1 Steam Cars : Phorum
General Steam Car topics
reducing exhaust pressure
Posted by: peter heid (IP Logged)
Date: August 01, 2004 12:40PM
<HTML>I was reading over the Stumpf Unaflow book again and something caught my interest in the locomotive section about exhausting steam in the smoke stack. It seems some experimentation had been successfully performed reducing exhaust back pressure on unaflow engines by the action of the exhaust steam from another cylinder. The experiment was performed on a 2 cylinder locomotive and energy left in the steam was used in a nozzel entering the main pipe in the stack to draw the steam from the other cylinder, by creating a slight vacuum. This engine was designed with 12% clearance volume so no compression was higher than the steam chest pressure. The indicator diagram shows a 30% reduction in atmospheric pressure, at the exhaust, at 60 Km/Hr. The text goes on to state that a 2 cylinder is not a good example for this design because the cylinders are in comunication for a short time and a 3 cylinder engine would use the design much more effectively.
I don't know if this idea could be applied to a condensing system very easily but for the big race or speed run it could be of immense value. The next logical step would seem to use the vehicle body draft in conjunction with this design to it's greatest effect. Even the best body designs have a point of low pressure behind the car at speed, not only could a vehicle benefit from the lowered exhaust pressure but the vehicle air drag might be lowered by using exhaust steam to at least partially fill the low pressure area behind the car.
Peter Heid</HTML>
I don't know if this idea could be applied to a condensing system very easily but for the big race or speed run it could be of immense value. The next logical step would seem to use the vehicle body draft in conjunction with this design to it's greatest effect. Even the best body designs have a point of low pressure behind the car at speed, not only could a vehicle benefit from the lowered exhaust pressure but the vehicle air drag might be lowered by using exhaust steam to at least partially fill the low pressure area behind the car.
Peter Heid</HTML>
Re: reducing exhaust pressure
Posted by: steamerjon (IP Logged)
Date: August 07, 2004 12:27AM
<HTML>This is an interesting point. as we all know, due to the bernoulli effect, the air pressure on the top of the car is lowered so much at the rear of an automobile traveling over 50 MPH that race cars have down-lift wings at the rear to counter the lift force there. the top rear of an auto would seem like a good exit point for non-condensing steam.</HTML>
Re: reducing exhaust pressure
Posted by: David K. Nergaard (IP Logged)
Date: August 11, 2004 11:20AM
<HTML>"Tuned" exhaust pipes are not new, they were used on some steam engines in the 1880s! They only work over a limited speed range, however.
For any race long enough to need more than one tank full of water, condensing better is much more important than minor improvement in engine power. Indeed, a long race might well be won by a less powerful car that enjoys TOTAL condensing.</HTML>
For any race long enough to need more than one tank full of water, condensing better is much more important than minor improvement in engine power. Indeed, a long race might well be won by a less powerful car that enjoys TOTAL condensing.</HTML>
Re: reducing exhaust pressure
Posted by: Peter Heid (IP Logged)
Date: August 11, 2004 03:55PM
<HTML>The effect could be used with a condensor also, just so long as the condensor can handle all the steam from the engine to the point of little or no pressure drop. Another benefit of low relative steam consumption that might be realized. Plus this is a method to use some of the energy left in the exhaust steam to possibly benefit overall efficiency by the reduction of exhaust pressure.
I was studying a guide on 2 stroke engine, expansion chamber design for a bit of information on the subject. The steam exhaust is more like a megaphone from pre expansion chamber days. The expansion chamber has 4 basic sections, the head pipe, the diverging cone, the converging cone and the stinger or outlet pipe. The head pipe length and size time the effect and as it slightly diverges to convert some of the exhaust pressure to velocity. The diverging cone finishes the job of converting pressure to velocity and creates a partial vacuum to pull the fresh mixture charge into the combustion chamber. The converging cone then slows the process down with a reverse wave, to prevent the charge from following the exhaust gasses out the exhaust port before it closes. The stinger, which can be internally or externally mounted, keeps the average pressure at a certain level.
For steam, only the portions required are the head pipe and diverging cone. The steam will come out in something of a puff and each puff has to work to help the next puff. This being so, the first puff must still be in the exhaust while the second is released in to it. If the first puff is out before the second enters, the work done by the first one is lost as atmospheric pressure enters the tube and fills the partial vacuum. It is easy to see how this works better with more cylinders providing the puffs at closer intervals and with better overlap.
To keep the puff in the exhaust, the required length of time, to the point where the second puff enters, would in most cases require a tube to connect the head pipe to the diverging cone and this length would decrease with increased RPM and the number of cylinders as well as the amount of steam exhausted. Increasing the diameter of the pipe will reduce the pressure drop somewhat but it slows the velocity of the steam and can reduce the effectiveness. The pipe size should be chosen to keep the exhaust steam in it's normal range of velocity.
Any number puffs can travel in the tube at any given time so long as there are at least 2, and many 2 stroke engines of multipule cylinders respond very well with the addition of a single expansion chamber ehhaust. With any engine there will be an RPM below which the exhaust will no longer remain effective in creating the partial vacuum. It is no trouble to make a long exhaust as smooth bends have little effect but at a point the pressure drop in the exhaust overcomes the effect of the vacuum will be reached.
