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Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests


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  #61  
Old 02-11-2016, 09:23:34 PM
Amax Amax is offline
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

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Originally Posted by imotorhead64 View Post
Hi Amax, for purposes of increasing efficiency using the Atkinson / Charon cycle a large expansion ratio is required... The advantage comes when very high compression pistons are used because they create a small combustion space. However if a full intake / compression stroke is used (Otto cycle) the peak pressure the 14:1 pistons will make is too high for common gasoline so the valve is ether closed early or late to create ( in effect) a short compression stoke with lower peak pressure and a longer expansion stroke. Does that make sense?
Yes, it does. Thanks!!
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Old 02-12-2016, 06:22:43 AM
Wayne Timms Wayne Timms is offline
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

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Originally Posted by imotorhead64 View Post
Another way to limit the compression is to close the intake valve early, this requires a valve spring capable of holding the valve shut while the piston pulls a vacuum on the cylinder. It seems to me this could be a more efficient method since moving the air fuel in and out of the cylinder requires some energy output... any guess why one method is better than the other?
Hi,

Another engine built around the same time as the Charon in the late 1880s was the French Niel. It closed all valves for 1/3 of the stroke causing a vacuum, as you can imagine there is a power loss but there is a return of power with the piston travelling back through the vacuum on the compression stroke.

The intake of the air and gas occurred through a rotary valve. This would eliminate the need for strong springs, but there was still the standard exhaust valve.

Neil may have produced a slide valve but I can't confirm this 100%.

I have included a photo of the Charon inlet cam and fuel cam. It is a sliding cam which slides along the sideshaft which is operated by the governor. As one increases it valve lift the other decreases. The engine has a 200mm bore, 340mm stroke and is rated at 6hp.

The other thing of note is the Niel was able to use hot tube ignition, because the size of the charge wasn't variable, the Charon had to use spark ignition due to the varying charge.

Regards,
Wayne

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Old 02-12-2016, 10:10:08 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Wayne T. Niel did patent a Slide Valve Engine on September 1st 1882 in England Patent Number #1026.

From what I can tell its operational cycle was similar to the opposed cylinder Stockport and Dickson design.
.

Last edited by Wayne Grenning; 02-12-2016 at 10:38:59 AM.
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Old 02-12-2016, 11:34:18 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

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Originally Posted by imotorhead64 View Post
I'm assuming that for full power the intake valve would be open the entire stroke?
The Otto and the Jacobson both use a rocker arm and pushrod setup. The governor moves the push rod along a ramped surface so the lift and duration would be changed. At full speed and under load the pushrod would be at the high point of the ramp so length of time the valve is open and how far the valve is open would be at max. At full speed and light load the pushrod would be at a lower point on the ramp so less duration and less opening. I see it as a fuel saving measure from a throttle governed engine the same as hit and miss was but it's not missing. If you wanted to change the speed you would change the governor setting and the pushrod would be on an even lower spot on the ramp.
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Old 02-12-2016, 12:30:39 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

I can see the benefits of limiting the volume of air / fuel by using the valves over a butterfly. With the butterfly there is some volume of A/F entering and exiting through the valves. As the piston reaches bdc it creates a maximum vacuum. As it begins to rise some volume of the A/F would move out of the cylinder until it becomes equal to the manifold vacuum . However reducing volume does not in any way increase the expansion ratio. For that you need to reduce the combustion space. An ideal engine would constantly adjust the combustion space according to the max peak pressure. In the way the engine could always operate at maximum efficiency regardless of load. There are many different schemes that propose to accomplish this, but I'm not aware of any that have made it into production. My favorite design is a diagonal slide outfitted to the original Atkinson which moves the pivot point to transition the engine from Otto to Atkinson.

http://www.osti.gov/scitech/servlets/purl/1014534/

https://www.youtube.com/watch?v=DdM2VbbdtB4

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Old 02-13-2016, 07:28:47 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

There were a number of variable expansion engines made over the years that use the intake valve as the means to vary the governing displacement over the other cycles, this was not really ideal ? until the advent of electronic engine management systems of late. One of the production engines of the past, patent US 1467998 combustion engine enjoyed a 20 year production run in single and multi cylinder design up to 60 hp, .... anyhow here are few old texts just for the interest.
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Old 02-13-2016, 12:31:51 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Hi typak, I'm not sure how variable valve timing can be used to create variable expansion ratio... the only way I'm aware of to vary the expansion ratio in these types of engines is to vary the combustion space. Valves can be used to vary the expansion in engines that do not compress in the same cylinder... like a steam or Brayton engine. The Corliss steam engine is a good example of valves being used to create a variable expansion ratio.

