Internal Combustion Engines

By Joey Dille

5th Grade Personal Exploration Project

What is an internal combustion engine? Why are they important? Some frequently asked questions. Then again, you may have just answered your own question. It has to be important since I am doing my entire PEP project on them. The internal combustion engine is the engine that powers your car, lawnmower, motorboat, weed whacker, even helicopter, (if you're lucky.) It is one of most common engines around. It uses fuel and air to convert heat energy into mechanical energy. How does it do this? If you read the rest of this you might just learn how.

What does an engine do that makes it important? It converts heat energy into mechanical energy. We know that! But how does it? Here's your answer. It takes in air and compresses it, then heats it by burning fuel with it, then the mixture is expanded, producing useful work, and then the exhaust exits the engine. Pretty simple huh? This process is the main principle of an internal combustion engine. All 5 engines that I will discuss use this principle. These 5 engines are: The 4-stroke, Wankel, Gas Turbine, Diesel, and 2-stroke.

Engine number 1 was invented by Nikolaus August Otto and Eugen Langen, two German engineers in 1876. It is the basic 4-stroke engine. This is the engine that is used in most vehicles. This engine uses the reciprocating motion of a piston to do the compression and expansion. It looks like a box with a tall tube coming up from the top. The box is called the crankcase, the tube is called the cylinder. Many cylinders can be put together to create more power and a smoother running engine. These cylinders can be arranged in patterns like straight (all the cylinders in line), V-type (in a V formation), or flat (across from each other.)

This engine has two shafts, the crankshaft and the camshaft. The former provides the output from the engine and the latter operates the valves, small mushroom shaped pieces that allow the inlet and outlet of gases. The piston is like a block on a rod. That rod, called the connecting rod, connects the piston to the crankshaft. They are connected in such a way so when the piston goes up and down the crankshaft turns, converting the reciprocating motion of the piston to a turning motion.

In each cylinder there is 4 strokes, or steps, to the process as the name suggests. The 4-stroke engine siphons fuel from a fuel tank and mixes it with air in a process called carburetion. The carburetor does this job. Not surprised? Me neither.

On the first stroke, intake, the piston descends and the intake valve opens. The motion of the piston sucks in the air/fuel mixture. On the second stroke, the piston rises and compresses the mixture into a small space at the top of the cylinder called the combustion chamber. A spark plug, a device creating sparks, is lit. It ignites the mixture, causing it to burn, which heats it up. Now the gas is rapidly expanding, forcing the piston down with more force than it took to compress it. Once the piston has gone all the way down the exhaust valve opens (the one leading to the muffler) the piston rises, pushing the gases out. Then the exhaust valve closes and the intake valve opens, beginning the process all over again. This process happens in a split second and will repeat as long as your engine is running.

Now that you have learned the "basic" engine. I presume you are ready to move on to more advanced stuff.

Engine number 2 is the Wankel, commonly called a rotary engine. Invented by Felix Wankel, another German engineer, in 1956. This engine uses the turning motion of a triangular rotor and a housing shaped like figure 8 with a wide middle to make power. There are no valves in this design, just openings called ports. No valves are needed because the rotor covers and uncovers the ports as it spins. This engine's cycle is similar to the 4-stroke's. When the rotor tip goes past the intake port the fuel/air mixture enters that section of the rotor. The next rotor tip seals off the intake port and the mixture is compressed between the rotor and the housing. As this section of the rotor passes the spark plug the fuel/air mixture is ignited which heats it up. The hot gases expand between the rotor and the housing, turning the rotor. Then the exhaust port is opened and the exhaust escapes as the rotor turns. Now the rotor has made a full cycle.

Since the rotor has three sides, this creates three different chambers that all operate at the same time. This makes the Wankel engine very compact for its power. The rotary motion is also much smoother than the reciprocating motion of a traditional piston engine. Unfortunately, this engine had several drawbacks, which are short life, high pollution and noise. It is no longer used.

