1. Introduction to Small Engines

2. Small Engine History
1680 Christian Huygens develops a internal combustion engine that utilized gunpowder as a fuel source
1698 Thomas Savery developed the Savery pump utilizing steam to force water from the ground
1712 Thomas Newcomen develops a steam engine in which many components are still used in engines today including the piston in a cylinder as well as valves and pivot arms

3. Small Engine History Continued
1801 Eugene Lebon developed and internal combustion engine that used coal gas ignited by an electric ignition source
1859 Etienne Lenoir introduces an internal combustion engine that mixed coal gas and air together
It was at this same time that there was an resurgence in steam power that put the internal combustion engine on standby until 1862

4. Small Engine History Continued
1862 Nikolaus Otto and Eugene Lange designed and built the first gasoline engine
1876 Otto successfully modified his gasoline powered engine and introduced the four-stroke cycle engine. Known as the Otto cycle.
1892 Rudolf Diesel patented an new type of internal combustion engine that ignited fuel under high pressure. Later to become know as the diesel engine
The first diesel engines used coal dust as a fuel source

5. Objectives
Identify the key differences between a 2-Stroke and 4-Stroke engine
Identify the four strokes of a 4-cylcle engine
Identify the two strokes of a 2-cycle engine
Identify the five events of both the 4 and 2 cycle engine

6. Engine Classification
External Combustion
Internal Combustion
Ignition
Spark
(Gasoline)
Two Stroke
Four Stroke
Compression
(Diesel)

7. Spark vs. Compression Igniton
A compression ignition engine uses compression of the air-fuel mixture to ignite the mixture
Most commonly use diesel fuel
A spark ignition engine uses an electrical spark to ignite the air-fuel mixture
Most commonly use gasoline as a fuel source

8. Four Stroke Engines
Intake
Compression
Power
Exhaust

9. Four Stroke Cycle Engine
Utilizes four strokes to complete one operating cycle
Four Stroke Engine Completes five distinct events during each cycle
Intake
Compression
Ignition
Power
Exhaust

10. Intake Stroke
Piston moving down creates vacuum in cylinder drawing in air-fuel mixture

11. Piston moving up compresses air-fuel mixture
Compression Stroke
Piston moving up compresses air-fuel mixture

12. Air-fuel mixture ignited by spark plug forces piston down
Power Stroke
Air-fuel mixture ignited by spark plug forces piston down

13. Piston moving up forces out exhaust gases
Exhaust Stroke
Piston moving up forces out exhaust gases

14. Two Stroke Engine
Intake/Compression
Power/Exhaust

15. Two Stroke Cycle Engine
Utilizes two strokes to complete one operating cycle
Completes the same five events as the four stroke engine
Intake
Compression
Ignition
Power
Exhaust

16. Intake/Compression Stroke
Air-fuel mix enters combustion chamber through transfer ports
piston moving up compresses air-fuel mix
air-fuel mix drawn into crankcase from intake port

17. Power/Exhaust Stroke
Air-fuel mix ignited by spark plug forces piston down compressing air-fuel mix in crankcase
Exhaust gas discharged through exhaust port

18. Energy Principles Two forms of energy:
Potential energy
Kinetic energy
Potential energy is stored energy
Kinetic energy is energy in motion

19. Small engine operating principles
All internal combustion engines operate by utilizing basic principles of
Heat
Force
Pressure
Torque
Work
Power
Chemistry

20. Heat
Definition
Heat is kinetic energy caused by matter in motion within a substance
Heat added to a substance causes velocity to increase
Heat removed from a substance causes velocity to decrease
We see this principle in action during the compression and power stroke

21. Heat
When the air-fuel mixture is compressed and heated up it changes the mixture to a gaseous state
This prepares the air-fuel mixture for efficient combustion

22. Force
Force is anything that changes or tends to change the state of rest or motion of a body(anything with mass)
For example if you push on an object a force has been exerted on that object
Force is measured in pounds(lb) in the English system or Newton's(N) in the metric system

23. Force Force does not always result in movement of an object
Force can be applied in different ways to produce pressure, torque or work

24. Pressure Pressure is a force acting on a unit of area
Area is the number of unit squares equal to the surface of an object
When force and area are known pressure is found by applying the formula
P=F/A
P= pressure (in lb/sq inch)
F= force (in lb)
A= area (in sq in.)

