STT 231 Notes - PDF

1 THE PETROL ENGINE FUEL SUPPLY SYSTEM The petrol engine fuel supply system (fig 1) consists of the following parts/components: 1. Petrol tank 2. Connecting pipes 3. Fuel filter 4. Fuel pump 5. Air cleaner 6. Inlet manifold 7. Carburettor Fig 1: Line di...

1 THE PETROL ENGINE FUEL SUPPLY SYSTEM The petrol engine fuel supply system (fig 1) consists of the following parts/components: 1. Petrol tank 2. Connecting pipes 3. Fuel filter 4. Fuel pump 5. Air cleaner 6. Inlet manifold 7. Carburettor Fig 1: Line diagram of the fuel supply system and parts FUNCTIONS OF THE PARTS OF FUEL SUPPLY SYSTEM Petrol Tank (Fuel Tank) The petrol tank serves as a reservoir for fuel. It is usually located at the rear of the vehicle particularly in a front engine vehicle. Connecting Pipe The connecting conveys the fuel from the petrol tank through the fuel filter, fuel pump, to the carburettor The Fuel Filter The fuel filter holds the dust and dirt of the fuel and so as to prevent the dust and dirt entering the carburettor The Fuel Pump In most modern vehicle the fuel tank is located below the level of the carburettor, a lift fuel pump is therefore provided in between the tank and the carburettor for forcing fuel from the tank to the carburettor of the engine. There two types of pump, namely; (1) mechanically operated pump which is usually mounted at the side of the engine and is driven by the cam. (2) Electrically operated pump which is electrically driven Air Cleaner The air cleaner helps to filter dust and dirt in the air that mixes with fuel in the carburettor.  2 The Inlet Manifold The fuel goes into the engine cylinder, through the inlet manifold of the engine. The Carburettor The function of the carburettor is to meter air and petrol, completely atomize or break up the fuel into a fine spray so that it mixes thoroughly with the air in correct proportions to supply the mixture strength suitable for good combustion under all possible varying climatic, road or load conditions. In essence the Carburettor performs the following functions: (i) Mixes the air and fuel thoroughly (ii) Atomises the fuel (break up the fuel into fine spray) (iii) Regulates the air-fuel ratio at different speeds and loads (iv) Supplies correct amount of mixture strength at different speeds and loads. The production of air-fuel mixture (charge) in the cylinder of petrol engine (spark ignition engine) is called carburetion and the component in which this process takes place is called carburettor. The basic principle of carburetion is based on the fact that when air flows over the end of a narrow tube/jet containing liquid, some liquid is drawn into the air stream. The quantity of liquid drawn into the air stream increases as the speed of air flow over the jet increases and also the quantity is greater if the jet is made larger. The term mixture strength is important in the principle of carburetion; mixture strength refers to the ratio of the weight of air and petrol in the fuel mixture. For instance, mixture strength of 15:1 means 15 parts of air to 1 part of petrol by weight. The following are categories of mixture strength required for different conditions; Mixture strength of 1:1 is required when the vehicle is starting from cold Mixture strength of 11.5:1 and 13:1 is necessary when the vehicle is idling Mixture strength of 12:1 is required for maximum power Mixture strength of 16:1 is required for economy https://www.youtube.com/watch?v=jWW0BsIQ2mQ  3 OPERATION OF A SIMPLE CARBURETTOR The carburettor is one of the essential components of the fuel supply system in a petrol engine. As explained in the previous lesson, the function of the carburettor is to meter air and petrol, completely atomize or break up the fuel into a fine spray so that it mixes thoroughly with the air in correct proportions to supply the mixture strength suitable for good combustion under all possible varying climatic, road or load conditions. A simple carburettor, Figure 1, has the following components: Figure 1: sectional view of a simple carburettor (i) The float chamber (ii) The float (iii) The throttle valve (iv) Venturi (v) Jet Float Chamber: the float chamber is the reservoir for fuel in the carburettor. In addition, the fuel level in the jet is maintained by a float chamber. The fuel levels in the jet and in the float chamber are always the same. The Float: As the fuel in the float chamber is consumed by the engine, the float in the float chamber also goes down and the needle valve comes off its seat allowing more fuel into the chamber from the fuel tank. When the fuel level rises to its correct level in the float Chamber, the float presses the needle valve back to its seat and cuts off the fuel flow into the float chamber. The Throttle Valve: controls the volume of charge (mixture or air/petrol) that fills the cylinder. The throttle valve can be made to open fully or partially open by the driver operating the accelerator pedal. When the throttle valve is nearly closed, a small quantity of the correct mixture is permitted to enter, the cylinder, when the throttle opening is increased by pressing the  4 accelerator pedal down, a larger quantity of charge enters into the cylinder and the engine runs faster. Venturi: the venture helps to reduce the pressure over the jet so as to increase the velocity of air flowing over the jet in order to enable the fuel to be sprayed as a fine spray. When the velocity of air is higher the pressure reduces (law of pressure and velocity: pressure is inversely proportion to velocity). In order for the fuel to leave the jet and eject as a fine spray into the air stream, the pressure in the float chamber must be greater than that over the jet. Air entering the venture gets to the reduced diameter and because the same mass of air has to pass through a smaller opening at the same time, it has to travel faster. Hence, the velocity of the air flowing over the jet is increased by a constriction in the venturi. Operation of a simple carburettor A simple carburettor is used in a single cylinder engine. The carburettor is mounted directly