Steam engines haven’t been in any production car since the 1930’s. Despite this, regular engines can be modified to accept it. In fact, that’s just what these Russian mechanics on Youtube are doing.
Converting a four-stroke piston engine to run on pressurized gas is actually very simple (in theory). All you need to do is to delete the compression and and power stroke. This leaves you with a just intake and exhaust–a two-cycle engine. The air just needs to push the piston down, and get out.
You can modify a regular engine to do this in one of two ways. You can double up lobes on the camshaft, or make the ratio between the crankshaft and the camshaft 1:1 (it is typically 1:2). Once you have done either of these things, just remove whatever carburetor or fuel injection system you had. Then, attach a source of pressurized gas to the intake manifold.
How They Decided to do it
Garage54 doubled up the cam lobes in probably the sketchiest way possible. They just welded some bar stock to the camshaft and ground it smooth. In this first video, they get it to run on just compressed air. They also demonstrate just how much air an engine actually consumes. Initially, a regular 8mm hose of compressed air is not sufficient to run the engine. The shop compressor cannot flow enough air to sustain even a small motor. Engines consume a lot of air. Imagine trying to get all of the air your car needs through a drinking straw. That’s basically what they were doing.
After realizing this, they hook up a massive air tank to the engine. The tank acts like a capacitor in a circuit, building up the necessary pressure until it can expend all of it at the necessary flow. Once they do this, they manage to get the car moving forwards. Interestingly, since no real combustion is actually taking place, the clutch is not necessary in this arrangement. It is indeed not necessary in any type of vehicle with a steam engine. That’s part of what makes them so useful in locomotives (imagine the size of a clutch required to start a train?).
Although this may be entertaining, I don’t recommend you do this. You need a frightening amount of pressure to actually drive anywhere. Also, this is definitely one of the most inefficient types of steam engines out there. Just buy a little engine kit on Amazon or something. Here’s the followup video if you’re interested to see this car driving around: