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You all have observed many times that diesel locomotives are kept idle in the yards and also when waiting for too long in the yards or station especially for goods train. Loco pilots can switch off the diesel engine and save fuel instead of running in IDLE condition.


1) The brake pipe pressure reduces due to the leakages and it takes a longer time to build up working pressure again. it is very crucial when waiting for the signal on the grade.

2) A proper checklist has to follow to crank the engine. It takes 10-15 min to do so when starting after a long shutdown.

3) To keep the compressor running, the engine must not be switched off as it is coupled with the engine.

4) As the diesel engine contains usually 16 or 12 cylinders and is also big in size, so it is quite difficult to achieve ignition temperature. There are many auxiliary components running so if one fails or some technical parameter changes may cause a problem in starting.

    A new technological improvement and upgradation is done in Indian railways. A new fuel saving device called APU (AUXILIARY POWER UNIT) are being installed in the diesel locomotives. In future, Indian railways plan to fit APU on 100 percent in newly-built diesel locomotives which will then result in savings of more than Rs 60 crore annually in future. Use of APU also results in lower CO2 emission and other pollutants like HC, NOx, CO etc.


    During idling a lot of fuel get wasted only to charge the batteries and to keep the air compressor running. By using APU, the main engine shuts down and the small 25hp engine starts, and charges batteries and air brake pipes, when the train is idle for more than 10 minutes. The diesel engine of APU consumes only three liters of diesel per hour in comparison to 25 liters by the main engine. Expected savings per locomotives fitted with APU is Rs 20 lakh per year on account of saving in fuel oil.

    APU is a self-contained unit containing a small diesel engine coupled to a compressor and alternator for battery charging. It has its own set of controls, accessories and is integrated into the existing microprocessor control system of locomotives.

    APU is located in the nose compartment under dynamic brake grid resistors and after the air brake panel.

    This is an Add-on unit to Microprocessor based loco control system.

    It is called as AESS with APU.

    It starts automatically and stops automatically as per the driver’s request.

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