Dieselisation
Dieselisation took place largely because of the tremendous reduction in operating costs it allowed. Steam locomotives require large pools of labour to clean, load, maintain and run. They also require extensive service, coaling and watering facilities. This was their biggest inferior measure as compared to the diesel locomotive in the number of ton-miles or passenger traffic miles either could run. Diesels could and did have a significantly higher initial price per unit-horsepower delivered. However, their far greater range between fueling stops, the absence of water stops, and the much higher unit availability between inspection repair and maintenance stops, were far better than steam. Diesels simply required significantly less time and labour to operate and maintain. Diesel power was also more scalable to power requirements, owing to the control systems that allowed multiple units to be controlled by one operator. "Double header" steam power required a crew for each locomotive. Initially, diesel locomotives were less powerful than the typical steam locomotives. Between the late 1930s and the late 1950s the power available with diesel locomotive engines roughly doubled, although the most powerful steam locomotives ever built still exceeded the power of the most powerful diesel locomotives from the late Twentieth Century.
Diesel locomotive
Early internal combusition locomotives and railcars used kerosene and gasoline as their fuel. Dr. Rudolf Diesel patented his first compression ignition engine in 1898, and steady improvements in the design of diesel engines reduced their physical size and improved their power-to-weight ratio to a point where one could be mounted in a locomotive. Internal combustion engines only operate efficiently within a limited torque range, and while low power gasoline engines can be coupled to a mechanical transmission, the more powerful diesel engines required the development of new forms of transmission.