Towards a two-stroke turbodiesel aero engine

This is for HDi Fun

Hi Paul

D'you know if petrol engine pistons and diesel engine pistons are much the same, structurally? I don't mean the details like built in combustion chambers, etc, I mean in general design.

The occasional diesel piston I've seen had a steel ring cast into it. Is the diesel "hammer"so bad, it would crack an unreinforced gudgeon pin lug???
Or have I just seen some oddities?

I'm familiar with a variety of petrol pistons - but are diesel ones gutsier in a big way???

Cheese

Malc
 
That was the siamesed exhaust pipes. Beautiful colour from the heat of welding!

Here are the camshafts, lying in the cam-boxes. The cams were cut out of solid, electrolytically, keyed onto the shaft,then lightly welded.

The head itself will come from the alloy block, almost finished.
:rolleyes:
 
Help !!

Anyone !

We are getting there. What a job.
But the subtleties of the injector are amazing. The problem is that we need 36 - 50 odd volts to drive the current fast enough. (The solenoid resists magnetisation, as you know, so we can't reliably fire it with 12 volts. Twenty four volts seems OK, we find, but cars use about 50 v).

The voltage stepper is buried somewhere in the road-going diesel's Engine Control Unit.
I can't seem to find any way of getting a circuit or hardware or anything that will give me the ideal 50-odd volts.

3 batteries (12 + 12 + 12) might be simplest.

But does anyone have any idea where this voltage stepper is, or what it is! ?

When I speak to auto-electricians, quite understandably, they don't understand circuitry!

Long shot - not holding my breath.

(In building this engine I have turned from a handsome male into something like a gnome on chemotherapy).

Gnomic Malc
 
Yep,thanks. I think that's it.
I'll use the existing Brain simply as a timing switch (because it's there) and then just have it run the 30 odd volts to the Injector. Thanks, Paul. It is PAUL, I think?

The Injector is incredibly sophisticated. I thought I understood it but it wouldn't work reliably with my controls.

There is very high pressure in it, about 1000 atmospheres (~14,000 psi !!!), and (as we have discussed) this is evenly balanced on each side of two surfaces which are part of the needle. When the solenoid allows pressure relief in the chamber above, the high pressure fuel on the lower side of the needle moves it up, and fuel squirts out. It goes off like the crack of a whip.

But what I didn't understand was that the critically sized choke, bleed, whatever we might call it, from below the needle that refills the chamber above, will simply allow the pressure below the needle to be reduced (so the needle doesn't lift) if there is any slowness in opening the solenoid valve. And slowness in this context must mean about a five hundredth of a second!! This is because of these astronomical pressures.
This little subtlety comes into play when (in a car) the driver goes downhill and takes his foot off the gas. It lets the system depressurise. The simple hammering to achieve pressure wastes energy and also gets the fuel very hot, very quickly. So that is avoided.
Very clever. Not widely known I suspect - and has allowed me to build a very sophisticated electronic brain, with great difficulty, only to find it's WRONG! I was driving the engine downhill and didn't know it. Ahh..hh.
Back to the (electronic) drawing board.
But the engine is looking good, even if it hasn't run yet.

Malc
 
It is Paul. Hello, mate, it's good that you're still persevering with your project and that it's going very well by all accounts.

You're right about the fuel rail pressures. My car allegedy runs at a peak of 1300 bar (1300 x atmospheric pressure). I've also been told that an injector that sticks open (thankfully very rare) can bore holes through piston crowns. No wonder it's dangerous to trigger them in the open - likely to cut off digits etc!

You have to wonder if the car industry has gone too far with diesel engines. Without question the performance will eclipse a similar capacity petrol unit. And they're now very refined. But, is it too much too soon?
 
It works!

We can now start it up quite easily and it runs nicely. These are early days and we lack power despite putting in too much fuel and we exhaust too much soot. But it goes!!!