Last edited by imotorhead64; 02-13-2016 at 03:29:59 PM.
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Old 02-13-2016, 12:54:07 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

varying the intake duration varies the amount of air/fuel intake which varies the the amount of heat generated during the burn cycle which affects the expansion rate.

More Heat = more Expansion.

Varying the valve timing also varies the 'effective' compression ratio even though the static compression ratio remains the same.

There's a little more to it than that, but yes it does affect it.

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Old 02-13-2016, 03:19:19 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

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varying the intake duration varies the amount of air/fuel intake which varies the the amount of heat generated during the burn cycle which affects the expansion rate.

More Heat = more Expansion.

Varying the valve timing also varies the 'effective' compression ratio even though the static compression ratio remains the same.

There's a little more to it than that, but yes it does affect it.
I agree that the density of the mixture inside the cylinder can effect the rate of expansion but it has nothing to do with the ratio of expansion... The ratio of expansion is the volumetric difference between the combustion space at TDC and the space created when the piston is at BDC or when the exhaust valve opens...

I'll go a little further and will say that increasing compression has nothing to do with efficiency. Power density yes.. but efficiency no.... In fact increasing compression can even make an engine less efficient... by now many of you likely think I'm nuts but bare with me and I'll prove my point...

This will make more sense if you ever operated an engine with a compression relief lobe which opens the exhaust valve during the compression stroke. Just this morning I got a call to help a buddy who has a 1902 curved dash Olds and it dawned on me while starting the car that this would make a good argument for my point. The engine is a 5-6 hp single cylinder. The car starts with a hand crank on the side of the seat. There is a pedal on the floor which slides the exhaust rocker to engage a compression relief lobe on the cam. Cranking it through without the compression relief is not an easy option... on this particular engine the exhaust valve closes just before TDC and creates a little compression. (maybe 10-20 psi) With the engine running you can engage and disengage the compression relief. With the relief engaged the engine actually gains a little rpm. Keep in mind that a good portion of the air /fuel that was sucked into the cylinder was expelled on the compression stroke. so there is obviously less fuel in the cylinder at the time of ignition yet as I mentioned before the engine rpm's increase when the relief is engaged. Anyone who has an engine with a compression relief can try this experiment... just make sure the engine does have some compression... Compression in and of itself is only useful for making power and not improving efficiency. Yes usually increased compression does result in increased expansion because of a smaller combustion space which does have a definite effect on efficiency. I hope this makes sense... I understand some of you may think I'm a little crazy but I'm ok with that...
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Old 02-13-2016, 11:00:29 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Hi imotorhead64,

I was aware that with the Charon the downside is there is no adjustment in the combustion space, while the amount of the air fuel mixture changes. I wonder whether they designed the combustion chamber to operate at optimum performance - low load, high load or in the middle.

I have included a photo of a Niel rotary valve, an early Charon with the crosshead and an advert of a French engine, which is also listed in "Moteurs a Gaz et a Petrole", by Aime Witz. This engine is in the same section of the book as the Atkinson, Niel and Charon, my French is not good enough to determine the cycle the engine runs on.

There are a number of other engines in this section of the book, including one from Forest, so it is quite possible that the French were building a number of these engines very early on in the piece.

Maybe someone more knowledge on early French engines could help?

Regards,
Wayne

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Old 02-14-2016, 08:21:24 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Thanks Wayne, Those are some interesting engines...

I found this description about the Neil and Charon in the book titled "Modern Gas and Oil Engines" by Fredric Grover 1902







Also a good description of Atkinson's engines



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Old 02-14-2016, 08:30:28 AM
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Old 02-14-2016, 08:35:29 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests



Also I though this diagram was interesting because it shows where the heat / energy goes.



In my opinion engine specifications should also include not just a compression ratio but an expansion ratio calculation. This is an often overlooked factor when determining an engines potential efficiency.


The book has a lots of good information and discusses many of the different engine types. Here is the link to it.

https://books.google.com/books?id=R_...charon&f=false

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Old 02-15-2016, 05:37:19 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

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Originally Posted by imotorhead64 View Post
I agree that the density of the mixture inside the cylinder can effect the rate of expansion but it has nothing to do with the ratio of expansion... The ratio of expansion is the volumetric difference between the combustion space at TDC and the space created when the piston is at BDC or when the exhaust valve opens....
Expansion Rate and Expansion Ratio kind of go hand-in-hand... regardless of Compression Ratio which is the difference between the combustion space at TDC & BDC.

If you have a very short intake duration and allow just a little air/fuel mixture into a high compression ratio engine you will get a quick explosion that heats and expands rapidly but then since it burned so quick will cool off quickly and quit expanding early in the power stroke.

