LESSON NOTES 102
FORCE: Force is any action that is applied against an object that will cause it to move or have a tendency to move. Force has a tendency to accelerate an object from a state of rest to a state of motion or movement. Force is pressure against an object and is used in calculating torque or horsepower. Force is measured in pounds.
There is an action tending to move an object but the object is not moving. Force is applied but since the object does not move, there is no work accomplished.
WORK: When a force is applied to move an object from a state of rest or accelerate the movement of an object from one place to another, work is done. Work also has a unit of measurement. Work is measured by multiplying the force by the distance the object is moved. So we have the formula:
WORK = FORCE X DISTANCE
POWER: Power is the rate of time that it takes to accomplish the work performed.
Power = force x distance/time.
In this formula we can see that power must increase if the time in which the work is done decreases.
HORSEPOWER: Horsepower is a unit of measurement of power. One horsepower has been designated as being able to do 33,000 foot-pounds of work in one minute.
Horsepower = pounds x feet/33,000 x minutes
BRAKE HORSEPOWER: When referring to engine horsepower, it is generally referred as brake horsepower or rated horsepower. Brake horsepower is the maximum horsepower from an engine as determined by a dynamometer. A dynamometer is an instrument used for testing engines.
This horsepower rating is usually stated as a maximum observed horsepower or corrected brake horsepower. Observed brake horsepower will vary under certain conditions such as temperature and atmospheric pressure. Corrected brake horsepower is the horsepower calculated from observed brake horsepower and is a means of comparing engines tested under varying conditions, such as temperature and atmospheric conditions.
RATED HORSEPOWER: Rated horsepower is used as a safety factor to keep from overloading an engine. If a gas engine is operated at its very maximum capacity at all times, we know it will have a very short life.
An engine being operated at its maximum rating will not have reserve power for overloads and would be subject to damage from overheating and rapid wear.
When an engine is selected for a particular job or load, the engine brake horsepower rating should be in excess of the expected normal operating load. Generally, it is recommended that an engine should not be operated in excess of 80% of the maximum brake horsepower. This gives a 20% margin for overload.
TORQUE: The “torque rating” of an engine is defined as the turning effort exerted by the output shaft when under load.
MEASURING TORQUE AND HORSEPOWER
DYNAMOMETER: Some dynamometers are available in small shops but they are very rare. They have a hydraulic or electric loading device and scales to indicate engine speed and load. Horsepower is then calculated by instruments.
ENGINE HORSEPOWER VARIATIONS: Engine efficiency will vary with the amount of air taken into the cylinder on each intake stroke. Due to this process, the air density has an effect on the horsepower output. Air density varies with both temperature and atmospheric pressure. Changes in air temperature, barometric pressure or elevation will cause a change in engine horsepower. Horsepower will decrease with elevation, drop in barometric pressure and rise in temperature.
BASIC ENGINE PRINCIPLES:
There are two basic designs used in most outdoor power equipment engines. The most common is called the 4 – cycle. These engines require a separate system for lubrication. The 2 – cycle engine is lubricated by premixing oil and the fuel. It has no separate oil supply like
The 4 – cycle engine.
Even though both of these engines produce basically the same results, certain applications make one or the other more adaptable to an individual operation.
Each have their desirable and undesirable features. Generally, the 4 – cycle engine is easier to start as raw fuel will ignite more easily than fuel mixed with oil. 2 – cycle engine is easier to maintain because there are fewer moving parts. Lubrication reaches every moving part on every stroke of the piston. Oil is always fresh and clean. Clean lubrication means longer life for any engine.
DISTINGUISHING FEATURES OF OUTDOOR POWER EQUIPMENT ENGINES
In order to meet the requirements of the many different applications, these engines are made with different features and designs. The engine itself is basically the same. Most of the variations are in accessories, such as different types of starters, carburetors and ignition system. One major difference is the number of strokes or cycles. One distinguishing feature of these engines is the position in which it is to be used.
There are three basic operating positions for most outdoor power equipment engines, which are as follows:
- VERTICAL CRANKSHAFT ENGINES – The vertical crankshaft engine has a cylinder that operates in a horizontal position. The vertical crankshaft engine is well adapted to mounting a mower blade or other equipment requiring horizontal movement.
- HORIZONTAL CRANKSHAFT ENGINES – The horizontal crankshaft engine may have its position either in the vertical, horizontal or at some intermediate slanted position.
2- CYCLE ENGINES
The 2- Cycle engine will operate in any position. The position is at right angles to the crankshaft, The reason this type of engine can be operated in any position depends on the way they are lubricated. This type of engine is often used on equipment requiring it to be used at extreme angles and sometimes even upside down. The chainsaw is a typical application of this engine.
THE PROBLEMS WITH OUTDOOR POWER EQUIPMENT ENGINES
Their problems of not working properly are often due to lack of understanding of how the engine works and how it should be cared for and maintained. Most engine troubles are generally due to lack of proper service, operation, maintenance and repair.
