The next part of the project was to design a uniflow-style cylinder for the engine. This design bears many similarities to a two-stroke cylinder, especially in the sense that the exhaust port is machined into the cylinder wall itself. But I couldn't use a cylinder from a two-stroke engine for a variety of reasons. First, because I had no need for intake or transfer ports, a two-stroke cylinder would have been unnecessarily complicated for my purposes. Also, according to period steam literature I've read, the optimal exhaust timing for a uniflow engine is 15% above bottom dead center (BDC) of a piston's stroke.
Because of the radically different nature of internal combustion (IC) engine physics, the ports are much larger and open much earlier in the stroke than would be efficient for the project. Assuming that the piston skirt covers the port when at top dead center (TDC) to prevent excess steam in the crankcase, the only consideration is maximizing the size of the port while maintaining the exhaust timing. In the case of this engine, I was able to machine four ports with a 6-mm diameter into the cylinder.
Of course, the only option was to once again make the parts myself. Cast iron is still the gold standard for cylinder liners, so I attempted to find a source. (I know I'll receive comments telling me all about coated aluminum liners, but bear with me - I'm a college student with basically no budget.). A funny thing about Denmark, though, is there aren't a whole lot of cast iron pipes lying around. I even tried going to the on-campus foundry, but they required me to make my own molds, specify the exact alloy desired (I had no idea), and wait for them to actually perform the production run.
 Instead, I decided to use a piece of carbon steel, machine it myself, and have it honed by the campus shop since it was a prototype and longevity wasn't an issue at that point. For future designs, I would prefer something less prone to oxidation, such as a Nikasil lining or stainless steel. After machining the liner, I shrank-fit it into an aluminum cylinder to reduce the weight and provide a place to run the mounting studs through. In my next blog entry, I will describe the creation of the cylinder head and timing chain.
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