Running the coffee cup engine on sunshine
Posted: Fri Apr 26, 2002 8:07 am
I am interested in sharing experiences of running the coffee cup
engine on sunlight. I shall start by saying what I did and hope to
hear from others who may have followed a similar path or may have
succeeded with a completely different approach.
To get the engine to run on solar radiation, the solar energy must
be directed to raise the temperature of the bottom plate well above
that of the crankcase. If you simply orient the engine with its
bottom plate facing the sun, there is some of the desired effect but
the exposed perimeter of the crankcase also absorbs solar radiation
causing some unwanted temperature rise at the other side of the
cylinder. I first tried to maximise the radiation absorbed by the
bottom plate and to minimise that absorbed by the crankcase by
painting the bottom plate matt black and covering the exposed
perimeter of the crankcase around the bottom plate with aluminium
cooking foil. This showed some benefit but not enough to make the
engine run in the rather weak sunshine in which I tried it. (But it
might be sufficient in a sunnier place)
The next step was to minimise heat loss from the bottom plate by
applying a transparent cover enclosing an air gap. In other words,
I was trying to turn it into a miniature flat-plate solar
collector. I found a very simple way of doing this. I took a piece
of rigid foam polystyrene packaging in the form of a board about 2
cm thick and cut a square just a little bigger than the base of the
engine crankcase. I then traced the outline if the round bottom
plate and cut a hole through the polystyrene to give a push fit over
the cylinder and stretched a clear plastic sheet over one side
fixing it with staples. When pushed over the cylinder, it shields
the bottom of the crankcase from the sun, insulates the edge of
cylinder and provides an air gap reducing convective heat loss from
the bottom plate. It works well, even in the relatively weak
sunshine that we have had here in England between showers in the
last two days.
engine on sunlight. I shall start by saying what I did and hope to
hear from others who may have followed a similar path or may have
succeeded with a completely different approach.
To get the engine to run on solar radiation, the solar energy must
be directed to raise the temperature of the bottom plate well above
that of the crankcase. If you simply orient the engine with its
bottom plate facing the sun, there is some of the desired effect but
the exposed perimeter of the crankcase also absorbs solar radiation
causing some unwanted temperature rise at the other side of the
cylinder. I first tried to maximise the radiation absorbed by the
bottom plate and to minimise that absorbed by the crankcase by
painting the bottom plate matt black and covering the exposed
perimeter of the crankcase around the bottom plate with aluminium
cooking foil. This showed some benefit but not enough to make the
engine run in the rather weak sunshine in which I tried it. (But it
might be sufficient in a sunnier place)
The next step was to minimise heat loss from the bottom plate by
applying a transparent cover enclosing an air gap. In other words,
I was trying to turn it into a miniature flat-plate solar
collector. I found a very simple way of doing this. I took a piece
of rigid foam polystyrene packaging in the form of a board about 2
cm thick and cut a square just a little bigger than the base of the
engine crankcase. I then traced the outline if the round bottom
plate and cut a hole through the polystyrene to give a push fit over
the cylinder and stretched a clear plastic sheet over one side
fixing it with staples. When pushed over the cylinder, it shields
the bottom of the crankcase from the sun, insulates the edge of
cylinder and provides an air gap reducing convective heat loss from
the bottom plate. It works well, even in the relatively weak
sunshine that we have had here in England between showers in the
last two days.