testprocedure compressor expander

8/20/2019 Testprocedure Compressor Expander

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FUERO WP6 Specification of test procedures for compressor/expander units Final Version 05/05/2004

1

Specification of

Test Procedures for

Compressor/Expander Units

Final Version

May 2004

Prepared by the FUERO Consortium

with CRF as principal author


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Preface

The FUERO consortium has developed this test procedure and it has been developed within a ResearchProgram partly funded by the European Commission. The work has been carried together with all the

partners in the FUERO consortium with CRF as the principal author and Volvo as the coordinator of the

activity.Comments and questions about this test procedure can be directed to CRF ([email protected],

[email protected] , [email protected]).


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Table of content

Preface........................................................................................................................................................ 2

Table of content......................................................................................................................................... 3

Introduction............................................................................................................................................... 5

1. Definitions, formulae and reference processes ............................................................................. 7

1.1 General ............................................................................................................................................ 7

1.2 Thermodynamics............................................................................................................................. 8

1.3 Energy, power, efficiency ............................................................................................................. 12

2. Symbols and units......................................................................................................................... 15

3. Pre request ..................................................................................................................................... 17

3.1 Requirements for the manufacturer............................................................................................... 17

3.2 Requirements of the test institute.................................................................................................. 17

3.3 Test bench and measurement equipment ...................................................................................... 18

4. General Measurement and instrumentation .................................................................................... 20

4.1 Measurement parameters .............................................................................................................. 20

4.2 Sampling frequency ...................................................................................................................... 21

4.3 Data Storage and Format............................................................................................................... 21

4.4 Safety Limits ................................................................................................................................. 21

4.5 Methods of measurements............................................................................................................. 21

4.5.1 Pressure measurement ................................................................................................................... 21

4.5.2 Temperature measurement ............................................................................................................ 22

4.5.3 Flow rate measurement...................................................................................................................... 23

5. Description of Test Procedures .................................................................................................... 24

5.1 Preliminary operations .................................................................................................................. 245.2 Aim of tests ................................................................................................................................... 25

5.3 Procedure #1 - STATIC TEST: Compressor/expander unit characteristics maps ........................ 26

5.3.1 Description......................................................................................................................................... 26

5.3.2 Test procedure ................................................................................................................................... 26

5.3.3 Shut down procedure ......................................................................................................................... 27

5.3.4 Data analysis and mapping ................................................................................................................ 27

5.4 Procedure #2 - DYNAMIC TEST: Dynamic evaluation of transient .......................................... 29


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5

Introduction

Scope

The following Procurement Specification concerns with bench test procedures of compressor/expander units for

air management subsystem in automotive Fuel Cell Systems. This operating instruction has the aim to supply onemethodology of bench tests in order to characterize electric compressor/expander units.

The proposed activity tends to define testing of compressor/expander units, in order to guarantee an accurate and

repetitive characterization, as to compare obtained map with that one eventually supplied from the manufacturer .

General

The following test procedure examines exclusively performances of motor-driven compressor/expander units,

consisting of a compressor, an expander and an integrated electric motor incorporated on a common shaft.

In this way, the resistant shaft torque is not directly measured, but it can eventually be deducted, in conditions of

stationary operation, from the electric motor map (when rotational speed and supply voltage are known), in case

the map has been supplied from the manufacturer.

Considering efficiency of the machine as one of the results of the test activity, in this test procedure, because of

the reference to an integrated system, it is referred mostly to global system efficiency. Unless other data are

available, it is not split into its factors: adiabatic efficiency, electric motor efficiency and transmission mechanical

efficiency.

In the Annexes, further tests, some of these going beyond the electric compressor/expander unit performance, are

introduced:

• Compressor/expander unit tests procedures with heater (annex B): expander air inlet temperature isimportant to recover energy.

• Air quality at the compressor outlet (annex C): air quality in terms of solid particles or oil content isimportant to be detected because of fuel cell requirements.

• Sound emission (annex D): compressor and expander are the most important rotating part in a fuel cellsystem, therefore they are the major source of noise from the propulsion system.

• Electric and electromagnetic behaviour (annex F): electric and electromagnetic tests should be done toevaluate the impact on other electric components on a vehicle.

Feasibility

This procedure can be applied in general way both when dynamic (centrifugal) and when volumetric machines

are used. The defined criteria can be applied whenever compressor/expander unit performances must be

evaluated; in this case performance means the capability to provide a certain quantity of pressurized air up to a

fixed pressure level and recover subsequent energy from the exhaust stream by means of the expander; this

operation usually implies less electric power consumption than the case without the expander. However the gain

of using an expander must be evaluated according to different applications.

