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Author Topic: What is the max peak cylinder pressure?  (Read 2357 times)
n2toh
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« on: January 11, 2006, 02:35:58 am »

What is the maximum peak cylinder pressure a Listeroid will withstand before some type of damage will occur? IE head gasket or bent parts?
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kyradawg
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« Reply #1 on: January 11, 2006, 02:48:04 am »

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« Last Edit: August 03, 2006, 06:50:41 pm by kyradawg » Logged
n2toh
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« Reply #2 on: January 11, 2006, 04:01:50 am »

It would be neet to have a chart starting with stock pressure and up the pressure untill each part fails.
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kpgv
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« Reply #3 on: January 11, 2006, 04:42:01 am »

Kinda like when the crash the NEW cars w/ the dummies in 'em.
Destructive testing is expensive...May I suggest a little nitrous to get the "ball" rolling...
Who's Buying!!!

Kevin
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n2toh
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« Reply #4 on: January 11, 2006, 04:46:55 am »

It can be done without damaging parts.
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kyradawg
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« Reply #5 on: January 11, 2006, 04:51:03 am »

Do tell?
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phaedrus
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« Reply #6 on: October 26, 2006, 04:11:38 pm »

Peak pressure, being transient, can be so brief that it matters very little. For example, back in the 1960's in "Project Orion" they were going to use nuclear bombs to push a 3000 ton spaceship to Mars, "bang, bang, bang". The "peak pressure of an atom bomb is HIGH! Yet the experiments showed that the entire flight, with 2600 A-bombs going "bang", produced less than 1 second of actual pressure on the "piston" aka "pusher plate".

In diesels engineers talk about "BMEP" or "brake mean effective pressure". That's the pressure that it would be necessary to hold throughout the power stroke to make the power that's being generated in a given engine. It's my understanding that the upper limit is determined primarily by the tensile strength of iron, and that this practical limit for BMEP in diesels is in the area of 500 PSI. In a small engine such as a Lister type one might be able to push that a bit, but why?
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diesel guy
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« Reply #7 on: October 26, 2006, 06:06:29 pm »

All engines gas or diesel has a Maximum Peak Cylinder Pressure (MPCP). This occurs in a very small timeframe when the fuel is at full burn and the piston is at approximately + or - Top Dead Center (TDC) , 5 degrees ATDC is optimum and all the thermal expansion is occurring in the combustion chamber.

The MPCP ramps up quickly when the piston approaches TDC and depletes quickly when the piston starts to move down the cylinder and increasing the volume, so the timing of such an event is crucial so the burning fuel can take full advantage of the mechanical leverage applied to the crankshaft per piston location. This force in turn is absorbed by the flywheels and held as a stored potential (kinetic energy). This kinetic energy is released throughout the required 720 degrees needed to complete the Intake, Compression, Power and Exhaust cycles. The heavier the flywheels the better they can absorb and release this potential throughout the 720 degrees (very constant speed).

So the MPCP must be precisely timed to maximize the BTU content of the fuel used for economy and if the timing is to advanced premature engine wear will occur. If the timing is to retarded, there will be un burnt fuel in the exhaust with low output power and carbon build up will form at an accelerated rate. 

Diesel Guy


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GIII
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« Reply #8 on: October 26, 2006, 08:22:16 pm »

I don't know about the Lister type engines, but the Atlas Imperial has relief valves set at 800 psi to limit combustion pressures in case of injector malfunction, at which time they sound something like a 12 ga shotgun being fired.  Of course 800 psi on a 13" piston is a fair load, too.

George
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Shadow
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« Reply #9 on: October 26, 2006, 09:35:28 pm »

According to the book 'The Lister CS Story', In the starting position the compression pressure is changed from the normal 450 lbs per sq inch (15 to 1)to 600 lbs per sq inch(19 to 1). Once the engine is running its returned back to normal 450 lbs per sq inch.
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phaedrus
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« Reply #10 on: October 26, 2006, 10:09:46 pm »

