Lecture 1 Flashcards
In thermodynamics and engineering, is a device which transforms
the chemical energy of a fuel into thermal energy and uses this energy to produce useful mechanical work
The term is also used to all devices that produces useful
work either from combustion of a fuel or heat transfer through heat exchangers.
heat engine
Classification of Heat Engine
Heat engine may be characterized by the following:
- It absorbs heat energy from higher temperature source
- Some of heat absorbed will be converted into mechanical work
- The remaining heat that is not converted into mechanical workwill be rejected to
the lower temperature sink
Heat Engine is majorly categorized into two types
- External combustion engine
- Internal combustion engine
In this engine, the combustion process takes place outside the cycle boundaries and the thermal energy (heat) is transfer to the working fluid through heat transfer. It uses different source for different type of cycle such as furnace, heat recovery steam generator, geothermal well and nuclear reactor
- Power Plant that uses steam as working fluid i.e. coal power plant, geothermal power
plant, nuclear power plant, combined cycle power plant, solar power plants, etc. - In a closed cycle gas turbine, which uses secondary fluid such as helium, hydrogen,
air or argon etc.
External Combustion Engine
In this engine, the combustion takes place within the cycle boundaries and used as the direct motive force. In an internal combustion engine, to generate useful mechanical energy, the thermodynamic expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable component of the engine.
Internal Combustion Engine
Comparison between external combustion engine and internal combustion engine.
- Combustion of air-fuel is outside the engine cylinder or outside the system boundaries vs inside the engine cylinder.
- The engines are running smoothly and silently vs noisy operated engine.
- Heavy and cumbersom vs lightweight and compact.
- It can use cheaper fuels including solid fuels vs high grade fuels, mostly liquid and gaseous fuels.
- Higher requirement of water for rejection of heat through cooling system vs Lesser requirement for water since air can also be used as a cooling medium.
- Takes a lot of time in engine start-up vs Quick engine start-up.
- Self-starting vs not self-starting
According to the cycle of operation or the number of stroke per cycle-
(a) Two stroke engine
(b) Four stroke engine
According to the motion of movable components
(a) Reciprocating engine (Use of cylinder piston arrangement),
(b) Rotary engine (Use of turbine)
According to the valve location
(a) I head Engine – valves are located at cylinder head or usually called
Overhead Valve
(b) L head Engine/ T head Engine – valves are located at cylinder block
or usually called as Flat head Valve.
(c) F head Engine – one valve is positioned on cylinder head and one in the cylinder block
According to the type of fuel used-
(a) Petrol engine
(b) Diesel engine
(c) Gas engine (CNG, LPG)
(d) Alcohol engine (ethanol, methanol etc)
According to the method of igniting the fuel-
(a) Spark ignition engine (S.I) – igniting the fuel using Spark Plug
(b) Compression ignition engine (C.I) – self-ignites due to high
temperature in the combustion chamber caused by high
compression
According to the number of Cylinders
(a) Single Cylinder
(b) Multi-Cylinder
According to the working cycle-
(a) Otto cycle (constant volume cycle) engine,
(b) Diesel cycle (constant pressure cycle) engine
(c) Dual combustion cycle (combination of Otto and Dual cycle) engine,
(d) Open-Brayton cycle
According to the positioning or arrangement of Cylinders (for reciprocating multicylinder engine)
- In-line or straight
- V engine
- W engine
- Opposed Cylinder
- Opposed piston
- Radial engine
According to air intake process
(a) Naturally Aspirated.
No intake air pressure boost system.
(b) Supercharged.
Intake air pressure increased with the compressor driven off of the engine crankshaft
(c) Turbocharged.
Intake air pressure increased with the turbinecompressor driven by the engine exhaust gases
(d) Crankcase Compressed.
Two-stroke cycle engine which uses the crankcase as the intake air compressor
According to methods of Fuel Input for SI Engines
(a) Carbureted.
(b) Multipoint Port Fuel Injection. One or more injectors at each cylinder intake
(c) Throttle Body Fuel Injection. Injectors upstream in intake manifold.
According to Application
(a) Automobile, Truck, Bus.