The test configuration installation concerns compressor/expander units plumbed both in inlet and in outlet.

The procedures are intended for a manual use of the test bench, i.e. the operator has to take part directly in field

for regulating and managing both components and the instrumentation. If the procedure is run automatically, it

should be assured that an automatic shut off is used in case of exceeded boundary levels.


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6

Normative references

This test procedure refers to the following International (ISO), Italian (UNI) Standards and volumes:

ISO 1217 -1996: Displacement compressors - Acceptance tests

ISO 5168 -1978: Misure di portata - stima delle incertezze di misurazione

ISO 5389 -1992: Turbocompressors - Performance test code

ISO 5801: 1997 (E): Industrial Fans – Performance testing using standardized airways

UNI 10531 -1995: Ventilatori industriali - Metodi di prova e condizioni di accettazione

CEI 301-1 – 1997: Azionamenti elettrici - Dizionario

G. Pignone, U. Vercelli - Turbomacchine - Ed. Ulrico Hoepli - MILAN


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1. Definitions, formulae and reference processes

In this section symbols, definitions and equations, which will be used in the following test procedure, are

introduced. Most of them are taken from current Standards (ISO, UNI, CEI). Refer to Normative References for

further details.

NOTEIn order to distinguish different inlet/outlet points of the components the following numbers are used:

Compressor inlet point/condition → 1 Compressor discharge point/condition → 2 Expander inlet point/condition → 3 Expander discharge point/condition → 4

PPee

PPmm ηM

ηC

Compressor

IN

Electric Motor

m

Expander

ηE

OUT

PPmm

PPcc PPtt

Fuel Cell

1

2

4

3

PPmm

Figure 1 - Compressor/expander unit diagram with numeration inlet/outlet

1.1 General

Definitions used to define inlet/outlet conditions of a single component (which are valid both for the compressor

and the expander) are the following:

Standard inlet point: inlet point considered representative for each component and which varies with design

and type of installation

Standard inlet condition: condition of the air at the standard inlet point of the component


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Standard discharge point: discharge point considered representative for each component and which varies with

design and type of installation

Standard discharge condition: condition of the air at the standard discharge point of the component

1.2 Thermodynamics

Within this procedure, equation of state of perfect gases is applied:

T R p

⋅=⋅ ρ

being:

p = pressure [Pa]

ρ = density [kg/m3]R = mass constant for air = 287 J/kg/K

T = absolute temperature [K]

Standard conditions1 are defined according to ISO/CAGI/PNEUROP:

- temperature = 293.15 K (20 °C)

- pressure = 1 atm

Real gases become ideal in the limit of low density, experimentally. In fact at low density the average distance

between gas molecules becomes large and forces existing between real gas molecules become attenuated; this is because non-electrostatic forces between molecules fall off very rapidly with distance, about the 6th power of the

reciprocal of the distance.

Practically, instead of using the limit of low density, it is useful to use the limit of low pressure. Sometimes also

the limit of large volume is used, which for fixed number of moles also means low density.

A useful quantity for real gases is the compressibility factor Z :

T R

p Z

ρ =

Generally Z becomes larger than 1 as the pressure is increased, because under those conditions the gas molecules

are forced to be close enough together that their repulsive forces dominate; at lower pressures the attractive forces

predominate, producing the typical dip and rise of these plots. Of course, it is exactly Z=1 for an ideal gas.

1 According to API/NASA standard conditions are: temperature = 288 K, pressure = 1 atm


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Isentropic exponent k is defined for ideal gas and isentropic process:

const p

k = ρ

k = 1.4 for atmosphericair

Specific heat capacity at constant pressure: c p

Rk

k c p

1−=

Sound speed (or sonic velocity) is defined as:

kRT c s =

Mach Number, M: ratio of the gas velocity to the sound speed

sc

c M =

being:

c [m/s] = fluid speed

Air at standard conditions has a cs = 340 m/s. If c = 50 m/s, M = 0.15.

Static temperature T : absolute temperature measured by a sensor in motion with the speed of the fluid.

Total temperature (stagnation temperature) T0 : absolute temperature in a stagnation point during a

isentropic transformation for ideal gas flow without

heating or energy supply.

For a pipe in aspiration area T0 is the absolute temperature of test ambient: T0 = Ta.

