PCMAI Cursul no.1

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    INTERNAL COMBUSTION

    ENGINE HISTORY

    J.J.Lenoir (1822-1900)-developed the first engine for commercial

    use burned coal-gas air mixtures at atmospheric pressure. No

    compression before combustion.

    The charge was ignited with a spark, pressure increased and thendelivered power to the piston. The cycle was completed with an

    exhaust stroke. Efficiency 5%. No. of engines= 5000

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    Nicolaus Otto (1832-1891) and Eugene Langen (1833-1895) -In 1867 use

    the pressure rise resulting from combustion of the fuel-air chargeEfficiency 11%.

    This was an atmospheric engine.

    Otto propsed an engine cycle with four piston strokes:intake stroke,

    compression stroke, expansion or power stroke and exhaust stroke.

    The prototype four stroke ran in 1876.

    In 1884, an unpublished French patent issued in 1862 to Alphonse Beau

    de Rochas was found which describe the principle of the four stroke

    cycle.

    By the 1880s several engineers: Dugald Clerk, James Robson, in

    England and Karl Benz in Germany had developed two-stroke intrnal

    combustion engines.

    In 1892 Rudolf Diesel proposed a new form of internal combustion

    engine.

    His concept of initiating combustion by injecting a liquid fuel into air

    heated solely by compression.

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    A wide variety of experimental rotary engines have been proposed.

    The first practical rotary internal combustion engine was tested by

    Felix Wankel in 1957

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    Engine classifications

    a) Application:Automotive

    Locomotive

    Light aircraft

    MarinePower generation

    b)Basic engines design:

    (arrangement of cylinders)In-line

    V-engine

    U-engine

    W-engineRadial

    Opposed

    (rotary engines)

    WankelOther geometries

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    c) Working cycle

    Four stroke

    Naturally aspirated

    Supercharged

    Turbocharged

    Two-stroke cycle

    Crankcase scavenged

    Supercharged

    Turbocharged

    Six stroke engine

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    d) Valve or port design and location

    Overhead valves (I- head)Underhead valves (L-head)

    Rotary valves

    Cross-scavenged porting( inlet and exhaust ports on opposite side of

    cylinder)

    Loop-scavenged porting (inlet and exhaust ports on same side of

    cylinder)

    Through-or uniflow-scavenged(inlet and exhaust ports and valves at

    different ends of cylinders)

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    e)Fuel

    Gasoline (petrol)

    Fuel oil (diesel fuel)

    Natural gas

    Liquid petroleum gasAlcohols (methanol, ethanol)

    Hydrogen

    Dual fuel

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    f)Method of mixture preparation

    Carburetion

    Fuel injection into the intake port or intake

    manifold

    Fuel injection into the engines cylinder

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    g)Method of ignition

    Spark ignition(in conventional engines where the mixture is uniformed

    in stratified charge engines where the mixture is non

    uniform)

    Compression ignition(in conventional diesels, as well as ignition in gas engines

    by pilot of fuel oil)

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    h)Combustion chamber design

    Open chamberDisc

    Wedge

    HemisphereBowl in piston

    Divided chamberSwirl chamber

    Prechamber

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    j)Method of load control

    Throttling of fuel and air flow (the mixture composition is

    unchanged)

    Control of fuel flow

    Combination of methods

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    l)Method of cooling

    Water cooled

    Air cooled

    Uncooled

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    http://en.wikipedia.org/wiki/Image:4-Stroke-Engine.gif
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    http://upload.wikimedia.org/wikipedia/commons/4/45/Four_stroke_cycle_intake.png
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    http://en.wikipedia.org/wiki/Image:Four_stroke_cycle_compression.png
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    http://upload.wikimedia.org/wikipedia/commons/c/ce/Four_stroke_cycle_spark.png
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    http://en.wikipedia.org/wiki/Image:Four_stroke_cycle_power.png
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    http://upload.wikimedia.org/wikipedia/commons/b/b1/Four_stroke_cycle_exhaust.png
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    Engine Operation

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    Objective

    The objective of this lesson is to:

    Learn the three vital systems.Understand the basic operation of an

    engine.

    Diagnose problems in the system.

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    Three vital systems

    Compression or Air

    Fuel

    Ignition or Fire

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    The Four Stroke Cycle

    Intake

    CompressionPower

    Exhaust

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    Intake

    Intake valve opens

    Air fuel mixture enters the cylinder

    Piston moves down

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    Compression

    Piston moves upward

    Intake valve closed

    Air-fuel mixture is compressed

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    PowerSpark plug fires

    Ignition proceeds

    Piston is forced down

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    ExhaustExhaust valve opens

    Piston moves upward

    Spent gas pushed into exhaust system

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    Questions ????

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    Geometrical properties of reciprocating

    enginescompression ratio rc=(Vd+Vc)/Vc

    Vd-is the displaced or swept volume,Vd=L(B2/4)

    Vc-is the clearance volume,

    mean speed of piston Wm=L.n/30=2a/ [m/s]where:=n/30 [rad/s]

    wm=1017[m/s] for car engine wm= 8.12[m/s] for truck engine

    Ratio of cylinder bore to piston stroke

    Rbs=B/L

    Ratio of connecting rod length to crank radius:

    R=l/a

    The stroke and crank radius are related by:

    L=2a

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    Typical values of these parameters are:

    rc=8.12 for SI enginesrc=12.24 for CI engines

    B/L=0.8.1.2 for small and medium size engines,decreasing to about 0.5 for large slow-speed CI engines;

    R=3.4 for small and medium size engines, increasing to

    5 to 9 for large slow-speed CI engines.

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    Four-stroke cycleThe intake stroke-starts with the piston at TDC and ends with the

    piston at BDC, which draws fresh mixture into cylinder. To increase

    the mass of the charge the inlet valve opens shortly before the stroke

    starts and closes after it ends.

    The compression stroke-when both valves are closed and mixtureinside the cylinder is compressed to a small fraction of its initial

    volume. Toward the end of the compression stroke, combustion is

    initiated and the cylinder pressure rises more rapidly.

    The power stroke or expansion stroke, which starts with the piston atTDC and ends at BDC as the high temperature, high pressure, gases

    push the piston down and force the crank to rotate. As the piston

    approaches BDC the exhaust valve opens to initiate the exhaust

    process and drop the cylinder pressure to close to exhaust pressure.The exhaust stroke-where the remaining burned gases are swept out

    by piston as it moves toward TDC. As that piston approaches TDC

    the inlet valve opens. After TDC the exhaust valve closes and a new

    cycle starts.

    Two-stroke cycle

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    Two-stroke cycle

    The compression stroke-starts by closing the inlet and

    exhaust ports, and then compresses the cylinder contents

    and draws fresh charge into the crankcase. As piston

    approaches TDC, combustion is initiated.

    The power or expansion stroke, similar to that in the four

    stroke cycle until the piston approaches BDC, when firstthe exhaust ports and then the intake port are uncovered.

    Most of the burnt gases exit the cylinder in an exhaust

    blow down process.When the inlet ports are uncovered,

    the fresh charge which has been compressed in the

    crankcase flow into cylinder. The piston an the ports are

    shaped to deflect the incoming charge from flowing

    directly into the exhaust ports and to achieve effectivescavenging of the residual gases.

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    http://upload.wikimedia.org/wikipedia/commons/5/52/Arbeitsweise_Zweitakt.gif
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    http://upload.wikimedia.org/wikipedia/commons/f/fc/Wankel_Cycle_anim_en.gif