Transcript Propulsion Introduction

Propulsion Introduction
Force, Energy & Power
Thermodynamics
What makes ships go?
Force
Energy
Power
FORCE
Units:
 Pounds (lbs)
 Tons (1 Ton = 2000 lbs)
 Newtons (1 N = 0.225 lbs, 1 lb = 4.45 N)
Examples:
 Thrust Force: produced by propeller to
drive ship)
 Resistance Force: determined by hull
shape & vessel speed—opposes thrust
FORCE
RES
THR
THRUST = RESIST (equilibrium)


Ship proceeds at a constant speed
Velocity = distance / time
o 1 knot = 1 nautical mile / hour
o 1 naut mi. = 6090 ft = 1.15 statute mi.
FORCE
THRUST > RESIST


Ship accelerates
Resistance increases with speed
o Until Resistance = Thrust
o Ship at new, faster speed
FORCE
RESIST > THRUST


Ship decelerates
Resistance decreases with speed
o Until Resistance = Thrust
o Ship at new, slower speed
RESISTANCE = K x V2
K is a function of hull

Doubling velocity
requires 4 times the
thrust
o at 5 kt  T = 25K
o at 10kt  T = 100K

at 20 kt  T = 400K
o (16 times the thrust at
5 kt)
Thrust (multiple of "K")
shape & condition
450
400
350
300
250
200
150
100
50
0
0
5
10
15
Knots
20
25

Each increasing knot
requires more thrust
than the previous 1knot increase
o
From 5 to 10 kt required
an increase of 75K
o
From 15 (225K) to 20
(400K) is an increase of
175K tons of thrust
Thrust (multiple of "K")
RESISTANCE = K x V2
450
400
350
300
250
200
150
100
50
0
0
5
10
15
Knots
20
25
What makes ships go?
Force
Energy
Power
ENERGY (mechanical)
Force x Distance
Units:
 Pounds x Feet (lb-ft)
 Newtons x meters (1 N-m = 1 joule)
 Other: Tons-miles; oz-inches; etc.
Examples:
 Thrust x Distance (port A to port B)
 Since Thrust = K x V2, ship speed
significant in energy (fuel) costs
ENERGY in many forms
Mechanical Energy (“work”):
 Force x Distance (lb-ft; Ton-mi; N-m; etc.)
Thermal Energy (“heat”):
 1 BTU will raise 1 lb of H2O 1oF
 1 BTU equivalent to 778 lb-ft of mechanical “work”
 The amount of heat released in the combustion of 1 lb
of fuel (BTU/lb) is the Higher Heating Value (HHV) of the
fuel
Electrical Energy (“kW-Hrs”):
 One 60-watt (0.06 kW) bulb burning for 24 hrs consumes
1.44 Kw-Hrs of energy (at 15 cents per Kw-Hr, a 60
watt bulb burning for a month costs 0.06 x 24 x 30 x
$0.11 = $4.75)
What makes ships go?
Force
Energy
Power
POWER
Rate of Energy Production or consumption
Force x Distance / Time:
 lb-ft/min; Ton-mi/hr; N-m/sec (=joule/sec = watt)
 550 lb-ft/sec = 33,000 lb-ft/min = 1 horsepower
 1 horsepower = 746 watts = 0.746 kW
= 0.707 BTU/sec = 2545 BTU / Hr
Force x Distance / Time = Force x Velocity
 Thrust x Velocity = K x V2 x V = K x V3
=Ship’s Effective Horsepower (EHP)
 EHP proportional to speed cubed!
EHP = THRUST x VELOCITY
At any constant speed
Thrust = Resistance = K x V2
 So Thrust x Velocity =
K x V2 x V = K x V3
(Doubling V requires 8 x HP!)



