# Engine Fundamentals TRF 210.

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Engine Fundamentals TRF 210

Engine Types External-combustion Internal-combustion

The Combustion Process
HC + O = H2O + CO2 + Heat Fuel and air compressed Spark Combustion Incomplete combustion results in Carbon Monoxide and some unburned gasoline

Effect of Heat Purpose of the combustion process is to produce heat
Heat to do work Heat will cause most substances to expand Heat will cause air to expand

Increase in Pressure Pressure measured in PSI or Pounds per square inch Air pressure will increase when heated if it is in a enclosed area (air 32 degrees will be degrees) Air pressure will increase if it is compressed (1/6 to 1/8 original volume in gasoline engines)

Increase in Temperature
Air pressure and temperature increased when compressed Gasoline engine temperature is raised several hundred degrees Diesel temperature increase is even greater (more compression)

Terms Thermometer measures temperature by the expansion of metals
Thermostat different metals expand at different rates. This difference is used in thermostats by wielding two different metals together Gravity attractive force between all objects gives objects there weight

Terms cont. Atmospheric Pressure air has weight 1 cubic foot of air weighs 0.08 lbs The blanket of air that surrounds the earth amounts to many cubic feet of air. This combined weight amounts to about 15 psi at sea level Vacuum the absence of air of any other substance

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

Piston Engine Operation
Imagine a large can with one end cut out Inside that can is a slightly smaller can that fits snuggly Now push the smaller can into the larger can trapping air between the two this compresses the air If the air contains some fuel and a spark is supplied combustion can take place

Piston Engine Operation cont.
Heat from the combustion causes the air to expand pushing the smaller can back To make the engine run this process must be repeated (reciprocate)

Engine Cylinder A round hole in a block of metal
No set number of cylinders ( , etc)

Piston and Piston Rings
Power depends on pressure in the cylinder that pressure created by the piston Too tight clearance too loose clearance problems will occur Piston rings allow for a good seal between the cylinder wall and the piston 2-cycle engines 1 or 2 rings 4-cycle engines have 3 to 4 rings

The Crank Reciprocating motion up and down movement of the piston
This motion must be changed into rotary motion before it can be used Rotary motion is required to make shafts and wheels turn Connecting rod connects the piston to the crank The crank is an offset part of a shaft Piston up and down motion causes crank shaft to turn

Engine Crankshaft Crank is off set section of crankshaft
As the piston goes up and down it rotates the crank shaft in a full circle Crank shaft is assembled with flywheels (inertia) and counter weights That help balance the weight of the crank pin and the piston-and-connecting rod assembly This allows for the engine to run smoothly

Engine Bearings Any where there is rotary motion in a engine bearings are used to support the moving parts The purpose of a bearing is to reduce friction and allow parts to move easily Two types of bearing used in engines sliding and rolling

Sliding Bearing Plain bushing or sleeve bearing Split sleeve bearings
Forms the shape of a sleeve and fits around the rotating shaft Made of relatively soft metal so the bearing will wear

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

Making the Engine Run Gas/air mixture enters the cylinder
Mixture is compressed by the upward movement of the piston A spark is then introduced and combustion takes place The combustion heats and expands the air forcing the piston down ( this produces the power to turn the crank shaft) Burned gasses must be removed and a fresh charge of air and fuel brought into the cylinder This process must continue along as the engine is running

The Piston Stroke The movement of the piston from one limiting position to another The upper limited position of the piston is Top Dead Center TDC The lower limited position of the piston is Bottom Dead Center BDC