2Six Classifications of Engines Combustion – whether the engine is internal or external combustion.Ignition – compression versus spark ignitionNumber of Strokes – 2 stroke or 4 strokeCylinder Design – vertical, horizontal, slant, V, opposed, inlineShaft Orientation - vertical or horizontalCooling System – liquid cooled or air cooled
3Combustion Engine Types Two types of Engines based on CombustionExternal Combustion EnginesInternal Combustion Engines
4External Combustion Engines External combustion engines separate the heat source from the source of power.The external heat source heats an internal fluid, through a heat exchanger of some typeThe heated fluid expands creating pressureThe pressure drives a turbine which provides power for use.
5Most common types of External Combustion Engines Steam enginesStirling engines
6Steam Engines first invented by Thomas Newcomen in 1705. powered all early locomotives, steam boats and factoriesacted as the foundation of the Industrial Revolution.
7How Steam Engines WorkHeat is obtained from fuel burnt in a closed fireboxThe heat is transferred to the water in a pressurized boiler, boiling the water and transforming it into saturated steam.The steam is transferred to the motor unit which uses it to push on a piston sliding inside a cylinder to power machinery.The used, cooler, lower pressure steam is exhausted to atmosphere
9Stirling Engines Invented by Robert Stirling in 1816, Has the potential to be much more efficient than a gasoline or diesel engine.Today, Stirling engines are used only in some very specialized applications, like in submarines or auxiliary power generators for yachts, where quiet operation is important
10How Stirling Engines Work The Stirling cycle engine uses air as its liquid, which resolves many of the issues with steam. It is not as dangerous as steam and does not lose as much energy in transition, because it does not transition.The gasses used inside a Stirling engine never leave the engine. There are no exhaust valves that vent high-pressure gasses, as in a gasoline or diesel engine, and there are no explosions taking place. Because of this, Stirling engines are very quiet.
11How Stirling Engines Work The key principle of a Stirling engine is that a fixed amount of a gas is sealed inside the engine.Stirling cycle involves a series of events that change the pressure of the gas inside the engine, causing it to do work.
12How Stirling Engines Work Heat is added to the gas inside the heated cylinder (top), causing pressure to build. This drives the hot piston in its power stroke. This is the part of the Stirling cycle that does the work
13How Stirling Engines Work The heated gas expands and pushes the hot piston to the bottom of its travel in the cylinder.The expansion continues in the cold cylinder, which is 90° behind the hot piston in its cycle, extracting more work from the hot gas.
14How Stirling Engines Work The gas is now at its maximum volume. The hot cylinder piston begins to move most of the gas into the cold cylinder, where it cools and the pressure drops
15How Sterling Engines Work Almost all the gas is now in the cold cylinder and cooling continues. The cold piston, powered by flywheel momentum (or other piston pairs on the same shaft) compresses the remaining part of the gas
17Why aren’t Stirling Engines more common? Because the heat source is external, it takes a little while for the engine to respond to changes in the amount of heat being applied to the cylinder -- it takes time for the heat to be conducted through the cylinder walls and into the gas inside the engine. This means that:The engine requires some time to warm up before it can produce useful power.The engine can not change its power output quickly.
18Internal Combustion Engines An internal combustion engine is one in which:the combustion of a fuel is used to push a piston within an cylinderthe pistons movement turns a crankshaft that provides mechanical powermechanical power moves the other parts of the drive train
19Seven main types of internal combustion engines 2 stroke cycle4 stroke cycleCompression (diesel)RotaryRocketGas TurbineJet (Hache)
21Sparks FlyFuel and air in the cylinder have been compressed, and when the spark plug fires the mixture ignites.The resulting explosion drives the piston downward. Note that as the piston moves downward, it is compressing the air/fuel mixture in the crankcase.As the piston approaches the bottom of its stroke, the exhaust port is uncovered. The pressure in the cylinder drives most of the exhaust gases out of cylinder.
