Course Outline
• Boiler Types:Fire tube and water tube designs; Boiler fuels; Mountings and Accessories.
• Flow of Steam Through Nozzles: Steam turbines; impulse and reaction types;
classification of turbines; backpressure and extractive turbines.
• Air-conditioning and Ventilation:Basic heat transfer and mass transfer; principles of air conditioning; Comfort and industrial air conditioning; Application to textile industry;
refrigeration equipment; primary and secondary refrigerants; ventilation equipment.
• Water Supply and Sewerage: Sources of water; Demand for water, maximum demand, estimation of demand. Wells of different types; flow of water into wells; infiltration
galleries; water intake, Services reservoirs and water towers; service connection; valves and other appurtenances; cleaning of pipes; pumps for water supply, Different types of pipes; lying of pipes; tracking of leakages.Quality of water; chemical analysis; sampling;
microscopic examination
Reference Books:
A text book of Thermal Engineering by R.S. Khurmi and J.K GuptaMachine &
Engine
Definition
A machine is basically a tool that consists of one or more parts, and uses energy to meet a particular goal.
An engine is a device which transforms the chemical energy of a fuel into thermal energy and uses this energy to produce mechanical work.
Difference
Machine is a device which converts any available form of energy into useful work where as engine is a device which converts thermal energy into useful work.
Heat Engine
In thermodynamics and engineering, a heat engine is a system that converts heat or thermal energy—and chemical energy—to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state
temperature to a lower state temperature.
CLASSIFICATION OF HEAT ENGINES
Based on combustion of fuel:
(i) External combustion engine (ii) Internal combustion engine.
Based ignition of fuel
1. Spark ignition engine (Carburetor type engines)
2. Compression ignition engine ( injector type engines) Based on working cycle
3. Four stroke cycle engine
4. Two stroke cycle engine
CLASSIFICATION OF HEAT ENGINES
Based on fuel used
1.Diesel engine : Diesel is used as fuel 2.Petrol engine : Petrol is used as fuel
3.Gas engines : propane, butane or methane gases
are used
Internal Combustion Engine
Internal-combustion engine, any of a group of devices in which the reactants of
combustion (oxidizer and fuel) and the products of combustion serve as the working
fluids of the engine. Such an engine gains its energy from heat released during the
combustion of the non-reacted working fluids, the oxidizer-fuel mixture.
Working of ECE
Self study: Difference between ICE and ECE
Main Components of an
ICE
Some
Terminology
• Top-Dead-Center (TDC): The highest point in a cylinder that a piston head reaches.
• Bottom-Dead-Center (BDC): The lowest point of a cylinder that a piston head reaches.
• Bore: Diameter of the cylinder.
• Stroke Length: Movement distance of the piston from one extreme position to the others (distance from TDC to BDC).
• Clearance Volume: Minimum volume in the combustion chamber with the piston at TDC.
• Displacement Volume: Volume displaced by the piston as it travels through one stroke.
Some
Terminology
• Spark Ignition (SI): An engine in which the combustion process in each cycle is started by use of a spark plug.
• Compression Ignition (CI): An engine in which the combustion process starts when the air-fuel mixture self-ignites due to high temperature in the combustion chamber caused by high compression.
• Supercharger: A supercharger is an air compressor that increases the pressure or density of air supplied to an internal combustion engine. This gives each intake cycle of the engine more oxygen, letting it burn more fuel and do more work, thus increasing power.
• Turbocharger: A turbine-driven forced induction device that increases an engine’s efficiency and power by forcing extra air into the combustion chamber.
The key difference between a turbocharger and a conventional supercharger is that the supercharger is mechanically driven by the engine, often through a belt connected to the crankshaft, whereas a turbocharger is powered by a turbine driven by the engine’s exhaust gas.
Compared to a mechanically driven supercharger, turbochargers tend to be more efficient, but less responsive.
Engine Subsystem
TWO STROKE CYCLE
ENGINE
TWO STROKE CYCLE ENGINE
Top of Upstroke - Compression
The piston has passed Bottom Dead Centre (BDC) and is now rising. The inlet and exhaust ports are both
covered, so the fuel-air mixture in the combustion chamber is being pressurised and is heating up. At the same time, a vacuum is developing in the crankcase, so a fresh charge of fuel-air is being drawn into the crankcase from the carburettor. As the piston rounds TDC, a high voltage discharge from the spark plug ignites the mixture in the combustion chamber.
• Top of Downstroke - Ignition/Power
With both ports still closed, the pressure of the expanding gases forces the piston down again. The pressure in the crankcase is already rising. Later in the downstroke the exhaust port will be uncovered, allowing the spent gases to escape. Very shortly after that the inlet/transfer port will also be uncovered, which takes the engine back to where it was at the start of the cycle.
Working Principle of Four Stroke Petrol Engine
• Intake Stroke: The intake valve opens at the beginning of the stroke. The piston starts to move downward form TDC to BDC and creates a vacuum inside the cylinder. Mixture of air and vaporized fuel is being pushed by atmospheric pressure into the cylinder through the intake valve.
• Compression Stroke: The intake valve closes at the beginning and the piston starts to move
on upward direction form BDC to TDC. This motion compresses the charge and increase the
temperature and pressure inside the engine cylinder.
Working Principle of Four Stroke Petrol Engine
• Power Stroke: The piston reaches the top of its travel on the compression stroke, an electric spark is produced at the spark plug. The spark ignites the air/fuel mixture. The mixture burns rapidly and cylinder pressure increases to as much as 600 psi. All of this pressure against the piston forces it down in the cylinder. Through connecting rod it moves to crankshaft and the crankshaft starts to rotate due to the force.
• Exhaust Stroke: At the beginning of this stroke the exhaust valve opens and the piston starts to move upward, from BDC to TCD. This causes a high pressure inside the engine cylinder. Due to this pressure exhaust gas moves out of the cylinder and it becomes ready to start another cycle.
SI Engine
The term spark-ignition engine refers to internal combustion engines, generally petrol engines, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug.
CI Engine
The diesel engine (correctly known as a compression-ignition or CI engine) is an internal
combustion engine in which ignition of the fuel that has been injected into the combustion chamber is caused by the high temperature which a gas achieves (i.e. the air) when greatly compressed
Valve Timing Diagram
• For a successful run of an engine the precise timing of opening and closing of inlet and exhaust valves
and exact ignition timing is important.
• The diagram that shows the timing of valve opening, closing and ignition time at different crank angle is called valve timing diagram.
Ideal Valve Timing Diagram
• TDC: Top dead center
• BDC: Bottom dead center
• IVO: Inlet valve open
• IVC: Inlet valve close
• EVO: Exhaust valve open
• EVC: Exhaust valve close
Valve Timing Diagram
Actual Valve Timing Diagram (SI &
CI)
• TDC: Top dead center
• BDC: Bottom dead center
• IVO: Inlet valve open
• IVC: Inlet valve close
• EVO: Exhaust valve open
• EVC: Exhaust valve close
• IS: Ignition start
• FVO: Fuel valve open
• FVC: Fuel valve close
SI Engine
CI Engine
How to calculate Engine capacity ?
