II-C Power

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II-C Power Energy SystemsDennis
Buckmasterdbuckmas_at_purdue.eduhttps//engineering
.purdue.edu/dbuckmas/

• OUTLINE
• Internal combustion engines
• Hydraulic power circuits
• Mechanical power transmission
• Electrical circuit analysis (briefly)

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References

• Engineering Principles of Agricultural Machinery,
  2nd ed. 2006. Srivastava, Goering, Rohrbach,
  Buckmaster. ASABE.
• Off-Road Vehicle Engineering Principles. 2003.
  Goering, Stone, Smith, Turnquist. ASABE.

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Other good sources

• Fluid Power Circuits and Controls Fundamentals
  and Applications. 2002. Cundiff. CRC Press.
• Machine Design for Mobile and Industrial
  Applications. 1999. Krutz, Schueller, Claar. SAE.

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Engines

• Power and Efficiencies
• Thermodynamics
• Performance

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Engine Power Flows
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Power Efficiencies

• Fuel equivalent
• Pfe,kW (HgkJ/kg?f,kg/h)/3600
• Hg 45,000 kJ/kg for No. 2 diesel
• Indicated
• Pi,kW pime,kPaDe,lNe,rpm/120000
• Brake
• Pb,kW 2pTNmNe,rpm/60000
• Friction
• Pf Pi-Pb

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Power Efficiencies

• Indicated Thermal
• Eit Pi/Pfe
• Mechanical
• Em Pb/Pi
• Overall (brake thermal)
• Ebt Pb/Pfe EitEm
• Brake Specific Fuel Consumption
• BSFC ?f,kg/h/Pb,kW

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Dual Cycle ?
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Related equations

• Compression ratio r
• r V1/V2
• Displacement
• De,l (V1-V2)( cylinders)
• p(borecm)2(strokecm)( cyl)/4000
• Ideal gas
• p1V1/T1 P2V2/T2
• Polytropic compression or expansion
• p2/p1 rn
• n 1 (isothermal) to 1.4 (adiabatic), about
  1.3 during compression power strokes

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Related equations

• Air intake
• ?a,kg/h .03De,lNe,rpm?a,kg/cu m?v,decimal
• From Stoichiometry (fuel chemistry)
• A/F air to fuel mass ratio 151 for cetane

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What is the displacement of a 6 cylinder engine
having a 116 mm bore and 120 mm stroke?
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For this same engine (7.6 l displacement, 2200
rpm rated speed), what is the air consumption if
it is naturally aspirated and has a volumetric
efficiency of 85? Assume a typical day with air
density of 1.15 kg/m3. With a
stoichiometric air to fuel ratio based on cetane,
at what rate could fuel theoretically be burned?
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Consider the this same (595 Nm, 137 kW _at_ 2200
rpm) engine which has a high idle speed of 2400
rpm and a torque reserve of 30 peak torque
occurs at 1300 rpm. Sketch the torque and power
curves (versus engine speed).
Torque (Nm)
Power (kW)
Speed (rpm)
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A quick problem

• Diesel engine generating 60 kW at 2300 rpm
• Q torque available

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Alternative fuels

• What has to be similar?
• Self Ignition Temperature
• Energy density
• Flow characteristics
• Stoichiometric A/F ratio

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Power Hydraulics

• Principles
• Pumps, motors
• Cylinders

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About Pressure

• 14.7 psia STP (approx __ in Hg)
• Gage is relative to atmospheric
• Absolute is what it says absolute relative to
  perfect vacuum
• What causes oil to enter a pump?
• Typical pressures
• Pneumatic system
• Off-road hydraulic systems

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Liquids Have no Shape of their own
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Liquids are Practically Incompressible
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Pascals Law

• Pressure Exerted on a Confined Fluid is
  Transmitted Undiminished in All Directions and
  Acts With Equal Force on Equal Areas and at Right
  Angles to Them.

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Application Principles
10 lbs (4.5kg)
10 sq in (6.5cm2)Piston Area
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Hydraulic lever
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Types of Hydraulic Systems
Open Center Closed Center
The control valve that regulates the flow from
the pump determines if system is open or
closed. Do not confuse Hydraulics with the
Closed Loop of the Power Train. (Hydro)
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Closed Center Hydraulics
Open CenterFlow in Neutral
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Extend
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Retract
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Neutral Again
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Pumps
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Pump Inefficiency

• Leakage you get less flow from a pump than
  simple theory suggests.
• Increases with larger pressure difference
• Friction it takes some torque to turn a pump
  even if there is no pressure rise
• Is more of a factor at low pressures

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Efficiency of pumps motors

• Em mechanical efficiency lt 1 due to friction,
  flow resistance
• Ev volumetric efficiency lt 1 due to leakage
• Eo overall efficiency Em Ev
• Eo Power out/power in

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Qgpm Dcu in/rev Nrpm /231
Flow
Speed
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Tinlb Dcu in/rev ?Ppsi /(2p)
Torque Required
Pressure Rise
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Flow
Pressure
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Flow
Pressure
Php Ppsi Qgpm/1714
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• 1a. If a pump turns at 2000 rpm with a
  displacement of 3 in3/rev, theoretically, how
  much flow is created?
• 1b. If the same pump is 95 volumetrically
  efficient (5 leakage), how much flow is created?

