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INTERNAL COMBUSTION ENGINE
INTRODUCTIONGroup 1
Engine Definition
Historically : Any machine that does work, no matter how it is powered (eg. wind mills, water wheels)
Origin of word "engine" - Latin and Greek roots of invention.
Modern : Prime movers that operate automatically/continuously to convert some form of energy into useful mechanical power.
Heat Engine History (Early 19th)Sadi Carnot (1824) - Essentially stated the first and
second laws of thermodynamics.James Joule (1850) - Measured the fixed ratio
between work and heat; defining the first law.Wm. Rankine (1889) - Wrote the first formalized
thermodynamics textbook; defining the second law - "absolute" temperature scale.
Alternatives to steam engines had been developed in the 19th century (1800s).
Mid 19th CenturyDespite of generally good
recoed of engineering development, steam engine was not satisfactory for all purposes - due to poor efficiency and other disadvantages.
Therefore, search for new engine started.
Opportunity presented by new fuel, "gases" from cooking ovens.
Stanley Steamer
History of IC Engine
1800’s - Nikolaus Otto is considered the inventor of IC engine and founder of the industry.
1876 – Otto developed a 4-stroke engine, which often referred as Spark Ignition as it needs spark to ignite the fuel-air mixture.
1864 – 1878 – Otto and Langen developed the Otto Langen Atmosphere engine.
Limited design, poor power & fuel consumption, noisy
Early Attempts Impacts of IC Engine – almost all transportation powered
by IC engine (Spark ignition).1900’s – IC Engine is replaced with Steam Engine, with
same working principle
1897 – Rudolph Diesel developed the Diesel cycle; also known as compression ignition engine (No spark plug)
Diesel engine - noisy, large, slow, single-cylinder engines, however, it is generally more efficient than spark ignition engines.
1920’s - multicylinder compression ignition engines, used in today automobile and trucks.
Background of IC Engine “IC Engine is a heat engine that converts chemical
energy in a fuel into mechanical energy, usually made available on a rotating output shaft”.
Some basic activities of IC engine includes the following: A working fluid Injecting heat to fluid Recover a great amount of work Return to initial state by removal of some heat
Internal Combustion Engine
Petrol engine Gas engine
Closed system Open system
Background of IC Engine
Basic Process of IC Engine
1) Ingest a mixture of fuel and air
2) Compress it
3) Cause it to react, thus effectively adding heat through converting chemical energy into thermal energy
4) Expand the combustion products
5) Eject the combustion products and replace them with a new charge of fuel and air
Basic Process of IC Engine
1) Type of IgnitionSpark Ignition
Generally homogeneous mixture (air-fuel mixture)
Ignition occurs with the presence of spark plug
Controlled energy released Intake air throttled Limited variation in A/F
ratio Distinct fuel requirements Relatively low cost High efficiency
Compression Ignition Non-homogeneous
mixture Ignition due to high
temperature No throttling of air intake Wide range of A/F ratio Needs high compression
ratio (no knock limitation)
Classification of IC Engine
1) Type of IgnitionSpark Ignition
Generally volatile fuel (gasoline); does not ignite spontaneously at lower temperatures
Lower compression ratio (knock limited)
Lighter construction; higher rpm
High fuel consumption Turbocharger; optional for
high performance engines
Compression Ignition
Generally distillate oil (diesel); must ignite at lower temperatures
Heavier construction; limited rpm
Low fuel consumption Turbocharger is
necessary except for small diesel engines
Four Stroke Engine CycleFour Stroke Spark Ignition
Air-fuel mixture introduced into cylinder through intake valve (Stroke 1)
Air-fuel mixture is compressed (Stroke 2)
Combustion (at constant volume) occurs and product gases expand producing work (Stroke 3)
Product gases pushed out of the cylinder through the exhaust valve (Stroke 4)
Four Stroke Compression Ignition
Air is introduced by intake valve into the cylinder (Stroke 1)
Air is compressed (Stroke 2) Combustion (at constant
pressure) occurs and product gases expand producing work (Stroke 3)
Product gases pushed out of the cylinder through the exhaust valve (Stroke 4)
Four Stroke Spark Ignition
Four Stroke Compression Ignition
Four Stroke Engine Cycle
Two Stroke Cycle
In a two-stroke engine all the processes are the same but the cycle is completed in two strokes of the piston.
