This is an elaboration of [acurafan07]'s idea, "Two Stroke Diesel Miller Cycle" (q.v.), which got me to thinking about sleeve valves to time the scavenge phase. So, how about dispensing with poppet valves altogether, and using single sleeve valves with two sets of ports? The intake ports would be near
the bottom of the stroke, as on a Detroit Diesel, and the exhaust ports near the top. Intake and exhaust timing is then controlled by the same relatively simple mechanism.
Apart from relative simplicity, huge port areas are possible, with substantial scavenge cooling, which would keep exhaust temperatures within the region of sanity.
Moreover, the absence of overhead valve gear allows a considerable saving in the height of the engine. The nicest diesels are the Edwardianesque sort, that is, big, simple, slow-revving, durable, field-reparable, surprisingly light for their size, and extremely efficient. Those characteristics also render them physically bulky, and anything that allows them to be made more compact is to be welcomed.-- Ned_Ludd,
Aug 23 2007
Two_20Stroke_20Diesel_20Miller_20Cycle [Ned_Ludd, Aug 23 2007]
Tiny 4-stroke sleeve valve
http://www.dtic.mil...20W Micro-Generator [MisterQED, Jul 24 2008]
Good idea [+].-- acurafan07,
Aug 23 2007
ace idea...if you used a rotary valve big enough to cover the whole top of the piston if would flow fast enough and creat a big enough pressure differential to scavenge the cylinder and then close the rotary vlave in time for there to be some remaining miller cycle effect to be had...2 stroke = twice the power of 4 stroke in theory so a twin charged (centrifugal supercharger and turbo) 1l 2 stroke should be able to thrash a 2.5l turbo...IMHO
Jul 24 2008
If you are describing sleeve valves in the traditional sense of a sleeve around the piston sleeve that slides up and down to open the ports then "realative simplicity" is not a term that I might use in its description.
Further the concept presented in both this idea and acurafan's is kind of a red herring. The miller cycle is advantageous to 4 cycle engines because it reduces wasted energy on compression(of course it increases energy draw to run a SC) The Design of a 2 stroke already incorporates this sort benefit in that compression only occurs near the top end of the stroke, and the addition of a supercharger to the system allows for greater performance potential. The addition of a fancy intake valve setup does not really benefit the engines performance in any way as the traditional static intake ports can simply be tuned in the the way you describe.
Essentially what you are both discussing is a Detroit 2 stroke diesel that has been around for the better part of 80 years.-- jhomrighaus,
Jul 24 2008
Yeah i later realized that the Miller effect is designed to increase efficiency at the exact point that the supercharger would already be pushing air through on a 2-stroke diesel anyway, making my idea not only useless but somewhat baked by the design of the 2-stroke diesel in general. Good to see you're still on here talking about engines, [jhomrighaus].-- acurafan07,
Jul 25 2008