If static temperature T is measured, it is possible to go back to the total temperature T 0 by means the following

relation:

−+= 202

11 M k T T

NOTE.

When c < 50m/s, it can be assumed: T0 = T = Ta [K].

Static specific enthalpy h : h = c p T

Total specific enthalpy h0 : h0 = c p T0


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Static pressure, p : absolute pressure measured by a sensor in a point in which fluid is at rest with respect

surrounding fluid.

Measured pressure in a specific area x of a pipe is the static pressure p.

Total pressure (stagnation pressure) p0 : absolute pressure in a stagnation point in which fluid is brought to

rest in a isentropic way.

If static pressure p is measured, it is possible to go back to the total pressure p0 by means the following relation:

120

2

11

−

−+=k

k

M k

p

p

NOTE.

When M


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1

22is

20is20

10

p02is = p02

p1

p01

p2is = p2

Entropy - S

c12/2

c22/2

T e m p e r a t u r e - T

Figure 2 - Temperature-Entropy diagram for air compression

Expander pressure, pt : difference between the stagnation pressure at the standard inlet point and the

stagnation pressure at the standard discharge point

0

4

0

3 p p pt −=

Expander pressure ratio, βt : ratio of the stagnation pressure at the standard inlet point and the stagnation pressure at the standard discharge point

0

4

0

3

p

pt = β

4

3

40is40

30

p

0

4is = p

0

4

p3

p03

p4is = p4

4is

c32/2

c42/2

T e m p e r a t u r e - T

Entropy - S Figure 3 - Temperature-Entropy diagram for air expansion


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1.3 Energy, power, efficiency

Compression isentropic work per mass unit Lcis :

Lcis = h2is0 - h1

0

Expansion isentropic work per mass unit Ltis :

Ltis = h30 - h4is

0

Compression work per mass unit Lc :

Lc = h20 - h1

0

Expansion work per mass unit Lt :

Lt = h30

- h40

Compression power Pc : power supplied from compressor to air

Pc = m& Lc

Expansion power Pt : power supplied from air to expander

Pt = m& Lt

Shaft rotational speed, n : number of revolutions per minute of the common shaft

Shaft rotational frequency, ω : number of revolutions per unit time of the common shaft

Shaft power, Pm: mechanical power supplied from electric motor to common shaft

Pm = C ω being:

C = shaft torque [Nm]

Motor output power, Po : shaft power output of the motor (or other prime mover)

Electric motor voltage, V : voltage measured at electric motor drive

Electric motor current, I : current supplied to electric motor drive

Motor input power Pe : electrical power supplied at the terminals of the electric motor drive

Pe = V I


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Compressor total-total isentropic efficiency: relationship between necessary work to make an isentropic

transformation and compression work; in this definition the kinetic component is considered entirely recovered in

pressure:

1

1

1

1

0

1

0

2

1

0

1

0

2

0

1

0

2

0

1

0

2

0

1

0

2

0

1

0

2

0

1

0

2

0

1

0

2

−

−

=

−

−

=−

−=

−

−==

−

T

T

p

p

T

T

T

T

T T

T T

hh

hh

L

L

k

k

is

isis

c

cis

TT η

being:

k

k

is

p

p

T

T 1

01

0

2

01

0

2

−

= the air temperature rise due to compression and 02

0

2 p p is =

Compressor total-static isentropic efficiency: relationship that considers the discharge kinetic term completely

lost:

1

1

0

1

0

2

1

0

1

2

0

1

0

2

0

12

0

12

−

−

=−

−=

−=

−

T

T

p

p

hh

hh

L

hh

k

k

is

c

is

TS η

Expander total-total isentropic efficiency: relationship between expansion work and necessary work to make an

isentropic transformation; in this definition the kinetic component is considered entirely recovered in pressure:

k

k

istis

t TTt

p

p

T

T

hh

hh

L

L1

0

3

0

4

0

3

0

4

0

4

0

3

0

4

0

3

1

1

−

−

−=

−−

==η

Expander total-static isentropic efficiency: relationship that considers the discharge kinetic term completely

lost:

k

k

isis

t TSt

p

p

T

T

hh

hh

hh

L1

0

3

4

0

3

0

4

4

0

3

0

4

0

3

4

0

3

1

1

−

−

−=

−−

=−

=η


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Compressor overall efficiency, ηe : ratio of the compression isentropic power to shaft power

