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


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  #81  
Old 02-17-2016, 08:41:44 AM
JSWithers JSWithers is offline
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Quote:
Originally Posted by OTTO-Sawyer View Post

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)

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.
I would have to agree with OTTO that the mechanical combustion ratio remains constant. The only way to change it would be to change the variables such as bore, stroke, combustion chamber size, etc like the Aitkinson engine tried to do through it's elaborate way of trying to change the stroke,etc.

OTTO, I had always heard it called Dynamic compression ratio. Modern engines use a variety of ways to change that. In the good old days the cam manufacturers tried all sorts of valve overlap tricks. If you didn't care how your engine idled or that it ran rough at low RPM's then there was a lot of overlap. My 2014 Ford F150 has as system known as Tri-VCT...cam torque actuated twin independent variable camshaft timing. It is a dual overhead cam, 32 valve (4 valves per cylinder) set up with 10.5:1 compression ratio. Rather high for a modern pump gas daily driver. It also has electronically controlled sequential multi port fuel injection. And electronically controlled ignition system. It produces 360hp and is set up for flexfuel. I've always figured that modern engines were never really set up for ethanol until a set up like this with higher compression. We made a 2400 mile round trip to Coolspring last June and I averaged 19 mpg. Not bad for a 4 door 4 wheel drive pickup with 3 big guys in it with all there stuff. I grew up with regular cab 4 wheel drive pickups that didn't have that kind of power and comfort and didn't get 10 mpg.

My point is that in the good old modern days everything about an engine was pretty much a static spec. Now everything thing is infinitely variable...except compression ratio. Don't you just love modern technology?

I am certainly not an expert. I have only been playing with engines for over 50 years.
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Old 02-17-2016, 12:06:42 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Hi Guys... I understand my referring to compression ratio as the ratio to which the gas is actually compressed might be confusing. Maybe the most correct term would be effective compression ratio. My point is that the expansion ratio is often overlooked but is a very important consideration. I would imagine the main reason JSWithers truck gets 19 MPG is because it has 10:1 expansion ratio not because it has a 10:1 compression ratio. And I would imagine it would get even better mileage if it had a 15:1 expansion ratio... however it would sacrifice performance because you can't compress air and fuel to 15:1 because the temperature of the air would ignite the fuel. What you could do is lower the compression pressure by ether closing the intake valve early or late thus reducing the "effective" compression ratio. Now we could have a 9:1 compression with a 15:1 expansion. This results in less fuel charge in the cylinder because of the smaller combustion space (low performance) yet more expansion of the gasses because of the expansion ratio (higher efficiency) Does that make sense?

The real holy grail for engine designers is a variable stroke engine that can produce smaller combustion space (ideal for high efficiency at light engine load) and larger combustion spaces (needed for for making power at high loads).

Otto here is a link if you are interested in Brayton engines. I think this is the best book I have seen on the subject.

https://books.google.com/books?id=rP...%20...&f=false

Last edited by imotorhead64; 02-17-2016 at 12:47:35 PM.
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Old 02-17-2016, 03:13:28 PM
JSWithers JSWithers is offline
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

I think that was my point. The engine has a variable dynamic (effective) compression ratio because of the variable cam design. Basically the system is changing the timing of the camshaft allowing more or less overlap. The engine is also controlling the detonation by electronically controlling the fuel delivery amount and timing with the sequential multi port fuel injection and electronically controls the engine spark timing as well. Pretty complex engine management system that was never dreamed of back at the beginning of engine development. All of this is working to control the expansion ratio to what's needed at that moment. All these variables to control all the variables. Today we have everyday cars with more horsepower, fuel economy, etc on garbage gasoline as compared to the hottest muscle cars of the 60's and early 70's. 1973 was the beginning of trying to manage these things electronically for better "air quality" and horsepower and fuel economy suffered. I believe that air quality, performance, fuel economy, etc are all dependent on engine efficiency and I think that is being proven today. The smog era cars of the 70's, 80's, and 90's all had a static compression ratio of about 8.5:1 compared to the 10:1 to 11.5:1 of the 60's and early 70's. Today's compression ratio's are creeping back up like the 10.5:1 in my truck. They need to start somewhere. Everything else is controlled now by the engine management system. Heck, the computer controls all aspects of the engine while coupled together to control the anti-lock brakes, the steering, the transmission for the stability control system. The truck has no mechanical accelerator pedal linkage, no mechanical brake linkage, no mechanical steering linkage. Basically if I start to spin out on wet or icy roads the truck takes over to control itself...and protect you. Underneath it all is still the same engine design that Otto created. The only modern day company that I have heard with something different is SAAB. They are working on a variable combustion chamber.
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Old 02-18-2016, 01:09:15 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Quote:
The only modern day company that I have heard with something different is SAAB. They are working on a variable combustion chamber.
Many engine manufactures are working on variable compression concepts,

