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04-08-2012, 02:44 PM
Post: #1
FOUR STROKE PETROL ENGINE
FOUR STROKE PETROL ENGINE

.docx  A petrol engine print.docx (Size: 357.42 KB / Downloads: 137)
INTRODUCTION
A PETROL ENGINE IS AN INTERNAL COMBUSTION ENGINE WITH SPARK-IGNITION, DESIGNED TO RUN ON PETROL (GASOLINE) AND SIMILAR VOLATILE FUELS.
IN MOST PETROL ENGINES, THE FUEL AND AIR ARE USUALLY PRE-MIXED BEFORE COMPRESSION (ALTHOUGH SOME MODERN PETROL ENGINES NOW USE CYLINDER-DIRECT PETROL INJECTION). THE PRE-MIXING WAS FORMERLY DONE IN A CARBURETOR, BUT NOW IT IS DONE BY ELECTRONICALLY CONTROLLED FUEL INJECTION, EXCEPT IN SMALL ENGINES WHERE THE COST/COMPLICATION OF ELECTRONICS DOES NOT JUSTIFY THE ADDED ENGINE EFFICIENCY. THE PROCESS DIFFERS FROM A DIESEL ENGINE IN THE METHOD OF MIXING THE FUEL AND AIR, AND IN USING SPARK PLUGS TO INITIATE THE COMBUSTION PROCESS. IN A DIESEL ENGINE, ONLY AIR IS COMPRESSED (AND THEREFORE HEATED), AND THE FUEL IS INJECTED INTO VERY HOT AIR AT THE END OF THE COMPRESSION STROKE, AND SELF-IGNITES.
WITH BOTH AIR AND FUEL IN A CLOSED CYLINDER, COMPRESSING THE MIXTURE TOO MUCH POSES THE DANGER OF AUTO-IGNITION — OR BEHAVING LIKE A DIESEL ENGINE. BECAUSE OF THE DIFFERENCE IN BURN RATES BETWEEN THE TWO DIFFERENT FUELS, PETROL ENGINES ARE MECHANICALLY DESIGNED WITH DIFFERENT TIMING THAN DIESELS, SO TO AUTO-IGNITE A PETROL ENGINE CAUSES THE EXPANSION OF GAS INSIDE THE CYLINDER TO REACH ITS GREATEST POINT BEFORE THE CYLINDER HAS REACHED THE "TOP DEAD CENTER" (TDC) POSITION. A TYPICAL SPARK IGNITION OCCURS JUST A FEW DEGREES OF CRANKSHAFT ROTATION BEFORE THE PISTON REACHES TDC, WHICH ALLOWS TIME FOR THE GAS TO BEGIN TO EXPAND. THEN THE BULK OF THE EXPANSION OCCURS JUST AFTER THE PISTON HAS ROTATED BEYOND TDC. HIGHER OCTANE PETROL BURNS SLOWER, THEREFORE IT HAS A LOWER PROPENSITY TO AUTO-IGNITE AND ITS RATE OF EXPANSION IS LOWER. THUS, ENGINES DESIGNED TO RUN HIGH-OCTANE FUEL EXCLUSIVELY CAN ACHIEVE HIGHER COMPRESSION RATIOS.
PETROL ENGINES RUN AT HIGHER SPEEDS THAN DIESELS, PARTIALLY DUE TO THEIR LIGHTER PISTONS, CONNECTING RODS AND CRANKSHAFT (A DESIGN EFFICIENCY MADE POSSIBLE BY LOWER COMPRESSION RATIOS) AND DUE TO PETROL BURNING FASTER THAN DIESEL. HOWEVER THE LOWER COMPRESSION RATIOS OF A PETROL ENGINE GIVE A LOWER EFFICIENCY THAN A DIESEL ENGINE. TO GIVE AN EXAMPLE, A PETROL ENGINE IS LIKE OPERATING A BICYCLE IN ITS LOWEST GEAR WHERE EACH PUSH FROM YOUR FEET ADDS LITTLE ENERGY TO THE SYSTEM, BUT YOU STILL EXPEND ENERGY TO MOVE YOUR LEGS BACK TO THE TDC POSITION. A DIESEL ENGINE IS LIKE OPERATING THAT SAME BICYCLE IN ITS HIGHEST GEAR, WHERE EACH PUSH IMPARTS SUBSTANTIALLY MORE ENERGY TO THE SYSTEM THAN IN THE LOWER GEAR, BUT WITH THE SAME EFFORT BEING USED TO MOVE YOUR LEGS BACK TO TDC.