m

isc

ec P

P =η

being: Pcis = m& Lcis

Expander overall efficiency, ηe : ratio of the expansion isentropic power to shaft power

m

ist

et P

P =η

being: Ptis = m& Ltis


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2. Symbols and units

Symbol Quantity SI unit Dimensions

A Area m2

L2

cs Sound speed m/s LT-1

C Torque Nm ML2 T

-2

c Absolute velocity m/s LT-1

c p Specific heat at constant pressure J/kg/K LT-2

Θ-1

cv Specific heat at constant volume J/kg/K LT-2

Θ-1

Dx Internal diameter of a circular pipe in the x plane m L

h Specific enthalpy J/kg LT-2

k Isentropic coefficient dimensionless

I Current A

Lc Compression work per mass unit J/kg L2

T-2

Lt Expansion work per mass unit J/kg L2 T

-2

.

m Mass flow rate Kg/s

MT-1

qV Volume flow rate m3/s L

3 T

-1

M Mach number dimensionless

n Rotational speed rpm LT-1

pa Absolute pressure2 Pa ML-1 T-2

pd Dynamic pressure Pa ML-1

T-2

pg Gauge pressure Pa ML-1 T-2

p0

Stagantion (total) pressure Pa ML-1

T-2

2 Most common used is bar. 1 bar = 105 Pa.

In the following sometimes is used also the millibar (mbar) for the atmospheric pressure. 1 mbar = 102 Pa


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Pc Compression power W ML2 T-3

Pt Expansion power W ML2

T-3

Pe Motor input power W ML2 T

-3

Pm Shaft power W ML2 T

-3

PO Motor output power W ML2 T

-3

R Specific gas constant J/kg/K LT-2

Θ-1

T

Absolute temperature K Θ

t Temperature °C Θ

ta Ambient temperature °C Θ

T0

Stagnation temperature K Θ

V Electric motor voltage V

Z Compressibility factor dimensionless

βc Compressor pressure ratio dimensionless

βt Expander pressure ratio dimensionless

µ Dynamic viscosity Kg/m/s ML-1 T-1

ηe Overall efficiency Dimensionless

ηTS Total-static isentropic efficiency Dimensionless

ηTT Total-total isentropic efficiency Dimensionless

ρ Density Kg/m3 ML-3

ω Rotational frequency rad/s


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3. Pre request

3.1 Requirements for the manufacturer

Compressor, expander and motor should be properly, clearly and permanently marked by the manufacturer with

some notes and specific data, possibly summarised in one table:

• part number and serial number

• specifications (weight, voltage, power, control…)

• operational limits (temperature, flow rate, pressure)

Further information should be supplied in the attached documentation:

• commercial data (name and address of the manufacturer, reference for information requests,compressor, expander and electric motor drawings)

• test pre conditioning (set points for flow rates, pressure and temperature at different power levels);

3.2 Requirements of the test institute

The test bench should provide the following facilities needed for the test:

• measurement equipment (calibrated gas flow meters, pressure gauges and temperature sensors withsuitable measuring range for the actual constituents of gas with traceable calibration)

• all necessary components to perform the test, such as back-pressure regulating valve, circuit connecting pipes, power supply systems,

• data acquisition systems (displays for measured parameters and PC acquisition data systems)

Before starting the tests, a test plan must be prepared by the test institute. The test plan shall clearly state all tests

planned, referring to the procedures in this document, and describe and justify any deviations from the test

procedures.


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3.3 Test bench and measurement equipment

Test bench consists of the following components and facilities, connected as in the Figure 4 :

• Compressor/expander unit with integrated electric motor

• Back-pressure regulating valve on compressor delivery to control pressure into the circuit and simulatethe pressure drop of the fuel cell stack

• Circuit connecting pipes with relative fittings

• Measurement devices (described in the following)

• Electrical devices to supply power to instrumentation and actuators

• Devices for control of the electric motor

• Displays for measured parameters• PC acquisition data systems and software

Necessary measurement equipment for testing is:

• Flow meter

• Temperature sensors (thermocouples or resistive temperature devices) to measure air temperature atinlet/outlet of compressor and inlet/outlet of expander

• Pressure transducers at inlet/outlet of compressor and inlet/outlet of expander

• Rotational speed meter (if applicable)

• Torque meter (only upon request)

• Wattmeter measuring power supplied to electric motor

• Reading instruments (or PC acquisition data) of output signals indicated by parameter sensors (massflow, temperature, pressure and electric power)

• Power supply for components and test equipment

NOTE

Equivalent test equipment in the following description may be substituted but must be equal or superior in

accuracy and performance.

