Gas turbines and diesel engines are the most commonly used power plants on ships. For half a century, they have been widely used in ships and are excellent power devices on ships. However, their working principles are quite different. Gas turbine is a kind of rotating machinery, and its mechanical energy is obtained by the rotation of impeller, while the kinetic energy obtained by impeller depends on the transformation of high temperature and high pressure gas. Diesel engines are different. This is a reciprocating machine. It obtains mechanical energy because it has a group of pistons with power output, and the connecting rod reciprocates in the cylinder. What makes them reciprocate is that the high-pressure air in the cylinder explodes into high-pressure combustion gas due to the injection of fuel. So the way to generate mechanical energy is completely different. The rotational speeds of the two are also far from each other. The rotating speed of the output shaft of marine gas engine is generally about 3000-5000 rpm for high and medium power, and above 5000 rpm for low power. The speed of medium-speed diesel engine is usually 500- 1000 rpm, and that of high-speed diesel engine is above 1000 rpm.

The principle of steam turbine is similar to that of our common windmill. The wind blows the blades and the blades rotate to do work. The gas turbine ignites the oil in the combustion chamber, and there is an opening in the combustion chamber, through which the expanded gas blows to the blades, and the blades rotate to do work. Then through the mechanical transmission device, the rotation of the blade is converted into the rotation of the propeller, and it is OK. The steam turbine uses coal or heavy oil as fuel, and the water is heated into steam by the boiler, and then the steam blows the blades to rotate. The reactor of a nuclear-powered aircraft carrier will generate enough heat to heat water into superheated steam. However, these vapors are radioactive and cannot be used directly. So we designed a heat exchange device (the principle of this device is similar to air conditioning), which uses superheated steam generated by nuclear reactor to reheat ordinary water into steam, which is like a steam turbine. The coolant of a nuclear reactor can be water, heavy water or other media, but the principle is the same.