Or you can hold the valve open longer and allow more air/fuel into a lower compression engine and even though it will light up and burn slower it will burn longer and continue expanding throughout the power stroke.

And yes you can do just the opposite and hold the valve open longer on the high compression and for a shorter time on the low compression engine and make an even bigger difference.

Simply put, the hotter the burn and/or the longer the burn, the more expansion you get whether it's in a high compression ratio or a low compression ratio engine.

There's always a chance I could be way off on that, but it seems so logical to me that it makes perfect sense in my mind.


Less Air/Fuel admitted = Small fire = less heat & less expansion....
More Air/Fuel admitted = Big fire = more heat & more expansion.


Equal amounts of Air/Fuel admitted in to higher compression = Quicker Expansion because it starts from a smaller space but that quicker Expansion Ratio will be for a Shorter Duration because it will burn quicker at the higher compression ratio. Add in Higher Octane with the Higher compression and then you get a slower/longer burn that continues expanding longer or farther down the cylinder.



---------- Post added at 05:37:19 PM ---------- Previous post was at 05:20:46 PM ----------

Quote:
Originally Posted by imotorhead64 View Post
Isky sold them as Mile-A-More cams... Crower also sold them as an economy kit which included new pistons. I once spoke to Bruce Crower about them and he told me it was useless to just replace the cam without replacing the cam without the 12-14:1 pistons. The engines had about a 9:1 compression ratio with the cams installed.
I hadn't looked back through this entire thread before, but those engines built with 12:1 or 14:1 pistons still had 12:1 or 14:1 with their special ground cams.

The cam timing lowered the cranking compression by bleeding off some of the pressure giving them an "Effective compression ratio" of around 9:1 with the lower compression pressure, but they were still 12:1 or 14:1 Static Compression Ratio.

Compression Ratio does not change with the cam timing
. It is built in to the engine with the TDC & BDC CC's

Changing the cam only changes the cranking pressure not the compression ratio.

I don't remember who built it and it would take me 30 years to go back through 30 years worth of magazines stacked up in the house to find it again, but back in the mid/late 1980s someone had a special ground cam and built an engine with 17:1 Compression Ratio that would run on regular 91 octane pump gas by limiting the Cranking Pressure to avoid detonation.

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Last edited by OTTO-Sawyer; 02-15-2016 at 05:50:12 PM. Reason: added the 17:1 line
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Old 02-15-2016, 11:12:09 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Hi Otto, I don't want to come off as a know-it-all because I have a lot to learn... However I have done a lot of engine / efficiency experimentation with various compression/expansion ratios. It seems you have your version of expansion ratio and I have mine... I don't think think expansion ratio and expansion rate are the same thing at all. An engine could have a fast expansion rate and a low expansion ratio. This would result in low efficiency due to a large pressure loss (loss of potential energy) when the exhaust valve opens.

The point I was trying to make is that it is often stated that higher compression ratio alone can improve efficiency. I was merely pointing out that higher compression ratio almost always results in higher expansion ratio, however that fact is often ignored.

Quote:
Compression Ratio does not change with the cam timing.
Changing the cam only changes the cranking pressure not the compression ratio.
I think you are mistaken here... for maximum compression closing the intake at BDC is the best option... yes some high performance engines will close just after BDC to take advantage of the momentum of air which has a slight supercharging effect thus raising the compression pressure but not the compression ratio. Late or early closing of the intake valve will result in a shortened compression stroke thus reducing the effective compression ratio. The compression ratio is the volumetric difference from the point the piston starts to compress (not always BDC) to the space that left when the piston is at TDC.

There is much information about this. Also here is a patent addressing it.

http://www.google.com/patents/US5682854

Quote:
Less Air/Fuel admitted = Small fire = less heat & less expansion....
More Air/Fuel admitted = Big fire = more heat & more expansion.
This is absolutely correct.

also keep in mind that less air results in a lower compression pressure.

By allowing less air / fuel to enter the cylinder the combustion space can be made smaller until the maximum peak pressure is attained. This results in a higher expansion ratio thus a less powerful yet more efficient engine.






Last edited by imotorhead64; 02-15-2016 at 11:38:30 PM.
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Old 02-16-2016, 09:09:27 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

I have very little to add to this scientific discussion.

I will observe and ask the following:

Compression ratio must be independent of the cam timing because it is measured with the engine apart and the camshaft in a box on the shelf. Compression ratio is a mechanical fact, the big (BDC) volume divided by the small (TDC) volume.

Once one adds movement (rpm), intake port shape and size, valve size, lobe profile, etc. it all gets interesting because of the many dynamic effects, some of which could work against the others.