on to the inlet valve port. However, in a multi cylinder engine e.g. four-cylinder engine, using one or more carburettor the intakes of the carburettor are joined together by the inlet manifold. As piston moves down the cylinder during the induction stroke, air flows at atmospheric pressure through the carburettor intake, collecting fine spray of fuel at the jet, past the throttle valve and goes into the cylinder. A throttle butterfly valve provides an adjustable obstruction in the induction pipe. It is used to control the flow of air-fuel mixture to the engine. As the butterfly valve is turned into the accelerate position, the airflow over the jet increases and more fuel is drawn out into the air stream, keeping the mixture strength constant. A second butterfly valve called choke is used to provide a richer mixture for the engine to start in cold condition. The choke controls the volume of air entering into the venturi Site for tutorial https://www.youtube.com/watch?v=oT3q4uogd78 https://www.youtube.com/watch?v=6YzIki62ga8 https://www.youtube.com/watch?v=wkiUsYahUYo  5 OPERATION OF ELECTRONIC FUEL INJECTION SYSTEM IN A SPARK IGNITION ENGINE (PETROL ENGINE) Electronic fuel injection permits a more even and consistent ignition in the combustion chamber. The carburettors rely on the vacuum created by the engine to draw fuel into the cylinders during the induction stroke of a petrol engine. Fuel injection system is controlled by Electronic control unit (ECU) popular called ‘brain box’ and so it precisely delivers a consistent volume of fuel into the cylinder which makes it more reliable than the carburettors. Modern cars use electronic fuel injection system which uses electromagnetic fuel injectors for injecting the fuel into the cylinders. Figure 1: Electromagnetic fuel injectors The main objectives of the use of electronic fuel injection system are efficiency and emission control. The Air- Fuel Ratio (AFR) is the mass of air to fuel present during the combustion. When this mixture of air and fuel is combined in a balanced way (adequate mixture strength), it is very important for anti- pollution and performance reasons. When adequate mixture strength is achieved, the engine has its best performance. For instance, mixture strength of 12:1 is required for maximum power, i.e 12 part of air to 1 part of fuel by weight. If there is less air in the ratio, there will be fuel left over after combustion because of lack of oxygen, the underburned fuel creates pollution. However, if the mixture has more than 12 part of air, that mixture is considered a lean and it results in a waste of fuel and consequently bad performance. The obvious reason is that the fuel will have its space occupied by the large amount of air present. This kind of mixture is bad because it tends to produce more nitrogen-oxide, which is a pollutant, and, in some cases, it can cause poor performance and even engine damage. In essence, the main advantages the electronic fuel injection system has over the carburettor are: i. Improved efficiency of the engine; ii. Lower emissions of pollutants into the atmosphere; iii. Better atomization of fuel by supplying adequate mixture strength iv. Better flow due the elimination of the venturi of the carburettor; v. Reduced response time to rapid changes in input because it is electronically controlled:  6 Figure 2: Schematic diagram of electronic fuel injection system The electronic fuel injection system is of two types: i. Single point injection ii. Multipoint injection Single point injection: A type of electronic fuel injection system that uses a single injector or pair of injectors mounted in a centrally located throttle body. The throttle unit resembles a carburettor except that there is no fuel bowl float or metering jets. Fuel is sprayed directly into the throttle bore(s) by the injector(s). See figure 3 Figure 3: single point injection The single point injection has sensors and actuators which perform different functions as follows:  7 Sensors i. Inductive pickup - position of the crankshaft and speed of the engine: This sensor gives the electronic control unit the position of the crankshaft, and the engine speed, to calculate the injection time and it is also used for ignition timing and revolution per minutes measurement. ii. Automotive oxygen sensors, known as O2 sensors, help determine, in real time, if the air fuel ratio of a combustion engine is richer or lean iii. Lambda probe (O2 sensor); Automotive oxygen sensors, known as O2 sensors, help determine, in real time, if the air fuel ratio of a combustion engine is richer or lean iv. Temperature sensors: gives the Electronic control units the cooling water system and air intake system: v. Throttle potentiometer: The throttle potentiometer indicates the ECU the exact amount of throttle opening at the moment Actuators i. Fuel injector: The fuel injector is an electromagnetic injectors controlled by the ECU. It acts as the fuel dispensing nozzle. It injects liquid fuel directly into the engine's air stream. ii. Throttle plate control: This is system is used to control the minimum airflow during idle speed. It actuates directly in to the Throttle plate, this is normally done by a small electric motor applied directly to the throttle plate Multipoint injection The multipoint injection was invented to overcome the shortcomings of the single injection system. With the single injection system, the amount of fuel deliver to the each of the cylinders is not the same in the case of multi cylinder engine e.g. four-cylinder engine. In addition, the injection is done in the intake manifold; hence, the timing is still being determined by the camshaft. In the Multipoint Injection System, there is one injector per cylinder; the injector injects the fuel into the admission valve which admits the fuel and air into the cylinder. This gives an individual control on this cylinder, improving the fuel consumption in relation of the Single point injection. See figure 4.  