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Hit & Miss Gas Engine Discussion

Brayton Cycle Engines


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  #61  
Old 02-20-2013, 05:24:10 AM
imotorhead64
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  #62  
Old 02-20-2013, 03:08:43 PM
joelr4 joelr4 is offline
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Default Re: Brayton cycle engines

Here are a couple more articles on the Brayton Engine:

Brayton petroleum engine

Brayton Two-Cycle Gas Engine


Joel
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  #63  
Old 02-21-2013, 01:23:42 AM
imotorhead64
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Big thanks Joel!
Those are great articles with complete explanations on how Braytons engines really worked.
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  #64  
Old 02-21-2013, 03:23:43 AM
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I didn't know about the combustion area and piston crown being lined with soap stone... also this solved the mystery of the cylinder that Paul G posted earlier... I thought it was connected to one of Braytons later 4 stroke engines.. I now see the compressed air is supplied through pipe A and fuel through pipe B. And that the Valve C is actually the admission valve. Interesting that valve C is so small... it all passes down pipe D where it is atomized and then ignighted by burning wick E. Maybe the valve that's in the center of the piston allowed some air to enter if there was a vacuum in the cylinder or expansion was incomplete? I'm also surprized by the volume of dead space.. No advantage to that IMO... . Anyone have thoughts on this?

---------- Post added at 02:23 AM ---------- Previous post was at 01:25 AM ----------







Some good drawings of Brayton's early engines

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  #65  
Old 02-21-2013, 04:40:27 AM
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I read it again and now I see the engine in fig 61 and 62 is really a 4 stroke engine.
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  #66  
Old 02-23-2013, 09:22:44 AM
imotorhead64
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Default Re: Brayton cycle engines

Wayne T was asking about the linkage on the early walking beam engine... I guess this is the later red engine but it might give some clues as to what was on the early engine?

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  #67  
Old 10-23-2013, 03:20:29 PM
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Default Re: Brayton cycle engines

I was curious, what was the publication and date the last engraving came from ??

Thanks - Wayne
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  #68  
Old 12-25-2013, 10:37:51 AM
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Default Re: Brayton cycle engines

Here is one I finished, but am still sorting out the fuel delivery amount. It is a model of the patent model posted previously. It uses a spark plug to ignite the charge initially instead of the lit taper. My pump is delivering twice the needed fuel so I need to dial it back...
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  #69  
Old 12-25-2013, 10:40:40 AM
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Default Re: Brayton cycle engines

Another view... Test mule cobbled up from bits lying about in the shop. I'll replace those unsightly modern fasteners when I get it running...
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Old 12-25-2013, 06:51:20 PM
Wayne Timms Wayne Timms is offline
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Default Re: Brayton cycle engines

Hi Paul,

Thanks for posting.
Will keep an eye on this space.

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Wayne
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Old 12-27-2013, 02:42:54 PM
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Default Re: Brayton cycle engines

Paul, I will be keeping an eye on this thread as well. Hopefully we will see a Youtube video of it running soon. Great effort !!!
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  #72  
Old 12-27-2013, 06:47:27 PM
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Default Re: Brayton cycle engines

Hey Nick, where did the fourth picture of the arched engine come from in post #53??? Never seen that one...

Last edited by PaulGray; 12-27-2013 at 06:49:06 PM. Reason: Forgot post number
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  #73  
Old 07-19-2014, 01:46:27 AM
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Default Re: Brayton cycle engines

Dear All.
I am new here, i don't know if this is appropriate or i should have a new post, or not at all, so please forgive me my error.

But in response to imotorhead64 invite for discussion about Brayton engines, I thought some one might be interested in knowing that I am working a Concentric Rotary Expansion Brayton engine.

Where I have a regular piston compressor, a separate combustion chamber, and another separate cocentric rotor work/expansion space.

I have only done the theoretical part of it, since it would be a waste of money just to build a design idea without basing it on some real numbers.

I think i have used the Van der Walls equations correctly.
I now have to do, speed of air transfer under pressure, deflagration speed calculation if ever, volumetric efficiency, work extracted, etc.

in preparation that some day i will actually buy the metals and present the designs to the CNC work shop and see it through.

I sure do welcome any engineering help.

Thank you all and best regards.
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  #74  
Old 10-29-2014, 09:14:56 AM
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Default Re: Brayton cycle engines

Hi Issa, I think you will find it difficult to make an efficient rotary expander capable of working at the high temperatures.

---------- Post added at 07:53 AM ---------- Previous post was at 07:50 AM ----------

Hi Paul, Any updates on the engine?

