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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.

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Small Gasoline Engines

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Small gasoline engines

Small Gasoline Engines



  • Define Engine:

Are these engines?

What is the primary difference between these engines and modern engines?

Heat engine

Heat Engine

How does modern engines use heat?

Two general categories based on how the heat is used

Two general categories based on how the heat is used.

External combustion engine

Internal combustion engine

Internal combustion engines

Internal Combustion Engines

Small engine development pg 5

Small Engine Development(pg 5)

  • YearEngineDesigner/developer

  • 1680GunpowderChristian Huygens

  • 1698Savery PumpThomas Saverly

  • 1712Newcomen SteamThomas Newcomen

  • 1763Watt Double-acting steamJames Watt

  • 1801Coal gas/electric ignitionEugene Lebon

  • 1802High pressure steamRichard Trevithick

  • 1859Pre-mixed fuel and airEtienne Lenoir

  • 1862GasolineNikolaus Otto

  • 1876Four cycle gasolineNikolaus Otto

  • 1892DieselRudolf Diesel

  • 1953Die-cast aluminum B&S

Internal combustion intro

Internal Combustion--Intro

  • Engine designs can be classified by:

  • Size

  • Ignition system

  • Strokes per cycle

  • Cylinder orientation

  • Crankshaft orientation

  • Control system

  • Cooling system

1 engine size

1. Engine Size

Engines are available in a wide range of sizes.

Industry definition: “A small engine is an internal combustion engine rated up to 25 horsepower.”

1 size largest

1. Size - Largest

  • The Wartsila-Sulzer RTA96-C turbocharged two-stroke diesel engine is the most powerful and most efficient prime-mover in the world today.

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.

1 size smallest

1. Size - Smallest

  • Not much bigger than a stack of pennies, the "mini engine" is the first engine of its size to deliver power on a continuous basis.

  • Currently will produce 2.5 watts of electricity (0.00335 hp).

  • Uses 1/2 fluid ounce of fuel per hour

2 ignition

2. Ignition

  • Spark ignition

Compression ignition

What is the primary difference?

3 cycles

3. Cycles

  • Four stroke

Two stroke

Name one common use for each type.

4 cylinder orientation

4. - Cylinder Orientation

Four common cylinder orientations for small engines

  • There is no limit on the number of cylinders that a small engines can have, but it is usually 1 or 2.




Multi position

Give an example of a use for each.

4 cylinder orientation cont

4. - Cylinder Orientation—cont.

Three common cylinder configuration in multiple cylinder engines:


Horizontally opposed


Can you identify one application for each of these types?

5 crankshaft orientation

5. Crankshaft Orientation

Small gas engines use three crankshaft orientations:




Identify a use for each one.

6 controls

6. Controls

  • Traditionally engines are controlled by mechanical means.

    • Governor

    • Throttle

    • Choke

    • Etc.

  • Honda has an engine with an electronic control unit (ECU).

  • ECU - Electronic Control Unit

    • Monitors and controls engine functions including Throttle, Choke, Ignition Timing, Oil Alert

    • Offers programmable governor and throttle modes for unprecedented flexibility and diagnostic LED for trouble shooting

    • Stepper motors precisely control throttle and choke position

7 cooling system

7. Cooling System

  • Small engines use two types of cooling systems:

    • Air

    • Water

Why does an internal combustion engine need a cooling system?

Why what are the advantages and disadvantages of both systems?

How is excess heat moved within and removed from the engine

7. Cooling System—cont.

How is excess heat moved within and removed from the engine?

7 cooling system cont

7. Cooling system—cont.

  • Which one(s) of the heat transfer methods are used by the following engine systems?

  • Cooling

  • Lubrication

  • Fuel

Physical principles of engines

Physical Principles of Engines



  • Energy is the capacity for doing work.

What are the two forms of energy?

Which form are these?

Boyle s laws

Boyle’s Laws

  • Boyle’s Law: the volume of gas varies inversely with the pressure.

    • Any confined gas will double its pressure when the volume is decreased by one half.

Small gas engines use a compression ratio of 8:1.

  • Theoretical compression pressure.

    • Using an atmospheric pressure of 14.7 psi and a compression ratio of 8:1 the theoretical compression pressure is: 117.6 psi

Note: The actual cylinder press will be different because of the losses that occur and the complex relationship between gas pressure and temperature.

Charles law

Charles Law

  • The pressure and temperature of a confined gas are directly proportional.

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:

Small gasoline engines


  • “Anything that changes or tends to change the state of rest or motion of a body.”

  • A force can result in pressure, torque or work, depending on how it is applied.

Small gasoline engines


Pressure is a force acting on a unit of area.

  • The cylinder pressure is not constant.

    • Increases during compression.

    • Sharp spike after combustion

    • Decreases through power stroke

How high can the pressure reach in a combustion chamber?

Small gasoline engines


  • In an engine the pressure produced in the combustion chamber is converted to a force.

    • The pressure is applied uniformly to all surfaces, including the head of the piston.

Small gasoline engines


  • “A force acting on the perpendicular radial distance from a point of rotation.”

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.



  • Power is the rate of doing work.

Problem: How much power is an engine producing if the torque is 154 lb-ft and the engine operates at 3,000 RPM.

Small gasoline engines

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?

The end

The End

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