The Bucket Foundry

[speedpro]

I myself was thinking of throwing together a HCCI engine only last week.

[Flettner]

Little piston in the head ended up at 8mm (originaly going to be 5mm) stroke because the gear ratio dropped to 2 to 1 (not three to one as I originaly intended) so I needed a little more stroke to get a rapid compression rise at TDC ( or at least ten degrees after ish) . Two to one because I had the pullys on the shelf. Compression goes from about 14 to 1 then the little piston quickly makes it 21 to 1, fuel air MUST go off ??.
By rights it should be able to be controlled by fuel only, I think.

[Ocean1]

Compression goes from about 14 to 1 then the little piston quickly makes it 21 to 1, fuel air MUST go off ??.
By rights it should be able to be controlled by fuel only, I think.

Less fuel = less compression. That's going to affect timing. Enough to be a problem?

[Moooools]

Less fuel = less compression. That's going to affect timing. Enough to be a problem?

Assuming the fuel is a nice incompressible puddle, and hence looking at the effective compression ratio of the air alone:

At 14.7:1 AFR and 21:1 CR the effective CR of the air is 21.047:1

At 20:1 AFR (lean) and 21:1 CR the effective CR of the air is 21.034:1

As a note, with no fuel the effective CR of the air is 21:1.

Make of that what you will.

[Ocean1]

Assuming the fuel is a nice incompressible puddle, and hence looking at the effective compression ratio of the air alone:

At 14.7:1 AFR and 21:1 CR the effective CR of the air is 21.047:1

At 20:1 AFR (lean) and 21:1 CR the effective CR of the air is 21.034:1

As a note, with no fuel the effective CR of the air is 21:1.

Make of that what you will.

Of course, it's all arriving together.
So not very much, and not likely to be a timing issue, but any variation will be in the wrong direction, yes?

[husaberg]

https://www.researchgate.net/publica...ke_HCCI_Engine

[speedpro]

I see in the link Husa' posted that the combustion chamber diagram included a regular squish area. I would have thought it unneccessary, and undesireable, in a HCCI engine. Flettner what's the chamber profile you have gone for? Also, how is the litle piston moved? The way you were describing it earlier you are using a small crank and rod assembly. I would have thought a cam arrangement might have allowed swifter compression with the combustion pressure pushing it back so it follows the cam profile to it's retracted position. With a cam that need not happen while the motor is in it's useful power extraction part of the stroke. A quick change of cam would also allow for easy changes of compression during testing by varying the small piston travel

[Flettner]

I see in the link Husa' posted that the combustion chamber diagram included a regular squish area. I would have thought it unneccessary, and undesireable, in a HCCI engine. Flettner what's the chamber profile you have gone for? Also, how is the litle piston moved? The way you were describing it earlier you are using a small crank and rod assembly. I would have thought a cam arrangement might have allowed swifter compression with the combustion pressure pushing it back so it follows the cam profile to it's retracted position. With a cam that need not happen while the motor is in it's useful power extraction part of the stroke. A quick change of cam would also allow for easy changes of compression during testing by varying the small piston travel

No, there is no squish.
I hates cams
It's like this, I'd imagined that the engine might run a little like a Diesel, no matter how small the number of fuel molecules there would always be oxygen around it (harmoginized) so as the pressure and temperature rise rapidly (at the right time and you would need a full load of air each cycle to keep things consistent combustion pressure wise) it would "go off", burn. We are not limiting the start of combustion to a small electric fire that has to have the right quantity and quality moving around that spark plug.
My old Diesel truck has no working glow plugs so a small squirt of petrol up it's intake as the starter is operated fires it into life. If the injectors were disconnected it would run until the fuel vapour was gone then stop. It has no timing adjustment as the petrol just lights up when it feels like it yet the truck engine starts and runs without knock of fuss.

[Frits Overmars]

Little piston in the head ended up at 8mm (originaly going to be 5mm) stroke because the gear ratio dropped to 2 to 1 (not three to one as I originaly intended) so I needed a little more stroke to get a rapid compression rise at TDC ( or at least ten degrees after ish) . Two to one because I had the pullys on the shelf. Compression goes from about 14 to 1 then the little piston quickly makes it 21 to 1, fuel air MUST go off ??. By rights it should be able to be controlled by fuel only, I think.

You could nourish it with diesel; nice low octane number; should go off like a dream .
On a more serious note: if you feed it a homogeneous diesel-air mixture and then provoke HCCI, you might even succeed in making a diesel engine rev.
VW, Audi, BMW and Mercedes will be queuing at your doorstep.

[husaberg]

You could nourish it with diesel; nice low octane number; should go off like a dream .
On a more serious note: if you feed it a homogeneous diesel-air mixture and then provoke HCCI, you might even succeed in making a diesel engine rev.
VW, Audi, BMW and Mercedes will be queuing at your doorstep.

I heard VW already had a clean running Two stroke with zero emissions............

[WilDun]

Good luck with your project Neil, I've started to lag behind lately and haven't been keeping up with things, sounds good!
Anyway Merry Christmas everybody! (To you overseas guys. - Santa Claus has been here already).

[Frits Overmars]

the gear ratio dropped to 2 to 1 (not three to one as I originaly intended) so I needed a little more stroke to get a rapid compression rise at TDC

You could even get your rapid compression rise with a one to one ratio. Ever considered the weird gears in the picture below? I used them in the design of an Aspin-type rotary exhaust valve because with a constant rotation velocity it would not open quick enough, and I wanted a low rotation velocity when compression and combustion pressure were acting on the valve. For you it would have to be just the opposite: a quick rotation near TDC and a leisurely pace before and after.
http://www.google.de/?gws_rd=cr&ei=N...and+generation

[Frits Overmars]

I heard VW already had a clean running Two stroke with zero emissions............

You're referring to Dieselgate?

[Flettner]

You could even get your rapid compression rise with a one to one ratio. Ever considered the weird gears in the picture below? I used them in the design of an Aspin-type rotary exhaust valve because with a constant rotation velocity it would not open quick enough, and I wanted a low rotation velocity when compression and combustion pressure were acting on the valve. For you it would have to be just the opposite: a quick rotation near TDC and a leisurely pace before and after.
http://www.google.de/?gws_rd=cr&ei=N...and+generation

Yes I've seen them. Not that easy to build, had a similar project that was going to use oval gears for the same reason.
Turns out that this engine might be a little harder to control than I though what with combustion chamber pressure changes as the pipe starts to work. I think it will need a serious timing change system?

Edit, SO, it runs!! I can't hold the phone camera and operate the engine at the same time, drill start, (clearly just a male) so when I get somone else around I'll get video and post it. Much excitment.

[TZ350]

SO, it runs!! .... Much excitement.

HCCI .............