4Classification of I. C. Engines Nature of Thermodynamic Cycle1. Otto cycle engine.2. Diesel cycle engine.3. Dual combustion cycle engine.Type of the Fuel- used1. Petrol engine.2. Diesel engine.3. Gas engine.4. Bi-fuel Engine.5. Dual Fuel Engine
5Classification of I. C. Engines Number of Strokesstroke enginestroke engineMethod of Ignition1. Spark ignition engine, [S.I. Engine].2. Compression ignition engine, [C.I. engine].Number of Cylinders1. Single cylinder engine.2. Multi-cylinder engine.
6Classification of I. C. Engines Position of the Cylinder1. Horizontal engine2. Vertical engine3. V- engine.4. Radial engine.Method of Cooling1. Air cooled engine.2. Water cooled engineSpeed of the Engine1. Low speed engine.2. Medium speed engine.3. High speed engine.
9I. C. Engine Terms and Definition Clearance volumeValveSpark plugTDCBDCBoreStrokePistonTDC (top dead center):It is the top most position of the piston towards head side of the cylinderBDC (bottom dead center):The lowermost position of the piston towards the crank end side of the cylinder.
10Stroke:It is the linear distance traveled by the piston when it moves from one end of the cylinder to the other endBore:It is the inside diameter of the cylinder.Stock to Bore Ratio: L/dd ˂ L Under Squared =L Squared ˃L Over Square
11Swept volume or (Displacement volume) It is the volume swept through by the piston in moving between TDC and BDCVs = A x L = (π/4)d2 LClearance volume:It is the volume contained in the cylinder above the top of the piston, when the piston is at TDC.
12Total volume = swept volume + clearance volume. Compression ratio: “r”It is the ratio of total cylinder volume to clearance volume.r = Total volume = VTclearance volume VCValue of “r” for,petrol engine lies between 7 to 9Diesel engine lies between 15 to 22Cubic CapacityVS x K ( K= No of Cylinders)
13Working of 4-S Petrol Engine The petrol engines work on the principle of “OTTO CYCLE”, also known as constant Volume cycle.The engines operating on this cycle use either petrol or other spirit fuels or the gases such as LPG / CNG as their fuels.
14In a 4-Stroke petrol engine, the charge is admitted to the engine cylinder is a homogeneous mixture of petrol and air.Depending on the load on the engine, the fuel and air is mixed in proper proportions and sent in to the cylinder by a popular device known as “carburetor”.
15In a 4-stroke petrol engine there are four main events taking place, they are 1. Suction2. Compression3. Working or power or expansion, and4. ExhaustSo in a cycle there are four events to take place, and each of this is performed during a single stroke of the pistonSince ignition in these engines is due to a spark, they are also called spark ignition engines .
17INTAKE [Suction]: During the intake stroke, the piston moves down ward, drawing a fresh charge of vaporized fuel-air mixture, This operation is represented by the line AB on the P-V diagram. Pressure [P]TDCBDCABVolume [V]
182. Compression Stroke: During compression stroke, the piston moves from BDC to TDC, thus compressing air petrol mixture. Due to compression, the pressure and temperature are increased and is shown by the line BC on the P- V diagram. Just before the end of this stroke the spark - plug initiates a spark which ignites the mixture and combustion takes place at constant volume as shown by the line CD DPressure [P]TDCCBDCABVolume [V]
193. Working Stroke: The expansion of gases due to the heat of combustion exerts a pressure on the piston. Under this impulse, the piston moves from TDC to BDC and thus the work is obtained in this stroke as shown by the line DEDPressure [P]TDCCEBDCABVolume [V]
204. Exhaust Stroke: At the end of the power stroke, the exhaust valve is opened & greater part of the burnt gases escapes because of their own expansion. The drop in pressure at constant volume is represented by the line EB. During this stroke the piston moves from BDC to TDC and pushes the remaining gases to the atmosphere. This stroke is represented the line BA on the P-V diagram.DPressure [P]TDCCEBDCABVolume [V]
21P V diagram for SI Engine / Otto cycle engine BEDPressureVolumeTheoretical Otto cycleTDCBDC
22Diesel EnginesThis engine was invented in 1892 by a German mechanical engineer named Rudolph Diesel.At first this engine was known as the compression engine but later was named Diesel after its inventor.