I can't even imagine how a F1 engine designer handles this with four-stroke motors that can spin at 18,000 rpm. What does the intake charge behave like at that speed? Is it still like gas blowing through an orifice, does it behave lumpy like extruding clay through a die, or is an entire column of air reverberating like a slinky?

Volkswagen and some other manufacturers tried to vary the size of the combustion chamber. The VW design tilted the head and increased the size of the CC by opening the wedge, IIRC. None of these experiments panned out as far as I know.

What about Army multifuel engines? Don't they have compression ratios higher even than a diesel? They must be the most 'efficient' around.
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Old 02-16-2016, 10:37:19 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Hi Amax, I really think we are all more or less on the same page... the only thing is we have different definitions of the same thing...

you stated:

Quote:
Compression ratio must be independent of the cam timing because it is measured with the engine apart and the camshaft in a box on the shelf. Compression ratio is a mechanical fact, the big (BDC) volume divided by the small (TDC) volume.
and Otto stated:

Quote:
I hadn't looked back through this entire thread before, but those engines built with 12:1 or 14:1 pistons still had 12:1 or 14:1 with their special ground cams.

The cam timing lowered the cranking compression by bleeding off some of the pressure giving them an "Effective compression ratio" of around 9:1 with the lower compression pressure, but they were still 12:1 or 14:1 Static Compression Ratio.

Compression Ratio does not change with the cam timing. It is built in to the engine with the TDC & BDC CC's

Changing the cam only changes the cranking pressure not the compression ratio.
So it seems in your mind and Otto's that the compression ratio is only measured by the cylinder volume when the piston moves from BDC to TDC irregardless of the timing for closing the intake valve?

If you are using that definition it's difficult to make a comparison between an Otto , miller and Atkinson cycle.

Using your definition how would you describe or compare the compression and expansion ratios of an Otto, Miller and Atkinson cycle engine?

My definition of compression ratio is the volumetric difference between the working fluid when it enters the cylinder and the space it is compressed to at TDC. So if the engine had a 20:1 difference from BDC to TDC if the intake valve closed 1/2 way in between top and bottom I would define that as a 10:1 compression ratio 20:1 expansion ratio engine.
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Old 02-16-2016, 12:25:30 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

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Originally Posted by imotorhead64 View Post
Hi Amax, I really think we are all more or less on the same page... the only thing is we have different definitions of the same thing...

you stated:



and Otto stated:



So it seems in your mind and Otto's that the compression ratio is only measured by the cylinder volume when the piston moves from BDC to TDC irregardless of the timing for closing the intake valve?

===> Yes

If you are using that definition it's difficult to make a comparison between an Otto , miller and Atkinson cycle.

===> Agreed

Using your definition how would you describe or compare the compression and expansion ratios of an Otto, Miller and Atkinson cycle engine?

===> I cannot. I am only familiar with the Otto cycle although I have a cursory understanding of the attempts automakers have used to approximate the features of an Atkinson and/or Charot cycle as is being discussed in this thread.

My definition of compression ratio is the volumetric difference between the working fluid when it enters the cylinder and the space it is compressed to at TDC. So if the engine had a 20:1 difference from BDC to TDC if the intake valve closed 1/2 way in between top and bottom I would define that as a 10:1 compression ratio 20:1 expansion ratio engine.
I understand your point but what I believe it boils down to is that you are using 'expansion ratio' to describe what we all call 'compression ratio' and furthermore you consider 'compression ratio' to be a variable driven by valve events and timing - anecdotaly, that would probably be called something like 'effective compression ratio'.

(I am not criticizing the concepts you've advanced, just trying to get tehe foundations laid out in my own mind.)
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Old 02-16-2016, 04:49:10 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

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Originally Posted by imotorhead64 View Post

My definition of compression ratio is the volumetric difference between the working fluid when it enters the cylinder and the space it is compressed to at TDC. So if the engine had a 20:1 difference from BDC to TDC if the intake valve closed 1/2 way in between top and bottom I would define that as a 10:1 compression ratio 20:1 expansion ratio engine.
Your definition with the volumetric difference based on when the valve closes is what I'm referring to as the "Effective" compression ratio which will vary the cranking pressure.

But again... the STATIC Compression Ratio is still Locked In based on the difference between TDC & BDC and does not change

I understand what you're saying about closing the valve late and having an "Effective" compression ratio of a theoretical 10:1 lowering the cylinders cranking pressure (to avoid detonation) and still having the 20:1 expansion ratio (based on your example) but in that example the STATIC Compression Ratio is Still 20:1 while the "Effective" ratio would be approximately 10:1. and I say approximately because the valve would ramp up and down and would have to start closing before the half way mark to be fully closed at 1/2 stroke.

