Battery or Coil Ignition System PDF

**Battery or Coil Ignition System:** **-**used in 4-wheelers, but now-a-days it is more commonly used in 2-wheelers. **Primary Circuit** -consists of 6 or 12 V battery -200-300 turns of 20 SWG (Sharps Wire Gauge) gauge wire, contact breaker, capacitor. **Secondary Circuit:** -have 21000 turns...

**Battery or Coil Ignition System:** **-**used in 4-wheelers, but now-a-days it is more commonly used in 2-wheelers. **Primary Circuit** -consists of 6 or 12 V battery -200-300 turns of 20 SWG (Sharps Wire Gauge) gauge wire, contact breaker, capacitor. **Secondary Circuit:** -have 21000 turns of 40 (S WG) gauge wire. -voltage goes unto 28000-30000 volts. **Magneto Ignition System:** \- magneto will produce and supply the required current to the primary winding or coil -no battery required -during starting the quality of spark is poor due to slow speed **Disadvantage of conventional ignition systems** **-**Poor starting: After few thousands of kilometres of running, the timing becomes inaccurate, which results into poor starting (Starting trouble). -performance is poor because of inertia effects of the moving parts in the system. **the advantages of electronic ignition system:** \(a) Moving parts are absent-so no maintenance. \(b) Contact breaker points are absent-so no arcing. \(c) Spark plug life increases by 50% and they can be used for about 60000 km without any problem. \(d) Better combustion in combustion chamber, about 90-95% of air fuel mixture is burnt compared with 70-75% with conventional ignition system. \(e) More power output. \(f) More fuel efficiency. **Firing order:** -4 cylinder engine (inline) = 1-3-4-2 1-2-4-3 -4 cylinder horizontal opposed engine(Volkswagen engine) = 1-4-3-2 -6-cylinder in line engine = 1-5-3-6-2-4 -8 cylinder in line engine 1-6-2-5-8-3-7-4 -8 cylinder V type 1-5-4-8-6-3-7-2 **Ignition timing:** very important, since the charge is to be ignited just before (few degrees before TDC) the end of compression, since when the charge is ignited, it will take some time to come to the required rate of burning. **Ignition Advance:** The purpose of spark advance mechanism is to assure that under every condition of engine operation, ignition takes place at the most favorable instant in time i.e. most favourable from a standpoint of engine power, fuel economy and minimum exhaust dilution. **Factors affecting energy requirement of ignition system** [Effect of series resistance:] -longer discharge time [Effect of electrode material:] -ignition energy for electrode gaps larger than the quenching distance varies with materials [Effect of spray inductance: ] -presence of small stray inductance cause oscillatory discharge [Effect of electrode configuration: ] -reduction in the capacitance reduces the discharge time and increase in the gas resistance **Stages of SI engine combustion** In SI engine homogeneous mixture of vaporised fuel, air and residual gases is ignited by a single intense and high temperature spark between the spark plug electrode (electrodes exceeds 10,000 ᵒC) **I-Ignition lag or preparation phase (AB):** -growth and development of a semi propagating nucleus of flame -Ignition lag is very small and lies between 0.00015 to 0.0002 seconds -ignition lag of 0.002 seconds corresponds to 35 deg crank rotation when the engine is running at 3000 RPM **II-propagation of flame (BC):** -flame propagates at the constant velocity -Heat transfer to the cylinder wall is low **III-After burning (CD):** -After point C, the heat release is due to the fuel injection in reduced flame front after the starts of expansion stroke -no pressure rise during this period **[Effect of engine variables on Ignition lag]** **Fuel**: High self-ignition temperature of fuel longer the ignition lag. **Initial temperature and pressure**: increasing the intake temperature and pressure, increasing the compression ratio, chemical reaction rate and retarding the spark all reduce the ignition lag **Electrode gap**: lower the compression ratio and higher the electrode gap is desirable -voltage required at the spark plug electrode to produce spark is found to increase with decrease in fuel-air ratio and with increase in compression ratio and engine load Turbulence: directly proportional to engine speed **\*Effect of engine variables on flame propagation** -Rate of flame propagation affects the combustion process in SI engine. [The factors which affect the flame propagations are ] 1\. A:F ratio: The mixture strength influences the rate of combustion and amount of heat generated. 2\. Compression ratio: The higher compression ratio increases the pressure and temperature of the mixture and also decreases the concentration of residual gases. 