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/developer
1680
1698
1712
1763
Gunpowder
Savery Pump
Newcomen Steam
Watt Double-acting steam
Christian Huygens
Thomas Saverly
Thomas Newcomen
James Watt
1801
1802
1859
1862
1876
1892
Coal gas/electric ignition
High pressure steam
Pre-mixed fuel and air
Gasoline
Four cycle gasoline
Diesel
Eugene Lebon
Richard Trevithick
Etienne Lenoir
Nikolaus Otto
Nikolaus Otto
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
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
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
Slanted
Horizontal
Give an example of a use for each.
Multi position
4. - Cylinder Orientation—cont.
Three common cylinder configuration in multiple cylinder engines:
V
Horizontally opposed
In-line
Can you identify one application
for each of these types?
5. Crankshaft Orientation
Small gas engines use three crankshaft orientations:
Multi-position
Horizontal
Vertical
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
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?
7. Cooling System—cont.
How is excess heat moved within and removed from the engine?
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:
psi cylinder press will be
Note: 117.6
The actual
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
An engine with a 21:1
compression ratio and an
initial temperature of 72
oF, the compression
temperature will be:
For an engine with a 8:1 compression
ratio and an initial temperature of 72 oF,
the compression temperature will be:
T2 = T1 x n 0.4
= 72 o F x 80.4
T2 = T1 x n0.4
= 72 o F x 210.4
 243 o F

 165 o F
Force
“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.
Force--Pressure
Pressure is a force acting on a unit of area.
Cylinder Pressure
800
Pressure (psi)
700
600
The cylinder pressure is not constant.
500
–Increases during compression.
400
300
–Sharp spike after combustion
200
100
0
0
25
50
75
100 125 150 175 200
Time
–Decreases through power stroke
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.
 lb 
Pressure 2  x Area in2 = Force (lb)
in 
 

Torque
“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.
 lb 
Force(lb)= Pressure  x Area(in 2 )
in2 
 lb   B2
= 250   x
4
in2 
 lb 
= 250   x
in2 
= 1484 lb
To = Force (lb) x Lever (ft)
3.14 x 2.75
1 ft
= 1484 lb x 1.25 in x
4
12 in
= 154 lb - ft
2
Power
Power is the rate of doing work.
P=W
Problem: How much power is an
engine producing if the torque is
154 lb-ft and the engine operates at
3,000 RPM.
lb - ft  154 lb - ft
rev
P 
=
x
3,000

 min 
rev
min
lb - ft
= 46,200
min 
T
FxD
P=
T
P = To x RPM
Horsepower
A unit of power developed by James
Watt to provide a basis for comparing
the amount of power produced by
horses and other engines.
1 Hp = 33,000 ft-lb/min
Problem: How many horsepower is
an engine producing if the power is
46,200 ft-lb/min?
1 Hp
ft - lb
33,000
min
ft - lb
1 Hp
= 46,200
x
ft - lb
min
33,000
min
= 1.4 Hp
Hp = Power x
The End