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Working Principles of a Gasoline Engine

Working Principles of a Gasoline Engine

Introduction: (Initial Observation)

Gasoline engines are used in every automobile and are the driving force for many electric generators and other industrial and household machines. Gas powered lawn mowers, chainsaws, blowers and trimmers are among the well known household and garden equipment that you may have seen.

Have you ever wondered how does gasoline produce power to drive a machine? Where does such a force come from?

After all gasoline is a clear liquid. Can all liquids produce energy to drive a machine?

This project is an opportunity to learn about the structure and design of gasoline engines.

Adult supervision, help and safety precautions is required for this project.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.  

Project advisor

Why is this a good project? What do I learn from this?

Gasoline engine is invented after discovering the explosive reaction of fuel and air mixture. We call it fuel because it does not have to be gasoline and many other flammable gases and liquids can do the same. But what is an explosive reaction?

Certain mixtures of air and any flammable material can burn instantly and produce a large amount of hot gases. Sudden production of a large amount of gas is called explosion. Explosion is more dangerous if it happens inside an enclosure that may break. Such explosions can through the broken pieces around and can cause injury and death.

In a gasoline engine explosion happens inside a strong steel cylinder and produces large volume gases that pushes the piston away.

So one thing that we learn about this project is that a mixture of air with fuel is very dangerous. Every year many welders and iron workers die as a result of an explosion while welding an empty drum or empty tank that used to have some flammable material. Such drums and tanks look empty but they really contain a mixture of air and some vapors of flammable material.

Surprisingly wood dust, grain dust and even the dust of some metals such as aluminum and zinc can cause explosion if they are mixed with air in an explosive ratio.

In this project we will see how the pressure of gas can be used to produce a rotational motion.

Information Gathering:

Find out about Gasoline engines. Read books, magazines or ask professionals who might know in order to learn about the principles of gasoline engines. Visit antique engine website to see simple design of the first gasoline engines. Keep track of where you got your information from.

The Physics of gasoline engine

also known as

Four-Stroke Internal Combustion Engine

The most commonly used type of car engine today, is based on the Otto cycle, named after its creator Nikolaus Otto. The term, four-stroke refers to the four distinguished motions that the piston goes through during the conversion of chemical energy into rotational energy that can be harnessed for a practical use, in this case, to propel a car.

This picture is used as a reference of the parts of the engine which are mentioned on this page of the website.
A simple engine includes one cylinder, one piston, a spark plug mounted at one end of the cylinder and a crankshaft on the other end of the cylinder. Cylinder also includes two valves. One valve is for the mixture of air and gasoline to enter and the other valve is for hot gases to exit.








1.Intake Stroke:

The first stroke of the cycle is described as the intake cycle, where the piston that starts at the top of the cylinder chamber, begins to move downward. At the same time that the piston begins it path downward, the intake valve opens and allows air to be drawn into the cylinder chamber by the downward moving piston. Also during this time a small quantity of gasoline is squirted into the chamber through a fuel injector and mixes with the air. The gasoline must be mixed with the air because liquid gasoline will not burn so it must be vaporized by the injector and mixed with air. The perfect air to gas ratio is 14 parts air to one part fuel. This ratio is electronically controlled by a computer connected to the fuel pump and injectors that supply the amount of fuel in relation to the amount of air that the engine can draw into the cylinder.




2. Compression Stroke:

The second stroke, also known as the compression stroke, begins with the closing of the intake valve. As the intake valve closes a sealed chamber is created between the piston and the top of the cylinder where the valves are located. The piston then begins its upward path, the gasoline and air mixture is compressed at a ratio of roughly 10:1. This ratio comes from the differences in volume between the volume of the cylinder chamber at the top of the pistons stroke compared to the volume of the cylinder chamber when the piston is at the bottom of its path. The greater that this ratio can be made the more power an engine can produce. When cars a given 454 in3 or 5.0 liters, this is the total volume of all cylinders at their intake stroke. Therefore the 454 in3 engine with 8 cylinders can hold 56.75 in3 per cylinder and therefore with a compression ratio of 10:1 can compress this to 5.67 in3. This compression creates a lot of pressure in the cylinder chamber.