EHP(10) = K x 1000
EHP(20) = K x 8000
“K” for TSES VI is ≈ 2
EHP (multiple of "K")

9000
8000
7000
6000
5000
4000
3000
2000
1000
0
X8
X2
0
5
10
15
Knots
20
25
EHP = THRUST x VELOCITY
So EHP = K x V3
& Doubling V requires 8 x HP
 EHP(10) = K x 1000
 EHP(20) = K x 8000


1011 kt:
331xK increase in HP
1920 kt:
1141xK increase HP
EHP (multiple of "K")

9000
8000
7000
6000
5000
4000
3000
2000
1000
0
0
5
10
15
Knots
20
25
Propeller as a Screw

PITCH (ft or m)
PITCH =
theoretical
advance of
propeller in 1
revolution

PITCH x Total Revs in 1 day = ENGINE MILAGE

Slip = Eng mi – Obs mi

Eng mi
Pitch x RPM x 60 min/hr = ship speed (knots)
6077 ft/n.mi
Propeller as a Pump



Moves a
quantity of
water (GPM)
And raises
pressure (psi)
Propeller Horsepower = GPM x PSI
1714
Gal (231 cu.in.) x lbs = force x distance
min (60 sec) sq.in
time

Press Difference (DP) x Propeller Area =
THRUST
Efficiency
Losses
PWR in
Process
PWR out
or
System
Efficiency
Eff = Pout =
Pout
= Pin - Losses
Pin
Pout + Losses
Pin
Nothing is 100% efficient!
Efficiency

Delivered Horsepower (DHP)= energy
per unit time delivered to the propeller
DHP
EHP
Losses
Stern Tube

Propulsive Efficiency = EHP
DHP
(30% or more)
Efficiency

Shaft Horsepower (SHP)= energy per
unit time delivered to the tailshaft
SHP
DHP
EHP
Losses
Line shaft
Stern Tube
(30% or more)
Tailshaft Losses (< 1%)
Efficiency
Heat for Auxiliaries & Losses
BTU/min
to engine
BTU’s Released:
HHV x Fuel Rate
FUEL



DHP
BHP
SHP
Engine
Transmission & Shafting
Brake Horsepower (BHP)= engine output delivered
to drive train (line shaft losses: 2-5%)
ENGINE converts Thermal Energy to Mechanical
Energy (efficiencies < 50%)
Thermal Energy produced by the combustion of fuel
EHP
Propulsion Plants
BTU/min
to engine
BHP
FUEL


Engine
Transmission & Shafting
Many Energy Conversion (thermal  Mechanical)
Alternatives including …
STEAM (conventional or nuclear), DIESEL
(slow speed or medium speed), and GAS
TURBINE
Steam Propulsion
STEAM
REDUCTION
GEAR
BOILER
or
REACTOR
TURBINES
WATER
Advantages:
 Conventional plants can burn very low grade
fuel
 Nuclear plants can go years without
refueling
 Good efficiency over a wide range of speeds
Disadvantages
 Large Space requirements
 Long start-up time
 Difficult to completely
automate (large crew sizes)
 High initial (capital) costs
(Slow Speed) Diesel Propulsion
Advantages:
 Simple to automate (“unmanned”
engine room & Bridge Control)
 Can burn low grade fuel
 Relatively short start-up time
Disadvantages
 Low efficiency at low speed
 Restricted maneuverability
 Many parts—failure of one
causes downtime
(Medium Speed) Diesel Propulsion
G
G
G
G
M
G
Advantages:
 Flexible engine arrangements
 Suitable for electric drive
 Short start-up time
Disadvantages
 Burns higher grade fuel
 Multiple engines required for
high hp ships
 Significant maintenance
burden
Gas Turbine Propulsion
Gas Generator
(jet engine)
Power
Turbine
Advantages:
 Short start-up time
 Engines (Gas Generators) changed out
for regular maintenance
Reduction/
reversing Gear
Gas Turbine Propulsion
G
M
G
G
M
Advantages:
Disadvantages
 High grade (jet) fuel
 Short start-up time
 Engines (Gas Generators) changed out  Non-reversing—requires
auxiliary gear for astern
for regular maintenance
operation
 Suitable for electric drive