Old Internal Combustion Engine — Drawing

How Your Car Engine Works

By Mike Ales

Here’s what you know: You buckle up and turn the key. Your car comes to life. You pull the shifter into “D” and you drive. Oh, maybe you push a start button instead, or maybe you have to push in the clutch pedal because you sport around with a five- or six-speed manual transmission. Still, as comfortable as you are operating your car, truck, or SUV, do you know how it works? It could be that you are perfectly content with the knowledge that, as long as you take your vehicle in for regular maintenance it will start every time you get behind the wheel. But, maybe you are curious as to what makes it tick. What lies beneath the hood. If so, here is an overview of how your engine works.

Energy to get up and move

Here is one way to look at how a car engine works. You put fuel (gasoline) into the tank. Somehow that fuel is changed into motion. How? Chemical energy stored in the fuel is ignited inside cylinders in the engine. Thermal energy is released as a result of the combustion and is converted to kinetic energy as rapidly expanding gases force pistons to move in the cylinders. The linear energy of the pistons moving up and down is converted to rotational energy as they turn the crankshaft. The power produced by the engine is then handed off to the transmission, that transfers the energy to the wheels.

YAWN! Too abstract? Then consider the bicycle.

Pedaling a bike

The pistons inside your car’s engine move up and down in succession, effectively “pedaling” the crankshaft in the way that you would pedal a bicycle. When you pedal a bike, you are converting chemical energy (stored in the food you eat and processed by your body) into kinetic energy (the muscles in your legs moving the pedals). The linear movement of your legs up and down on the offset pedals transfers energy to the rotating crank connecting the pedals. Attached to the crank is the sprocket that moves the chain and ultimately the back wheel. Your car does the same kind of thing. The pistons pedal the crankshaft and the transmission, like the chain and sprocket on your bike, transfers power to the wheels.

Too simple? Okay, here is a fuller scoop.

Suck, squeeze, bang, blow

The internal combustion engine beneath the hood of your car is what is known as a “four-stroke” or “four-cycle” engine. That means each piston goes through four motions (or strokes) as it turns the crankshaft. Together, these four motions total one cycle.

First, a mixture of fuel and air is drawn, or “sucked”, into the cylinder during the intake stroke. Next, the fuel/air mix is squeezed (compressed) during the compression stroke before it is lit on fire by the spark plug. This is the “bang”, the power stroke where the expanding combustion gases force the piston downward in the cylinder. Finally, the exhaust stroke “blows”, or releases, the exhaust gases before another intake stroke begins the next cycle. Intake, compression, power, and exhaust. Suck, squeeze, bang, blow. That’s how your internal combustion car engine works.

Now, to make that happen, there are many parts executing their roles in the play. From beginning to end, here are some of the major players.

The engine block has a series of four to eight (sometimes ten or twelve, but not usually) cylindrical holes or cavities inside. These holes are called cylinders. If the engine has four cylinders, it is considered a (wait for it) “four-cylinder” engine. If it has six cylinders, well, you get the picture. When it comes to car engines, therefore, a V8 is not a spicy tomato beverage, it is an eight-cylinder engine.

Inside each cylinder lives a piston, a solid cylindrical object that slides up and down inside the cylinder. Think of the plunger inside a syringe. The syringe body is like a cylinder and the plunger is like the piston. The pistons in your engine fit snugly inside their cylinders yet, lubricated by engine oil, slide up and down the length of the cylinders.

The area above the top of the piston inside the cylinder is the combustion chamber. This is where the fiery action takes place. When the piston is pulled down in the cylinder, a vacuum is created that draws in fuel and air. Once the fuel/air mixture is inside the cylinder, the piston moves upward and compresses the gases. When the piston reaches its highest position, the spark plug ignites the compressed gases and a controlled “explosion” (a chemical reaction, really) happens and forces the piston downward again. The energy released in combustion moves the piston with a lot of force.

The piston is connected at the bottom by way of connecting rods to the crankshaft. The crankshaft is a thick, heavy, weighted rod that spins in response to the movement of the pistons. This is where the bicycle analogy comes in. The pistons “pedal” the crankshaft.

Of course, just as you can’t push down on both bicycle pedals at the same time, all of the cylinders cannot fire simultaneously. So, your engine is made to harness a series of explosions in rapid fire all happening at the proper times. Think about it. Let’s say your engine has four cylinders. Each cylinder has to breathe in fuel and air. The gasses must be compressed by the piston. The compressed mixture must be ignited and the spent gases must be released. And all of those things have to happen in all four cylinders at the right time and in the right order.

Enter the valves. Sitting above the cylinders is the intake manifold. This is where the air and fuel enters the engine. The intake manifold is perched on top of the cylinder head(s). The head is the cap on the top of the cylinders. Protruding through the head is the spark plug as well as the intake and exhaust valves.

The intake valve opens to allow the fuel and air to get into the combustion chamber and closes to allow compression to take place. The exhaust valve opens to release the spent gases and closes to allow intake to happen. These operate in succession in each cylinder.

In order for all of these functions to happen in concert, a conductor is needed. In your engine, the conductor that keeps everything in perfect time is known as the timing belt, a ribbed rubber belt that spins one or more crankshaft(s), which in turn opens and closes each valve when it is supposed to. Some engines feature a timing chain instead of a belt, but the object is the same.

All this and more…

Of course, there is a lot more that goes into keeping your engine going. Heat from the combustion process has to be handled by the cooling system — the water pump, radiator, thermostat, fans, and coolant. The starting and charging system uses a battery, starter, and alternator (among other things) to start the engine and power all the electrical needs of your car. The air conditioning compressor keeps the AC working and the power steering pump makes turning a lot easier. Each of these systems is driven by the engine, some by way of a fan belt (the serpentine belt). Then there are the sensors, emission controls, and more. And all feeding data to a computer (the engine control module, or ECM) that controls, well, almost everything.

TMI? It goes on from there. But at least you have a rough run-through of how your engine works. It is no surprise, with all of its complexities, that it takes a lot of training and experience for a professional to adequately service your engine. Now that you have a basic understanding, why not have an informed conversation with the folks at a trusted repair shop about how your engine is working.

Riverside Automotive | Author: Mike Ales | Copyright September 2018

This article is intended only as a general guidance document and relying on its material is at your sole risk. By using this general guidance document, you agree to defend, indemnify and hold harmless Riverside Automotive and its affiliates from and against any and all claims, damages, costs and expenses, including attorneys’ fees, arising from or related to your use of this guidance document. To the extent fully permissible under applicable law, Riverside Automotive makes no representations or warranties of any kind, express or implied, as to the information, content, or materials included in this document. This reservation of rights is intended to be only as broad and inclusive as is permitted by the laws of your State of residence.

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