3. Combustion Stroke:

The third stroke of the cycle, the power stroke refers to the combustion itself. Now that the cylinder chamber is full of highly compressed air and gasoline, a spark from a spark plug initiates an explosion in the chamber that causes a rapid expansion of the compressed mixture, resulting in the piston being forced downward very quickly. The expansion of gas, caused by the combustion is the single most important stage of the cycle. It is also very important that there are no leaks in the system or the pressure will be lost and result in a power loss.







4. Exhaust Stroke:

The fourth and final stroke, is known as the exhaust stroke. Once the piston reaches the bottom of its path after the explosion, all that remains in the cylinder chamber is waste. Once the piston begins its movement upward in the cylinder the exhaust valve opens and the piston forces the exhaust out of the chamber and away from the engine. Following this exhaust removal the intake valve opens allowing air to enter the chamber and continue the cycle.








Upon completion of this chapter, you should be able to do the following:

  • Explain the principles of a combustion engine.
  • Explain the process of an engine cycle.
  • State the classifications of engines.
  • Discuss the construction of an engine.
  • List the auxiliary assemblies of an engine.

The automobile is a familiar object to all of us. The engine that moves it is one of the most fascinating and talked about of all the complex machines we use today. In this chapter we will explain briefly some of the operational principles and basic mechanisms of this machine. As you study its operation and construction, notice that it consists of many of the devices and basic mechanisms covered earlier in this book.


We define an engine simply as a machine that converts heat energy to mechanical energy. The engine does this through either internal or external combustion.

Combustion is the act of burning. Internal means inside or enclosed. Thus, in internal combustion engines, the burning of fuel takes place inside the engine; that is, burning takes place within the same cylinder that produces energy to turn the crankshaft. In external combustion engines, such as steam engines, the burning of fuel takes place outside the engine. Figure 12-1 shows, in the simplified form, an external and an internal combustion engine.

The external combustion engine contains a boiler that holds water. Heat applied to the boiler causes the water to boil, which, in turn, produces steam. The steam passes into the engine cylinder under pressure and forces the piston to move downward. With the internal

Figure 12-2.-Cylinder, piston, connecting rod, and crankshaft for a one-cylinder engine.

combustion engine, the combustion takes place inside the cylinder and is directly responsible for forcing the piston to move downward.

The change of heat energy to mechanical energy by the engine is based on a fundamental law of physics. It states that gas will expand upon the application of heat. The law also states that the compression of gas will increase its temperature. If the gas is confined with no outlet for expansion, the application of heat will increase the pressure of the gas (as it does in an automotive cylinder). In an engine, this pressure acts against the head of a piston, causing it to move downward.

As you know, the piston moves up and down in the cylinder. The up-and-down motion is known as reciprocating motion. This reciprocating motion (straight line motion) must change to rotary motion (turning motion) to turn the wheels of a vehicle. A crank and a connecting rod change this reciprocating motion to rotary motion.

All internal combustion engines, whether gasoline or diesel, are basically the same. They all rely on three elements: air, fuel, and ignition.

Fuel contains potential energy for operating the engine; air contains the oxygen necessary for combustion; and ignition starts combustion. All are fundamental, and the engine will not operate without any one of them. Any discussion of engines must be based on these three elements and the steps and mechanisms involved in delivering them to the combustion chamber at the proper time.

How to do the project:

This project in most part is a research and display project. You will make drawings or cut color papers or cardboard models of components of a simple internal combustion engine. Mount everything on your display board with proper description. Information that you need to do that is above and the rest is art work and depends on your creativity.

Additional project ideas:

You may want to study on certain aspect of internal combustion engines. Following are some examples and guidelines:

How does the temperature of an internal combustion engine affect the efficiency of the engine?

