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The document provides information on internal combustion engines. It discusses the key components and workings of both spark ignition (SI) and compression ignition (CI) engines. SI engines use an electric spark to ignite an air-fuel mixture, as in gasoline engines. CI engines compress air to a high temperature and pressure and inject fuel to ignite it, as in diesel engines. The document also summarizes the four strokes of a four-stroke engine - intake, compression, power, and exhaust strokes - and how a two-stroke engine combines the strokes into single revolutions.

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IC ENGINES MODULE IV PART II
INTERNAL COMBUSTION ENGINE A device which transforms one form of energy into another form is called an engine. An engine which converts thermal energy into mechanical energy is called heat engine. Heat engine transforms the chemical energy of a fuel into thermal energy and this thermal energy is converted into mechanical energy to perform useful work. HEs broadly classified into two catagories:  External combustion engines (EC engines)  Internal combustion engines (IC engines)
In an EC engine, a working fluid is used for transferring the heat of combustion to the engine where the heat of combustion is converted into mechanical energy. E.g. Steam engines, steam turbines etc. In an IC engine air is taken from the atmosphere and the combustion of fuel and air occurs in the engine (inside the cylinder) which converts thermal energy into mechanical energy.  eliminates the need for heavy and bulky devices such as boilers and heat exchangers.  high thermal efficiencies can be achieved These factors led to the wide use of IC engines for mobile power plants such as those used in automobiles, ships and slow speed aircrafts
IC ENGINE COMPONENTS
1. Cylinder Cylindrically shaped container within which the piston reciprocates. The cylinder is closed by the cylinder head at one end and the other end is covered by the moving piston. Combustion of fuel takes place inside the cylinder and power is developed.
2. Cylinder head Acts as a cover to close the cylinder. Contains provisions for placing inlet and exhaust valves. In petrol engines, it houses a spark plug for igniting fuel air mixture.  In diesel engines, it houses a fuel injector for injecting the fuel into the cylinder.
3. Piston It is a close fitting member which reciprocates inside the engine cylinder. Transmits the force exerted by the high pressure gas to the connecting rod. It is shaped like an inverted cup and is generally made of aluminium alloy.
4. Inlet and exhaust valves Provided in the cylinder head for the admission of fresh air into the engine cylinder and for the rejection of burnt gases from the engine cylinder. These valves are usually kept closed by valve springs.  Openings of these valves are made mechanically by means of a device called cam.
5. Inlet manifold The metal tube which connects the intake system to the inlet valve of the engine and through which air or air fuel mixture is drawn into the cylinder is called inlet manifold 6. Exhaust manifold The metal tube which connects the exhaust system to the exhaust valve of the engine and through which the product of combustion escape is called exhaust manifold.
7. Connecting rod Interconnects the piston and the crank. Connecting rod transmits the gas force from the piston to the crank shaft and transforms the reciprocating motion of piston inside the cylinder into rotary motion of the crank.
8. Crank It is a rotating member which receives power from the connecting rod and transmits to the crank shaft. 9. Crankshaft It is the shaft at which useful positive work is available from the piston- cylinder arrangement. Reciprocating motion of piston gets converted into rotary motion of crankshaft. 10. Flywheel It is a heavy wheel mounted on the crank shaft. Its main function is to maintain the angular velocity of crank shaft fairly constant
11. Cams and Camshafts Cams are mounted upon camshaft for opening and closing the valves at right timings and for correct duration. Camshaft gets motion from crankshaft through timing gears.
NOMENCLATURES USED IN IC ENGINES
1. Cylindrical Bore: The inside diameter of cylinder is called cylinder bore. 2. Top Dead Centre (TDC) or Inner Dead Centre (IDC): The extreme position of the piston at the top of the cylinder is the top dead centre (TDC). In horizontal engines it is known as inner dead centre (IDC). 3. Bottom Dead Centre (BDC) or Outer Dead Centre (ODC): The position of the piston when it is farthest from the top of the cylinder is the bottom dead centre (BDC). In horizontal engines, it is known as outer dead centre (ODC)
4. Stroke: The travel of the piston from one dead centre to the other is called stroke. The distance between the two dead centres is called the stroke length 5. Swept volume: The volume of the cylinder in between the two dead centres is the swept volume. It is denoted by Vs. 6. Clearance volume: The volume of the cylinder in between the top dead centre and the cylinder head is the clearance volume. It is denoted by Vc. 7. Compression ratio: The ratio of the volume of the cylinder between the bottom dead centre and the cylinder head to the clearance volume is the compression ratio of the engine. It is denoted by ‘r’.
CLASSIFICATION OF IC ENGINES 1. Based on the ignition system According to the ignition system employed for igniting the charge in the engine cylinder, IC engines are classified as I. Spark Ignition (SI) engines: in which an electric spark is used for igniting the fuel air mixture. Most of the engines using petrol belong to this category. II. Compression Ignition (CI) engines: in which air is compressed to a very high temperature and pressure and fuel is injected to it in the form of a spray. The fuel gets ignited due to the high temperature of the compressed air. Most of the engines using diesel as fuel belong to this category.
2. Based on the number of strokes per cycle I. Four stroke engines: in which one cycle of operation is completed in four strokes of the piston, ie., one power stroke is obtained in four strokes of the piston ie., in two revolutions of the crank shaft. II. Two stroke engines: in which one cycle of operation is completed in two strokes of the piston, giving one power stroke per two strokes of the piston ie., in each revolution of the crank shaft.
4. Based on the type of fuel used I. Gas engines: in which gaseous fuel such as methane is used as the main fuel. II. Petrol engines: in which highly volatile liquid fuel such as petrol is used. III. Diesel engines: in which less volatile liquid fuel such as diesel oil is used. IV. Dual - fuel engines: in which a gaseous fuel or a highly volatile liquid fuel is supplied along with air during the suction stroke and a viscous liquid fuel is injected into the combustion space near the end of the compression stroke.
5. Based on the working cycle. I. Otto engine: in which the engine works based on the Otto cycle (constant volume cycle). Most of the petrol and gas engines work on this cycle. II. Diesel engine: in which the engine works based on the diesel cycle. Most of the low speed oil engines work on this cycle. III. Dual combustion engine: in which the engine works on the dual combustion cycle. Most of the high speed oil engines work on this cycle. 6. Based on the application of the engine I. Stationary engines ii. Mobile engines
6. Based on the cooling system I. Air cooled engines: II. Water cooled engines: 7. Based on the speed of the engine I. Low speed engines (up to 350 rpm) II. Medium speed engines (350 - 1000 rpm) III. High speed engines (above 1000 rpm) 8. Based on the number of cylinders I. Single cylinder engines II. Multi cylinder engines 9. Based on the cylinder arrangement I. Vertical engine II. Horizontal engine III. In - line engine: IV. V- engine V. Radial engine: VI. Opposed cylinder engine:
SPARK IGNITION (SI) ENGINE • SI engines employ external ignition system for initiating the combustion process. • Fuel is ignited by an electric spark. • Electrical discharge produced between the spark plug electrodes by the ignition system starts the combustion process close to the end of compression stroke. • Spark plug is the most commonly used ignition method used in spark ignition engines
• A homogeneous mixture of air and petrol is supplied to the engine cylinder during the suction stroke. • The fuel air mixture (charge) gets compressed during the compression stroke. • At the end of this stroke, fuel is ignited and combustion occurs at constant volume. • Thus heat is supplied at constant volume. • The gas expands and moves the piston downwards, doing work. • The product of combustion is exhausted at constant volume.
FOUR STROKE SI ENGINE • Four stroke petrol engines require 4 strokes of piston or 2 revolution of crank shaft to complete 1 cycle of operation. • One power stroke is obtained in four strokes of the piston. • A stroke refers to the full travel of the piston along the cylinder from one dead centre to the other.
