Some technology of yester-year that is not very well know is that of hot plug engines.
These engines use a system similar to long stroke diesel engines and but do not develop the pressure that normal diesel engines do and so require a “hot” plug to be heated to ignite the fuel ,
these engines were common in tractors in the 1890’s and so on, until diesel engines were more reliable.
This technology is interesting to us because it requires less precise machining
These engines were slow running (300-400 RPM) and mostly with cast iron parts including pistons,
the engine uses a carburettor because the charge only ignites when the mixture is compressed into the bulb .
A big attraction with the hot-bulb engine was its ability to run on a wide range of fuels. Even poor-burning fuels could be used since a combination of vaporiser- and compression-ignition meant that such fuels could be made to combust. The usual fuel used was fuel oil, similar to modern-day diesel, but natural gas, kerosene, paraffin, crude oil, vegetable oil or creosote could also be used.
Compared with steam, petrol, and diesel engines, hot-bulb engines are simpler and therefore have fewer potential problems. There is no electrical system, as found on a petrol engine, and no external boiler and steam system as on a steam engine.