8 Figure 4: Multipoint Injection System The multipoint injection system has the following sensors and actuators: Sensors i. Inductive pickup - position of the crankshaft and speed of the engine ii. Lambda probe iii. Temperature sensors for cooling water system and air intake system iv. Throttle potentiometer v. Air-flow meter: An air flow meter, commonly abbreviated to AFM, also known as an air consumption meter, is a device that measures the amount in terms of quantity and speed of air flowing through a tube. It does not measure the volume of the air passing through the tube Actuators i. Fuel injector ii. Throttle control or Idle Air Control Valve (IACV) iii. Cut-off fuel valve: used to cut of fuel supply when the engine is switched off. iv. EGR Control valve (exhaust gas recirculation): exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in most petrol/gasoline and diesel engines In the Multipoint injection system, there are two ways of deliver the fuel to the injectors, one is by a fuel distributor with individual pipes or tubes to feed each injector and the second possibility that is the mostly use is a fuel rail. A fuel rail is essentially a pipe (usually resembling a rail) used to deliver fuel to individual fuel injectors. It is designed to have a pocket or seat for each injector as well as an inlet for a fuel supply. Some fuel rails also incorporate an attached fuel pressure regulator. Types of Injection System in a Multipoint Injection System There are two types of injection system in a multipoint injection system, namely: i. Multipoint injection system with indirect injection ii. Multipoint injection system with direct injection Multipoint injection system with indirect injection With the indirect fuel injection in a petrol engine, the injector supplies fuel into the inlet manifold and together with the intake air, an homogenous air/fuel mixture is formed and passes through the inlet  9 manifold port into the cylinder when the inlet valve opens. (See the attached tutorial for more explanation) Multipoint injection system with direct injection With direct injection in a petrol engine, fuel is injected directly into the cylinder and the inlet valve opens allowing air into the cylinder simultaneously as the injector injects the fuel into the cylinder directly. Direct benefits, include a more even fuel air mixture (with no fuel left behind in the runner or on the back of the valve) and a cooling effect inside the cylinder. With a direct injection, the fuel gets to skip a step and add a bit of efficiency. Instead of hanging out in the air intake manifold, fuel is squirted directly into the combustion chamber (See the attached tutorial for more explanation) Figure 5: Multi-point with direct injection Indirect https://www.youtube.com/watch?v=jAqC0qxIiL8 Direct https://www.youtube.com/watch?v=LjJSbHxIvnM  10 AUTOMOBILE IGNITION SYSTEM: THE MAGNETO The high voltage required causing a spark to jump across a plug and ignite the mixture of petrol and air in the cylinder during the compression stroke of a petrol engine is provided by the ignition system. The working principle of ignition system in a petrol engine is based on electromagnetic induction. Types of Ignition System There are four major types of ignition system in a petrol engine: 1. Magneto ignition system 2. Coil ignition system 3. Electronic ignition system 4. Distributorless ignition System Magneto Ignition System Small petrol engine such as motor cycle engines and some aircraft engines use the magneto ignition system for supplying ignition spark. A magneto is an electrical generator that uses permanent magnets to produce alternating current for generation of spark in engine. A magneto uses a magnetic field in the vicinity of a coil, called the armature, to produce an electric current. A flywheel with strong magnets is used to create a magnetic field around the armature. On each rotation, an electromagnetic field is built in the coils on the armature. A cam on the electric unit creates contact with the armature, disrupting the field and creating electrical voltage in the primary coil. In a magneto system, no outside source of electricity is necessary. The basic parts of a magneto ignition system as presented in Figure 1, are:  11 Figure 1: The magneto ignition system circuit 1. Transformer core 2. Contact Breaker 3. Cam 4. Capacitor 5. Ignition Switch 6. Distributor 7. Spark Plug Transformer core: There are two types of winding in Magneto Ignition System as follows: 1. Primary Winding: The main function of this winding is to draw the power from the source. 2. Secondary Winding: This winding has more turns of wire (the number is 1000 of turns of wire ) as compared to the primary winding. This is connected to the Distributor (Which is having a rotor ). Contact Breaker: The contact breaker is regulated by the cam and when the breaker is open, current flows through the capacitor and charges it. Cam: Cam is connected to the North and south magnet and helps to open and close the contact breaker point. Capacitor: The main work of the capacitor is to Store the charger. The capacitor used here is a simple electric capacitor. Ignition switch: To switch on and off the engine Distributor: This is connected to the spark plug and Distributor having the rotor. Spark Plug: The main work of the spark plug is firing the explosive mixture in the engine. Working Principle of Magneto Ignition System: In the Magneto Ignition System, magneto is used. When ignition of the engine is switched on, it helps the magneto to rotate and thus it's producing the energy in the form of high voltage then, one end of the magneto is grounded through a contact breaker, and the ignition capacitor is connected to its parallel. The contact breaker is regulated by the cam and when the breaker is open, current flows through the capacitor and charges it, then, a high electromagnetic force (EMF) is generated in the secondary windings of the Coil. The capacitor is acting as a charger in the system. This increased high voltage flows through the distributor which distributes the high voltage current to each of the spark plugs in the correct firing order. At the starting stage, the speed of the engine is low and hence the  12 voltage generated by the magneto is low. But as the rotating speed of the engine increases, it also increases the voltage generated by the magneto thus the flow of the current is also increased. Applications of Magneto Ignition System: Application of Magneto Ignition System is found in: 1. two-wheeler vehicles (SI Engine) 2. Motor cycles 3. Tractors, 4. Buses, 5. Marine Engines, 6. Natural Gas Engines. Advantages of Magneto Ignition System: 1. It requires less maintenance as compared to the Battery ignition system. 