a 0.5 mm drill from a Proxxon set.

The first trials with ‘normal’ 0.2 mm drills didn’t work as it was not possible to drill a deep enough hole in the end of the rod. I then purchased some, expensive, 0.2 mm drills with a 1 mm shank with which I could make a nozzle drill although I had to use silver steel to make the support rod as the ~0.2 mm wall thickness in brass was too weak.

Is a 0.2 mm nozzle on a needle injector better than the easier 0.5 mm nozzle? I don’t know. The atomization appears to take place in the anulus between the needle and the nozzle, nozzle bore may just affect the spray cone angle.

View attachment 164864

View attachment 164865

Hello, I will use the ones in the photo you posted. I have looked at those drill bits and they are good.

 

[Motorman1946]

Hi Roger - you mention using the injection pump and injector on a petrol engine. May I ask what pump and injector, and at what injection pressures did you use? Did the injector have a wide or narrow spray pattern?
I have an idea for an IC engine but it requires petrol injection!
Thanks - Chris

 

[Roger B]

Hello Chris,

I have two engines running with petrol injection using 2 different injection pumps. The first is a 25cc four stroke using a simple wedge controlled pump and a mushroom style injector spraying into the inlet pipe. The pump is driven by an excentric to give a long injection period during the inlet stroke. This runs quite well without needing to adjust the stroke. I guess that the leakage past the fuel pump plunger gets less as the speed increases. The petrol is fed to the injection pump at around 0.8 bar via a small electric gear pump and pressure relief valve. If the fuel is not pressurised it vaporises on the suction stroke causing bubbles and disrupting the injection. The same is necessary on automotive engines with mechanical petrol injection. This picture is the injection pump without the feed pump. I could see bubble in the clear fuel inlet tubing.



This is the slide throttle with the injector behind.



This is the engine being load tested.




The second engine is a 12 cc four stroke twin using a helix controlled pump and a mushroom style injector spraying into the inlet pipe. This has a 360° crankshaft and the injection pump is operated by an excentric running at engine speed giving an injection every revolution to match the alternate induction strokes. The leakage from this injection pump appears to be greater so the working stroke needs to be decreased as the throttle is opened using a shaped sector. The fuel is pressurized by a diaphragm pump driven from the camshaft.





The injection pressure in both cases is probably around 10 bar and the spray is a fairly narrow cone. I haven’t studied this as it does not seem to be critical.

 

[Motorman1946]

Hello Roger,

Thank you so much for your detailed reply complete with those informative photos - very nice work there.

I was a little surprised at first hearing that you had to supply the injection pump with pressurised fuel and not rely on the head of fuel from the fuel tank - until I quickly realised that at the rpm the pump was working at it could - would - indeed give rise to pulling a vacuum on the suction stroke and hence give rise to (literally!) air bubbles. Nice to have that heads up so early in the project. Injection pressure is a bit higher than I expected, was mentally contemplating about half that, but the narrow injection cone is good to know.

I am familar with the two means you employ to control the injection pump, but also marvel at your ability to produce such fine tolerances within the home workshop; however, although I am familar with the needle type injector, the mushroom type is a new one on me. Do you have a photo, or ever better, a drawing of that please?

The fuel injection process commonly seems to be based on a given start point but with a varying duration hence varying end point, depending on power required; I would like to reverse that and have a given end point with a varying start point - but am not sure how I will achieve that as yet. Early days but!

Chris

PS. Just an afterthought - would a mushroom injector be somewhat similar to a normal poppet valve, and does it have to have the same close tolerance of a needle injector?

 

[Roger B]

This is a drawing of a mushroom type injector. The only precise piece is the cone and seating. It also doesn't need a leak off pipe.

And this is the components:

A fixed end of injection and variable start is easy with a wedge controlled pump. The injection will always end when the cam or excentric reaches the end of it's travel. The start and hence the volume will depend on the wedge position.

 

[Motorman1946]

Thank you so much for the drawing and picture Roger - very interesting and informative indeed.

Now you mention how the fuel pump wedge works in reality it becomes obvious that it would achieve what I required - I had for some reason thought it was the other way round. Never mind.

The mushroom injector is much as I had eventually imagined it may be, but what blows me away is the size. With the mushroom head 1.4 mm, then the stem immediately above the head must be only somewhere in the parish of 1.0mm diameter, and about 1.3mm or so above that; I am struggling to imagine how I would produce such a tiny thing in one piece without bending it, damaging it or otherwise mucking it up! Having said that, the bottom bit is over quite a relatively short length, looks only about 10-12mm long, so doable with care!!! Simple it might be, but so tiny.

Not for the first time, I take my hat off to your abilities in admiration!

Chris

 

[Roger B]

Thank you Chris,

The machining sequence for these needles took a little experimentation. The bore in the nozzle is 1.4mm. This needs to be at a minimum reamed, maybe lapping would help, as it form part of the seating. The needle is made from 2 mm diameter silver steel (drill rod). I usually use a long enough piece to make two needles, either in case of mistakes or to try different angles.

I have made them on my Hobbymat but the Proxxon FD150 is more convenient. The first step is centre drilling with a 0.5 mm centre drill followed by turning the required length to 1.4 mm and threading M1.4. For the next stage you need to make a brass bush with a 1.4 mm hole that is a close fit over the threaded portion of the needle. This is then used to support the threaded end of the needle whilst the section behind the cone is turned to 1 mm. I use aluminium (DCGT) inserts set as close as possible to centre height.

The cone is then turned to the required angle, well supported by the 2 mm rod close to the chuck, and then the needle is parted off.

I then move to my Proxxon MF70 to mill 4 feed slots where the 1.4 mm diameter section of the needle enters the nozzle. The dimensions can be changed so that the 1.4 mm section does not enter the nozzle and the needle ‘floats’ but I have had more consistent results with a guided needle.

Finally the cone is hardened and polished with a fine abrasive stone.

 

[Motorman1946]

Hi Roger, you are very kind to have given me a detailed scheme of work on how to manufacture the injector, I greatly appreciate the help you have given me - and others reading this - by describing in such detail your manufacturing methods. A problem shared is a problem halved they say - you have done more than that, very much appreciated, thank you.

Chris