AUTOMOTIVE PETROL ENGINES

AUTOMOTIVE PETROL ENGINESSAUX1001INTERNAL COMBUSTION ENGINESUNIT.1 ENGINE CONSTRUCTION AND OPERATIONLESSON PLANNINGConstruction details of petrol engine.Working principle of petrol engine.Air standard Otto cycleTwo stroke engine construction & operationComparison of 4S &2S engineFiring orderValve and Port timing diagram.Introduction :=HEAT ENGINE : Heat engine is a device which transforms the chemical energy of a fuel into thermal energy and utilizes this thermal energy to perform useful work. Examples of heat engines include: steam engine, diesel engine, and gasoline (petrol) engine.

On the basis of how thermal energy is being delivered to working fluid of the heat engine, heat engine can be classified as: internal combustion engine external combustion engine.

ENGINES CLASSIFICATIONtypes of heat enginesexternal combustioninternal combustionReciprocating engine(steam engine)Rotary engine(steam turbine)Reciprocating engine(S.I&C.I-engine)Rotary engine-(wankel engine)4

Internal Combustion EngineThe internal combustion engine is an engine in which the combustion of a fuel (normally a fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber.

2 Stroke EngineRotay Engine4 Stroke Engine6External Combustion EngineAn external combustion engine (EC engine) is a heat engine where an (internal) working fluid is heated by combustion in an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine, produces motion and usable work. The fluid is then cooled, compressed and reused (closed cycle), or (less commonly) dumped, and cool fluid pulled in (open cycle air engine).

Locomotive engineJet EngineRotary EngineA rotary engine is essentially a standard Otto cycle engine, but instead of having a fixed cylinder block with rotating crankshaft as with a conventional radial engine, the crankshaft remains stationary and the entire cylinder block rotates around it. In the most common form, the crankshaft was fixed solidly to an aircraft frame, and the propeller simply bolted onto the front of the crankcase.

Wankel( rotary engine)

Advantages:higher power outputno reciprocating mass simpler and lighter constructionDrawbacks:increased wear of rubbing partshigher fuel consumptionrequirement for better materials9Reciprocating EngineA reciprocating engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. The main types are: the internal combustion engine, used extensively in motor vehicles; the steam engine, the mainstay of the Industrial Revolution

4 Stroke Engine2 Stroke EngineENGINES CONFIGURATIONInline Engines: The cylinders are arranged in a line, in a single bank. V Engines: The cylinders are arranged in two banks, set at an angle to one another. Flat Engines: The cylinders are arranged in two banks on opposite sides of the engine

Cylinder layouts

12Internal Combustion Engines multi-cylinder -

13

CONSTRUCTION DETAILS

Cylinder Block :Foundation of the engine and contains pistons, crank shaft,cylinders, timing sprockets and sometimes the cam shaft.

Cylinder block is the main supporting structure for the various components. The bottom portion of the bock is called the crankcase. It is made of cast iron or aluminium.ENGINE COMPONENTS:Cylinder : The circular cylinders in the engine block in which the pistons reciprocate back and forth.

Cylinder head

Head : The piece which closes the end of the cylinders, usually containing part of the clearance volume of the combustion chamber. The cylinder head is mounted on the cylinder block. It contains cooling fins or water jackets and the valves. Some engines contains the cam shaft in the cylinder head. Combustion chamber: The end of the cylinder between the head and the piston face where combustion occurs.The size of combustion chamber continuously changes from minimum volume when the piston is at TDC to a maximum volume when the piston at BDC.

CONNECTING ROD

It interconnects the piston and the crankshaft and transmits the gas forces from the piston to the crankshaft. The two end of the connecting rod are called big end and small end(gudgeon pin).PistonA movable part fitted into a cylinder, which can receive and transmit power. Through connecting rod, forces the crank shaft to rotate.

Piston RingsFour stroke: Three ringsTop two are compression rings (sealingthe compression pressure in the cylinder)and the third is an oil ring (scrapesexcessive oil from the cylinder walls) Two Stroke: Two RingsBoth the rings are Compression rings.

