II-C Power & Energy Systems

7/27/2019 II-C Power & Energy Systems

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II-C Power & Energy SystemsDennis Buckmaster

[email protected]://engineering.ecn.purdue.edu/~dbuckmas/

OUTLINE

Internal combustion engines

Hydraulic power circuits Mechanical power transmission

Electrical circuit analysis (briefly)
mailto:[email protected]:[email protected]


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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/kgf,kg/h)/3600

[Hg = 45,000 kJ/kg for No. 2 diesel] Indicated

Pi,kW = pime,kPaDe,lNe,rpm/120000

BrakePb,kW = 2TNmNe,rpm/60000

Friction

Pf

= Pi

-Pb


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Power &

Eff iciencies

Indicated Thermal

Eit = Pi/Pfe

MechanicalEm = Pb/Pi

Overall (brake thermal)

Ebt = Pb/Pfe = Eit*Em Brake Specific Fuel Consumption

BSFC= f,kg/h/Pb,kW


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Dual Cycle


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Related equations

Compression ratio = rr = V1/V2

Displacement

De,l = (V1-V2)*(# cylinders)= (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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Air intakea,kg/h = .03De,lNe,rpma,kg/cu mv,decimal

From Stoichiometry (fuel chemistry) A/F = air to fuel mass ratio = 15:1 for cetane

Related equations


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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 @ 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)

Speed (rpm)

Power (kW)


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A quick problem

Diesel engine generating 60 kW at 2300 rpm

Q: torque available


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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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21

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.

22


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Application Principles

1 lb (.45kg)Force

1 sq in (.65cm2)

Piston Area

1 psi

(6.9kpa)

10 sq in

(6.5cm2)

Piston Area

10 lbs (4.5kg)

23


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24

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 thePower Train. (Hydro)


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Trapped Oil

Closed Center HydraulicsOpen Center

Flow in Neutral


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Extend 27


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Retract 28


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Neutral Again 29


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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 < 1 due to

friction, flow resistance

Ev

volumetric efficiency < 1 due to

leakage

Eo =overall efficiency = Em * Ev

Eo

= Power out/power in


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Speed

Flow

Qgpm = Dcu in/rev Nrpm /231


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Pressure Rise

Torque

Required

Tinlb = Dcu in/revPpsi /(2)


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Pressure

Flow

Theoretical pump

Effect of leakage

Relief valve or pressure

compensator


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Pressure

Flow

Constant power curve

Php = Ppsi Qgpm/1714

1 If t t


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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 muchflow is created?

Example pump

problems

2 If 8 i i d


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Example pump

problems

2a. If 8 gpm is required

and the pump is to turn

at 1750 rpm, what

displacement istheoretically needed?

2b. If the same pump willreally be is 90%

volumetrically efficient

(10% leakage), what is

the smallest pump tochoose?


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3a. A 7 in3/rev pump is to

generate 3000 psi

pressure rise; how much

torque will it theoreticallytake to turn the pump?

3b. If the same pump is91% mechanically

efficient (9% friction &

drag), how much torque

must the prime moverdeliver?

Example pump

problems


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Example motor

problemIf a motor with 2 in3/rev

displacement and 90%

mechanical and 92%volumetric efficiencies

receives 13 gpm at

2000 psi

a. How much fluid poweris 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: FexternalP1 * A1 P2 * A2


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42

3000 psi system

2 bore cylinder

Extends 24 inches in 10seconds

Q: max force generated

max work done

power used

flow required

Example cylinder

problem

Tractor source with 2500 psi


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Tractor source with 2500 psiand 13 gpm available

Return pressure tax of 500 psi

Cylinder with 3 bore, 1.5 roddiameters

Q1: How much force will thecylinder 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 power

a torque for speed torque 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 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 = 2.78Secondary 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

FIRST GEAR

If 50 kW @ 2400 d iE l


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If 50 kW @ 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

If th f l tE l l t


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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 planetcarrier? Teeth on gears are

sun: 20 and ring: 100.

Example planetary

gear problem

If a belt dri e from a 1750 rpmE l b lt


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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 sheavehas a pitch diameter of 4

Q1: What should the pitch

diameter of the other pulleybe?

Q2: Which shaft gets the small

sheave?

Q3: How much torque doesthe 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 = Vvolts*Iamps

VI R

Th T f Ci it


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Three Types of Circuits

SeriesSame current, voltage divided

+

-12 v.

Parallel

Same voltage, current divided

Series / Parallel

A 12 V DC solenoid aE l 12 V DC


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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

Q1: Identify specifications forE l 12 V DC


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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 60Wlamps.

Q2: Would the lamps be wiredin series or parallel?

Example 12 V DC

problem


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Good luck on the PE Exam!

My email address:[email protected]

My web page:https://engineering.ecn.purdue.edu/~dbuckmas/

Note ASABE members can access ASABEtexts electronically at:

http://asae.frymulti.com/toc.asp
mailto:[email protected]://cobweb.ecn.purdue.edu/~dbuckmas/http://asae.frymulti.com/toc.asphttp://asae.frymulti.com/toc.asphttp://cobweb.ecn.purdue.edu/~dbuckmas/mailto:[email protected]

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II-C Power & Energy Systems