Module 1. Classification of Farm Power Sources
Module 2. Classification of IC Engines & Therm...
Module 3. Performance Characteristics
Module 4. Engine Components
Module 5. Engine Operating System
Module 6.:Engine Fuel System
Module 7. Engine Governor
Module 8. Engine Cooling & Lubrication system
Module 9. Engine Ignition System
LESSON 30 COMPRESSION IGNITION – COMPONENTS & FUNCTION
Compression ignition system
Diesel engines are compression ignition engines in which no external component is required for igniting the fuel. The air sucked by the engine during the downward motion of the piston in the suction is compressed by the piston when it moves upward during the compression stroke. With compression, the temperature of air rises to such a high level that when atomized fuel (diesel) is injected into the combustion chamber through the nozzles (injectors) the fuel is ignited.
To initiate the ignition in first power stroke, electrical system is required in diesel engines also which comprises of a battery and starting motor. An electric current of 500 amperes at 12 to 24 volts from the battery is provided to the starting motor which further actuates the cranking of piston and generates the first power stroke. If the engine does not start in the first attempt, subsequent attempts are made to make the connections between battery and starting motors but continuous and frequent attempts are to avoided damage to the battery and motor. Once the engine is started, the battery gets disconnected from the motor and power strokes come in continuation as per the firing orders in multiple cylinders. However, in single cylinder engine, the flywheel restores sufficient energy to complete the engine cycle. Sometimes glow plugs are also provided in the diesel engines to heat the air entering into the cylinder through inlet manifolds, particularly in winters or in the excessive cold areas. These glow plugs are connected with the battery. Following are the different types of compression ignition diesel engines.
i) Using electric motor driven by battery
ii) Starting by hand cranking using rotating lever
Electric motor with battery is most commonly used method in small, medium and large sized tractors. Whereas, hand cranking is used for small and stationary, single cylinder engines.
Battery Ignition System
Tractors these days are provided with a battery and starting motor to initiate the engine ignition process. Electric current from the battery is generated and it is used to run the starting motor which further helps in initial cranking and hence ignites the fuel in engine. Once, the fuel is ignited in the engine, the starting motor gets disconnected from the engine.
Battery : Battery used in tractors is usually of three to six cells which develop around 2.2 volts each. Each cell is having positive and negative plates which are separated by the separators. Positive plates are made of lead and antimony and negative plates are generally made of spongy lead. Wooden or rubber material is being used to make separators. A mixture of sulphuric acid and distilled water is used as electrolyte with specific gravity of 1.280 when it is fully charged and it comes down to 1.150 or below when the battery gets fully discharged. The battery should be charged regularly and maintained properly by keeping the desired level (above the plate) of electrolyte in the battery case/body. The terminals of battery should be kept clean always.
Starting motor : 12 or 24 volts motors are used in tractors (diesel engines) which have a drive to actuate automatic engagement of pinion with the engine flywheel ring. This engagement of pinion with the ring gear initiates the engine cranking. Once the engine is started, the pinion is disengaged from the ring gear. The motors should generate sufficient power to crank the engine by moving the piston against heavy loads. Positive meshing of pinion and ring gear is must to crank the engine otherwise multiple attempts made continuously or in a short interval of time leads to discharge of battery.