Heat Engines PDF

HEAT ENGINES Prepared by Daniel Sierra COURSE The chapter aims to: OBJECTIVES Determine the basic concept of heat engine and its application in agriculture; Discuss the two types of heat engine; Identify the basic parts and functions of...

HEAT ENGINES Prepared by Daniel Sierra COURSE The chapter aims to: OBJECTIVES Determine the basic concept of heat engine and its application in agriculture; Discuss the two types of heat engine; Identify the basic parts and functions of internal combustion engine; Compare the different types of internal combustion engine; Familiarize on engine auxiliary systems; and, Explain the engine operation and maintenance. COURSE Heat Engine OUTLINE External Combustion Engine (ECE) Internal Combustion Engine (ICE) Parts of ICE Classification of ICE Ignition Systems Lubrication Systems Cooling Systems Engines Engine - a machine that converts energy into mechanical motion. Heat engine – a system that converts heat energy of fuels (chemical energy to thermal energy) to mechanical energy Engines Application in agriculture: Tractors are now used for tilling operations, crop establishment and crop maintenance. Different implements are used at different soil conditions and farming operations Aside from tractors, other engines that is used in agriculture includes water pumps, harvesters, and some post harvest machineries. Engines Engines Engines Types of Heat Engine: - External Combustion Engine (ECE) - Internal Combustion Engine (ICE) External Combustion Engine (ECE) It is an engine in which combustion of fuel take place outside of the engine. The heat energy is applied indirectly to a piston by an intermediate medium, usually water vapor. It is generated by burning of fuel and use to convert the water or other low boiling temperature fluid into steam. External Combustion Engine (ECE) Steam engines are widely used before the development of internal combustion engine. The first tractors to hit the market near the turn of the 20th century were hulking masses of steel weighing more than 18,000 kg which were powered by steam. Internal Combustion Engine (ICE) It is an engine in which the fuel and air ignite and burned inside the cylinder and resulting to the transmission of work through the piston. The internal combustion engines replaced the steam engines in the market. Basic engine parts Cylinder part of the engine that provide the space in which the piston operate to draw in the fuel mixture, compress it, and allow it to expand and generate power Basic engine parts Cylinder head It closes in the top of the cylinder, forming the combustion chamber. It also helps in cooling the engine by allowing the coolant to circulate for effective cooling Basic engine parts Cylinder block It is the structural framework of the engine It contains the cylinder and other parts of ICE. It is designed to withstand a variety of temperatures and loads. Basic engine parts Cylinder head gasket seal the cylinders to ensure maximum compression and avoid leakage of coolant or engine oil into the cylinders Basic engine parts Piston assembly composed of piston, piston rings, and connecting rod. piston transfers the pressure of combustion to the piston pin, connecting rod, and crankshaft Basic engine parts Piston assembly Piston the first part to begin movement and to transmit power to the crankshaft as a result of the pressure and energy released by the combustion of the fuel. Basic engine parts Piston assembly Piston rings this is to retain compression and, at the same time, reduce the cylinder-wall and piston- wall contact area to a minimum, thus preventing friction losses and excessive wear. Basic engine parts Piston assembly Piston pin joins the connecting rod to the piston and, at the same time, provide a flexible or hinge-like connection between the two. Basic engine parts Piston assembly Connecting rod serve as connection between piston and crankshaft. Basic engine parts Crankshaft converts the straight-line force from the piston and connecting rod into rotary force Basic engine parts Flywheel heavy, round disk mounted to the back of the crankshaft that helps to keep the crankshaft spinning between power strokes and smooth engine operation  Basic engine parts Valve system The valve train consists of the valves, camshaft and other associated parts. A cylinder has at least two ports or two valves. The intake port or valve allows the fuel mixture to enter the combustion chamber on the intake stroke, while, the exhaust port or valve allows the products of combustion to escape following the explosion and expansion. Basic engine parts Camshaft driven from the crankshaft by a chain drive or by timing gears operates the intake and exhaust valves through cams, cam followers, push rods and rocker arms Basic engine parts Timing gear It is connected by chain, gears or belt to the crankshaft at one end and the camshaft on the other. The marks correspond to degrees of timing from the straight-up timing position of the camshaft and crankshaft. Basic engine parts Spark plug ignites fuel by means of electric spark in gasoline engine Basic engine parts Carburetor Blends air and fuel of gasoline engine in a proper ratio Basic engine parts Fuel injector nozzle or valve through which fuel is sprayed in combustion chamber in diesel engine Classification of ICE According to method of ignition 1. Spark Ignition Engine Also known as Otto cycle engine named after Dr. Nikolaus August Otto. This four-stroke cycle engine utilizes an electric spark produced by