Peter Heid</HTML>
I was studying a guide on 2 stroke engine, expansion chamber design for a bit of information on the subject. The steam exhaust is more like a megaphone from pre expansion chamber days. The expansion chamber has 4 basic sections, the head pipe, the diverging cone, the converging cone and the stinger or outlet pipe. The head pipe length and size time the effect and as it slightly diverges to convert some of the exhaust pressure to velocity. The diverging cone finishes the job of converting pressure to velocity and creates a partial vacuum to pull the fresh mixture charge into the combustion chamber. The converging cone then slows the process down with a reverse wave, to prevent the charge from following the exhaust gasses out the exhaust port before it closes. The stinger, which can be internally or externally mounted, keeps the average pressure at a certain level.
For steam, only the portions required are the head pipe and diverging cone. The steam will come out in something of a puff and each puff has to work to help the next puff. This being so, the first puff must still be in the exhaust while the second is released in to it. If the first puff is out before the second enters, the work done by the first one is lost as atmospheric pressure enters the tube and fills the partial vacuum. It is easy to see how this works better with more cylinders providing the puffs at closer intervals and with better overlap.
To keep the puff in the exhaust, the required length of time, to the point where the second puff enters, would in most cases require a tube to connect the head pipe to the diverging cone and this length would decrease with increased RPM and the number of cylinders as well as the amount of steam exhausted. Increasing the diameter of the pipe will reduce the pressure drop somewhat but it slows the velocity of the steam and can reduce the effectiveness. The pipe size should be chosen to keep the exhaust steam in it's normal range of velocity.
Any number puffs can travel in the tube at any given time so long as there are at least 2, and many 2 stroke engines of multipule cylinders respond very well with the addition of a single expansion chamber ehhaust. With any engine there will be an RPM below which the exhaust will no longer remain effective in creating the partial vacuum. It is no trouble to make a long exhaust as smooth bends have little effect but at a point the pressure drop in the exhaust overcomes the effect of the vacuum will be reached.
Peter Heid</HTML>
Re: reducing exhaust pressure
Posted by: Ben in Maine (IP Logged)
Date: August 11, 2004 07:36PM
<HTML>Crossley,,a gas engine builder in England used a 85 foot long pipe tuned for the speed they used, Found this in a engine book of the period years ago,,,,Cheers Ben</HTML>
Re: reducing exhaust pressure
Posted by: Andy Patterson (IP Logged)
Date: August 11, 2004 08:58PM
<HTML>Hi peter
I have looked at the expansion chamber idea. One killer of the idea is the low RPM of a steam engine. The pipe and demensions would be enormas as far as I can figure. The steam density also increasses the demensions needed to achieve a vacule draw on the cylander.
Still worth some expermenting though.
Andy</HTML>
I have looked at the expansion chamber idea. One killer of the idea is the low RPM of a steam engine. The pipe and demensions would be enormas as far as I can figure. The steam density also increasses the demensions needed to achieve a vacule draw on the cylander.
Still worth some expermenting though.
Andy</HTML>
Re: reducing exhaust pressure
Posted by: Ben in Maine (IP Logged)
Date: August 11, 2004 09:25PM
<HTML>Hi,,,We used 35'' to 50'' pipe length on a single cyl motorcycle top rpm around 6500--7200,,,,,so,,, as the 2cyl da steam engine has the same power impulses as a 8 cyl gas engine ,,one every 90 deg' divide the 7000 by 8 ,,,,,there is a lot more room on a car for a pipe,,,,Wheres' the problem ,,,,,, Has someone got a sliderule to work the numbers,,,,back then we just cut the pipe 2'' at a time til it went good,,,set a stock class record that stood 4 years,,,,[Tom Connors //1966 BSA,hornet,,in 1968//Epping dragway ,,New hampshire] [John Clarke 1950Vincent 'Flash,, 2 jr an 3 rd overall in 100mi Ontario Province GP,,1970,,,an' they didnt have a vintage class then,, :-) Cheers Ben p/s I dont think anny of this will apply to a condenser system,,if thats anny consideration,,cb</HTML>
Re: reducing exhaust pressure
Posted by: George Nutz (IP Logged)
Date: August 12, 2004 09:42AM
<HTML> A three cylinder DA steam engine has three times the exhaust pulses of a 4 cylinder gas engine---that is the exhaust pulses would be the same for a 3000rpm such gas engine and 1000rpm for the steam engine.
George</HTML>
George</HTML>
Re: reducing exhaust pressure
Posted by: Bill Gatlin (IP Logged)
Date: August 21, 2004 04:39PM
<HTML>Gentlemen,
While reading through this thread, somthing occured to me about reducing exhaust pressures and the Coanda effect. An article in a Hot Rod magazine I read when I was a kid. It had to do with using a Coanda cone in the tuned exhaust system. Also was mentioned that turbojet engines use this Coanda effect cone to reduce their back pressure and increase thrust.
