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Turbocharged 2-stroke with poppet valves and camshaft rotating same speed as crank?

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Posted by: Daniniowa

Fist, start with a normal 4 stroke engine. Then, custom grind a cam(s) so that the intake and exhaust both open and close in roughly 90 degrees. Spin the cam at the same speed as the crank. Now, turbo charge it so that the intake charge is forced in to the cylinder when the piston is at BDC. Basically it is now a turbocharged 2 stroke with poppet valves, but cleaner.
What are some potential problems with this design?

1. Would the cam profile be to extreme to open and close poppet valves in roughly 90 degrees? Wouldn't this just limit maximum RPM? What if pneumatic valves were used?

2. The exhaust gasses are not scavenged completely, but wouldn't it be benifical as a type of EGR?

Just wondering...


Posted by: matt-itude

It wouldnt start. You would have to use a mechanicaly driven positive displacement supercharger. (to get the air flow while starting the engine)


Posted by: flyinzuki

Sounds like a Detroit Diesel.
I used to drive a truck with a 6-71....


Posted by: dklink2000

Sounds just like a engine that both Crysler and BMW developed independently about 5-10 years ago. The BMW's was an inline six that is said to sound like a 12.


Posted by: BMWPower

I would like to know more about this engine, and also can someone post up some info on the BMW engine? thanks


Posted by: dklink2000

I'll see if I can dig up the article for you.


Posted by: BMWPower

thanks


Posted by: BMWPower

anyone ????


Posted by: steve.emma

hmm intersesting.... i may be really stupid BUT if the charge is forced in to the cylinder when the piston is at bdc then the engine must have just completed its power stroke, so therefore the cylinder should be full of burnt hot gases i.e exhaust. so how do these gases exit the cylinder if new fuel/air charge is being forced in as the piston comes up to compression?? (remember you said start with a four stroke engine... so there are no cylinder ports etc..)


Posted by: splatt

Quote:
Originally Posted by flyinzuki
Sounds like a Detroit Diesel.
I used to drive a truck with a 6-71....



Pretty much. If I remember right they had intake ports like a 2s bike and poppet type exhaust valves. The thing is that all the parts needed to make it work would add weight and complexity.

Steve


Posted by: steve.emma

yeah no question the detroit 2t diesel is a proven design. but the engine described by Daniniowa in the thread title would not be a 2 stroke as it would not complete 1 power stroke every revolution.


Posted by: flyinzuki

In the original post Dan said to spin the cam at the same speed as the crank, in most cases that would do the same for the ignition. what part did I miss


Posted by: steve.emma

the part you missed is the idea where this engine would work!
All internal combustion engines have to complete 4 cycles to run e.g. intake,compression,ignition,exhaust. a four stroke does 2 cycles every revolution ,a 2 stroke does 4 cylcles every revolution.
in this case it doesnt matter what speed you spin the cam or how often you fire a spark, without ports or by using the crankcase (as in a 2 stroke) then its just going to be a 4 stroke, or in this case not run...


Posted by: Mechanicsn

An EMD diesel engine operates in the manner described, with ports in the cylinder for the inlet and poppet valves for the exhaust in the head. They also use a pair of superchargers (one per bank) to move the fresh air in and the exhaust out. Injection is direct into the top of the cylinder head. Look for info on EMD locomotive engines, it's very interesting technology. EMD stands for Electromotive Division of General Motors. Who'd have guessed that a large percentage of the locomotives running the rails in the US were made by GM?


Posted by: Daniniowa

Yes, I'll admit in a quick train of thought, I never realized that it would be almost impossible to start. But once running, my thoughts were that an air/fuel charge was ignited near TDC. The exhaust valve starts to open as the piston is about half way down, and closes near BDC, just as the inlet valve starts to open. The turbo would have to have enough pressure to keep the air in the cyclinder until the piston was about half way to the top and the intake valve closed. The rest of the upward stroke is used for compression. It is indeed a 2 stroke cycle. You just can't start it. That is why the Detroit diesels use superchargers.

It's too bad sleeve valve engines died at the end of WWII. They would seem to be a good fit for a locamotive application.


Posted by: steve.emma

All credit to you for sitting down and thinking this up... but you need to read back to yourself what you have written down and ask yourself "does this make any sense?" because it doesn't.
if the exhaust valve starts to open when the piston is halfway down then you have allready wasted half the available power as the burning mixture will just go straight out the exhaust and not push the piston down any more. also if the exhaust valve closes at BDC then what makes the remaining exhaust gases go out through the exhaust valve? (if anything they would be sucked back into the cylinder through the open valve). you say the inlet starts to open at BDC also,and if its supercharged then air is being forced into the cylinder when the inlet opens so this incoming mixture will only serve to push the remaining exhaust gases back to the bottom of the cylinder as the piston is trying to come back up the bore. if the inlet is open as the piston is coming up to TDC then the compression pressure will (always) overcome the intake air pressure and force the intake charge back out through the inlet valve.

the reason the detroit 2 stroke diesels use superchargers is because they have to have a forced intake charge to start, then the forced induction is used to externally provide 1 of the four operating cylces. in this case induction at near BDC through a port into the bottom of the cylinder. As the mixture is forced into the bottom of the cylinder through the port it also pushes the exhaust gases out the (open) exhaust valve completing another cycle - exhaust. the piston then comes up for compression,is ignited, and pushed back down for the power stroke.

im sorry mate but starting is not your problem ,this engine would never run,and as ive stated before it is NOT a 2 stroke engine anyway as there are no ports.


Posted by: SFO

depends on your definition of a port


Posted by: steve.emma

fair point. im talking about ports that protrude into the cylinder swept area and are opened or closed by the piston or a rotary valve. in other words NOT ports into the head controlled by valves, as in a 4 stroke.



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