I am no electronics wizz. But I try different capacitors to time the injection period. This evening I might have gone too far with too short an injection interval to work. We'll see.
'
The Delphi injector is very clever also. And gradually understanding it has taken some doing as there seemed no quantitative data available. But a Delphi workshop manual was very useful and gave a clue that was otherwise missing. It mentioned that the injector acted as a pressure relief valve - something that doesn't fit with the "usual" concept of its actions. I've mentioned that before. So we can run the engine and try to adjust speed by (1) shortening injection time (this doesn't work and I think it's because we are always putting in excess fuel with each injection. This is the area where we most seek to improve our understanding. (2) reducing flow into the High Pressure pump, thus reducing injection pressure. This works very nicely - if you change the signal between 200mA and 600mA, the engine slows as less fuel is delivered - but it's still not the right mixture. And (3) changing the time of the injection.

Regarding (3), we started at putting in fuel at TDC but that didn't work at all. We advanced it sensibly and it still wouldn't fire. Then I thought, if you see the fuel injected into a bottle. it's so finely atomised that it's like smoke, so we could put the fuel in very early and be compressing this mist. I lost patience and timed it at 50 degrees BTDC (!!!) and it worked!!. We've come forward to 37 degrees BTDC at present.

It's not producing much power yet and a question remains:
Will my combustion chamber be too cool (in every sense) for high power output??
Watch dis space.

But we do have a compact two stroke, using certain features of high performance petrol four strokes, with potential advantages.

Malc :))
 
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OK
I'm using these Esteemed Pages as a sort of log. They don't reflect the daily grind or should I say milling and machining (and soldering, as I puzzle over the circuitry for the injectors). And...

!! Winter is here and it ruddy cold !! Lockerbie - Ah those were the days. Blizzards and then down into the warm (0 degrees) Clyde valley.

Too true. I'm in a huge workshop (Sheffield) with holes in the roof and steam on my breath, with four layers of wool and hands cramping if I take the gloves off too long.

But to the task: the circuitry for the injector signal has two parts, one timed to fire briefly at very high current, about 20 A, and then a Hold circuit timed to last about 5 millisecs at about 8 A. That's all far too long.

The timing is based on the idea that a capacitor discharges at a predictable rate and this is the inbuilt clock. A smaller Cap speeds things up. I have just gone from 36 nanofarads (via a 220k Ohm resistor) in the Fire circuit and 66 nf in the Hold circuit (via 220k resist) down to 0.47 nf in Fire and 3 nf in Hold, in steps. This time I might have overdone it and have too short a signal, but I think it'll be OK. We'll see.
I bought two smallish 12v batteries and put then in series (25v) with a big capacitor and that helped straight away.

The separate minor problem is that oil is leaking badly from the cam drive which isn't surprising as we adapted it without putting a proper seal in. That's trivial and just a technicality - or is it?

I'm beginning to think it's air that's limiting us. Must get the turbo running properly. not idly.

Malc
 
To :HDi fun; paxmanmerv; and anyone -

Sorry, missed the last posts.

The single cylinder experimental engine is very promising. I'm already planning the 4 cylinder version.

But Question: what diesel car of SMALL capacity has a small turbo on it? I need a (scrap) turbocharger smaller than the Clio (1.5L) I'm using at present.
 
I should add:

The electronic circuit is now very impressive, its lights flash away faster & faster as the flywheel accelerates. At about 3000 rpm (more than I need), the bench starts to rock so we switch off. We still haven't run it under much load so don't yet know its power output.

Why not? We haven't built the dynomometer yet. All we need is to key a shaft and gear wheel together. I impressed myself by machining a couple of CVJs to join the engine to the dynomometer. They are of course aligned but move slightly out of line as the load goes on.
But keyways etc is beyond me. And it's a delay. Damn.

If you think of a four stroke, four cylinder, running at a max of 4000 rpm (approx), it's only firing each cylinder 500 rpm. Our electronics and (common rail without the common-ness) is happy at 3000 rpm. I'm amazed!

Malc
 
sounds like its coming on well now,

VAG used to use a 1.4 diesel but cant see it being any smaller than the clios
whats the new diesel smartcar got ? might be hard to find just now however
 
You can use a petrol turbo in a diesel engine. They are used to the extra heat so will effectively be much stronger than you need. Then look to something like the Charade GTTi a 1.0 Turbo or a 1.3 Metro turbo perhaps.
 