Piston rings: Metal rings that fit into circumferential grooves around the piston and form a sliding surface against the cylinder walls.

Piston, crankshaft, & fly wheeltimeOutput torqueCrank ShaftConverts up and down or reciprocating motion intocircular or rotary motion. The crankshaft is enclosed in a crankcase.

FlywheelAttached to the crankshaft.Reduces vibration.Cools the engine (air cooled)Used during initial start-up

Transfers power from engine to drivetrain.Camshaft : the camshaft and its associated parts control the opening and closing of the two valves.

Cam Lobe: Changes rotary motion into reciprocating motion.

pistonvalverockervalve liftercamshaftcamcrankshaftpush rodValve Mechanisms:

Timing marksPartsExhaust Valve lets the exhaust gases escape the combustion Chamber. (Diameter is smaller then Intake valve)

Intake Valve lets the air or air fuel mixture to enter the combustion chamber. (Diameter is larger than the exhaust valve)Valves: Minimum Two Valves pre Cylinder

Crankcase : Part of the engine block surrounding the crankshaft.In many engines the oil pan makes up part of the crankcase housing.Exhaust manifold : Piping system which carries exhaust gases away from the engine cylinders, usually made of cast iron .

Intake manifold :Piping system which delivers incoming air to the cylinders, usually made of cast metal, plastic, or composite material.In most SI engines, fuel is added to the air in the intake manifold system either by fuel injectors or with a carburetor.The individual pipe to a single cylinder is called runner.Carburetor : A device which meters the proper amount of fuel into the air flow by means of pressure differential.For many decades it was the basic fuel metering system on all automobile (and other) engines.Spark plug : Electrical device used to initiate combustion in an SI engine by creating high voltage discharge across an electrode gap.EnginesIt provides the means of ignition when the gasoline engines piston is at the endof compression stroke, close to Top Dead Center(TDC) Spark Plug

The difference between a "hot" and a "cold" sparkplug is that the ceramic tipis longer on the hotter plug.

Top Dead Center (TDC): Position of the piston when it stops at the furthest point away from the crankshaft.Top because this position is at the top of the engines (not always), and dead because the piston stops as this point. Because in some engines TDC is not at the top of the engines(e.g: horizontally opposed engines, radial engines etc.) Some sources call this position Head End Dead Center (HEDC). Some source call this point TOP Center (TC).When the piston is at TDC, the volume in the cylinder is a minimum called the clearance volume.ENGINE NOMENCLATURE:

Bottom Dead Center (BDC): Position of the piston when it stops at the point closest to the crankshaft.Some sources call this Crank End Dead Center (CEDC) because it is not always at the bottom of the engine.Some source call this point Bottom Center (BC).

Stroke : Distance traveled by the piston from one extreme position to the other : TDC to BDC or BDC to TDC.Bore :It is defined as cylinder diameter or piston face diameter; piston face diameter is same as cylinder diameter( minus small clearance).Swept volume/Displacement volume : Volume displaced by the piston as it travels through one stroke.Swept volume is defined as stroke times bore.Displacement can be given for one cylinder or entire engine (one cylinder times number of cylinders).Clearance volume : It is the minimum volume of the cylinder available for the charge (air or air fuel mixture) when the piston reaches at its outermost point (top dead center or outer dead center) during compression stroke of the cycle. Minimum volume of combustion chamber with piston at TDC.Compression ratio : The ratio of total volume to clearance volume of the cylinder is the compression ratio of the engine. Typically compression ratio for SI engines varies form 8 to 12 and for CI engines it varies from 12 to 24Displacement is the cubic inch (cu. in.) or cubic centimeter (cc) volume displaced or swept by all of the pistons. The diameter of a cylinder is called the bore. The distance the piston travels down in the cylinder is called the stroke.

36Compression ratio (CR) is the ratio of the volume in the cylinder above the piston when the piston is at the bottom of the stroke to the volume in the cylinder above the piston when the piston is at the top of the stroke.

