Having almost no free time due to half-time work, other half-time study I am restricted to posting all kinds of drivel removed from reality on this site instead of building my own diesel bike or meddling with my diesel engine. So please bear with me a lil' while longer
As we all know, bike-able two stroke diesel engines and replacement parts for them are few and far between, but they beckon with 1.7 times or so more power from the same volume and weight.
The most viable option here is to convert existing diesels to two-stroke operation.
Sure, sez you, graft two-stroke cylinders on them, have the engine inject twice as often, add some air compressor for scavenging - and earn, together with the benefits, also the risk of coked piston rings and engine runaway, not to mention the hassle with accomodating longer piston skirts. Or use inefficient valve scavenging which eats up the theoretical power benefits of a two-stroke - self-defeating.
Yes, that's what I have thought to this day, too. But the latter option - valve scavenging - only has to be done right to gain all, lose zilch - the only question is how.
Enter these real bright Finnish guys.
Their Z-cycle is a hybrid of the Scuderi split-cycle and the classic two-stroke cycle: Unlike in the Scuderi, there IS scavenging taking place in the working cylinder; but unlike classic two-stroke, it happens very late - midway in the compression stroke, which is therefore also an exhaust stroke from BDC to stroke-middle. After the very short scavenging period, the exhaust valve closes, high-pressure pre-compressed air is further pressed into the cylinder, then the intake valve closes, compression stroke completes, fuel is injected and combustion and working stroke take place.
Meaning that when the scavenging takes place, there is much less exhaust gas to push from a much smaller cylinder space into the exhaust header. (Of course, the air pressure from your scavenging compressor must be appropriate, around 5:1 or so, or you'll lose power, but that is comparatively easy to do: Just bolt an appropriately sized small piston compressor and overdrive it with an according ratio.)
This promises a lot of benefits: Less cylinder space and less exhaust gas to scavenge means one can make do with the much less efficient loop scavenging through the valves to the same effect as the much more efficient uniflow scavenging of the complete cylinder with the same results. The possibility of satisfactory valve scavenging results means you need not use a longer piston skirt; additional oil pump and centrifugal de-foaming oil filter and the more frequent oil changes inherent to port-scavenging designs also fall away.
And most of all, the only changes to be done to the engine itself is fabrication of a new 1:1-driven camshaft with according valve and injection pump timing and in the head, mild widening of the intake port in direction away from exhaust port.
Also, that way, water-cooled engines can be converted as well - after all, the water-cooling mantle of the cylinder is left well alone because you don't need to add scavenging ports to the cylinder barrel.
Whaddya think?