Fundamental of Fundamental of the Engine the Engine operationsoperations

Fundamental of the Engine operations Engine: is a machine that converts heat energy into mechanical energy.

The heat from burning a fuel produces power which moves the vehicle.

Automotive engine are internal combustion (IC) engine because the fuel that runs them is burned internally, or inside the engines. There are two types of engine

Reciprocating engine: piston moving up and down, or back and forth Rotary engines: have rotor that spin or rotate

Essential for Engine Operation The automobile engine has cylinders Piston moves up and down in each cylinder

The car moves because the piston move Engine must have available fuel for moving up and down the piston Gravity, atmospheric pressure, and vacuum make it possible for the fuel to

get into the engine cylinders. Fuel burns to produce power. Vacuum is the absence of air.

When a piston moves down in a cylinder, the pistons creates a partial vacuum.

Engine Cylinder

There are at least two valve ports at the top of the cylinder Intake and exhaust valve ports Valve enter in each of the ports.

A valve is a device that can be opened and closed to control the flow of gas.

Engine valve is a plug with a round head on a long stem It moves up and down at the proper time by the valve train When the port is closed, no A/F mixture enter or exhaust

leave the cylinder A/F enters into the cylinder when the intake valve open Exhaust leaves the cylinder when the exhaust valve open.

Actions in the Engine Cylinder The intake valve closes after the piston passes it bottom position

and starts to move up again The bottom position of the piston into the cylinder is called bottom dead

center (BDC). The piston moves up, compresses the A/F mixture into a confined

space is called combustion chamber The piston reaches the top position and spark plug fire

The top position of the piston into the cylinder is called top dead center (TDC).

The spark sets the fire to ignite the compresses the A/F mixture. The temperature of the burning A/F mixture goes up as high as

33160C. The high temperature makes the pressure as high as 4140 kPa The 4140 kPa push down the piston of up to 17,792 N

This 17,792 N pushes the piston down The downward movement, carried through the connecting rod, rotates the

crankshaft The crankshaft turns the gears and drive shafts to move the car.

Four Stroke Cycle: 1.Intake

2. compression3. power

4. exhaust

Engine constructionPiston and piston ring

Piston: are made of aluminum alloy. Its diameter is slightly smaller than the cylinder which allows the piston to slide up and down It is called sliding fit

Piston rings are installed on the pistons ring grooves for preventing excessive blow-by. Compression ring: these form a sliding seal between the

piston and the cylinder wall. Oil control ring (oil rings) :These scrape off most of the

lubricating oil splashed on the cylinder wall and return the oil to the crankcase

Engine Operation A diesel engine requires three of these systems:

Fuel system Electric ignition system Lubricating system Cooling system

Fuel system: supplies gasoline or diesel fuel to the engine by the fuel pump. The fuel mixes with the air to form a combustible mixture. Then the mixture is compressed, ignite, and burn. A fuel pump sends fuel from the tank to the fuel injectors.

Fuel injectors are controlled by Electronic control module (ECM) Fuel delivery continues as long as the valve open.

The fuel flow time and amount is controlled by ECM When the proper amount of fuel has sprayed out, the ECM turns off

the injector. Carburetors, were part of most fuel systems. It is called mixing

device. Air passing through the carburetor picks up and mixes with the fuel to

provide a combustible mixture. It is replaced now by ECM control fuel-injection system

Operational Parameters Foranyonecylinder,thecrankshaft,connectingrod,

piston,andheadassemblycanberepresentedbythefollowinggeometry: b=Boreofthecylinder L=connectingrodlength a=crankradius s=strokelength q=Crankangle,degree

Thetopdeadcentre(tdc)ofanenginereferstothecrankshaftbeinginapositionsuchthatq=00

Thevolumeinthispositioniscalledclearancevolume(Vc)

Bottomdeadcentre(bdc)referstothecrankshaftbeingq=1800

ThevolumeVLismaximumatbottomdeadcentre

Thecompressionratioisdefinedasthemaximumtominimumvolume,r=Vbdc/Vtdc=VL/Vc

Thedisplacementvolume(Vd)isdefinedasthedifferencebetweenthemaximumandminimumvolumeforasinglecylinder,Vd=VLVC=s(b2/4)Foramultiplecylinderengine,thetotaldisplacementistheproductofthenumberofcylinder(nc)andthedisplacementvolumeofacylinder.

Theinstantaneousvolumeatanycrankangleis,V(q)=vc+y(b2/4)

Themeaneffectivepressure(mep)istheworkdoneperunitdisplacementvolume.Twousefulmeaneffectivepressureparameters:

imep:Theindicatedmeaneffectivepressureisthenetworkdoneperunitofdisplacementvolumebythegasduringcompressionandexpansion.

bemp:istheexternalshaftworkperunitvolumedonebytheengine.Volumetricefficiency:itisdefinedasthemassoffuelandairinducedintothecylinderdividedbythemassthatwouldoccupythedisplacedvolumeatthedensity(i)intheintakemanifold.

Engine power is power available from the crankshaft to do work.

The unit of engine power is in kW (or hp) Three types of works are normally defined in case of

engine power, Indicated horse power (ihp) : is the power developed inside the

combustion chambers during combustion Frictional horse power (fhp): is the power required to overcome

the friction of the internal moving parts. Brake horse power (bhp) : is the power available from the

engine crankshaft to do the work. It is normally measured by braking the crankshaft. Dynamometer: is used to measure the bhp.

bhp = ihp - fhpMechanical efficiency: is defined as the ratio of bhp to

ihp.