The main part of an automobile is the engine. This device allows mechanical power to move the vehicle by using what is called a drivetrain. In general, we say forms of energy can be transformed to mechanical energy, such as heat, chemical, electrical, solar and nuclear.
As we study engines, we will learn how the various forms of energy are transformed from one form to another to supply this mechanical power. We will also have the student recognize how the different parts of the system (automobile) work to make the total system operate effectively and efficiently.
This section can satisfy Performance Objectives 5.2d, 2.3, 2.4, and 2.5 for grades 9 -12.
The development of engines has produced both positive and negative results. On the positive side, it has allowed us to do work faster with less effort on our part. We know that without the engines, our quality of life would not be the same. On the negative side, pollution from some of these devices has damaged our environment. We realize the need for these types of machines and we are now trying to make them become more environmentally friendly.
Before we start dealing with environmental concerns, we should investigate the development of engines and the impact they have had on our way of life. The engines we will discuss are referred to as heat engines. They burn various types of fuel to produce a type of heat energy in a process we call combustion. Theses engines are differentiated by where the combustion occurs.
If the combustion occurs outside the engine, we refer to it as an external combustion engine. If the combustion occurs inside the engine, we call it an internal combustion engine.
If a teacher would like to collaborate with a social studies teacher, this would be a great opportunity to discuss the Industrial Revolution starting with the invention of the steam engine.
The Steam Engine is an external combustion type of engine. In earlier times, this was a source of energy for steamboats, trains and factories that were primarily responsible for the start of the Industrial Revolution.
The steam engine changes thermal energy to mechanical energy causing the engine to perform the intended task. One way to show how steam can make an object move is to do
an investigation called the “steam rocket engine.” This can be found online by asking “how to make a steam powered rocket.”
This investigation shows that when heated, water changes to steam and like the earlier investigation with the flask and the balloon, it will expand. However, this time the steam has an opening to escape and move the object. Explain that in a steam engine, the steam causes a piston to move and do mechanical work.
Let’s take a closer look at the steam engine. We know that it uses some of the simple machines such as the wheel and axle as part of the total system (train). But, an engine is used to do most of the work. Just how does this work? We saw from the demonstration with the steam rocket, that heating water causes it to change phase. (liquid to gas) In the gaseous state, the pressure is increased. The steam escaped through the opening causing the “rocket” to move in the opposite direction. In the steam engine, as the gas increases in pressure and volume, it is directed to a piston by the use of valves. We can then make it do useful work.
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What happens during this operation is that the steam alternates coming into the cylinder. This causes the piston to move back and forth. You may then connect the piston to a device to do work.
The boiler is a very important component of the steam engine. This is where the water is heated and changed to steam. If you have looked at old western movies and a train was involved, you saw water towers at the train stations. These were necessary to replace the water that was used by the train to produce steam.
The website http://www.geocites.com/Athens/Acropolis/6914/thermod3e/htm shows the theoretical cycle of a double-acting steam engine. This animation shows what is happening during the cycle of the steam engine.
If you plan to do a Science Fair Project on the steam engine, there are some web sites that show you how to make a simple steam engine. I would suggest this be done only with the supervision of an adult.
There is a lot of flexibility with your research paper. The focus of the paper will depend upon your purpose/problem and hypothesis.
The next type of engine we should investigate is the internal combustion engine. A good way to start this investigation is to have the student(s) put together a model car. Remember, if you are doing this as a project, no more the two students (grades 7&8) or three students(grades 5&6) are allowed to work together on a project.
This activity will allow them to see where some of the parts are located in the automobile in relation to the engine. You can then direct your attention to what and why most of these objects move. The internal combustion engine.
