Can you only run a combustion engine, petrol or diesel, on hydrogen? -yes, but not without making certain changes. As we have previously covered, the combustion speed is much faster on hydrogen than on petrol and diesel. It can be useful if you just know how to handle this speed. When you run an engine on petrol, you have to have an earlier ignition at high revs so that all the fuel has time to burn before the next stroke starts, otherwise you risk losing power, getting worse exhaust gas values ​​and higher engine temperatures. With hydrogen in the tanks, it's almost the opposite, you can not use a traditional ignition system from a gasoline combustion engine. Due to hydrogen's flammability, there is a risk of ignition occurring too early, which in that case can lead to spikes, which can also lead to worse exhaust gas values. An engine that continues to be used in this way risks major engine damage as a result, major damage to pistons and valves, in the worst case engine crash. This problem can be solved by instead having a later ignition, just before the piston has reached its top dead position, or close to zero. This works well on the hydrogen fuel because the burning rate is so high. At low revs, on the other hand, it is an advantage if you have a slightly higher ignition. In simplified terms, you could say that you need an ignition system that works exactly the opposite of an ignition system that you have today in a gasoline engine.