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Reliability and redundancy

Sulzer RT-flex. Reliability and redundancy

Reliability and safety has the utmost priority in the RT-flex system. Although particular attention is given to the reliability of individual items of equipment in the RT-flex system, the common-rail concept allows for increased reliability and safety through its inherent redundancy.
High-pressure fuel and servo-oil delivery pipes, the electrically-driven control oil pumps, and essential parts of the electronic systems are duplicated for redundancy. The duplicated high-pressure delivery pipes have spot cocks at both ends to isolate any failed pipe. Each single pipe is adequate for the full delivery. All high pressure pipes are double-walled for safety.

With a more traditional injection arrangement of one fuel high-pressure pump to each cylinder, a failure of one pump leads to the loss of that cylinder and the imbalance in engine torque requires a drastic power cut. In contrast, with the RT-flex system in which all high-pressure supply pumps are grouped together and deliver in common to all cylinders, the loss of any pumps has much less effect. Indeed with larger RT-flex engines having several fuel pumps and several servo oil pumps there can be adequate redundancy for the engine to deliver full power with at least one fuel pump and one servo oil pump out of action. Should further pumps be out of action, there would be only a proportional reduction in power.

Fig 10. Typical injection pattern of Sulzer RT-flex engines with all injection nozzles acting in unison showing needle lift, fuel rail pressure, injection pressure and cylinder pressure when all injection nozzles are operating simultaneously
Every injection nozzle is independently monitored and controlled by the WECS. In case of difficulties, such as a broken high pressure line or malfunctioning injector, the affected injection valve can be cut out individually without losing the entire cylinder.
The injection control unit ICU hydraulically excludes the injection of an uncontrolled amount of fuel. During the entire working cycle of the metering cylinder, there is never a direct hydraulic connection between fuel rail and the injectors. The maximum injection quantity is limited to the content of the metering cylinder as the travel of the metering piston is monitored. If the travel of the metering piston should be measured as out of range, the subsequent injections of that ICU will be suppressed and an engine slow-down activated.
The ICU also serves as a flow fuse: if the metering piston should travel to its physical limit, it cannot return hydraulically and no further injection would be possible until it is reset. 
If the stroke measuring sensor fails, the WECS system switches the ICU to a pure time control and triggers the signal based on the timing of the neighbouring cylinders, 
Two redundant crank angle sensors measure the absolute crank angle position which is evaluated through WECS. WECS is able to decide which sensor to follow in case of a discrepancy.
The WECS main controller and all essential communication interfaces such as CAN-bus cablings are duplicated for redundancy. WECS monitors the momentary position of each rail valve for proper function of each cycle before starting the next.

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