Steam locomotive Diesel Kitson-Still
By Alain Lovato
At a time when a barrel of oil is trading at $ 54, and when our leaders are once again considering energy savings, we are to regret that various promising experiments, carried out a long time ago, n has not been continued, or taken over since then.
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One of these promising experiments took place in the field of railway traction in 1924, that is to say, just 80 years ago. At that time, we were already trying to save ... coal, fuel for steam locomotives. The steam locomotives had an efficiency of around 10% (when it was not 7 or 8), and above all, required very heavy maintenance. The increase in labor costs in these post-World War I years therefore prompted the railways to try to use more economical traction equipment. Where electric traction was not an option, we thought very early on of diesel traction; The problem lay at the time in transmission; We did not know how to transmit the great powers necessary for pulling trains, from diesel engines to the wheels of the locomotive. In this context, the Kitson company, of Leeds developed a completely extraordinary machine, making it possible to satisfy the requirements mentioned above; Have a diesel traction machine with a reliable and proven transmission. To do this, this company equipped this locomotive with a completely astonishing engine: The Still engine, which knew its hours of glories on fixed and marine machines.
In a conventional diesel engine, a maximum of 35% of the thermal energy supplied by the combustion of diesel or fuel oil is transformed into mechanical energy. In other words, it is almost 65% of the engine energy, which is lost in the form of heat, in the exhaust gases. Still's idea was to recover a large part of these calories, to heat a boiler, and produce steam, which was used in the diesel / steam engine.
The Kitson company therefore built a locomotive fitted with 3 Still engines. The motors were double-acting; Diesel on one side and steam on the other, and could be driven only by steam. An oil burner allowed the pressure to rise, when the machine started; at 10 km / h, the fuel was injected on the diesel side. The full power being reached after 2 turns, the steam supply was then cut off, until the next stop, unless it was necessary to supplement the power, in a strong ramp for example.
It may seem surprising to cut off the steam supply, but this is due to the particularity of rail traction; The maximum effort is requested at start-up, then only lower power is required to maintain speed. In the Still engine, the fact of requesting the diesel part of the engines, made it possible to maintain them in temperature, and to recover the calories in the boiler which played the role of energy accumulator. Steam traction would have caused the diesel temperature to drop, which, worsened by steam consumption, would have caused the pressure in the boiler to drop.
Still engines had an efficiency of almost 40% more than the internal combustion engines of the time, and the Kitson-Still locomotive consumed about a fifth of an equivalent steam engine. But it would have required heavy investments to optimize it, increase its power, and allow the marketing of this very promising prototype. The Kitson company could not afford it, and despite the great success of the demonstrations, it went bankrupt, and the Kitson-Still fell into oblivion.