23Diesel EnginesDiesels come in two stroke and four stroke versions and operate much like the gasoline driven engines.Diesels have a greater compression ratio than gasoline engines.Diesel 16:1 – 23:1Gasoline 6:1 – 12:1
24Diesel Engine Principles of Operation Intake StrokeThe intake valve opens.The piston moves downward.Only air is pulled into the cylinder or pumped in using a turbo charger (fan).
25Diesel Engine Principles of Operation Compression StrokeThe upward movement of the piston compresses the air increasing the temperature to approximately 538 degrees Celsius.
26Diesel Engine Principles of Operation Power StrokeAs the piston reaches the top, fuel is injected at just the right moment and ignited by the heat, forcing the piston back down.
27Diesel Engine Principles of Operation Exhaust strokeThe piston moves back to the top and pushes the burned gases out of the exhaust valve or port.
28Working of 4-S Diesel Engine The basic construction of a four stroke diesel engine is same as that of four stroke petrol engine.Except that instead of a spark plug, a fuel INJECTOR is mounted in its space.Fuel injector injects the fuel in to the cylinder as a fine spray at very high pressure
29In case of diesel engine, the air enters the inside the cylinder during suction, and it will get compressed during the compression stroke. (i.e.. charge is only air)At the end of the compression stroke the diesel is injected in to the cylinder in the form of fine sprayWhen this fine spray diesel comes in contact with hot air in the cylinder, it auto ignites and results in a combustion of injected diesel fuel.Since ignition in these engines is due to the temperature of the compressed air, they are also called compression ignition engines.
31INTAKE [Suction]:During the intake stroke, the piston moves down ward, drawing a fresh charge [AIR]. This operation is represented by the line AB on the P-V diagram. Pressure [P]TDCABDCBVolume [V]
322. Compression Stroke: During compression stroke, the piston moves from BDC to TDC, thus compressing air. Due to compression, the pressure and temperature are increased and is shown by the line BC on the P- V diagram. Just before the end of this stroke, a metered quantity of Diesel is injected into the hot compressed air in the form of fine sprays by means of fuel injector. The fuel starts burning at constant pressure shown by the line CD.DCPressure [P]TDCABDCBVolume [V]
333. Working Stroke: The expansion of gases due to the heat of combustion exerts a pressure on the piston. Under this impulse, the piston moves from TDC to BDC and thus the work is obtained in this stroke as shown by the line DEDCPressure [P]TDCEABDCBVolume [V]
344. Exhaust Stroke: At the end of the power stroke, the exhaust valve is opened & greater part of the burnt gases escapes because of their own expansion. The drop in pressure at constant volume is represented by the line EB. During this stroke the piston moves from BDC to TDC and pushes the remaining gases to the atmosphere. This stroke is represented the line BA on the P-V diagram.DCPressure [P]TDCEABDCBVolume [V]
35P V diagram for C.I. Engine / Diesel Cycle Engine BEDPressureVolumeTheoretical Diesel cycleTDCBDC
36Comparison between Petrol & Diesel Engine Petrol engineDiesel engine1It works on Otto cycle.It works on diesel cycle.2Air and petrol are mixed in the carburetor before they enter into the cylinder.Diesel is fed into the cylinder by fuel injection and is mixed with air inside the cylinder.3It compresses a mixture of air and petrol and is ignited by an electric spark. (Spark Ignition)It compresses only air and ignition is accomplished by the heat of compression. (Compression Ignition)
37Cylinder is fitted with a spark plug. 4Cylinder is fitted with a spark plug.Cylinder is fitted with a fuel injector.5Less thermal efficiency and more fuel consumption.More thermal efficiency and less fuel consumption.6Compression ratio ranges from 4:1to10:1Compression ratio ranges from 12:1 to 22:17Less initial cost and more running cost.More initial cost and less running cost.8Light weight and occupies less space.Heavy and occupies more space.
