# The Engine Quiz!

By: Staff

7 Min Quiz

Image: refer to hsw

## About This Quiz

It's under the hood of every car, truck and SUV (unless the vehicle is electric), but how many people really know how an engine works? Do you know a spark plug from a fuel injector? Test your auto smarts in our engine quiz.
Have you ever opened the hood of your car and wondered what was going on in there? A car engine can look like a big confusing jumble of metal, tubes and wires to the uninitiated. You might want to know what's going on simply out of curiosity. Or perhaps you are buying a new car, and you hear things like "3.0 liter V-6" and "dual overhead cams" and "tuned port fuel injection." What does all ­of that mean? The ­principle behind any reciprocating internal combustion engine: If you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas. You can use that energy to propel a potato 500 feet. In this case, the energy is translated into potato motion. You can also use it for more interesting purposes. For example, if you can create a cycle that allows you to set off explosions like this hundreds of times per minute, and if you can harness that energy in a useful way, what you have is the core of a car engine! Almost all cars currently use what is called a four-stroke combustion cycle to convert gasoline into motion. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867. The four strokes are illustrated in Figure 1. They are: 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. 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. So you go out one morning and your 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 rundown on how these problems affect your engine: Bad fuel mix - A bad fuel mix can occur in several ways: Most engine 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, beginning with the valve train. 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. 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. See How Car Cooling Systems Work for details. So now you know how and why your engine stays cool. But why is air circulation so important? 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 pressurized (so that more air/fuel mixture can be squeezed into each cylinder) to increase performance. The amount of pressurization 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. When it comes to day-to-day car maintenance, your first concern is probably the amount of gas in your car. How does the gas that you put in power the cylinders? The engine's 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. Using all of this information, you can begin to see that there are lots of different ways to make an engine perform better. Car manufacturers are constantly playing with all of the following variables to make an engine more powerful and/or more fuel efficient. Increase displacement - More displacement means more power because you can burn more gas during each revolution of the engine. You can increase displacement by making the cylinders bigger or by adding more cylinders. Twelve cylinders seems to be the practical limit. Here is a set of engine-related questions from readers and their answers: What is the difference between a gasoline engine and a diesel engine? In a diesel engine, there is no spark plug. Instead, diesel fuel is injected into the cylinder, and the heat and pressure of the compression stroke cause the fuel to ignite. Diesel fuel has a higher energy density than gasoline, so a diesel engine gets better mileage. See How Diesel Engines Work for more information. What is the difference between a two-stroke and a four-stroke engine? Most chain saws and boat motors use two-stroke engines. A two-stroke engine has no moving valves, and the spark plug fires each time the piston hits the top of its cycle. A hole in the lower part of the cylinder wall lets in gas and air. As the piston moves up it is compressed, the spark plug ignites combustion, and exhaust exits through another hole in the cylinder. You have to mix oil into the gas in a two-stroke engine because the holes in the cylinder wall prevent the use of rings to seal the combustion chamber. Generally, a two-stroke engine produces a lot of power for its size because there are twice as many combustion cycles occurring per rotation. However, a two-stroke engine uses more gasoline and burns lots of oil, so it is far more polluting. See How Two-stroke Engines Work for more information. You mentioned steam engines in this article -- are there any advantages to steam engines and other external combustion engines? The main advantage of a steam engine is that you can use anything that burns as the fuel. For example, a steam engine can use coal, newspaper or wood for the fuel, while an internal combustion engine needs pure, high-quality liquid or gaseous fuel. See How Steam Engines Work for more information. Are there any other cycles besides the Otto cycle used in car engines? The two-stroke engine cycle is different, as is the diesel cycle described above. The engine in the Mazda Millenia uses a modification of the Otto cycle called the Miller cycle. Gas turbine engines use the Brayton cycle. Wankel rotary engines use the Otto cycle, but they do it in a very different way than four-stroke piston engines. Why have eight cylinders in an engine? Why not have one big cylinder of the same displacement of the eight cylinders instead? There are a couple of reasons why a big 4.0-liter engine has eight half-liter cylinders rather than one big 4-liter cylinder. The main reason is smoothness. A V-8 engine is much smoother because it has eight evenly spaced explosions instead of one big explosion. Another reason is starting torque. When you start a V-8 engine, you are only driving two cylinders (1 liter) through their compression strokes, but with one big cylinder you would have to compress 4 liters instead.

# What is an engine’s redline?

An engine’s redline, which is shown on the tachometer, determines its maximum revolutions per minute, or rpms.

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# What is an octane rating?

The octane rating relates to how much the fuel can be compressed before it spontaneously ignites. A rating that’s too low can cause the engine to run poorly.

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# A turbocharger is:

<a href='http://auto.howstuffworks.com/turbo.htm' style="font-weight: bold;">Turbochargers</a> and <a href='http://auto.howstuffworks.com/supercharger.htm' style="font-weight: bold;">superchargers</a> are both air compression systems. They pressurize the air moving into the engine, increasing the engine's power.

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# Why don’t we use steam engines for cars anymore?

Internal combustion engines are a lot more efficient than external combustion engines, which is why steam engines fell out of favor for cars.

