Common Rail Systems for Diesel Locomotives

Basically a diesel electric locomotive has two control systems. One control system controls the speed of the locomotive. The other system is locomotive control system which controls the locomotive as a whole. Governor monitors various pressures and temperatures like boost air pressure, lube oil pressure, fuel oil pressure, engine water temperature, fuel oil temperature, lube oil temperature etc and takes various control actions. In earlier days, locomotives have mechanically controlled governors. But now a day they are getting replaced with electronic governors. Common Rail system is such an electronic governor which controls the engine rpm and the load on the locomotive.

Well, as I said earlier governors are mechanically controlled. There is a rack kind of mechanism which is operated by an actuator which is pwm controlled. In Common Rail system the control is a bit different. As the name itself implies common rail direct injection system, this system precisely controls the timing of start of injection and thus it improves the overall fuel efficiency and results in much efficient engine output power. The second advantage is as the fuel is completely burnt, the system considerably reduces the output CO and NOx emissions. Thus this system is completely Eco friendly.

System level implementation:

This system monitors various temperatures and pressures like engine water temperature, fuel oil temperature, lube oil temperature, boost air pressure, fuel oil pressure, lube oil pressure etc; and takes various control actions like BAP based fuel quantity limitation, ewt based engine control, lop based warning and shutdown etc; these control actions are necessary for the proper working of the locomotive. It takes input from speed sensors mounted on crankshaft / camshaft to measure the EngineRpm. This EngineRpm is controlled as per the set notch. If the system is not able to maintain the required speed at any particular notch, then system generates load control signal to locomotive control system. Then locomotive control system shall reduce the excitation there by the load on the system is reduced and engine rpm can be controlled. The system has various digital outputs to show the engine status to the loco pilot. Apart from input and output, the system continuously records the engine parameters in flash memory and can be downloaded through pen drive. The system is interfaced to locomotive control system through CAN / RS485. Thus all health data of Common Rail system is communicated to locomotive control system. 

Components of the Common Rail system:

Common Rail system has the below main components:

1. Pressure, temperature and speed sensors
2. Injectors
3. HP pump and common rail assembly
4. Common Rail System control unit(ECU)

1. Pressure temperature and speed sensors:

Generally pressure sensors are required to measure Pressure in the common rail, boost air pressure, Lube oil pressure, Fuel Oil Pressure etc; these sensors are 2 wire output types which generate 4-20mA output current signals.

These signals are conditioned, optically isolated and given to micro controller.

2. Injectors

These Solenoid injectors are required to be energized to precisely control the Injection pulse widths. There is a particular injector current profile for proper opening and closing of Injector.

Common Rail Injector

Injector Current Profile

3. HP pump and common rail Assembly

HP pump is controlled through PWM and common rail pressure is continuously controlled by taking feedback from Common rail sensor.

High Pressure Pump

4. CReDI Control Unit(ECU)

Control Unit generates PWM pulses to control on off timing of injectors and hp pump to maintain certain rail pressure. Apart from the control functions, this control unit records the engine parameters and fault data packs in Flash memory. This can be downloaded through Pendrive. This control unit can be interfaced to PC through RS232, USB etc; for user level parameter configuration.