When you first start an engine, it is cold and after a while it gets hot. If temperature does affect the efficiency, manufacturers can adjust their design in a way that engine gets to it’s efficient temperature in less time. When engine is working at high efficiency, all the fuel will burn and get converted to carbon dioxide and water. If the engine does not have high efficiency, it simply means that part of the fuel and gases such as CO that indicate incomplete burning will exit from the exhaust (Muffler). These are harmful gases that we try to avoid. In inspection stations, computerized test equipment measure the amount of CO and unburned fuel that comes out of the exhaust. For simple experiment, you may use a regular CO detector that is available at many hardware stores and test the gases that comes out of the exhaust. Ask your helping adult to start the car and while it is still cold, check the exhaust gases for presence of CO. Leave the engine running and repeat your test every one minute. Record the engine temperature as displayed inside the car along with your readings of CO. Write the results in a table and draw a graph if needed. Use your results table for analysis and conclusion.

How much CO is released in the air each day by internal combustion engines?

You can do this research with or without an experiment. Do a search and find out the production of oil or gas in the world. The weight of carbon dioxide is roughly 3 times more that the weight of fuel that is burned. You can even do an experiment to see what percentage of the gases that exists an engine is carbon dioxide. A large balloon can be used to store the gasses. (record how many seconds did it take for the engine to produce that much gas.) Tie a string to close the balloon. Measure the volume of the balloon (This needs some calculations). Then fill up a test tube or a small glass bottle with ammonia solution. Carefully place the balloon opening over the ammonia container and secure it so the gas does not leak. Now open the string so the gas inside the balloon comes in contact with ammonia. Ammonia absorbs carbon dioxide so the volume of the balloon will decrease in a few hours. Measure the volume again. The difference in volume will be the volume of carbon dioxide.
If you don’t have a large balloon, use a large plastic bag. You can get a similar result with some care.

If you calculate the amount of CO2 (carbon dioxide) produced by each car in each second or minute, you can use it to calculate the amount of carbon dioxide produced by all cars in a town or in a country or in the world.

The above examples are not all that you can do with this project. Think yourself and ask others in order to come up with more ideas.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to learn and display the principles of an Internal Combustion Engine.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

As a display project you will not need to define variables. But if you decide to study on one feature such as the effect of engine temperature on efficiency of engines, then you will need to define variables. For example the engine temperature will be an independent variable and the efficiency will be a dependent variable.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

As a display project you will not need a hypothesis. But if you decide to study on one question such as the effect of engine temperature on efficiency of engines, then you will need to have a hypothesis. For example you may hypothesize that the efficiency of engine will increase with any increase on engine temperature.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Use the information on the “gathering information” section and the links offered at the reference section to prepare your display board. If you have a sample of a small engine such as those used in model airplanes, you can use that as a part of your display.

You may also use wood to make a model of a simple one cylinder engine.

If you want to make a simple model to show “how internal combustion happens?“, you may make a potato gun as described in the following experiment.

Adult supervision, help and safety precautions is required for this experiment.

Experiment 1: (Engine Model)

Make a wooden or cardboard model of a simple engine to show how does the gas pressure on piston can be used to produce a rotational motion. You may substitute the material described in the following procedure or change the sizes and still make a working model.

Material and equipment:

  • Heavy card board or wooden board to mount other components.
  • Round piece of wood or cardboard to represent crank shaft. In the following image we have cut gears on that wheel but you don’t have to.
  • A wooden stick to be used as piston rod.
  • A rectangular piece of wood to represent the piston.
  • Two pieces of wood to represent the sides of a cylinder. Piston will slide between these two.
  • Wood dowels


  1. Start by making holes that will be used to connect the components. You will need one one end of the base board to mount the crank shaft wheel, Two holes on the crank shaft wheel, one in the center and another off the center to be attached to the piston rod. Piston rod also needs one hole on each end. Finally make one hole on the piston piece.
  2. Use a short wood dowel to connect the wheel to the board and connect the piston rod to the wheel.
  3. Connect the other side of the piston rod to the piston and rotate the wheel so the piston will be as far as possible from the wheel.
  4. Place to piece of woods on the sides of the piston and secure them on the base board (Use screw or wood glue).
  5. Now rotational movement of wheel must result the piston to go up and down. Also the movement of piston up and down may spin the wheel. For this action wheel needs to be made of heavy material and friction must be very low.