https://www.youtube.com/watch?v=oxR-3Un6WkU

https://www.youtube.com/watch?v=DdM2...-KORwQm0rHvQUg

http://www.extremetech.com/extreme/2...uel-efficiency

http://www.greencarcongress.com/2006...illars_va.html

http://www.nissan-global.com/EN/TECH...RVIEW/vcr.html

https://lup.lub.lu.se/luur/download?...fileOId=625830

http://www.autozine.org/technical_sc...h_engine_4.htm

I thought you might also like to check this out... Basically a Brayton engine.

https://www.youtube.com/watch?v=WID-...HJqwYpXar6G6-w

Last edited by imotorhead64; 02-18-2016 at 02:27:34 AM.
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Old 02-18-2016, 11:31:55 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 OTTO-Sawyer View Post
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.

.....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.
This little video of a single cylinder flat-head kind of shows what I was saying about the top fuel dragsters shooting flames out the headers and the "Expansion ratio" being much higher than the compression ratio as it shows the gases still burning as they start to get pushed out the exhaust.

Granted it is nowhere near as high of static or dynamic CR as a top fuel dragster, but it does have enough air/fuel admitted for an extended burn time and more heat/expansion as it's still burning as it leaves the cylinder.



Depending on how they're set up and adjusted when running at very slow rpms, a lot of our old hit and miss engines will blow out nice cool exhaust indicating that all or most of the burning/heating/expanding happened early in the cycle as there is no more heat left when coming out the exhaust so their 'expansion ratio' would likely be at or maybe even slightly below the static compression ratio as the intake is sucked open by atmospheric pressure and at low speeds suck in even less than when running at their rated speed.

Kind of like what I said in this part of the same post I quoted from at the beginning of this post..... (except that our old hit and miss engines are very low CR and admitting a small amount of air/fuel)

"" 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. ""

I think we're actually more IN Agreement than disagreeing with each other
.... just trying to learn each others terminology on the subject.
Biggest hangup seems to be the difference between static CR and dynamic or effective CR

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Old 02-24-2016, 01:22:00 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Otto, that's a neat video...

Quote:
but it does have enough air/fuel admitted for an extended burn time and more heat/expansion as it's still burning as it leaves the cylinder.
I think it shows that opening the exhaust valve while there is still a fire burning thus wasting potential expansion is a wasteful thing to do.

With regards to your comment

Quote:
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.
I think you are confusing the point by bringing other variables into the discussion. Yes some fuels can create more heat thus create more expansion from the same volume of air... but that has little to do with efficiency. The expansion I'm referring to is the volumetric difference between the combustion space and the space in the cylinder when the exhaust valve opens.

Earlier I made the comment that compression is not responsible for efficiency, compression can actually reduce efficiency but it creates more power due to the higher density of air / fuel packed into a small combustion space. Higher expansion creates efficiency by utilizing more of the heat created by burning fuel. High compression traditionally (in an Otto cycle engine) creates high expansion thus often mistakenly compression gets the credit for improving efficiency when the real credit should go to the increased expansion.

Here's a pretty good explanation of the point I'm trying to make...



a little more explanation...

http://www.curbsideclassic.com/blog/...ted-out-to-be/

Last edited by imotorhead64; 02-24-2016 at 11:35:24 AM.
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Old 02-24-2016, 06:51:40 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Hi,

I have taken the plug out of the Charon, just to get an idea of the static compression ratio. I can't measure the valve chest side of the combustion chamber, but looking at the cylinder and combustion chamber minus the valves gives a compression ratio of 10:1.