38Easy to start even in cold weather. 9Easy to start even in cold weather.Difficult to start in cold weather and requires heater plugs.10Requires frequent overhauling.They run for longer periods between overhauls.11Fuel (petrol) is costlier and more volatile.Fuel (diesel) is cheaper and less volatile.12Used in light vehicles like cars, motor cycle, scooters, etc.Used in heavy duty vehicles like tractors, trucks, buses, locomotives, etc.
39Working of the Two Stroke Engine In a two stroke engine, a cycle is completed by the two strokes of the piston.Out of the four strokes, the two strokes that are eliminated are, suction and exhaust strokes.However, the exhaust process is achieved by the admission of charge which is extremely compressed, which drives out the burnt gases out and this process is popularly called as SCAVENGING.
40In case of the two stroke engines instead of valves, ports are used. Ports in the cylinder liner, opened and closed by the piston motion itself
41Working of Two Stroke Petrol Engine First strokeSecond stroke
42Working of Two Stroke Petrol Engine First stroke (Downward) As soon as the charge is ignited, the hot gases force the piston to move downwards, rotating the crankshaft, thus doing the useful work. During this stroke the inlet port is covered by the piston and the new charge is compressed in the crank case as shown in the fig.
43Further downward movement of the piston uncovers first the exhaust port and then the transfer port. The burnt gases escape through the exhaust port.As soon as the transfer port opens, the compressed charge from the crankcase flows into the cylinder.As the compressed charge enters into the cylinder, it pushes out the exhaust gases from the cylinder.The process of removal of exhaust gases by the fresh incoming charge is known as scavenging.
44Second stroke: (upward) Here the piston moves from BDC to TDC, during the process the exhaust port and transfer port are covered and the charge in the cylinder is compressed.Simultaneously, vacuum is created in the crankcase, and a new charge is drawn into the crankcase through the uncovered inlet port.
45The compressed charge is ignited in the combustion chamber by a spark provided by the spark plug and the cycle of events is then repeated.
46Working of Two Stroke Diesel Engine First strokeSecond stroke
47First stroke (Downward) Combustion starts once the diesel is injected in to the hot compressed air, the hot gases force the piston to move downwards, rotating the crankshaft, thus doing the useful work. During this stroke the inlet port is covered by the piston and the new charge [air] is compressed in the crank case as shown in the fig.
48Further downward movement of the piston uncovers first the exhaust port and then the transfer port. The burnt gases escape through the exhaust port.As soon as the transfer port opens, the compressed charge from the crankcase flows into the cylinder.As the compressed charge enters into the cylinder, it pushes out the exhaust gases from the cylinder.The process of removal of exhaust gases by the fresh incoming air is known as scavenging.
49Second stroke: (upward) Here the piston moves from BDC to TDC, during the process the exhaust port and transfer port are covered and the fresh air in the cylinder is compressed. Simultaneously, vacuum is created in the crankcase, and a new charge [air] is drawn into the crankcase through the uncovered inlet port.
50At the end of the compression diesel is injected to the compressed air which is at a temperature higher than the self ignition temperature of diesel. Hence, the injected diesel auto ignites when it comes in contact with hot air. And the cycle of events is then repeated.
51Comparison between 4 - stroke & 2 - stroke Engine 1One Working stroke for every two revolution of the Crank shaftOne working stroke for each revolution of the crank shaft2Turning moment on the crank shaft is not even, hence heavier flywheel is requiredTurning moment on the crank shaft is more even, hence lighter flywheel is required3Less fuel consumptionMore fuel consumption.
