Running tests on the engine - still cycling by hand, not yet running on heat.
From cycling the engine we've found three design improvements that we need to make.
1) Displacer is just too heavy - this one clocks in at 22lbs - design weight is 14 lbs and thats still is too heavy. To lighten this component up, we'll re-cast and dropp the extra weight and then actually drill out lightening holes on the back side of the fins - target weight is about 8 lbs. This will add some machining time to the displacer caps, but this is crucial component for engine efficiency and worth getting it skinnyed up as much as possible.
2) Key way for displacer to piston alignment - in cycling the engine wer're seeing some minor rotation of the piston in the cylinder, relative to the displacer. This alignment between the piston and the displacer must be tight or the fins will crash into the piston. The design change will incorporate a small aluminum channel on the displacer rod that will match like a key to the piston center gasket and maintain this alignment.
3) Support Axle bearings - in cycling the engine we are seeing some deflection of the axle bearings. To better suppor the axles we are going to add an ear (once we get it in place we'll show you a picture and it will make sense) and an additional bearing on each axle.
Everything else tests out pretty well, noticing a small narrowing of the cold cylinder bore, we re-sized the rings to a custom fit and it seems to be working well. Going to want to beef up the bore cutting head tool on the next set of cylinders that we bore out so we get rid of this distortion.
Currently we running heated trials of about 450 F on the hot end of firebox and seeing about 300 F on the engine head - we'll need to get up closer to the 450 F temp on the head - don't see that being a problem - just need a bit of insulation on the firebox. We've been running these tests at ambient temperatures of about 30 F, so from one end to the other end of the firebox we are seeing a big drop.
We've got the new displacer caps cut and are getting ready for a casting pour to get those underway. At the same time, you'll be happy to hear we have started to cut 5 sets of foam for the first 5 engines, so as to get the production process turned up. New schedule should be out shortly.
One other note - one of our early supporters (in Slovenia) was motivated to build his own engine based on the Volo design (minus the displacer / piston / head fins) - just got it running after about a years time - looks very cool and is running (although with out the fins - the performance and output is very low) - Check it out here - Love to see the engine start spreading -