3\. Load on Engine: With increase in load, the cycle pressures increase and the flame speed also increases. In S.I. engine, the power developed by an engine is controlled by throttling. 4.Turbulence: Turbulence plays very important role in combustion of fuel as the flame speed is directly proportional to the turbulence of the mixture. *Engine Speed* -The turbulence of the mixture increases with an increase in engine speed. *Engine Size* -Engines of similar design generally run at the same piston speed. **\*Detonation or knocking** Knocking is due to auto ignition of end portion of unburned charge in combustion chamber. **\*Auto ignition** A mixture of fuel and air can react spontaneously and produce heat by chemical reaction in the absence of flame to initiate the combustion or self-ignition. **\*Pre-ignition** Pre-ignition is the ignition of the homogeneous mixture of charge as it comes in contact with hot surfaces, in the absence of spark. *Effects of Pre-ignition* -It increase the tendency of denotation in the engine **\*Effect of detonation** The harmful effects of detonation are as follows: *Noise and roughness:* knocking produces a loud pulsating noise and pressure waves. *Mechanical damage:* High pressure waves generated during knocking can increase rate of wear of parts of combustion chamber. *Carbon deposits:* Detonation results in increased carbon deposits. *Increase in heat transfer:* Knocking is accompanied by an increase in the rate of heat transfer to the combustion chamber walls. *Decrease in power output and efficiency:* Due to increase in the rate of heat transfer the power output as well as efficiency of a detonating engine decreases. a. Low speed engine (n˂1500 rpm): b. Medium speed engine (n=1500-3000 rpm): **TESTING AND PERFORMANCE** *1. Measurement of speed:* -One of the basic measurements is that of speed. ***2. Fuel consumption measurement:*** Fuel consumption is measured in two ways: \(a) The fuel consumption of an engine is measured by determining the volume flow in a given time interval and multiplying it by the specific gravity of the fuel which should be measured occasionally to get an accurate value. \(b) Another method is to measure the time required for consumption of a given mass of fuel. **Gravimetric Fuel Flow Measurement** The efficiency of an engine is related to the kilograms of fuel which are consumed and not the number of liters. ***3. Measurement of air consumption:*** In IC engines, the satisfactory measurement of air consumption is quite difficult because the flow is pulsating, due to the cyclic nature of the engine and because the air a compressible fluid. ***4. Measurement of brake power:*** The brake power measurement involves the determination of the torque and the angular speed of the engine output shaft. **Absorption Dynamometers** These dynamometers measure and absorb the power output of the engine to which they are coupled. **Transmission Dynamometers** In transmission dynamometers, the power is transmitted to the load coupled to the engine after it is indicated on some type of scale. These are also called torque-meters. **Prony brake dynamometer** One of the simplest methods of measuring brake power (output) is to attempt to stop the engine by means of a brake on the flywheel and measure the weight which an arm attached to the brake will support, as it tries to rotate with the flywheel. **Rope brake** It consists of a number of turns of rope wound around the rotating drum attached to the output shaft. **Hydraulic Dynamometer** Hydraulic dynamometer works on the principle of dissipating the power in fluid friction rather than in dry friction. **Eddy Current Dynamometer** It consists of a stator on which are fitted a number of electromagnets and a rotor disc made of copper or steel and coupled to the output shaft of the engine. **Swinging Field d.c. Dynamometer** Basically, a swinging field d.c. dynamometer is a d.c. shunt motor so supported on trunnion bearings to measure their action torque that the outer case and filed coils tend to rotate with the magnetic drag. Hence, the name swinging fiel **Fan Dynamometer** It is also an absorption type of dynamometer in that when driven by the engine it absorbs the engine power. **Transmission Dynamometers** Transmission dynamometers, also called torque meters, mostly consist of a set of strain-gauges fixed on the rotating shaft and the torque is measured by the angular deformation of the shaft which is indicated as strain of the strain gauge. ***Measurement of friction power:*** -The difference between indicated power and the brake power output of an engine is the