The Engine 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.

answer: “Diesel and gas turbine engines are both types of internal combustion engines.”,
question: “A car engine is what type of combustion engine?”
answer: “The four-stroke combustion cycle is also known as the Otto cycle invented over 140 years ago.”,
question: “Nikolaus Otto invented the four-stroke combustion cycle in what year?”
answer: “The piston moving down allows air and gasoline for combustion.”,
question: “The stroke that lets in air and gasoline is the _____ stroke.”
answer: “The piston moving back up compresses the gasoline and air.”,
question: “The stroke that makes the explosion more powerful is the ______ stroke.”
answer: “The explosion the spark plug ignites causes the piston to move down.”,
question: “During the combustion stroke the ____________ ignites the gasoline.”
answer: “The connecting rod connects the piston to the crankshaft.”,
question: “The _________ connects the piston to the crankshaft.”
answer: “The exhaust valve opens at the bottom of the piston’s stroke allowing the exhaust to exit.”,
question: “During the exhaust stroke the exhaust leaves the engine and goes out the __________ .”
answer: “Rotational motion is the type needed to rotate the wheels of the car.”,
question: “The ___________ is the part of the engine that changes the linear motion of the piston into rotational motion.”
answer: “Most cars have either four, six, or eight cylinders in their engines.”,
question: “The piston moves up and down inside of the _________ .”
answer: “Inline, V, & flat cylinder arrangements each have their own advantages and disadvantages.”,
question: “The three most common arrangement of cylinders in an engine are inline, V, and _______ .”
answer: “The simple inline arrangement makes these engines easier to manufacture than V and flat types. “,
question: “The _______ arrangement of cylinders has all of the cylinders in a line in a single bank.”
answer: “Timing the spark plug ignition is critical for the engine to work correctly.”,
question: “The spark plug _________ the air and fuel.”
answer: “The piston tightly fits inside the cylinder to seal air and gas and control the combustion process.”,
question: “What moves up and down inside the cylinder?”
answer: “The overhead cam design with the camshaft above the valves is the most common type found in modern engines.”,
question: “Engines using overhead cams have their camshaft located _______ the valves. ”
answer: “Synchronizing the crankshaft and camshaft is important for the valves and pistons to perform their best.”,
question: “A timing belt or timing chain links the ______ and the ________ so valves and pistons stay in sync.”
answer: “Gearing allows the camshaft to turn once for every two turns of the crankshaft.”,
question: “A camshaft turns at ______ the rate of the crankshaft.”
answer: “Creating the spark to ignite the air/fuel mixture requires a precisely timed high-voltage electrical charge.”,
question: “The spark plug needs a _________________ from the ignition system to work.”
answer: “Air-cooled engines run hotter which typically reduces engine life and performance.”,
question: “Air-cooled engines are typically lighter but run _______ than liquid-cooled engines.”
answer: “Normal aspiration means air only needs to pass through a filter before it enters the cylinders.”,
question: “Most cars use an air circulation technique known as ______________ .”
answer: “Pressurizing the air helps increase the performance of the engine.”,
question: “Turbocharged and supercharged engines first do what to the air before mixing it with fuel?”
answer: “Higher pressure means a bigger boost.”,
question: “The pressurization amount used in turbocharging and supercharging engines is called:”
answer: “To start your engine it takes a powerful motor to get things going!”,
question: “What spins the engine a few revolutions so the combustion process can start?”
answer: “Mixing the proper amount of gas and air makes sure your engine is working efficiently.”,
question: “The fuel system of an engine takes gas from a gas tank and mixes it with what?”
answer: “If the carburetor doesn’t mix air and gas in the right amount it could be wasting gas or cause the engine to produce less power.”,
question: “The device that mixes gas into air as the air flows into the engine is called the ________ .”
answer: “The exhaust system clears the way for the next round of combustion inside the engine.”,
question: “The exhaust pipe and the muffler are part of what system?”
answer: “Oil helps lubricate the engine parts like pistons and bearings to help those parts move more easily and reduce wear.”,
question: “The liquid used in the engine’s lubrication system is _______ .”
answer: “An emission control system helps clean harmful chemicals from the exhaust by running the exhaust through the catalytic converter before it exits the tail pipe.”,
question: “The purpose of a catalytic converter is to:”
answer: “The powerful 12-volt battery runs the starter motor and then is recharged by the alternator once the engine is running. “,
question: “The battery in most cars used to start the motor which in turn starts the engine is typically what kind?”
answer: “More displacement means you can burn more gas which means more power.”,

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.

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.

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.

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.