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Compression System
Katie Lynn Johnson
Class and Grade / Ag II, SophomorePathway / Ag Mechanics
Unit/Area/Enterprise / Small Gas Engines
Lesson Title/Job / Becoming Familiar with the compression system of small gas engines
Situation/Rationale / This is the second lesson in this unit, because the compression system it is the easiest to understand and the components of this system are the major and most notable parts of the engine. Once the students understand this system and its components, the other systems will be easier to understand.
Colorado Ag Ed Standards/ Competencies / · AME 11/12.04
o The student will demonstrate how to be a cooperative contributor who participates effectively to accomplish a group activity in agricultural mechanics.
· .04 Perform engine assembly
· AME11/12.05E
o The student will demonstrate the use of current technology and principles of Agricultural Electrification.
· .06 Start, stop, and install electric motors
· .07 Identify and select electric motors
· AME11/12.05FP
o The student will demonstrate the use of current technology and principles of Farm Power Systems,
· .01 Dissemble, repair, and reassemble a small gas engine
· .02 Service ignition system
· .03 Service cooling system
· .05 Service lubrication system
· .06 Service fuel system
· .07 Understand carburetor
· .08 Understand engine nomenclature and operating principles.
· .09 Troubleshoot engine
· .10 Understand requirements for engine storage
· .15 Service spark plugs
Student Learning Objectives / Upon completion of this lesson the student will be able to:
1. identify all parts and components involved in the compression system.
2. describe the 4 strokes of an engine.
3. disassemble and reassemble an engine.
Time: / 2: 50 minute periods, including a mechanics shop portion.
References and Resource(s): / Briggs & Stratton maintenance and repair handbook.
Instructions, Tools, Equipment & Supplies / ● Briggs and stratton Motors, Notes sheets, all essential tools, care and repair books, fly wheel brace, socket wrench
Introduction/Context / Yesterday we started the small gas engines unit, today we will be looking at the compression system, but before we get started, who can tell me what a micrometer is used for? And how do we use plastic feeler guage? Allow students to answer and review from the day before.
Hand out the notes sheets to all the students. As well as the care and repair books for the students to use as a reference.
Interest Approach/Motivation / You all drive vehicles right? What kind of engines are in your vehicle? A V6, V8, allow students to brag up their cars, talk about all the cool things, the Hemmis, or whatever is brought up. This will get discussion about different engines, and actual components. Use teacher time and make sure the students are staying on topic.
All engines have 4 basic systems that make them operational, does anyone know these systems?
* Compression System, Fuel system, Ignition system, Lubrication and cooling system, and the governor system.
* Other supplemental systems can include the braking system, and electrical system.
Today we are going to be looking at the compression system, and diving into the dis-assembly of our engines. So lets get started.
Lesson Body and Content
Objective 1: / TLW identify all parts and components involved in the compression system.
Has anyone heard the term of internal combustion? This term is used to describe the mixture of air and fuel vapor inside the combustion chamber inside the engine. The compression system is what is used to actually compress the air and vapor prior to ignition. The system actually compresses the air and vapor to 1/6th of its original volume. The exactness of the compression system is what will indicate the engines efficiency.
Before we can begin understanding the compression system and its function an purpose, we need to know all of the parts involved within the system, take a few minutes and label all the parts on the diagram using a partner and your book for assistance. Allow students time to label the diagram, answer questions and keep them on task!
Go through the diagram and make sure all the students have the parts labeled correctly. ** See the attached diagram and notes sheets!!
Objective 2: / TLW describe the 4 strokes of an engine.
The engines we will be working with are 4 stroke engines, there are 2 stroke engines, however you will only be responsible for knowing the 4 stroke engine components. Is there anyone who knows the 4 strokes of an engine?
* Intake, Compression, Ignition, and Exhaust
The strokes of an engine are correlated to the position of the piston and engine valves. These are timed with the crank shaft and are controlled through the CAM and the cam lobes, as the crank shaft turns, it turns raises and lowers the piston. Attached to the CAM is the cam lobe, these push the tappets up and down, which either opens or closes the valves. We are going to look at each individual stroke, to get a better understanding of how compression in the engine works.
The first stroke is the intake stroke, during this stroke, the piston rotates from all the way up to all the way down, the intake valve is open and the exhaust valve is closed. Air and fuel vapors enter the compression chamber.
Has anyone ever drawn a shot up in a syringe? This is the exact same concept of the intake stroke, the piston and the plunger of the syringe work in the same fashion. As the piston moves down, the there is low pressure in the chamber, and the air-fuel mixture is drawn into the chamber through the intake valve. As the piston reaches the bottom of the chamber, the intake valve closes, and now the chamber has been sealed.
After the vapors and air have been brought into the chamber, the next step is the compression stroke. During this stroke, the piston rises, while both the valves are closed. Again the air is compressed into 1/6th its original volume. This compression allows for a more efficient burn, and for more energy to be released faster during ignition.
Once the air-fuel mixture has been compressed, the ignition stroke is next, this stroke is known as both the ignition stroke or the power stroke. This stroke is where the engine gets its power from. The valves are still closed from the compression stroke, as the piston is approaching the top of the chamber, the spark plug initiates the combustion which creates a flame to burn the compressed mixture.
The final stroke is the exhaust stroke. The piston is being forced downward from the combustion, once it reaches bottom, the exhaust valve opens allowing the exhaust to exit the chamber.
Once he 4 strokes have been completed, the entire cycle is finished. For each cycle, there are 2 total rotations of the crank shaft.
Are there any questions? What are the 4 strokes of an engine, what is the position of the piston during each? What are the 2 valve names?
Objective 3: / TLW disassemble and reassemble an engine
Alright, now that we have completed the compression system, we are going to start with the disassembling process. Yesterday we were in the shop, and looked at the engine room, got familiar with the tools, and found our partner and area assignment.
We are going to start taking apart your engines. It is ABSOLUTELY critical that you are VERY organized during this process. We suggest even sketching your engine or taking picture of your engine to help you when we start putting everything back together. The more organized and meticulous you are during this process, the better prepared you will be in re-assembling your engine, and the more likely it will be for your engine to successfully start.
Today we are going to start by removing the fly wheel, the cover case, and start removing all parts of the engine. Once we get out to the shop, I will give you a demonstration on removing the fly wheel. Please get your safety glasses, coats, and meet me out in the engines room.
· Give a demo on how to set up the fly wheel brace, how to secure the engine, and then how to remove the nut, and make sure students know how to remove the fly wheel.
· During this time, be there to answer questions and keep the students on task. It does not make a difference which parts are removed in what order, It only matters that things are done in an organized fashion.
Review, Summary or Closure / Once clean up is complete outside, have the students return to the classroom. Have a brief review session, and include some of the following questions.
· What is the purpose of the tappet?
· How many rotations of the crank shaft are needed to complete one entire cycle?
· If the piston is at the maximum highest point in the chamber, what stroke is then engine in?
Evaluation or Assessment / The completion of the notes sheet will be used for assessment in the classroom. As well in the shop the students are evaluated on work ethic, shop safety, and participation.
Evaluation Answer Key or Scoring Rubric/Procedure
Small Gas Engines
Name:______
UNDERSTANDING SMALL GAS ENGINES
BASICS
What are the basic systems that contribute to the function of a small gas engine?
THE COMPRESSION SYSTEM
Fill in the diagram with the following parts.
Describe the 4 strokes of this engine:
How many rotations of the crankshaft are there per cycle of the engine?