Converting 4 stroke into 2 stroke plus turbo

IG.

Registered
I posted in General, but din't get much of a reaction, so I am re-posting here, where it's probably more appropriate.

I've been thinking... Tell me where I am going wrong.

You take a 4-stroke engine, and make the following changes.

o  Change crank and cam ratio to 1:1 instead of 2:1, so for every revolution of the crank, the cams also turn once. Cams profiles have to be changed (new cams of course).

o  Intake air is pressurized (5 - 10 psi).

o  FI maps have to be re-adjusted.

o  Ignition times have to be adjusted.

Here is how it is "supposed" to work. Let's start from ignition at TDC, and go 360 deg till next ignition.

-30 - 0 deg: ignition (negative degree for advance)
100 deg: exhaust valve opens
140 deg: intake valve opens, compressed air purges exhaust gases
170 deg: exhaust valve closes
180 deg: intake valve closes
230 deg: fuel injected, compression continues
300 - 360 deg: next ignition

All degrees are to just illustrate the principle. Of course, extra cooling is a separate matter.

That would be a two stroke turbo (edit: my mistake - supercharged, not turbo). What do you think?



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Not quite possible... 2 stroke diesel engines have been around for a long time and operate almost exactly as you've described.  The only difference is there is no intake valve on the diesels, it's a port that is uncovered in the engine about midway through the stroke.  

Here's the problem with you're idea:  Air has mass.  Some dead guy said "objects in motion tend to remain in motion, and objects at rest tend to remain at rest.  Unless acted apon by an outside force."  By opening an intake valve at the top of the motor, there is no way to effectively evacuate all the combustion gases out of the cylinder.  Especially at 10,000 RPM!  It's only open for 30 degrees, or about 9% of the total revolution.  At 12,000 RPM a piston makes 200 trips down and up per second.  That means you've got 9% of 1/200th of a second to get the exhaust gases out. A regular camera shutter is open for about 1/60th of a second (=0.016667seconds).  Your exhaust valve would be open for 0.00045 seconds.  I don't think that's long enough ;) . Our regular exhaust valves are open for about 0.003 seconds, or roughly 6 times longer.

 Excellent thinking though.  It's guys like you that get new ideas off the ground  :beerchug:



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Thanks for responses, guys.

Noltez, yeah I realize now that no amount of pressure is gonna effectively get rid of exhaust gasses, most of it is probably gonna stay except for the top part of a cylinder. No wonder the diesel engine has intake on the other end of a cylinder, so the air is forced through the entire cylinder, and exhaust gasses get flushed.


I am pretty curious person, and sometimes just want to get to the bottom of things.

Thanks for clarification.

Since we are on the subject, and you seem to know a lot, and don't seem to mind my questions, let me run by you another idea.

RAM air intake adds a little air pressure at high speeds, thus adding more power. I am guessing on top end it would add something in the ballpark 0.5 - 1.0 psi to normal air pressure (around 15 psi), so we can get 3% - 7% power increase at high speeds.

Now, what if we take that air stream which has low pressure and high velocity, and convert it into another air stream with higher pressure, but slower velocity (using simple mechanical device)? So long as amount of air is enough to satisfy the engine, we could increase the pressure for free.

If let's say a bike goes 100 mph, and that creates additional 0.2 psi. We convert that to 20 mph air flow with the pressure of 1 psi - that becomes something noticeable.

At 130 mph, additional pressure could reach (I am guessing of course) let's say 0.4 psi, so converting the air flow would get us 2 psi.

What do you think?
 
With any conversion you lose something, in this case you would lose volume for the pressure increase. You would need such large scoops that it would affect your areodynamics.

Personally, I think the 2 stroke cycle gasoline engine would work. You could use some of the stearling cycle principals and open the exhaust valve well BBDC, even prior to uncovering the intake ports. The majority of the power come is nthe first 1/2 half of the stroke anyway. I think you'd have enough time to exhaust the exhaust.

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Mikey's got it, about the air pressure conversion idea. The only logical way to increase ram effect is either larger scoops or increase the intake air speed. Since there is always going to be a high pressure area in front of a vehicle at speed, the designers have simply taken advantage of it. The RC51 is the most obvious example of this, with it's intake ducting going RIGHT THROUGH the steering head!

Again, the 2 stroke cycle can't work with the intake valve(s) at the top of the engine. Mikey has suggested opening the exhaust well before bottom dead center. If you look at a valve timing chart (a 720 degree chart), you'll see that they already do open well before bottom dead center. PERHAPS, a well designed cylinder head could invoke a swirl in the cylinder using incredibly high boost to force the exhaust gases out in such a short time, but then you'd need increasingly stiff intake springs to keep the intake valve closed (against that boost, remember!) until the piston begins it's compression stroke. Plus that high pressure air still needs to be compressed, so we'd have to start with an engine with really low compression ratios. That means zero torque, and an easily stalled engine. And with F1 valve technology comming down the pipeline (read: pnumatic valves), rev limits are going to keep going up and up.

I'm not an engineer, simply an auto mechanic that has done a lot of studying on engine dynamics. As far as I know, 16,000 is about the highest engineers can go with spring actuated valves on an engine that has to last. BMW is working on electical solenoid-actuated valves in their M-series cars; no camshaft. That means new duration and lift maps would be a simple reprogramming away! VTEC (Honda) taken to the next level. Mazda has revived their rotary engine that, IIRC, spins up to 12,000 RPM!

I encourage everyone to keep thinking up these new ideas.
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