What's going on in there?
A car engine can look like a big confusing jumble of oily bits of metal, tubes and wires to a muppet like our Editor....however the internet came to the rescue...

What the hell does "5.0 liter V-8" and "dual overhead cams", "tuned port fuel injection", "headers", "TurboChargers" and "SuperChargers" mean. Typically the Ed. thought "ET's" were cute little aliens.

What does all of that oily speak mean?

The Basics

The purpose of a petrol car engine is to convert all your money into petrol which you then stick into your gas-guzzler's fuel tank. Then like a miracle, something mysterious happens to it and it's all converted into the motion of your car ....hopefully in the direction you wishyour pride'n'joy to go....

The easiest way to create motion from petrol is to burn the petrol inside an engine. Therefore, a car engine is an internal combustion engine -- combustion takes place internally. You're royally stuffed if the combustible material is burning outside your engine....

Two things to note:

• There are different kinds of internal combustion engines. Diesel engines are one form and petrol engines are another. Only engine worth bothering with is the petrol....
  
• There is such a thing as an external combustion engine. A steam engine in old-fashioned trains and steam boats are the best example of an external combustion engine. (I'm a fan of all things engineering/mechanical/electrical/steam so I don't discount 'em)....

Inside a typical car engine

Combustion Is the Key to motion.

Combustion means explosion by detonation of flammable material. Ideally you want anything that's exploding
containing within an enclosed space to maximise the explosive power of the heat/energy produced when combustion takes place. The enclosed space is called a combustion chamber. A chamber to 'combust' the flammable stuff. Explosions create heat / energy that expand outwards. Remember the pressure cooker...?

Heat expands stuff like air, gasses and metal. Your body burns up the fuel you stuff into it by using it to provide you with energy to be mobile, which in turn needs more fuel to keep you going or warm. All this provides waste product from the fuel (burgers) you've ingested and it has to exit through your exhaust pipe (arsehole).

Air that is Oxygen is necessary for combustion. Can't have a fire without it. We'll deal with the carburetor later when I've read up about 'em.

When the air has expanded in a closed chamber like your pressure cooker/stomach / bowel because your body has combusted your burgers into power/energy/heat....it has to find an exit or you'll blow up. Ergo you fart or burp.
Farting is a safety mechanism other wise we're talking walking bomb and entrails on the walls. Farting through your exhaust (arsehole) prevents dangerous gas build up.

Something has to ignite the fuel - a petrol engine uses a spark plug, which creates a 'spark' in the combustion chamber (diesels don't). When the petrol is ignited it creates heat and expanded gasses in the big oily thing's stomach -combustion chamber, requiring an exhaust for the exit of waste gasses etc. or it'll explode....

We all recognise the exhaust, or I do having spent a season wrapping bandages around my twin exhausts. The reason for twin exhausts will be explained later when I've worked it out.

The basic idea behind how an internal combustion engine works is to use a cannon as an example.
Load the cannon with gun powder and load a cannon ball down the tube then and light gunpowder...and run.... That is internal combustion. Remember the 'Spud gun'?

Remember your fart is expanded gas and the exit force can be awesome. Imagine if you put a tiny drop of petrol in a small pipe and then say that you stuff a potato down the pipe then light/add spark to the petrol. Like this:

 

What you have here is a device commonly known as a potato cannon. When you introduce a spark, you can ignite the fuel.

A potato cannon can launch a potato about 500 feet through the air! There is a huge amount of energy in a tiny drop of petrol.

Internal Combustion
The potato cannon uses the basic principle behind the internal combustion engine: If you put a tiny amount of high-energy fuel (petrol) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas. However if you block the passage you have a potato bomb or your entrails all over the place...

Valves open and close. They let stuff in and stuff out depending on whether they are open or closed. They are sealed doors (or should be sealed). Just like a stomach.

We need to let the petrol (burgers) into our combustion chamber - stomach so we can set fire/digest it. Petrol gets into the chamber (stomach) through the Inlet Valve it lets the petrol IN. Just like the gullet lets the food down into your tummy.

When the petrol is ignited the engine needs to get maximum energy / power from the petrol burned so it contains the power by closing any doors/valves in the combustion chamber.
To get rid of the waste gas it uses another Valve/ Door to let exhaust OUT the Exhaust Valve. You hopefully should have a bowel which acts like an exhaust system....it emits your emissions....hopefully nowhere near me...