22Fuel IntakeAs the piston reaches the bottom the intake port is uncovered.The piston's movement has pressurized the mixture in the crankcase, so it rushes into the cylinder, displacing the remaining exhaust gases and filling the cylinder with a fresh charge of fuelThe piston is shaped so that incoming fuel doesn’t simply flow right over the top of the piston and out the exhaust.
23The Compression Stroke the momentum in the crankshaft starts driving the piston back toward the spark plug for the compression stroke.As the air/fuel mixture in the piston is compressed, a vacuum is created in the crankcase.This vacuum opens the reed valve and sucks air/fuel/oil in from the carburetor.Once the piston makes it to the end of the compression stroke, the spark plug fires again to repeat the cycle.
24Two-Stroke AnimationIt's called a two- stoke engine because there is a compression stroke and then a combustion stroke.
25Advantages of Two-Stroke Two-stroke engines do not have valves, which simplifies their construction and lowers their weight.Two-stroke engines fire once every revolution, while four-stroke engines fire once every other revolution. This gives two-stroke engines a significant power boost.Two-stroke engines can work in any orientation, which can be important in something like a chainsaw. A standard four-stroke engine may have problems with oil flow unless it is upright, and solving this problem can add complexity to the engine.
26Disadvantages of the Two-stroke The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear a lot faster so engines don’t last as long.Two-stroke oil is expensive, and you need about 4 ounces of it per gallon of gasTwo-stroke engines do not use fuel efficiently, so you would get fewer miles per gallon.Two-stroke engines produce a lot of pollution -- so much, in fact, that it is likely that you won't see them around too much longer. The pollution comes from two sources:The first is the combustion of the oil. The oil makes all two-stroke engines smoky to some extent, and a badly worn two-stroke engine can emit huge clouds of oily smoke.The second reason is that each time a new charge of air/fuel is loaded into the combustion chamber, part of it leaks out through the exhaust port. That's why you see a sheen of oil around any two-stroke boat motor
27Common uses of Two-Strokes Chain sawsLawn cuttersSnowmobilesOutboard motorsDirt bikes
29Intake StrokeThe cycle begins at top dead center (TDC), when the piston is farthest away from the axis of the crankshaft.The intake valve opens.The piston descends from the top of the cylinder, reducing the pressure inside the cylinder.A mixture of fuel and air is forced (by atmospheric or greater pressure) into the cylinder through the intake (inlet) port.
30Compression StrokeWhen the piston reaches the lower limit of its travel, it begins to move upward.The intake (inlet) valve (or valves) closeAs the piston moves upward, the air/fuel mixture is compressedThe compression stroke compresses the fuel– air mixture.The compression process also causes the air/fuel mixture to increase in temperature.
31Power StrokeAs the piston reaches the top of its travel on the compression stroke, a high voltage electric spark is produced at the spark plug.The air–fuel mixture is then ignited near the end of the compression stroke:by a spark plug (for a gasoline or Otto cycle engine)by the heat and pressure of compression (for a Diesel cycle or compression ignition engine).The resulting pressure of burning gases pushes the piston through the power stroke.The power impulse is transmitted down through the piston, through the piston rod (connecting rod), and to the crankshaft. The crankshaft is rotated due to the force.
32Exhaust StrokeAs the piston reaches the bottom of its travel, the exhaust valve opens.In the exhaust stroke, the piston pushes the products of combustion from the cylinder through an exhaust valve or valves.When the piston reaches the top of its travel, the exhaust valve closes, and the intake valve opens.The cycle repeats again with the intake stroke.
33Four-Stroke Animation These four strokes require two revolutions of the crankshaft. The process continuously repeats itself during the operation of the engine.Thus the engine only fires once every four strokes or every second time the piston reaches the top of its travel.3RcVcHI
34Advantages of Four Strokes Over Two Strokes use much less fuel than 2 strokesproduce less pollutionhave a wider power band (the engine RPM range over which the engine produces its most power.have a dedicated lubrication system which means thatThey usually last longerThey do not burn oil
35Disadvantages of Four Stroke Engines They are heavy, more complicated and more expensive to buildThey do not create as much power as a same size 2 stroke.They cannot operate in a non-vertical position.
