Internal combustion engine 1

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Automobile Engineering



Engine Parts



Piston and Piston Rings



Parts



OHV Engine Design

4-cylinder 8 valves OHV engine



OHC or SOHC Engine

4-cylinder 8 valves SOHC engine



DOHC or Twin cam engine

4-cylinder 16 valves DOHC engine



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



Lecture 1

Engine Terminology

Engine Classifications

Carburetors



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



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



Classification of Engines

External vs. Internal Combustion

Spark Ignition vs. Compression Ignition

Cylinder Configuration

Valve Location

2 Stroke or 4 Stroke



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




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




Cylinder Configurations

Radial (Aircraft)

V(Automobile)

In Line

(Automobile)

Horizontally Opposed

(Subaru)

Opposed Piston(crankshafts

geared together)




Valve Location

Most common: overhead-valve or I-head

Exhaust

valve

Intake

valve




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)



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



Briggs Engine - Intake



Compression



Power Stroke



Exhaust Stroke



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!



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:



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



Flo-Jet Carburetor

Fuel tank is above

carburetor

Fuel is fed directly to

carburetor by gravity

Why the vent?



Flo-Jet Carburetor

Fuel from tank

Air flow

Air-fuel

mixture



Pulsa-Jet Carburetor

Incorporates a diaphragm type fuel pump

and a constant level fuel chamber



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




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




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



Parts of anIC Engine

CROSS SECTION OF OVERHEAD VALVE FOUR CYCLE SI ENGINE

Name as many

parts as you can

Name: ________________

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Internal combustion engine 1