(b) Locomotive
(c) Stationary: Industrial engine and Prime mover for electrical
generators
(d) Marine Propulsion
(e) Aircraft Propulsion
(f) Small Portable: Chain Saw, Grass cutter
According to Method governing
(a) Hit and miss governed engines,
(b) Quantitatively governed engines
(c) Qualitatively governed engine
Method of Starting
(a) Manual: Rope, crank, kick
(b) Electric: Battery and electric motor
(c) Compressed air
(d) Using of other engine
The first fairly practical gas engine. Brake thermal efficiency up to 5%.
A single-cylinder, two-stroke engine with electric ignition of ilumination gas (not gasoline).
1860 Jean J. Lenoir
Patents a two-stroke internal combustion engine building on Lenoir’s. Patents a practical four-stroke internal combustion engine.
1867 & 1877 Nicolaus A. Otto
Invernted ________’s Ready Motor and went into commercial production, this used constant pressure combustion, and was the first commercial liquid fuelled internal combustion engine.
1872 George Brayton
Invernted ________’s Ready Motor and went into commercial production, this used constant pressure combustion, and was the first commercial liquid fuelled internal combustion engine.
1872 George Brayton
Development of compression ignition engine which is the same _____ engine known today.
1892 Rudolf Diesel
Development of ______ engine which is a type of internal combustion engine using an eccentric rotary design to convert pressure into rotating motion.
1957 Felix Wankel
Also called piston engine. An engine in which the piston moves up and down or back and forth, as a result of combustion in the top of the cylinder.
Reciprocating Internal Combustion Engine
Body of engine containing the cylinders, made of cast iron or aluminum. The block of water-cooled engines includes a water jacket cast around the cylinders. On air-cooled engines, the exterior surface of the block has cooling fins
Block
A rotating lobe of irregular shape or eccentric or offset portion of the shaft (cam). It changes rotary motion of cam shaft to reciprocating or variable motion of valve lifter resting on it.
Cam
– A part which is held in contact with the cam and to which the cam motion is imparted and transmitted to the push rod
Cam follower (valve lifter)
The shaft in the engine which has a series of cam lobes (simply called
cams) for operating the valve mechanisms, driven by gears or sprockets and chain from the crankshaft. It is used to push open valves at the proper time in the engine cycle
Cam shaft
Metal fins on the outside surfaces of cylinders and head of an aircooled engine. These extended surfaces cool the cylinders by conduction and convection.
Cooling fins
The end of the cylinder between the head and the piston
face where combustion occurs.
Combustion chamber
: A link that connects the piston with the rotating crankshaft,
usually made of steel or alloy forging in most engines but may be aluminum in
some small engines.
Connecting rod
A device for converting reciprocating motion of the piston into rotary
motion of the crank shaft
Crank
It houses cylinder and crankshaft of the IC engine and also serves as
sump for the lubricating oil.
Crank case
The main rotating member, or shaft running along the length of the
engine.
The _____ is connected to the engine block with the main bearings. The special steel alloys are used for the manufacturing of the _______. It consists of eccentric portion called crank
Crankshaft
It is the main part of the engine inside which piston reciprocates to
and from. The ordinary engine is made of cast iron and heavy duty engines are
made of steel alloys or aluminum alloys. In the multi-cylinder engine, the cylinders are cast in one block known as cylinder block
• Cylinder
It is the main part of the engine inside which piston reciprocates to
and from. The ordinary engine is made of cast iron and heavy duty engines are
made of steel alloys or aluminum alloys. In the multi-cylinder engine, the cylinders are cast in one block known as cylinder block
• Cylinder
The basic framework of the engine to which the other engine
parts are attached. It includes the engine cylinders and the upper part of the crankcase
Cylinder block
The top end of the cylinder is covered by cylinder head over
which inlet and exhaust valve; spark plug or injectors are mounted.
Cylinder head
Piping system which carries exhaust gases away from the
engine cylinders, usually made of cast iron.
Exhaust manifold
Rotating mass with a large moment of inertia connected to the
crankshaft of the engine.
