Please Check my Calcs....
Posted: Fri Feb 12, 2016 8:09 am
Hello all,
ive been planning a tin can gamma engine to be built from scratch
ive found two cans that seem to be a good starting point
and ive built an excel spreadsheet that calculates volumes
as well as calculating the stroke length of the power piston for a range of diameters Vs. a range of ratios
it even then highlights the strokes that are within 20% of its diameter so its easy to find which diameter power piston cylinder is square
so making it easy to select a power piston and tell you the stroke required so long as you know what ratio to use
ive then researched ratios used in existing models to try to inform my own ratio choise, and found the following
1:1.5 high temp gas burners only
1:7 coffee cup engine (candle or hot water)
5:1 to 8:1 range for a stove top fan engine
1:16 stove top example
1:10 to 1:20 LTD
ive also designed a crank shaft that runs on roller bearings and should be able to have an adjustable stroke on both pistons
allowing me to dial in on the perfect ratio with live testing (although there would naturally be limits as to how big an adjustment can be made)
below is the dimensions of my plan (all in mm)
displacer diameter _______ 53 (displacer length is 1/3 of stroke)
cylinder diameter ________ 61
cylinder length __________146 (just short of 3x its width as convention suggests )
end clearance ___________ 3 (displacer stops short of stroke 3mm at each end to prevent suction at the cost of dead space)
wall clearance __________ 4 ( power piston will have 4mm clearance between it and cylinder wall, regenerator fills this space later)
dead space _____________117814
displacer volume ________ 100749
cylinder volume ________ 426680
stroke volume___________ 308866
this engine is designed to be a small desktop model powered by a single candle flame
my question is... what sort of ratio would you suggest?
this is seemingly impossible to calculate, and pretty hard for me to guess,
a candle flame is quite high temp but not a much total energy output.
Do my plans and dimensions look right so far?
i know its hard to imagine from a table of numbers, but do the sizes and proportions seem like a working engine,
or is there anything that needs changing?
is the power piston ratio relative to stroke volume?
perhaps a fairly basic but important thing to ask...
when using ratios to determine the volume of one piston to another
do you use the volume of the displacer cylinder or the volume of the stroke of the displacer
which would therefor be 3x the volume of the displacer
ive been planning a tin can gamma engine to be built from scratch
ive found two cans that seem to be a good starting point
and ive built an excel spreadsheet that calculates volumes
as well as calculating the stroke length of the power piston for a range of diameters Vs. a range of ratios
it even then highlights the strokes that are within 20% of its diameter so its easy to find which diameter power piston cylinder is square
so making it easy to select a power piston and tell you the stroke required so long as you know what ratio to use
ive then researched ratios used in existing models to try to inform my own ratio choise, and found the following
1:1.5 high temp gas burners only
1:7 coffee cup engine (candle or hot water)
5:1 to 8:1 range for a stove top fan engine
1:16 stove top example
1:10 to 1:20 LTD
ive also designed a crank shaft that runs on roller bearings and should be able to have an adjustable stroke on both pistons
allowing me to dial in on the perfect ratio with live testing (although there would naturally be limits as to how big an adjustment can be made)
below is the dimensions of my plan (all in mm)
displacer diameter _______ 53 (displacer length is 1/3 of stroke)
cylinder diameter ________ 61
cylinder length __________146 (just short of 3x its width as convention suggests )
end clearance ___________ 3 (displacer stops short of stroke 3mm at each end to prevent suction at the cost of dead space)
wall clearance __________ 4 ( power piston will have 4mm clearance between it and cylinder wall, regenerator fills this space later)
dead space _____________117814
displacer volume ________ 100749
cylinder volume ________ 426680
stroke volume___________ 308866
this engine is designed to be a small desktop model powered by a single candle flame
my question is... what sort of ratio would you suggest?
this is seemingly impossible to calculate, and pretty hard for me to guess,
a candle flame is quite high temp but not a much total energy output.
Do my plans and dimensions look right so far?
i know its hard to imagine from a table of numbers, but do the sizes and proportions seem like a working engine,
or is there anything that needs changing?
is the power piston ratio relative to stroke volume?
perhaps a fairly basic but important thing to ask...
when using ratios to determine the volume of one piston to another
do you use the volume of the displacer cylinder or the volume of the stroke of the displacer
which would therefor be 3x the volume of the displacer