MT 313 IC ENGINES LECTURE NO: 02 (17 Feb, 2014) Khurram [email protected] Yahoo Group Address: ICE14 HEAT ENGINES I.C. Engines Rotary Reciprocating Open Cycle Gas Turbine Wankel Gasoline Diesel E.C. Engines Reciprocating Rotary Steam Stirling Steam Close Cycle Gas Turbine Internal Combustion Engine. (I. C. Engine) 3 Classification of I. C. Engines • Nature of Thermodynamic Cycle • 1. Otto cycle engine. • 2. Diesel cycle engine. • 3. Dual combustion cycle engine. • Type of the Fuel- used • • • • • 1. Petrol engine. 2. Diesel engine. 3. Gas engine. 4. Bi-fuel Engine. 5. Dual Fuel Engine Classification of I. C. Engines • Number of Strokes • 1. 2 - stroke engine • 2. 4 - stroke engine • Method of Ignition • 1. Spark ignition engine, [S.I. Engine]. • 2. Compression ignition engine, [C.I. engine]. • Number of Cylinders • 1. Single cylinder engine. • 2. Multi-cylinder engine. Classification of I. C. Engines • Position of the Cylinder – – – – 1. Horizontal engine 2. Vertical engine 3. V- engine. 4. Radial engine. • Method of Cooling – – 1. Air cooled engine. 2. Water cooled engine • Speed of the Engine – 1. Low speed engine. – 2. Medium speed engine. – 3. High speed engine. PARTS OF I.C. ENGINES I C Engine Parts I. C. Engine Terms and Definition Spark plug • TDC (top dead center): It is the top most position of the piston towards head side of the cylinder Valve Clearance volume TDC Bore Stroke • BDC (bottom dead center): The lowermost position of the piston towards the crank end side of the cylinder. BDC Piston 9 • Stroke: It is the linear distance traveled by the piston when it moves from one end of the cylinder to the other end • Bore: It is the inside diameter of the cylinder. Stock to Bore Ratio: L/d d ˂ L Under Square d =L Square d ˃L Over Square • Swept volume or (Displacement volume) It is the volume swept through by the piston in moving between TDC and BDC Vs • = A x L = (π/4)d2 L Clearance volume: It is the volume contained in the cylinder above the top of the piston, when the piston is at TDC. • • • Total volume = swept volume + clearance volume. Compression ratio: “r” It is the ratio of total cylinder volume to clearance volume. r = Total volume = VT clearance volume VC Value of “r” for, petrol engine lies between 7 to 9 Diesel engine lies between 15 to 22 • Cubic Capacity VS x K ( K= No of Cylinders) Working 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. • • In 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”. In a 4-stroke petrol engine there are four main events taking place, they are 1. Suction 2. Compression 3. Working or power or expansion, and 4. Exhaust So in a cycle there are four events to take place, and each of this is performed during a single stroke of the piston Since ignition in these engines is due to a spark, they are also called spark ignition engines . INTAKE [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] TDC BDC A B Volume [V] 2. 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 Pressure [P] D TDC C BDC A B Volume [V] 3. 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 DE Pressure [P] D TDC C E BDC A B Volume [V] 4. 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. Pressure [P] D TDC C E BDC A B Volume [V] P V diagram for SI Engine / Otto cycle engine D TDC C Pressure E A BDC B Volume Theoretical Otto cycle Diesel Engines • This 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. Diesel Engines • Diesels 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 – Gasoline 16:1 – 23:1 6:1 – 12:1 Diesel Engine Principles of Operation • Intake Stroke – The intake valve opens. – The piston moves downward. – Only air is pulled into the cylinder or pumped in using a turbo charger (fan). Diesel Engine Principles of Operation • Compression Stroke – The upward movement of the piston compresses the air increasing the temperature to approximately 538 degrees Celsius. Diesel Engine Principles of Operation • Power Stroke – As the piston reaches the top, fuel is injected at just the right moment and ignited by the heat, forcing the piston back down. Diesel Engine Principles of Operation • Exhaust stroke – The piston moves back to the top and pushes the burned gases out of the exhaust valve or port. Working 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 In 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 spray When 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. 1. INTAKE [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 PV diagram. Pressure [P] TDC BDC A B Volume [V] 31 2. 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 intoDthe hot compressed C air in the form of fine sprays by means of fuel injector. [P] at constant pressure shown by The fuel startsPressure burning TDC the line CD. BDC A B Volume [V] 3. 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 D obtained in this stroke Cas shown by the line DE Pressure [P] TDC E BDC A B Volume [V] 4. 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 D C BDC to TDC and pushes the remaining gases to the atmosphere. This stroke Pressure [P] is represented the line BA on TDC the P-V diagram. E BDC A B Volume [V] P V diagram for C.I. Engine / Diesel Cycle Engine D C D TDC Pressure E A BDC B Volume Theoretical Diesel cycle Comparison between Petrol & Diesel Engine 1 Petrol engine Diesel engine It works on Otto cycle. It works on diesel cycle. 