NOTE

No detailed information about the distance between different components are given in Figure 4 because different

technologies have different requirements. Please refer to manufacturer’s specification for installation

requirements. For additional information, in Annex E there are some details concerning installation requirements

of different flow meters.


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2-5 D

Integrated Integrated

electric electric motor motor

Compressor Compressor Back-pressure

valve

MMTI2TI2

PI2

5-10 D

FI1

2-5 D

TI1PI1

Flow meter

INLETINLET

DISCHARGEDISCHARGE

TI3PI3

2-5 D

Expander Expander

TI4PI4

5-10 D

Rpm control system

PI = pressure indicator

TI = temperature indicator

Figure 4 - Possible scheme of the layout in the compressor/expander unit test bench


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4. General Measurement and instrumentation

4.1 Measurement parameters

A summary of parameters to be measured with relative instrumentation is shown in the following table:

PARAMETER UNIT Symbol MEASURE EQUIPMENT

Compressor inlet temperature [K] T1 Thermocouple

Compressor discharge temperature [K] T2 Thermocouple

Compressor inlet pressure [Pa] p1 Pressure (absolute)

Compressor discharge pressure [Pa] p2 Pressure (gauge or absolute)Expander inlet temperature [K] T3 Thermocouple

Expander discharge temperature [K] T4 Thermocouple

Expander inlet pressure [Pa] p3 Pressure (absolute)

Expander discharge pressure [Pa] p4 Pressure (absolute)

Inlet mass flow [kg/s] m& Mass flow-meter

Revolutions per time unit [rpm] N Tachometer

Motor shaft torque [Nm] C Torque-meter

Motor’s supply voltage [V] V Voltmeter

Motor’s supply current [A] I Ampmeter

Motor’s supply power [W] W Wattmeter

Motor’s control signal [V] Ctrl Voltmeter

Table 1. List of parameters to be measured during tests

NOTE

It is possible to measure revolutions per time and shaft torque only if it is possible to reach compressor/expander

unit motor shaft, after having removed possible covers.

NOTE

Compressor, expander and electric motor should be equipped with temperature sensors placed on them in order to

perform a detailed measurement. In Table 1 these signals are not reported because they are not directly involved

for test aims. They act in order to preserve components integrity.

During preliminary operations as well as tests, always check temperature; if temperature exceeds limits according

to data sheets from manufacturer, shut down electric motor and wait until temperature has reached acceptable

values. In many cases manufacturer itself provide a temperature sensor, on electric motor windings, which gives a

feedback to motor control.


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4.2 Sampling frequency

The parameters listed above should be recorded and stored with a frequency high enough to ensure that allrelevant changes in the parameters are recorded for later data analyses. In order to be able to use data series

recorded during components testing dynamic response has to be taken into account; the sampling frequency shall

be 10 Hz or higher.

4.3 Data Storage and Format

During the tests all measured data should be stored indefinitely, together with derived values, measurement date

and other relevant information. Measured values should be stored with as much precision as is available. They

should not be rounded to reflect the accuracy of the instruments.

4.4 Safety Limits

The safety limits given by the manufacturer must be respected. Examples of such safety limits are highest

allowable operating temperature, highest allowable gas flow rate and output pressure or any other limit specified

by the manufacturer. The manufacturer shall supply a list with all safety limits to the company who is testing the

components. The tests in the procedures in this document shall be performed as complete as possible with the

restriction that the safety limits must NOT be violated.

4.5 Methods of measurements

4.5.1 Pressure measurement

In a pipe area defined for measurement, static pressure must be measured in a pressure port in which it is

necessary insert a small connecting pipe for the pressure transducer; each pressure port is formed by a hole

through the pipe wall (maximum diameter is 0.1 D, being D the inner diameter of the pipe).

In order to obtain a more accurate measure, it would be appropriate evaluation of pressure in 4 equally distanced

pressure ports around the circumference, connected with small pipes of the same length before being placed in the pressure transducer ( see Figure 5).