37ENGINE SPECIFICATIONSCOMPRESSION RATIO

38The SAE standard for automotive engine rotation is counterclockwise (CCW) as viewed from the flywheel end (clockwise as viewed from the front of the engine). The flywheel end of the engine is the end to which the power is applied to drive the vehicle. This is called the principal end of the engine. The nonprincipal end of the engine is opposite the principal end and is generally referred to as the front of the engine, where the accessory belts are used.Engine rotation

WORKING PRINCIPLE OF 4-STROKE ENGINE

Piston moves up and down in the cylinder causing crankshaft to rotateHow engine works?AirFuelMixingCombustionExhaustPowerUseful WorkCarburetorIgnition(spark plug)ValvesFlywheelCrankshaftTypical S.I. Fuel System Layout (Simplified)Fuel TankFuel PumpFuelFiltersCarburettorOr SinglePoint ThrottleBody HousingFuel Injector orCarburettorVenturiFuel Not used is returned to the fuel tankInlet ManifoldEngine CombustionChamberFuel PressureRegulatorEFI Only4 Stroke Spark Ignition EngineA four-stroke engine, also known as four-cycle, is an internal combustion engine in which the piston completes four separate strokesintake, compression, power, and exhaustduring two separate revolutions of the engine's crankshaft, and one single thermodynamic cycle.Working Principle of 4 Stroke Spark Ignition EngineINTAKE stroke: on the intake or induction stroke of the piston, the piston descends from the top of the cylinder to the bottom of the cylinder, reducing the pressure inside the cylinder. A mixture of fuel and air, or just air in a diesel engine, is forced by atmospheric (or greater) pressure into the cylinder through the intake port. The intake valve(s) then close. The volume of air/fuel mixture that is drawn into the cylinder, relative to the volume of the cylinder is called, the volumetric efficiency of the engine.COMPRESSION stroke: with both intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the air, or fuel-air mixture into the combustion chamber of the cylinder head.POWER stroke: this is the start of the second revolution of the engine. While the piston is close to Top Dead Center, the compressed airfuel mixture in a gasoline engine is ignited, usually by a spark plug, or fuel is injected into the diesel engine, which ignites due to the heat generated in the air during the compression stroke. The resulting massive pressure from the combustion of the compressed fuel-air mixture forces the piston back down toward bottom dead centre.EXHAUST stroke: during the exhaust stroke, the piston once again returns to top dead center while the exhaust valve is open. This action evacuates the burnt products of combustion from the cylinder by expelling the spent fuel-air mixture out through the exhaust valve(s).Internal Combustion Engines four stroke -

starting positiona. piston starts moving downb. intake valve opensc. air-fuel mixture gets in

1. intakea. piston moves upb. both valves closedc. air-fuel mixture gets compressed