---------- Post added at 08:14 AM ---------- Previous post was at 07:53 AM ----------

Something I wanted to ad to the discussion is that I think the timing and the way in which Brayton added heat was important to making his engines operate. I think a lot of folks who just step into the piston Brayton cycle believe making a running engine is as simple as having a compressor and a combustor and an expander.. The Roper, Trewella and the Buckett engine also the Ericsson cycle all add heat between the compressor and expander... The Ericsson does it externally and uses a regenerator but all those engine operate much like the turbine Brayton cycle. They also produce very low power. However I think it's important to consider that Brayton was adding heat as the compressed air entered the expander. Brayton engines were intermittent combustion engines not continuous combustion engines as many believe. I believe this was a critical component to the engines success. I should also note that delaying the combustion event until after the admission valve has closed can provide even better performance by reducing the work required by the compressor.
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  #75  
Old 10-29-2014, 07:27:30 PM
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Default Re: Brayton cycle engines

Imh64- I got a chance to study the ready motor at the smithsonian annex near Bethlehem and see no way for the engine to add heat to the admission air. In fact, the very expansion of the air in the receiver as it enters the cylinder would cool it..you know the old pv=nRT rule...it is the addition of heat in the form of burning fuel which gives you a net work out. Further, the early Braytons lost considerable heat energy as the air was compressed and stored in the receiver. The table above with the efficiencies no doubt neglect the pumping losses. If you read Dugald Clerks review of the engine, he also says these losses really hurt efficiency. In a modern turbine, you do not lose the adiabatic heating of the air as it enters the combustor. Some of the newer designs are operating at pressure ratios of near 50:1 !!! In the Otto cycle, you retain a lot of the adiabatic heating as the gas is compressed. Adiabadic refers to a change in pressure without a loss of energy to the surroundings. Making a working replica piston Brayton engine requires a careful balance between the incoming air, the amount of fuel and the receiver pressure. I am still working on mine. I almost had it running but a jammed piston and bent rod put it on hold. Since I am using a spark plug to ignite the incoming charge, I realized I have to only fire the plug for a short time at the beginning of the combustion stroke. I had too much fuel being injected into the cylinder and this jammed the piston in the up position, bending the piston rod. I also need to reduce the receiver volume so the pressure recovers more quickly (I think!). I will be working on mine this winter and maybe I'll get some satisfaction.
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  #76  
Old 10-29-2014, 10:08:12 PM
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Hi Paul... thanks for the update.. [QUOTE=PaulGray;1099636]Imh64- I got a chance to study the ready motor at the smithsonian annex near Bethlehem and see no way for the engine to add heat to the admission air. In fact, the very expansion of the air in the receiver as it enters the cylinder would cool it [quote] I didn't mean to imply that the air was being heated in a Brayton other than by means of combustion... on my test engine I experimented with a recupertor heat exchanger where the latent exhaust heat was applied between the compressor and expander... this was only useful when no air reservoir was used and the cranks were phased at about 45 degrees or less. I think Brayton may have been injecting the fuel after the admission valve closed... If you have any pics to share that would be great... [quote] Further, the early Braytons lost considerable heat energy as the air was compressed and stored in the receiver. [quote] well I know heat energy from compression was lost in the receiver but I'm not sure it was all that considerable. Most of the historical data talks about the receiver pressure on the Braytons being somewhere in the 60 psi range. Compressing to a higher PSI in a single stage is kind of wasteful... Using a compressor temperature calculator with 70 degree inlet air this produces an outlet temperature of roughly 150-180 degrees. Now if the heat is lost while in the receiver I agree it is a loss.. but not likely a huge loss... [quote] If you read Dugald Clerks review of the engine, he also says these losses really hurt efficiency. [quote] I did read Dugalds account of the Brayton in "Internal fire" about where they had neglected to calculate the pumping losses of the compressor. [quote]In a modern turbine, you do not lose the adiabatic heating of the air as it enters the combustor. Some of the newer designs are operating at pressure ratios of near 50:1 !!! [quote] yes I know... multi stage aero and aero derived turbines run at very high pressures... however some cool between the stages.. and some are recuperated or regenerated using exhaust heat after the compressor [quote]In the Otto cycle, you retain a lot of the adiabatic heating as the gas is compressed. Adiabadic refers to a change in pressure without a loss of energy to the surroundings. [quote] yes I know... when the air is compressed in the combustion cylinder most of the work of compressing the air is returned to the engine. [quote] Making a working replica piston Brayton engine requires a careful balance between the incoming air, the amount of fuel and the receiver pressure. [quote] yes I know... it also took me a while to get a good running engine.. and I learned things along the way... Brayton engines used an open flame pilot device to initiate the combustion. one of the nice things is the air / fuel ration is not so important with an open flame... lean is ok. one thing I learned is that starting the combustion event after the admission valve was closed produced the best result. I kind of think the Braytons may have injected fuel after or as the admission valve was closing...
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I am still working on mine. I almost had it running but a jammed piston and bent rod put it on hold. Since I am using a spark plug to ignite the incoming charge, I realized I have to only fire the plug for a short time at the beginning of the combustion stroke. I had too much fuel being injected into the cylinder and this jammed the piston in the up position, bending the piston rod. I also need to reduce the receiver volume so the pressure recovers more quickly (I think!). I will be working on mine this winter and maybe I'll get some satisfaction.
you may want to try firing the spark plug later .. as in after the air admission valve has closed. your admission valve should close shortly after the expander leaves TDC.. If you can get the fuel / air to ignite your engine should run.
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  #77  
Old 10-30-2014, 05:17:34 AM
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Default Re: Brayton cycle engines