APPLICATIONS
PETROL ENGINES HAVE MANY APPLICATIONS, INCLUDING:
• MOTOR CARS
• MOTORCYCLES
• AIRCRAFT
• MOTORBOATS
• SMALL ENGINES, SUCH AS LAWN MOWERS, CHAINSAWS AND PORTABLE ENGINE-GENERATORS
WORKING CYCLES
PETROL ENGINES MAY RUN ON THE FOUR-STROKE CYCLE OR THE TWO-STROKE CYCLE. FOR DETAILS OF WORKING CYCLES SEE:
• FOUR-STROKE CYCLE
• TWO-STROKE CYCLE
COOLING
PETROL ENGINES MAY BE AIR-COOLED, WITH FINS (TO INCREASE THE SURFACE AREA ON THE CYLINDERS AND CYLINDER HEAD); OR LIQUID-COOLED, BY A WATER JACKET AND RADIATOR. THE COOLANT WAS FORMERLY WATER, BUT IS NOW USUALLY A MIXTURE OF WATER AND EITHER ETHYLENE GLYCOL OR PROPYLENE GLYCOL. THESE MIXTURES HAVE LOWER FREEZING POINTS AND HIGHER BOILING POINTS THAN PURE WATER AND ALSO PREVENT CORROSION, WITH MODERN ANTIFREEZES ALSO CONTAINING LUBRICANTS AND OTHER ADDITIVES TO PROTECT WATER PUMP SEALS AND BEARINGS. THE COOLING SYSTEM IS USUALLY SLIGHTLY PRESSURIZED TO FURTHER RAISE THE BOILING POINT OF THE COOLANT.
COMPRESSION RATIO
THE COMPRESSION RATIO IS THE RATIO BETWEEN THE TOTAL VOLUMES OF THE CYLINDER AND THE COMBUSTION CHAMBERS – AT THE BEGINNING, AND END OF THE COMPRESSION STROKE. BROADLY SPEAKING, THE HIGHER THE COMPRESSION RATIO, THE HIGHER THE EFFICIENCY OF THE ENGINE. HOWEVER, COMPRESSION RATIO HAS TO BE LIMITED TO AVOID PRE-IGNITION OF THE FUEL-AIR MIXTURE WHICH WOULD CAUSE ENGINE KNOCKING AND DAMAGE TO THE ENGINE. MODERN MOTOR-CAR ENGINE OVERALL HAVE COMPRESSION RATIOS OF BETWEEN 9:1 AND 10:1, BUT THIS CAN GO UP TO 11 OR 12:1 FOR HIGH-PERFORMANCE ENGINES THAT RUN ON HIGHER OCTANE FUEL
IGNITION
PETROL ENGINES USE SPARK IGNITION AND HIGH VOLTAGE CURRENT FOR THE SPARK MAY BE PROVIDED BY A MAGNETO OR AN IGNITION COIL. IN MODERN CAR ENGINES THE IGNITION TIMING IS MANAGED BY AN ELECTRONIC ENGINE CONTROL UNIT.
ENGINE
• AN ENGINE IS THE POWER HOUSE OF ANY VEHICLE
• AN ENGINE CONVERTS THE FUEL ENERGY IN TO KINETIC ENERGY USED TO PROPELL THE VEHICLE ON ROAD
• ENGINE IS ALSO PROVIDED WITH THE ACCESSORIES AND MOUNTINGS FOR EFFICIENT WORKING OF THE ENGINE
• ENGINE COMPONENTS
WORKING OF ENGINE
• THE ENGINE WORK IN FOUR DIFFERENT STROKES
• SUCTION
• COMPRESSION
• POWER
• EXHAUST
TYPES OF WORKING CYCLES
• TWO STROKE:- IN THIS TWO WORKING STROKES ARE COMPLETED IN SINGLE STROKE
• FOUR STROKE:- EACH STROKE IS COMPLETED IN DIFFERENT STROKE
• MAIN COMPONENTS OF ENGINE
• ENGINE BLOCK
• ENGINE HEAD
• SUMP
• PISTON
• PISTON RINGS
• CRANK SHAFT
• CAM SHAFT
• CONNECTING ROD
• VALVE
• FLYWHEEL
• INTAKE MANIFOLD
• EXHAUST MANIFOLD
• TIMING CHAIN
• AIR FILTER
ENGINE BLOCK
• ENGINE BLOCK IS THE MAIN PART IN THE ENGINE ASSEMBLY.