2. It requires no source of electricity supply such as battery 3. It occupies less space in the engine. 4. An electric circuit is generated by the magneto 5. No battery is needed, so no problem of battery discharge 6. Efficiency improves due to high-intensity spark. Disadvantages of Magneto Ignition System: 1. During starting, the quality of spark is poor due to low speed. List of Cites for tutorial https://studentlesson.com/magneto-ignition-system-definition-function-components-working/ https://www.youtube.com/watch?v=J-kGyWAF4SI https://www.youtube.com/watch?v=cC2Yo5CT_jo  13 The Coil Ignition System Function The operation of the petrol engine is dependent upon the burning and expansion of air/petrol mixture within each cylinder. The mixture cannot burn or expand unless it is ignited by a spark produced by the ignition system. The function of the coil ignition system is to provide at the correct time in correct sequence, a series of sparks of sufficient intensity to ignite the highly compressed mixture of air and petrol in the cylinders of the engine. The coil ignition circuit presented in Figure 1, consists of: i. Battery (as a source of energy) ii. Ignition coil iii. Contact breaker point iv. Condenser v. Distributor vi. Spark plugs vii. Low and high tension wires viii. primary circuit and secondary circuit The primary circuit is composed of the ignition switch, resistant wire to the ignition coil, the primary winding in the ignition coil, the contact breaker points, condenser (capacitor) and low voltage wiring that connects these units as presented in Figure 2. The secondary circuit comprises the secondary winding in the coil, the coil to distributor’s secondary cable (high tension cable), the distributor cap and rotor, spark plug cables and spark plugs as shown in Figure 2.  14 Figure 1: coil ignition system circuit Figure 2: Primary circuit and secondary circuit Operation of Coil Ignition System When the ignition is switch on, the battery current is passed through the primary winding to the contact breaker points. When the contact points are closed the current flowing in the primary windings set up a magnetic field around the soft iron core of the coil and it is being concentrated. Opening the contact points, at a time when the spark is required interrupts the current flowing in the primary circuit and the magnetic field collapses. This motion of the fields across the windings again induces a current in each winding at a faster rate and the currents are much greater, i.e. the field collapses faster that it was built. The lines of force created by the collapse of the magnetic field cut the secondary winding and induce a high electromagnetic force (E.M.F) in the secondary windings than that acting on the primary windings, since the secondary windings of the coil contains more turns of wires. The high tension current produced in the secondary winding is therefore supplied to the spark plugs through the high tension cable to the rotor arm which in turn distributes the current to the distributor’s segments in correct firing orders to the spark plugs of the seperate cylinders.  15 Functions of the Coil Ignition Components Battery: is usually 6 or 12 volts which supplies voltage to force a small current through the primary winding of the ignition coil Ignition coil: it converts the battery voltage into a high voltage enough to cause a spark to jump the gap of the spark plug. The battery produces in a car usually has 12volts capacity, the coil multiples the 12 volts above 10,000volts. Contact breaker points: interrupts the flow of battery current through the primary winding of the coil at a regular and predetermined intervals Condenser (capacitor): helps to provide a stronger spark by ensuring a quicker collapse of the magnetic fields and also reduce the arcing or burning of the points of the contact breaker. Spark Plug: this introduces the spark into the compressed mixture of air and fuel in the cylinder. Distributor:- directs the high voltage current produced in the secondary winding of the coil to the spark plugs in the correct firing order  16 ELECTRONIC IGNITION SYSTEM The electronic ignition system performs the same function as the coil ignition system; however, the electronic ignition system is controlled by the Electronic control module. It uses Armature. The armature replaces the contact breaker points in the coil ignition system. The shortcomings of the magneto and coil ignition systems are overcome by the electronic ignition system. One of the shortcomings is that the contact breaker points wear out or burn out over time and when it is operated with heavy current. Secondly, the contact breaker is only a mechanical device that cannot operate precisely at high speed due to the dwell period which is not sufficient for building up the magnetic field to its full value at that particular speed. The conventional contact breaker can give satisfactory performance only about 400 sparks per second which limits the engine speed. At low speeds, relatively high current is drawn from the battery due to the contacts remaining closed for a longer time. Thus, the system becomes inefficient at low speeds. These disadvantages of the convention contact breaker assisted ignition system can be completely eliminated by the use of an electronic controlled ignition system using an armature and electronic control unit. The basic difference between coil ignition system and electronic ignition systems is in the primary circuit. In the electronic ignition systems, the primary circuit is opened and closed by the electronic control unit. The secondary circuits are practically similar to previous systems. The parts of the Electronic ignition system as shown in Figure 1, are: 1. Battery 2. Ignition Switch 3. Electronic Ignition Module or Electronic control unit (ECU) 4. Ignition Coil 5. Armature 6. Distributor 7. Spark Plug NOTE: The battery, ignition switch, ignition coil, distributor and spark plugs perform the same function as described in the coil ignition system.  