Prime Movers Flashcards
Four stroke engines come in these two types
Naturally aspirated or supercharged
Compression ratios of diesel engines
16:1 - 23:1 (gas engines are 6:1 - 13:1)
Diesel engines use these to preheat the combustion chamber
Glow plugs (not needed to keep running)
How is fuel supplied in a Diesel engine
fuel injection (mechanical most common)
How is fuel supplied to a gas engine
Carburetor (atomized) or fuel injection
These gas burning engines are designed to burn different, or combinations of fuels
High-compression gas burning engines
What are the four strokes of a four-stroke engine
Intake (intake valve open), compression (valves closed), power (valves closed), exhaust (exhaust valve open) (done in two revolutions of the crankshaft)
When does ignition take place in a ICE?
BTDC
This provides a smooth transition between power strokes
Flywheel (clutch mounts to this)
At the end of the exhaust stroke where both intake and exhaust valves are open this is called
valve overlap
In a two-stroke engine these two things happen while the piston is at BDC
Intake and exhaust (not during a stroke)
two-strokes are completed in how many revolutions of the crankshaft
one
If a two-stroke does not use exhaust valves or blowers it used this instead
Scavenging valve (in the crankcase)
This supports the pistons and transfers energy of motion
Crankshaft (takes reciprocating motion and turns to rotary)
How is oil supplied to bearings of a 4 stroke
oil holes in crankshaft
This connects the piston to the crankshaft
Connecting rod (wrist pin to piston)
Do gas engines use cylinder liners?
No
This consists of valves, valve springs, rocker arms and rocker arm shaft
cylinder head assembly
The camshaft goes how fast compared to the crankshaft
One half the speed
The engine block is made of
cast iron, cast aluminum
These are powered by exhaust waste gases
turbochargers (speeds of 10k to 100k rpm)
These are mechanical blowers and found in lots of two-stroke engines
superchargers (rotary lobe)
Steam turbines use this and convert it to kinetic energy
superheated steam (400-560C 750-1050F) (200psi - 450psi)
The greater the temperature difference across the turbine, the more _____ it is
efficient
What is each stage of a turbine consist of
a stationary nozzle followed by a rotating blade (staging used to maximize energy of the steam as it flows through)
This controls the amount of steam admitted to the turbine for speed control
Governor (SAV)
in this turbine steam flow is perpendicular to the turbine shaft
Radial flow (no stationary nozzles other than first stage, every set of blades move in opposite direction)
The main use for back-pressure turbines
draft fans, water pumps (low pressure)
This turbine uses high pressure steam to drive the turbine and exhausts to a low pressure system
Back pressure/extraction (steam can be extracted at intermediate pressures)
What does closing an extraction valve do
extracts MORE steam (extraction valve has a check valve)
This is the most efficient steam turbine
Condensing (produces a vacuum at the exhaust, causes largest pressure drop)
What does a condensing turbine use to condense steam
tube and shell heat exchanger used to cool and condense steam
What energy do impulse blades produce
kinetic
What energy do reaction blades produce
potential
In an impulse/reaction turbine which blades are used first
impulse (on higher pressure side)
How are blades of steam turbines attached to the shaft
disc or drum
What does shrouding do
Keeps blades rigid, directs steam, less vibration (wires used on large blading)
Types of bearings used in steam turbines
Journal, thrust, and dummy pistons (balance)
Where are the first nozzles found in a steam turbine
In the steam chest (later stages are in diaphragms)
Nozzles in steam turbines are designed to _______ towards the outlet
converge (inlet larger than outlet)
What do the shaft seals in steam turbines do
keep high pressure steam from leaking into the surrounding area
stop air from being admitted into the turbines
(Carbon and labyrinth)
How are seals lined up in a steam turbine
Gland seal system. Labyrinth first, carbon behind it (low pressure steam supplied to seals at start up)
What removes the non condensible gases in a hot well
steam injectors or small vacuum pump
Order of valves in a steam turbine
Stop valve, throttle valve (emergency trip integrated), governor, extraction, non return on extraction valve, exhaust
What does the throttle valve do
bring turbine up to speed until governor takes over speed control, warms up turbine
What must always be one of the trips for emergency trip valves
overspeed (throttle valve must be closed before trip can be reset)
What supplies hydraulic governors with oil
main oil pump (integral), auxiliary oil pump (electric), emergency oil pump (battery)
What controls the bearing temps in a steam turbine
in-line oil coolers
What is the desired bearing oil outlet temp in a steam turbine
55 - 66 C
The process of turning a turbine until it is cooled is called
barring
What turns a turbine when it is shut down
turning gears (barring gears)
Major difference between a steam and gas turbine
gas turbine has a compressor
Three main sections of a gas turbine
compressor, combustor, turbine
