 The next thing we're going to take a look at is the engine terminology. Whenever we're working problems involving either a spark ignition or a compression ignition engine, there's a lot of terminology that goes with it and consequently I find it quite helpful to review some of the terminology. For those of you who have taken a high school mechanics course or like to play with engines and work on them, then a lot of this will be a bit of a review. But for those of you who have not had the time or the chance or the opportunity to play with engines, then you may find this to be somewhat beneficial. So what we'll begin doing is sketching out a schematic of a vertical single cylinder engine and the type that we will look at could either be compression ignition or it could be spark ignition because I will not specify whether or not there's a spark plug in it. However, I'll begin by sketching that out. So there we can see a schematic with all of the different components of the engine drawn on it and what we have is the piston cylinder device within the engine and so here the piston is in this part right here of our engine drawing and it is within the cylinder and it moves up and down. At the top of its stroke it is at top dead center which is TDC and at the bottom it is at bottom dead center. There is a little bit of clearance at top dead center so it doesn't go all the way to the top. You'll notice there are a couple of things sticking in here and I didn't note them on the drawing. These are valves and so you'll have your inlet and your exhaust valve. Those open and close depending on what part of the cycle you are in. There are rings around the piston and what the rings do is they ensure a seal. So we have high pressures developing within our engine and they ensure that we have a seal within the engine and there's also another ring it's called the oil ring and what that does is it wipes the oil down off the wall of the cylinder itself. The piston moves up and down as we bring air in and there's also a fuel that would be mixed in with the air. It then moves up and compresses and if it's a compression ignition engine there would be a glow plug somewhere right in here or if it's spark ignition there would be a spark and that would cause the our charge to detonate and then start to combust and then you would expand down and moves back up and it exhausts out through the delivery and down below you'll notice the piston is connected through a connecting rod which is shown here and it's connected through a crank pin into a crank and a crankshaft. The crankshaft moves around and that is what connects then to the transmission of your car or whatever device you're looking at extracting power from. There's oil in the bottom and that oil provides lubrication for the engine itself. So that's kind of a quick schematic of the engine. What we're going to do now is I'll write out some of the terminology and and the definitions of the the terminology so that you're aware if you come across them as you're reading about these cycles. So I had mentioned TDC that refers to top dead center and that is when the piston is at the highest point in the cylinder we had BDC and that refers to bottom dead center. Now I'm talking here about stroke but I have not defined the stroke it was on the drawing that refers to the distance that the piston moves up and down and it says it's moving up and down from top dead center to bottom dead center. We had on the drawing bore what bore refers to is the diameter of our cylinder. On the drawing I had clearance volume that is the volume of the gas in the cylinder that when we're at top dead center. There's also a displacement volume and what that is that's the volume displaced by the piston as it goes from top dead center to bottom dead center. Compression ratio we will talk quite often about the compression ratio of different engines and what this is it's a very important thing because it enables us to quantify the efficiency of the engine but numerically it is designed or defined as being Vmax over Vmin so the volume at bottom dead center divided by the volume at top dead center. So it basically quantifies how much we're compressing the air fuel mixture that we would have within our piston or within our cylinder. Another is MEP and you'll hear this quite often in discussion of engines that this is the mean effective pressure and we can quantify this by writing out the network out of the engine is equal to the mean effective pressure times the piston area times the stroke and so with that we can isolate for mean effective pressure is the network out of the engine divided by Vmax minus Vmin. So that would be a way that you could calculate your mean effective pressure and finally two other acronyms that we will see sometimes we write SI and that refers to spark ignition that would be the type where you have a spark plug at the top of your engine and it sparks when you have compressed your charge and there's also CI and that refers to a compression ignition engine it's the diesel that we talked about earlier. So those are some of the terminology that the terms that we will need as we look at engines and engine cycle analysis specifically the spark ignition and the compression ignition engine. What I want to do next is take a look at two different types of spark ignition engines.