17 Figure 1: Electronic ignition circuit The Electronic Module The electronic module senses the signal produced by the pickup coil and stops the current flow from the primary circuit. The timing circuit inside the ignition module turns ON and thereby the current will flow again into the circuit when the voltage is not produced. Armature: Contact breaker points of the battery ignition system are replaced by an armature. When the Armature tooth comes in front of the pickup coil, a voltage signal is generated. The electronic module senses the signal produced by the pickup coil and stops the current flow from the primary circuit. Operation of Electronic Ignition System: When the ignition switch is turned ON, current flows from the battery through the ignition switch to the coil primary windings. When the armature tooth comes in front of the pickup coil, a voltage signal is generated. The electronic module senses the signal produced by the pickup coil and stops the current flow from the primary circuit. When the armature tooth moves away from the pickup coil, a voltage signal is not generated and due to this, the timing circuit inside the ignition module turns ON and thereby the current will flow again into the circuit. Due to the continuous make and break of the current, a magnetic field is generated in the ignition coil. Due to the magnetic field, an electromotive force (EMF) is induced in the secondary winding causing the voltage to increase up to 50,000 volts. This high voltage is then transferred to the distributor. The rotor inside the distributor rotates according to the ignition timing. As the rotor come exactly in front of the distributor point the voltage jumps due to the air gap from the rotor to the point. A high voltage is then transferred from the distributor to the spark plug terminal through the high tension cable. https://www.youtube.com/watch?v=QYx8J_5l5wY https://www.youtube.com/watch?v=eo_H8PnevtQ  18 DISTRIBUTORLESS IGNITION SYSTEM The distributor in an electronic ignition system in a multiple cylinder engine e.g. four cylinder engine wears out over time because it is a mechanical component. The wear and tear renders the distributor ineffective or less efficient which invariably affects the operation of the ignition system. The Distributorless Ignition System (DIS) is the ignition system in which the distributor of the electronic ignition system is replaced with a number of induction coils. In the Distributorless ignition system, there is one coil per cylinder or one coil for pair of cylinders, and the timing of the spark is controlled by an Ignition control unit (ICU) and the Engine control unit (ECU), which makes this system more efficient and accurate. The use of one ignition coil per cylinder provides direct voltage to the each of the spark plugs in the engine. This system is also known as Direct Ignition System (DIS). It should be recalled that electronic ignition system uses distributor like the coil ignition system. The distributor is used to distribute the high voltage signal from the ignition module to the spark plugs. The distributor used is a mechanical device having a rotor that completes the circuit and also controls the spark timing, which make this system little less efficient and this system also faces mechanical and electrical wear and tear. The spark timing accuracy of the electronic ignition system decreases with time. Hence, the Electronic ignition system requires higher maintenance than Distributorless ignition system because the wear and tear in the distributor and rotor components needs to be checked periodically and change when required. Modern vehicles are fitted with distributorless ignition system. The spark time accuracy of the distributorless ignition system is increased by using an electronic control unit along with ignition module and the distribution of the voltage signal to the spark plugs is made direct using one ignition coils per cylinder, which decreases the wear and tear of the system and makes the system the most efficient and reliable ignition system. The components of this distributorless ignition system as shown in Figure 1 is the same as that of electronic ignition system except that there is no distributor in this system 1. Battery 2. Ignition Switch 3. Spark Plug 4. Ignition coil and Ignition Control Module: In the Distributorless ignition system, a complete assembly of ignition coils and module is used to make the system compact and less complicated. i. Ignition Coils: Unlike the electronic ignition system in which a single ignition coil is used to generate high voltage, distributorless ignition system uses a number of ignition coils i.e. each coil per spark plug which generates high voltage individually for each spark plug. ii. Ignition Control Module (ICM) or Ignition Control Unit: It is the programmed instruction given to the chipset which is responsible for setting the primary coil circuit to ON or OFF, 5. Magnetic Triggering Devices: i. Camshaft Triggering Device: Mounted on the camshaft and used for sensing valve timing. ii. Crankshaft Triggering Device: Mounted on the crankshaft and used for sensing the piston position or stroke.  