LESSON 2:

ENGINES

Welcome to the Engines Lesson!

What really happens when you turn the key and your engine starts up? Most of us give little thought to the miraculous technologies that are found under our own hoods!

In this lesson we will explore the operation of the four-stroke engine that is at the heart of the automobiles we have been driving for decades. We will learn how these engines burn gasoline or diesel in order to produce the power needed to propel us down the road.

We live in exciting times in relation to our society’s

transportation challenges. While hybrids and other alternate-fueled vehicles are on the increase, even most of these vehicles are powered by the same types of internal combustion engines we are familiar with now.

How an Engine Works:

An engine is made up of pistons that travel up and down inside of cylinders in a housing called an engine block. As each piston goes down, it pulls in air and fuel, and then it comes back up and compresses that air/fuel mixture. Next, the mixture is ignited, causing an explosion which forces the piston back down. Finally, the piston travels back up, forcing out the “leftover” exhaust gases.

As the pistons move up and down, they cause the crankshaft to turn, much like

the pedals on a bicycle.

An engine must convert the stored energy in fuel (gasoline or diesel) into the power needed to propel the vehicle down the road. It does this by burning the fuel inside the engine (internal combustion). Here’s how it works:

Crankshaft (green)

Pistons (gray)

Engine ValvesFor each piston in the engine, there are two valves. One is called the intake valve, and opens to allow the air and fuel to come into the cylinder. The other is called the exhaust valve and opens to allow exhaust gases to escape.

The valves are pushed open at exactly the right times by the “lobes” on a camshaft, as shown in the

animation to the right.

Camshaft

Lobes

What is a four-stroke engine?

You may have heard the terms, “four-stroke engine” and “two-stroke” engine.” These names refer to the number of steps that must take place inside the engine in order for the engine to complete one power cycle.

All of our automobile engines and most lawn mower and ATV engines today are “four-stroke engines,” while two stroke engines can be found in chainsaws, weed eaters, and some motorcycles.

For our purposes, we will only discuss four-stroke engines. In the next four slides, we will examine each “stroke” of your car’s engine.

Optional link: Click here to learn more about two-stroke engines.

1st Stroke: Intake

The intake stroke occurs as the intake valve opens and the piston moves down, sucking in fresh air mixed with fuel vapor. The air comes from the atmosphere and must pass through the air filter before entering the engine. The fuel is injected, (or sprayed) into this incoming air right before it enters the engine.

Did you know? Ideally, the air-to-fuel ratio is 14.7 parts of air to 1 part

fuel for gasoline engines. If too much or too little fuel is mixed with the incoming air, the car will run poorly, possibly damaging the engine. Your car’s computer

carefully meters the amount of fuel that is injected into your engine.

2nd Stroke: Compression

The compression stroke plays an important role in the combustion process. With air and fuel now in the cylinder, the piston travels up, compressing the mixture. There are two reasons that the compression stroke is necessary:

1. It makes the mixture compact and dense, so that when it is ignited, the pressures will be higher.

2. Compressing the air/fuel mixture heats it up, preparing to be burned efficiently and completely.

3rd Stroke: Power

During the power stroke, a spark occurs at the spark plug, igniting the air/fuel mixture, causing a rapid expansion of gases inside the cylinder. This forces the piston back down in the cylinder.

The purpose of the previous two strokes was to get the air and fuel in the cylinder and to prepare it to be ignited. The power stroke is what actually makes the engine turn, giving the crankshaft and pistons the momentum they need continue moving in the other strokes.

4th Stroke: Exhaust

The exhaust stroke is where the left-over, or spent gasses from combustion are cleared out of the cylinder. It is necessary to clean out the exhaust gases in preparation for the next intake stroke so that there is a fresh charge of air and fuel. The exhaust valve opens and the piston simply pushes out the exhaust gasses as it travels upward.

As soon as the exhaust stroke is over, the exhaust valve closes and the intake valve begins to open, beginning another intake stroke.

Engine Video:

Watch the video clip listed below. While watching, pay especial attention to the second half of the video, and try to understand what really occurs inside an internal combustion engine.

After watching the clip, see if you can:

1. From memory, list the FIVE events that make the engine operate.

2. Explain what the pistons and the valves are doing during each event.

Click HERE to view the movie

Timing Chain / Timing Belt

Now that you understand how an engine works, you may recognize that the pistons and valves need to be synchronized in order to work. Obviously, if the intake valve didn’t open during the intake stroke, or if either valve opened during the compression or power strokes, the engine could not run. For this reason an engine must have either a timing chain or a timing belt.

To complete an entire four-stroke cycle, a piston must go up and down twice, but each valve only opens once. This means that the camshaft turns half as fast as the crankshaft.

A timing chain or a timing belt ensures that the camshaft and the crankshaft maintain this ratio, so that the valves open at exactly the right times.

Timing ChainCrankshaft sprocket

Camshaft sprocket

Timing Belt MaintenanceWhile timing chains require no scheduled maintenance, timing belts do! You should know whether your car’s engine has a timing belt or a timing chain, because it is imperative that you know when it needs to be serviced. Typically, timing belts need to be changed about every 80,000 miles, but check your owner’s manual to find out specifically when your timing belt should be changed.

