ENGR 100
Engine Dissection Project Information
Engine Dissection Project
(ref. 2, Used by permission of Briggs and Statton,
©1992, all rights reserved)
3.5 HP single
cylinder, 4 cycle
engine, made by
Briggs and
Stratton in
Milwaukee,
Wisconsin.
Used in lawn
mowers, snow
blowers, go-carts,
etc.
Engine Dissection Project
Divide into groups.
Start engine.
Disassemble engine (follow directions!)
Review parts and functions – Ask
questions!
Reassemble engine (follow directions!).
Re-start engine.
Engine Project Assignments
Group Assignment:
Engine Questions (HW points)
Individual Assignments:
Engine Dissection Report
explain how the engine works
you can choose to explain a different engine
(requires instructor’s permission)
Engine Team Contribution Survey
Engine background
Engine converts gasoline into motion.
Internal combustion engine:
the gasoline is burned inside an engine
External combustion engine:
the gasoline is burned outside an engine
Example:
steam engine – fuel burns outside the engine to
create steam, and the steam creates motion
inside the engine.
Engine basics
reciprocating internal
combustion engine:
small amount of highenergy fuel (like
gasoline) in an enclosed
space
fuel is ignited
energy is released in the
form of expanding gas
this energy is converted
into motion
Four-stroke combustion cycle
a.k.a. Otto cycle (invented by
Nikolaus Otto in 1867).
Four strokes:
intake
compression
power (combustion)
exhaust
Engine parts
Intake Stroke
Intake
valve
opens,
admitting
fuel and
air.
Exhaust
valve
closed.
Compression Stroke
Both valves
are closed.
Fuel/air
mixture is
compressed
by rising
piston.
Spark plug
ignites
mixture at
end of
stroke.
Combustion Stroke
Fuel-air
mixture burns,
increasing
temperature
and pressure.
Expansion of
combustion
gases drives
piston down.
Both valves
are closed.
Exhaust valve
opens at end
of stroke.
Exhaust Stroke
Exhaust valve
open.
Exhaust
products are
displaced
from cylinder.
Intake valve
opens at end
of stroke.
4-stroke
cycle repeats.
Four-stroke combustion cycle
1
Intake Valve
Intake
Manifold
Cylinder
2
Exhaust Valve
Exhaust
Manifold
3
4
Spark
Plug
Piston
Connecting
Rod
Intake Stroke
Intake valve opens,
admitting fuel and air.
Exhaust valve closed
for most of stroke
Crank
Crankcase
Compression Stroke
Both valves closed,
Fuel/air mixture is
compressed by rising
piston. Spark ignites
mixture near end of
stroke.
Combustion Stroke
Fuel-air mixture burns,
increasing temperature
and pressure, expansion
of combustion gases
drives piston down. Both
valves closed - exhaust
valve opens near end
of stroke
Exhaust Stroke
Exhaust valve open,
exhaust products are
displaced from cylinder.
Intake valve opens
near end of stroke.
1. Intake
3. Combustion
2. Compression
4. Exhaust
Animation of four strokes
Engine parts: crankshaft
Turns the
piston's up
and down
motion
(linear
motion) into
circular
motion.
Think of
pedaling a
bicycle.
Image from
http://www.eng.iastate.edu/explorer/topics/car/engine.htm
Engine parts: crankshaft
Image from toyotaperformance.com/crankshaft_kits.htm
Engine parts: piston
Image from
www.eng.iastate.edu/explorer/topics/car/engine.htm
Piston rings provide a
sliding seal:
prevent the fuel/air
mixture and exhaust
in the combustion
chamber from leaking
into the sump during
compression and
combustion.
prevent the oil in the
sump from leaking
into the combustion
area (“burning oil”).
Engine parts: camshaft
Rod with a series of oblong
protrusions called lobes.
As the camshaft rotates,
the lobes push against the
valves (usually via an
intermediate component
known as a tappet or lifter),
causing them to open at the
appropriate time.
The valves are springloaded, closing after the
protruding camshaft lobe
Image from
releases the valve.
http://www.ul.ie/~kirwanp/camshaftanimation.htm
Overhead camshaft
Image from http://www.keveney.com/otto.html
Camshaft is positioned
at the top of the
cylinder.
Camshaft is driven by
the crankshaft via
gears.
