True diesel

TRUE MODEL DIESEL ENGINE
by Find Hansen

IN 1995 I tried to build a true diesel model engine with injected fuel, but with no success and it ended up as a hot bulb engine. Since then I have dreamed of building a diesel engine again, and now I have one running. The engine has a bore of 20 mm. A stroke 40 mm. And a compression ratio of 21:1. The engine do not use a pre-chamber, but has direct injection and the fuel is, for now, kerosene. The engine is vertical, and has an A frame construction, like old Danish build B&W blast injection diesel engines. I built the crankshaft and the engine stronger with thicker journals, to withstand the high compression. I drilled an oil way in the crankshaft to have a continuously lubricated big end. Notice the heavy flywheel used. This was found not to be necessary. Click photos to enlarge.

Starting the engine At the first start attempt I tried to start the engine using Ether and Diesel start, it started and ran, but only at the diesel start, not on the engine fuel. At the third start attempt the flywheel broke loose. I fixed the flywheel, tried again still using Diesel start, this time it started and ran on the fuel, I tell you I was happy. Next start attempt still using diesel start, the engine started, but with an awful noise. The connecting rod was bent, but luckily nothing else had happened to the engine. I made a new connecting rod, now 6 mm. thick, the old one was 5 mm. thick. For the next start attempt I thought “no more diesel start”, why not try to use your wife’s hair dryer. I tried the hair dryer, and when it was about hand warm, I tried to start. I could not hand crank it, because of the high compression, so I used a hand drilling machine and, to my surprise, it started and ran. Since then I have made experiments with the injection pressure, the injection timing and different kind of fuel. I found that it is very important that the injection timing is right, a few degrees before or after and the engine will not run properly.

Photos show (top) handle coupled to the governor system, to stop the engine, or to change the speed. (next) operating the inlet rocker arm, (below) operating the governor spring handle for controlling speed. (Finally) operation of the injection pump handle, used to bleed the fuel system.

Final thoughts on building a diesel
1. The compression must be about 100% with no leaky piston rings, gaskets or valves, because the compression heat is the only igniter. 2. The compression ratio must at least be 20:1 for an easy start and 22:1 would be better. You should not be afraid of the high compression. The engine starts, runs and works much better. 3. The injector must atomize the fuel very well, because the compression heat is the only thing to vapourize the fuel before it is ignited. 4. Using a light fuel such as kerosene instead of diesel is better, because it vapourizes and ignites more easy and is not as smoky as diesel. 5. The crankshaft, crankshaft bearings, big end bearing, piston pin and connecting rod must be made bigger and stronger to withstand the high compression, because the load on about a 20 mm piston with a compression ratio of say 21:1 is about 160 kg, and when the fuel is ignited the load is about 180 kg. When pre-ignition occurs (diesel knocking) the load rises to about 220 kg. It is a wonder that the engine will stand this heavy load. Also, the whole engine construction must be made stronger.
Find used the same injection pump as on his hot bulb engines - see article here.

See the engine run here.

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