Diesel locomotives are always kept running, even when they’re not moving. This practice might seem strange, but it serves practical purposes:
Brake Pressure: When a diesel engine is turned off, brake pipe pressure decreases due to leaks. Restarting the engine takes time, which is crucial when waiting for signals on gradients.
Engine Cranking: Restarting a diesel engine after a long shutdown requires a proper checklist and can take 10-15 minutes. Loco pilots avoid this delay.
Compressor Operation: The compressor, coupled with the engine, must remain running. Turning off the engine would affect brake systems.
Ignition Difficulty: Large diesel engines (with 16 or 12 cylinders) struggle to achieve ignition temperature. Auxiliary components add complexity.
To address fuel wastage, modern locomotives use Auxiliary Power Units (APUs). These units charge batteries and air brake pipes while the main engine remains off, resulting in fuel savings and reduced emissions.