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Pipe axle

D

= 0.1 D

Pressure

transducer

Figure 5 - Scheme for pressure measurement

Typical specifications of a pressure transducer are the following:

• absolute pressure reference

• input power supply 12-24Vdc

• output indication 0-20 mA or 4-20mA or 0-10V or direct reading (1Volt = 1bar)• accuracy +/-0.5% full scale and repeatability +/- 0.25 % full scale

• full scale range from 0 to 5 bar and maximum temperature 150°C

• standard connection (DIN 43650/ISO 4400) and ZERO regulation

• protection class IP65

• port size according to manufacturer

4.5.2 Temperature measurement

Temperature can be measured via a diverse array of sensors. All of them infer temperature by sensing some

change in a physical characteristic. Two principal types are used: thermocouples and resistive temperature

devices (RTDs and thermistors).

The sensing element of the sensor must be inserted in the pipe for 1/3 of the inner diameter of the tube.

For example thermocouples with calibration type T (Cu+Cu-Ni) are used for range of temperature from -40°C to+350°C with precision class 1 (tolerance +/-0.5°C or 0,4% of the measured temperature) according to the

European normative IEC 584-2, or calibration type J (Fe+Cu-Ni) are used for range of temperature from -40°C to

+750°C according to requirement.


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4.5.3 Flow rate measurement

Flow rate measurement, in this instruction, can be made according ISO 5167 and/or ISO 3966 normative (flowmeter in line). The flow meter is placed at inlet of the compressor in the ambient.

Alternative measurement devices, when other methods are used, are allowed if their are of equal or better

accuracy.

With reference to Figure 4, if a mass flow meter is used, it can be placed also at the compressor outlet.


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5. Description of Test Procedures

5.1 Preliminary operations

Pressure and temperature of the test room shall be set to standard conditions (20 °C and 1 atm)

Compressor/expander unit with integrated electric motor has to be installed on test bench, after checking that

components are free from dents, breakage, distortion, burrs, oxidized parts or any defects which could bedetrimental to service or life requirements.

Install equipment following the annexed scheme (Figure 4), taking care of mechanical connections between

components, piping and instrumentation.

Preliminary operations, before starting every procedure described in the following, are:

1. Turn on data acquisition system

2. Start experiment control program3

3. Turn on power supply devices

4. Set back-pressure valve “completely open”

5. Set motor controller output signal at zero value (no power to compressor electric motor)

6. Check values of measurement parameters as coming from instrumentation:

• mass flow = 0 [kg/s]

• inlet/outlet compressor and expander gauge pressure = 0 [Pa]

• voltage output to compressor = 0 [V]

• electric motor rotational speed = 0 [rpm]

3 If the experiment is not completely managed by a computer based program and measured parameters are seen through a display, this

item can be neglected


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5.2 Aim of tests

The purpose of this test is to map the characteristic compressor/expander unit curves, comparing results with

values specified by design or annexed specifications data sheet.

Both compressor map and expander map are performed on the compressor/expander unit.In particular the compressor map consists of a series of constant electrical motor speed lines plotted for different

ratios of pressure ratios versus mass flow rates; this is obtained by setting the electrical motor to a particular speed

and then back pressuring the compressor outlet to obtain the desired pressure ratio and measuring the flow rate.

The expander is characterized by a flow rate versus expansion pressure ratio for different electrical motor speeds;

this flow rate versus pressure ratio map is obtained by setting a particular expander pressure ratio and measuring

the different speeds by setting the compressor with the flow rate resulting.

Other useful curves concerns with electrical power, temperature or efficiency as parameter. So the aim of testing

is to obtain compressor maps plotting βc = f ( m& , x) and expander maps plotting m& = f (βt , x), being x a different parameter (motor speed, electrical power, motor efficiency, …).


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5.3 Procedure #1 - STATIC TEST: Compressor/expander unit characteristics maps

5.3.1 Description

This test consists of discrete increasing of electric motor revolutions per minute and back pressure valve cross

area to change air mass flow and pressure into the circuit4.

Aim of this static test is to confirm compressor/expander maps according to data sheets from manufacturer.

5.3.2 Test procedure

1. Set voltage output of the power supply device at nominal value of the electric motor

2. Set motor control in order to obtain a pre-determined minimum revolution per minute (for example:minimum speed according to manufacturer data sheets)

3. Increase motor revolution speed to a fixed value according to a sufficient number of samples (for example

a discretization step of 10% respect to maximum electric motor speed)

4. Set back pressure regulation valve5 to obtain desired minimum compression ratio value βc, measuring

pressure at compressor delivery p2.

5. Before readings begin, for each test step, the unit should be run for a sufficient time in order to ensure that

steady state conditions are reached, so that no systematic changes occur in the instrument readings.

