Why are large diesel engines used in ships and locomotives?

Large diesel engines are favored for ships and locomotives primarily due to their high power output, reliability, and efficiency.12

Marine Applications

In the maritime industry, diesel engines are categorized by speed to suit specific vessel needs. Low-speed engines are highly valued for large ships because they can be coupled directly to the propeller without needing complex speed-reducing gears. Furthermore, their large cylinder displacement allows them to burn the lowest-quality, most cost-effective fuels. Medium-speed engines are chosen when a more compact or lighter power plant is required, offering a balance between initial cost and performance.3

Locomotive Applications

Diesel engines superseded steam power in railroads because they offer superior operating efficiency and flexibility. Key advantages include:1
* Operational Efficiency: They can run for long periods with minimal maintenance compared to steam engines.1
* Performance: They provide smoother acceleration and higher sustained speeds.1
* Energy Economy: Diesel units have significantly higher thermal efficiency, consuming less fuel energy.1
* Flexibility: Multiple units can be combined and controlled by a single operator.1

Modern diesel-electric locomotives also benefit from advanced electronics that improve load-hauling capability and adhesion, further reducing maintenance costs.4