Working Principle of Four Stroke Petrol Engine • Working Principle of Petrol Engine can be explained by 4 processes or strokes. They are 1. Suction stroke (intake stroke / Induction stroke) 2. Compression stroke 3. Power stroke (Working stroke / Expansion stroke) 4. Exhaust stroke
PV diagram of four stroke petrol (SI) engine
Suction stroke (Process 5-1) • Piston moves from TDC to BDC. • inlet valve opens and the air-fuel mixture is drawn into the engine cylinder. • exhaust valve remains closed throughout this stroke. • The pressure inside the cylinder is lower than the ambient pressure by an amount that depends upon the speed of engine. • Represented by the line 5-1
Compression stroke (Process 1-2) • air-fuel mixture is compressed as the piston moves from BDC to TDC. • both inlet and outlet valve remains closed. • The air-fuel mixture is compressed to a high pressure and the pressure at the end of compression process depends upon the compression ratio. • Represented by the curve 1-2
Power stroke (Process 3-4) • Ignition Process (Process 2-3) : • Just before the end of this stroke, the spark plug initiates a spark which ignites the mixture and combustion takes place at constant volume (line 2-3). • Both the inlet and exhaust valves remains closed • As the fuel air mixture burns, hot gases are produced which drive the piston towards BDC and thus work is done (Piston moves from TDC to BDC). • Expansion process is shown by the line 3-4. • Both the valves remain closed during this stroke. • 4-1: Constant volume heat rejection.
Exhaust stroke (Process 1-5) • The removal of the burnt gases is accomplished during this stroke. • The piston moves from BDC to TDC and the exhaust gases are driven out of the engine cylinder. • Represented by the line 1-5 in fig. • During this stroke the exhaust valve remain opened and the inlet valve remains closed. • By this one cycle is completed and the engine is ready to suck the charge again.
COMPRESSION IGNITION (CI) ENGINE • In Compression Ignition (CI) engines, air is drawn inside the cylinder and compressed to a very high temperature & pressure. • The fuel is injected to it in the form of a spray. • The fuel gets ignited due to the high temperature of the compressed air. • CI Engines works on the basis of diesel cycle
• Diesel engine is based on the work of Rudolph Diesel. • Operates based on the theoretical air cycle known as Diesel cycle. • These engines operate on four stroke or two stroke cycle. • Atmospheric air is drawn into the engine cylinder during the suction stroke and is compressed by the piston during the compression stroke to high pressure and temperature. • The temperature of compressed air will be above the ignition temperature of fuel.
• Just before the end of the compression stroke a metered quantity of fuel under pressure is injected in the form of fine spray by means of a fuel injector. • Due to very high pressure and temperature of the air the fuel ignites and the gases expand, displacing the piston. • After doing work on the piston the burnt gases escape from the engine cylinder through the exhaust valve. • As the ignition takes place due to heat of compressed air, it is called compression ignition engine (CI engine).
FOUR STROKE CI ENGINE • Four stroke diesel engines require 4 strokes of piston or 2 revolution of crank shaft to complete 1 cycle of operation. • The operation of C.I. engines (or diesel engines) is practically the same as those of S.I. engines. • The cycle in both the types, consists of suction, compression, ignition, expansion and exhaust.
Working Principle • Working Principle of diesel Engine can be explained by 4 processes or strokes. They are 1. Suction stroke (intake stroke / Induction stroke) 2. Compression stroke 3. Power stroke (Working stroke / Expansion stroke) 4. Exhaust stroke
Pressure
Suction stroke (Process 5-1) • Piston moves from top dead centre (TDC) to bottom dead centre (BDC). • The inlet valve opens and air at atmospheric pressure is drawn into the engine cylinder. • The exhaust valve remains closed. • Operation represented by line 5-1
Compression stroke (Process 1-2) • Piston moves towards TDC to BDC and compresses the enclosed air to high temperature and pressure. • Operation represented by curve 1-2. • Both the inlet and exhaust valves remains closed
Power stroke (Process 3-4) • Ignition process (Process 2-3): • Towards the end of compression stroke a metered quantity of fuel is injected into the hot compressed air in the form of fine spray by means of a fuel injector. • The fuel starts burning, theoretically, at constant pressure and pushes the piston from TDC. • Represented by line 2-3.
• At point 3, fuel supply is cut off. • The high pressure gas in the cylinder expand upto point 4, doing work on the piston • Piston moves from TDC to BDC. • The inlet and exhaust valves remain closed. • At the end of this stroke the exhaust valve opens • Process 4-1; Constant volume hear rejection
Exhaust stroke (Process 1-5) • The piston moves from BDC to TDC. • Burnt gases escape through the exhaust valve. • Inlet valve remains closed while exhaust valve remains opened . • Represented by the line 1-5. • This stroke completes the cycle and the engine is ready to suck air again.
TWO STROKE PETROL (SI) ENGINE • Two stroke petrol engines require 2 strokes of piston or 1 revolution of crank shaft to complete 1 cycle of operation. • One cycle of operation is completed in two strokes of the piston by eliminating separate suction and exhaust stroke. • Here ports are provided instead of valves.
Working of Two stroke petrol engine
• During the upward stroke of the piston, the air fuel mixture in the cylinder is compressed. • At the same time fresh air - fuel mixture enters the crank case through the inlet port. • Towards the end of this stroke, the fuel air mixture is ignited using an electric spark from the spark plug. • Combustion process is assumed to take place at constant volume.
• The piston, then travels downwards due to the expansion of the gases (fig ii) and near the end of this stroke the piston uncovers the exhaust port and the burnt gases escape through this port. • The transfer port is then uncovered (fig iii) and the compressed air fuel mixture from the crankcase flows into the cylinder. • The incoming fresh air fuel mixture helps to remove the burnt gases from the engine cylinder.
• Remember – For Two stroke engines, suction process is happening when the air and fuel mixture is taken from crank case to the cylinder through transfer port (not when the air and fuel mixture enters the crank case through inlet port).
TWO STROKE DIESEL (CI) ENGINE • Two stroke diesel engines require 2 strokes of piston or 1 revolution of crank shaft to complete 1 cycle of operation. • In two stroke engines one cycle of operation is completed in two strokes of the piston by eliminating separate suction and exhaust stroke. • One power stroke is obtained in two strokes of the piston.
Working of Two stroke diesel engine
• During the upward stroke of the piston, the air in the cylinder is compressed. At the same time fresh air enters the crank case through the air inlet port. • Towards the end of this stroke fuel is introduced in the form of fine spray by the fuel injector and due to the high pressure and temperature of the air, the fuel starts burning. • The piston, then travels downwards due to the expansion of the gases and near the end of this stroke the piston uncovers the exhaust port and the burnt gases escape through this port. • The transfer port is then uncovered and the compressed air from the crankcase flows into the cylinder. The incoming fresh air helps to remove the burnt gases from the engine cylinder.
Comparison of Four Stroke and Two Stroke Engines Criteria Four Stroke Engine Two Stroke Engine Thermodynamic cycle Cycle is completed in 4 strokes. One power stroke in 2 revolutions of crankshaft. Cycle is completed in 2 strokes. One power stroke in 1 revolutions of crankshaft. Thermal efficiency Higher at normal and partial loads Lower at normal and partial loads Volumetric efficiency Higher due to more time for suction Lower due to less time for suction Power output by weight ratio Lower, a heavier engine is required to produce a given output because of one power stroke in two revolutions Higher, a lighter and compact engine produces the given output because of one power stroke in each revolution Cooling & Lubrication Normally water cooled, Except in 2 or 3- wheelers. Less wear and tear, less lubricant required Normally air cooled, wear and tear is more. Usually oil is mixed with fuel, more lubrication is required Valve mechanism Required, design gets complicated Not required, design is simplified Initial cost High Low Use Heavy duty vehicles where efficiency is more important Light vehicles where compactness and weight are more important. Effect on environment Low More polluting gases
Efficiencies of IC Engines Mechanical Efficiency • It is defined as the ratio of brake power to the indicated power ⴄmech = BP/IP • BP is the power available at the crankshaft. • Measured using dynamometer. Unit of BP = kW • IP is the total power developed within the cylinder in one complete cycle neglecting the losses. • Can be also defined as the sum of the power produced at the crankshaft and the power consumed by the losses • Mechanical efficiency is thus indicator of how efficiently indicated power is converted into brake power.