6. Measure the following variables:

• air mass flow;

• compressor inlet temperature T1 and outlet temperature T2 ;

• expander inlet pressure p3 ;

• expander inlet/outlet temperature T3 and T4 ;

• electrical power absorption by the electric motor;

• motor speed (revolutions per minute);

• motor shaft torque (upon request).

7. Change6 back pressure valve regulation with a reasonable discrete increment (for example: in case of

solenoid valve control 4-20 mA with step 0.5 mA)

8. Repeat step from 4. to 7. until the back pressure valve is 90% closed

9. Repeat from step 3.

4 Indicate circuit characteristics: length, diameter, curves, material at compressor suction and delivery.

5 In case of solenoid valve set reference control command according to data sheets (pressure-control map).

6 Increase motor control until 90% of maximum value and close back pressure valve until 90% of diameter.


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Change electric motor rpm

(from minimum up to 90% of maximum value)

Change back-pressure valve regulation

(from “completely open” to 90% close)

Wait for steady state conditions

Parameters acquisition or reading

(pressure, temperature, mass flow, current)

GO OUT

if valve range has been completely checked

Set back-pressure valve to

minimum compression ratio

Figue 6. Test bench procedure flow chart

5.3.3 Shut down procedure

This procedure applies when all data, following 5.3.2, have been recorded or when a test must be stopped. The

aim is leaving the bench ready for a next test.

1. Decrease motor rotational speed down to zero rpm;

2. Open completely back-pressure valve;

3. Check the motor is stopped;

4. Check for instrumentation to give rest values;

5. Turn off power supply devices

5.3.4 Data analysis and mapping

Compressor maps:

• Plot values βc = f ( m& , n) that is compression ratio vs. air mass flow, connecting iso-motor speeds(revolutions per minute).

• Plot values βc = f ( m& , Pe) on compression ratio vs. air mass flow, connecting iso-electric motor power points.


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• Plot values βc = f (m& , T2) on compression ratio vs. air mass flow, connecting iso-dischargetemperature points.

• Plot values βc = f ( m& , η) on compression ratio vs. air mass flow, connecting iso-motor efficiency points.

Expander maps:

• Plot values m& = f (βt, n) on mass flow vs. expansion ratio, connecting iso-motor speeds (revolutions per minute) points.

• Plot values m& = f (βt, T3) on mass flow vs. expansion ratio, connecting iso-inlet temperature points.


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5.4 Procedure #2 - DYNAMIC TEST: Dynamic evaluation of transient

5.4.1 Description

This test consists of instant increasing of electric motor revolutions per minute from minimum to nominal value

speed, fixed the nominal conditions of the system.

Scope of this dynamic test is to check start-up transient duration up to nominal conditions, determining time

necessary to catch up the conditions of nominal operation of the compressor/expander unit.For development of this test it is necessary to verify that used instrumentation is compatible with the expected

dynamics of the components.

5.4.2 Test procedure

1. Set desired compression ratio βc, by means of back pressure valve’s regulation7.

2. Set data acquisition system to measure parameters (overall mass flow) versus time during transients up to

dynamic equilibrium condition8.

3. Change motor control with an instant increment from minimum to value corresponding to nominal rpm for

pre-set compression ratio (for example: 0÷5000 rpm only one step), multiplied for a safety factor (90% ofmaximum value of control).

4. Repeat for different compression ratio values setting valve cross area with discrete increment.

5.4.3 Data analysis and mapping

• Plot values (t, m& ) on air mass flow vs. time diagram

• Plot values (t, n) on revolution per minute vs. time diagram

• Plot values (t, βt) on compression ratio vs. time diagram

• Plot values (t, Pe) on compression ratio vs. time diagram

• Plot values (t, T2) on output temperature vs. time diagram

• Plot values (t, T3) on output temperature vs. time diagram

NOTE

A sampling time as 10Hz at least should be used in this dynamic test for modeling of dynamic behaviour.

7 To settle desired valve position refer to previous STATIC TEST.

8 Acquisition time intervals must be shorter than transient duration – maximum 0.1 sec.


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6. Results

Check that there is no failure after previous tests and perform a detailed test report.

The report should contain the following chapters:

• Introduction

• Test samples

• Test equipment

• Test program

• Test results

• Conclusions

6.1.1 Introduction

This chapter should give the overall scope of the report, a brief description of the compressor/expander unit that

has been tested (for example giving indication of the technology) and the purpose of the tests; the chapter should

include also a summary of the most important results of the testing activity.