Of course the engine doesn't compress anywhere near this amount. The variation between its maximum and minimum compression travel is around 100mm, on a 200mm diameter.

Interestingly in the post above, during the video at around 1.24mins, they claim that engines in the late 1800s didn't have variable valve timing (VVT) not to be confused with VVL. Clearly they haven't looked at the Charon engine.

The picture below shows the plug out of the Charon and how easy it was to make a measurement on the compression ratio.

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Wayne

www.bluefuel-whitesmoke.com
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Old 02-24-2016, 01:02:37 PM
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Thumbs up Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Wayne T, No wonder those engine were efficient... 1:10 is a good expansion ratio. Just curious if you have ever measured the peak compression pressure?



Quote:
Of course the engine doesn't compress anywhere near this amount. The variation between its maximum and minimum compression travel is around 100mm, on a 200mm diameter.

At which point in the compression stroke does the intake valve close? I assume the governor closes the valve later for low power and earlier in the compression stroke for higher power?

Quote:
Interestingly in the post above, during the video at around 1.24mins, they claim that engines in the late 1800s didn't have variable valve timing (VVT) not to be confused with VVL. Clearly they haven't looked at the Charon engine
Ha I agree... sadly history rarely gives credit where credit is due...

Thanks for taking the time to check the compression / expansion ratio of your engine. It's an interesting thing to know.
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Old 02-25-2016, 07:03:58 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

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At which point in the compression stroke does the intake valve close? I assume the governor closes the valve later for low power and earlier in the compression stroke for higher power?
Hi John,

Using the same formula as in my previous post, not counting the valve chest. The maximum compression is 5.7:1 and the minimum is 3.1:1. These are based on roughly 1/2 to 2/3rds piston travel.

Yes, the governor closes the valve later for low power and earlier in the compression stroke for higher power.

The valve chest is quite large from the outside, I have no idea how large the combustion chamber is in the valve chest.

Regards,
Wayne

www.bluefuel-whitesmoke.com
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Old 02-27-2016, 03:24:03 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

I could be wrong.... but I believe that 'Car Tech 101' video is mistaken in comparing variable valve timing to the Atkinson cycle.

VVT is basically what we've been discussing (before I threw in the fast/slow burning fuel variables) and how it changes the Effective or Dynamic Compression Ratio by either opening late and drawing in less or in their case closing late and bleeding off some of the pressure.

The Atkinson Cycle is actually changing the STATIC Compression Ratio by changing the Length of the Intake/Compression cycle Stroke shorter than the Expansion/Exhaust Cycle Stroke thereby lowering Both the Static Compression Ratio AND the Affective/Dynamic Compression Ratio at the same time without altering the valve timing, while still having the longer expansion (power) stroke.

While still not the same since this one moves the entire stroke lowering BOTH the Static Compression AND the Effective/Dynamic Compression farther down in the cylinder lowering the CR by making the TDC combustion chamber bigger in comparison to BDC than it is when the whole assembly is raised up, it is closer to the Atkinson cycle as it is changing the STATIC CR where the Variable Valve Timing only changes the Effective/Dynamic CR, but still Different from the Atkinson Cycle in that the Expansion/Exhaust cycle is the same Static Ratio as the intake (Unless they are able to cycle the adjusting piston & rocker arm assembly up and down every other stroke for low compression/high expansion which it doesn't show in the video which would make it as close to the Atkinson Cycle as you're likely to get without duplicating it exactly)

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Old 02-27-2016, 05:11:58 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 OTTO-Sawyer View Post
I could be wrong.... but I believe that 'Car Tech 101' video is mistaken in comparing variable valve timing to the Atkinson cycle.

VVT is basically what we've been discussing (before I threw in the fast/slow burning fuel variables) and how it changes the Effective or Dynamic Compression Ratio by either opening late and drawing in less or in their case closing late and bleeding off some of the pressure.

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Old 02-27-2016, 08:43:55 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

I think the trick is to keep the combustion space as small as possible (maximum expansion) without exceeding the pressure which will cause preignition. When more power is needed the combustion space is made bigger and more A/F is admitted by closing the intake valve near BDC . When less power is needed the combustion space is made smaller and the valve closes late so the cylinder pressure does not get too high. The timing of intake valve closing manages the pressure and the combustion space is adjusted for the volume of air / fuel required to make the desired power and also maximum possible expansion.

