Small Gasoline Engines. Engine. Define Engine:. Are these engines?. What is the primary difference between these engines and modern engines?. Heat Engine. How does modern engines use heat?. Two general categories based on how the heat is used. External combustion engine.
Are these engines?
What is the primary difference between these engines and modern engines?
How does modern engines use heat?
External combustion engine
Internal combustion engine
Engines are available in a wide range of sizes.
Industry definition: “A small engine is an internal combustion engine rated up to 25 horsepower.”
The cylinder bore is just under 38" and the stroke is just over 98".
Each cylinder displaces 111,143 cubic inches (1,820 liters) and produces 7,780 horsepower.
Total displacement comes out to 1,556,002 cubic inches (25,480 liters) for the fourteen cylinder version.
What is the primary difference?
Name one common use for each type.
Four common cylinder orientations for small engines
Give an example of a use for each.
Three common cylinder configuration in multiple cylinder engines:
Can you identify one application for each of these types?
Small gas engines use three crankshaft orientations:
Identify a use for each one.
Why does an internal combustion engine need a cooling system?
Why what are the advantages and disadvantages of both systems?
7. Cooling System—cont.
Physical Principles of Engines
What are the two forms of energy?
Which form are these?
Small gas engines use a compression ratio of 8:1.
Note: The actual cylinder press will be different because of the losses that occur and the complex relationship between gas pressure and temperature.
The increase in temperature can be approximated by:
For an engine with a 8:1 compression ratio and an initial temperature of 72 oF, the compression temperature will be:
An engine with a 21:1 compression ratio and an initial temperature of 72 oF, the compression temperature will be:
Pressure is a force acting on a unit of area.
How high can the pressure reach in a combustion chamber?
To (lb-ft) = Force x Radius
Problem: Determine the amount of torque that will be produced for an engine that has an average combustion pressure of 250 psi, a 2.75 inch bore and 1.25 inch throw.
Problem: How much power is an engine producing if the torque is 154 lb-ft and the engine operates at 3,000 RPM.
1 Hp = 33,000 ft-lb/min
A unit of power developed by James Watt to provide a basis for comparing the amount of power produced by horses and other engines.
Problem: How many horsepower is an engine producing if the power is 46,200 ft-lb/min?