If a timing belt is not changed on time, it may break while the engine is running, causing the pistons and valves to hit each other. While it may cost $250-$500 to have the timing belt changed, it could cost $2000-$6000 to repair engine damage and you will be left stranded if the belt breaks.

Note: Your timing belt is under a cover and cannot be seen when you open your hood. Do not confuse it with your accessory belts that you can see. The timing belt should be changed by a professional, as major engine damage can easily result if it is done incorrectly.

This photo shows the top of a piston that was

hit by valves when a timing belt broke.

Timing BeltCamshaft sprocket

Crankshaft sprocket

Here’s a chance to identify some engine components:

More engine videos!Take some time to view two more videos. They are well-worth watching and will help you to see how engine parts fit together and to understand how the combustion process works… enjoy!

They are accessed from the next two slides.

While watching the videos, identify the following:

1. Pistons2. Crankshaft3. Valves4. Cam shaft(s)5. Timing chain6. Engine block7. Identify the Four strokes

Engine Operation Video:If the video below doesn’t start playing automatically, return to I-learn and watch

the two videos entitled “Engine Operation” and “Engine Components.” Both videos are excellent and worth watching.

Engine Components Video:If the video below doesn’t start playing automatically, return to I-learn and watch

the two videos entitled “Engine Operation” and “Engine Components.” Both videos are excellent and worth watching.

IMAGINE THIS!The videos you just saw show how all of the components work together to make an

engine work. However, in your car, it happens a lot faster than this. When you are stopped at a stoplight and your engine is idling, the crankshaft is turning about 1000 revolutions per minute (RPM). This means that each piston in your engine goes up and down over 16 times per second.

When the light turns green and you accelerate quickly, the engine may run at nearly 4000 RPM. This means each piston travels up and down 66 times per second, and each valve opens 33 times per second! And to top it off, your engine will continue to run like this for many years and for hundreds of thousands of mile—if you take care of it!

This may seem incredible, but it is real—and it demonstrates just one of the miraculous technologies that makes our cars run. The people who have invented and improved upon the internal combustion engine over the years have obviously been inspired by our Heavenly Father to do so. If we are observant enough to notice, we will see His hand in all of his creations around us; “yea, and all things denote there is a God; yea, even the earth, and all things that are upon the face of it . . . do witness that there is a Supreme Creator.” –Alma 30:44

The Need for Cooling & Lubrication

You already know how fast the engine parts move. You may also be interested to know that combustion temperatures inside the engine can reach as high as 4500°F. However, the engine components must be kept at about 200°F or the engine will be damaged.

As you can imagine, keeping the engine block, pistons, valves, and all the

other moving parts in an engine cool and well-lubricated is critical to engine life. Motor oil is often referred to as the engine’s ‘life blood’. Without motor oil and coolant the engine would literally get hot and parts would seize together within 30 – 60 seconds of operation. On the other hand, with proper lubrication and cooling system maintenance a typical gasoline or diesel powered engine should last at least 200,000 miles, and often much more!

More than ever, today’s vehicles require very specific oils and coolants, and have very specific maintenance schedules. Using the

right fluids and changing them at the right times is crucial. Next week’s lesson will cover this in greater detail, but if you are not

familiar with the maintenance schedule in your car’s owner’s manual, now is the time to get acquainted with it!

Starting an Engine

To start an engine, the crankshaft must be rotated, which causes the pistons and valves to begin their jobs of creating the four strokes.

In the old days, people “cranked” their engines by hand—something we still do when we pull-start a small engine like a lawn mower. As you can guess, cranking a large automobile engine by hand was inconvenient and even dangerous at times.

Today, when a driver turns the key to the “start” position, an electric motor is energized, which “cranks” the engine

automatically by turning a gear on the crankshaft.

How is Engine Size Determined?

In the previous lesson, you learned how to find the size of your car’s engine by looking on the under-hood sticker, and that engine size is usually measured in Liters. But what does this size mean?

Engine size is determined by the volume of the cylinders that the pistons travel in. Increasing the size or number of cylinders in the engine will increase the “engine size.”

You may have heard the terms “V8 engine” or “inline-4 engine.” These refer to different engine designs and to how the pistons are laid out. For example, an “inline-4” engine has four cylinders (and four pistons) all in a row. A “V8” has eight cylinders that sit at an angle, resembling a V.

Opposed-4

V-6Inline-4

CONCLUSION

The internal combustion engine has been around for many years and will be for years to come. Most of the alternative energy sources being developed for our transportation needs still incorporate a piston engine. One day we may see proven technologies compete with it, but for now and for the foreseeable future many of our society’s needs will still be met with the four-stroke, fossil-fueled piston engine.

Gaining an understanding of how an engine operates helps us to be more conscientious car owners. Hopefully, it will also help us to appreciate the importance of maintaining and caring for the amazing machines we rely on to get us around each day!