The "Z Engine Theory" (a la SCC magazine)

  • Thread starter Thread starter RedWolfRacer
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RedWolfRacer

RedWolfRacer

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Now before anyone brings their opinion of Sports Compact Car magazine into this, their "local geek" stumbled across an interesting engine design. The engine is what's important here:

Basically it's a hybrid engine in that it combines two-stroke and four-stroke engine properties. Two-stroke because it combusts upon every revolution; four-stroke because it uses normal fuel and parts (for the most part--no oily fuel like 2 stroke and it's under MASSIVE pressure). Instead of having an exhaust stroke, the intake is super-compressed to over 200 psi or so to force the exhaust out JUST before TDC and combustion etc. This way it combusts on every rotation and makes a relatively steady powerband--in theory. It also rotates at the same rate as the camshaft etc. and could utilize (again, in theory) half the cylinders for the same amount of power of a four-stroke engine.

Has anyone seen this or does anyone have any ideas on this or information even?
 
Sounds like a plan. I'd hate to see when one malfunctions though. 200psi go splode.
 
Don't exactly follow the design.

But I am betting that it will never pass emissions. If intake and exhaust are in the same stroke, then some unburned fuel will be blown through, and this is not acceptable. CARB/the govt. doesn't even like four-strokes with a lot of cam overlap.
 
Ive never seen this before but Ive thought in my head many many times of ways to combine 2 stroke and 4 stroke properties togther and came up with ideas. Looks like others have been doing the same.
 
It sounds interesting... and 200psi is not exactly that extreme, as four stroke engines are up to 120-150psi right now... but it likely won't get past the EPA... probably die a quiet death, just like lean-burn engines, if anyone bothered developing it.
 
Could be an interesting idea for racing (where the rules don't ban or restrict this kind of technology anyway). Possibly a much higher power/weight ratio than a conventional 4 stroke, possibly more reliability than rotory engines. Fuel consumption doesn't sound too good though :lol:
 
Well, with all that super-compressed air, it's not unlike an extremely turbo-charged, if unorthodox, engine. The theory behind turbo (as most of us ought to know) is to inject more air into the combustion chambers which isn't too far from what this supercompression does. I think the other thing to remember is that there isn't much room for "normal" compression (the air being pushed by the piston etc) so the supercompression-device/thing can take care of that right before shoving the air/fuel mixture into the combustion chamber. I think it could be made into a viable engine if it weren't for that huge supercompressor thing sticking out of it.

I think this theory may be found at www.sportscompactcarweb.com or some such thing. A google search may net a similar thing. I still think it's a cool idea. Just not practical at the moment.
 
It sounds very similar to a 2T diesel. Although all the 2T diesels I've seen have typical 2 stroke cylinder based intake ports, with the overhead valves all exhausts, but it should work with overhead intakes.

It would be a dirty engine though; if I'm seeing it correctly, at TDC or thereabouts you'll have the spark event (petrol fuel) and combustion as the piston descends. Just before BDC, say 10-20 degrees or so, open the exhaust valves and the combustion pressure will blow most of it out. If the valves remain closed, you're just doing excess work compressing the combustion products. I'm guessing at about 20 degrees BTDC open the intakes and the 200psi charge will fly in and blow the rest of the exhaust out. The point when the exhaust closes is the key, too early, and you leave the exhaust products in the cylinder, reducing torque and efficiency, too late and you push raw fuel into the exhaust.

Thinking about it, you'll also need time to recompress the charge after the exhaust closes. With the intake valve shut, just before it opens, the entire intake tract is filled with 200psi charge. When the intake opens, the exhaust is open, so technically open to atmosphere. Removal of the constriction will allow the pressure to drop, helpfully this will reduce the temperature too. When the exhaust valve shuts the compressor needs time to recompress the charge (reheating it, unfortunately) in the cylinder and open intake tract before shutting the intake valve.

The design has merits and should make good power, but I think it might have trouble at high engine speeds.

Kurtis.
 
Yeah. One of the problems would probably be valve float. That and the fact that you'll need REALLY strong springs and valves to control 200psi of boost. Since the valves must operate at every rotation, it could wreak havoc on the engine block and its components so a really strong material resistant to heat would be obviously favorable.

I think the design could be pulled off but I doubt there will be an immediate market. It'll just be one of those really cook quirky ideas that floats around for a while before it takes off.
 
RedWolfRacer
Yeah. One of the problems would probably be valve float. That and the fact that you'll need REALLY strong springs and valves to control 200psi of boost. Since the valves must operate at every rotation, it could wreak havoc on the engine block and its components so a really strong material resistant to heat would be obviously favorable.

I think the design could be pulled off but I doubt there will be an immediate market. It'll just be one of those really cook quirky ideas that floats around for a while before it takes off.
Click to expand...

I agree, there's loads of this sort of thing about on the net. There's one I saw a while back called a "six-stroke engine", combining opposing pistons and two and four stroke theory. An aussie bloke built it and has some running ones, but it just seems a bit like snake oil to me.


Kurtis.
 

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