36Common uses of Four-Strokes AutomobilesATV’s (4 wheelers)SnowmobilesSnowblowersLawnmowersMotorcycles
37Rotary EngineRotary engines use the four-stroke combustion cycle, which is the same cycle that four-stroke piston engines use. But in a rotary engine, this is accomplished in a completely different way.The heart of a rotary engine is the rotor. This is roughly the equivalent of the pistons in a piston engine. The rotor is mounted on a large circular lobe on the output shaft. This lobe is offset from the centerline of the shaft and acts like the crank handle on a winch, giving the rotor the leverage it needs to turn the output shaft. As the rotor orbits inside the housing, it pushes the lobe around in tight circles, turning three times for every one revolution of the rotor.
38Intake StrokeThe cycle starts when the tip of the rotor passes the intake port.When the intake port is exposed to the chamber, the volume of that chamber is close to its minimum.As the rotor moves past the intake port, the volume of the chamber expands, drawing air/fuel mixture into the chamber.
39Compression StrokeAs the rotor continues its motion around the housing, the volume of the chamber gets smaller and the air/fuel mixture gets compressed.By the time the face of the rotor has made it around to the spark plugs, the volume of the chamber is again close to its minimum. This is when combustion starts.
40Combustion StrokeWhen the spark plugs ignite the air/fuel mixture, pressure quickly builds, forcing the rotor to move.The pressure of combustion forces the rotor to move in the direction that makes the chamber grow in volume. The combustion gases continue to expand, moving the rotor and creating power.Most rotary engines have two spark plugs. The combustion chamber is long, so the flame would spread too slowly if there were only one plug.
41Exhaust StrokeOnce the peak of the rotor passes the exhaust port, the high-pressure combustion gases are free to flow out the exhaust.The rotor continues to move forcing the remaining exhaust out of the port.When the rotor passes the intake port and the whole cycle starts again.
44Engine Ignition TypesA small engine is a Spark Ignition or Compression Ignition engine based on how the fuel is ignited.Spark ignitionthe fuel mixture is ignited with an electrical sparkCommonly use gasolineCompressionThe fuel mixture is ignited by compressing the fuel mixture under pressure and heatCommonly use diesel fuel
45Engine Stroke TypesA stroke is one complete travel of the piston from top dead center to bottom dead center or vice versa.Two (2) StrokeUtilizes two strokes to complete the intake, compression, power (ignition) and exhaust cycleFuel intake and compression on one strokePower (ignition) and exhaust on the other strokeFour (4) StrokeUtilizes four strokes to complete the intake, compression, power (ignition) and exhaust cycleIntake, compression, power (ignition) and exhaust occurs on a different stroke.
46Engine Cylinder Design Vertical – pistons travel up and down verticallyHorizontal - pistons travel back and forth in the horizontal planeSlant – pistons are oriented at an angle to the verticalV – pistons are divided into two banks at an angle to the vertical forming a v-shapeInline – pistons are all oriented in the same direction
47Vertical Cylinder Design the cylinders are arranged inline in a single bank that move vertically:
48Horizontal Cylinder Design also known as horizontally opposed or a boxerthe cylinders are arranged in two banks on opposite sides of the engine:
49Slant Cylinder Designthe cylinders are arranged inline and specifically designed such that the cylinders are inclined at a 30- degree angle from vertical.
50V Cylinder DesignV - the cylinders are arranged in two banks set at an angle to one another:
51Inline Cylinder Design the cylinders are arranged in a line in a single bank. Can be arranged vertically or slanted.
52Shaft Orientation Vertical Horizontal The shaft extends from the bottom of the engine.common applications of a vertical engine include:walk-behind rotary lawnmowersyard tractorsHorizontalThe shaft extends from one side of the engine and rotates parallel to the ground.Generatorssnow throwerswater pumpspressure washers.
54Engine Cooling Systems Air CooledAir is circulated around the cylinder block and cylinder head to maintain the desired temperatureLiquid CooledLiquid is circulated through cavities in the cylinder block and cylinder head to maintain the desired temperatureHeat is also removed through the exhaust system and radiant heat from the engine components.