Since there is one power stroke per revolution, one would expect the power output of a 2-stroke engine to be twice that of a 4-stroke engine for the same displacement.
* Power delivered to the crankshaft on every revolution
compressed, combustion initiated at the end of the stroke
Stroke 2:Combustion products expand doing work and then exhausted
Stroke 1:Fuel-air mixture is introduced into the cylinder
Advantages of the two stroke engine
Power to weight ratio is higher than the four stroke engine since there is one power stroke per crank shaft revolution.
Simple valve design Most often used for small engine applications such as lawn
mowers, marine outboard engines, motorcycles….
Disadvantages of the two-stroke engine: Incomplete scavenging or to much scavenging Burns oil mixed in with the fuel
Valve Location Valves in Head (overhead valve), also called I Head
Engine. Valve in Block (Flat head), also called L Head Engine or
T Head Engine. One valve in Head and one valve in Block, also called F
Head engine.
F Head Engine T Head Engine OverHead Engine
Basic Design Reciprocating Engines Linear motion of piston in a cylinder and
conversion of linear into rotary motion using crankshaft.
Advantages- better sealing of high pressure gases ease of lubrication lower surface area less wear on rings/seals
Disadvantages- reciprocating mass and force unbalance vibrations lower power density (based on mass) larger physical size
Rotary
Rotary motion of rotor-direct output at the shaft. Advantages:
compact size power plant higher power density smooth vibration-free operation lower height
Disadvantages: sealing of high pressure gases and leakage cost and durability of seals lubrication of seals larger surface area
Wankel Engines
No valves needed Continuous motion less vibration Leaks through seals low compression ratio pollution (high levels of
HC and CO)
Position and Number of Cylinders of Reciprocating Engines
Single Cylinder. In-Line V Engine Opposed Cylinder Engine W Engine Opposed Piston Engine Radial Engine
NUMBER OF CYLINDERSSingle-cylinder engine gives one power stroke per
crank revolution (2 stroke) or two revolutions (4 stroke). The torque pulses are widely spaced, and engine vibration and smoothness are significant problems. Used in small engine applications where engine size is more important
Multi-cylinder engines spread out the displacement volume amongst multiple smaller cylinders. Increased frequency of power strokes produces smoother torque characteristics. Engine balance (inertia forces associated with accelerating and decelerating piston) better than single cylinder.
Cylinder Arrangements Most common :
In-line 4-cylinder
V-6
V-8
Air Intake Process
Naturally Aspirated Supercharged Turbocharged Crankcase Compressed
Super Charger and Turbo Charger
Supercharger and Turbocharger are devices used to increase the power of an IC engine by raising the intake pressure in order to make more fuel to be burned per cycle.
Knock or autoignition phenomenon limits the amount of precompression.
Supercharger An air compressor used for
forced induction of an internal combustion engine.
The greater mass flow-rate for more oxygen to support combustion, which allows more fuel to be burned and more work to be done per cycle, increasing the power output of the engine.
Turbocharger
gas compressor used for forced induction of an internal combustion engine.
turbocharger increases the pressure of air entering the engine to create more power.
It has the compressor powered by a turbine.
Super Charger
They suck engine power simply to produce engine power. They’re run off an engine belt connected to the crankshaft, so superchargers are significantly less efficient
For lag this is where the supercharger has its biggest advantage. Since it is powered by a belt, it always produces boost, even at low RPM.
Turbo Charger
For efficiency the turbocharger should be more economical as it operates through energy created by exhaust gases that would otherwise be lost.
The turbo Needs to spool up its turbine before making boost, which creates lag.
The bigger the turbo the higher the lag.