Volumetric Efficiency • It is defined as the ratio of the volume of air sucked inside per cycle per cylinder at the ambient condition to the stroke volume of the cylinder • ⴄvol = (Volume of air inducted at ambient condition) / (Stroke volume) = (mass of air inducted at per cycle) / (Mass of air occupying the stroke volume at ambient condition)
Thermal Efficiency Thermal efficiency of an IC engine is expressed as the ratio of power output and the rate of energy input in the form of fuel. It can be defined on the basis of indicated or brake power output. Indicated thermal efficiency • It is defined as the ratio of indicated power output and the rate of energy input in the form of fuel. • 𝜂𝑖𝑡ℎ = 𝐼𝑃 𝑚𝑓×𝐶.𝑉 • Where IP = Indicated Power • 𝑚𝑓 = Mass of fuel supplied, kg/s • CV = Calorific value of the fuel, j/kg
Brake Thermal Efficiency • It is defined as the ratio of brake power output and the rate of energy input in the form of fuel. • 𝜂𝑏𝑡ℎ = 𝐵𝑃 𝑚𝑓×𝐶.𝑉 • Where BP = Brake Power • 𝑚𝑓 = Mass of fuel supplied, kg/s • CV = Calorific value of the fuel, j/kg • Relation between efficiencies • 𝜂𝑚𝑒𝑐ℎ = 𝐵𝑃 𝐼𝑃 = 𝜂𝑏𝑡ℎ 𝜂𝑖𝑡ℎ
Air and Fuel system Air system for petrol engine • Air system for petrol engine essentially consists of air filter and carburetor. • For burning of fuel, oxygen is required. • In Internal combustion engine oxygen is obtained from the atmospheric air. • Air after cleaning in the air filter is mixed with fuel in correct ratio using a carburetor.
• For complete combustion, the air - fuel ratio must be about 15:1 by weight. • There is a range of air - fuel ratio within which combustion of fuel can occur. • This range of air-fuel ratio is approximately 8:1 to 20:1 by weight. • Outside this range the mixture is either too rich or too lean.
• The carburetor provides air fuel mixture in the required ratio in accordance with the requirements of the engine. • At the time of starting of the engine a rich mixture, about 10:1 is required. • During normal running a comparatively lean mixture, 15:1, serves the purpose. • During acceleration period a rich mixture is needed.
• The air fuel mixture is supplied to the engine cylinder through the inlet valve. • Inside the cylinder, the mixture is burned and there by the chemical energy of fuel is converted into thermal energy. • The product of combustion, after expanding, is discharged to the atmosphere. • Generally, a silencer or muffler is used to reduce the noise.
Fuel system for petrol engine • Fuel supply system for a petrol engine consists of a fuel storage tank, fuel pump, filter, carburetor, and inlet manifold from where the fuel enters the engine cylinder through inlet valve
• The fuel can be supplied to the engine either under gravity or using a pump. • In the gravity system, the fuel storage tank is placed at a higher level than the carburetor so that the fuel flows to the carburetor under gravity. • When storage tank is kept below the level of carburetor fuel pump is required to force the fuel to the carburetor. • The fuel pump and the carburetor are the main components of the fuel supply system.
Carburetor • Carburetor is used to discharge the desired quantity of liquid fuel into the air stream to produce a homogeneous air - fuel mixture. • A good carburetor must produce automatically the desired air-fuel ratio at all speeds and loads of the engine. • The basic principle used in carburetor is that when a volatile fuel is placed in the passage of high velocity air, the fuel gets vapourised at a faster rate.
• It consists of a jet situated at the centre of a venturi tube. • Petrol is supplied to the venturi from a float chamber. • A throttle valve controls the amount of air fuel mixture delivered to the engine. • Petrol is pumped into the float chamber by means of a fuel pump. • The level of petrol in the float chamber is maintained constant at a correct height by a float. • When the fuel level is below normal, the float needle gets lowered and fuel enters the float chamber.
• When the fuel level attains its normal level, the float needle closes the fuel supply line • When the engine is running, the suction of engine causes air to run through the venturi tube. • The diameter of venturi tube surrounding the tip of the fuel nozzle (fuel jet) is reduced (known as venturi throat). • This will increase the velocity of air at the throat and reduce the pressure. The pressure at this point is less than atmospheric . • In the float chamber the pressure is atmospheric. Due to this pressure difference , fuel will flow into the air stream at the venturi throat and gets vapourised.
• The function of the throttle is to Control the speed and power of the engine. • The more the throttle is closed, the greater will be the obstacle to the flow of air and less will be the quantity of mixture delivered to the cylinder. • As the throttle is opened, more air flows through the venturi tube, and consequently the power of the engine increases.
Fuel system for diesel engines • The main parts of this system are fuel pump and fuel injector. • The fuel is supplied at very high pressure from the fuel pump to the fuel injector and is injected to the engine cylinder towards the end of compression stroke. • There are two types of injection systems. (i) Air injection (ii) Solid injection
Air injection • In this method, fuel is forced into the cylinder by means of compressed air. • This method is obsolete these days as it requires multistage air compressor which increases the engine weight and cost. • Moreover the compressor consumes about 10 % of the power developed by the engine and hence the output of the engine is reduced.
Solid injection (Mechanical injection) • In this method a fuel pump is used to supply measured quantity of fuel at high pressure to the injector. • The injector injects the fuel at a very high velocity into the engine cylinder in the form of fine spray
FUEL PUMP • The pump produces the high pressure necessary for injection, in the order of 100 – 400 bar, depending upon the engine size and the type of combustion chamber used. • It also controls the amount of fuel pumped for different loads and speeds.
FUEL INJECTOR
• The needle valve is kept in the seat by a helical spring. • The tension of the spring can be adjusted manually by a nut on the top of the injector to vary the pressure of injection. • Fuel under pressure from the fuel pump enters the pressure chamber through the fuel duct. • Because of high pressure, the needle valve is lifted up against the spring tension. • When the valve is lifted, the fuel rushes out through the fine hole (single hole or multiholes) in an atomised form and rapidly mixes with the compressed air which will be turbulent inside the combustion chamber.
COOLING SYSTEMS IN IC ENGINES • Due to the combustion of fuel inside the cylinder, very high temperature is produced (2300-2500°C) • Any metal tends to become weak at high temperature. • If the engine is not cooled, parts such as the cylinder, the cylinder head, the piston, the piston rings, and the valves will get overheated resulting in the reduction of strength and possibility of distortion of components. • Overheating may even cause seizure of the piston. • Properties of the lubricating oil will change at high temperature and it may decompose resulting in carbon deposit in the cylinder and piston. • At the same time, overcooling should be avoided. • At full load, about 30% of the heat liberated by the fuel is lost in cooling.
AIR COOLING
• 1. Air Cooling • This system is adopted for motorcycles, scooters, aero engines and also in some cars. • The basic principle is to have a current of air flowing continuously over the heated surface from where the heat is to be removed. • Cooling fins are provided in the cylinder and cylinder head. • In large sized engines, arrangement is made to circulate the air around the cooling fins. • The amount of heat dissipated depends on the area of cooling fins, the amount of air circulated, the velocity of air and the temperature difference with the surroundings.