Example pump problems
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Example pump problems

• 2a. If 8 gpm is required and the pump is to turn
  at 1750 rpm, what displacement is theoretically
  needed?
• 2b. If the same pump will really be is 90
  volumetrically efficient (10 leakage), what is
  the smallest pump to choose?

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Example pump problems

• 3a. A 7 in3/rev pump is to generate 3000 psi
  pressure rise how much torque will it
  theoretically take to turn the pump?
• 3b. If the same pump is 91 mechanically
  efficient (9 friction drag), how much torque
  must the prime mover deliver?

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Example motor problem

• If a motor with 2 in3/rev displacement and 90
  mechanical and 92 volumetric efficiencies
  receives 13 gpm at 2000 psi
• a. How much fluid power is received?
• b. What is its overall efficiency?
• c. How fast will it turn?
• d. How much torque will be generated?

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Cylinders
Force balance on piston assembly
Fexternal
P2 A2
P1 A1
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• 3000 psi system
• 2 bore cylinder
• Extends 24 inches in 10 seconds
• Q max force generated
• max work done
• power used
• flow required

Example cylinder problem
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• Tractor source with 2500 psi and 13 gpm available
• Return pressure tax of 500 psi
• Cylinder with 3 bore, 1.5 rod diameters
• Q1 How much force will the cylinder generate?
• Q2 How long will it take to extend 12 inches?

Example cylinder problem
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Power Transmission
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Transmissions transform powera torque for speed
tradeoff
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Gears
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Planetary Gear Sets
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Belt Chain Drives

• Speed ratio determined by sprocket teeth or belt
  sheave diameter ratio

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FIRST GEAR
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FIRST GEAR
First gear speeds if Input shaft 1000
rpm Main countershaft 1000 (22/61) 360 rpm
Ratio input speed/output speed 1000/360
2.78 Ratio output teeth/input teeth 61/22
2.78 Secondary countershaft 360 rpm (41/42)
351 rpm Output shaft 351 rpm (14/45) 109
rpm RATIO input speed/output speed 1000/109
9.2 Product of output teeth/input teeth
(61/22)(42/41)(45/14) 9.2
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• If 50 kW _at_ 2400 rpm drives a pinion gear with 30
  teeth and the meshing gear has 90 teeth (assume
  98 efficiency)
• Q1 What is the speed of the output shaft?
• Q2 How much power leaves the output shaft?
• Q3 How much torque leaves the output shaft?

Example gear problem
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• If the sun of a planetary gear set turns at 1000
  rpm, what speed of the ring would result in a
  still planet carrier? Teeth on gears are sun 20
  and ring 100.

Example planetary gear problem
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• If a belt drive from a 1750 rpm electric motor is
  to transmit 5 hp to a driven shaft at 500 rpm and
  the small sheave has a pitch diameter of 4
• Q1 What should the pitch diameter of the other
  pulley be?
• Q2 Which shaft gets the small sheave?
• Q3 How much torque does the driven shaft receive?

Example belt problem
Php Tft-lbNrpm/5252
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Electricity

• Voltage Current Resistance
• Vvolts Iamps Rohms
• Power voltage times current
• PWatts VvoltsIamps

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Three Types of Circuits

• Series
• Same current, voltage divided

• Parallel
• Same voltage, current divided

Series / Parallel
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• A 12 V DC solenoid a hydraulic valve has a 5 amp
  fuse in its circuit.
• Q1 What resistance would you expect to measure
  as you troubleshoot its condition?
• Q2 How much electrical power does it consume?

Example 12 V DC problem
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• Q1 Identify specifications for a relay of a 12 V
  DC lighting circuit on a mobile machine if the
  circuit has four 60W lamps.
• Q2 Would the lamps be wired in series or
  parallel?

Example 12 V DC problem
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• Good luck on the PE Exam!
• My email address
• dbuckmas_at_purdue.edu
• My web page
• https//engineering.purdue.edu/dbuckmas/
• Note ASABE members can access ASABE texts
  electronically at
• http//elibrary.asabe.org/toc.asp