The purpose of the ____ is to store energy and furnish a large angular momentum that keeps the engine rotating between power strokes and smooths out engine operation.
On some aircraft engines the propeller serves as the ___, as does the rotating blade on many lawn mowers.
Flywheel
Rotating mass with a large moment of inertia connected to the
crankshaft of the engine.
The purpose of the ____ is to store energy and furnish a large angular momentum that keeps the engine rotating between power strokes and smooths out engine operation.
On some aircraft engines the propeller serves as the ___, as does the rotating blade on many lawn mowers.
Flywheel
A pressurized nozzle that sprays fuel into the incoming air on SI
engines or into the cylinder on CI engines.
On SI engines, fuel injectors are located at the intake valve ports on multipoint port injector systems and upstream at the intake manifold inlet on throttle body injector systems. In a few SI engines, injectors spray directly into the combustion chamber
Fuel injector
Small electrical resistance heater mounted inside the combustion
chamber of many CI engines, used to preheat the chamber enough so that combustion will occur when first starting a cold engine. The glow plug is turned off after the engine is started.
Glow plug
Small electrical resistance heater mounted inside the combustion
chamber of many CI engines, used to preheat the chamber enough so that combustion will occur when first starting a cold engine. The glow plug is turned off after the engine is started.
Glow plug
Piping system which delivers incoming air to the cylinders,
usually made of cast metal, plastic, or composite material. In most SI engines, fuel is added to the air in the intake manifold system either by fuel injectors or with a carburetor. Some intake manifolds are heated to enhance fuel evaporation. The individual pipe to a single cylinder is called a runner
Intake Manifold
Oil reservoir usually bolted to the bottom of the engine block, making up part of the crankcase. Acts as the oil sump for most engines.
Oil Pan
: The cylindrical-shaped mass that reciprocates back and forth in the
cylinder, transmitting the pressure forces in the combustion chamber by the burning of charge to the connecting rod then to the rotating crankshaft.
Piston:
Metal rings that fit into circumferential grooves around the piston
and form a sliding surface against the cylinder walls.
These are housed in the circumferential grooves provided on the outer surface of the piston and made of
steel alloys which retain elastic properties even at high temperature.
Piston rings
2 types of Piston rings
Compression ring
is upper ring of the piston which provides air tight seal to prevent leakage of the burnt gases into the lower portion.
Oil ring
is lower ring which provides effective seal to prevent leakage of the oil into the engine cylinder.
In an I-head engine, a device that rocks on a shaft or pivots on a
stud as the cam actuates the push rod causing the valve to open.
Rocker arm
Electrical device used to initiate combustion in an SI engine by
creating a high-voltage discharge across an electrode gap. _______ are usually made of metal surrounded with ceramic insulation.
Some modern _____ have built-in pressure sensors which supply one of the inputs into engine control.
Spark plug
A device that can be opened or closed to allow or stop the flow of a fluid (liquid or gas or vapour) from one to another place.
Valves
A device that can be opened or closed to allow or stop the flow of a fluid (liquid or gas or vapour) from one to another place.
1.____ is responsible for air and fuel flow control while
- _____ is responsible for exhaust gas flow control.
- Intake Valve
- Exhaust Valve
The amount of heat required to raise one gram of water through 1°C i.e.,
from 17 to 18°C.
_____ is unit of heat.
Calorie
The maximum flame temperature attained when the fuel is
burnt.
Calorific Intensity
: The heat value of a fuel, expressed in either BTU per pound or
CHU per pound or kilocalories/kg. The amount of heat produced by burning unit weight of fuel.
Calorific valve (or value dapat?)
: A series of thermodynamic processes through which the
working gas passes to produce one power stroke. The full cycle is intake, compression, power and exhaust.
Combustion Cycle
Pressure in the combustion chamber at the end of the
compression stroke, but without any of the fuel being burned.
Compression pressure
Combustion which occurs without a change in pressure.
In an engine, this is obtained by the slower rate of burning than withconstant volume combustion.
Constant Pressure Combustion
A series of events which continuously repeat in definite order.
In an engine, the cycle constitutes the four operations that complete the working process and produce power.
Cycle
Fuel injection into the main combustion chamber of an
engine.