To PGARNER,
Thanks. A Bora, Eh? I could just do with a con rod for design of the about-to-be designed 2L four cylinder engine!! (You have to buy 6 at a timne, at > 600 quid).
;)
 
NOOOO you cant have mine :lol:
had i been going down the big turbo way then i would have gave you them but im not,
(standard crank and rods good or around 300-350)
if you want ill try and dig up sizes and price for them ( i have etka so can check what VAG want for 1 )
 
Ok etka is showing :
226049c1570a1d932.jpg
prices might be slightly out of date as not installed any updates ( aorund 15 to be done )

also not sure if its in Euros or pound
 
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just had a look under audi. the 210bhp and 225bhp conrods part number is
06A-198-401 B. same price ( think these are the stronger parts )

prices include rod, bearing shells, bolts, nuts, and piston head bush all X 4
 
A tale of two camshafts -
or two tales of a camshaft.

We built the camshafts from EN40, nitrided for hardness. The cam acts on a "penny" sat on the so-called cam-follower. The cam-follower is an inverted "bucket" which presses on the flat top of a little mushroom tappet. Its short stem presses the end of the valve stem. The cam-follower slides up and down in a thick steel plate, which fits snugly in the cam box.

We knew that oil would get under the cam-follower and into the well for the valve spring. Usually, this is drained away to the sump.
We decided to keep the oil in the box containing the cam assembly and drilled galleries to get it squirted back to the top.

What we found (in the early days when we couldn't even start the engine) was that the engine turned over OK but after a variable time, odd noises came from the cam boxes, getting more and more unpleasant. When we took the tops off to have a look, there was nothing special except the cams looked a bit battered.

One evening, imagining I was the oil being pushed around, I saw that the cam-follower acting like a piston, was pushing oil back to the top, passing the junction between the bottom of the cam box and the steel plate. The oil squeezed into that and with the large surface area, lifted the whole plate up, till it was able to meet the rotating cam lobe.

Fixing the plate to the floor solved that. Sounds obvious but it was quite mysterious.

Tale No 2. Worse. The engine was turning at about 3k rpm - its max - and it clanged to a halt, sounding very expensive. Stripped down (good little engine) it had taken this hammer well. The Audi inlet valves were an interesting shape and had stopped the piston. Bang.
I was puzzled to find when I opened the cam boxes that on the inlet side, the oil had all gone (simple seal failure, I think) and the "penny" mentioned above was ground into a slight wedge shape. The work required for the cam to slap open the penny and cam follower had got too great without lube, so the cam drive had failed and the valves jammed part open as the piston came up.

Never run a car without oil.

So a bit of work but it gives an opportunity to think about combustion chamber design (heady stuff).

More anon....

:rolleyes:
 
Mmmm.

We machined the "pennys" for the cam follower but missed the hardener. He does batches and we missed this afternoon's run. The hardener operates 24 hours a day, all week, keeping the temperature right, so we should get them in soon.

Meantime, we had some thoughts about the piston. We are getting into deep water here, not what I anticipated. We are producing too much smoke and one possibility is that we aren't getting enough temperature in some part of the combustion process, or we are squirting fuel where it can't burn.

The combustion chamber is tent shaped and part of the flat piston top comes to face the flat underside of the cylinder head. Almost no air left, but probably some fuel. Also, weird thought, could we have a local refrigerator as the little bit of air in that region is expanded rapidly as the piston accelerates down? It's possible. A fridge next to your combustion chamber is a recipe for smoke and no power.

So we put the piston in a big gentle chuck mounted on a nice big turntable, centred it, and machined out a horseshoe shape on the piston top, the part that meets the cylinder head. So there is a shallow (2/3) ring-like depression on the piston top to ensure air gets left there, to burn the fuel. Of course, if I say "gets left", I mean highly turbulent air. With luck, combustion will independently start there as well as in the main chamber.

Hard to explain. I look forward to running the engine again soon to see if we've got a more viable machine.

Each time, we seem to move forward a little bit.