• The advantages of air cooling includes simplicity, lightness, cheapness and, absence of water and its circulation system. • The main disadvantage of this system is the non uniformity in cooling. • Also, it is difficult to control the cooling rate.
WATER COOLING Thermostat
• 2. Water Cooling • This system is commonly used in cars, buses and lorries. Water passages between the double walls of the cylinder and the cylinder heads are called the water jackets. • Water is circulated through jackets by a pump driven by the crank shaft. • When the circulating water becomes hot, it is cooled in a radiator. • Water used in the radiator should be free from salt and other impurities. Otherwise, the deposit will block the water tubes. It is desirable to add some anticorrosion solution in the water. • In cold places, antifreeze solution should also be added in the water.
• During the warm-up period of the engine, the thermostat valve is closed. • When the normal operating temperature of about 60°C is reached in the water, the thermostat valve opens due to the evaporation of ether (or wax) in the bellows and permits the water to circulate through the radiator.
Difference between Air Cooling and Water Cooling
LUBRICATION SYSTEM Main functions of a lubrication system: 1. To reduce the friction between the rubbing parts and reduce the wear and tear. 2. To reduce the temperature of the working parts. 3. To reduce the noise. 4. To keep the rubbing parts clean by removing worn-out materials and carbon dust. 5. To act as a sealing between the cylinder and piston and to prevent the leakage of gases.
Parts to be Lubricated 1. Reciprocating parts like piston. 2. Rotating parts like crank shaft. 3. Oscillating parts like connecting rod. Types of Lubricants • 1. Liquids like mineral oil, vegetable oil, etc. • 2. Semi-liquids like grease. • 3. Solid lubricants like graphite powder, either alone or mixed with oil or grease.
Requirements of a good Lubricating Oil 1. High viscosity index (if the change of viscosity with temperature is less, the oil is rated to have a high viscosity index). 2. High flash point and low pour-point temperatures. 3. Non-corrosive. 4. Good detergent quality to keep the rubbing surfaces clean. 5. High film strength (ability to maintain a thin film of oil even at high load). • The quality of lubricating oil is improved by adding different types of additives such as the viscosity index improvers, the corrosion inhibitors, the detergent additives, and the film strength additives. • Lubricating oils are graded in SAE number according to the viscosity. For example, the viscosity of oil SAE 40 is higher than that of oil SAE 30.
TYPES OF LUBRICATION SPLASH LUBRICATION
• The splash lubrication system is suitable only for small capacity engines. • During the working of the engine, the scoop dips into the lubricating oil in the crank case and throws the oil to the piston, cylinder and other parts. • simplest method of lubrication. • Such systems are usually designed with an oil reservoir in the base of the engine. • employed in small single cylinder stationary engines and on scooter engines.
PRESSURE LUBRICATION SYSTEM
` • In the pressure lubricating system, the oil in the crank case is filtered by an oil filter. • The filtered oil enters the oil pump and its pressure is raised to the desired value and distributed to the different parts. • For the lubrication of the crank pin and the piston pin, small holes are provided in the crank shaft, and connecting rod crank pin through which oil flows. • For lubrication of light spark ignition engines, lubricating oil is directly mixed with petrol and this is known as the petroil method
COMMON RAIL DIRECT INJECTION (CRDI) • CRDI is a type of advanced fuel injection technology used in Diesel engine fuel systems. • CRDI consists of a common fuel rail to supply fuel to injectors. • Common rail distributes the fuel to the computer controlled injectors at a constant pressure of up to 1600 bar. • The rail is fed by a high pressure fuel pump. • The pressure in the rail, as well as the start and end of the signal that activates the injector for each cylinder are electronically controlled.
• Electronic control unit(ECU) receives signals from various sensors and uses those signals to operate injection. • ECU calculates injected fuel quantity, start of injection, duration of injection and control the correct functioning of the injection system as a whole. • Common rail engines maintain a constant pressure regardless of the injection sequence. • More accurately measured and timed fuel spray in the combustion chamber significantly reduces unburned fuel and increases the fuel efficiency.
Elements of CRDI • Low pressure circuit: comprises of fuel tank, fuel pump and fuel filter. Responsible for transporting the fuel to the high pressure circuit • High pressure circuit: comprises of high pressure pump with pressure control valve, common rail with rail pressure sensor and injectors. • ECU and Sensors: ECU receives and evaluates the signal from the sensors, viz., speed sensor, air temperature sensor, air mass meter and rail pressure sensor.
• Advantages of CRDI • Flexibility in controlling both the injection timing and injection rate. • Deliver 25% more power and torque • Lower level of noise and vibration • Higher mileage • Lower emission and improved performance • Disadvantages of CRDI • Costly spare parts • More maintenance
MULTI POINT FUEL INJECTION(MPFI) • MPFI is used in SI engines for fuel injection. • In single point injection system one or two injectors are mounted inside the throttle body assembly of the engine. • Multi Point Fuel Injection [MPFI] system has one injector for each engine cylinder.
PRESSURE SENSOR
• Fuel is injected in more than one location. • This system injects fuel into individual cylinders based on commands from the on board engine management system computer popularly known as Engine Control Unit. [ECU]. • The ECU primarily controls the ignition timing and quantity of fuel to be injected. • The ECU is controlled by the data input from a set of sensors located all over the engine and its auxiliaries. • These sensors detect the various operating conditions of the engine and the performance required out of it
• In MPFI system, air enters into the intake manifold. • The manifold pressure sensor detects the intake manifold vaccum and sends the information to the ECU. • The speed sensors also sends information about the rpm of the engine to the ECU. • The ECU in turn sends commands to the injector to control the amount of petrol supply for injection. • When the injectors spray fuel into the intake manifold the petrol mixes with the air and the mixture enters the cylinder of the engine.
Advantages of MPFI • The difference in power developed in each cylinder is minimum. • Vibration of engine equipped With the system is less. • Immediate response to sudden acceleration and deceleration • Since the engine is controlled by ECU more accurate amount of air fuel mixture will be supplied and as a result complete combustion takes place. This leads to effective utilization of fuel supplied and hence low emission level. • Better fuel economy and lower emissions Disadvantages • Expensive setup • System is complex
HYBRID ENGINES • A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle • Concept of hybrid drive combines the best aspects of IC engines and Electric drives. • The basic principle with hybrid vehicles is that the different motors work better at different speeds; the electric motor is more efficient at producing torque, or turning power, and the combustion engine is better for maintaining high speed • Switching from one to the other at the proper time while speeding up yields a win-win in terms of energy efficiency, as such that translates into greater fuel efficiency, for example.
Series hybrid
• In series hybrid engines, The IC engine turns a generator, and the generator can either charge the batteries or power an electric motor that drives the transmission. The operations can be; • Engine mode operation: Engine operates a generator, that operates a motor, which in turn drive the wheels. • Battery mode operation: Battery directly drives the motor which in turn drive the wheels
Parallel hybrid
• Fuel tank supplies fuel to the engine and a set of batteries that supplies power to the electric motor. • Depending on requirement, Engine alone or Motor alone or Engine and Motor together can drive the wheels. • This system permits the engine to recharge the battery while powering the vehicle.

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IC ENGINES.pptx

  • 1.
  • 2.
    INTERNAL COMBUSTION ENGINE Adevice which transforms one form of energy into another form is called an engine. An engine which converts thermal energy into mechanical energy is called heat engine. Heat engine transforms the chemical energy of a fuel into thermal energy and this thermal energy is converted into mechanical energy to perform useful work. HEs broadly classified into two catagories:  External combustion engines (EC engines)  Internal combustion engines (IC engines)
  • 3.