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Old 02-27-2016, 10:15:26 PM
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Photo Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Another way to accomplish that getting different compression/expansion ratios with the basic OTTO Cycle engine is to simply Offset the Cylinder from the Crankshaft Center-line.

In the early 1900s-1920s they used to offset the cylinders as much as 1/6th the bore which would be as much as a 1/2 inch offset on a 3 inch bore or as much as a full One Inch offset on a 6 inch bore.

I'm not sure what make/model the engine is in the picture where I drew the lines showing the offset, but it is representative of how a lot of our early hit & miss and throttle governed engines were built, as well as the automotive and tractor engines of the day.

The second picture with a couple lines underlined for quick reference is out of a 1923 engine theories and principals book I have.

The Offset Bore design should work equally as well on the Brayton Cycle or the Atkinson Cycle as it does on the Otto Cycle.

The main benefit of an offset bore is that it gives a better rod angle on the power stroke with the side benefit of having slower piston travel on the compression stroke.

About the only thing it wouldn't work on would be on Reversible Engines like the Fairmont Motor Car engines or any other reversible gas engine, (or for that matter, on a reversible steam engine) which you would want ON-Center so you have the same operating characteristics in both directions.

Watching your Brayton engine videos I see it runs backwards from most hit & miss engines, so if you were offset the bore on it you would want to lower the cylinder, where most of our other old engines the cylinder would set above the center-line of the crankshaft as shown in the first picture.
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Old 02-27-2016, 10:28:22 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

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Old 02-27-2016, 10:57:26 PM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Hi Otto. I'm aware of offset cranks to reduce side load on the piston. As you say It can improve the rod angle and it does produce other characteristics... but I don't think it offers any efficiency advantage by changing the expansion ratio of the engine. TDC and BDC are still the same... The advantage of the variable compression engine is the ability to tune the combustion space continuously for maximum expansion. The Brayton can easily be set up to run in ether direction. I made it turn backwards because it was easier to crank the flywheel and mess with the adjustments at the same time... also I like to do things a little different...

http://www.google.com/patents/US2773490

https://www.google.com/patents/US869...FdBHAQ6AEIJDAB

https://www.google.com/patents/US417...FdBHAQ6AEIMjAD

https://www.google.com/patents/US190...FdBHAQ6AEIQDAF

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Old 02-28-2016, 01:31:50 AM
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Photo Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

I'd have to do a LOT of digging to ever find the magazines again, but back in the 1980s or early 90s there were a few write-ups about an old trick the drag racers stumbled across by accident in the mid/late 50s when they "messed up" and put the pistons in backwards.

Modern engines have the wrist pins offset to cut down on piston slap and they found out the engines ran stronger when the pistons were put in backwards giving them a better rod angle on the power stoke.

With the short pistons compared to the old engines, they rattle more with the pistons rocking sideways when they fired, but made more power as long as they held together (until they broke the piston skirts anyway). And that was with just a .060 to .090 offest which is a far cry from 1/6th the bore of the early engine.

You can attribute the power increase to the straighter rod angle giving more leverage on the crank during the power stroke, or to increased efficiency from the piston speed being slower in relation to the crank speed (and taking better advantage of the expansion while still at or near maximum pressure) than it is with the more laid-over rod angle where the piston moves down faster (and farther) while the crank is going from TDC to 90 degrees, or to a combination of the two.... Piston speed vs crank speed (efficiency) AND more leverage.

Pardon the crude sketches, but I HOPE they show what I'm trying to say as far as the rod angle and leverage. It just popped in my head about cranking an engine by hand with a straight arm versus bent at the elbow and I tried to find a couple pictures of arms bent and straight that I could work with on short notice. (just ignore the dumb-bell in the hand and the fact that I exaggerated the offset closer to 3/4 or 7/8ths instead of 1/6th)

And as we've both noted before.... I don't want to come off as a know-it-all because I TOO STILL have a lot to learn...... Some of this I'm just trying to remember (or re-learn) and/or correct myself on as I think it through and TRY to explain it as best I can while still contemplating what you're saying. Some of what you've pointed out has made me re-think some of my ideas and what I've learned in the past, and I hope maybe some of it helps going the other way as well.

