Sulzer RT-flex. Very slow running
Sulzer RT-flex engines have also demonstrated their ability to run stably at very low speeds, lower than engines with mechanically-controlled injection.
They can run without smoking at about ten percent nominal speed. This makes for easy ship handling when manoeuvring or in river and canal passages.
Such slow running was well confirmed in service in the Gypsum Centennial. Slow running was taken to a new “low” during the testing in May/June 2004 of the first 12-cylinder RT-flex96C engine. Owing to its number of cylinders, it could run steadily at just seven revolutions per minute.
The very slow running is made possible by the precise control of injection, together with the higher injection pressures achieved at low speed, and shutting off injectors at slow speeds. Reducing the number of injection valves in operation makes injection of the reduced fuel quantities more efficient, especially as the injection pressure is kept up to a higher value than in a mechanically-injected engine at the same speeds.
Fig 11. Sulzer RT-flex engines have the unique ability to shut off individual fuel injectors, here shown schematically. This feature is used to assure clean combustion for smokeless, stable running at very low speeds
Shutting off injectors is enables by the separate control of individual fuel injection valves. This feature is unique to Sulzer RT-flex engines. Usually the injection valves operate in unison but, as the engine speed is reduced, one injection valve can be shut off and at a lower speed a second injection valve can be shut off. Thus at minimum speed, the engine runs on all cylinders but with just one injection valve in each cylinder.
If the RT-flex engine then runs for a period in single-injector operation, the electronic control system switches between the three injection valves in a cylinder so that the thermal load is equalised around the combustion chamber.