# Bruce-MacBeth gas engine model



## Rustkolector (Sep 10, 2011)

A good friend and I started this project about 2 years ago. We built two engines. The model is a 1/10th scale model of a 1912 vintage Bruce-MacBeth 100 hp stationary gas engine. These engines commonly drove generators, as well as air and ammonia compressors in continous duty applications. The model is a 1" x 1.12" b x s engine fabricated from brass and steel. The prototype uses a top mounted camshaft driven by a vertical shaft through two pairs of miter gears from the center of the crankshaft. Unique only to Bruce-MacBeth as far as I know. The model crankshaft is split in two to accomodate the center mounted spur gear for the valve train. The engine uses water jacketed cylinders, heads, and exhaust manifold. The first model completed runs for demo only and uses blow-by from a fuel/oil mix to lubricate cylinders and bottom end. This model uses splash lubrication. 

This engine, true to its prototype, uses a gaseous fuel (propane) for fuel. Propane is an excellent fuel, extremely clean burning, but not easily adapted to a throttled engine if you expect a smooth running engine. I became frustrated with fine tuning the running character of this engine. So, I took a break and started the second part of the build; the generator (actually an alternator).

The generator loosely follows the Westinghouse and Fairbanks-Morse designs of the same era. It is a single bearing design driven directly off the crankshaft at engine speed. It operates at a maximum speed of 700 RPM due to insulation limitations, and produces 120vac at 700 RPM. I operate it at about 650 RPM at 100vac output. 

The cooling system uses a small gaming computer radiator and a variable speed fan driven off the generator. It keeps the engine at about 150F while operating with a small electrical load. The coolant pump is a gear pump following Jerry Howells design. 

The previous running issues relative to the propane fuel seem to be mostly resolved. It needs a few more details added, but for the most part, the project is complete. The video shows the first run with the fuel system improvements. It is running at about 620 RPM with about a 15-20 watt load. The clear inspection cover is helping me determine a good oil level.

[ame]http://www.youtube.com/watch?v=2-qdar5TEpQ[/ame]


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## metalmad (Sep 11, 2011)

Real nice job :bow:
That computer radiator and fan is an interesting idea and I may borrow that for my Wallaby.
Pete


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## JorgensenSteam (Sep 11, 2011)

That is a very nice engine.
I like that slow speed like the old ones.

Did you custom-make the alternator, or adapt one from something?

Pat J


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## ozzie46 (Sep 11, 2011)

Well done. It sounds great.

  What are you powering with the gen/alt?

  Ron


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## Rustkolector (Sep 11, 2011)

Thanks. The alternator stator started out as an old 18 pole ceiling fan motor. The stator winding coil connections were dug out and reconnected for the lowest possible voltage. The rotor was fabricated using rare earth magnets for excitation. 

The radiator fan is powered from the generator output through a variable voltage switch mode power supply. The main generator load currently is a string of 5 watt incandescent Christmas tree lights. The bulbs are screwed in or out to select the desired load. 

Jeff


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## JorgensenSteam (Sep 11, 2011)

Very creative electrical setup.
There have been discussions on this forum about making an electric brake to load steam engines, using the same method to change load (screwing in more or less light bulbs).

Seems like with the power that is packed into small motors these days, you could use one medium sized DC electric motor to accurately load a wide variety of steam engine sizes, from say a 3/4" bore up to perhaps a 2" bore, especially if the motor were fan or water cooled.

Pat J


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## Rustkolector (Sep 13, 2011)

Pat,
Small motors are are notoriously inefficient when used as genertors whether DC or AC. They are fine for demo loading a model, but if you want to quantify the engine power output it would be difficult. The generator efficiency would be difficult for me to measure. All I can measure is the electrical work the generator is doing and that is only a portion of the work the engine is producing. Some of the model IC engines can produce a surprising amount of power, and in my opinion, pushing them to their limits repeatedly is risky. Especially ones built with my level of machining skills. But engines, even models, do sound better with a little load and that is what I was after. So, to minimize temptation I have a carb on my model generator that limits both load and RPM. 

Jeff


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