Towards a two-stroke turbodiesel aero engine

[pgarner]

Originally Posted by malc9141

I got my car remapped last week. Now I drive Sheffield to Manchester via Glasgow. "At the next roundabout.."

thats a bit of a drive

[malc9141]

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

[pgarner]

Bad luck mate, least if you get it working you can say youve built your own engine form the ground up

[malc9141]

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

[malc9141]

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.

[pgarner]

sorry i knw it had been running, didnt relise you had it going again after the last mishap

[malc9141]

The saga continues. But it doesn't look good in a real sense ; I mean I wanted this really to be up-scaleable, not a joke in a shed.

yet
1) We began to test ignition. We have 5 tiny injection holes in the injector, arranged very precisely at 72 deg, pointing down at 20 deg. We aim them perfectly into 5 small combustion chambers on the piston top (all of which we've worked out and made. The foto shows the neat jig which ensured we were doing right). This improves combustion enormously.
2) Commercial road engines have had megabucks spent to optimise low-temperature burning to reduce NO2, but that is against efficiency. We don't have that problem, and are putting extra air into the exhaust port to set fire to carbon (seen as soot) and get more out of the Turbo-charger. (So immediately an electronic problem occurs which we haven't tracked yet - scream -I work at it more slowly now, so as not to go completely mad).
3) We are not getting the torque we want. We can't understand this but are working on it. Obviously, it's "not enough air". You only have a quarter of a rev in non-motor bike two stroke to get the air in. You need force. Big time.

Malc

[petescustompipes]

i think your a god'n sir. (Removed disguised attempt at swearing as per our T&C's) all the haters that dont want it to work. it will work. what about a supercharger????

[malc9141]

Well, thank you.
Thermodynamically, it is a great mystery that with a centrifugal supercharger (which is in place) the air density (that I need) is proportional to air pressure, but air pressure is determined by air flow. Not the other way round.
This is strange. You'd think you'd get pressure and flow would follow - but not so.

(I am working with a bypass of air to increase flow - hoping to get more pressure)

[malc9141]

I am working with a bypass of air to increase flow - hoping to get more pressure

This is not helping as I 'd hoped.

[rhampton]

Good luck you crazy engine building person you. I wouldn't know where to start with all these shenanigans. But I do know that the world would be a duller place without tinkerers and underfunded dreamers.

Take frank whittle for instance

[malc9141]

Thanks.

Some diesel experts said I'd be lucky even to get it running. It's been as hard as I expected. Things that seemed impossible were relatively easy, things I assumed would work were not.
I have had a journey with numerous very steep learning curves, ranging from elementary thermodynamics to electronics. Many parts had to be machined and I was very fortunate there.
Throw in odd failures, hard to trace, and it's more maddening than rewarding.
And it still isn't much good!!!!

(Before a mountain walk - several Cairngorm hills - about 10 years ago, I said, "Well, we can always turn back" My daughter said "We are the two people in the world who never turn back").

At present, I can't understand why my supercharger bypass (air going round in a circle) does not improve pressure.

[jarrus]

Maybe it's because you are effectively equalising the pressure that the supercharger creates, pressure going in is the same as going out...

does this engien have a turbo also?

[malc9141]

Well, fair comment. But it is a recognised way of making a "big" compressor avoid getting stuffed when it can't provide forward flow. In a nutshell, I thought if a portion of the air is fed back to the sealed intake plenum (wait for clarification!), it would add to intake energy and get an extra push, adding to net pressure at compressor outlet. I think this is an OK idea - I thought it out but it is written in to "How to Deal with Surge," a complex thesis entirely beyond me written in English by a Dutch guy. (Surge proves to be a well known Russian criminal known to enjoy damaging turbocompressors). My bypass dimensions are guess-work (but small compared to main airflow) so safe.

There is a turbocharger which does add net pressure to a plenum from which the supercharger gets its air. The bypass feeds into this, streamlined, then expanding. So it's turbocharger, then compressor. At start up the compressor easily sucks air through the turbocharger.

I was puzzled as to why Airflow determines Pressure in a centrifugal compressor. I would have thought Pressure would create the Flow. But the answer is obvious, now I've been told:
A rotating wheel makes stationary air move incredibly fast (invariably > Mach 0.3). The air is both spinning and moving sideways. This involves adding lots of energy to it. It's kinetic, moving, energy. But we want pressure, not movement (Well, a bit of movement).
The "nozzle" in the casting/machining of the compressor feeds into the widening spiral diffuser which slows it down. Where does all that energy go? Into pressure. So Flow=speed>slowing>Pressure. (The volume flow doesn't get back to "base", ie what was being sucked in).

Finally I get it! Aaagh....

Racing car diffuser: simpler version of these goings on. No energy added. Volume flow is same, and pressure drops.

But I am giving it a rest for a while.