MTU 12 V 2000 P12 Operating Instructions Manual page 30

Speed - injection control
Functions of the closed-loop engine speed control integrated in the engine governor:
• Maintaining the desired engine speed under changing load conditions.
• Adjusting the engine speed when the setting is changed by the operator.
Additional tasks with an effect on closed-loop engine speed control:
• Setting a defined fuel injection quantity on starting the engine.
• Engine safety shutdown.
• Optimizing operation, exhaust emissions and fuel consumption.
• Protecting the engine against overloading.
Speed droop calculation
Speed droop influences the effective setpoint speed depending on engine power. Maximum, speed-de‐
pendent engine power is limited by the DBR curve. The setpoint speed is not influenced by speed droop
at 100% power. The effective setpoint speed increases at lower power. This allows power to be balanced
when operating a number of engines in a network.
Switchable speed droop
Two different speed droops may be selected at the engine governor for stationary genset engines. Which
speed droop is active depends on whether the genset is running in isolated operation or in a parallel
network with other gensets feeding a common busbar.
The speed droop is selected by a binary input (BE4) at the engine governor.
Speed droop is required to balance the load of coupled prime movers. Speed droop can be adjusted to
meet plant requirements via the dialog unit.
Dynamic quantity limitation
Dynamic quantity limits protect the engine against overloading and optimize exhaust emission values.
The engine governor determines the maximum injection quantity based on preset and stored engine per‐
formance maps.
Following limits are applied:
• Speed-sensitive fuel quantity limitation (DBR).
• Fuel quantity limitation as a function of fuel temperature.
Fixed quantity limitation
Fixed quantity limitations are used for power limitation and power reduction to protect the engine in case
of:
• Electronic malfunctions.
• Supply voltage out of tolerance.
Fuel quantity control during engine start
The quantity of fuel injected during engine start increases along a time ramp from a set initial value to a
specified value. This value is calculated by the function q = f . This limits the quantity of fuel in‐
inject (speed)
jected as a function of speed. This fuel quantity limitation is effective until idling speed has been reached.
Cylinder cutout
Only half of the injectors are activated when cylinder cutout is active. The other half of the injectors are
activated on expiry of a switchover time. This prevents white smoke being emitted when the engine is
running.
Desired speed handling
The desired speed is the command variable for the engine speed control loop.
When the engine is started it runs up to an internally programmed desired speed (for 50 Hz network fre‐
quency: 1500 rpm, for 60 Hz network frequency: 1800 rpm).
30 | General Information | MS150025/02E 2012-10