If your Brayton engine is reversible then you would likely want to leave it on center. If you plan on running it one direction only, then it might help to offset the cylinder.

To be honest, I'd never even heard of the Brayton cycle before, or if I had heard of it I never paid any attention to it so what you're doing there is ALL NEW to me, and I have to say I am impressed with what you've been doing with it. Same goes for the Atkinson cycle, which while I had heard of it many times over the years I'd never seen a video showing its motions to see what it was doing. Far that matter, even with the Aeromotor 8-cycle engines I've seen a few and watched them run, but I've never read up on them or studied them to see what they're doing different. I'd say I definitely have a LOT to learn yet, but what I Do Know (or THINK I Know), I think I have down pretty good for the most part.
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Old 02-28-2016, 04:00:38 AM
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

Hi Otto, I don't disagree that offsetting the crank may have some benefits for efficiency due to decreased friction and increased leverage. Longer connecting rods also produce higher piston speed in the middle of the stroke and more dwell time at the top and bottom. but I think that is getting off topic since we had been discussing the advantages of engines with a higher than normal expansion ratio and valves that limit the volume of A/F entering the cylinder.

Quote:
Long rod pros:
Less rod angularity
Higher wrist pin location
Helps resist detonation
A lighter reciprocating assembly
Reduced piston rock
Better leverage on the crank for a longer time
Less ignition timing is required
Allow slightly more compression to be used before detonation is a problem
Less average and peak piston velocity
Peak piston velocity is later in the down stroke
Less intake runner volume is needed

Cons:
Closer Piston-to-valve clearances
Makes the engine run a little more cammie at low rpm
Reduces scavenging at low rpm

Short rod pros:
Increased scavenging effect at low rpm
Helps flow at low valve lifts (a benefit if the heads are ported with this in mind)
Slower piston speeds near BDC
Allows the intake valve to be open longer with less reversion
More piston-to-valve clearance
Can allow for a shorter deck height

and cons:
More rod angularity
Lower piston pin height (if the deck is not shorter)
Taller and heavier pistons are required (again, if the deck height is not reduced)
More ignition timing is required for peak power
http://www.yellowbullet.com/forum/sh...d.php?t=464436

Quote:
If your Brayton engine is reversible then you would likely want to leave it on center. If you plan on running it one direction only, then it might help to offset the cylinder.
I have no intention to make it reversible and no desire to go to the trouble to offset the crank... I think it would produce a minimum of improvement if any.

Quote:
To be honest, I'd never even heard of the Brayton cycle before, or if I had heard of it I never paid any attention to it so what you're doing there is ALL NEW to me, and I have to say I am impressed with what you've been doing with it.
about 20 years ago I had read internal fire and knew of the Brayton engine but I never took the time to really understand how it worked. About 15 years ago I got on a kick of building Stirling engines... the attraction of the Stirling was the high potential for efficiency, up to 47% however the tough thing with the Stirling is you must get all of the heat into and out of the engine using heat exchangers which are very complex to make. ... I started to learn about the Ericsson engines which were open cycle hot air engines with a regenerator and thought maybe internal combustion could be applied. I call it the BELL cycle. After a bit of studying I built my first little test engine and started to learn about the cycle. There is little information and understanding of piston Brayton engines since none have been produced since about 1900. supposedly the last time an original was running was in the 1920's. Many people didn't even realize they existed... I once was talking to a professor at UC Davis and was telling him about the Brayton piston engine and he told me there was no such thing.

here's a diagram that might help you understand the Brayton.



Here you can see the Brayton's similarity to the Stirling engine.



Here is one of my Stirling engines



This is my first Brayton type engine in 2002


Last edited by imotorhead64; 02-28-2016 at 08:54:04 PM.
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Old 03-13-2016, 11:30:39 AM
imotorhead64
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Default Re: Historical Engine Article Series I - Early Crossley Slide Valve Engine Tests

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In the early 1900s-1920s they used to offset the cylinders as much as 1/6th the bore which would be as much as a 1/2 inch offset on a 3 inch bore or as much as a full One Inch offset on a 6 inch bore.

Otto I thought you might like to see this offset crank. It's on an O S Kelly engine.



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