 From this diagram, we are going to learn how basically an automobile engine works. This is a cylinder. This is basically one cylinder that we have. And these are the walls of the cylinder. And this is the piston that we have. And this piston is what moves up and down. And we have two inlets. One inlet is for fuel and air to come in a mixture. And this is a valve that opens and closes. And there is another outlet here that takes out the exhaust gases. And there is another valve that opens and closes at appropriate times. And when the fuel and air mixture is inside, this spark plug provides a spark to ignite the mixture. Now let's see in sequence what happens in this cylinder. This piston basically moves up and down. So the first step is to bring the fuel and oxidizer or air inside the mixture. So this valve opens up. This valve, of course, is closed. And this fuel and air mixture comes in as this piston is pushed down. This acts like a syringe, a medical syringe. When we push this down, the fuel and air mixture is basically sucked in, and it fills up this entire wall room as this piston comes down. That is the first step or stroke. This is a four stroke engine that we are talking about. First stroke is intake. And the second stroke now, the second step, is we close both of these valves and push this mixture. This mixture is, again, by pushing the piston up, this mixture that is in here is compressed to very high pressures, roughly about eight times to nine times. And this piston moves back up here. And again, we have to spend energy to move this piston up or compress this mixture here. When this mixture is compressed to the pre-determined pressures, at that time this spark plug ignites this mixture. And this flame front travels all the way and burns all this fuel. And this fuel reaches very high temperatures and it pushes the piston all the way down, all the way down. So this is actually the power stroke. The first stroke is intake. The second stroke is compression. Compression. And the third stroke is the power stroke. That is the stroke that gives us the power from this engine. And the first stroke and the second stroke, we have to supply the energy that is required to bring in the oxidizer and fuel and also to compress. And after this mixture expands or pushes the piston down, this valve, this exhaust valve, will open. And of course, this valve is still closed. And the piston, again, moves back up, for which we have to supply the power. And all these gases go out through this exhaust. And once the exhaust gases are out, this cylinder, this valve closes again and this valve opens and the entire cycle again repeats. So the fourth stroke is the exhaust stroke. So this is a force, basically, four stroke engine that we are talking about. We need to know the four strokes and the important components of this engine cylinder. And there generally will be multiple cylinders. We are talking about one here and there could be four. There could be six. There could be eight or even 10 or even 12 sometimes. So as the engine becomes bigger and bigger, you have more cylinders. And that gives us more power.