2. compression47Internal Combustion Engines four stroke -ignition

a. air-fuel mixture explodes driving the piston down

3. powera. piston moves up b. exhaust valve opensc. exhaust leaves the cylinder

4. exhaust48

Working principle

1.SUCTION/INTAKE STROKE: Intake of air fuel mixture in cylinder through intake manifold.The piston travel from TDC to BDC with the intake valve open and exhaust valve closed.This creates an increasing volume in the combustion chamber, which in turns creates a vacuum.The resulting pressure differential through the intake system from atmospheric pressure on the outside to the vacuum on the inside causes air to be pushed into the cylinder.As the air passes through the intake system fuel is added to it in the desired amount by means of fuel injectors or a carburetor. Four strokes of SI Engine Cycle :2. COMPRESSION STROKE: When the piston reaches BDC, the intake valve closes and the piston travels back to TDC with all valves closed. This compresses air fuel mixture, raising both the pressure and temperature in the cylinder. Near the end of the compression stroke the spark plug is fired and the combustion is initiated.COMBUSTION of the air-fuel mixture occurs in a very short but finite length of time with the piston near TDC (i.e., nearly constant volume combustion).It starts near the end of the compression stroke slightly before TDC and lasts into the power stroke slightly after TDC.Combustion changes the composition of the gas mixture to that of exhaust products and increases the temperature in the cylinder to a high value.This in turn increases the pressure in the cylinder to a high value.3. EXPANSION STROKE/POWER STROKE : With all valves closed the high pressure created by the combustion process pushes the piston away from the TDC. This is the stroke which produces work output of the engine cycle.As the piston travels from TDC to BDC, cylinder volume is increased, causing pressure and temperature to drop.4. EXHAUST STROKE: By the time piston reaches BDC, exhaust blowdown is complete, but the cylinder is still full of exhaust gases at approximately atmospheric pressure. With the exhaust valve remaining open, the piston travels from BDC to TDC in the exhaust stroke.This pushes most of the remaining exhaust gases out of the cylinder into the exhaust system at about atmospheric pressure, leaving only that trapped in the clearance volume when the piston reaches TDC.Near the end of the exhaust stroke before TDC, the intake valve starts to open, so that it is fully open by TDC when the new intake stroke starts the next cycle.Near TDC the exhaust valve starts to close and finally is fully closed sometime after TDC.This period when both the intake valve and exhaust valve are open is called valve overlap, it can be clearly seen in valve timing chart given below.

2 STROKE SPARK IGNITION ENGINESir Dugald Clark (18541932) invented the two stroke engine. It is for this reason, the two-stroke cycle is sometimes referred as the Clark cycle. In two stroke engine the cycle is completed in one revolution of the crankshaft. Two strokes are sufficient to complete the cycle , one for compressing the fresh charge and the other for expansion or power strokeCONSTRUCTION OF 2-STROKE SI ENGINE

Working of 2-stroke Engine1.Induction & Compression stroke1.Piston : Piston moves from BDC to TDC2.Intake: The fuel/air mixture is inducted into the crankcase through the spring loaded inlet valve (reed valve) when the pressure in the crankcase is reduced due to upward movement of the piston during compression stroke.3.Compression. The fuel- Mixture present in the combustion chamber is compressed due to the upward (BDC to TDC )movement of the piston.

induction-compression stroke.FIRST STROKE(INDUCTION AND COMPRESSION)

2.Power & Exhaust Stroke1.Piston:piston moves from TDC to BDC.2.Power(Expansion). At the end of the compression stroke ,the spark plug ignites the fuel-mixture. The burning fuel expands, driving the piston downward. During the expansion stroke the charge in the crankcase is compressed.Exhaust: a) Near the end of the stroke, the piston uncovers the exhaust ports and the cylinder pressure drops to atmospheric pressure as the combustion products leave the cylinder. b) Further movement of the piston uncovers the transfer ports, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder.c) This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder. This process is called scavenging

SECOND STROKE (POWER AND EXHAUST)

Internal Combustion Engines two stroke -Advantages:lack of valves, which simplifies construction and lowers weightfire once every revolution, which gives a significant power boost can work in any orientationgood power to weight ratioDrawbacks:lack of a dedicated lubrication system makes the engine to wear faster. necessity of oil addition into the fuel low efficiency produce a lot of pollution63AIR STANDARD CYCLES The operating cycle of an internal combustion engine can be broken down into a sequence of separate process: intake, compression, combustion, expansion and exhaust.The ICE operate on an open cycle in which the working fluid enters the system at one set of condition and leaves at another.The accurate study and analysis of I.C.E. processes is very complicated. To simplify the theoretical study "Standard Air Cycles" are introduced, these cycles are similar to the open cycles, but some simplifying assumptions are made: The working medium is assumed to be perfect gas and follows the relation pv=mRT.There is no change in the mass of the working medium.All the processes are reversible.There is no loss of heat from the system to the surrounding.The working medium has constant specific heats throughout the cycle.

Otto cycleThe different types of cycles are:Internal combustion engineOtto cycle(petrol engine)Diesel cycle(diesel engine)Gas turbines Brayton cycleRefrigerationReversed Brayton cycleOtto cycle :Nikolaus August Otto(1836-91),a German, built in 1876, a practical engine on the principles set by Beau De Rochas.Ottos engine can be said to founded the combustion engine technology.

