Building The "Nano" - A 0.1cc Compression Ignition Engine
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The Nano is a 0.1cc (that's less than 0.01 cuin) compression ignition engine - most frequently, if somewhat inaccurately, referred to as a "diesel". It was designed by Richard Gordon and the plans were inluded as a supplement with the British Magazine Model Engineer in the early 1990's. The plan reprint is still available from Nexus in the UK (Quote plan PE40).
An idea of the size of the Nano is given by this picture. From backplate to drive washer is less than 1 inch. There are no exotic materials required. The crankcase is hacked from a solid cube of aluminium (I used 2024-T3), 3/4" on a side. The piston and contra piston are cast iron. The crankshaft and liner are any old steel from the scrap box.
Here is an exploded view of the engine. The odd looking thing in the foreground is a special Nano-Spanner required to tighten the backplate. It also fits the fuel nipple. The construction is extremely conventional - only the scale is unusual.
Like all model IC projects, there are a few special jigs and tools required to construct the Nano. All are fully detailed in the plan, which includes step by step instructions with photos. The cutter is made from water hardening drill rod (called "silver steel" in the UK because of its appearance - it contains no silver). I formed the teeth with an abrasive Dremal-type cut-off wheel.
The cutter is used to form the exhaust ports in the cylinder. There are three of these, spaced at 120 degrees with sufficient space (!?) between them for the angled transfer ports to slightly overlap the timing. The crown of the piston is conical to assist transfer. The contra piston has a matching concave conical depression.
As mentioned previously, the crankcase is formed from a cube of aluminum. The venturi is machined separately and secured with Lok-Tite before the final reaming of the crankshaft journal. Notice the three transfer passages in the photo. These terminate in a transfer belt below the cylinder seat that matches with the cylinder transfer ports. If you look very closly, you'll also see the stuff-up that turned away part of the venturi opening. Always happens on the last operation!
There's nothing special in the crankshaft components. Another jig (not shown) is made to hold the shaft in the 3 jaw chuck, offset by half the throw for forming the crank pin. Even at these sizes, final lapping to size is no different from larger engines in terms of the amount of metal that must be LEFT for removal. Only the microscopic size makes things difficult. The prop driver knurls were formed with a thread form tool, set on edge and used as a shaper. The prop nut is anodized in the usual way.
Again, apart from their size, there's nothing special about the needle valve components. I made the needle itself from steel and "blued" it by a quick heat in a gas flame followed by water quenching. No big deal, but the amazing thing is the attention it draws with people who examine the engine. If I had a buck (better make that US$10.00, for inflation) for every "is that a Cox needle valve?" comment...
Now, the question you've all been waiting for: does it run? Well, yes, and no! It's fired and run briefly, oscillating back and forth about TDC like over compressed diesels with small mass fly wheels are wont to do. If that qualifies as running, then it's run! The plan calls for a spring starter which I've not made yet. One noted English mini-diesel authority, I forget who, says spring starters are the only way to start ultra small diesels - hand propping (like I was doing) just won't work. Also, the fuel for mini diesels needs a lot of ether - as high as 50% by volume. On the single starting session, I used some old stuff from a very old can that still had a feint wiff of ether, but not a lot.
So I believe, that with high ether fuel and a spring starter, the little Nano will burst into life. Richard Gordon claims it will turn 40,000 rpm - yes, that's no typo, forty thousand revolutions per minute. American engine builder Ron Colona used to demo his at model engineering shows and turning at better than 20,000 rpm, so I suppose it's possible. Just have to be carefull nobody swats it by mistake!