52Less output due to mixing of fresh charge with the burnt gases. 4More output due to full fresh charge intake and full burnt gases exhaust.Less output due to mixing of fresh charge with the burnt gases.5Higher thermal efficiencyLower thermal efficiency6Engine design is complicatedEngine design is simple.7Lesser rate of wear and tear.Greater rate of wear and tear.8It has inlet and exhaust valvesIt has inlet and exhaust ports
53For the same power, the engine is light and compact. 9Engine is heavy & bulky.For the same power, the engine is light and compact.10It requires lesser cooling and lubricationIt requires greater cooling and lubrication. (consumes more lubricating oil)11More initial costLess initial cost.12Less running noiseMore running noise due to the sudden release of the burnt gases.13Used in cars, trucks, buses, tractors, etc.Used in mopeds, motor cycles, scooters, etc.
54Rotary (Wankel) Engine Designed in 1958 by a German scientist named Felix Wankel.Wankel engines do not use pistons.
55Wankel EngineThe wankel engine uses a triangular shaped rotor housed in an oval shaped cylinder.As the rotor is rotated it moves around the cylinder producing the four basic functions to produce a power stroke.
56Wankel Engine Principles of Operation Intake StrokeThe production of power begins with the rotor at point A.The intake port is uncovered allowing a new air/fuel mixture to enter the combustion chamber.
57Wankel Engine Principles of Operation Compression StrokeAs the rotor rotates the combustion chamber is reduced in size compressing the mixture.
58Wankel Engine Principles of Operation Power StrokeAt the highest point of compression the air/fuel is ignited.The hot expanding gases push on the rotor causing it to rotate.
59Wankel Engine Principles of Operation Exhaust StrokeThe continued rotation of the rotor uncovers the exhaust port allowing the exhaust gas to escape.The cycle then repeats when a new air/fuel mixture is permitted to enter the combustion chamber.
60Diesel VS Gasoline Engines Different type fuel (Diesel fuel).Diesel engines operate at a much higher compression ratio.Diesel engines do not use spark plugs.Glow plugs are used to help get the engines going on very cold days.
61Diesel Engine Advantages Greater fuel economy (25% more efficient than gasoline engines).Produces more power.Requires less maintenance.
62Diesel Engine Disadvantages Must be constructed heavier to withstand the higher pressures.Shortage of qualified mechanics in some areas.
63Two Stroke Advantages Advantages Requires fewer moving parts to accomplish the same amount of output as four stroke engines.Cheaper to maintain than four stroke engines.Smaller and simple in construction than four stroke engines.Can work in any orientation.
64Two Stroke Disadvantages Less fuel efficient than four stroke.Quicker wear of the engine’s moving parts.More polluting than four stroke engines since oil is burnt with the fuel and air mixture.
65Wankel Engine Advantages Less vibration than piston driven engines.A two rotary engine is as powerful as a six cylinder piston engine.Power output can be increased by adding additional rotors to the engine.
66Wankel Engine Disadvantages Sealing the rotor in the odd shaped cylinder is very difficult requiring costly maintenance.Construction cost are high for this engine.Shortages of trained mechanics to service this engine type.
67DIESEL PETROL Uses: In diesel engines, heating systems In petrol enginesMade from:Petroleum/ Crude oilPetroleum/ Crude OilEnergy content:38.6 MJ/litre34.6 MJ/litreMade by:Fractional distillationFractional distillation
68DIESEL PETROL Torque (for 10L engine): 1000 Nm @ 2000 rpm Power (for 10L engine):rpmrpmPower = torque*RPM:More torque at low speedsRuns at higher RPMAuto-ignition temperature:210°C246°C
69DIESEL PETROL CO2 emission: More than gasoline(petrol). Diesel fuel produces approximately 13% more CO2 gas per gallon of fuel burned, compared to gas (petrol) engines.Lower than diesel.Viscosity:increase at lower temperaturesNo changeUS Consumption (2006):50 Billion gallons148 Billion gallons
70Qusetions Define , Engine and Heat Engine? How I.C. engines are classified?What are the important basic components of an I.C. engine?Define , Bore, Stroke, Clearance volume, compression ratio, displacement volume and cubic capacity?Explain the working principle of the four stock S.I. engine?Differentiate between C.I. and S.I.?Explain Otto cycle?Explain Diesel cycle ?Compare between Petrol and Diesel engines?