    In an ECengine, a working fluid is used for transferring the heat of combustion to the engine where the heat of combustion is converted into mechanical energy. E.g. Steam engines, steam turbines etc. In an IC engine air is taken from the atmosphere and the combustion of fuel and air occurs in the engine (inside the cylinder) which converts thermal energy into mechanical energy.  eliminates the need for heavy and bulky devices such as boilers and heat exchangers.  high thermal efficiencies can be achieved These factors led to the wide use of IC engines for mobile power plants such as those used in automobiles, ships and slow speed aircrafts
  • 4.
  • 6.
    1. Cylinder Cylindrically shapedcontainer within which the piston reciprocates. The cylinder is closed by the cylinder head at one end and the other end is covered by the moving piston. Combustion of fuel takes place inside the cylinder and power is developed.
  • 8.
    2. Cylinder head Actsas a cover to close the cylinder. Contains provisions for placing inlet and exhaust valves. In petrol engines, it houses a spark plug for igniting fuel air mixture.  In diesel engines, it houses a fuel injector for injecting the fuel into the cylinder.
  • 10.
    3. Piston It isa close fitting member which reciprocates inside the engine cylinder. Transmits the force exerted by the high pressure gas to the connecting rod. It is shaped like an inverted cup and is generally made of aluminium alloy.
  • 12.
    4. Inlet andexhaust valves Provided in the cylinder head for the admission of fresh air into the engine cylinder and for the rejection of burnt gases from the engine cylinder. These valves are usually kept closed by valve springs.  Openings of these valves are made mechanically by means of a device called cam.
  • 14.
    5. Inlet manifold Themetal tube which connects the intake system to the inlet valve of the engine and through which air or air fuel mixture is drawn into the cylinder is called inlet manifold 6. Exhaust manifold The metal tube which connects the exhaust system to the exhaust valve of the engine and through which the product of combustion escape is called exhaust manifold.
  • 16.
    7. Connecting rod Interconnectsthe piston and the crank. Connecting rod transmits the gas force from the piston to the crank shaft and transforms the reciprocating motion of piston inside the cylinder into rotary motion of the crank.
  • 18.
    8. Crank It isa rotating member which receives power from the connecting rod and transmits to the crank shaft. 9. Crankshaft It is the shaft at which useful positive work is available from the piston- cylinder arrangement. Reciprocating motion of piston gets converted into rotary motion of crankshaft. 10. Flywheel It is a heavy wheel mounted on the crank shaft. Its main function is to maintain the angular velocity of crank shaft fairly constant
  • 22.
    11. Cams andCamshafts Cams are mounted upon camshaft for opening and closing the valves at right timings and for correct duration. Camshaft gets motion from crankshaft through timing gears.
  • 24.
  • 25.
    1. Cylindrical Bore:The inside diameter of cylinder is called cylinder bore. 2. Top Dead Centre (TDC) or Inner Dead Centre (IDC): The extreme position of the piston at the top of the cylinder is the top dead centre (TDC). In horizontal engines it is known as inner dead centre (IDC). 3. Bottom Dead Centre (BDC) or Outer Dead Centre (ODC): The position of the piston when it is farthest from the top of the cylinder is the bottom dead centre (BDC). In horizontal engines, it is known as outer dead centre (ODC)
  • 26.
    4. Stroke: Thetravel of the piston from one dead centre to the other is called stroke. The distance between the two dead centres is called the stroke length 5. Swept volume: The volume of the cylinder in between the two dead centres is the swept volume. It is denoted by Vs. 6. Clearance volume: The volume of the cylinder in between the top dead centre and the cylinder head is the clearance volume. It is denoted by Vc. 7. Compression ratio: The ratio of the volume of the cylinder between the bottom dead centre and the cylinder head to the clearance volume is the compression ratio of the engine. It is denoted by ‘r’.
  • 27.
    CLASSIFICATION OF ICENGINES 1. Based on the ignition system According to the ignition system employed for igniting the charge in the engine cylinder, IC engines are classified as I. Spark Ignition (SI) engines: in which an electric spark is used for igniting the fuel air mixture. Most of the engines using petrol belong to this category. II. Compression Ignition (CI) engines: in which air is compressed to a very high temperature and pressure and fuel is injected to it in the form of a spray. The fuel gets ignited due to the high temperature of the compressed air. Most of the engines using diesel as fuel belong to this category.
  • 28.
    2. Based onthe number of strokes per cycle I. Four stroke engines: in which one cycle of operation is completed in four strokes of the piston, ie., one power stroke is obtained in four strokes of the piston ie., in two revolutions of the crank shaft. II. Two stroke engines: in which one cycle of operation is completed in two strokes of the piston, giving one power stroke per two strokes of the piston ie., in each revolution of the crank shaft.
  • 29.
    4. Based onthe type of fuel used I. Gas engines: in which gaseous fuel such as methane is used as the main fuel. II. Petrol engines: in which highly volatile liquid fuel such as petrol is used. III. Diesel engines: in which less volatile liquid fuel such as diesel oil is used. IV. Dual - fuel engines: in which a gaseous fuel or a highly volatile liquid fuel is supplied along with air during the suction stroke and a viscous liquid fuel is injected into the combustion space near the end of the compression stroke.
  • 30.
    5. Based onthe working cycle. I. Otto engine: in which the engine works based on the Otto cycle (constant volume cycle). Most of the petrol and gas engines work on this cycle. II. Diesel engine: in which the engine works based on the diesel cycle. Most of the low speed oil engines work on this cycle. III. Dual combustion engine: in which the engine works on the dual combustion cycle. Most of the high speed oil engines work on this cycle. 6. Based on the application of the engine I. Stationary engines ii. Mobile engines
  • 31.
    6. Based onthe cooling system I. Air cooled engines: II. Water cooled engines: 7. Based on the speed of the engine I. Low speed engines (up to 350 rpm) II. Medium speed engines (350 - 1000 rpm) III. High speed engines (above 1000 rpm) 8. Based on the number of cylinders I. Single cylinder engines II. Multi cylinder engines 9. Based on the cylinder arrangement I. Vertical engine II. Horizontal engine III. In - line engine: IV. V- engine V. Radial engine: VI. Opposed cylinder engine:
  • 36.
    SPARK IGNITION (SI)ENGINE • SI engines employ external ignition system for initiating the combustion process. • Fuel is ignited by an electric spark. • Electrical discharge produced between the spark plug electrodes by the ignition system starts the combustion process close to the end of compression stroke. • Spark plug is the most commonly used ignition method used in spark ignition engines
  • 37.
    • A homogeneousmixture of air and petrol is supplied to the engine cylinder during the suction stroke. • The fuel air mixture (charge) gets compressed during the compression stroke. • At the end of this stroke, fuel is ignited and combustion occurs at constant volume. • Thus heat is supplied at constant volume. • The gas expands and moves the piston downwards, doing work. • The product of combustion is exhausted at constant volume.
  • 38.
    FOUR STROKE SIENGINE • Four stroke petrol engines require 4 strokes of piston or 2 revolution of crank shaft to complete 1 cycle of operation. • One power stroke is obtained in four strokes of the piston. • A stroke refers to the full travel of the piston along the cylinder from one dead centre to the other.
  • 39.
    Working Principle ofFour Stroke Petrol Engine • Working Principle of Petrol Engine can be explained by 4 processes or strokes. They are 1. Suction stroke (intake stroke / Induction stroke) 2. Compression stroke 3. Power stroke (Working stroke / Expansion stroke) 4. Exhaust stroke
  • 41.
    PV diagram offour stroke petrol (SI) engine
  • 42.