friction power. **Willan's line method** -In this method, gross fuel consumption vs. *bp* at a constant speed is plotted and the graph is extrapolated back to zero fuel consumption. **Morse Test** -The Morse test is applicable only to multicylinder engines. **Motoring Test** -In the motoring test, the engine is first run up to the desired speed by its own power and allowed to remain at the given speed and load conditions for some time so that oil, water, and engine component temperatures reach stable conditions **Difference between *ip* and *bp*** i. The method of finding the *fp* by computing the difference between *ip*, as obtained from an indicator diagram, and *bp*, as obtained by a dynamometer, is the ideal method. ***Heat balance sheet:*** The performance of an engine is usually studied by heat balance-sheet. The main components of the heat balance are: -Heat equivalent to the effective (brake) work of the engine, -Heat rejected to the cooling medium, -Heat carried away from the engine with the exhaust gases, and -Unaccounted losses. **Performance of SI engine:** -At full throttle the brake thermal efficiency at various speeds varies from 20 to 27 percent, maximum efficiency being at the middle speed range. **ENGINE COOLING** cooling must be satisfactory to avoid pre-ignition and knock. **\*Requirements of cooling system in the IC engine** -The temperature of the burning gases in the engine cylinder reaches up to 1500 to 2000°C, which is above the melting point of the material of the cylinder body and head of the engine. (Platinum, a metal which has one of the highest melting points, melts at 1750 °C, iron at 1530°C and aluminum at 657°C.) Therefore, if the heat is not dissipated, it would result in the failure of the cylinder material. **Effect of overcooling:** -Thermal efficiency is decreased due to more loss of heat carried by the coolant -The vaporization of the fuel is less resulting in lower combustion efficiency -Low temperature increases the viscosity of lubricant causing more loss due to friction **Air Cooled System:** -Air cooled system is generally used in small engines say up to 15-20 kW and in aero plane engines. **Advantages of air cooled engines** Air cooled engines have the following advantages: 1\. Its design of air-cooled engine is simple. 2\. It 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. 3\. It is cheaper to manufacture. **Disadvantages of air cooled engines** -Relatively large amount of power is used to drive the cooling fan.™ -Engines give low power output.™ **Water cooling system:** Cooling water jackets are provided around the cylinder, cylinder head, valve seats etc. [Antifreeze mixture ] In western countries if the water used in the radiator freezes because of cold climates, then ice formed has more volume and produces cracks in the cylinder blocks, pipes, and radiator. [Water cooling system mainly consists of: ] -Radiator -Thermostat valve -Water pump -Fan -Water Jackets -Antifreeze mixtures ***Thermo-syphon cooling:*** This system works on the principle that hot water being lighter rises up and the cold water being heavier goes down. ***Forced or pump cooling:*** -This system is used in large number of vehicles like car, buses, trucks and other heavy vehicles. ***Cooling with thermostatic regulator:*** -Whenever the engine is started from cold, the coolant temperature has to be brought to the desired warm up time to avoid corrosion damage due to condensation of acids as well as help in easy starting of the engine. ***Pressurized water cooling system:*** In the case of the ordinary water-cooling system where the cooling water is subjected to atmospheric pressure, the water boils at 212°F. ***Evaporative cooling system:*** -In this system, the engine will be cooled because of the evaporation of the water in the cylinder jackets into steams. **Descriptions of different parts of water cooling system** **Radiator:** The purpose of the radiator is to cool down the water received from the engine. *[Gilled tube radiator: ]* This is perhaps the oldest type of radiator, although it is still in use. In this, water flows inside the tubes. *[Tubular radiator]:* The only difference between a gilled tubes radiator and a tubular one is that in this case there are no separate fins for individual tubes. **Water Pump:** This is a centrifugal type pump. **Fan:** The fan is generally mounted on the water pump pulley, although on some engines it is attached directly to the crankshaft. **\*Advantages of water cooling system** -Because of even cooling of cylinder barrel and head (due to jacketing) makes it possible to reduce the cylinder head and valve seat temperatures. **\*Disadvantages