Author Topic: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine  (Read 5576 times)

Online Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 12999
  • Hampshire, england.
Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #120 on: December 13, 2019, 09:29:02 PM »
Have you seen my other Stirling engines run JB  ::)

 

 I am expecting the same out of this one the problem is that the displacer piston is thicker than the displacer cylinder so that while the outer one warms up the inner one does not at the same rate and, as I have learnt, trying to heat it up faster with these high efficient surfaces is not a good idea  :hellno:

Any way I was trying a quick run without any plumbing: The plumbing is there to cool the power cylinder not warm the displacer piston which is what is required. One of the next jobs is the water pump but I am thinking about modifications to it so it might take longer than just bashing it out..

Jo
Enjoyment is more important than achievement.

Offline Jasonb

  • Full Member
  • *****
  • Posts: 6879
  • Surrey, UK
Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #121 on: December 14, 2019, 07:18:27 AM »
I have Jo. I did not say the tea light would not work, you made that decision by using another heat source.  I said that if you were getting the end red hot in a "couple of seconds" that your burner was too hot.

I have also noticed that there are far more linkages and pivots on this engine together with a light aluminium flywheel. The tea light may well work when all is run in but a LITTLE more heat may be needed to get things started initially.

As for the preheating suggestion. Heat travels from coldest to hottest, by preheating the alloy castings will be warm so rather than acting as a heat sink and drawing all your initial heat away from where you want it the heat will go to the cooler parts of the engine which is where you want it. Bringing the engine inside for a few hours and standing near the woodburner will also do a similar thing.
« Last Edit: December 14, 2019, 07:27:59 AM by Jasonb »

Online Alyn Foundry

  • Full Member
  • ****
  • Posts: 916
  • North Wales, Great Britain.
Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #122 on: December 14, 2019, 01:49:45 PM »
Good afternoon folks.

There seems to be a little confusion about the role played by the " Displacer " piston in a Sterling engine. I'll try to explain.

Any gas, air in our case, expands in volume when heated. If we confine this volume in a sealed system then the expansion becomes a pressure increase acting upon the container. If we allow part of this container to move ( power piston ) then that pressure will move the piston outwardly. Conversely, when we cool the container the gas reduces in volume and the power piston will naturally return to its starting position.

Putting aside the role of " Regeneration " for a moment, let's consider the " displacer " piston. Ideally this piston needs to remain " temperature neutral " as its single task is to move the working fluid, air, between the two temperature differentials, the hot and cold ends. In practice, although air is a poor conductor of heat the bottom of the displacer piston will heat up, partially due to radiation from the heat being applied from the outside.

By phasing the two pistons movements by 90 degrees we can now get the air to either heat up
( expansion ) or cool down ( contraction ) to act upon the power piston. This reciprocating action is then converted, by the crank into a rotary motion. During its development many different ways of providing this phasing were tried, by far having the cylinders placed at the 90 degree angle was the simplest and least energy sapping of them all.

The Robinson model has a crude form of " regenerative " displacer piston. The housing contains a large volume of densely packed wire wool that try's to " grab " some of the heated air as it is passed towards the cold end. Conversely as the air is being moved back towards the " hot end " some of the captured heat is given back, slightly aiding the efficiency.

The Ericsson model has a totally sealed displacer piston so the air has to travel around it rather than through it. Not that it matters it's the displacement part that really counts. The transfer of the working fluid between the two differentials, hot and cold.

The only reason a hot air ( Stirling cycle ) engine works is because we have the two different temperature zones
( extremes ) if you will. Once those differences near equilibrium nothing is going to happen.

Cheers Graham.



Online Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 12999
  • Hampshire, england.
Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #123 on: December 17, 2019, 04:03:26 PM »
Thanks Graham  :)

I have not yet returned to trying to run the engine as I have been allowed another set of castings  :D on condition I take my cold away with me to the Workshop and work on the water pump for this engine.

The original design is based around the use of a piece of 19mm square brass. I have a piece of this Thank you Dave   :ThumbsUp: About this point I will be deviating from the published design: I will be making the main body in two parts with a flange joining the two bits more like the original... I already have the rear mounting plate so the next bit is the upper part of the pump body. This should be a simple turning and reaming job but the reamed hole is of course a deep hole and longer than your standard reamer  :Doh: This just means I had to be really careful reaming with a standard length reamer. The end is then tapped for the gland nut.

The lower part of the main body is also taken from a piece of 19mm square brass, this time 25mm long which is held offset to enable the plumbing hole boss to be turned and the thread tapped.

Next up I need those two flanges  :thinking: But it is getting late and I have a new set of castings to fondle :naughty:

Jo
Enjoyment is more important than achievement.

Online Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 12999
  • Hampshire, england.
Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #124 on: December 20, 2019, 03:26:31 PM »
The two flanges were cut from a piece of 3mm thick brass 19mm wide. first the holes were drilled and the two centred bored to fit the end of the main body of the pump before filing to shape. The bottom of the pump then needed to have a register turned on to it before drilling the water hole that doubles up as the seat for the bronze ball that is going to act as the clack valve.

The two sides have been cut out of a bit of scrap-bin-ium. Originally I was going to waste use a piece of 25mm wide by 1.6mm brass and have to cut it down to the required 19mm wide. Instead I found a piece of 19mm angle the right thickness that someone had taken a chunk out of for something which still had one side of the angle intact so I used that instead.

Finally I was ready to solder everything up... The instructions in the book say use soft solder but I should have used hard solder as the brass retains its heat for a long time and things can still move  :facepalm2: Once soft soldered up the bottom of the pump was filed to shape and I have an almost acceptable pump body  :)

Jo
Enjoyment is more important than achievement.