Anyway in reviewing the subject on the web I came across vortex generators that use compressed gas to create a large temperature differential. The compressed gas in the 100 psi range goes into the mid area of a tube at a tangent and creates a intense vortex or cyclone within. The pressure difference from the inside core to the outside of the cyclone is responsible for the temperature differential, rather dramatic.
>[www.artxltd.com]
This is the website , but I hade trouble with Google picking it up directly, searched under "vortex tubes" and found it rather quickly however.
If this thing could be somehow adapted to the exit steam before the condenser than the remaining work left in the exhaust at about 30 lbs would produce 3-400 degree steam at one outlet and snow out the other. Many possibilities emerge, namly increased economizer efficiency and reject heat at a higher temperature resulting in a more compact condenser.
Now, if the vortex tube were to be used in a super-critical boiler to drop the pressure to 1000 lbs the hot outlet would run the expander (engine) and the cool outlet would absorb heat from the condenser. This would in effect recover a large portion of the heat rejected and make the thermodynamic cycle no longer "appear" as a Rankine but a more verticle front end on a TS diagrahm.
Vortex tubes are easy to build.
OK-----------------------Bill G.</HTML>
While reading through this thread, somthing occured to me about reducing exhaust pressures and the Coanda effect. An article in a Hot Rod magazine I read when I was a kid. It had to do with using a Coanda cone in the tuned exhaust system. Also was mentioned that turbojet engines use this Coanda effect cone to reduce their back pressure and increase thrust.
Anyway in reviewing the subject on the web I came across vortex generators that use compressed gas to create a large temperature differential. The compressed gas in the 100 psi range goes into the mid area of a tube at a tangent and creates a intense vortex or cyclone within. The pressure difference from the inside core to the outside of the cyclone is responsible for the temperature differential, rather dramatic.
>[www.artxltd.com]
This is the website , but I hade trouble with Google picking it up directly, searched under "vortex tubes" and found it rather quickly however.
If this thing could be somehow adapted to the exit steam before the condenser than the remaining work left in the exhaust at about 30 lbs would produce 3-400 degree steam at one outlet and snow out the other. Many possibilities emerge, namly increased economizer efficiency and reject heat at a higher temperature resulting in a more compact condenser.
Now, if the vortex tube were to be used in a super-critical boiler to drop the pressure to 1000 lbs the hot outlet would run the expander (engine) and the cool outlet would absorb heat from the condenser. This would in effect recover a large portion of the heat rejected and make the thermodynamic cycle no longer "appear" as a Rankine but a more verticle front end on a TS diagrahm.
Vortex tubes are easy to build.
OK-----------------------Bill G.</HTML>
Re: reducing exhaust pressure
Posted by: Peter Heid (IP Logged)
Date: August 23, 2004 02:02PM
<HTML>Bill,
The coanda effect can be used with a condensor to provide more thrust for the vehicle. In practice it seems difficult to acheive but a few race vehicles have been built with this idea in mind for their radiators. The more heat coming out of the radiator the more thrust it generates, while most radiators are a wind drag.
The vortex genrerator is one of my top choices for air conditioning of a steam vehicle.
Peter Heid</HTML>
The coanda effect can be used with a condensor to provide more thrust for the vehicle. In practice it seems difficult to acheive but a few race vehicles have been built with this idea in mind for their radiators. The more heat coming out of the radiator the more thrust it generates, while most radiators are a wind drag.
The vortex genrerator is one of my top choices for air conditioning of a steam vehicle.
Peter Heid</HTML>
Re: reducing exhaust pressure
Posted by: Bill Gatlin (IP Logged)
Date: August 23, 2004 10:39PM
<HTML>Peter
The vortex tube running at super-sonic velocitys really picqued my intrest. Do you have any idea as to their efficiencys? They are basically refrigeraters using the same medium as the motor that drives them. The nozzle being the motor and the vortex being the compressor and expander.
I can see that the coanda effect would work with a radiator to produce thrust under some ideal circumstance, but I wouldn't want to depend on it. What occured to me though is that a fanjet uses the coanda effect to compress air for it's turbine. It's a specially shaped fan whose blades converge slightly (the gap between the blades narrows) and it produces much more compression than a standard turbine blade would at the same speeds.
Turning such a fan blade around behind a radiator may provide enough thrust to the air passing through it to significantly reduce it's power requirements. This I think would be a total build and see experiment but would be interesting.
Have fun------------------Bill G.</HTML>
The vortex tube running at super-sonic velocitys really picqued my intrest. Do you have any idea as to their efficiencys? They are basically refrigeraters using the same medium as the motor that drives them. The nozzle being the motor and the vortex being the compressor and expander.
I can see that the coanda effect would work with a radiator to produce thrust under some ideal circumstance, but I wouldn't want to depend on it. What occured to me though is that a fanjet uses the coanda effect to compress air for it's turbine. It's a specially shaped fan whose blades converge slightly (the gap between the blades narrows) and it produces much more compression than a standard turbine blade would at the same speeds.
Turning such a fan blade around behind a radiator may provide enough thrust to the air passing through it to significantly reduce it's power requirements. This I think would be a total build and see experiment but would be interesting.
Have fun------------------Bill G.</HTML>
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