Why are train engines not turned off? How long do train engines last?

 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

But they don't do because

• The brake pipe pressure reduces due to the leakages and it takes longer time to build up working pressure again. It is very curcial when waiting for the signal on the grade.
• A proper checklist have to followed to recrank the engine . It takes 10-15 min to do so when starting after a long shutdown.
• To keep the compressor running , engine must not be switched off as it is coupled with the engine.
• As the diesel engine contains usually 16 cylinders and are 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 problem in starting.

During idling a lot of fuel get wasted only to charge the batteries and to kept the air compressor running. By using APU, main engine shuts down and 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 litres of diesel per hour in comparison to 25 litres 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 to the existing microprocessor control system of locomotive.

• 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 drivers request.

The Tier 4 locomotive is designed for a typical lifespan of 25 to 30 years.