spark plug to ignite the compressed air and fuel mixture. The engine uses gasoline, and metering is done by a device called carburetor. Classification of ICE According to method of ignition 2. Compression Ignition Engine Also known as Diesel cycle engine named after Dr. Rudolph Diesel. This engine utilizes the heat of compressed air to ignite fuel as it is being injected inside the combustion chamber. The fuel used is diesel and metering is accomplished by fuel injection system. Classification of Engines Source: UPLB Agricultural Engineering Board Review Materials Classification of ICE According to fuels used 1. Diesel engine (C16H34). These engines use diesel as the fuel. These are used in trucks, buses, etc. 2. Petrol engine (C8H18). These engines use petrol as the fuel. These are used in bikes, sport cars, luxury cars etc. 3. Gas engine. These engines use CNG (CH4) and LPG (C3H8 & C4H10) as the fuel. These are used in some light motor vehicles. Classification of ICE According to number of strokes per cycle Four stroke engine In a four stroke engine piston moves two times up and down inside the cylinder and complete two crankshaft revolutions during single time of fuel burn. It has higher speed compare to two stroke engine. It is generally used in scooters, cars, truck etc. Classification of ICE According to number of strokes per cycle Four stroke engine Classification of ICE According to number of strokes per cycle Four stroke engine 1. Intake Stroke – intake valve is open, air or air-fuel mixture passes through the open valve. Valve closes toward the end of this stroke. 2. Compression stroke - intake and exhaust valve closed, air or air-fuel mixture are compressed as piston moves up. Ignition occurs as piston approaches the end of compression stroke. Spark-Ignition engines – ignited by spark plug Compression-Ignition - ignited due to heat of compression when fuel is injected. 3. Power stroke – intake and exhaust valve are close. Exhaust valve opens before the end of stroke and permits burned gases to escape. 4. Exhaust Stroke – piston moves toward cylinder head forcing the burned gases out through open exhaust valve. At the end of stroke, exhaust valve closes and inlet valve opens for another cycle. Classification of ICE According to number of strokes per cycle Two stroke engine In a two stroke engine a piston moves one time up and down inside the cylinder and complete one crankshaft revolution during single time of fuel burn. It has higher torque compare to four stroke engine. It is used in scooters, pumping sets, etc. Classification of ICE According to number of strokes per cycle Two stroke engine 1. Intake and exhaust 2. Compression 3. Ignition and power Classification of ICE According to number of strokes per cycle Two stroke engine 1. Intake and Exhaust. Air (Compression-Ignition) or fuel-air mixture (Spark- Ignition) is introduced into the engine at the same time the burned gases are being exhausted. This event starts just before the completion of the power stroke and ends just after the start of the compression stroke. 2. Compression. Both valves are close and the air or fuel-air mixture trapped above the piston is compressed as the piston moves towards the cylinder head. This piston movement is one of the strokes in the 2-stroke cycle and occurs during one-half of a crankshaft revolution. 3. Ignition and Power. Ignition occurs towards the end of compression stroke. The expansion of the burning fuel and resulting pressure increase cause the piston to be driven away from the cylinder head during the power stroke. The power stroke is the second stroke in the 2-stroke cycle and occurs during one- half of crankshaft revolution. Classification of Engines Source: UPLB Agricultural Engineering Board Review Materials Classification of ICE According to number of cylinder 1. Single cylinder engine. In this type of engines have only one cylinder and one piston connected to the crank shaft. 2. Multi-cylinder engine. In this type of engines have more than one cylinder and piston connected to the crank shaft. Classification of ICE According to number of cylinder Small engines, stationary engines or engines used in motorcycles and even small cars have one, two or three cylinders. Automotive engines usually have two, four or six cylinders. Marine engines have more than 8 cylinders. Classification of ICE According to number of cylinder Multi-cylinder engine Classification of ICE According to cylinder arrangements Vertical or In-line engine All cylinders of engine arranged in linearly and all of them transmit power to a single crankshaft. Four and six cylinders is popular in automotive industries. Classification of ICE According to cylinder arrangements V Engine V engines have two cylinder banks and one crankshaft. It is literally the assembly of two inline engine arrangement (appear to be in "V" shape). Engines with more than six cylinders adopts this arrangement. Classification of ICE According to cylinder arrangements V Engine V engines have two cylinder banks and one crankshaft. It is literally the assembly of two inline engine arrangement (appear to be in "V" shape). Engines with more than six cylinders adopts this arrangement. Classification of ICE According to cylinder arrangements Opposed cylinder or flat engine Radial engine Opposed piston engine  Classification of ICE According to cylinder arrangements Delta type engine or X Engine H Engine W Engine Napier Deltic engine Classification of ICE According to valve arrangements The types are classified