Otto cycleOtto Cycle P-V & T-s Diagrams

Pressure-VolumeTemperature-Entropy

For a constant volume heat addition

For constant volume rejection process

Assuming constant specific heat:

For an isentropic compression (and expansion) process:

where: = Cp/Cv

Hence substituting,

Otto Cycle Derivation

The compression ratio (rv) is a volume ratio and is equal to the expansion ratio in an otto cycle engine.Compression Ratio

where Compression ratio is defined as Otto Cycle DerivationThen by substitution,

The air standard thermal efficiency of the Otto cycle then becomes:Otto Cycle DerivationEffect of compression ratio on Otto cycle efficiency

Efficiency :1.increased by increasing compression ratio.2.independent on the heat added or load.3.increased by increasing specific heat constant ratioFOUR-STROKE VERSUS TWO-STROKE ENGINESThe two-stroke engine performs twice as many power strokes per cylinder per revolution. In theory at least, this might be expected to produce twice the performance of a four-stroke engine of equivalent size. Unfortunately, this is not realized in practice because of the difficulties encountered in effectively purging the exhaust gases from the cylinder and then filling it completely with a fresh combustible charge. The scavenging efficiency of the basic two stroke petrol engine is therefore poor.In performing twice as many power strokes per revolution, the two-stroke engine can deliver a smoother flow of power, but this may be less true at low engine speeds when irregular firing or four-stroking can result from poor scavenging.An obvious practical advantage of the basic two-stroke engine is the mechanical simplicity conferred by its valve-less construction, which contributes to a more compact and lighter engine that should be less expensive to make.Reduced maintenance requirements might reasonably be expected with the basic two-stroke engine by virtue of point 3. There is, however, the well-known tendency for carbon formation to have a blocking effect on the exhaust ports, which impairs engine performance by reducing scavenging efficiency.The fuel consumption of the basic two-stroke engine is adversely affected by the poor cylinder scavenging, which allows part of the fresh charge of air and fuel to escape through the exhaust port before final compression of the charge takes place.Lubrication of the two-stroke petrol engine is complicated by the need to introduce oil into the fuel supply to constitute what is generally termed a petroil mixture. The working parts of the engine are thus lubricated in aerosol fashion by oil in the air and fuel charge, and this tends to increase harmful exhaust emissions. It is for this reason that the basic two-stroke petrol engine is now obsolescent for cars.There is a greater danger of overheating and piston seizure with a two-stroke engine, which can set a limit on the maximum usable performance. It is more difficult to cool 2 satisfactorily, because it does not have the benefit of the second revolution in the four-stroke cycle when no heat is being generated.FOUR STROKE CYCLEThe cycle is completed in four stroke of the piston or in two revolution of crankshaft. Thus on power stroke is obtained in every two revolution of the crankshaft.Turning movement is not so uniform and hence heavier flywheel is neededBecause of one power stroke in two revolution lesser cooling and lubrication requirement. Lesser rate of wear and tear.The four stroke engine contains valves and valve mechanism.

TWO STROKE CYCLEThe cycle is completed in two-stroke of the piston or in one revolution of crankshaft. Thus on power stroke is obtained in each revolution of the crankshaft.Uniform turning movement and hence lighter flywheel is neededBecause of one power stroke in one revolution greater cooling and lubrication requirement. Greater rate of wear and tear.The two-stroke engine have only ports.Because of heavy weight and complication of valve mechanism, higher in initial cost.Volumetric efficiency more due to greater time of induction.Thermal efficiency higher.Used where efficiency is important, in car, buses, trucks, aero plane, etc.Because of light weight and simplicity due to the absence of valve mechanism, cheaper in initial cost.Volumetric efficiency lesser due to lesser time of induction.Thermal efficiency lower.Used where ,low cost, compactness and light weight is importantFIRING ORDERThefiring orderis the sequence of power delivery of each cylinder in a multi-cylinderreciprocating engine.This is achieved by sparking of thespark plugsin a gasoline engine in the correct order, or by the sequence of fuel injection in aDiesel engine. When designing an engine, choosing an appropriate firing order is critical to minimizingvibration, to improveengine balanceand achieving smooth running, for long enginefatiguelife and user comfort, and heavily influences crankshaft design.In a gasoline engine, the correct firing order is obtained by the correct placement of the spark plug wires on thedistributor. In a modern engine with anengine management systemanddirect ignition, theEngine Control Unit(ECU) takes care of the correct firing sequence. Especially on cars with distributors, the firing order is usuallycaston the engine somewhere, most often on the cylinder head, the intakemanifoldor thevalvecover(s).

