Heat Engines 1 External Combustion Engines steam engine
Heat Engines 1. External Combustion Engines – steam engine 2. Internal Combustion Engines – automobile engine What is I. C engine? The internal combustion engine is a heat engine in which the burning of a fuel occurs in a confined space called a combustion chamber. This exothermic reaction of a fuel creates gases of high temperature and pressure, which are permitted to expand.
Classification of I. C Engines 1. According to the type of fuel used (a) Petrol Engines (b) Diesel Engines (c) Gas Engines 2. According to the method of igniting the fuel (a) Spark Ignition Engines (S. I Engines) (b) Compressed Ignition Engines (C. I Engines) 12/12/2021
3. According to the number of strokes per cycle (a)Four Stroke cycle Engines (b)Two Stroke cycle Engines 4. According to the number of cylinder (a)Single cylinder engines (b)Multi cylinder engine
IC Engine Parts 1. Cylinder Head 2. Cylinder Block 3. Piston 4. Connecting Rod 5. Crankshaft 6. Crank Case and Sump 7. Piston rings
Cylinder: It is the one of the most important parts of the engine in which combustion takes place and piston moves to and froth. The engine cylinder has to withstand a high pressure (more than 50 bar) and temperature (more than 2000˚C). Cylinder Head: It is fitted on the end of the cylinder, and act as cover to close the cylinder bore. It contains inlet valve for admitting fresh charge and exhaust valve for removing the burnt gases after expansion. Apart from this, it also contains spark plug for petrol engine and fuel injector for diesel engine. Piston: Its function is to transmit force exerted by the burning of charge to the connecting rod. Piston rings: They are provided to make air tight seal at the upper portion of the piston and to make seal at the lower to prevent leakage of the lubricating oil into the cylinder. Connecting Rod: It is used to transmit force from piston to the crankshaft. Crankcase: It holds the cylinder and crankshaft. Flywheel: It is a big wheel, mounted on the crankshaft whose function is to maintain a constant speed of the crankshaft.
Engine valves
Piston assembly
Crank shaft assembly
Stages of operations: Suction stroke Compression stroke Expansion stroke Exhaust stroke Two stroke and Four stroke cycle engine: In two stroke engine, suction & compression is completed in one stroke and expansion & exhaust is completed in one stroke. In four stroke, each stage is completed in individual stroke.
Four Stroke I C Engine In a four stroke I C Engine, one cycle of operation is completed in four strokes of the piston in the engine cylinder The strokes are: 1. Suction (Induction) stroke 2. Compression Stroke 3. Power Stroke 4. Exhaust Stroke
The four-stroke engine
1. Induction Stroke • Engine pulls piston out of cylinder • Low pressure inside cylinder • Atmospheric pressure pushes fuel and air mixture into cylinder • Engine does work on the gases during this stroke
2. Compression Stroke • Engine pushes piston into cylinder • Mixture is compressed to high pressure and temperature • Engine does work on the gases during this stroke
3. Power Stroke • Mixture burns to form hot gases • Gases push piston out of cylinder • Gases expand to lower pressure and temperature • Gases do work on engine during this stroke
4. Exhaust Stroke • Engine pushes piston into cylinder • High pressure inside cylinder • Pressure pushes burned gases out of cylinder • Engine does work on the gases during this stroke
Scavenging is the process of pushing exhausted gas-charge out of the cylinder and drawing in a fresh draught of air or fuel/air mixture for the next cycle Supercharging: The method of increasing the inlet charge density (air for diesel and air-fuel mixture for petrol engine) is called supercharging. Rating of SI engine fuel: Knocking tendency of a fuel is measured by Octane number. Octane Number: The percentage (by volume) of iso-octane in a mixture of isooctane(100) and n-heptane (0)which gives the same knocking tendency of the given fuel is known as octane number of the given fuel. Greater the octane number less the knocking tendency.