• IT COMPRISES THE MOVING PARTS.
• THE BLOCK IS PROVIDED WITH THE PROVISION FOR ACCESSORIES AND
MOUNTINGS.
• THE ENGINE BLOCK IS CASTED AS SINGLE IN SAND CASTING.
• THE POPULAR MATERIAL FOR THE ENGINE BLOCK IS CAST IRON, ALUMINUM ALLOY ETC
• THE ENGINE BLOCK IS PROVIDED WITH THE WATER JACKETS FOR CIRCULATING THE COOLANT AROUND THE CYLINDER BORE.
• THE LATEST ENGINE BLOCK MATERIALS CONTAINS ALUSIL & NIKASIL
CYLINDER HEAD
• CYLINDER HEAD IS THE TOP PORTION OF THE ENGINE IT COMPRISES THE VALVE TRAIN.
• THE CYLINDER HEAD CONTAINS THE POPPET VALVES AND THE SPARK PLUGS, ALONG WITH TRACTS OR 'PORTS' FOR THE INLET AND EXHAUST GASES
• THE CYLINDER HEAD ALSO SUPPORTS THE SPARK PLUGS AND FUEL INJECTORS.
• IT ALSO PROVIDED WITH THE WATER JACKETS.
• THE CYLINDER HEAD IS CASTED AS SINGLE PIECE IN CAST IRON CASTING OR ALUMINUM
• THE ALUMINUM IS THE MOST PREFERRED MATERIAL FOR THE CYLINDER HEAD AS IT IS THE LIGHTEST, CORROSION RESISTANT
CRANK SHAFT
• CRANK SHAFT IS THE ROTATING MEMBER IN THE ENGINE ASSEMBLY
• THE RECIPROCATING MOTION OF THE PISTON IS TRANSMITTED INTO THE ROTARY MOTION WITH THE HELP OF CRANK SHAFT.
• CRANK SHAFT IS ROLL FORGED OR CASTED, BUT THE ROLL FORGED CRANK SHAFT IS MOST POPULAR IN COMMERCIAL VEHICLES.
• THE CRANK SHAFT IS PROVIDED WITH JOURNALS
• IT ALSO PROVIDED WITH THE OIL HOLES FOR SUPPLYING OIL
GENERAL WORKING OF CRANK SHAFT
PISTON ASSEMBLY
• PISTON IS THE RECIPROCATING PART INSIDE THE CYLINDER BORE
• PISTON IS RESPONSIBLE FOR THE SUCTION AND COMPRESSION OF THE CHARGE INSIDE THE CYLINDER CAVITY
• PISTONS ARE DIE CASTED WITH ALUMINUM ALLOY AND SOMETIMES WITH CAST IRON.
• PISTONS ARE PROVIDED WITH THE PISTON RINGS USUALLY THREE IN NOS. VIZ TWO COMPRESSION AND ONE OIL CONTROL RING
• FOR IMPROVING THE LIFE OF PISTONS THEY ARE COATED WITH TIN, GRAPHITE
CONNECTING ROD
• THE CONNECTING ROD IS THE CONNECTING MEMBER BETWEEN PISTON AND CRANK SHAFT
• THE CONNECTING RODS ARE MOST USUALLY FORGED OF STEEL FOR PRODUCTION ENGINES CAST IRON FOR APPLICATIONS SUCH AS MOTOR SCOOTERS, ALUMINUM ALLOYS
• THEY ARE NOT RIGIDLY FIXED AT EITHER END, SO THAT THE ANGLE BETWEEN THE CONNECTING ROD AND THE PISTON CAN CHANGE AS THE ROD MOVES UP AND DOWN AND ROTATES AROUND THE CRANKSHAFT.
• THE JOURNAL BEARINGS ARE PROVIDED AT CRANK END AND OTHER END IS CONNECTED WITH PISTON WITH THE HELP OF GUDGEON PIN.
