Internal combustion engine 1
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Transcript of Internal combustion engine 1
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Automobile Engineering
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Engine Parts
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Piston and Piston Rings
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Parts
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OHV Engine Design
4-cylinder 8 valves OHV engine
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OHC or SOHC Engine
4-cylinder 8 valves SOHC engine
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DOHC or Twin cam engine
4-cylinder 16 valves DOHC engine
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ME240/107S: Engine Dissection
You are dissecting a 3.5HP single cylinder, 4 cycleengine, made by Briggs &
Stratton in Milwaukee, WI
These engines aretypically used in lawnmowers, snow blowers,go-carts, etc
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Lecture 1
Engine Terminology
Engine Classifications
Carburetors
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Engine Terminology:
Stroke and Displacement
Stroke
amount of vertical travel of the piston from bottomdead center (BDC) to top dead center (TDC)
Displacement (D)
space displaced by thepiston during a stroke
D = (stroke)(T)(Bore)2/4BDC
TDC
Bore
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Engine Terminology:
Compression Ratio
Compression ratio (CR):
ratio of total volume to the volume of thecombustion chamber
spark ignition engines have CR = 7-12
CR = (C + D)/C
where C = volume of
combustion
chamber
D = displacement
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Classification of Engines
External vs. Internal Combustion
Spark Ignition vs. Compression Ignition
Cylinder Configuration
Valve Location
2 Stroke or 4 Stroke
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Engine Classification:
External vs. Internal Combustion
External combustion
combustion of an air-fuel mixture transfersheat to a second fluid which becomes themotive (working) fluid that produces power
E.g., steam driven engine
Internal combustion the products of combustion are the motive
fluid
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Engine Classification:
Spark vs. Compression Ignition
Spark ignition (SI) engines
a compressed, homogeneous air-fuel mixture(15:1 ratio of air to fuel by mass) is ignitedusing a spark
Compression ignition (CI) engines
rapid compression of air to a high pressureraises the temperature so that fuel, whendelivered into combustion chamber,spontaneously ignites without need for a spark
often referred to as a Diesel engine
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Engine Classification:
Cylinder Configurations
Radial (Aircraft)
V(Automobile)
In Line
(Automobile)
Horizontally Opposed
(Subaru)
Opposed Piston(crankshafts
geared together)
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Engine Classification:
Valve Location
Most common: overhead-valve or I-head
Exhaust
valve
Intake
valve
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Engine Classification:
2 Stroke
Compression
(ports closed)
Air Taken Into
Crankcase
Combustion
(ports closed)
Exhaust
(intake port closed)
Air compressed in crankcase
Scavenging
and Intake
(ports open)
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Intake Stroke
Intake valve opens,
admitting fuel and air.
Exhaust valve closed
for most of stroke
Compression StrokeBoth valves closed,
Fuel/air mixture is
compressed by rising
piston. Spark ignites
mixture near end of
stroke.
Intake
Manifold
Spark
PlugCylinder
Piston
ConnectingRod Crank
Power StrokeFuel-air mixture burns,
increasing temperature
and pressure, expansion
of combustion gases
drives piston down. Both
valves closed - exhaust
valve opens near end
of stroke
1 2 3 4
Exhaust StrokeExhaust valve open,
exhaust products are
displaced from cylinder.
Intake valve opens
near end of stroke.
Crankcase
Exhaust
Manifold
Exhaust ValveIntake Valve
Engine Classification: 4 Stroke
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Briggs Engine - Intake
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Compression
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Power Stroke
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Exhaust Stroke
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Carburetors
Purpose of the carburetor is to produce a
mixture of fuel and air on which the engine
can operate
Must produce economical fuel consumption
and smooth engine operation over a wide
range of speeds
Requires complicated device rather than a
simple mixing valve; price is very important!
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Venturi (nozzle)
Use force of atmospheric
pressure and artificially
created low pressure areato mix fuel and air
Use a venturi nozzle to
lower air pressure in
carburetor to create
suction to ³pull´ fuel into air Venturi (nozzle)
P+1/2 VV2 = ConstantBernoulli Principle:
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Venturi-type Carburetor
Ref. Obert
Constant level is
maintained in bowl -
as float moves down,valve stem moves
down, allowing more
fuel into bowl, float
moves up and closes
valve
Valve StemFuel Inlet
Float
Metering Orifice
Throttle Plate
Air/Fuel Mixture To
Engine
Choke Plate
Fuel
Nozzle
Inlet Air
Bowl
Atomized Fuel
Venturi
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Flo-Jet Carburetor
Fuel tank is above
carburetor
Fuel is fed directly to
carburetor by gravity
Why the vent?
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Flo-Jet Carburetor
Fuel from tank
Air flow
Air-fuel
mixture
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Pulsa-Jet Carburetor
Incorporates a diaphragm type fuel pump
and a constant level fuel chamber
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Pulsa-Jet Carburetor Operation
Intake stroke of piston
creates a vacuum in
carburetor elbow
Pulls cap A and pump
diaphragm B inward and
compresses spring
Vacuum thus created on
³cover side´ of diaphragm
pulls fuel up suction pipe S
into intake valve D
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Pulsa-Jet Carburetor Operation
When engine intake stroke
is complete, spring C
pushes plunger A outward
Gasoline in pocket above
diaphragm to close inlet
valve D and open
discharge valve E
Fuel is then pumped into
fuel cup F
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Pulsa-Jet Carburetor Operation
Venturi in carburetor is
connected to intake pipe
I which draws gasoline
from fuel cup F
Process is repeated on
the next stroke, keeping
the fuel cup full
Since fuel cup level is
constant, engine gets
constant air-fuel ratio
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Parts of anIC Engine
CROSS SECTION OF OVERHEAD VALVE FOUR CYCLE SI ENGINE
Name as many
parts as you can
Name: ________________