Hi! I'm Chris!
I'm new here, a relatively new machinist ( coming up on ten years ), former software engineer and current commercial helicopter pilot.
I'm building two of Jerry Howell's fan designs and planning a rhombic next.
I have read a lot of the standard texts, and have Andy Ross' 1970s 11cc rhombic drawings.
I'm wanting an engine to drive a small boat about 700-1000 watts and I'm considering scaling up that 11 cc rhombic by a factor of three.
I believe that this will make a rhombic of nearly 300ccs and that if lightly pressurized this should be capable of nearly 1kw.
Now I know enough to know that it won't work very well if it is ONLY scaled up as it has plain annular heater, cooler, and no regenerator.
My plan would be to design and build a finned cooler and heater and add a foil or wire mesh regenerator.
My main question is this: If I build it simply first, I.E. with the simple annular heat exchangers and no regenerator, will it run at all?
If it would this would then allow the incremental improvements to the initial running model with ongoing measurements.
I've read Andy's free book and also some of the books on the Philips engines so I know there is precedent for engines at this displacment and power level.
Thanks in advance!
Chris
Engine Scaling
Re: Engine Scaling
Hi Chris
Chopper pilot eh, I'm ATPL fixed wing, retired, spent 7 years running a CAD/CAM CNC based precision engineering company from the shop floor as a sub contractor for one of the F1 teams, not formally trained as a machineist but I've picked up a few tricks along the road. Like you, I find the idea of a SE powered small boat appealing, but to date have only achieved 135w so am currently using electric power (BLDC motor and SLA batteries) but am still working an various designs to get near to a 1Kw SE.
Lets start from your destination and work backwards, as the Irishman said when asked for directions, 'if I were going there I wouldn't start from here'.
However, if you do a fantastic job with the design you might achieve 20% internal thermal efficiency (watts into the working gas vs watts at the flywheel), but more likely, even with slotted heat exchangers, you will see 10% TE and don't be surprised if it's only 5%! If we start at 10% then you will need to impart 10Kw into the WG and just as importantly you will need to extract the best part of 9Kw from the cooler. As I've said many times before, air is a very good insulator which is why our clothes work, helium would be a much more logical choice but I can sympathise trying to get away with air. The following picture
is an extract from a research program for a proposed piece of military medical equipment and demonstrates the heat transfer from a solid to air through slot gaps in a heat exchanger, probably the most relevent graph a SE designer will ever see.
I'll let you do the sums but it will become very obvious to you, quite quickly, the amount and configuration of the heat exchangers required to achieve 1Kw at the flywheel.
You may also find the following link of interest, I beleive the double acting gamma to be the layout most likely to fit our desires.
http://www.starspin.com/stirlings/jimd6.html
Happy designing.
GeoffV
ps your rhombic with plain exchangers probably won't run.
Chopper pilot eh, I'm ATPL fixed wing, retired, spent 7 years running a CAD/CAM CNC based precision engineering company from the shop floor as a sub contractor for one of the F1 teams, not formally trained as a machineist but I've picked up a few tricks along the road. Like you, I find the idea of a SE powered small boat appealing, but to date have only achieved 135w so am currently using electric power (BLDC motor and SLA batteries) but am still working an various designs to get near to a 1Kw SE.
Lets start from your destination and work backwards, as the Irishman said when asked for directions, 'if I were going there I wouldn't start from here'.
However, if you do a fantastic job with the design you might achieve 20% internal thermal efficiency (watts into the working gas vs watts at the flywheel), but more likely, even with slotted heat exchangers, you will see 10% TE and don't be surprised if it's only 5%! If we start at 10% then you will need to impart 10Kw into the WG and just as importantly you will need to extract the best part of 9Kw from the cooler. As I've said many times before, air is a very good insulator which is why our clothes work, helium would be a much more logical choice but I can sympathise trying to get away with air. The following picture
- IMAG0396.jpg (140.04 KiB) Viewed 3692 times
I'll let you do the sums but it will become very obvious to you, quite quickly, the amount and configuration of the heat exchangers required to achieve 1Kw at the flywheel.
You may also find the following link of interest, I beleive the double acting gamma to be the layout most likely to fit our desires.
http://www.starspin.com/stirlings/jimd6.html
Happy designing.
GeoffV
ps your rhombic with plain exchangers probably won't run.
Re: Engine Scaling
beez,have a look at Robert Sier's web site, there is a section in that on boats, worth looking at. Ian S C
Re: Engine Scaling
Ian
I know all the SE boat owners in the UK, one, a very large rhombic produces 250W when slightly pressurised the rest produce less than one hundred watts. I for one do not think anything less tham 300W is worth messing about with and given any wind or a stream above 1Knt comsiderably more power in necessary.
GeoffV
I know all the SE boat owners in the UK, one, a very large rhombic produces 250W when slightly pressurised the rest produce less than one hundred watts. I for one do not think anything less tham 300W is worth messing about with and given any wind or a stream above 1Knt comsiderably more power in necessary.
GeoffV
Re: Engine Scaling
The easiest way to get more power ma be to use multiple cylinders of a moderate size, or more than one motor. The Transferator motor might be worth looking into. Ian S C