Kitson-Still locomotive

A steam diesel hybrid locomotive was a railway locomotive with a piston engine which could run on either steam from a boiler or diesel fuel. Examples were built in the United Kingdom, Russia and Italy but the relatively high cost of fuel oil meant that the designs were not pursued.

In 1926 Kitson and Company, Leeds, built an experimental example for the London and North Eastern Railway, using as their model the Still engine already in use for stationary and marine applications. It was on trial until 1934, but then scrapped. It was designed because a steam engine offered a high starting torque while a diesel engine offered a high fuel efficiency and it was considered desirable to combine the two.

In outline the machine resembled a conventional 2-6-2T steam locomotive, but it had four pairs of horizontally opposed cylinders mounted longitudinally above the frame and driving a crankshaft placed between them, with the further drivetrain by gears. The cylinders were made double-ended, with one end of each cylinder for steam and the other fitted with a diesel injector. (Some drawings, published in contemporary magazines, show only two pairs of cylinders and it seems that this was one of the design features that was changed during development.) The boiler, with a diameter of only fifty-one inches (130 cm) and a small internal firebox, was mounted above. The driving position was in the usual place behind the boiler and tanks for fuel and water were mounted on the frame at the rear.

The sequence of operation was to heat the boiler in the normal way, but using fuel oil instead of coal. The start from rest would be made with steam power, but at about five mph (8 km/h) the diesel injectors would be started and the steam turned off. The waste heat from the cylinder jackets and diesel exhaust then maintained the boiler in steam for auxiliary functions (brakes and whistle) and in readiness to supplement the diesel power if required, or for the next start. By using steam for starting, no form of variable transmission was necessary and a permanent reduction geartrain of 1·878 to 1 ratio was fitted.

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