Engine Engine FundamentalsFundamentals

TRF 210TRF 210

Engine TypesEngine Types

External-combustionExternal-combustion Internal-combustionInternal-combustion

The Combustion ProcessThe Combustion Process

HC + O = H2O + CO2 + HeatHC + O = H2O + CO2 + Heat Fuel and air compressedFuel and air compressed Spark Spark CombustionCombustion Incomplete combustion results in Carbon Incomplete combustion results in Carbon

Monoxide and some unburned gasolineMonoxide and some unburned gasoline

Effect of HeatEffect of Heat

Purpose of the combustion process is to Purpose of the combustion process is to produce heatproduce heat

Heat to do workHeat to do work Heat will cause most substances to Heat will cause most substances to

expandexpand Heat will cause air to expandHeat will cause air to expand

Increase in PressureIncrease in Pressure

Pressure measured in PSI or Pounds per Pressure measured in PSI or Pounds per square inchsquare inch

Air pressure will increase when heated if Air pressure will increase when heated if it is in a enclosed area (air 15psi @ 32 it is in a enclosed area (air 15psi @ 32 degrees will be 17psi @100 degrees)degrees will be 17psi @100 degrees)

Air pressure will increase if it is Air pressure will increase if it is compressed (1/6 to 1/8 original volume in compressed (1/6 to 1/8 original volume in gasoline engines)gasoline engines)

Increase in TemperatureIncrease in Temperature

Air pressure and temperature increased Air pressure and temperature increased when compressedwhen compressed

Gasoline engine temperature is raised Gasoline engine temperature is raised several hundred degreesseveral hundred degrees

Diesel temperature increase is even Diesel temperature increase is even greater (more compression)greater (more compression)

TermsTerms

Thermometer measures temperature by Thermometer measures temperature by the expansion of metalsthe expansion of metals

Thermostat different metals expand at Thermostat different metals expand at different rates. This difference is used in different rates. This difference is used in thermostats by wielding two different thermostats by wielding two different metals togethermetals together

Gravity attractive force between all Gravity attractive force between all objects gives objects there weightobjects gives objects there weight

Terms cont.Terms cont.

Atmospheric Pressure air has weight 1 Atmospheric Pressure air has weight 1 cubic foot of air weighs 0.08 lbs The cubic foot of air weighs 0.08 lbs The blanket of air that surrounds the earth blanket of air that surrounds the earth amounts to many cubic feet of air. This amounts to many cubic feet of air. This combined weight amounts to about 15 combined weight amounts to about 15 psi at sea levelpsi at sea level

Vacuum the absence of air of any other Vacuum the absence of air of any other substancesubstance

Producing a VacuumProducing a Vacuum

Engines produce a partial vacuum in the Engines produce a partial vacuum in the cylinder by the action of the piston (this cylinder by the action of the piston (this allows the air fuel mixture to be drawn allows the air fuel mixture to be drawn into the cylinder by the force of into the cylinder by the force of atmospheric pressure)atmospheric pressure)

Piston Engine Operation Piston Engine Operation

Imagine a large can with one end cut outImagine a large can with one end cut out Inside that can is a slightly smaller can Inside that can is a slightly smaller can

that fits snugglythat fits snuggly Now push the smaller can into the larger Now push the smaller can into the larger

can trapping air between the two this can trapping air between the two this compresses the aircompresses the air

If the air contains some fuel and a spark If the air contains some fuel and a spark is supplied combustion can take placeis supplied combustion can take place

Piston Engine Operation Piston Engine Operation cont.cont.

Heat from the combustion causes the air Heat from the combustion causes the air to expand pushing the smaller can backto expand pushing the smaller can back

To make the engine run this process To make the engine run this process must be repeated (reciprocate)must be repeated (reciprocate)

Engine CylinderEngine Cylinder

A round hole in a A round hole in a block of metalblock of metal

No set number of No set number of cylinders (1-2-4-6-8, cylinders (1-2-4-6-8, etc)etc)

Piston and Piston RingsPiston and Piston Rings

Power depends on pressure in the cylinder that Power depends on pressure in the cylinder that pressure created by the pistonpressure created by the piston

Too tight clearance too loose clearance Too tight clearance too loose clearance problems will occurproblems will occur

Piston rings allow for a good seal between the Piston rings allow for a good seal between the cylinder wall and the pistoncylinder wall and the piston

2-cycle engines 1 or 2 rings 2-cycle engines 1 or 2 rings 4-cycle engines have 3 to 4 rings 4-cycle engines have 3 to 4 rings

The CrankThe Crank

Reciprocating motion up and down movement of the Reciprocating motion up and down movement of the pistonpiston

This motion must be changed into rotary motion before This motion must be changed into rotary motion before it can be usedit can be used

Rotary motion is required to make shafts and wheels Rotary motion is required to make shafts and wheels turnturn

Connecting rod connects the piston to the crankConnecting rod connects the piston to the crank The crank is an offset part of a shaftThe crank is an offset part of a shaft Piston up and down motion causes crank shaft to turnPiston up and down motion causes crank shaft to turn

Engine Crankshaft Engine Crankshaft

Crank is off set section of crankshaftCrank is off set section of crankshaft As the piston goes up and down it rotates the As the piston goes up and down it rotates the

crank shaft in a full circlecrank shaft in a full circle Crank shaft is assembled with flywheels Crank shaft is assembled with flywheels

(inertia) and counter weights(inertia) and counter weights That help balance the weight of the crank pin That help balance the weight of the crank pin

and the piston-and-connecting rod assemblyand the piston-and-connecting rod assembly This allows for the engine to run smoothly This allows for the engine to run smoothly

Engine BearingsEngine Bearings

Any where there is rotary motion in a Any where there is rotary motion in a engine bearings are used to support the engine bearings are used to support the moving partsmoving parts

The purpose of a bearing is to reduce The purpose of a bearing is to reduce friction and allow parts to move easily friction and allow parts to move easily

Two types of bearing used in engines Two types of bearing used in engines sliding and rollingsliding and rolling

Sliding BearingSliding Bearing

Plain bushing or Plain bushing or sleeve bearingsleeve bearing

Split sleeve bearingsSplit sleeve bearings Forms the shape of a Forms the shape of a

sleeve and fits sleeve and fits around the rotating around the rotating shaftshaft

Made of relatively Made of relatively soft metal so the soft metal so the bearing will wearbearing will wear

Rolling BearingsRolling Bearings

Uses balls or Uses balls or cylinders between cylinders between the stationary the stationary support and the support and the rotating shaft rotating shaft

Making the Engine RunMaking the Engine Run

Gas/air mixture enters the cylinderGas/air mixture enters the cylinder Mixture is compressed by the upward movement of the Mixture is compressed by the upward movement of the

pistonpiston A spark is then introduced and combustion takes placeA spark is then introduced and combustion takes place The combustion heats and expands the air forcing the The combustion heats and expands the air forcing the

piston down ( this produces the power to turn the crank piston down ( this produces the power to turn the crank shaft)shaft)

Burned gasses must be removed and a fresh charge of Burned gasses must be removed and a fresh charge of air and fuel brought into the cylinderair and fuel brought into the cylinder

This process must continue along as the engine is This process must continue along as the engine is runningrunning

The Piston StrokeThe Piston Stroke

The movement of the piston from one The movement of the piston from one limiting position to anotherlimiting position to another

The upper limited position of the piston is The upper limited position of the piston is Top Dead Center TDCTop Dead Center TDC

The lower limited position of the piston is The lower limited position of the piston is Bottom Dead Center BDCBottom Dead Center BDC