Aviation Training Tip: Spark vs Compression Ignition

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1:07binders and tracking, quizzes, logbook audits, endorsements, and more. And you can try every single one of our courses for free for as long as you would like at Wi-Fi-CFI.com. There's basically two different types of ignition that you can also have in these reciprocating engines. First, there's spark ignition, and this is where spark plugs combust the fuel and air mixture in the cylinders. This historically has been more popular in GA aircraft, but there are also compression ignition. And you'll find these in both like cars and aircraft. So spark ignition, you'd see that in some cars, and some compression ignition, you would see that in some cars and aircraft as well. Historically, like I said, spark ignition is more popular in general aviation aircraft, but that does not mean that some aircraft are not compression ignition. There are definitely compression ignition aircraft out there, and they do seem to be getting more popular because they seem to have more reliability since they have less parts. So spark ignition, that's where you have

2:10spark plugs. Within these cylinders, if we go back here, I show you again, we've got a 1, 2, 3, 4 cylinders. Fuel and air is getting drawn into these cylinders. It's sucking fuel and air in, and we're going to talk about how that works in a minute. But once the fuel in the air goes in there, there needs to be some way to make an explosion. We need to ignite that fuel and air mixture, because once we explode it, that's how the, that's what pushes the pistons back and forth, and that's what makes the pistons move. So when we're talking about ignition, we're talking about how do we explode that fuel and air mixture where you can have spark plugs, right, which we just said. And these are little plugs, which we'll see in a minute that create a little spark, and that explodes it. Or with the compression ignition, there are no spark plugs. How this works is that ignition happens by compressing the fuel and air mixture to the point where they ignite under their own heat. We're compressing that fuel and air so hard and so tight that it gets so hot and it just ignites on its own. Does not need the electricity from a spark plug

3:13to do it. So these engines do not utilize spark plugs. If you want to know what your aircraft has, hop into your aircraft's POH and you'll be able to find out if it's spark or compression ignition. Both engines use, whether it's spark or compression, it doesn't matter. Both engines use cylindrical combustion chambers and pistons, which we were just talking about, pistons convert linear motion to rotary motion through the crank shaft. So the piston motion, this is linear motion back and forth. If it goes back and forth, it causes the crank shaft to spin, which the crank shaft will be going this way. The only difference between the spark and compression ignition is how the fuel air mixture is ignited. We just said that. And this is a little diagram. This isn't exactly really how most aviation spark ignition aircraft look, because most airplanes, like small GA aircraft, will actually have two of these spark plugs. So this would be more like for a car. But we are going to look at some pictures in just a minute where the engine has two different

4:18spark plugs. All right. So here we go. This is our piston right here inside the cylinder. The cylinder is just kind of this whole unit. Here's the fuel and air mixture is getting compressed by the piston. And then the spark plug ignites and causes the explosion. Over here on compression ignition, you can see we've got no spark plug. But you can also see the piston goes a little bit higher. It condenses this fuel air mixture even tighter and makes it really, really hot. And then it just explodes on its own. So you don't need a spark plug in a compression ignition engine. Just spark ignitions.