    Suction stroke (Process5-1) • Piston moves from TDC to BDC. • inlet valve opens and the air-fuel mixture is drawn into the engine cylinder. • exhaust valve remains closed throughout this stroke. • The pressure inside the cylinder is lower than the ambient pressure by an amount that depends upon the speed of engine. • Represented by the line 5-1
  • 43.
    Compression stroke (Process1-2) • air-fuel mixture is compressed as the piston moves from BDC to TDC. • both inlet and outlet valve remains closed. • The air-fuel mixture is compressed to a high pressure and the pressure at the end of compression process depends upon the compression ratio. • Represented by the curve 1-2
  • 44.
    Power stroke (Process3-4) • Ignition Process (Process 2-3) : • Just before the end of this stroke, the spark plug initiates a spark which ignites the mixture and combustion takes place at constant volume (line 2-3). • Both the inlet and exhaust valves remains closed • As the fuel air mixture burns, hot gases are produced which drive the piston towards BDC and thus work is done (Piston moves from TDC to BDC). • Expansion process is shown by the line 3-4. • Both the valves remain closed during this stroke. • 4-1: Constant volume heat rejection.
  • 45.
    Exhaust stroke (Process1-5) • The removal of the burnt gases is accomplished during this stroke. • The piston moves from BDC to TDC and the exhaust gases are driven out of the engine cylinder. • Represented by the line 1-5 in fig. • During this stroke the exhaust valve remain opened and the inlet valve remains closed. • By this one cycle is completed and the engine is ready to suck the charge again.
  • 46.
    COMPRESSION IGNITION (CI)ENGINE • In Compression Ignition (CI) engines, air is drawn inside the cylinder and compressed to a very high temperature & pressure. • The fuel is injected to it in the form of a spray. • The fuel gets ignited due to the high temperature of the compressed air. • CI Engines works on the basis of diesel cycle
  • 47.
    • Diesel engineis based on the work of Rudolph Diesel. • Operates based on the theoretical air cycle known as Diesel cycle. • These engines operate on four stroke or two stroke cycle. • Atmospheric air is drawn into the engine cylinder during the suction stroke and is compressed by the piston during the compression stroke to high pressure and temperature. • The temperature of compressed air will be above the ignition temperature of fuel.
  • 48.
    • Just beforethe end of the compression stroke a metered quantity of fuel under pressure is injected in the form of fine spray by means of a fuel injector. • Due to very high pressure and temperature of the air the fuel ignites and the gases expand, displacing the piston. • After doing work on the piston the burnt gases escape from the engine cylinder through the exhaust valve. • As the ignition takes place due to heat of compressed air, it is called compression ignition engine (CI engine).
  • 49.
    FOUR STROKE CIENGINE • Four stroke diesel engines require 4 strokes of piston or 2 revolution of crank shaft to complete 1 cycle of operation. • The operation of C.I. engines (or diesel engines) is practically the same as those of S.I. engines. • The cycle in both the types, consists of suction, compression, ignition, expansion and exhaust.
  • 50.
    Working Principle • WorkingPrinciple of diesel Engine can be explained by 4 processes or strokes. They are 1. Suction stroke (intake stroke / Induction stroke) 2. Compression stroke 3. Power stroke (Working stroke / Expansion stroke) 4. Exhaust stroke
  • 52.
  • 53.
    Suction stroke (Process5-1) • Piston moves from top dead centre (TDC) to bottom dead centre (BDC). • The inlet valve opens and air at atmospheric pressure is drawn into the engine cylinder. • The exhaust valve remains closed. • Operation represented by line 5-1
  • 54.
    Compression stroke (Process1-2) • Piston moves towards TDC to BDC and compresses the enclosed air to high temperature and pressure. • Operation represented by curve 1-2. • Both the inlet and exhaust valves remains closed
  • 55.
    Power stroke (Process3-4) • Ignition process (Process 2-3): • Towards the end of compression stroke a metered quantity of fuel is injected into the hot compressed air in the form of fine spray by means of a fuel injector. • The fuel starts burning, theoretically, at constant pressure and pushes the piston from TDC. • Represented by line 2-3.
  • 56.
    • At point3, fuel supply is cut off. • The high pressure gas in the cylinder expand upto point 4, doing work on the piston • Piston moves from TDC to BDC. • The inlet and exhaust valves remain closed. • At the end of this stroke the exhaust valve opens • Process 4-1; Constant volume hear rejection
  • 57.
    Exhaust stroke (Process1-5) • The piston moves from BDC to TDC. • Burnt gases escape through the exhaust valve. • Inlet valve remains closed while exhaust valve remains opened . • Represented by the line 1-5. • This stroke completes the cycle and the engine is ready to suck air again.
  • 58.
    TWO STROKE PETROL(SI) ENGINE • Two stroke petrol engines require 2 strokes of piston or 1 revolution of crank shaft to complete 1 cycle of operation. • One cycle of operation is completed in two strokes of the piston by eliminating separate suction and exhaust stroke. • Here ports are provided instead of valves.
  • 60.
    Working of Twostroke petrol engine
  • 61.
    • During theupward stroke of the piston, the air fuel mixture in the cylinder is compressed. • At the same time fresh air - fuel mixture enters the crank case through the inlet port. • Towards the end of this stroke, the fuel air mixture is ignited using an electric spark from the spark plug. • Combustion process is assumed to take place at constant volume.
  • 62.
    • The piston,then travels downwards due to the expansion of the gases (fig ii) and near the end of this stroke the piston uncovers the exhaust port and the burnt gases escape through this port. • The transfer port is then uncovered (fig iii) and the compressed air fuel mixture from the crankcase flows into the cylinder. • The incoming fresh air fuel mixture helps to remove the burnt gases from the engine cylinder.
  • 64.
    • Remember –For Two stroke engines, suction process is happening when the air and fuel mixture is taken from crank case to the cylinder through transfer port (not when the air and fuel mixture enters the crank case through inlet port).
  • 65.
    TWO STROKE DIESEL(CI) ENGINE • Two stroke diesel engines require 2 strokes of piston or 1 revolution of crank shaft to complete 1 cycle of operation. • In two stroke engines one cycle of operation is completed in two strokes of the piston by eliminating separate suction and exhaust stroke. • One power stroke is obtained in two strokes of the piston.
  • 66.
    Working of Twostroke diesel engine
  • 67.
    • During theupward stroke of the piston, the air in the cylinder is compressed. At the same time fresh air enters the crank case through the air inlet port. • Towards the end of this stroke fuel is introduced in the form of fine spray by the fuel injector and due to the high pressure and temperature of the air, the fuel starts burning. • The piston, then travels downwards due to the expansion of the gases and near the end of this stroke the piston uncovers the exhaust port and the burnt gases escape through this port. • The transfer port is then uncovered and the compressed air from the crankcase flows into the cylinder. The incoming fresh air helps to remove the burnt gases from the engine cylinder.
  • 68.
    Comparison of FourStroke and Two Stroke Engines Criteria Four Stroke Engine Two Stroke Engine Thermodynamic cycle Cycle is completed in 4 strokes. One power stroke in 2 revolutions of crankshaft. Cycle is completed in 2 strokes. One power stroke in 1 revolutions of crankshaft. Thermal efficiency Higher at normal and partial loads Lower at normal and partial loads Volumetric efficiency Higher due to more time for suction Lower due to less time for suction Power output by weight ratio Lower, a heavier engine is required to produce a given output because of one power stroke in two revolutions Higher, a lighter and compact engine produces the given output because of one power stroke in each revolution Cooling & Lubrication Normally water cooled, Except in 2 or 3- wheelers. Less wear and tear, less lubricant required Normally air cooled, wear and tear is more. Usually oil is mixed with fuel, more lubrication is required Valve mechanism Required, design gets complicated Not required, design is simplified Initial cost High Low Use Heavy duty vehicles where efficiency is more important Light vehicles where compactness and weight are more important. Effect on environment Low More polluting gases
  • 69.