As stated earlier, the combustion takes place within a cylinder. For our purposes, we will discuss the four-stroke cycle engine. Each up and down movement of the piston inside the cylinder is called a stroke. The cylinder has at least two opening, one for the intake of air and fuel and the other to rid the cylinder of the exhaust. To start a discussion and get a better overview of this process, have the students look at the brief movie called “engines” at http://www.brainpop.com if you have access to computers,
The cylinder is where the action takes places in the internal combustion engine as we have just seen from the “Brainpop” presentation. Let’s revisit what happens during each stroke of this engine at a slower more controlled pace. Again, if you have access to computers, visit the website of “How Stuff Works.” This section takes you through the steps of what happens in the cylinder during the four-stroke cycle. I think we all realize that students learn and retain more if they are actively involved in the learning process. By using this website, we can work at our own pace and visually observe an animation of what is happening in the cylinder.
This is basically what happens during this four-stroke cycle:
- Intake - A premixed fuel in introduced into the cylinder from the fuel-injection system.
- Compression - A piston compresses the fuel and air mixture.
- Power - A spark plug ignites the fuel mixture.
- Exhaust - The exhausted fuel is pushed out of the cylinder to a catalytic converter, muffler, and tailpipe and enters the atmosphere.
Most automobiles in the United States have 4, 6, or 8 cylinder engines. The bigger the engine and the more cylinders it has, the more fuel it will use and the more pollution it adds to the atmosphere.
A research paper on “The History of the Automobile” could be done for social studies.
Diesel Engines
The inefficiency and resource consumption of the steam engine prompted Rudolph
Diesel to develop the diesel engine. This engine uses the high temperature of compressed air to ignite the fuel when it is introduced into the cylinder instead of a spark.
The diesel engine is much more efficient when it comes to changing the potential energy to mechanical energy. The gasoline engine has a compression ratio of 8:1 to 12:1 while the efficiency rating of the diesel engine is 14:1 up to 25:1. The higher ratio means better efficiency for the diesel engine.
Again, go to “How Stuff Works” to see the working of the diesel engine.
During the oil crisis in the United States (1970’s) Americans began buying diesel
powered automobiles. Records show that 85% of Peugeot’s, 70% of Mercedes Benz, 58% of Isuzu’s and 50 % of Volkswagen’s sales were diesel-powered vehicles.
What caused us to turn away from diesel fueled engines? The main reason was that prices stabilized and the need for conservation was lessened and the other reason was that the diesel engines did not stand up well due to the higher compression needed for their operation. They were also very sluggish. However, the diesel engine has been improved and many of the initial drawbacks have been reduced or eliminated.
Again we are faced with unstable fuel prices but because of new technology we may not revert back to the use of diesel powered engines no matter what benefit the diesel can do to help the environment.
Automobiles And Environmental concerns
Automobiles affect the environment from their production to the acquisition of petroleum products. We will just concern ourselves with the by-products of combustion.
Pollution from exhaust is the major concern for impacting the environment. As the combustion process is not perfect, pollutants are added to our environment.
The pollutants of concern and their effects are:
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- Carbon Dioxide (CO2) - Emitted from automobile exhaust, contributes to global warming.
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- Particulate Matter - Respiratory and cardiovascular disease, lung disease and cancer.
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- Nitrogen Oxides (NO & NO2) - Respiratory problems, reacts in air to cause “bad” ozone (smog), acid rain, and nitrification of wetlands leading to algae growth and the death of fish.
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- Sulfur Dioxide (SO2) - Secondary particulate formation, lung irritant, and acid rain. Interferes with the operation of catalytic converters.
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- Hydrocarbons (HC) - Various forms of air pollution, can cause cancer and birth defects, and “bad” ozone.
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- Carbon Monoxide (CO) - Impairs the flow of blood to the brain and other parts of our body. May cause death.
In December of 1997, an agreement to control emissions of greenhouse gases that cause global warming was held in Kyoto, Japan. This agreement called for wealthier nations to significantly reduce their greenhouse gas emissions by 2008-2012. However, the United States did not ratify this treaty.
We must hope that the automobile industry will keep experimenting with environmentally friendly vehicles and during this same period of time, produce more fuel efficient vehicles instead of SUVs.