56Air-Cooled EnginesMost small, single-cylinder engines are cooled by a stream of air developed by fan blades on the flywheel.The air stream is deflected around the cylinder and cylinder head by a metal or plastic cover called a shroud.Additional engine heat is dissipated through cooling fins around the cylinder.
58Liquid CooledThe cooling system on liquid-cooled cars circulates a fluid through pipes and passageways in the engine.As this liquid passes through the hot engine it absorbs heat, cooling the engine.After the fluid leaves the engine, it passes through a heat exchanger, or radiator, which transfers the heat from the fluid to the air blowing through the exchanger.
59Engine DefinitionA machine that converts a form of energy into mechanical force.Combustion engines generates heat from an internal or external source and converts that energy into rotation force on the crankshaft.A small engine is an internal combustion engine that converts heat energy from the combustion of a fuel into mechanical energy generally rated up to 25 horsepower.
60Energy ConversionEnergy is the resource that provides the capacity to do workTwo forms of energy are:Potential energyStored energy due to its position, chemical state or conditionWater behind a dam, because of its positionGasoline based on its chemical stateKinetic energyIs energy of motion (released potential energy)Water falling over a damA speeding automobile
61Small Engines and Energy Small gasoline engines convert the stored potential energy of gasoline into kinetic energy of the rotating shaftThe rotating shaft of the engine is used to do work required by the engine application ie. Mow grass, throw snow etc.
62Other Energy Principles All internal combustion engines operate by utilizing basic principles of :HeatForcePressureTorqueWorkPowerChemistry
63Heat All matter is composed of atoms that are in constant motion. Heat is the kinetic energy caused by atoms and molecules in motion within a substanceHeat added to a substance causes the particles velocity to increase resulting in a higher internal energyHeat removed from a substance causes particle velocity to decrease resulting in decreased internal energy.
64States of Matter A substance can be a liquid, solid or gas The state of a substance depends upon the intensity of vibration of the moleculesTo change to or from one state to another requires the addition or removal of heat energy.When heat is added to ice it changes to water, when heat is added to water it changes to steam (vapor)As the compression in a cylinder increases, heat increases, the liquid gasoline droplets in the fuel mixture change to a gaseous state preparing the fuel for more efficient combustion.
65Heat TransferHeat is transferred (flows) from one substance to another when a temperature difference exists.Heat is always transferred from a substance with a higher temperature to a substance with a lower temperatureHeat transfer rates are proportional to the temperature difference between the two substances
66Methods of Heat Transfer There are three methods of heat transfer:ConductionOccurs when particles of a substance come in direct contact with each otherConvectionOccurs when heat is transferred by currents in a fluidRadiationOccurs when radiant heat travels without a material carrier
68Conduction Transfer of heat using direct contact Heat one end of a metal rod, kinetic energy is passed from one to another, heat is transferred from one end to the other.In a small engine:Engine oil is in direct contact with the hot engine parts.Heat is transferred from the hotter parts to the oilAs the oil moves to the oil reserve the cooler crankcase assemble conducts the heat from the oil to the air contacting the outside of the engine
69Convection Heat is transferred by currents in a fluid As air is warmed by a fire, the warm air rises and is replaced by cooler air. The movement of air continues as long as the air is heated by the fire.In a Small engine convection occurs in a liquid cooled radiator:A radiator is a multi-channeled container that allows air to pass around the channels to remove heat from the liquid withinWarm liquid is pumped into the top of the radiator cooled in the radiator and moves back into the engine
