autogyro wrote:If you are going the reduced capacity route, why not go rotary with exhaust turbo generator.
No reciprocation, no valves and far fewer moving parts.
Why? Do we want a higher fuel consumption? What about no relation with current roadcars? Not to mention that the rotary engine actually has a very high displacement. The reason rotaries produce very high hp/l is because they are usually rated with the wrong displacement. The common 1.3 liter Mazda rotary actually has a displacement of 3.9 litres, but had Mazda called it a 3.9 litre engine it had suffered because of the japanese tax for engines above 2 litres.
Had we only cared about few moving parts we would have used the two stroke instead!
Something along the line of a half current V8 should be reasonable, perhaps a little smaller, 1 litre or so and a reduced maximum speed to around 13,000 rpm. Then pneumatic valve springs shouldn't be required, and it should be possible to use direct injection with reasonable injection pressures aswell as camless engines. Boost pressure unlimited, but with restrictions on fuel flow, fuel consumption and perhaps also compressor wheel diameter.
Giblet wrote:They should open up the drive train to spherical valves as well, eliminating the problems with springs at high revs.
I don't know too much about the tech, but from what I have read, it seems to be able to run just about any speed, and have a lot less parts.
Hmmm.. on a better read about them, seems to be a bunch of issues, especially with forced induction.
So far no one has been able to show a successful rotary valve engine, to seal them from the combustion chamber pressure has been shown to be difficult while the poppet valve seals itself due to the combustion pressure. Rotary valves can't run at any speed, aside from the bottom end limits, they will be limited by port area and air velocity in the inlet ports. Current racing engines have a port area of approx. 1/3 of the bore area, and this restrict the engines to approx. 25 m/s mean piston velocity. To be able to use higher revs with maintained stroke, the port area in relation to the bore area must be increased.
Rotary valves are also more difficult to control in terms of variable valve timing. Today many roadcar engines are already equipped with variable cam phasing and the next step is to make variable valve lift and variable valve duration more common. With control over lift, duration and phasing we can get rid of the throttle plate and control the torque output with late or early valve closing instead; that is the Miller-Atkinson cycle with a much greater expansion ratio in relation to the compression ratio. Basically we could combine the fuel efficiency of a Toyota Prius engine at part load with the output of a racing engine at full load.