Rating of CI engine fuel: • Knocking tendency of a fuel in CI engine is measured by Cetane number: It is defined as the percentage (by volume) of cetane in a mixture of cetane and alpha-methyl-napthalene that produces the same ignition lag as the fuel being tested. Greater the cetane number less the knocking tendency
Comparison of Petrol and Diesel Engines PETROL ENGINE DIESEL ENGINE 1. Works on Otto Cycle 1. Works on Diesel Cycle 2. Fuel-air mixture is admitted 2. Fuel is injected at the end of during suction stroke compression stroke 3. Spark ignition 3. Compression ignition 4. Low compression ratios (6 to 10) 4. High compression ratios (10 to 20) 5. Lower engine efficiency 5. Higher engine efficiency 6. Higher fuel consumption 6. Lower fuel consumption 7. Lower engine vibrations and noise 7. Higher engine vibrations and noise 8. High running cost 8. Low running cost 9. Light duty application 9. Heavy duty application
AIR SYSTEM FOR PETROL ENGINE
Fuel Systems Petrol Engines
Fuel Injector
Fuel Injection system for diesel engine: • Air injection method • Solid injection method Cooling System for I. C engines: • Air cooling system (e. g motor cycle, scooters, three wheelers and aero planes) • Water cooling system (Car, bus, trucks etc).
Testing of I. C engine Brake power: The power at the engine output shaft. Indicated power: The power produced in the engine cylinder due to the burning of fuel. Mean effective pressure: The imaginary pressure acted on piston during expansion. Air-fuel ratio: The ratio of mass of air to the mass of fuel. Specific fuel consumption: It is defined as the amount of fuel consumed per unit power developed.
Blower A machine for supplying air at a moderate pressure, as to supply forced drafts or supercharge and scavenge diesel engines. What are the major difference between fan and blower? Generally blowers are more effective at higher pressures and fans at lower pressures. This is why blowers are typically used in duct distribution methods.
In practice - it is common to differentiate between Pumps compressors blowers fans as summarized below: Pumps A pump is a machine for raising a liquid - a relatively incompressible fluid - to a higher level of pressure or head. Compressors A compressor is a machine for raising a gas - a compressible fluid - to a higher level of pressure. Blowers A blower is a machine for moving volumes of a gas with moderate increase of pressure. Fans A fan moves large amounts of gas with low increase in pressure.
Fig: A Centrifugal Pump Fig: An Air compressor
Fig: Reciprocating Pump(Positive Displacement Pump)
CONTRUCTION DETAILS OF A RECIPROCATING PUMP: Components of reciprocating pumps: a) Piston or plunger: – a piston or plunger that reciprocates in a closely fitted cylinder. b) Crank and Connecting rod: – crank and connecting rod mechanism operated by a power source. Power source gives rotary motion to crank. With the help of connecting rod we translate reciprocating motion to piston in the cylinder. c) Suction pipe: – one end of suction pipe remains dip in the liquid and other end attached to the inlet of the cylinder. d) Delivery pipe: – one end of delivery pipe attached with delivery part and other end at discharge point. e) Suction and Delivery value: – suction and delivery values are provided at the suction end and delivery end respectively. These values are non-return values. WORKING OF RECIPROCATING PUMP Operation of reciprocating motion is done by the power source (i. e. electric motor or i. c engine, etc). Power source gives rotary motion to crank; with the help of connecting rod we translate reciprocating motion to piston in the cylinder (i. e. intermediate link between connecting rod and piston). When crank moves from inner dead centre to outer dead centre vacuum will create in the cylinder. When piston moves outer dead centre to inner dead centre and piston force the water at outlet.
The three basic types of air compressors are 1. Reciprocating 2. rotary screw 3. rotary centrifugal Pumps are in general classified as 1 Centrifugal Pumps (or Roto-dynamic pumps) and 2. Positive Displacement Pumps.
Centrifugal Pumps (Roto-dynamic pumps) The centrifugal or roto-dynamic pump produce a head and a flow by increasing the velocity of the liquid through the machine with the help of a rotating vane impeller. Centrifugal pumps include radial, axial and mixed flow units. Centrifugal pumps can further be classified as • end suction pumps • in-line pumps • double suction pumps • vertical multistage pumps • horizontal multistage pumps • submersible pumps • self-priming pumps • axial-flow pumps • regenerative pumps
Positive Displacement Pumps The positive displacement pump operates by alternating of filling a cavity and then displacing a given volume of liquid. The positive displacement pump delivers a constant volume of liquid for each cycle against varying discharge pressure or head. The positive displacement pump can be classified as: • Reciprocating pumps - piston, plunger and diaphragm • Power pumps • Steam pumps • Rotary pumps - gear, lobe, screw, vane, regenerative (peripheral) and progressive cavity
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