19 Figure 1: distributorless Ignition System circuit Operation of Distributorless Ignition System When the ignition is switched ON, the current from the battery starts to flow through the ignition switch to the electric control unit (which keeps on processing data and calculating timing) of the engine. The triggering wheels mounted on the camshaft and crankshaft have equally spaced teethes with one gap, and the position sensors which consists of the magnetic coil that constantly generates magnetic field as the camshaft and crankshaft rotates. When these gaps come in front of the positioning sensors, fluctuation in the magnetic field occurs and the signals of both the sensors are sent to the ignition module which in turn senses the signals and the current stops to flow in the primary winding of the coils.and when these gaps moves away from the sensors the signals of both the sensors are sent to the ignition module which turns ON the current to flow in the primary winding of the coils. This continuous make and break of the signals generate magnetic field in the coils which in turn induced high electromagnetic force in the secondary winding of the coils and increases the voltage up to 70000 volts. This high voltage is then sent to the spark plugs and the generation of sparks takes place. The timing of the spark plugs is controlled by electronic control unit by continuously processing the data received from the ignition control module. https://www.youtube.com/watch?v=FpGGpgSEU94  20 AUTOMOBILE COOLING SYSTEM The engine converts heat energy from the fuel into mechanical energy. As the mixture of air and fuel is burnt inside the cylinder; a great deal of heat energy is involved. However, only about three quarter of the heat energy is converted into mechanical energy. Hence, the remaining heat energy produced in the process has to be removed quickly and continuously from the engine in order to prevent the moving parts of the engine from being excessively expand and damaged. The function of the cooling system therefore is to dissipate about one third of the total heat produced by the burning mixture of gases in the engine. Hence, the Cooling System in automobile is a system that controls the engine temperature An engine must not be overcooled nor undercooled as both conditions have serious effects on the engine. The effects of overcooling and undercooling are discussed below: Overcooling: Overcooling simply means under-heating; an engine required an ideal equilibrium temperature of 750c-900c to function effectively. A temperature less than the equilibrium are termed overcooling. Effects of over cooling are as follows: 1. Some of the heat required to burn the mixture and air in the cylinder will be lost. 2. The fuel will not vaporized properly and some of the unvaporized gases will condense on the cylinder walls 3. The unvapourized fuel will lead to dilution of the oil in the sum with addition of corrosive acids 4. As the pistons move up and down the cylinder wall removing the unvaporized gases, the cylinder bore wears out. 5. It also leads to inadequate lubrication of the engine because the oil will not warm enough to flow freely, resulting in greater frictional losses 6. The life of the engine is at stake Undercooling: this simply means overheating. It is a condition where the heat in the engine is above the ideal equilibrium temperature. Effect of undercooling are; 1. It leads to engine seizure because most of the rotating parts of the engine may expand 2. It shortens valve life 3. It leads to distortion of the engine block 4. The top gasket may burn out 5. It also leads to pre-ignition- A condition where the mixture of air and fuel in the cylinder is ignited due to excessive heat before the timed ignition period thus causing loss of power and possibly damage to the engine 6. The water in the cooling system may boil and evaporate and should oil film burn away additional friction and wear will occur between piston and the cylinder Types of Cooling System There are two types of cooling systems: (i) Air cooling system (ii) Water-cooling system  21 AIR COOLING SYSTEM The air cooling system uses air as the cooling medium. Air-cooling is mostly used on motorcycles, small generators, small cars, small aircraft engines and some industrial engines where the forward motion of the machine gives good velocity to cool the engine. Fins are provided around the cylinder and cylinder head of the engine as shown in figure 1. The fins are metallic ridges, which are formed during the casting of the cylinder and cylinder head of the engine. The heat, which is conducted to the outer parts of the engine, is radiated and conducted away, through the fins, by the stream of air obtained from the atmosphere. In some small cars using air cooling system, fans are provided as part of the cooling system. The fan forces air over the fins, which cools the engine by transferring the heat to the air. The effectiveness of air-cooling depends upon the following factors: 1. The total area of the fin surfaces 2. The velocity of the cooling air 3. The temperature of fins as well as that of the cooling air. Figure 1: Fins for air cooling system in a motorcycle engine Advantages of Air Cooling System Air cooling system has the following advantages: 1. The design of air-cooling system is simple. 2. Engines with air cooling system is lighter in weight than water-cooled engines due to the absence of water jackets, radiator, circulating pump and the weight of the cooling water.  22 3. Air cooling system is cheaper to manufacture. 4. The air cooling system in the engine needs less care and maintenance. 5. This system of cooling is particularly advantageous where there are extreme climatic conditions in the arctic or where there is scarcity of water as in deserts. 6. No risk of damage from frost, such as cracking of cylinder jackets or radiator water tubes. Disadvantages of Air cooling system 1. It can only be used on small engines and not suitable for multi-cylinder engines 2. The air cooling system effectiveness depends on climatic weather condition; hence it is less effective in hot weather regions 3. The control of temperature in air cooling system is not accurate 4. Cooling of cylinder, cylinder head and valves is not uniform.  