The engine is built by clever people to create a cycle that allows the engine to set off explosions like this hundreds of times per minute, it can harness that energy and what you have is the core of a car engine!

The combustion chamber contains a snug fitting (hopes) Piston. This is like a snug fitting plug that gets pushed down on a rod that is connected to the Piston called a Conrod which is also connected to a lump of metal called a Crankshaft.

Almost all cars currently use what is called a four-stroke combustion cycle to convert petrol into motion. The four strokes are illustrated in Figure 1. They are:

• Intake stroke - the input of fuel/air into the chamber.
• Compression stroke - compressing it ready for firing
• Combustion stroke - setting fire to the mix
• Exhaust stroke - getting rid of the waste

Figure 1

This setup is enlosed in it's own Cylinder...

Understanding the Cycles

 

Figure 1
You can see in the figure that the piston replaces the potato in the potato cannon. The piston is connected to the crank shaft by a connecting rod. As the crankshaft revolves, it has the effect of "resetting the cannon." Here's what happens as the engine goes through its cycle:

1. The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and petrol. This is the intake stroke. Only the tiniest drop of petrol needs to be mixed into the air for this to work. (Part 1 of the figure)
2. Then the piston moves back up to compress this fuel/air mixture. Compression makes the explosion more powerful. (Part 2 of the figure)
3. When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the petrol. The petrol charge in the cylinder explodes, driving the piston down. (Part 3 of the figure)
4. Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tail pipe. (Part 4 of the figure)

Now the engine is ready for the next cycle, so it intakes another charge of air and gas.

Notice that the motion that comes out of an internal combustion engine is rotational, while the motion produced by a potato cannon is linear (straight line). In an engine the linear motion of the pistons is converted into rotational motion by the crankshaft. The rotational motion is nice because it's used to turn (rotate) the car's wheels.

Now let's look at all the bits that work together to make this happen.

Counting cylinders
The core of the engine is the cylinder, with the piston moving up and down inside the cylinder. The engine described above has one cylinder. That is typical of most lawn mowers, but most cars have more than one cylinder (four, six and eight cylinders are common). In a multi-cylinder engine, the cylinders usually are arranged in one of three ways: inline, V or flat (also known as horizontally opposed or boxer), as shown in the following figures.

Figure 2. Inline - The cylinders are arranged in a line in a single bank.

Figure 3. V - The cylinders are arranged in two banks set at an angle to one another.

Figure 4. Flat - The cylinders are arranged in two banks on opposite sides of the engine.

Different configurations have different advantages and disadvantages in terms of smoothness, manufacturing-cost and shape characteristics. These advantages and disadvantages make them more suitable for certain vehicles.

 

Displacement
The combustion chamber is the area where compression and combustion take place. As the piston moves up and down, you can see that the size of the combustion chamber changes.

It has some maximum volume as well as a minimum volume. The difference between the maximum and minimum is called the displacement and is measured in liters or CCs (Cubic Centimeters, where 1,000 cubic centimeters equals a litre).

Here are some examples:

• A chainsaw might have a 40 cc engine.
• A motorcycle might have a 500 cc or a 750 cc engine.
• A muscle car might have a 5.0 liter (5,000 cc) engine.

Most normal car engines fall somewhere between 1.5 liter (1,500 cc) and 4.0 liters (4,000 cc) but the really great cars have big stonking V8's stuffed into 'em and the cc's can be awesome.

If you have a 4-cylinder engine and each cylinder displaces half a liter, then the entire engine is a "2.0 liter engine." If each cylinder displaces half a liter and there are six cylinders arranged in a V configuration, you have a "3.0 liter V-6." Ergo 8 cylinders in a V setup is a V8.

Generally, the displacement tells you something about how much power an engine can produce. A cylinder that displaces half a liter can hold twice as much fuel/air mixture as a cylinder that displaces a quarter of a liter, and therefore you would expect about twice as much power from the larger cylinder (if everything else is equal). So a 2.0 liter engine is roughly half as powerful as a 4.0 liter engine.