25. Pressure
In an internal combustion engine pressure is applied to the top of the piston head.
Piston motion is transferred from the connecting rod to the crankshaft .

26. Determining Pressure
How much pressure is exerted if a force of 2000 pounds is applied to an area of 4.91 square inches?
P=F/A

27. Answer
P=2000/4.91
P= psi

28. Additional practice
What is the pressure exerted if 60 pounds of force is applied to an area of 4 square inches?
What is the pressure if a 1000 pound force is applied to an area of 5 square inches?

29. Answers
P=F/A
P=60/4
P=15 psi
P=1000/5
P=200 psi

30. Torque
Torque is a force acting on a perpendicular radial distance from a point of rotation
Torque is equal to force times distance
The result is a twisting or turning force expressed as pound feet (lb-ft) or in newton-meters (Nm)

31. Torque
When force and radius are know, torque is found by applying the formula:
T=F*r
T=torque (in lb-ft or Nm)
F= force (in lb)
r= radius (distance)

32. Example
What is the torque developed if a 60 lb force is applied at the end of a 2 foot lever arm?
T=F*r
T=60*2
T=120 lb-ft
The same amount of torque would be applied if 120 lb. force was placed at the end of a 1’ lever

33. Additional Practice T=F*r
You have a 2’long wrench and apply 25 lbs of force how much torque has been applied?
How could you apply the same amount of torque but apply less force?

34. Levers
Lever- a simple machine that consists of a rigid bar that pivots on a fulcrum (pivot point) with both resistance and effort applied
Main purpose is to overcome large resistance with reduced effort

35. One of the main examples of a lever in a small engine is the crankshaft
Provides lever distance from the center line of the crankshaft
Converts force applied by the piston to result in rotation of the crankshaft

36. Calculating Stroke
Stroke is the linear distance a piston travels inside the cylinder from the cylinder head end to the crankshaft end
Stroke is determined by throw of the crankshaft
Throw is the measurement on a crankshaft from the centerline of the crankshaft to centerline of the connecting rod (offset)

37. Work
Work is force applied through a parallel distance causing linear motion.
Work occurs only when the force results in motion
Work is measured in lb-ft or Nm

38. Work Requires only enough force to complete the desired task
If additional force is applied that force will result in acceleration
Work and torque are similar
The only true difference is torque does not always result in perceptible motion

39. Work Formula
When force and distance are known, work is found by applying the formula:
W=F*D
W= work
F= force(in lb)
D=distance (in lb)

40. Example
What is the amount of work performed if a mower pulled a container that weighed 330 lb 100 feet?
W= 330*100
W=?

41. Additional Practice
How much work is performed when lifting a 72 lb engine from the floor to the top of a 3 foot high workbench?
W=F*D

42. Power Power is the rate at which work is done.
Power adds in a time factor
Power can be expressed in several ways
Force
Distance
speed

43. Power Typical examples include Horsepower Watts (W) Kilowatt (kWh)
Both watt and horsepower measure how fast work is completed

44. Power
When force and distance are known, power is found by applying the following
P=W/T
P=power (in lb-ft/min)
W= work (force*distance)(in lb-ft)
T= time (in min)

45. Example P=W/T P=power (in lb-ft/min)
W= work (force*distance)(in lb-ft)
T= time (in min)
What is the power output of an engine that performs 100,000 lb-ft of work in 6 minutes?

46. Answer
P=W/T
P=100,000/6
P= 16, lb-ft/min

47. Horsepower
Horsepower (HP) is a unit of power equal to 746 watts (W) or 33,000 lb-ft per minute, 550 lb-ft per second
HP is used to rate and rank the power produced by an engine based on a finite engine speed.

48. HP HP was developed by James Watt in the 1800’s
Developed HP to give a reference of power to the steam engine that he produced for the mining industry
He based his observations of power on the average horse

49. Horse Power
He determined that an average horse could move/lift 33,000 lb on a linear plane, 1’in 1 minute.
This is the basis for the standard 550 lb-ft per second that is still used today
Horsepower is found by applying the following

50. Horse Power HP=W/T*33,000 HP= horsepower
W=work (force*distance) in lb-ft
T=time ( in min)
33,000=HP constant (in lb-ft)

51. Example
What is the horsepower rating of an engine that produces 412,500 lb-ft in 2.5 minutes?
HP=W/T*33000
HP=?

52. Answer
HP=412,000/2.5*33000
HP=412,000/82,500
HP=5 Hp