23 WATER COOLING SYSTEM The water cooling system uses water as the cooling medium. Modern automobiles use water and some forms of coolants and antifreeze solutions as the cooling medium. Hence, the term liquid cooling system is sometimes used for water cooling system. As the engine is running, water/coolant is made to circulate in the water jacket provided around the cylinder head and block. The main parts of the water Cooling System figure 2, are: 1. Radiator and Pressure Cap 2. Pump 3. Radiator Fan 4. Water/coolant 5. Water jackets 6. Thermostat Valve 7. Temperature Gauge 8. Rubber Hose pipes Figure 2: water cooling system Radiator: It is main water reservoir in the water cooling system. It comprises an upper tank and lower tank and between them is an aluminium core. The upper tank is connected to the water outlets from the engines jackets by a rubber hose pipe and the lover tank is connect to the jacket inlet through water pump by means of rubber hose pipes.. When the water is flowing down through the radiator core, it is cooled partially by the fan which blows air and partially by the air flowing through the forward motion of the vehicle.  24 Thermostat: Prevents flow of water from the engine to radiator so that engine readily reaches its maximum efficient operating temperature. After attaining maximum efficient operating temperature, the valve in the thermostat automatically opens to allow the circulation of water in the cooling system. Water Pump: water pump is used in a pump circulating system. The pump is used to circulate water. Impeller type pump is mounted at the front end. Pump consists of an impeller mounted on a shaft and enclosed in the pump casing. Fan: the fan blows air over the radiator for cooling purpose. It is driven by the belt that drives the pump, Pressure Cap and reserve tank: As coolant gets hot, it expands and pressure in the system starts to increase. The radiator pressure cap is a simple device that will maintain pressure in the cooling system up to a certain point. If the pressure builds up higher than the set pressure point a spring loaded valve in the pressure cap opens to release the pressure. Water Jackets Cooling water jackets are provided around the cylinder, cylinder head, valve seats and any hot parts which are to be cooled. Heat generated in the engine cylinder, conducted through the cylinder walls to the jackets. The water flowing through the jackets absorbs this heat and gets hot. This hot water will then be cooled in the radiator. Hoses: There are several rubber hoses that make up the plumbing to connect the components of the cooling system. The main hoses are called the upper and lower radiator hoses. These two houses are approximately 2 inches in diameter and direct coolant between the engine and the radiator. Anti-Freeze in Water Cooling System In some countries that have winter climate, water may become freeze due to cold weather condition. If water is allowed to freeze in an engine, the ice formed has more volume. This may result in cracks in the cylinder blocks, pipes, and radiator In order to prevent the water in the cooling system from freezing, some chemical solutions which are known as anti-freeze solutions are mixed with water. The following are used as antifreeze solutions: (a) Methyl, ethyl and isopropyl alcohols. (b) A solution of alcohol and water. (c) Ethylene Glycol. (d) A solution of water and Ethylene Glycol. (e) Glycerine along with water, Characteristics of Anti-Freeze 1. It should dissolve in water easily. 2. It should not evaporate. 3. It should not deposit any foreign matter in cooling system. 4. It should not have any harmful effect on any part of cooling system. 5. It should be cheap and easily available. 6. It should not corrode the system  25 Advantages of Water Cooling System 1. Uniform cooling of cylinder, cylinder head and valves. 2. Fuel consumption of engine is more accurate by using water cooling system. 3. Control of engine operating temperature is more accurate 4. Engine is less noisy as compared with air cooled engines because it has water for damping noise. Disadvantages of Water Cooling System 1. It depends upon the supply of water. 2. The water pump which circulates water absorbs considerable power. 3. If the water cooling system fails then it will result in severe damage of engine. 4. The water cooling system is costlier as it has more number of parts. Also it requires more maintenance and care for its parts. Types of Water Cooling System There are two types of water cooling system: 1. Thermo Syphon System: In this system the circulation of water is due to difference in temperature (i.e. difference in densities) of water. So in this system pump is not required but water is circulated because of density difference only. 2. Pump Circulation System: In this system circulation of water is obtained by a pump. This pump is driven by means of engine output shaft through V-belts Thermo Syphon System In the thermo syphon water cooling system shown in Figure 3, when the engine is running, the water in the cylinder head absorbs heat and expands. The same volume of heated water therefore weigh less than cooler water and rises to the highest point of the system passing out of the cylinder head into the top tank of the radiator. Colder water from the radiator bottom tank moves in to take its place and so a slow circulation of the water is obtained by means of convention currents. As the heated water passes down through the tubes of the radiator most of it heat is extracted by stream of air which passes around the tubes of the radiator. By careful design the water temperature can be kept within the range of temperature at which the engine operates most efficiently and most economically.  