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

Internal combustion engine

Internal Combustion Engines

Small Engine Development(pg 5)

Year Engine Designer/developer1680 Gunpowder Christian Huygens

1698 Savery Pump Thomas Saverly

1712 Newcomen Steam Thomas Newcomen

1763 Watt Double-acting steam James Watt

1801 Coal gas/electric ignition Eugene Lebon

1802 High pressure steam Richard Trevithick

1859 Pre-mixed fuel and air Etienne Lenoir

1862 Gasoline Nikolaus Otto

1876 Four cycle gasoline Nikolaus Otto

1892 Diesel Rudolf Diesel

1953 Die-cast aluminum B&S

Internal Combustion--Intro

Engine designs can be classified by:

1. Size

2. Ignition system

3. Strokes per cycle

4. Cylinder orientation

5. Crankshaft orientation

6. Control system

7. Cooling system

1. Engine Size

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

Engines are available in a wide range of sizes.

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

• 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

Spark ignition

Compression ignition

What is the primary difference?

3. Cycles

Four stroke

Two stroke

Name one common use for each type.

4. - Cylinder Orientation

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

Four common cylinder orientations for small engines

Vertical

HorizontalSlanted Multi position

Give an example of a use for each.

4. - Cylinder Orientation—cont.

VHorizontally opposed

In-line

Three common cylinder configuration in multiple cylinder engines:

Can you identify one application for each of these types?

Horizontal

Vertical

Small gas engines use three crankshaft orientations:

5. Crankshaft Orientation

Multi-position

Identify a use for each one.

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

Small engines use two types of cooling systems:

– Air

– Water

7. Cooling System

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.

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

Energy

Energy is the capacity for doing work.

What are the two forms of energy?

Which form are these?

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 psiNote: The actual cylinder press will be

different because of the losses that occur and the complex relationship between gas pressure and temperature.

Charles Law

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

The increase in temperature can be approximated by:

€

T2 = T1 x n0.4

T1= initial temperature

T2 = final temperature

n = Compression ratio

For an engine with a 8:1 compression ratio and an initial temperature of 72 oF, the compression temperature will be:

€

T2 = T1 x n0.4

= 72 oF x 80.4

= 165 oF

An engine with a 21:1 compression ratio and an initial temperature of 72 oF, the compression temperature will be:

€

T2 = T1 x n0.4

= 72 oF x 210.4

= 243 o F

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

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

Force

The cylinder pressure is not constant.

–Increases during compression.

–Sharp spike after combustion

–Decreases through power stroke

Pressure is a force acting on a unit of area.

Force--Pressure

How high can the pressure reach in a combustion chamber?

Force—Pressure—cont.

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.

€

Pressurelb

in2

⎛ ⎝ ⎜

⎞ ⎠ ⎟ x Area in2

( ) = Force (lb)

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

To (lb-ft) = Force x Radius

Torque

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.

€

Force(lb) = Pressurelb

in2

⎛

⎝ ⎜

⎞

⎠ ⎟ x Area(in2 )

= 250 lb

in2

⎛

⎝ ⎜

⎞

⎠ ⎟ x π B2

4

= 250 lb

in2

⎛

⎝ ⎜

⎞

⎠ ⎟ x

3.14 x 2.752

4

= 1484 lb

€

To = Force (lb) x Lever (ft)

= 1484 lb x 1.25 in x 1 ft

12 in= 154 lb - ft

Power

Power is the rate of doing work.

€

P = WT

P =F x D

T P = To x RPM

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

€

P lb - ftmin

⎛

⎝ ⎜

⎞

⎠ ⎟=

154 lb - ftrev

x 3,000 revmin

= 46,200 lb - ftmin

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.

Horsepower

Problem: How many horsepower is an engine producing if the power is 46,200 ft-lb/min?

€

Hp = Power x 1 Hp

33,000 ft - lbmin

= 46,200 ft - lbmin

x 1 Hp

33,000 ft - lbmin

= 1.4 Hp

The End