When doing a hydrogen combustion test, can you see water dripping down? Of course not! This is because the temperature during combustion is very high, and water exists in the form of gas. At this time, the volume of water changes It is very large, so there is thrust.
In fact, the hydrogen-oxygen engine should be called a hydrogen-oxygen fuel cell. It uses the recombination reaction of hydrogen and oxygen produced by electrolyzing water. The principle is Equivalent to a primary battery, the electric energy generated drives the motor to rotate, thus providing power.
When a submarine sails underwater, there is no air and cannot be driven by a diesel engine. At this time, the battery is used to provide power to the submarine. And the submarine When sailing on the water, the diesel engine not only provides power, but also drives the generator to charge the battery. Hydrogen-oxygen fuel cells are currently the research direction of submarine batteries. Because this kind of battery is clean and environmentally friendly, unlike lead-acid batteries, which are polluting.
The hydrogen-oxygen engine on the rocket uses liquid hydrogen and liquid oxygen to burn to produce a large amount of high-temperature water vapor to provide thrust.
Hydrogen-oxygen engines are currently only used in a small number of spacecraft. Launch, because there is no good way to store hydrogen yet.
To add to your question, let me explain it again. As mentioned above, the fuel hydrogen and oxygen in the rocket engine are burned to form high temperature and high pressure. Gas. Thermodynamics has the formula:
pV=nRT
Among them, p represents pressure, V represents volume, nR can be regarded as a constant, and T represents thermodynamic temperature .
It can be seen from this formula that the temperature of hydrogen and oxygen combustion is from 3500K, and the temperature of water vapor increases by almost 3000K. That is, the original 10 times pV value also increases by 10 times. When water After the steam is ejected, the pressure decreases, about 1/10 of the original value. Therefore, the volume of high-temperature water vapor expands more than 100 times. But when liquid hydrogen and oxygen change to gaseous state, the temperature decreases, so the value of pV That is to say, decrease. The storage pressure of liquid hydrogen and oxygen is only 50 atmospheres at most. When it is reduced to normal pressure, the volume will expand up to 40 times, which is incomparable with high-temperature water vapor. Do you understand this?