of water cooling system** -The system requires more maintenance. -The engine performance becomes sensitive to climatic conditions. ™ **LUBRICATION SYSTEM** Due to continuous movement of two metallic surfaces over each other, there is wearing moving parts, generation of heat and loss of power in the engine. Direct frictional losses: -power absorbed due to the relative motion of different bearing surfaces such as piston rings, main bearings, cam shaft bearings etc. Pumping loss: -net power spent by the piston on the gas during intake and exhaust stroke -more in case of four stroke engine compared to two stroke engine Power loss to drive components to charge and scavenge: -In four stroke supercharged engine, compressor used to provide high pressure air which is mechanically driven by the engine. This is counted as negative frictional loss. Power loss to drive the auxiliaries: -Some power is used to drive auxiliaries such as water pump, lubricating oil pump, fuel pump, cooling fan, generator etc. **Function of lubrication:** **Reducing frictional effect:** The primary purpose of the lubrication is to reduce friction and wear between two rubbing surfaces. **Cooling effect:** The heat, generated by piston, cylinder, and bearings is removed by lubrication to a great extent. Lubrication creates cooling effect on the engine parts. **Sealing effect:** The lubricant enters into the gap between the cylinder liner, piston and piston rings. **Cleaning effect:** Lubrication keeps the engine clean by removing dirt or carbon from inside of the engine along with the oil. **Lubrication theory:** There are two theories in existence regarding the application of lubricants on a surface: (i) Fluid film theory and (ii) Boundary layer theory. **Fluid film theory:** According to this theory, the lubricant is, supposed to act like mass of globules, rolling in between two surfaces. **Boundary layer theory:** According to this theory, the lubricant is soaked in rubbing surfaces and forms oily surface over it. **Properties of Lubricant:** ***viscosity**:* Viscosity is a measure of the resistance to flow or the internal friction of the lubricant. ***Viscosity Index**:* It is used to grade lubricants. Viscosity is inversely proportional to temp. ***Oiliness**:* It is the property of a lubricating oil to spread & attach itself firmly to the bearing surfaces as well as provide lubricity. ***Flash Point:*** Flash point of oil is the min. temp. at which the vapors of lubricating oil will flash when a small flame is passed across its surface. ***Fire Point**:* If the lubricating oil is further heated after the flash point has been reached, the lowest temp. at which the oil will burn continuously for 5 seconds is called fire point. ***Cloud Point**:* It is the temp. at which the lubricating oil changes its state from liquid to solid. ***Pour Point**:* It is the lowest temp. at which the lubricating oil will not flow or totally form wax or solidify. ***Corrosiveness**:* The present of acid (mineral acid, petroleum acid) is harmful to the metal surfaces. ***Oxidation stability**:* It is resistance to oxidation. Due to oxidation the oil will form deposits on the piston rings and lose its lubricating property. ***Cleanliness**:* Lubricating oil must be clean. ***Carbon residue**:* after evaporation of a mass sample of lubricating oil under specific condition may remain as carbonaceous residue. **Types of lubricants:** Lubricants are at following three types. 1\. Solid: graphic, mica etc 2\. Semi solid: grease 3\. Liquid: Lubricants are obtained from animal fat, vegetables and minerals. Lubricants made of animal fat, does not stand much heat. It becomes waxy and gummy which is not very suitable for machines. **Lubrication system:** ***Mist lubrication system:*** -Used where crankcase lubrication is not suitable \- Generally adopted in two stroke petrol engine line scooter and motor cycle. It is the simplest form of lubricating system. ***Wet sump lubrication system:*** Bottom of the crankcase contains oil pan or sump from which the lubricating oil is pumped to various engine components by a pump. \(i) Splash system- oil is stored in an oil sump \(ii) Splash and pressure system- Lubricating oil is supplied under pressure to main \(iii) Pressure feed system- the engine parts are lubricated under pressure feed **Gear system:** -Used for a medium sized diesel engine -It is a forced-feed system of lubrication and uses the oil contained in the bed plate as a reservoir. ***Dry sump lubrication system:*** -Supply of oil is carried in external tank -Oil pump draws oil from the supply tank and circulates it under pressure to various bearings of the engine