Engine number 3 is the gas turbine engine. This engine is commonly used in airplanes and helicopters. It was invented by the Norse engineer Aegidius Elling in 1903. It is very powerful for it's size. This is not a reciprocating engine, nor is it a true rotary engine. It uses bladed devices called compressors and turbines to make its power. The whole engine looks like a tube, a bit wider in the front than the rear. This is because the front is where the air intake is. As you may or may not know, the more air you put into an engine the more power it will make. The front of the engine is designed to do exactly that. Inside the front of the engine there are specially designed fan blades spinning around. They are the compressors. The air runs through these blades and becomes more compact and increases in pressure. Then it enters the combustion section where fuel is injected and the air is heated by the combustor. The combustor is like a large gas grill. Then the hot, high-pressure gas expands in the turbine section. A turbine is like a compressor, but it expands gases instead of compressing them. The turbine generates work from the expanding gas. The compressor and turbine are connected to the same shaft and the turning of the turbine spins the compressor. There is even extra power left over to turn the wheels of a car or something else.

Engine number 4 is the Diesel engine. This engine is commonly used for jobs where size and weight are not a problem such as buses, tractor-trailers, trains and ships. Rudolph Diesel, another German mechanical engineer, invented it in 1897. This engine is much like the 4-stroke, except with no spark plug. Instead there is a fuel injector. There are two major differences. One, it only takes in air and two, the power stroke. On the compression stroke the air is compressed so much that it isvery hot. How hot is it? So hot, that when fuel is injected it immediately combusts, heating the air even more. The rest is just like the 4-stroke. Hot gases expand against the piston on the downward stroke. Then the exhaust is expelled out the engine. Blah, blah, blah. The diesel engine is very efficient. They also tend to be heavy because the high pressure requires heavy walls.

The last engine is the 2-stroke, which was also invented by Nikolaus August Otto and Eugen Langen (The same guys who invented the 4-stroke.) in 1876. It uses the same principle as the 4-stroke and the same piston, just with no valves. I will explain a reed valve type two-stroke engine. When the piston rises the air/fuel mixture is admitted through a reed valve into the crankcase (The area at the bottom of the cylinder). When the piston descends the reed valve closes and the mixture goes through a tube to the transfer port into the combustion chamber. The piston rises on the compression stroke, compressing the mixture. The spark plug fires when the piston is at the top, heating the gas. The hot gas expands pushing the piston down until the exhaust ports open allowing the exhaust to escape. Then the cycle repeats itself. The two-stroke engine is used in a lot of portable devices due to its compactness and lightness. They are very cheap to make. The two-stroke is not very efficient and tends to create a lot of pollution though.

Then comes along the most nagging question, will the internal combustion engine ever be replaced by a new, more efficient, longer lasting engine? Well, I'll show you some alternatives and let you be the judge. A new car that is currently under development is the Hybrid. It uses an electric motor, a generator, a battery, and a four-stroke engine to make its power. Complicated? Not exactly. Most of the work is done by the electric motor that can be run through a generator connected to the four-stroke or by a battery that is charged when the car is stopped. When you are going at slow speeds the four-stroke isn't even on!
The Honda Insight and Toyota Prius are already on the roads. Other car companies have some in development too.

The other alternative is the fuel cell, a device that is working well but has some problems. It takes hydrogen and oxygen and turns it into water. It uses the electrons in the hydrogen to power the car. Hydrogen and oxygen are put in separate sides of a fuel cell. In the middle is the PEM or proton exchange membrane. It lets the two hydrogen ions pass but blocks the two electrons. Instead they take a wire around to the oxygen and power the car in the process. When they reach the oxygen they turn into water that drips out the back of the car. Simple? Not quite. For one, you don't just drive up to your Mobil station, put in your speed pass and fill up your tank with hydrogen! It is difficult to store it in a car too. Some companies are working on a way to convert other substances to hydrogen. But even if they succeed, they will be hard to fit on a car. That was just the first problem. The second problem is that it takes a lot of them to produce enough voltage to power the car. But this problem is being conquered.

Now you know about the internal combustion engine. How it works, who invented it, and the different types. You've even learned about the ways it could be replaced. Why? It puzzles me. Because this is the best engine I know.


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