CAM SHAFT
• THE CAM SHAFT IS THE ROTARY COMPONENT RESPONSIBLE FOR OPENING AND CLOSING OF THE INLET AND EXHAUST VALVES
• THE CAM SHAFT IS ROTATED WITH THE HELP OF TIMING CHAIN OR
TIMING GEAR
• THE CAM SHAFT IS PROVIDED WITH THE CAM LOBES WHICH CAUSES THE WORKING OF THE VALVES
• THE NORMAL MATERIAL FOR CAM SHAFT IS CHILLED IRON CASTINGS, BILLET STEEL
• THE TIMING OF CRANK SHAFT AND CAM SHAFT IS SO ADJUSTED THAT THE VALVES OPENS AND CLOSES AT CORRECT TIME
VALVES
• VALVES ARE THE GATEWAYS FOR THE INTAKE CHARGE AND EXHAUST GASES
• THE VALVES ARE OPERATED WITH THE HELP OF CAM SHAFT AND CAM LOBES
• THE OPENING AND CLOSING OF THE VALVE IS DONE WITH THE HELP OF TIMING GEAR OR TIMING CHAIN
• THE VALVES ARE COOLED WITH COOLANT
• THE SODIUM COOLED VALVES ARE SELF COOLED USED FOR EXHAUST
• VALVE SEATS MADE OF IMPROVED ALLOYS SUCH AS STELLITE
SPARK PLUG
• SPARK PLUG IS USED TO IGNITE THE CHARGE INSIDE THE ENGINE
• SPARK PLUGS ARE THE ELECTRICAL COMPONENT IN THE ENGINE ASSEMBLY
• THE SPARK PLUG PRODUCES THE SPARK OF ABOUT 10-15 THOUSAND VOLTS WHICH PRODUCES 500-600̊ DEGREE TEMPERATURE
• THE SPARK IS PRODUCED IN EACH CYLINDER DURING POWER STROKE WHICH IS DISTRIBUTED WITH DISTRIBUTOR ACCORDING TO FIRING ORDER
FUEL INJECTORS
• FUEL INJECTORS ARE USED TO INJECT THE METERED AMOUNT OF FUEL INSIDE THE CYLINDER DURING POWER STROKE
• THE FUEL IS SPRAYED INSIDE THE CYLINDER IN THE FORM OF LITTLE DROPLETS FORMED DUE TO PRESSURIZED FUEL SUPPLY
• THE INJECTOR IS CONNECTED WITH THE FUEL PUMP
17-08-2012, 11:15 AM
Post: #2
RE: FOUR STROKE PETROL ENGINE
FOUR STROKE PETROL ENGINE


.docx  1FOUR STROKE.docx (Size: 11.6 KB / Downloads: 69)

ABSTRACT

In a four stroke cycle internal combustion engine, a combustion chamber is disposed above the cylinder head and is connected by a passage to the piston chamber. The piston at its top dead center almost contacts head. Inlet and outlet valves and spark plug means are associated with the top portion of the combustion chamber. The injecting device protrudes into the combustion chamber is surrounded by another chamber, which communicates with the combustion chamber through slots, which open into the top portion of the combustion chamber. The lower portion of the surrounding chamber communicates through openings whith the combustion chamber. The openings are smaller in cross-section than the slots so that the explosive gases flow from the combution chamber into the surrounding chamber and flow back through the poenings into the surrounding chamber. This results in turbulence and mixing as in a cyclone so that a good combustion is ensured. Downwardly flaring conical openings are additional provided, which open into the surrounding chamber at its bottom and extend throuh the cylinder head toward the piston so that the surrounding chamber will be effectively scavenged during the exhaust stroke.

Basic principles

To help, you understand how on engine works. We will use a simplified version of a real engine.
When pressure is applied to the head of the piston, it is forced downwards. The piston pushes against the connecting rod which pushes against an arm of the cranckshaft causing it to rotate. Thus, the up and down motion of the piston is converted to a rotary motion of the crankshaft.
When you turn the key to start a vehicle, the startor (an electic motor) rotates the crankshaft thus moving the pistons up or down, depending on the initial position of the piston. As a piston moves down from the top dead centre point, a mixture of petrol and air is sucked into its cylinder. This is called the intake stroke. The starter continues to totate the crankshaft. As it compressed in the space between the piston head and the cylinder block. This is called the compression stroke. As the piston reaches the top of its travel, the petrol-air mixture is igniited by a spark jumping across the gaps of the sparking plug. The burning mixture then begins to expand rapidly, in a kind of controlled explosion. This expanding gas forces the piston downwards. This is the power stroke.
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