70Radiation Occurs when radiant heat travels without a material carrier Radiant energy travels through space without producing heat. Heat is produced when the waves strike an opaque object.Heat is produced on earth by radiant energy from the sunIn a small engine radiant energy is produced by the heated metal that radiates heat away from the parts where there is little air flow
71Radiator ExampleThe primary function of the radiator is to transfer waste heatThe processes that accomplish this are:ConvectionConductionRadiationThese processes are dependent upon 3 variables:The existence of temperature differences between liquid and airThe existence of temperature differences between coolant and air flowThe design of the heat transfer surfaces to maximize their potential
72Measuring HeatTemperature is the measurement of the degree or intensity of heatTemperature can be measured by a glass thermometerA glass tube is filled with alcohol or mercuryThe tube has a scaleBased on the known expansion rate of the material
73Quantity of HeatThe quantity of heat is the amount of heat required to produce an accepted standard of physical change in matterA British Thermal Unit (BTU) is the amount of heat energy required to raise the temperature of one pound (lb) of Water 1oF (Fahrenheit)A Calorie is the amount of heat energy required to raise the temperature of one gram (g) of Water 1oC (Celsius)
74ForceForce is anything that changes or tends to change the state of rest or motion of a bodyForce is measured in pounds (lb) in the English system and newtons (N) in the metric systemOne or more forces can act on bodyForce acting on a body does not always produce motionForce applied in different ways can produce pressure, torque or work
75Pressure Pressure is a force acting on a unit of area Area is the number of unit squares equal to the surface of the objectIn an internal combustion engine force is exerted by combustion pressure applied to the area of the piston headP = F/AWhereP – pressure (in lb/sq. in.)F – Force (in lb)A – Area (in sq. in.)
76Pressure ExampleWhat is the pressure exerted on the top of a 4.91sq. in. piston if the combustion exerts a force of 2000 lb ?P = F/AP = 2000 lb/ 4.91sq. in.P = lb/sq. in.P = psi
77TorqueTorque is a force acting on a perpendicular radial distance from a point of rotationThe result is a twisting or turning force expressed in pound-feet (lb-ft) or newton- meters (Nm) that may or may not result in motionTorque is found by applying the formula:T = F x rWhereT – torque (in lb-ft or Nm)F - force (in lb or N)r – radius (in ft or m)
78Torque ExampleHow much torque is produced by a 60 lb force pushing on a 2’ lever arm ?T = F x rT = 60 lb x 2 ftT = 120 lb-ft
79WorkWork is the force applied through a parallel distance causing linear motion.Work is measured in lb-ft or NmTorque and work are very similar. The real difference is that torque may not produce motion.Work is found by applying the formulaW = F x DWhereW – work (in lb-ft or Nm)F - force (in lb or N)D – distance (in ft or m)
80Work ExampleWhat is the amount of work performed if a horse pulled a container that weighed 330 lb a distance of 100’ ?W = F x DW= 330 lb x 100 ftW= 33,000 lb-ft
81Power Power is the rate at which work is done Power ratings include horsepower, the watt (W) or kilowatt (kW)Power is found applying the formula:P = W/TWhereP – power (in lb-ft/min or W)W – work (in lb-ft or Nm)T - time (in min)
82Power ExampleWhat is the power output of an engine that produces 100,000 lb-ft of work in 6 min. ?P = W/TP = 100,000 lb-ft / 6 min.P = 16, lb-ft/ min.
83Horsepower Horsepower (HP) is a unit of power equal to: 746 watts (W)33,000 lb-ft/min550 lb-ft/sHorsepower is commonly used to rate power produced by and engines at a finite speedThe formula for Horsepower is:HP = W/(T x 33,000)WhereHP – horsepower (in HP)W – work (in lb-ft/min)T - time (in min)
84Horsepower ExampleWhat is the horsepower rating of an engine that produces 412,500 lb-ft in 2.5 minutes ?HP = W/(T x 33,000)HP = 412,500 lb-ft /(2.5 min x 33,000)HP = 412,500 lb-ft /(82,500 min)HP = 5 HP
85ChemistryAll internal combustion engines utilize some form of fossil fuel (hydrocarbon)Combustion chemistry involves the combining of hydrocarbon fuel with oxygen from the atmosphere.When ignition occurs in the engine a chemical reaction between the hydrocarbon molecule and atmospheric oxygen causes an exchange of elements which releases heat energy2 C8H O N CO H2O + 94 N2Fuel Mixture Exhaust Gasses