page_title: Paxman Hi-Dyne engine
section_title: Fell locomotive
hierarchical_section_title: Paxman Hi-Dyne engine / Engines / Fell locomotive
caption_attribution_description: English: Experimental LMR Diesel-Mechanical 4-8-4 at Derby. View eastward from Derby Station towards the Locomotive Works. LMS/Fell 2-D-2 Diesel-Mechanical No. 10100 was designed as a prototype 2,000hp locomotive and built in 1950, but only began trials in 1/51. In 1/52 it began scheduled work on passenger trains between Derby and Manchester Central by the Peak Line: it continued, with some prolonged interruptions, on this line until it broke down in 10/58 and was withdrawn, but it was not scrapped until 7/60. Although a comparative success, the design was not perpetuated. Here in 1957 No. 10100 is outside Derby Locomotive Depot - and over to the left is a very much older but very useful Midland 3F 0-6-0 steam locomotive.
context_page_description: The Paxman Hi-Dyne engine was a form of experimental diesel engine developed for rail transport use by the British engine makers Paxman of Colchester. They used variable supercharging to give a constant power output across their speed range.
  The name "Hi-Dyne" is a reference to dyne, a CGS unit of force, and implicitly to torque.
context_section_description: The same concept of a constant-power diesel engine by variable supercharging had earlier been used in the multi-engined 2,000 bhp mechanical transmission Fell locomotive (British Rail 10100). This used six engines in total: four Paxman 12RPH power engines and two AEC A210D engines solely to drive the Holmes-Connersville Roots superchargers. At low speeds, up to 24 mph, the four engines were brought into gear one-by-one. Above this speed, and up to the locomotive's maximum of 84 mph, the supercharger engine speed was controlled by a governor to maintain the supercharged mass-flow and thus maintain the output power as a constant. At full speed, the supercharging effect had been reduced to almost nothing, as the flow through the supercharger was now equivalent to the normal demand of the main engines at this speed. Although this system proved flexible in providing a smooth drive and was reliable in service, it had the drawbacks of complexity and also that the potentially more powerful engines were not working at their maximum when demands on the locomotive were at their maximum.
caption: The Fell locomotive
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