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# A crankshaft's job in an engine is to:

When <a href='http://science.howstuffworks.com/gasoline.htm' style="font-weight: bold;">gasoline</a> ignites in a cylinder, the piston moves in a straight line. Your wheels, on the other hand, need to turn. The piston moves a connecting rod, which turns the crankshaft, producing the rotational motion.

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# A car uses a four-stroke engine. The four strokes are:

In the intake step, a cylinder gets some fuel and air to burn. Then, it compresses the fuel to make the combustion step (the explosion) more powerful. In the last step, the cylinder releases its exhaust.

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# A car engine's job is to:

There's a lot of heat in a car's engine -- and a lot of exhaust coming out of it -- but these are byproducts of the engine's true purpose. An engine has to use fuel to create motion to move the <a href='http://auto.howstuffworks.com/tire.htm' style="font-weight: bold;">tires</a>.

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# What might happen if water gets into your gas tank?

Water will prevent the gasoline in the system from burning properly, which will cause combustion problems in the engine, which will prevent the car from starting or cause it to run poorly.

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# In a car engine's cylinder, valves let fuel in and exhaust out. The ______ moves these valves.

A <a href='http://auto.howstuffworks.com/camshaft.htm' style="font-weight: bold;">camshaft</a> is a rotating rod that uses a series of lobes to open and close the valves. Most modern engines have overhead cams -- the camshaft is directly above the valves.

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# There are three basic failures that can happen in an engine: bad fuel mix, lack of compression and:

Lots of things can go wrong under the hood, but the big three in the engine involve fuel, compression and <a href='http://science.howstuffworks.com/fire.htm' style="font-weight: bold;">fire</a> .

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# Which of the following commonly uses air-cooled engines?

Many motorcycles are powered by air-cooled engines.

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# What are the three functions of engine oil?

Most people know that engine oil lubricates to help with metal-on-metal contact, but it also helps cool and clean the engine as it circulates.

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# What are the three common ways to deliver fuel to an engine?

Carburetion, port fuel injection and direct fuel injection all get the fuel where it needs to go.

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# Why does engine oil need to be changed?

Because engine oil cleans the engine, it picks up dirt and debris as it circulates, which gradually reduces its efficiency.

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# Modern cars use internal combustion engines, but some early models used external combustion engines. What is one example of an external combustion engine?

Steam engines were most commonly used in trains and boats, but did power some types of cars.

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# What does ECM stand for, and what does it do?

ECM is the engine control module, and it’s the computer that manages the engine’s functions.

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# What are two of the main advantages to a 4-cylinder engine?

The 4-cylinder engine did not become popular in the United States until the 1980s, when Japanese manufacturers demonstrated how small and efficient it could be.

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# When you turn the key to a car, the starter motor:

The starter motor has a big job -- it has to overcome friction, cold weather and other factors to get your engine started. If it fails, nothing happens in the engine when you turn the key.

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# What are the two main components of the engine cooling system in most cars?

With a water-cooled engine, which is the most common type of cooling system, the radiator and water pump circulate water to absorb heat and move it away from the engine.

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# Which of these cars features a popular example of an air-cooled engine?

The Volkswagen Beetle was designed with an air-cooled engine specifically for its simplicity.

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# A timing belt or timing chain links these two components together so that the valves are in sync with the pistons:

A timing belt or timing chain links the crankshaft to the <a href='http://auto.howstuffworks.com/camshaft.htm' style="font-weight: bold;">camshaft</a> so that the valves are in sync with the pistons.

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# What are two other terms for engine knock?

Pinging is another way to describe the sound, and detonation describes what’s causing it.

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# What happens if your car leaks or burns off all of its oil?

Oil lubricates the pistons so they can move smoothly inside the engine, and without oil, the engine will seize.

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# What are the three common ways to arrange an engine’s cylinders?

An engine’s cylinders are most often arranged in a line (inline), in two rows set at an angle (V) or in two opposite banks (flat).

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# When a car's engine is running, power to operate the radio, CD player, headlights and windshield wipers comes from the:

A large battery is used to start the engine when you turn the key; however, once the engine is running, power for the car's accessories comes from the <a href='http://auto.howstuffworks.com/alternator.htm' style="font-weight: bold;">alternator</a>. The alternator is connected to the engine by a belt and generates electricity to recharge the battery, too.

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# What is the steam engine’s main advantage?

A steam engine just needs to create steam, so it can burn anything as fuel. That's why in those old silent movies, when the hero runs out of coal to power the train, he starts burning his coat and hat.

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# Name one of the causes of engine knock.

There are several causes of engine knock, and experts say that installing the wrong spark plugs is a common problem.

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# Why does a diesel engine get better mileage than a gasoline engine?

Diesel has a higher energy density than gasoline, meaning that each gallon burned makes more power.

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# A device that works on the same principle as a car engine is:

In a both <a href='http://science.howstuffworks.com/spud-gun.htm' style="font-weight: bold;">spud gun</a> and a car engine, you ignite a small amount of fuel, releasing a large amount of energy. (And it's equally unwise to get in front of a moving car or a loaded spud gun.)

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# What’s another name for the four-stroke engine cycle?

The Otto cycle is named after its inventor, Nikolaus Otto.

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