VARIOUS FIRING ORDERS FOR DIFFERENT ENGINE LAYOUTS

Odd and even firing orderFiring order affects thebalance,noise, vibration, smoothness, and sound of the engineEVEN FIRING ORDER:Engines that are even-firing will sound more smooth and steady, Most racing engines such as those inFormula Oneoften have an even firing order, mostly for quicker acceleration, less vibrations, and more efficient exhaust system designs. Examples of odd-firing engines are any crossplane V8 (such as theGM LS engine),Harley-Davidson Evolution engines, andChevrolet straight-6 engines.ODD FIRING ORDER:Engines that are odd, or uneven firing will have aburble or growlingsound in the engine note, and, depending on the crankshaft design, will often have more vibrations due to the change of power delivery.Examples of even-firing engines are most current productioninline 4s, most current productionV6s, allFerrariproduction engines,Lotus Esprit V8,Porsche 918 Spyder,McLaren M838T engine,Toyota LR engine,.THE PRINCIPLES OF VALVE TIMINGValve timing is the regulation of the points in the cycle at which the valves are set to open and close.In ideal cycle inlet and exhaust valves open and close at dead centers, but in actual cycles the open or close before or after dead centers.In actual cycle the following factors are taken into consideration, Inertia effects of the incoming and outgoing cylinder gasesElastic nature of the incoming and outgoing cylinder gasesMechanical stresses imposed by rapidly opening and closing the valves.The ideal cycle is modified by providing for the lead (advance time) and lag (delay time) of the inlet and exhaust valve periods of opening.INLET VALVEThe inlet valve is given a lead in opening before the piston reaches top dead center on the exhaust stroke, so that least resistance is offered to the incoming flow of air and petrol mixture as the piston begins its induction stroke. It is also provided with a lag in closing after the piston reaches bottom dead center and is beginning the compression stroke, so as to take advantage of the reluctance of the incoming mixture to cease flowing as the piston ends its induction stroke. EXHAUST VALVE The exhaust valve is given a lead in opening before the piston reaches bottom dead centre on the power stroke , so that the burnt gases are already leaving the cylinder under their own pressure as the piston begins its exhaust stroke. Therefore the engine expends less energy on expelling the exhaust gases than would otherwise be the case. The exhaust valve is also provided with a lag in closing after the piston reaches top dead centre and is beginning the induction stroke.The opening of the inlet valve before top dead centre on the exhaust stroke, and the closing of the exhaust valve after top dead centre on the induction stroke, result in a period when both valves are either partially or fully open. The part of the valve periods where the inlet valve opens before the exhaust valve closes is termed the valve overlap

Medium-performance carHigh-performance carFor convenience of expression the opening and closing points of the valves have been shown in the form of a valve timing diagram.

Question for ExamPart-ACompare valve timing and port timing diagram?What is firing order? State its significance?What is compression ratio ?What is swept volume in I.C engine?What is scavenging?What is valve overlap?

Part-BExplain about the construction and working of four stroke petrol engine with neat sketches?Discuss about the valve timing diagram and port timing diagram with neat sketches?explain about the construction and working of two stroke petrol engine with neat sketches?Explain the difference between four stroke and the two stroke engine?Explain the Otto cycle? Derive the thermal efficiency and compression ratio relation?