Classification of Internal Combustion Engine
Method of Fuel Input for SI Engine • Carburetted • Multipoint Port Fuel Injection • Throttle Body Fuel Injection
Fuel-Air Mixing
In spark ignition engines the air and fuel are usually mixed prior to entry into the cylinder.
The ratio of mass flow of air to the mass flow of fuel must be held roughly constant at about 15 for proper combustion.
Initially a purely mechanical device known as a carburettor was used to mix the fuel and the air.
Most modern cars use electronic fuel-injection systems.
Basic CarburettorThe carburettor has
two swivelling valves above and below the venturi. At the top, there's a valve called the choke that regulates how much air can flow in. If the choke is closed, less air flows down through the pipe and the venturi sucks in more fuel, so the engine gets a fuel-rich mixture.
Fuel Injection SystemA fuel injector is nothing but an Electronically Controlled Valve.
It is supplied with pressurized fuel by the fuel pump in your car, and it is capable of opening and closing many times per second.
When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing the pressurized fuel to squirt out through a tiny nozzle. The nozzle is designed to atomize the fuel to make as fine a mist as possible so that it can burn easily.
The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open. This is called the pulse width, and it is controlled by the ECU.
The injectors are mounted in the intake manifold so that they spray fuel directly at the intake valves. A pipe called the fuel rail supplies pressurized fuel to all of the injectors.
In order to provide the right amount of fuel, the engine control unit is equipped with a whole lot of sensors.
Diesel Fuel Injection System
With diesel engines fuel is sprayed directly into the cylinders power is varied by metering the amount of fuel added (no throttle)
Diesel fuel injection systems operate at high-pressure.fuel pressure must be greater than the compression pressureneed high fuel jet speed to atomize droplets small enough for rapid
evaporation
Direct Injection (DI) Engine
Hybrid engines that combines the best features of SI and CI engines:operate at optimum compression
ratio (12-15) for efficiency by injecting fuel directly into engine during compression (avoiding knock associated with SI engines with premixed charge)
ignite the fuel as it mixes (avoid fuel-quality requirement of diesel fuel)
control engine power by fuel added (no throttling no pumping work)
Need bowl in piston design with high swirl in order to achieve rapid fuel-air mixing
Direct-Injection Stratified-Charge Engines Create easily ignitable fuel-air mixture at the spark plug and a
leaner fuel-air mixture in the rest of the cylinder. Lean burn results in lower emissions.
Classification of Internal Combustion Engine
Fuel Used
GasolinDiesel Oil of Fuel OilGas, Natural Gas,
MethaneLPGAlcohol – Ethyl,
MethylDual FuelGasohol
Application
Automobile, Truck, Bus
LocomotiveStationaryMarineAircraftSmall Portable,
Chain Saw, Model Airplane
Type of CoolingAir Cooled.Liquid Cooled,
Water Cooled.
What are the five basic parts of any engine?
Cylinder Head Function
The cylinder head is made up of many channels or passageways. These passageways are used as a conduit to enable air and fuel, a fluid mixture vital to efficient engine operation, to reach the combustion chamber. Exhaust fumes also exit the combustion chamber and reach the exhaust valve via these passageways.
Cylinder Function
A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block
Cylinder Arrangement
Flat Inline
V
Piston Function
It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod.
Connecting Rod Function
The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston moves and the crankshaft rotates.
Connecting rods are commonly made from cast aluminum alloy and are designed to withstand dynamic stresses from combustion and piston movement.
Crankshaft Function
The crankshaft transforms the linear motion of the pistons into a rotational motion that is transmitted to the load.
Other important components Spark Plug
To produce the sparks necessary to ignite the gas and air in the engine, initiating a combustion reaction that provides energy to run the engine
Valves
Engine valves are located in the cylinder head. The main function of the engine valves is to let air in and out of the cylinders. That air is used to help ignite the fuel which will drive the pistons up and down.
There are two types of engine valves; intake and exhaust valves.
Intake valves: Let air in
Exhaust valves: To let exhaust air out
Air Cleaner Function
Prevents abrasive particulate matter from entering the engine's cylinders, where it would cause mechanical wear and oil contamination.
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