Tommy Cookers wrote:thinking of useful things for the 'dummy' crankshaft to do, I thought ..... turn a 'Comprex' supercharger
this might be interesting
http://e-collection.library.ethz.ch/ese ... 831-02.pdf
if you have a single with inherent vibration there's merit in a elastomer mounting pseudo-pivoted around the centre of percussion (like MZ used)
the Condors built for the Swiss army were (4 stroke) 350 Ducati singles with the engine mounting modified in this way
ok the 4 stroke big single makes a 90 deg V twin etc look attractive
some new engine types seem to be powered by conflation or moving goalposts
if designed for optimal efficiency, the big 1950s aircraft engines would have approached 40% bte (compounded Merlin schemed and Wrights built)
but they had designed-in a cr around 7 to allow eg 67" abs 'boost' for very high takeoff power, though 'boost' in cruise was only 36" abs
(and the Nomad had no better efficiency (just cheaper fuel) than the Wright)
40% best bte does not also give 40% bte at typical (low) power
Swiss auto have done a lot of development on the PWS and now call it the Hyprex, they have dropped the direct drive to the engine and use the exhaust enthalpy to assist rotor rotation, controlling the angle the exhaust enters via rotating the exhaust housing combined with a small 250 watt electric motor to 'trim' the speed. They have developed a simplified real time physics model to use to control throtles, and valves based on temperature and pressure sensors of each port to achieve really good response and performance. Here is a link to the paper Titled "Modeling and Control of Pressure-Wave Supercharged Engine Systems" Just realised it was the same one you referenced !!! and one good reason to use the new Automotive ARM 64 bit SoC's with 96 GPU cores for doing the real time physics calculation.
e-collection.library.ethz.ch/eserv/eth: ... 831-02.pdf
The fast engine torque respose and the high boost pressure available over the entire engine speed range make them preferable over turbo or supercharging with small engines, up to 2.65 bar of boost is available. Someone has developed a controller for constant torque, that is an interesting boost graph, Control over the external EGR is possible, and they're talking of coating the rotor to act as the catalytic converter.
I remember Buell came up with a fancy engine mount system for his first sports bikes to direct mount the HD engine, controlling the DOF to minimise that engines heart beat. The first Buell's also had a decent aero package and used the cooling flow to provide a small thrust.
That Variable Speed Ring/Sun gear Manolis posted would be interresting read more information on, explaining the cut on the gears.
Where it gets interesting in reading the 2015 RMIT paper on a two stroke Rotax modified with direct injection and hydrogen assisted jet ignition mentioned previously by JAW that also references the Pattakon two stroke. Was in the different combustion processes they could achieve by timing when events happened. Early, stratified and diffusion combustion gave some control over pressure when the crank rod angle is more efficient at converting cylinder pressure to rotational torque and less negative energy. Using Hydrogen to simplify the combustion simulation to compare with experimental data.
Best BTE I remember when my Father rebuilt a Seagull 5.5 hp outboard that was likely 15% efficienct (He also worked on the Blue Streak Missile project in South Australia), towing another boat with that engine didn't slow down just used more fuel! It had a 20:1 fuel oil ratio, and wouldn't start after it was rebuilt, not cold on that fuel oil ratio.
Modern engines are nearly three times that now, 50% should be possible with small engines, if well optimised. Like the Pattakon OPRE that uses the slower acceleration of piston motion around bdc for the, late compression, combustion and early power period, that is clever, the kind of thinking needed to achieve good efficiency. Rather than the rapid acceleration as the big end moves away both vertically and horizontally, where peak piston speed is ~76 degrees, and midstroke ~82 degrees.
Another interesting item I noticed was Solvay who provided materials and support for the Solar Impulse 2 flying around the world on solar power, is reviving the Polimotor project. Using light weight composite reinforced polymers to make engine components, including parts of the crank train (piston, oil ring, connecting rod, gudgen pin) in a high performance turbocharged engine. The valve guides, water and fuel pump impellors and housings, fuel rails, gears, turbo (compressor?) housing, inlet runners, coolant ducting and connections, and the 4 cylinder block, sump pan . . . Weight reduction and near net shape injection moulding or 3d printed.
Making the piston skirt from injection molded polymers a two part piston, each part optimised for its requirements, alloy (2.85 grams/cm3) crown and cfrp (1.7grams/cm3) skirt. Has advantages, a larger piston can be lighter where that suits. The crown can use thermal barrier coatings on top to reflect heat for better combustion and underneath to insulate heat from the skirt, galleries for cooling and other complex geometries are easier as the skirt comes out of the mould in nearly net shape using less energy to manufacture and less machining effort afterwards.
One thing I know is that the Bishop valve on the 450 single, produced over 70 hp and around 55 nm, without pushing the bottom end and the engine was ~3 kg lighter, making the bike really light. Not many light engines perform this well.
