The Lanz Bulldog was born out of necessity after the First World War when German farmers were short of conventional fuels like petrol (gasolene) and diesel. In response Lanz designed a tractor using an engine based on a design by an Englishman, Herbert Ackroyd Stuart, which ran on almost any liquid fuel, including crude oil, tar oil, spirit, vegetable oil, and so on, by using a hot bulb.

This two-stroke engine differed from the diesel which compresses air and fuel is injected into the hot air at the top of the stroke. The diesel requires a high compression ratio.

In contrast the hot bulb engine injects fuel via the pre-heated bulb and ignition takes place when the rising piston forces air into the cylinder. That requires a compression ratio of only 5:1 rather than the 20:1 of the diesel.

The rest of the tractor was designed to be simple for the farmer to use and maintain. To start the engine he had to pre-heat the bulb for 20-minutes using a blow torch.

Last week Find Hansen described his model of the smallest two-stroke hot bulb engine. This design is too small for most model engineers to make a working hot bulb engine and so includes a vacuum engine to make an interesting alternative for a model in this scale which retains an external heat source. The drawings are based on those originally by C. P. Hendrikx.

Click on drawings to download - for personal use only.

PART TWO HERE   PART THREE HERE

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