 The last thing that I want to cover in today's class is just a few more terms, acronyms and terminology pertaining to engines and gas power cycles. Now typically the engines that you'll find in a car are liquid cooled engines and so the cooling is provided by a liquid jacket which surrounds the engine. There are other types of engines typically like the ones that we saw for the two stroke and the four stroke for the edge tremor as well as the lawnmower. Those are air cooled engines and the way that you can detect an air cooled engine by looking at it is you'll see cooling fins sticking off of the engine itself and so in air cooled engines fins provide cooling and so if you've taken a course in heat transfer you would look at the efficiency of fins and a very famous car that had this was the old Volkswagen Beetle. That was what we call an air cooled engine early aircraft also had air cooled engines that you would find in the 1910s 1920s and the advantage of air cooled is you have a weight reduction you don't need to have the cooling jacket and all of the pumps and the radiators and things associated with liquid cooled engines and liquid cooled engines we have a water jacket surrounding the engine and what this does is it provides cooling because the engine gets hot and we need to reject that heat and within the cooling jacket what we would be running is a fluid typically a mixture of ethylene glycol and water. Now some other things uh if if you see engines or cars on the road sometimes you'll see numbers on the side of the engine like 5.0 4.4 3.0 quite often that is referring to the total engine displacement and they now do that well at least in North America and leaders they used to do it in I think it was cubic inches actually a 302 uh I don't think it was cubic centimeters I believe it was cubic inches but anyways what this refers to would be essentially the displacement of the engine so it'd be the swept volume so the bore squared that's the diameter of your cylinder and then so the area of that times the stroke multiplied by the number of cylinders typically that could be anywhere from a four cylinder engine to a six cylinder engine you could have an inline six a v six so they're in a v configuration in line would just be straight eight cylinder engine and 12 cylinder engines and other variabilities of that but for the engine displacements you've probably seen numbers like 5.0 liter 2.2 liter 4.0 liter that's what they're referring to when you see those numbers other terminology distributor less ignition on old engines they used to have a distributor and what that would do it was doing the timing of triggering when the spark would actually fire and so you had the distributor which was connected to some of the mechanical components of the engine for timing and control and it would spin around and you would have a mechanical contact which would then send a high voltage to the spark plug which would cause a spark and it was timed properly in order to have the combustion at the right point of the cycle so for that we had an ignition coil which essentially is a device that could generate a very high voltage for us for each spark plug other acronyms that you may see on engines DOHC that refers to double overhead cam and what the cam is if you've taken a course in doing cam design as part of mechanical engineering programs the the cams are used to open and close the valves and those are the things that allow the fresh air and fuel mixture to come in and then the exhaust gas go out but with a double overhead cam that particular design is one cam is for the inlet valves or the intake valves and the other the exhaust valves and there are a lot of different designs for that sometimes there will be a rocker arm in the at the top of the engine that the cams are connected to and that rocker is basically like a teeter totter and that is what opens and close the valves the valves will have a spring connected to them which keeps them in the closed position normally but then you would depress to open them so that's double overhead cam OHV that's overhead valve and here you would have your camshaft in the engine block and then that is connected to push rods which go up to your rocker arm to open and close the valves and so to draw a little schematic of this down here would be your crankshaft your camshaft might be connected to that mechanically with either a timing chain or some other mechanical connection and then there's a lobe on the cam on the camshaft and then that pushes this push rod up and down and then here you would have your rocker arm so I'll just draw it like that like I said it's a teeter totter and then it would be connected to your valve which is over here and the valve itself would have this spring on it on the top so normally it would be in the closed position and as this moves up this is going to move down and given that it has a lever advantage it could then push and open the valve or it would close the valve so that's the mechanism by which the overhead valve would work EFI you won't see this very often now because most engines will have it but electronic fuel ignition this was coming out in the 1980s if you look at older engines you will have and here what we have is a fuel injector sprays fuel into the inlet manifold which is where the air is coming into the engine it goes through an air cleaner first to get all the particulate and dust and particles out but then it'll be flowing into the engine the fuel injection or the fuel ignition the fuel injector will spray fuel in that then flows into your cylinder which would then be compressed and and combust but you would do this instead of a beautiful piece of mechanical engineering instead of using you would have your fuel injector but it's replacing what used to be used which was the carburetor which is a beautiful piece of mechanical engineering if you ever get a chance to take one apart and study it the reason is because you have a combination of fluid mechanics and thermodynamics all in this one device where essentially you have a venturi and you accelerate the flow down and so this is the jet of your carburetor and in here and there are many many different designs but you have a low pressure zone by Bernoulli's equation you're accelerating the air coming in and that would be the air going out but you're accelerating and consequently you're at a low pressure and that draws the fuel in and so you get little fuel droplets here carburetors weren't very efficient though because you wouldn't atomize the fuel that well you could flood the carburetor you could do all kinds of things but with electronic fuel injection instead you have a device that a very high pressure will spray in a mist and that that's how the fuel then enters into the air stream much more efficient in terms of the combustion that you get out of that other things you might find knock sensors and what this is it's a device that detects pinging and what that is pinging of an engine is pre-ignition where the combustion process is beginning too early so while the piston is moving up you you want the combustion to start a little bit before it gets the top dead center but not too much earlier or what will happen is you get expansion while the piston is still moving up and that will cause all kinds of problems for your engine it could destroy it with time and that's sometimes referred to as being knocking and a mechanic would be able to detect the knocking of your engine if it's really bad you'll notice because it's going to be very very rough rough idle of your engine multi-valve engine here the standard is one exhaust one inlet per cylinder and what multi-valve has is two exhausts two intake per cylinder and you'll see these for example if it's a four-cylinder engine it would be 16 valve and you'll sometimes see this on the back of the car 16v that would denote 16 valve or sometimes you'll see even 24 valve double overhead cam these are different acronyms that you'll see on cars on the engine block itself and the advantage with having multi-valve engine is you have better volumetric efficiency of the engine and so what you're able to do is draw in the air you're essentially reducing pressure drop and so it can breathe better so it can draw in your air fuel mixture more efficiently and it can exhaust the burnt hydrocarbons and more effectively as well and a final thing that I want to say another acronym is VVTL-I variable valve timing and lift and there is a lot of other technology a lot of research has been done on internal combustion engines over the years and some of that research makes its way into practical applications and real world engines but this one is one that was developed and so it's variable valve timing and lift and then the dash I is with intelligence and what does this do it varies the amount of lift and for your valves and when they overlap so it's similar to having two different contours on your camshaft because if you've studied cam design you'll know that the shape of the cam itself can have an effect in terms of when your valve would open or close and so with this you could essentially have different types of cams and by just changing it electronically