Tommy Cookers wrote:an R1 or similar machine would be a very poor application for the twin crankshaft idea
because such machines are so greatly throttled in legal public highway, eg using guesstimated 98% throttled at 30 mph and 90% at 70 mph
they are as all SI vehicles controlled essentially by throttling to create inefficiency that matches the output to the load
so reduced piston friction would generally just mean increasing the throttling to further degrade efficiency, preventing a reduction in fuel consumption
a Junkers-type opposed piston engine could with long rods use the twin crankshafts (ie combustion chamber between the cranks)
this layout would have a relatively short external gear train coupling the cranks (but was under Lanchester patents then ?)
maybe this has now been reinvented after 100+ years
Junkers actual layout used conventional cranks coupled by a very long external train of gears
fortunately for development the supercharging and output power was greatly increased without increase in the coupling gear-transmitted power
the twin crankshaft makes most sense with 1, 2, or 3 cylinders ? (though in benefitting balance it will increase main bearing loads)
or ..... ideas for a Deltic-beater, anybody ?
I have been investigating the effects on inerta from the offset crankshafts, the effects of piston side thrust force on inertia
and the rate of change of inertia. The piston side thrust force is interrelated to piston friction in the zero offset crank, with large offsets they will not be as the opposing thrust forces cancel each other in the dual crank arrangement. The piston side thrust force and the big end motion create a couple moment normally, that couple is gone.
Looking into a single cylinder engine and how one could optomise the geometry and the effects to consider, looks like i'll be developing more code iterations to my ruby code that models piston motion, velocity, acceleration and change of rate of acceleration (thanks Manolis for your offset crank spreadsheet if your reading this, it confirmed i had an error in my velocity code, i re-wrote it too many times and ignored my failing tests, test driven development is cool), adding in the typical engine modeling of forces, to calculate friction.
Would be good to assess how the modifed piston motion effects the intake velocy, inertia and cylinder mass, pumping losses and viscous effects with surface friction. The heat added through the higher velocity compression stroke, and a 1D combustion model looking at cylinder pressure over crank angle, getting a simplified model for tji combustion would be handy, the ideal point of maximum heat release, location of peak pressure will all be a little bit different and involve a slighty different crank/rod angle giving more effective conversion of pressure to rotational torque. My code calculates two angles, theta = crank angle, phi is rod angle from cylinder axis, i'll need a name for the crank/rod angle, any suggestions ?
The versatility in lambda with the tji and its relation to the HR10 to HR90 duration presents tuning possibilities to engine load need to be explored, this will be the cylinder pressure over crank/rod angle ratio. The maximum cylinder pressure for large bore engines reduces about 4 times the mean which suits the geometry needed for dual offset crankshafts.
Calculating the friction from the major components using the latest engine models corrected for offset crankshafts, assessing the increased bearing friction, the differences with two lighter crankshafts vs one larger one, the larger crank has to deal with its own larger mass and forces, should allow the two cranks to be a litle bit lighter than would initially be thought. It might well be a very small increase in crank train bearing friction for a moderate to large reduction in piston friction depending on rpm.
Modelling the inertial torque, something makes me think it will be a little bit different than normal, given the offset and inertial force differences.
Maybe some interesting discoveries ahead, apart from the above.
The idea of a modern take on the Ducati Supermono appeals, especially one based on the Motoinno ts3 steering and suspension system. Even a ~200cc Ryger single (longer stroke for lower rpm, bigger bore for more torque) for ultimate light weight with the TS3 eliminating the mass associated with the heavy reinforcing typical needed for the steering head and no upper telescopic fork tubes giving rise to improved low turbulence intake air flow taken at a high pressure area of the bike. A really fuel efficient and clean tji ignited lpg direct injected engine with intake boost from a pressure wave supercharged, bishop rotary valve engine with dual contra-rotating crankshafts, what a mouthfull, a MutantNewton if their ever was one.
Full carbon fibre lpg pressure vessels are now a real thing, with some flexibility in geometry and not too heavy a tank holding 10-15kg of lpg should weight around 3-4kg, with good efficiency that should give over 350 kilometres.