The whole point of the Brayton concept is constant pressure combustion. To achieve this, the ignition has to occur at the beginning of the admission stroke. I read the starting instructions to come to this conclusions.
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  #78  
Old 10-30-2014, 08:45:43 AM
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Default Re: Brayton cycle engines

Paul,

The Brayton engine valves the air/gas mix to the power cylinder as it is moving up on the power stroke, and burns it throughout the stroke. Ignition has to occur through the entire power stroke, either by open flame as in the Bethlehem engine, or using a catalytic reaction (externally heated platinum wire/glow plug). That's why the flame arrestor was such a big deal in the non-liquid fueled engines. The gas/air mix was stored under pressure in a receiver until the power stroke, which could (and did) explode. The receiver had some sort of relief valve. The oil engines like the Bethlehem engine ran the compressed air through an oil saturated felt pad (replenished by a fuel pump) and past the constantly burning ignition flame into the power cylinder.
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Old 10-30-2014, 09:31:56 AM
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I agree Woody. Braytons did use a constant ignition source. and it sounds as though the fuel / air was burning as it entered the expander. However you did not mention the early cut off timing of the expander admission valve.. it's very important to make the engine run properly. The engine I made ran with both a carburetor where air and fuel were mixed at the compressor inlet and at one point it had an injection pump. When the air and fuel were pre mixed explosions / backfires did occasionally occur in the reciever. it's important to have a relief valve...! Like Paul I was using a spark plug to ignite the fuel. My expander inlet valve closed about 1/5 stroke after tdc. so I tried delayed the spark until after the closing of the valve and it was the best running version of my engine. It would run really good until the head of the eaxpander started getting hot enough to ignite the fuel. then it would loose power and the backfires / explosions would start. at one point I did away with the reciever and played with phasing the crank. In that version the compressor would compress and then transfer the air / fuel into the expander.. for sure combustion was occuring as the fuel / air entered the expander because after the engine was hot I could remove the ignition source. I also added an exhaust recuperator to preheat air after the compressor. the this version worked pretty well... but not the best. I later tried to make a small injector and fuel pump so there would be no fuel in the reciever tank but the engine could get hot and I could delay the combustion event. the idea was to inject fuel as of slightly after the expander inlet valve closed.. . it's because of my experiences that I'm convinced some heating was taking place in Brayton engines after the expander inlet valve was closed...
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Old 10-30-2014, 10:47:56 AM
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Default Re: Brayton cycle engines

The early Brayton did indeed have a mix of gas and air in the receiver and hence the need for the grating or flame arrestor to keep from igniting the mix in the receiver. The platinum/catylytic ignition refers to the final incantation of the engine which was in reality, a four cycle oil engine. If you look carefully at the patent drawings of the oil engines, there is a small diversion of the fuel air mix past the grating to act as a pilot flame in the oil engine versions once the thing got running. The lit taper was only for starting. As to the admission valve, the deal was it was open for about half of the power stroke. After it closed, the expanding gasses did additional work as they were allowed to finish pushing the piston to the end of the stroke. Brayton abandoned the gas air mix in the receiver very early on due to its danger and opted for the oil version for most of the production. The final version was possibly an attempt to get on board with the added efficiency of a four stroke cycle. Had the Otto cycle not come about, Braytons cycle may have found wider acceptance since in many ways, it resembled a "steam" engine which operates at constant pressure and has a cutoff before the end of the stroke to gain efficiency. Imh64 can you post a better video of you engine on YouTube to see the mechanisms?
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