Question

Steam engines of Indian railways are replaced with diesel engines. Justify this move with two scientific reasons.

Answer 1

Hint: Method of energy production differs in steam engines and diesel engines. Steam engines produce steam. This steam pushes the pistons, which are connected to the driving wheels that operate the locomotive. But, diesel engines produce energy by burning diesel.

Complete step-by-step solution:
Steam engines are bulky, compared to a diesel engine, which produces the same amount of energy. The efficiency of a steam engine is quite low compared to a diesel engine. To increase the efficiency of a steam engine, enough steam at a high enough temperature and pressure needs to be generated, which in turn requires more fuel. Steam engines take a lot of time to produce steam by heating water and cannot start instantly. Hence, they have high latency. But diesel engines can start immediately by using a compressor.
Hence steam engines are now replaced by diesel engines.

Additional information:
Diesel engines could work longer and run faster than steam engines. These engines are more fuel-efficient; they do not require frequent stops to replenish coal and water. Instead of generating steam in an enormous boiler, diesel is burned to power a generator that, in turn, powers the electric motors on the wheels. Steam engines use vast amounts of energy to build up steam pressure. Hence, steam engines have low thermal efficiency.

Note: Efficiency is an important factor of engines. Efficiency declines steadily with reduced power output. The efficiency is maximum for reversible engines.