So let's now have a look at some of the differences between a petrol engine and a diesel engine. Now I've loaded up another 3d model. And you can see this one's got some markings and indications on it. We'll load up the annotations so that we can actually click on each of these markings. And we'll get a bit of a description. And we can sort of read our way through some of the terms.

So we have our annotations. This model is also available online, so check the resources section of the course or just head over to sabri.com. Click here, you can see things such as the clearance volume, the cylinder bore, and things like that. I strongly recommend that you load up this 3d model yourself and check it out. It's especially useful if you want to learn some terminology. But the areas we're interested in alignment, our number eight, which is clearance volume, that's the distance From top dead center to the top of the cylinder liner.

In other words, if the piston travels up to this height here, the clearance value is from top dead center the top side of the piston up to the top side of the cylinder liner. So that is known as clearance volume. We have a look over here, number 14, this is the stroke. This is the difference between TDC and BDC. But we also refer to that as a swept volume. We say sweat volume because area is for example centimeters squared meters squared, inches squared.

If you are working with Imperial measurements, and it to calculate volume, we take the area and we multiply it by the length. Now the length in our example here is simply the distance between BDC and TDC. So we pool that swept volume. That is the volume the piston is sweeping as it moves upwards. The reason that I'm highlighting the clearance volume and swept volume is because when we compare them together, we end up with something called the compression ratio. The compression ratio is the sweat volume, plus the clearance volume.

So that is essentially the total volume within the combustion space, and then we divide it by the clearance volume. Now looking just for example, sweat volume here, we can see that the sweat value is perhaps 10 or 12 times bigger than the clearance volume. That's just an approximate guess let's say 12 times bigger. So our compression ratio here is 12 to one. One of the differences between petrol and diesel engines is that petrol engines have quite a small compression ratio compared to diesel engines. petrol engines will ever come ratio between about seven to 12 to one.

Diesel engines have a compression ratio between about 13 or 14 to one up to 25 to one. Now 25 to one is a very large compression ratio. So let's just say for argument's sake that petrol engines have a compression ratio of about eight to one. And diesel engines have a compression ratio of about 16 to one. So diesel engines have a compression ratio, which is double that of petrol engines. That's not always true, but let's just keep that as a rough approximation.

That makes the diesel engine more efficient. The power stroke is longer in a diesel engine comparatively compared to a petrol engine. Not only that, but the pressure reached within the combustion chamber. Because of this increase in the compression ratio. The pressure reached at the top as a piston approaches TDC is far greater than that that can be achieved in a petrol engine. This is also an aspect of what makes a diesel engine more efficient.

If you start with a higher pressure shortly before the power stroke, then you have more pressure energy that you can turn into mechanical energy. And that's exactly what a diesel engine does. Because we have a higher pressure within the combustion chamber of a diesel engine, all of the parts of the diesel engine will need to be slightly larger than that of a petrol engine. This is one of the reasons why diesel engines are heavier, and also why they're quite clunky. If you listen to a diesel engine, you'll hear that it's actually a little bit louder than a petrol engine. And it also just sounds a little bit slower.

The pulses from the exhaust gas manifold or the tailpipe is slightly louder and a little bit easier to identify. So next time you pass a car or a truck, have a listen and see if you can identify the type of engine that's installed. I can guarantee you they do sound very different. Another difference between petrol and diesel engines and some people would argue this point is that diesel engines tend to smell a little bit more than petrol engines. Now, I never really believed people so much when they said this, they're always saying our diesel stinks petrol not so much. But I can say after living in the city for almost 10 years that diesel does stink, not a petrol is particularly so much better, but in my opinion, burn diesel does give off a stronger smell than petrol.

Again, people would argue this point. And the final difference that's easy to identify between a diesel and a petrol engine is simply that a diesel engine does not have spark plugs. Remember, diesel engines are compression ignition engines. petrol engines are spark ignition engines, they require a spark plug. It's the heat in a compression ignition engine that causes the fuel to ignite. Whereas for a petrol engine, it's the spark that causes the fuel to ignite.

So if you see spark plugs, you will know immediately it's a petrol engine. Another difference that you may notice is the position of where the fuel is injected. Now I say may because some petrol engines inject fuel directly into the cylinder liner, and they'll look quite similar to a diesel engine except they will have spark plugs. So check the position of the injectors as well. If the fuel has been injected not directly into the combustion space, it will not be a diesel engine, diesel engines always inject the fuel into the combustion space directly. For petrol engines, this is more of an option rather than a certainty.

Another slight giveaway with diesel engines is that many of them are turbo charged. That allows us to get more air into the combustion space. But not all diesel engines are turbocharged. We can have a look at a turbo charger a little bit later in the course. So now you know some of the differences between a pectoral and a diesel engine. Let's go and have a look now what I refer to as the life support systems of an engine.