PCMAI Cursul no.1
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Transcript of 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In 1884, an unpublished French patent issued in 1862 to Alphonse Beau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