Engines have either one main combustion chamber (open chamber) or a divided combustion chamber made up of a main chamber and a smaller connected secondary chamber.
Direct Injection (DI)
Fuel injection into the secondary chamber of an engine with a divided combustion chamber
Indirect Injection (IDI)
The products of combustion coming out from an internal combustion engine.
Exhaust Gas
In an engine, the valve port or opening in which the valve
operates and through which the charge or burned gases pass
Port (Cylinder):
A method of cleaning a radiator or an engine cooling system
by flushing in the direction opposite to normal coolant flow.
Reverse flushing
A temperature sensitive device used in a cooling system to adjust
flow of coolant as coolant temperature changes.
Thermostat
In the engine, refers to timing of valves, and timing of ignition, and their relation to piston position in the cylinder.
Timing
The timing of valve opening and closing in relation to.
Valve Timing
A cylinder, hole, or the inside diameter of the cylinder or hole.
May refer to cylinder itself or to diameter of the cylinder. At very small clearance, this is the same with the diameter of the piston face.
Bore (B or D)
To bore out a cylinder larger than its original size
Rebore
: In an engine, the distance that the piston moves from BDC to
TDC or vice versa.
Stroke (S or L)
An engine having the bore and stroke of equal measurements.
(B = S)
Square Engine
Point at which the piston reaches its uppermost or lowermost
position in the cylinder. At these positions, at the end of the stroke, the crank and connecting rod are in a straight line.
Dead center
The piston position at which the piston has moved to
the top of the cylinder and the centre line of the connecting rod is parallel to the cylinder wall
Top Dead Centre (TDC)
Top because this position is at the top of most engines (not always),
and dead because the piston stops at this point. These term is also used even the piston the top dead center is not on the top of the engine e.g., horizontally opposed engines, radial engines, etc.
After TDC. After top dead centre
ATDC
Before top dead center, also called BUDC-before upper dead cente
BTDC
Lowest position of the piston in the cylinder orposition of the piston when it stops at the point closest to the crankshaft.
Some sources call this Crank-End- Dead-Center because it is not always at the bottom of the engine.
Bottom Dead Center (BDC):
After BDC. After bottom dead centre
ABDC
Before Bottom dead center
BBDC
The amount of space between two moving parts or between a moving
and a stationary part, such as a journal and a bearing, piston and cylinder.
Clearance
Total volume of the cylinder.
The sum of Clearance Volume and the Displacement Volume
Cylinder volume (V)
The volume remaining above the piston when the piston is at TDC. The volume of the combustion chamber
Clearance Volume (Vc)
The space swept through by the piston in all cylinders in moving from one end of a stroke to the other.
Volume displaced by the piston as it travels through one stroke. Displacement can be given for one cylinder or for the entire engine (one cylinder times number of cylinders).
Some literature calls this swept volume.
Displacement or Displacement Volume (VD or VS)
The volume of the combustion chamber when the piston is at TDC, measured in cubic centimeters
Combustion Chamber Volume
The ratio between the total volume of the cylinder when the piston is at BDC and the volume when the piston is at TDC.
The ratio between the Cylinder Volume and the Clearance Volume
Compression Ratio (rk)
Ratio of the total volume when the piston is at BDC to the
clearance volume when the piston is at TDC.
Expansion Ratio (re)
in Diesel Cycle, it is the ratio between the volume displacement at constant pressure and the Clearance Volume
Cut-off ratio
The ratio between two pressures at two specific cycle points. These pressure difference may happen due to isentropic compression and heat addition at constant volume
Pressure Ratio (rp):
Mean effective pressure (imaginary) which when assumed to be acting on the piston during the power stroke would result in the given Work output.
Mean Effective Pressure (Pmep)
Rate at which work is done
Power (Po)
A measure of the mechanical power, or the rate at which work is done. One ____ equals 746W
Horse Power (Hp)
Actual usable power delivered by an engine at the crankshaft for driving a vehicle or any other unit. Computed using the engine coupled to a dynamometer.
Brake Horse Power (Bhp)
The twisting force at the end of the crank shaft multiplied by the
distance of this force application from the shaft centre, measured in kilogram meters or Newton meters.