26 Figure3: Thermo syphon system Pump Circulation System or Pressurized System The pump circulation system type of water cooling system shown in Figure 4 is similar to the thermo syphon system except that the circulation of water is assisted by an impeller pump. This use of the pump allows for a wider and lower radiator and a thermostat. When the engine is hot, the impeller pump draws cooled water from the bottom tank of the radiator and passes it into the distributor tube. The tube directs cooled water through its perforation onto the hottest arrears of metal surrounding the combustion chambers and the exhaust ports. The cooled water absorbs most of the heat in the combustion chambers and the exhaust ports and passes up around the open valve of the thermostat and out of the cylinder head to the top tank of the radiator. As the heated water passes down the radiator fins the absorbed heat is removed by the air stream through the radiator fins and the cooled water is drawn into the impeller pump to be circulated. When the engine is cold, the circulation starts as soon as the engine is started, so the warming time would be unduly long if it were not for the action of the thermostat. Under cold condition the thermostat valve is closed and the impeller pump is only allowed to circulate the water in the cylinder head and block and block. This is made possible by use of a by-pass either internal or external, from the low-pressure side of the impeller to a point just below the thermostat valve. As the water absorbs heat its temperature rises and at about 77 oc the thermostat valve opens to allow water to pass into the radiator and cooled. Figure 4: pump circulation water cooling system  27 AUTOMOBILE ENGINE LUBRICATION SYSTEM Introduction Lubrication in an engine refers to presence of oil in the moving parts of the engine. If an engine runs without any oil in the surfaces of metal to metal contacts, the surfaces of metal to metal contact would produce so much heat that they would melt and run out. The piston would expand and seize in the cylinder and the engine stop to work. Hence, certain type oil is recommended by the vehicle manufacturers and a minimum level of oil must be maintained in the engine. Function of Lubrication in an Engine The functions of the lubrication system in an engine are as follows: 1. To minimize friction and wear between surfaces of metal to metal contacts in the engine 2. To keep the engine part clean, especially piston rings and ring groves, oil ways and filter 3. To absorb and carry away harmful substances resulting from incomplete combustion and prevent metallic components from corrosive attack by the acids formed during the combustion process and to resist oxidation, which causes sludge. 4. To act as cooling medium, transferring heat to the water jackets, crankcase and sump walls from piston and bearings 5. To provide a sealing medium between cylinder walls and piston rings to prevent ‘blow-by’ of the gases in the cylinder 6. To provide steady viscosity when hot and when cold Components of Engine Lubrication system The major components of the lubrication system in an engine are: i. Engine Lubrication Oil: serves as a medium of lubrication. Oils are given numbers that denotes whose viscosity falls within a certain range. Viscosity is a measure of thickness or thinness of oil. The Society of Automotive Engineers (S.A.E) of America classified oils by numbers which relates to the viscosity of the oil to the operating temperature of water cooled engine at 990c. The numbers are 10 for the thinnest oil, 20, 30, 40, and 50 S.A.E. manufacturers usually specified an oil of different viscosity for engine use at summer and winter. Some oil also carries suffix ‘W’ which refers to winter grade oil which relates to viscosity of the oil at -180c. The numbers are; 5W, 10W etc. nowadays the two numbers are quoted in some types of oil, for instance, SAE10/W30 indicating that the oil conforms to the requirements of both numbers. ii. The sump: The sump serves as reservoir for oil iii. Dip stick: used to check the level of oil in the engine. The dip stick provides at least three information, namely; (i) the minimum level of oil (ii) the maximum level of oil, (ii) the type of recommended oil. iv. The oil pressure switch: The oil pressure switch is installed in the oil circuit of the engine. It is activated by the pressure of the lubricating oil used in engines and serves to indicate to the driver, by means of a LED on the control panel, or dash board when the pressure of  28 the lubrication circuit is insufficient compared with the prescribed value. It monitors the oil pressure and turns off or on a warning light or controls an oil pressure indicator. v. Oil filter: helps to remove dirt and carbon debris from the oil during circulation in the engine vi. The pump: forces the oil in the sump in order to circulate the oil through the oil ways to the camshaft bearings and crankshaft main bearing. Three types of pumps are in use; gear pump, sliding vane type and eccentric rotor pumps. How Engine Lubrication System Works The engines employ a pressure circulation system. The pump draws oil from the sump of the engine and forces it under pressure to all the principal moving parts. The oil delivered by the pump eventually drains back into the sump. The oil therefore is in continual circulation while the engine is running. Although, the oil is subjected to pressure and extreme heat, the oil does not physically deteriorate as is often assumed. The molecular structure of the oil cannot be worn out but some of the oil is burnt and the burning produces substances which contaminate the oil, with undesirable results. Particles of carbon and other debris are also picked up by the oil. Oil Filters are provided in the lubrication system through which the oil is forced. The oil filters remove some of the contamination but they cannot remove it all. It is for this reason that all the oil in the engine has to be drained out at intervals and replaced with fresh oil. Types of Filtration System There are two types of filtration system in the lubrication system; 1. Partial flow 2. Full flow Partial flow or By-Pass: with partial flow system, figure 1, approximately 10% of the oil delivery passes through the filter and returns to the sump, while the remainder circulates through the engine bearing and moving parts. By reason of subsequent inter-mixing of the oil in the sum, this system effectively filters the whole of the oil in the sump.  29 Figure 1: Partial flow of by pass Full-flow: in the full-flow system, figure 2, the filter is located in the main oil supply and takes the full delivery of the oil from the sump before it reaches the moving parts of the engine. Figure 2: full flow system