reading posts here I see that the original question seems to have more than one interpretation, eg max pressure without firing, and max pressure firing as two basics, with further possibilities when reduced chamber volume (due to coking, etc) raises non-firing pressures and also incorrect injection timing producing very high pressures as well as max pressure firing in a coked engine. Further possibilities occur as well - for example pressure encountered in stalling or over-loading, "exotic" fuel mixtures producing un-designed burn rates, and so forth. It is also undefined as to cycle life...is this a time to failure question or not? Exceeding material limits slightly can be done for brief periods, as I described above, but why would anybody want to in a stationary engine? perhaps n2toh could further define his question... I assumed originally that he was interested in maximum peak firing pressure in a clean properly timed engine running designed fuel at sea level and at design load. rash assumption, as I see.... while experimental verification of the material limits could be done, with, for example, a test engine on a dyno and a supercharger, increasing power output to failure of the materials, it's just repeating the work that MAN, Sulzer, (Lister)etc. have done. The Atlas reliefs opening at 800 is interesting, didn't know that. I do know from experience that Enterprise in-line 8s (17" x 21" bore) have cylinder taps that one opens, then rolls the engine over to assure clear cylinders. these taps can be connected to indicating pressure recorders, but it's been years since I did it and I don't remember the pressure, peak or otherwise, except that it was fairly modest.
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slowspeed1953
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« Reply #11 on: October 27, 2006, 12:17:53 am »

Holy smokies a 6/1 @ 450psi is equal to 5125.781 pounds pushing down on the piston and @600psi 6834.375

Peace&Love Cheesy, Darren
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SHIPCHIEF
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« Reply #12 on: October 30, 2006, 12:00:56 am »

I suppose you really would want to see a Pressure / Volume Diagram, which shows pressure vertically and piston stroke horizontally on an 'indicator card'.
Typically the card was set on a rotating drum that was connected to the piston connecting rod. the cylinder pressure was taken from the valve in the head previously mentioned. this pressure was applied to a piston that moved the pen up and down the card.
So now the card is rotating back and forth while the pen is twitching up and down.
The pen is lowered to the card when the engine is running at the desired test condition, then lifted after the card is marked.
The card indication should look like the outline of a shoe.
(?) you say?
The top center is on the left and high pressure the top. As the cylinder pressure drops and the piston is moving the pressure line on the card is drawn from the upper left corner to the right, then down steeply, then flattens out (adiabatic expansion) until the exhaust valve opens, where it drops to the atmospheric line. Then the pen scribes the scavenging cycle, then the compression stroke scribes a rising line to the left and up to meet the beginning of combustion where it started.
Today, and electronic peressure transducer would be screwed into the head, and you could read the output on an osilloscope, using time to represent stroke.
You could drill and tap it into the precup plug.
Net cost: one transducer, some shop time, and borrow that 'scope from your electronic geek friend, who will operate it because he's just as curious as you are.
Now you will have peak firing pressure, and every other pressure too!
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aqmxv
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« Reply #13 on: October 30, 2006, 05:03:23 am »

Shipchief describes the high-tech way of taking instantaneous chamber pressure readings.  My understanding from someone who works in the business of tweaking engine control systems for a large OEM is that pressure transducers with sufficiently rapid reaction times are, ahem, not cheap.

I found the old, low-tech way of doing this in an engine design manual from the 1960s.  You use a small rotary valve turned at 1/2 crankshaft speed.  Chamber pressure goes to the center and the instantaneous pressure is read off of one or many ports on the outer ring.  If you have many ports, you hook each one up to a manometer, gauge, or transducer and get a realtime fingerprint of the compression and combustion cycle limited in resolution by the number of degrees of crank rotation between ports on the valve.

If you have one port, you have to be able to rotate the outer ring of the valve in a controlled way, probably with a worm gear and protractor.  You hook your pressure gauge up to the port and then rotate the gauge to and fro during the steady-state test run, taking measurements every x degrees to suit your resolution requirement.  When it's done, you have the data for your pressure-crank position plot.

The technique was described for use in small high performance four-stroke gasoline engines (Cosworths, etc).  Everything is applicable to our old, slow Diesels, and the lower speeds make things easier.  If you wanted to use your listeroid as an educational tool, or were supercharging, this sort of information might well be useful.  The one requirement is that one firing cycle be nearly identical to the next, which means steady-state operation and few misfires.  I would not be surprised to hear that this method was used at Dursley in the design phase of the CS.

In my case, I won't be making huge changes to the basic operating parameters of the engine.  I doubt I'll need to go this far to figure out what is going on.  I should be able to get by with applying a repeatable load to the engine and then tweaking the injector timing for best BSFC at 80% of max power.  Sure it'll involve a few starts and stops, but it doesn't involve lots of machining...

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