The Actual or Static Compression Ratio still remains unchanged though unless you shave the head or block to make the combustion chamber smaller or lengthen the stroke making a bigger difference between the TDC & BDC CCs

I still stand by examples of:
Less Air/Fuel admitted = Small fire = less heat & less expansion....
More Air/Fuel admitted = Big fire = more heat & more expansion.


and my:
Equal amounts of Air/Fuel admitted in to higher compression = Quicker Expansion because it starts from a smaller space but that quicker Expansion Ratio will be for a Shorter Duration because it will burn quicker at the higher compression ratio. Add in Higher Octane with the Higher compression and then you get a slower/longer burn that continues expanding longer or farther down the cylinder.

If you have a real high Static Compression ratio (using your example) of 20:1 and open/close the intake valve Real Late only admitting a very small amount of air/fuel you would get a small pop that would jerk the piston-rod-crankshaft into motion, and yes assuming it was enough of an explosion to gain enough momentum to push the crankshaft all the way around to (or past) BDC it would have expanded at that 20:1 'expansion' ratio but it wouldn't make much power in doing so, so even though it was a 20:1 ratio it might only have the power of say maybe a 2:1 "Effective" Compression ratio (and in turn an "Effective" Expansion Ratio of that same 2:1 Or Actually Somewhere Between the 2:1 and 20:1 ratios because of the burning/heating/expanding after being admitted cold and dense) because of the quick burn rate of the small amount of fuel admitted even though the Static Compression/Expansion Ratio remains 20:1.

But again, that's just MY thinking on the subject.


---------- Post added at 04:39:29 PM ---------- Previous post was at 04:24:40 PM ----------

Actually now that I think of it a little more.... IF you had a hot enough flame or long enough burn time to still be expanding (or have pressure left over) after hitting BDC then you would have a greater expansion ratio than the compression ratio which in reality I'm guessing a lot of engines probably do.... just the same as a steam engine has a greater expansion ratio as evidenced by the triple expansion engines that use the left over steam from the high pressure cylinder to feed a second cylinder and then the real low pressure (but Still Pressure) to feed the third cylinder.

If you have your theoretical 20:1 Compression Ratio engine and admit a lot of high octane fuel into it then your theoretical Expansion Ratio might be in the order of 25:1 or 30:1 or higher (?) depending on the burn rate and how much wasted fuel/heat/expansion goes out the exhaust like in the top fuel dragster shooting flames out the headers.

But in the end the 20:1 Static Compression/Expansion Ratio still does not change as it is built in to the engine.



---------- Post added at 04:49:10 PM ---------- Previous post was at 04:39:29 PM ----------

Your Expansion Ratio will change with a lot of variables Including the Static Compression Ratio, The Valve Timing & Duration affecting the Cranking Cylinder pressure aka Effective compression ratio, the octane rating and burn rate of the fuel, the air/fuel mixture ratio (lean/rich), the spark timing, and probably a few more things I missed all working together affecting the duration and intensity of the burning/heating/expanding within the cylinder.
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Old 02-17-2016, 02:10:45 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Looking at your Brayton Cycle Engine thread again (which YES I am Very Impressed with what you've accomplished so far with your engine) I see you've posted a lot more there since I last looked at it.

I see in the links you posted on post #272 the Hot Rod link is now calling it Dynamic CR instead of Effective CR (which is what they and Car Craft & most other mags called it not too long ago)

I have a lot of catching up to do on that reading when if/when I get more time to spend on it and so far have only skimmed through maybe 1/3rd of the Hot Rod link.

In some of their explanations that I've read so far they refer to Theoretical Thermal Efficiency, explaining that ""At lower rpm we find that the static CR is never realized because the intake valve is assumed to close exactly at BDC prior to the start of the compression stroke. This does not happen in reality."" which is where the "Effective" CR or what they now call "Dynamic" CR comes into play based on valve timing and duration.

But none of that changes the fact that the Static CR remains the same and is built into the engine and are the numbers usually referred to when comparing one engine to another or when ordering new higher compression pistons or any other engine parts that get swapped out in the build up as in changing from 9.5:1 CR to 11:1 CR. Then during the rest of the buildup you have to decide if you want to run 110 octane racing fuel to keep the engine from detonating or choose a different cam to lower the "Effective" or "Dynamic" CR limiting the cranking cylinder pressure.

And like you said..... I don't want to come off as a know-it-all because I TOO have a lot to learn.

You're light years ahead of me on the Brayton Cycle and I salute you on that.

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