You can get more displacement in an engine either by increasing the number of cylinders or by making the combustion chambers of all the cylinders bigger (or both).

    Other Parts of an Engine

An internal combustion engine

 

Spark plug
The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can occur.

The spark must happen at just the right moment for things to work properly.

Valves
The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust. Note that both valves are closed during compression and combustion so that the combustion chamber is sealed.

Piston
A piston is a cylindrical piece of metal that moves up and down inside the cylinder.

Piston Rings
Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two purposes:

• They prevent the fuel/air mixture and exhaust in the combustion chamber from leaking into the sump during compression and combustion.
• They keep oil in the sump from leaking into the combustion area, where it would be burned and lost.

Most cars that "burn oil" and have to have a couple of pints added every 1,000 miles are burning it because the engine is old and the rings no longer seal things properly.

Connecting Rod
The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston moves and the crankshaft rotates.

Crank Shaft
The crank shaft turns the piston's up and down motion into circular motion just like mincer turns and turns out minced meat from the meat shoved in the top.

Sump
The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom of the sump (the oil pan).

What Can Go Wrong
So you go out one morning and your Ford engine will turn over but it won't start... What could be wrong? Now that you know how an engine works, you can understand the basic things that can keep an engine from running. Three fundamental things can happen: a bad fuel mix, lack of compression or lack of spark. Beyond that, thousands of minor things can create problems, but these are the "big three." Based on the simple engine we have been discussing, here is a quick run-down on how these problems affect your engine:

Bad fuel mix - A bad fuel mix can occur in several ways:

• You are out of gas (duh), so the engine is getting air but no fuel.
• The air intake might be clogged, so there is fuel but not enough air.
• The fuel system might be supplying too much or too little fuel to the mix, meaning that combustion does not occur properly.
• There might be an impurity in the fuel (like water in your gas tank or you stick diesel in a petrol engine) that makes the fuel not burn.

Lack of compression - If the charge of air and fuel cannot be compressed properly, the combustion
process will not work like it should. Lack of compression might occur for these reasons:

• Your piston rings are worn (allowing air/fuel to leak past the piston during compression).
• The intake or exhaust valves are not sealing properly, again allowing a leak during compression.
• There is a hole in the cylinder.

The most common "hole" in a cylinder occurs where the top of the cylinder (holding the valves and
spark plug and also known as the cylinder head) attaches to the cylinder itself. Generally, the
cylinder and the cylinder head bolt together with a thin gasket pressed between them to ensure a
good seal. If the gasket breaks down, small holes develop between the cylinder and the cylinder
head, and these holes cause leaks.

Lack of spark - The spark might be nonexistent or weak for a number of reasons:

• If your spark plug or the wire leading to it is worn out, the spark will be weak.
• If the wire is damaged, cut or missing, or if the system that sends a spark down the wire is not working properly, there will be no spark.
• If the spark occurs either too early or too late in the cycle (i.e. if the ignition timing is off), the fuel will not ignite at the right time, and this can cause all sorts of problems.

Other Problems
Many other things can go wrong. For example:

• If you let a Chevy owner mess with your beloved Mopar.
• If the battery is dead, you cannot turn over the engine to start it.
• If the bearings that allow the crankshaft to turn freely are worn out, the crankshaft cannot turn so the engine cannot run.
• If the valves do not open and close at the right time or at all, air cannot get in and exhaust cannot get out, so the engine cannot run.
• If someone sticks a potato up your tailpipe, exhaust cannot exit the cylinder so the engine will not run.
• If you run out of oil, the piston cannot move up and down freely in the cylinder, and the engine will seize.

In a properly running engine, all of these factors are within tolerance.

An engine has a number of systems that help it do its job of converting fuel into motion. Most of these subsystems can be implemented using different technologies, and better technologies can improve the performance of the engine.

Let's look at all of the different subsystems used in modern engines.....

Valve Trains
The valve train consists of the valves and a mechanism that opens and closes them. The opening and closing system is called a camshaft. The camshaft has lobes on it that move the valves up and down, as shown in Figure 5.

