Philip (PJGD) found this interesting bicycle assist engine - 1950 Lohmann Motor cutaway by Thusius (here is the source pdf) - I tried to clean it a little... ... and found its components... ... from this file you can get a few dimensions ...and a small booklet Here is the short history from the aforementioned pdf:
The ‘Lohmann’ engine was invented by a German Engineer, Hermann Teegen (1899 – 1962) who worked on a series of engines all working with the ‘compression ignition’ principle and managed to get patents on three of the designs. This led to the development of the 18cc auxiliary bicycle engine known as the ‘Lohmann-diesel’, which was produced in the period 1949 till 1954 in the Lohmann Werke factory in Bielefeld, Germany. The Lohmann engine was officially released on the market early 1950 after a year of testing and demonstrations with the engine. Although test reports of those days mentioned that the Lohmann was not a real diesel engine, the Lohmann factory officially promoted the engine as the Lohmann-diesel, which helped to reach a large public. During the time the engine was in production (1949 – 1954), the design of the engine was improved several times, resulting in different models entering the market. Those models are referred to by their year of introduction (e.g. the ’52 model), but consistent documentation of changes in the different models has not been found. Changes include:
- Improved muffler to reduce exhaust noise
- Increased the size of the gudgeon pin from 10mm to 12mm
- Increased the number of piston rings from 2 to 3
Production of the different models in Bielefeld, Germany included an engine for the Spanish market under the name ‘Lohmann Hispania’ which only differed from the ’53 model on the gear cover with ‘Hispania’ logo. In 1954, a model was introduced that could run on both petrol and kerosene. The cylinder head design was slightly adapted to cope with the extra head generated. However, this model has never been a success. Till 1954, an estimated 51.000 units have been produced. It is not clear why production of the Lohmann-diesel was stopped in 1954. Comparable compression ignition auxiliary bicycle engines have been produced in Japan, Austria (the Junior) and Sweden, all under license of Lohmann.
What The Lohmann Enthusiasts Say:
During the project, communication was initiated with a German Lohmann enthusiast and expert, Uwe Peters. He has shared his experiences with Lohmann engines from which he draws the conclusion that the Lohmann engine is not suitable to drive a pump and that the Lohmann has some intrinsic disadvantages that hamper further application of the concept. His arguments include:
1. The compression needs to be adjusted continuously when the engine is in operation and delivering power, which is a direct result of heating and cooling of the engine and ambient temperature. Even on the bicycle, it is not possible to drive a 10km straight stretch without adjusting the compression
2. Due to the high engine speed, the engine wear is too high. The cylinder lining and piston of a Lohmann engine need to be replaced every 1.500 – 2.000 km
3. The engine is not a multi-fuel engine and does not work properly on different fuels
4. From today's perspective, the engine’s exhaust is too dirty, which is a combination of poor combustion of the fuel and the use of two-stroke oil in the fuel.
He further concludes ‘The Lohmann-Werke in Bielefeld spent 7 years working on development of this engine. The engine design was changed every year and in 1951 even three times. And although successful in producing bicycle parts, the company went bankrupt, which was the direct result of the Lohmann failure.’
P.S. Philip also made quite interesting remark: "That is a true HCCI engine controlled entirely by variable compression ratio. The fuel/air mixture is homogeneous, and the ignition is by high compression. Modern HCCI attempts would do much better if they had a variable compression ratio control. The Teegen/Lohmann engine as made by The Practica Foundation needed an engine developer to help them get the engine to work better." Right now I am reading some articles about these modern HCCI attempts... and essentially they all saying that this technology is not yet ready for production - you need FULLY flexible engine (with adjustable everything - camless valvetrain, VCR, etc.) Then, what about this engine designed almost 70 years ago? And I am starting to think that I should better look for really small engines (like the ones used in RC aircraft models) - if I am not mistaken, they also had compression ignition... Anyway, I know sometimes extremely knowledgeable folks are visiting this forum - it would be very interesting to read what you thinking about this engine!
Edited by Ventro, 05 December 2018 - 22:35.