After your model is working, you may want to disassemble all the parts and paint them to create a more attractive display. That is why it is good to use screw to connect cylinder parts. Of course they are not real cylinder parts. Instead they are two piece of wood that are mounted on the sides of the piston to represent cylinder walls.




Also cylinder is usually closed on one end where valves are located. So it is good if you paint an additional piece of wood to close the cylinder. Small space can be left to represent the valves.



Final model can be used as a part of your display.

Experiment 2: (Combustion spudgun) (For older students)

Adult supervision, help and safety precautions is required for this experiment.

A potato gun sometimes called a spudzooka or spud gun is weapon that can launch spuds at over 200 ft/s. It is a propellant based gun that uses any propane based aerosol as a propellant (most experiments use hair spray, for it is inexpensive and easy to use). The way it works is propellant is injected into the combustion chamber and ignited with a BBQ sparker, as the gas expands it pushes the potato up the barrel and out of the gun.

Building a potato gun is fairly simple provided some basic tools are available. The most basic potato gun consists of three main components: a combustion chamber, a barrel, and an igniter. The combustion chamber and the barrel are usually constructed out of pressure rated PVC or ABS piping and the igniter can be any type of sparker, but most potato gun experimenter’s prefer to use BBQ igniters, for they provide a large and effective spark.


  • 2 feet of 2 inch diameter PVC or ABS pressure rated pipe
  • 1 foot of 3 inch diameter PVC or ABS pressure rated pipe
  • screw off end cap for 3 inch pipe (note: clean out plug may be used)
  • slip to threaded 3 inch fitting
  • 3 to 2 in reducer
  • PVC or ABS cement (note: do NOT mix PVC pipes with ABS pipes or fitting, only use PVC cement on PVC and ABS on ABS)
  • BBQ igniter
  • 2 drywall screws
  • hair spray
  • plenty of spuds



Assembly Instructions

1. Cut pipes to correct length’s with a hacksaw

2. Glue the barrel and the chamber to the reducer as shown in the diagram. (if PVC is used don’t forget to apply primer first.

3. Close off the end of the chamber with the fitting and screw-on end cap or the drain plug cap.

4. Screw the drywall screws through the sides the combustion chamber so there is about a 1/4 to 3/8 inch gap

5. Connect the sparker to the drywall screw and make sure it fires properly, if no spark fires move screws closer and re-test.

6. Bevel the end of the barrel so that the potato will be cut to size when it is loaded. Beveling can be done with a Dermal or if one is not available a file can be used.

7. Let cement dry for about an hour (this time can be used to go buy some spuds!!)

Firing Tips

Caution: Only fire in open spaces far away from human life

1. Load the gun by cutting a large enough potato in half and then cutting it to the right size by pushing it into the barrel of the gun and letting the gun cut the potato’s shape. If the potato is too small the potato will not go very far, for most of the gas will escape. Providing a good seal is the key to distance spud launching. The gun barrel will be like a cylinder and the potato will be the piston in an internal combustion engine.

2. Get a stick that can be used to muzzle load the potato. Measure out how far on the stick the potato has to be pushed down to be right before the combustion chamber and push it down to that level.

3. Unscrew the back and fill with propellant. I like using pure propane from a blowtorch, but if one isn’t available then hair spray can be used. This is the trickiest part of all. The correct mixture of gas to air has to be present for the gun to fire. Experimenting is the best way. One thing that is important to remember is that the gas needs oxygen for combustion therefore after each time it is fired air must be allowed into the chamber.

4. Good Luck and be careful.

You can find more information about spud guns on the internet. Following link contains similar instructions.


Materials and Equipment:

Depends on your display or experiment that you may select.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.



Summery of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.