    Efficiencies of ICEngines Mechanical Efficiency • It is defined as the ratio of brake power to the indicated power ⴄmech = BP/IP • BP is the power available at the crankshaft. • Measured using dynamometer. Unit of BP = kW • IP is the total power developed within the cylinder in one complete cycle neglecting the losses. • Can be also defined as the sum of the power produced at the crankshaft and the power consumed by the losses • Mechanical efficiency is thus indicator of how efficiently indicated power is converted into brake power.
  • 70.
    Volumetric Efficiency • Itis defined as the ratio of the volume of air sucked inside per cycle per cylinder at the ambient condition to the stroke volume of the cylinder • ⴄvol = (Volume of air inducted at ambient condition) / (Stroke volume) = (mass of air inducted at per cycle) / (Mass of air occupying the stroke volume at ambient condition)
  • 71.
    Thermal Efficiency Thermal efficiencyof an IC engine is expressed as the ratio of power output and the rate of energy input in the form of fuel. It can be defined on the basis of indicated or brake power output. Indicated thermal efficiency • It is defined as the ratio of indicated power output and the rate of energy input in the form of fuel. • 𝜂𝑖𝑡ℎ = 𝐼𝑃 𝑚𝑓×𝐶.𝑉 • Where IP = Indicated Power • 𝑚𝑓 = Mass of fuel supplied, kg/s • CV = Calorific value of the fuel, j/kg
  • 72.
    Brake Thermal Efficiency •It is defined as the ratio of brake power output and the rate of energy input in the form of fuel. • 𝜂𝑏𝑡ℎ = 𝐵𝑃 𝑚𝑓×𝐶.𝑉 • Where BP = Brake Power • 𝑚𝑓 = Mass of fuel supplied, kg/s • CV = Calorific value of the fuel, j/kg • Relation between efficiencies • 𝜂𝑚𝑒𝑐ℎ = 𝐵𝑃 𝐼𝑃 = 𝜂𝑏𝑡ℎ 𝜂𝑖𝑡ℎ
  • 73.
    Air and Fuelsystem Air system for petrol engine • Air system for petrol engine essentially consists of air filter and carburetor. • For burning of fuel, oxygen is required. • In Internal combustion engine oxygen is obtained from the atmospheric air. • Air after cleaning in the air filter is mixed with fuel in correct ratio using a carburetor.
  • 74.
    • For completecombustion, the air - fuel ratio must be about 15:1 by weight. • There is a range of air - fuel ratio within which combustion of fuel can occur. • This range of air-fuel ratio is approximately 8:1 to 20:1 by weight. • Outside this range the mixture is either too rich or too lean.
  • 75.
    • The carburetorprovides air fuel mixture in the required ratio in accordance with the requirements of the engine. • At the time of starting of the engine a rich mixture, about 10:1 is required. • During normal running a comparatively lean mixture, 15:1, serves the purpose. • During acceleration period a rich mixture is needed.
  • 76.
    • The airfuel mixture is supplied to the engine cylinder through the inlet valve. • Inside the cylinder, the mixture is burned and there by the chemical energy of fuel is converted into thermal energy. • The product of combustion, after expanding, is discharged to the atmosphere. • Generally, a silencer or muffler is used to reduce the noise.
  • 77.
    Fuel system forpetrol engine • Fuel supply system for a petrol engine consists of a fuel storage tank, fuel pump, filter, carburetor, and inlet manifold from where the fuel enters the engine cylinder through inlet valve
  • 78.
    • The fuelcan be supplied to the engine either under gravity or using a pump. • In the gravity system, the fuel storage tank is placed at a higher level than the carburetor so that the fuel flows to the carburetor under gravity. • When storage tank is kept below the level of carburetor fuel pump is required to force the fuel to the carburetor. • The fuel pump and the carburetor are the main components of the fuel supply system.
  • 79.
    Carburetor • Carburetor isused to discharge the desired quantity of liquid fuel into the air stream to produce a homogeneous air - fuel mixture. • A good carburetor must produce automatically the desired air-fuel ratio at all speeds and loads of the engine. • The basic principle used in carburetor is that when a volatile fuel is placed in the passage of high velocity air, the fuel gets vapourised at a faster rate.
  • 82.
    • It consistsof a jet situated at the centre of a venturi tube. • Petrol is supplied to the venturi from a float chamber. • A throttle valve controls the amount of air fuel mixture delivered to the engine. • Petrol is pumped into the float chamber by means of a fuel pump. • The level of petrol in the float chamber is maintained constant at a correct height by a float. • When the fuel level is below normal, the float needle gets lowered and fuel enters the float chamber.
  • 83.
    • When thefuel level attains its normal level, the float needle closes the fuel supply line • When the engine is running, the suction of engine causes air to run through the venturi tube. • The diameter of venturi tube surrounding the tip of the fuel nozzle (fuel jet) is reduced (known as venturi throat). • This will increase the velocity of air at the throat and reduce the pressure. The pressure at this point is less than atmospheric . • In the float chamber the pressure is atmospheric. Due to this pressure difference , fuel will flow into the air stream at the venturi throat and gets vapourised.
  • 84.
    • The functionof the throttle is to Control the speed and power of the engine. • The more the throttle is closed, the greater will be the obstacle to the flow of air and less will be the quantity of mixture delivered to the cylinder. • As the throttle is opened, more air flows through the venturi tube, and consequently the power of the engine increases.
  • 85.
    Fuel system fordiesel engines • The main parts of this system are fuel pump and fuel injector. • The fuel is supplied at very high pressure from the fuel pump to the fuel injector and is injected to the engine cylinder towards the end of compression stroke. • There are two types of injection systems. (i) Air injection (ii) Solid injection
  • 86.
    Air injection • Inthis method, fuel is forced into the cylinder by means of compressed air. • This method is obsolete these days as it requires multistage air compressor which increases the engine weight and cost. • Moreover the compressor consumes about 10 % of the power developed by the engine and hence the output of the engine is reduced.
  • 87.
    Solid injection (Mechanicalinjection) • In this method a fuel pump is used to supply measured quantity of fuel at high pressure to the injector. • The injector injects the fuel at a very high velocity into the engine cylinder in the form of fine spray
  • 88.
    FUEL PUMP • Thepump produces the high pressure necessary for injection, in the order of 100 – 400 bar, depending upon the engine size and the type of combustion chamber used. • It also controls the amount of fuel pumped for different loads and speeds.
  • 89.
  • 90.
    • The needlevalve is kept in the seat by a helical spring. • The tension of the spring can be adjusted manually by a nut on the top of the injector to vary the pressure of injection. • Fuel under pressure from the fuel pump enters the pressure chamber through the fuel duct. • Because of high pressure, the needle valve is lifted up against the spring tension. • When the valve is lifted, the fuel rushes out through the fine hole (single hole or multiholes) in an atomised form and rapidly mixes with the compressed air which will be turbulent inside the combustion chamber.
  • 91.
    COOLING SYSTEMS INIC ENGINES • Due to the combustion of fuel inside the cylinder, very high temperature is produced (2300-2500°C) • Any metal tends to become weak at high temperature. • If the engine is not cooled, parts such as the cylinder, the cylinder head, the piston, the piston rings, and the valves will get overheated resulting in the reduction of strength and possibility of distortion of components. • Overheating may even cause seizure of the piston. • Properties of the lubricating oil will change at high temperature and it may decompose resulting in carbon deposit in the cylinder and piston. • At the same time, overcooling should be avoided. • At full load, about 30% of the heat liberated by the fuel is lost in cooling.
  • 92.
  • 93.
