Introduction to Small Engines

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

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

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

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

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

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

Four Stroke Engines Intake Compression Power Exhaust

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

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

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

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

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

Two Stroke Engine Intake/Compression Power/Exhaust

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

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

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

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

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

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

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

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

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

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.)

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 .

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

Answer P=2000/4.91 P=407.33 psi

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?

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

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)

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)

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

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?

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

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

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)

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

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

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)

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

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

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

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

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)

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?

Answer P=W/T P=100,000/6 P= 16,666.67 lb-ft/min

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.

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

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

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)

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

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