The German Diesel-Pneumatic Locomotive

The German 4-6-4 diesel-pneumatic engine was designed to solve the problem of power transmission between a diesel engine and the wheels.
== Background ==
This German 4-6-4 diesel-pneumatic locomotive was designed to solve the problem of power transmission between a diesel engine and the wheels. Time has shown that diesel-electric is the way to go, but in earlier years it was by no means obvious that dragging around a heavy generator and lots of electric motors and associated control equipment was a good idea.
The diesel-pneumatic locomotive was planned in 1924, an order being placed on the 18th September 1924 in response to a quotation made on the 11th April 1924. Construction took five years rather than the planned single year, which indicates some pretty serious technical difficulties had to be overcome. Completed in 1929, V3201 was the first high-performance Diesel loco on the Deutsch ReichsBahn. It used the MAN Lo6 Vu 45/42 engine, originally developed for use in U-boats. (surprise, surprise) It was a six-cylinder 1000/1200 hp engine direct-coupled to a MAN 2-cylinder double-acting single-stage air compressor. Air was delivered at 7 Bar. (102 psi) The design speed was 70 km/hr and the weight in operating condition 70 tons; the maximum axle loading was 18 tons.
It is a fundamental problem with pneumatic power transmission that a lot of energy is released as heat during compression. Usually this has to be dissipated-by either water-jacketing or water injection into the cylinders. On the other hand compressed air usually cools naturally before reaching the point where it is applied, making the overall process very inefficient. This locomotive tackled the problem by heating the air further after it left the compressor, using the diesel exhaust in long tubular heat exchangers, and this very hot air, at 320�C, then drove pistons exactly as if it was steam. I would imagine that the cylinder lubrication required some thought; steam is not so bad as condensation provides a measure of inherent lubrication, but the hot air would have been very dry indeed. On the other hand, air cools down considerably when it is expanded, (see the page on compressed-air propulsion) and this would have reduced the cylinder wall temperatures.
== Some of it's Service ==
Despite this measure to make the air hot when it reached the cylinders, it was still necessary to cool the compressor cylinders. This was done by water injection directly into the cylinders, introducing the need to carry around and refill tanks of water. Thus there was a certain small proportion of steam in the working fluid, but it would not qualify as an aero-steam engine. According to one source there was no water-jacketing of the compressor cylinders at all, which may have simplified the design but sounds like a mistake. This is however contradicted by the book quoted below, and it appears that water-jacketing was used.
On 10 April 1931, the British journal The Railway Gazette reported that the locomotive had successfully completed twelve months of testing by November 1930, during which it exceeded its design speed by 25 mph for long periods. On stripping it down there was no significant scaling due to the compressor water injection. It was reported that the officials of the Deutsche Reichsbahn were thoroughly satisfied with the trial results, and that the locomotive was being transferred to the hilly district around Stuttgart, and put into service for further test observations.
Nonetheless, it appears not to have been a total success; five years after it was delivered to the DRG, it was taken out of service, and the design was not repeated. Investigations are proceeding, but at the moment the only suggestion found as to why is that the compressor was prone to overheating despite the water injection. The technology was also expensive compared with steam engines. It is probably significant that this remains a unique experiment in Diesel-Pneumatic propulsion.
== Disposition ==
On 22 November 1929 a long test run was done with a 233 ton train from Stuttgart to Augsburg on a "Schnellzug" (express passenger) timetable, over the Geislinger Steige ("Steige" means "Increase" or slope) which is 6 km long with a gradient of 1:40. At a speed of 20 km/h here the diesel engine was not fully "belasted". I have been unable to translate that, but it presumably means the maximum power was not fully utilised. Even in heavy conditions, with severe curves on the 'hill', the train could pull away from standstill faster than a steam locomotive of the same size. The size and working of the coolers was such, that the cooler fan motors were not needed on this test run and the water was cooled by the passing air.
The locomotive was withdrawn and apparently scrapped in 1935.
== Models ==
You will be glad to know this remarkable locomotive is not wholly forgotten. Marklin had produced what appears to be a limited edition model of the V3201. 
== Gallery ==
File:Marklin V3201.jpg|A Model of V3201 that was made by Marklin
File:Marklin 2.jpg|Another shot of the model of V3201 that Marklin had made.
Category:Diesel locomotives
Category:Locomotive
Category:Pneumatic Locomotives
Category:German locomotives
Category:Germany
Category:Scrapped locomotives
Category:Experimental locomotives
Category:Built in 1929
Category:Standard gauge locomotives
Category:4 foot 8 1⁄2 inch gauge
Category:4-6-4 locomotives
Category:Locomotives