according to the valve arrangement of inlet and exhaust valve in the cylinder head or block. These arrangements are ‘L’, ‘I’, ‘F’ and ‘T’ head-engine. The arrangement follow the letter it represents. Classification of ICE According to valve arrangements L-head engine. The inlet and exhaust valves are arranged side by side and operated by a single camshaft. The cylinder and combustion chamber forms and inverted L. I-head engine. The inlet and exhaust valves are located in the cylinder head. A single valve actuates all the valves. These are mostly used in automobiles. F-head engine. It is a combination of I-head and F-head engines operated by single camshaft. One valve usually inlet valve is in the head and the exhaust valve lies in the cylinder block. T-head engine. The inlet valve located at one side and the exhaust valve on other side of the cylinder. Two camshafts are required to operate, one for the inlet valve and other is for exhaust valve. Classification of ICE According to air intake system 1. Naturally aspirated. Intake of air into cylinder occur by the atmospheric pressure 2. Supercharged engine. Air intake pressure is increased by the compressor driven by the engine crankshaft. 3. Turbocharged engine. In this type of engine, intake air pressure is increased by use of turbine compressor driven by the exhaust gases of burning fuel Classification of ICE According to crankshaft speed 1. Low speed – below 350 rpm 2. Medium speed – 350 to 1000 rpm 3. High speed – over 1000 rpm Ignition System The purpose of the ignition system is to generate a very high volt age from the automobile 12 volt battery , and to send this to each sparkplug in turn, igniting the fuel-air mixture in the engine 's combustion chambers. The ignition switch controls the flow of current between the battery and the ignition system. The coil consists of a metal casing containing two sets of insulated wire windings on a soft-iron central core. It acts as electrical power transformer to produce high voltage needed by spark plugs. The distributor directs the flow of high-tension current from the coil through the rotor arm, and distributes it to each sparkplug in turn. Ignition System Types of ignition system: Distributor automotive ignition system connect to camshaft with gears. The cam open and close the points of distribution of the current. Distributor-less automotive ignition system (DIS). This system determines spark timing based on two shaft position sensors and a computer. The Crankshaft Position Sensor (CKP) is mounted at the front of the crankshaft or near the flywheel on some vehicles, and the Camshaft Position Sensor (CMP) is mounted near the end of the camshaft Ignition System Types of ignition system: Coil-on-plug (COP) ignition system incorporates all the electronic controls found in a DIS car ignition system. Spark plug cables are eliminated because coil mounts directly on top of the spark plug. Fuel Injection Systems The objectives of the fuel injection system are to meter, atomize and distribute the fuel throughout the air mass in the cylinder. At the same time, it must maintain the required air- fuel ratio as per the load and speed demand on the engine. Fuel Injection Systems Direct injection – injects the fuel directly into the combustion chamber. Indirect injection – injects fuel in the pre-combustion chamber. Lubricating System The fundamental purpose of lubrication is to eliminate friction and the resulting wear and loss of power. Other functions of lubrication are: a) To absorb and dissipate heat; b) To serve as a piston seal c) To act as a cushion to deaden the noise of the moving parts, and absorb shock; and d) To assist in keeping the engine working parts clean and free of dirt, gum, corrosive acids, and other contaminants. Lubricating System Types of Lubrication System Mist lubrication system – It is used in a two-stroke engine. The fuel is mixed with the lubricating oil in the ratio of 3% to 6%.. The fuel is vaporized and the oil (mist form) goes through the crankcase into the engine cylinder. The mist lubricates the engine components. Wet sump lubrication system. An oil pan is present at the crankcase, sump from which the lubricating oil is pumped to various engine components by a pump Lubricating System Types of Lubrication System Dry sump lubricating system is used for the supply of oil and is carried out in an external tank. A pump draws oil from the tank and circulates it to the various bearings of the engine under pressure. Lubrication system Wet sump lubricating system Engine Cooling System Types of engine cooling system Indirect cooling system (water-cooled engine). Water is used as a coolant or cooling medium. Water circulates to interconnected coolant channels pumped driven by the crankshaft. The water is cooled by a heat exchanger called radiator. Direct cooling system (air-cooled engine). Air used as cooling agent through cooling fans. The block and cylinder head are made with deep fins on the outside. Engine Cooling System Types of engine cooling system Direct cooling system (water-cooled engine). Water is used as a coolant or cooling medium. Water circulates to interconnected coolant channels pumped driven by the crankshaft. The water is cooled by a heat exchanger called radiator. Indirect cooling system (air-cooled engine). Air used as cooling agent through cooling fans. The block and cylinder head are made with deep fins on the outside. Engine Cooling System Air-cooled engine cooling systems Water-cooled engine cooling systems