Torque
Revolutions per minute.
Rpm
Speed at which maximum torque occurs.
Brake Maximum Torque (BMT)
Ratio between the amount of fresh charge that actually enters an engine cylinder and the theoretical amount that could enter under ideal conditions.
Volumetric Efficiency (ηV)
Relationship between the power output and the energy in the fuel burned to produce the output.
Thermal Efficiency (ηth)
Ratio of heat equivalent of power output in the form of brake horse power to the corresponding heat input from fuel.
Brake Thermal Efficiency
ICE operation may be categorized mainly into cycle of operation or the number of stroke per cycle (___-stroke and __- stroke) and the method of igniting the fuel (______ and ______)
2 and 4 stroke
Spark Ignition and Compression Ignition
Method of Igniting the Fuel
- Spark Ignition (SI)
- Compression Ignition (CI)
An engine in which the combustion process in each cycle is started by
use of a spark plug. SI engine are often called Gasoline Engines
Spark Ignition (SI)
An engine in which the combustion process starts when the airfuel mixture self-ignites due to high temperature in the combustion chamber caused by high compression.
CI engines are often called Diesel engines, especially in the non-technical community
Compression Ignition (CI)
Comparison of SI engine and CI engine
- Works on Otto cycle vs Works on Diesel Cycle
- Petrol or gasoline or high octane fuel is used vs diesel or high cetance fuel is used
- High self-ignition temperature vs low self ignition temperature
- Fuel and air introduced as a gaseous mixture in the suction stroke vs fuel is injected directly into the combustion chamber at high pressure
- Carburettor used to provide the mixture vs injector and high pressure pump used to supply of fuel
- Use of spark plug for ignition system vs self-ignition by heat of compression
- Theoretical Compression Ratio (rk) is 6 to 10.5 vs 14 to 22
- Higher maximum RPM dure to lower weight. Hence, used in high speed engine application vs lower maximum RPM. Hence, used in low speed engine e.g. heavy equipment trucks, buses, construction equipments etc.
- Maximum efficiency lower due to lower compression ratio vs higher maximum efficiency due to higher compression ratio
- Lighter vs Heavier: Due to higher pressures, it requires large dimension for engine block.
Four-stroke spark ignition engines
In Four-stroke engines, Cycle of operation
completed in four strokes of the piston or two revolution of the piston
Enumerate 1-4
- Suction stroke
- Compression stroke
- Power stroke or Expansion stroke
- Exhaust stroke
In the original two-stroke cycle the compression and power stroke of the four-stroke cycle are carried out without the inlet and exhaust stroke.
These engines complete the cycle for only one revolution of the crankshaft.
Two-stroke engine
What happens in the First and Second Stroke of Two-stroke engines?
- First Stroke:
(a) Expansion Stroke or Power Stroke
(b) Exhaust Blowdown
(c) Intake and Scavenging - Second Stroke:
(a) Compression Stroke.
(b) Combustion
Comparison of a 4-Stroke & 2-Stroke Engine
- two revolution of crankshaft vs one revolution of crank shaft
- One power stroke in every two revolution of crankshaft vs one power strroke in each revolution of crankshaft
- Heavier flywheel because of non-uniform turning movement due to one power stroke in every two revolution of crankshaft vs lighter flywheel because of more uniform turning movement due to one power stroke in each revolution of crankshaft
- Power produce is less vs power produced is twice than the 4-stroke engine for the same size
- Heavy and bulky vs lightweight
- Lesser cooling and lubrication requirements vs greater cooling and lubrication requirements
- Less fuel consumption vs higher fuel consumption
- Uses valve and valve mechanism vs uses ports arrangement
- Higher initial cost vs cheaper initial cost
- Volumetric efficiency is more vs volumetric efficiency less
- Thermal efficiency is high vs thermal efficiency is low.
- It is used where efficiency is important. Ex: cars, buses, trucks, tractors, industrial engines, aeroplanes, power generation. vs It is used where low cost, compactness, and lightweight are important. Ex: lawn mowers, scooters, motor