2 Air 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. 3 It 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) 4 Cylinder is fitted with a spark plug. Cylinder is fitted with a fuel injector. 5 Less thermal efficiency More thermal efficiency and more fuel and less fuel consumption. consumption. 6 Compression ratio ranges from 4:1to10:1 Compression ratio ranges from 12:1 to 22:1 7 Less initial cost and more running cost. More initial cost and less running cost. 8 Light weight and occupies less space. Heavy and occupies more space. 9 10 11 12 Difficult to start in cold Easy to start even in weather and requires cold weather. heater plugs. They run for longer Requires frequent periods between overhauling. overhauls. Fuel (petrol) is Fuel (diesel) is cheaper costlier and more and less volatile. volatile. Used in heavy duty Used in light vehicles like cars, vehicles like tractors, motor cycle, trucks, buses, locomotives, etc. scooters, etc. Working 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. In 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 Working of Two Stroke Petrol Engine First stroke Second stroke Working 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. • Further 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. • Second 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. • The compressed charge is ignited in the combustion chamber by a spark provided by the spark plug and the cycle of events is then repeated. Working of Two Stroke Diesel Engine First stroke Second stroke • First 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. • Further 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. • Second 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. 49 • At 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. Comparison between 4 - stroke & stroke Engine 1 2 3 4 – stroke engine One Working stroke for every two revolution of the Crank shaft Turning moment on the crank shaft is not even, hence heavier flywheel is required 2- 2 – stroke engine One working stroke for each revolution of the crank shaft Turning moment on the crank shaft is more even, hence lighter flywheel is required Less fuel consumption More fuel consumption. 6 Engine design is complicated Less output due to mixing of fresh charge with the burnt gases. Lower thermal efficiency Engine design is simple. 7 Lesser rate of wear and tear. Greater rate of wear and tear. 8 It has inlet and exhaust valves It has inlet and exhaust ports 4 5 More output due to full fresh charge intake and full burnt gases exhaust. Higher thermal efficiency 9 10 11 12 13 Engine is heavy & bulky. It requires lesser cooling and lubrication More initial cost For the same power, the engine is light and compact. It requires greater cooling and lubrication. (consumes more lubricating oil) Less initial cost. More running noise due to Less running noise the sudden release of the burnt gases. Used in cars, Used in mopeds, motor trucks, buses, cycles, scooters, etc. tractors, etc. Rotary (Wankel) Engine • Designed in 1958 by a German scientist named Felix Wankel. • Wankel engines do not use pistons. Wankel Engine • The 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. Wankel Engine Principles of Operation • Intake Stroke – The 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. Wankel Engine Principles of Operation • Compression Stroke – As the rotor rotates the combustion chamber is reduced in size compressing the mixture. Wankel Engine Principles of Operation • Power Stroke – At the highest point of compression the air/fuel is ignited. – The hot expanding gases push on the rotor causing it to rotate. Wankel Engine Principles of Operation • Exhaust Stroke – The 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. Diesel 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. Diesel Engine Advantages • Advantages – Greater fuel economy (25% more efficient than gasoline engines). – Produces more power. – Requires less maintenance. Diesel Engine Disadvantages • Disadvantages – Must be constructed heavier to withstand the higher pressures. – Shortage of qualified mechanics in some areas. Two 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. Two Stroke Disadvantages • 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. Wankel Engine Advantages • 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. Wankel Engine Disadvantages • 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. DIESEL PETROL Uses: In diesel engines, heating systems In petrol engines Made from: Petroleum/ Crude oil Petroleum/ Crude Oil Energy content: 38.6 MJ/litre Made by: Fractional distillation Fractional distillation 34.6 MJ/litre DIESEL PETROL Torque (for 1000 Nm @ 2000 10L rpm engine): 300Nm @ 4000 rpm Power (for 490Hp @ 3500 rpm 10L engine): 600Hp @ 5500 rpm Power = More torque at low torque*RP speeds M: Runs at higher RPM Autoignition 246°C 210°C DIESEL PETROL CO2 emiss More than Lower than diesel. ion: gasoline(petrol). Die sel fuel produces approximately 13% more CO2 gas per gallon of fuel burned, compared to gas (petrol) engines. Viscosity: increase at lower temperatures US 50 Billion gallons Consumpti No change 148 Billion gallons Qusetions • 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?