Figure 5. The Camshaft

Most modern engines have what are called overhead cams. This means that the camshaft is located above the valves, as you see in Figure 5. The cams on the shaft activate the valves directly or through a very short linkage. Older engines used a camshaft located in the sump near the crankshaft. Rods linked the cam below to valve lifters above the valves. This approach has more moving parts and also causes more lag between the cam's activation of the valve and the valve's subsequent motion. A timing belt or timing chain links the crankshaft to the camshaft so that the valves are in sync with the pistons. The camshaft is geared to turn at one-half the rate of the crankshaft. Many high-performance engines have four valves per cylinder (two for intake, two for exhaust), and this arrangement requires two camshafts per bank of cylinders, hence the phrase "dual overhead cams."

Ignition System
The ignition system (Figure 6) produces a high-voltage electrical charge and transmits it to the spark plugs via ignition wires. The charge first flows to a distributor, which you can easily find under the hood of most cars. The distributor has one wire going in the center and four, six, or eight wires (depending on the number of cylinders) coming out of it. These ignition wires send the charge to each spark plug. The engine is timed so that only one cylinder receives a spark from the distributor at a time. This approach provides maximum smoothness.

Figure 6. The ignition system

Cooling System
The cooling system in most cars consists of the radiator and water pump. Water circulates through passages around the cylinders and then travels through the radiator to cool it off. In a few cars (most notably Volkswagen Beetles), as well as most motorcycles and lawn mowers, the engine is air-cooled instead (You can tell an air-cooled engine by the fins adorning the outside of each cylinder to help dissipate heat.). Air-cooling makes the engine lighter but hotter, generally decreasing engine life and overall performance.

Diagram of a cooling system showing how all the plumbing is connected

 

Air Intake System
Most cars are normally aspirated, which means that air flows through an air filter and directly into the cylinders. High-performance engines are either turbocharged or supercharged, which means that air coming into the engine is first pressurised (so that more air/fuel mixture can be squeezed into each cylinder) to increase performance. The amount of pressurisation is called boost.
A turbocharger uses a small turbine attached to the exhaust pipe to spin a compressing turbine in the incoming air stream.
A supercharger is attached directly to the engine to spin the compressor.

Starting System
The starting system consists of an electric starter motor and a starter solenoid. When you turn the ignition key, the starter motor spins the engine a few revolutions so that the combustion process can start. It takes a powerful motor to spin a cold engine. The starter motor must overcome:

• All of the internal friction caused by the piston rings
• The compression pressure of any cylinder(s) that happens to be in the compression stroke
• The energy needed to open and close valves with the camshaft
• All of the "other" things directly attached to the engine, like the water pump, oil pump, alternator, etc.

Because so much energy is needed and because a car uses a 12-volt electrical system, hundreds of amps of electricity must flow into the starter motor. The starter solenoid is essentially a large electronic switch that can handle that much current. When you turn the ignition key, it activates the solenoid to power the motor.

Lubrication System
The lubrication system makes sure that every moving part in the engine gets oil so that it can move easily. The two main parts needing oil are the pistons (so they can slide easily in their cylinders) and any bearings that allow things like the crankshaft and camshafts to rotate freely. In most cars, oil is sucked out of the oil pan by the oil pump, run through the oil filter to remove any grit, and then squirted under high pressure onto bearings and the cylinder walls. The oil then trickles down into the sump, where it is collected again and the cycle repeats.

Fuel System
The fuel system pumps gas from the gas tank and mixes it with air so that the proper air/fuel mixture can flow into the cylinders. Fuel is delivered in three common ways: carburetion, port fuel injection and direct fuel injection.

• In carburetion, a device called a carburetor mixes gas into air as the air flows into the engine.
• In a fuel-injected engine, the right amount of fuel is injected individually into each cylinder either right above the intake valve (port fuel injection) or directly into the cylinder (direct fuel injection).

Exhaust System
The exhaust system includes the exhaust pipe and the muffler/silencer. Without a muffler, what you would hear is the sound of thousands of small explosions coming out your tailpipe. A muffler dampens the sound. The exhaust system also includes a catalytic converter if you're unlucky enough to have one.

Electrical System
The electrical system consists of a battery and an alternator. The alternator is connected to the engine by a belt and generates electricity to recharge the battery. The battery makes 12-volt power available to everything in the car needing electricity (the ignition system, radio, headlights, windscreen wipers, power windows and seats, computers, etc.) through the vehicle's wiring.