At present, we have a fantastic electronic circuit, an amazing, neat, ingenious little dynomometer, and a heap of junk which vaguely drives a flywheel and which has yet to prove its worth. (I'm being very unfair).

De Aero, Diesel Aero, D'Aero, Daer?? Daer I sa mor?

:blink1:

Malc
 
no worries about the pic. if you need any more from seat audi vw or skoka give us a shout trying to get everything up to date (over 150 updates for VW alon. hour and a half later i had done around 50 of them )
 
4 pot 1796cc VAG eninge found in golfs, newer polos, bora, passat, A3, A4, A6, Skoda octavia, seat leon, etc. avalible in both NASP and turbo varients

if you want i can gey up one of the 1.9 diesel engine
 
Hi Paul
This might be OK.
At present, I'm looking at a Jaguar rod/piston, similar sizes.
The VW idea seems quite attractive, though.

I'll get back if the Jag idea stalls.
Malc mit thanx
 
Hi Guys,

There's no need to reply to this. I'm just logging activity.

On the little single cylinder two stroke, the cap on the cam follower wore down (because we hadn't hardened it - taking a risk. Soon learned) and jammed the valve open which of course hit the piston top.

We made new caps, and got them hardened.

Taking the engine to bits allowed us to think about combustion.
We machined tracks on each side of the piston top, to guide air towards the combustion chamber. I also machined a tiny bit out of the chamber itself. It all adds up. Because I knew we had a high Compression Ratio, I didn't calculate what we were doing.
We put the engine back together and it would not fire. I the CR was too low. We took it to bits again and indeed I had dropped the CR drastically - from ~19:1 to ~13:1.

I located a new piston and will machine very narrow (5mm wide) shorter tracks. I will add a disc 6 mm high, 27 mm dia, onto the piston top where it goes into the combustion chamber at TDC. This returns me 3 cc towards the CR. With the smaller tracks, we should be up at 19:1.
This disc will divide the combustion chamber and because the swirl is not the usual whirlpool type, but more like a surf wave, there will simply be two smaller waves. I'm interested to see how this works out, because we are straying from convention, though it seems quite logical.
But the piston hasn't arrived yet.

Separately, the plate which carries the cam-drive gear is slowly distorting under the load. So I reinforced that with a flat strip of 10 X 20 steel.

That's all for now folks,

Malc, who was getting quite sick of it last week.

I got my car remapped last week. Now I drive Sheffield to Manchester via Glasgow. "At the next roundabout.." :sad2:
 
Re: Towards a two-stroke turbodiesel aero engine THE END

Hi Guys

Diamond Aircraft, Vienna, Austria have been working on a diesel engine ( I thought they might) and it will blow my efforts away. It's 175 bhp, and has a gearbox on the front (?epicyclic, I'd guess).

They kept quiet till it was approved, a big step.

So there is no point in me trying further.
However, for my own interest, I will try with a modified piston to see if we reach the target I originally set.


Cheers for now

malc :confused:
 
Re: Towards a two-stroke turbodiesel aero engine PATENT

Yeah. Funnily enuff, the same day I found the Diamond data, I got a letter saying the Patent had been accepted. That's to use my valve layout plus ram filling to clean ouit the exhaust gas.

Here's a story Not very funny like this but it was at the time. I used to have a Hillman Minx for a while. Sit up and beg, panels thick steel. Automatic transmission, amazingly.

It had enormous wheels with High Profile Tyres (retreads of course). One day, I was on a dual carriageway which seemed very quiet so I decided to look into its Limit of Adhesion.
I drove down a hill and up the other side, as fast as I could, telling myself, if i got round the bend without tipping over, and there was no-one there in the way (unlikely), I could just about keep it on the road. Well, there was a Austin Maxi, just where i needed to go. I thought, Well, I might just scrape by, holding it in, as long as he doesn't change lanes or do something stupid.
At that point his front wheel fell off.

Amazing what you can do if you have to.

Malc
 
My engine does work OK so I can say I've built it from the ground up!


  • I just want to get it burning a bit hotter, but it's just to dot is and cross ts.
:embarrest:
 
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