    • 1. AirCooling • This system is adopted for motorcycles, scooters, aero engines and also in some cars. • The basic principle is to have a current of air flowing continuously over the heated surface from where the heat is to be removed. • Cooling fins are provided in the cylinder and cylinder head. • In large sized engines, arrangement is made to circulate the air around the cooling fins. • The amount of heat dissipated depends on the area of cooling fins, the amount of air circulated, the velocity of air and the temperature difference with the surroundings.
  • 94.
    • The advantagesof air cooling includes simplicity, lightness, cheapness and, absence of water and its circulation system. • The main disadvantage of this system is the non uniformity in cooling. • Also, it is difficult to control the cooling rate.
  • 95.
  • 96.
    • 2. WaterCooling • This system is commonly used in cars, buses and lorries. Water passages between the double walls of the cylinder and the cylinder heads are called the water jackets. • Water is circulated through jackets by a pump driven by the crank shaft. • When the circulating water becomes hot, it is cooled in a radiator. • Water used in the radiator should be free from salt and other impurities. Otherwise, the deposit will block the water tubes. It is desirable to add some anticorrosion solution in the water. • In cold places, antifreeze solution should also be added in the water.
  • 97.
    • During thewarm-up period of the engine, the thermostat valve is closed. • When the normal operating temperature of about 60°C is reached in the water, the thermostat valve opens due to the evaporation of ether (or wax) in the bellows and permits the water to circulate through the radiator.
  • 98.
    Difference between AirCooling and Water Cooling
  • 99.
    LUBRICATION SYSTEM Main functionsof a lubrication system: 1. To reduce the friction between the rubbing parts and reduce the wear and tear. 2. To reduce the temperature of the working parts. 3. To reduce the noise. 4. To keep the rubbing parts clean by removing worn-out materials and carbon dust. 5. To act as a sealing between the cylinder and piston and to prevent the leakage of gases.
  • 100.
    Parts to beLubricated 1. Reciprocating parts like piston. 2. Rotating parts like crank shaft. 3. Oscillating parts like connecting rod. Types of Lubricants • 1. Liquids like mineral oil, vegetable oil, etc. • 2. Semi-liquids like grease. • 3. Solid lubricants like graphite powder, either alone or mixed with oil or grease.
  • 101.
    Requirements of agood Lubricating Oil 1. High viscosity index (if the change of viscosity with temperature is less, the oil is rated to have a high viscosity index). 2. High flash point and low pour-point temperatures. 3. Non-corrosive. 4. Good detergent quality to keep the rubbing surfaces clean. 5. High film strength (ability to maintain a thin film of oil even at high load). • The quality of lubricating oil is improved by adding different types of additives such as the viscosity index improvers, the corrosion inhibitors, the detergent additives, and the film strength additives. • Lubricating oils are graded in SAE number according to the viscosity. For example, the viscosity of oil SAE 40 is higher than that of oil SAE 30.
  • 102.
  • 104.
    • The splashlubrication system is suitable only for small capacity engines. • During the working of the engine, the scoop dips into the lubricating oil in the crank case and throws the oil to the piston, cylinder and other parts. • simplest method of lubrication. • Such systems are usually designed with an oil reservoir in the base of the engine. • employed in small single cylinder stationary engines and on scooter engines.
  • 105.
  • 107.
    ` • In thepressure lubricating system, the oil in the crank case is filtered by an oil filter. • The filtered oil enters the oil pump and its pressure is raised to the desired value and distributed to the different parts. • For the lubrication of the crank pin and the piston pin, small holes are provided in the crank shaft, and connecting rod crank pin through which oil flows. • For lubrication of light spark ignition engines, lubricating oil is directly mixed with petrol and this is known as the petroil method
  • 108.
    COMMON RAIL DIRECTINJECTION (CRDI) • CRDI is a type of advanced fuel injection technology used in Diesel engine fuel systems. • CRDI consists of a common fuel rail to supply fuel to injectors. • Common rail distributes the fuel to the computer controlled injectors at a constant pressure of up to 1600 bar. • The rail is fed by a high pressure fuel pump. • The pressure in the rail, as well as the start and end of the signal that activates the injector for each cylinder are electronically controlled.
  • 109.
    • Electronic controlunit(ECU) receives signals from various sensors and uses those signals to operate injection. • ECU calculates injected fuel quantity, start of injection, duration of injection and control the correct functioning of the injection system as a whole. • Common rail engines maintain a constant pressure regardless of the injection sequence. • More accurately measured and timed fuel spray in the combustion chamber significantly reduces unburned fuel and increases the fuel efficiency.
  • 111.
    Elements of CRDI •Low pressure circuit: comprises of fuel tank, fuel pump and fuel filter. Responsible for transporting the fuel to the high pressure circuit • High pressure circuit: comprises of high pressure pump with pressure control valve, common rail with rail pressure sensor and injectors. • ECU and Sensors: ECU receives and evaluates the signal from the sensors, viz., speed sensor, air temperature sensor, air mass meter and rail pressure sensor.
  • 112.
    • Advantages ofCRDI • Flexibility in controlling both the injection timing and injection rate. • Deliver 25% more power and torque • Lower level of noise and vibration • Higher mileage • Lower emission and improved performance • Disadvantages of CRDI • Costly spare parts • More maintenance
  • 113.
    MULTI POINT FUELINJECTION(MPFI) • MPFI is used in SI engines for fuel injection. • In single point injection system one or two injectors are mounted inside the throttle body assembly of the engine. • Multi Point Fuel Injection [MPFI] system has one injector for each engine cylinder.
  • 114.
  • 116.
    • Fuel isinjected in more than one location. • This system injects fuel into individual cylinders based on commands from the on board engine management system computer popularly known as Engine Control Unit. [ECU]. • The ECU primarily controls the ignition timing and quantity of fuel to be injected. • The ECU is controlled by the data input from a set of sensors located all over the engine and its auxiliaries. • These sensors detect the various operating conditions of the engine and the performance required out of it
  • 117.
    • In MPFIsystem, air enters into the intake manifold. • The manifold pressure sensor detects the intake manifold vaccum and sends the information to the ECU. • The speed sensors also sends information about the rpm of the engine to the ECU. • The ECU in turn sends commands to the injector to control the amount of petrol supply for injection. • When the injectors spray fuel into the intake manifold the petrol mixes with the air and the mixture enters the cylinder of the engine.
  • 118.
    Advantages of MPFI •The difference in power developed in each cylinder is minimum. • Vibration of engine equipped With the system is less. • Immediate response to sudden acceleration and deceleration • Since the engine is controlled by ECU more accurate amount of air fuel mixture will be supplied and as a result complete combustion takes place. This leads to effective utilization of fuel supplied and hence low emission level. • Better fuel economy and lower emissions Disadvantages • Expensive setup • System is complex
  • 119.
    HYBRID ENGINES • Ahybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle • Concept of hybrid drive combines the best aspects of IC engines and Electric drives. • The basic principle with hybrid vehicles is that the different motors work better at different speeds; the electric motor is more efficient at producing torque, or turning power, and the combustion engine is better for maintaining high speed • Switching from one to the other at the proper time while speeding up yields a win-win in terms of energy efficiency, as such that translates into greater fuel efficiency, for example.
  • 120.
  • 121.
    • In serieshybrid engines, The IC engine turns a generator, and the generator can either charge the batteries or power an electric motor that drives the transmission. The operations can be; • Engine mode operation: Engine operates a generator, that operates a motor, which in turn drive the wheels. • Battery mode operation: Battery directly drives the motor which in turn drive the wheels
  • 122.
  • 123.
    • Fuel tanksupplies fuel to the engine and a set of batteries that supplies power to the electric motor. • Depending on requirement, Engine alone or Motor alone or Engine and Motor together can drive the wheels. • This system permits the engine to recharge the battery while powering the vehicle.