Each valve opens only
once during the fourstroke cycle; that is,
the camshaft makes
one rotation for every
two rotations of the
crankshaft.
rocker
valve
push rod
piston
valve lifter
camshaft
cam
Image from Automotive
mechanics, 8th ed. By William H.
Crouse
crankshaft
Timing marks
Lubrication
The lubrication system
makes sure that every
moving part in the engine
gets oil so that it can
move easily.
Oil is pumped under
pressure to all the moving
parts of the engine by an
oil pump.
The oil pump is mounted
at the bottom of the
engine in the oil pan.
The oil pump is connected
by a gear to either the
crankshaft or the
camshaft.
Image from
http://www.innerauto.com/innerauto/anim/engi.html
Engine parts: carburetor
Choke
Venturi (creates
low pressure)
Higher
Pressure
Outside
Engine
Throttle (controls
how much air can
flow through the
carburetor)
Fuel
Pressing the accelerator
causes the throttle to open.
Air moves into the
carburetor and is restricted
by the venturi.
Low pressure is created at
the restriction.
Fuel is drawn into the
venturi from the bowl
through and is mixed with
the air.
Air-fuel mixture exits
through the intake valves
into the cylinder.
Fuel injection
Forces the fuel through nozzles under
pressure, rather than using the force of
the air rushing through.
Precise control of the amount of fuel
mixed with air:
increase fuel efficiency,
decrease pollution.
Fuel injection
Monitored Engine
Operating Conditions:
Manifold Pressure
Engine Speed
Air Temperature
Coolant Temperature
Acceleration
COMPUTER
TRIGGER
INJECTOR DRIVE UNIT
Fuel
Filter
Pressure
Regulator
Injectors
FUEL TANK
Fuel
Pump
Typical cylinder arrangements
Image from http://www.familycar.com/engine.htm
Image from
http://www.sigetyracing.com/sigetyracing_008.htm
What to do first?
Divide into teams. Get each other’s email
address.
Team work (15 min): talk about your
experience with engines (if any), read
directions for the engine project and decide
who is doing what roles.
Get an engine, mount it on an aluminum plate
use at least two bolts
the starting cord must be over the excess plate
surface -- and the shaft should be reaching out over
open space.
What to do first (cont.)?
Note the manufacturer, model, and
serial number of your engine.
What is the idle RPM and rated
horsepower for this engine?
Starting the engine
Take the engine to the parking lot outside the
main door of the building.
Put a small amount of fuel in the gas tank
(about 1/4 cup).
Put about a 1/2 cup of oil into the oil filler
hole.
Engage the choke completely and open the
throttle all the way (to the "rabbit" position).
Two team members must hold the engine
steady by standing on each side of the plate.
Starting the engine (cont.)
Then, a third member pulls the cord to
start the engine.
Allow the engine to run only a few
seconds or it will get too hot to handle!
Stop the engine. Drain the fuel back into
the red fuel container, then drain the oil
into the black oil container.
Return the engine to the lab.
Begin engine dissection and answering
questions
How Do Engines Work?
How does the engine complete these Primary
Functions?
Get started?
Suck in fuel?
Suck in air?
Mix air and fuel?
Compress the mixture?
Ignite the mixture (at the right time)?
Make the combusting gases do work?
Make the work available to somebody?
Exhaust the gases?
Shut off?
How Do Engines Work?
How does the engine complete these
Secondary Functions?
Stay lubricated?
Operate the valves at the right time?
Smooth out the power pulses?
Store the fuel?
Keep cool?
Make it easy to start?
2-Stroke Process
Compression
(ports closed)
Air Taken Into
Crankcase
Combustion
(ports closed)
Exhaust
(intake port closed)
Air compressed in crankcase
Scavenging
and Intake
(ports open)
Wankel Rotary Engine
•Smoother
•Engine is continuously moving in one direction
rather than changing direction like in piston
engines.
•Slower
•Main moving parts move slower which increase
the reliability of the engine.
•Fewer Moving Parts
•The rotary engine consists of three main moving
parts while a piston engine contains at least 40
moving parts.
•Challenges
•Passing the US Emissions tests.
•Manufacturing costs are higher.
•Consumes more fuel.
This presentation created by former ENGR 100 students Sam Henry, Thomas Munsey, Grayson Deitering, Daniel Munro