You should first examine the conditions under which the engine operates. Most of the engines are designed to operate continuously at near top speed to prevent overload. All functions must be operating at top efficiency at all times. There is generally very little power to spare so every bit of it must be put use.
ENGINE ABUSE
The speed of the average outdoor power equipment engines may be sometimes around 3600 RPM. This equivalent to an automobile operating at over 80 miles per hour. This high RPM is generally the continuous operating speed when being used. Chainsaw, string trimmers and air/leaf blower engines operate at 4,000 – 10,000 RPM to develop the required power.
During operation, outdoor engines are often subjected to much abuse, overload and over-speeding. They are sometimes operated near ground level where dirt and dust are likely to get into their working parts. Often they not serviced and cleaned properly causing rapid wear. Few of these engines receive the proper servicing and maintenance that is given to other types of engines.
If you understand outdoor power equipment engines, you can apply this same basic knowledge to larger engines such as automobiles and tractors.
STUDY GUIDE NOTES
Good success teaching and tutoring program helps students attain maximum potentials and results in engineering, physics and math.
To attain maximum results, students should apply the following guidelines:
- SCHEDULE A QUALITY TIME
A good successful student must make a regular and systematic study approach for attaining maximum results with minimum time. It’s not in how long you study but in how smart and consistent you study towards a particular goal. Set your goal and map out suitable time and task each day or week for study will help you finish much faster than studying long hours on a haphazard manner.
- OBSERVE FRQUENT BREAKS
Make sure you observe breaks at regular intervals when you study longer periods in each session of you schedule. All works and no play makes Jack a dull boy. It is quite necessary from time to time to get up, stretch your legs walk around and forget about your studies for a little while.
Following the above suggestion will make you stay active and alert, which makes you gain a lot from the course of study towards a good success.
- CHOOSE A FAVORABLE STUDY AND WORK AREA
Find a convenient area where you can be by yourself – your own room, workshop, garage, library, and some other favorable areas.
The selected area should be well ventilated, with good lighting, power outlets and enough working space.
The place should be well arranged for easy access and placement of materials
- VENTILATION
Ventilation is extremely important when working with gasoline engines. If you are working an air-conditioned area where the air is recirculated, keep at least one window open or turn the air-conditioner to the “Exhaust” setting.
Since you will be working in the presence of gasoline, be sure to follow the recommended safety rules for storing and using products.
- WORK SURFACE
You need a good chair, table, work bench and computer stand.
HOW TO MAKE LEARNING EASY FOR MAXIMUM ACHIEVABLE SUCCESS
To achieve the best from every lesson, you must first read through it to get a general idea of what it covers. Then go back and read it again slowly topic by topic or chapter by chapter as well as by questions and answers.
As you read don’t be too concerned about “memorizing” facts or wordings. All you need to do is to form an understanding of the principles or procedures involved. If you know how a system or an object operates, you will never forget it and you can easily apply it towards a sustainable form of development.
Good success program is therefore starting with the principles and terms relating to simple machines for engineering students and engineers.
GRADE YOUR LESSONS AND SKILLS
Every student should make the best grades possible the more you learn and answer questions, the more you will profit from good success program.
From the questions and answers session, try to answer the questions on your own first and foremost. No cheating allowed by just using the answers included below.
You can grade yourself as follows:
90 – 100% = A (Excellent)
80 -89% = B (Very Good)
70 – 79 = C (Good)
60 – 69 = D (Pass)
ANSWERS FOR THE PRINCIPLES AND TERMS RELATING TO SIMPLE MACHINES AND ENGINES
A1. – is (b): False
EXPLANATION: 2 – Cycle engines are easier to maintain because there are fewer moving parts.
A2. – is (a): True
EXPLANATION: A 2 – Cycle engine is lubricated by premixing oil with fuel.
A3. – is (a): True
EXPLANATION: A 4 – Cycle engine has oil supply suspended in the fuel vapor and adheres to the surface of all moving parts, since the engine can only be operated in an upright position.
A4. – is (a): True
EXPLANATION: A vertical crankshaft engine has a cylinder that operates in a horizontal position.
A5. – is (b): Time
EXPLANATION: Power is the rate of time that it takes to accomplish the work performed.
A6. – is ( c ): Horsepower
EXPLANATION; Horsepower is the unit of measurement of power.
A7. – is (d): Torque
EXPLANATION: Torque is defined as the turning effort exerted by the output shaft when under load.
A8. – is (d): 4 – Cycle Engine
EXPLANATION: A 4 – Cycle engine is operated on straight fuel.
A9. – is (a): 4 – Cycle Engine
EXPLANATION: A 4 – Cycle engine has more moving parts than any other type of engine.
A10. – is ( c ): 1 minute
EXPLANATION: One horsepower has been designated as being able to do 33,000 foot-pounds of work in one minute.
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