How are gas turbines categorized
Cycle: the path the medium (air) passes
Shaft arrangement: One shaft or two
This gas turbine uses a recuperator and a precooler
Closed cycle
Combustion in a gas turbine works on this principle
flame propagation
This is the hottest part of the system in a gas turbine
flame tube (first to wear out) 900C
Gas turbines have to withstand
the greatest stress from heating and loading
How are the blades cooled in a gar turbine
Convection (compressed air, most common. reduces 300C)
Transpiration (steam)
This is an integral part of the design not auxiliary
How are gas turbine blades shaped
Impulse at the root, reaction at the top
Do gas turbines use mechanical governors
No
How are oil pumps driven in gas turbines
separately from the turbine
These support the field windings and act as a magnetic path between frame and armature
Field poles
The brushes of a DC motor ride on this
Commutator (feeds the external electrical supply into the rotating coils)
This DC motor has high starting torque but poor speed regulation
Series motor - can’t be operated under no load
This DC motor has good speed regulation but low starting torque
Shunt (parallel) - if operating at no load speed will rise very quickly
This DC motor has good starting torques and good speed regulation
Compound
What are the three types of ways to quick stop a DC motor
Dynamic braking
Regenerative braking
Plugging (reversal)
This AC motor is used for heavy loads that run for long periods of time
Synchronous
Types of three phase AC motors
Squirrel cage (Induced, no connection between rotor and stator) Starting torque normal to high
Wound rotor (rotor has insulated windings)
Synchronous (need assistance in starting, can run heavy loads for long periods)
Types of single phase AC motors
Split-phase: (auxiliary winding helps start motor)
Capacitor-start: High starting torque, switch disconnected 3/4 speed
Permanent-split capacitor: No centrifugal switch, low starting torque
Repulsion: Magnetic push, high torque, variable speed
This reduces crankshaft torsional vibration
harmonic balancer
This engine has a larger bore diameter than stroke length
oversquare engine
This engine has a longer stroke than bore diameter
undersquare engine (usually diesel)
The volume remaining above the piston at TDC
Clearance volume
Most engines are this efficient
25-35%
The leakage of burned and unburned gases past the compression rings into the crankcase
Blowby
Low speed engines operate below this rpm
500
Medium 500-1000rpm
High over 1000rpm
These engine types are built with a load as part of the engine
Integral
Running mates apply to
4 stroke engines only (reach TDC at the same time)
This is a warning device on small turbines
Sentinel valve
The total energy available from the steam is due to its heat, weigh, pressure and velocity. This is called
Enthalpy of steam
On a steam turbine where is the thrust bearing located
Steam inlet end
Assemble carbon rings according to their
match marks
These seals are used instead of labyrinth when axial movement is a factor
Annulus
The weight of the blade multiplied by radial distance to the centre of gravity of each blade
Moment weight
Overspeed trip setting set at
110-115% of operating speed
part of the rotor with several stepped diameters that the steam pressure in the turbine push against to counteract thrust
Dummy (balance) piston
How big should the foundation of a turbine be
2.5 times the mass of the turbine assembly
The highest pressure in a gas turbine is in the
diffuser
Drum rotors are for ___ speed, disk rotors are for ___ speed
Drum (low)
Disk (high)
Constant speed gas turbines do not use these
variable pitch stator blades
3 zones of the gas turbine combustion chamber
Primary (first part where fuel injection and combustion begins)
Intermediate (combustion mixes with secondary air)
Dilution (combustion complete, secondary air mixed with burnt gases)
Francis and kaplan are considered ______ turbines
reaction
The motor is momentarily converted to a generator, but cannot come to a full stop
Dynamic braking
If a motor requires sudden or repeated stops, this reverses the armature circuit polarity
Plugging
This hydro turbine uses water sources with high head
Pelton (impulse style buckets)
Four main parts of a wind turbine
Foundation, tower, nacelle, rotor
Francis and Kalpan turbines are used in these situations
low head, high flow (francis most common)
Frame motor sizes are classified by this
Diameter
Name the 4 DC motors
Series (high starting torque)
Shunt (speed control)
Compound (constant speed)
Permanent-Magnet (poor speed control)
Motors known for the constant speed characteristics
Three phase AC
These engines are used in pipelines
High-compression gas burning
Order of rings on a piston
2 compression rings at the top, oil ring on bottom
How is the camshaft driven
chain or gear from the crankshaft
The main stop valve is this type of valve
globe or parallel sliding gate
These governors are used on constant speed turbines
Mechanical
This compressor produces shock waves
Radial-centrifugal flow
Four styles of combustors
cannular, annular, can (most used), straight through
two ways of injecting fuel into gas turbine
atomizer (most common)
vaporizing