6.1.2 Test sample

This section shall describe the compressor/expander unit more in detail, with manufacturer’s technical data. Whenavailable, pictures and/or drawings with most relevant quotes of the sample should be included in the report.

If not already done, an identification number should be assigned to the sample.

6.1.3 Test equipment

The test equipment (sensors, transducers, actuators, drivers, data acquisition devices) should be described9.

Where possible, a drawing of the layout of the test bench showing the location of the instrumentation and main

geometrical dimensions should be included in the report.

Any factors that might influence results should be pointed out.

6.1.4 Test program

The test program should be described in detail. Test conditions (pressure, temperature, etc.) should be reported.

Any deviation from the test procedure should be commented upon.

9 The description of the test equipment may be done giving a list of the used instrumentation, referring to appropriate data sheet for an

evaluation of the performance. It would be preferable to report a short data sheet of each of the component used for the test activity


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6.1.5 Test results

The test results shall be reported in both tables and graphs.An output example graph should be presented according to figure given in Annex A.

6.1.6 Conclusions

This chapter should put its emphasis on conclusions from the test results on the technical performance of the

compressor/expander unit.


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Annex A(Informative)

Samples of components identification and graphical results (static tests)

Component: Electric compressor/expander unit

Type: Volumetric / dynamic (centrifugal)

Draw n.

Producer:

Date of manufacture:

Air-compressor map

mass flow

c o m p r r e s s i o

n r a t i o

rpm1

rpm2

rpm3

rpm4

rpm5

P1

P2

P3

P4

P5

T1

T2

T3

T4

Figure 7 - Volumetric compressor map: β c = f ( m& , x)


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Dynamic compressor map

mass flow

c o m p r e s s i o n r a t i o

rpm1

rpm2

rpm3

rpm4

rpm5

rpm6

Poli.(rpm6)

Poli.(rpm5)

Poli.

(rpm4)Poli.(rpm3)

Poli.(rpm2)

Poli.(rpm1)

surge line

Figure 8 - Dynamic (centrifugal) compressor map: β c = f ( m& , rpm)

Dynamic expander map

expansion ratio

m a s s f l o w

rpm4

rpm3

rpm2

rpm1

Figura 9 - Dynamic(centrifugal) expander map: m& = f ( β t , rpm)


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Annex B(Informative)

Compressor/expander unit test procedure with heater

The quantity of recovered energy into the expander depends on inlet air temperature. So in order to simulate the

fuel cell running and increase the energy, it is possible to insert into the circuit a heater before the expander (see

Figure 10). In this way it is possible to carry on the same procedure before suggested for different values of

temperature T3 at inlet of the expander.

2-5 D

Integrated Integrated

electric electric motor motor

Compressor Compressor

Back-pressure

valve

Rpm control system

MMTI2TI2

PI2

5-10 D

FI1

2-5 D

TI1PI1

Flow meter

INLETINLET

DISCHARGEDISCHARGE

TI3PI3

2-5 D

TI3PI3

5-10 D

Heater Heater

Expander Expander

Figure 10 Compressor/expander unit with heater


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Annex C(Informative)

Solid particles and oil content in air outlet

C.1 General

Fuel cell stack cathode requires air at the inlet without contaminants in order not to decrease stack performances.

Because of the environment in which stacks operate and available compressor/expander unit technology, it is

possible to identify two types of contaminants:

• oil droplets

• solid particles

Since there are no specifications about the maximum content which is allowed (mostly referred as “oil free”), the

aim of the procedure is to evaluate if there are or not contaminants in the air at different compressor rotational

speeds (maximum speed and 50% maximum speed)

C.2 References

In order to have some quantitative results, it is possible to identify air quality according to ISO 8573-1. In this

Standard, the highest air quality (“Class 1”) is characterized by:

• 0.1 µm as maximum diameter for solid particles• 0.01 mg/m3 as the maximum oil concentration.

C.3 Equipment

This test should be done without connecting compressor outlet to expander inlet. So figure 11 is the diagram of

reference for this procedure (this test is important in order to save fuel cell from contaminants).Because of the qualitative aim of this test, neither pressure, nor temperature, nor flow indicators are required.

Particular attention should be placed on the choice of piping materials.

A device able to remove particles and oil shall be installed at compressor downstream instead of back pressurevalve, placing particular attention to the pressure drop of the device

10. A device with an oil level indicator is

suggested.

10 Infact the device acts as a secondary pressure loss for which the higher is the filtration grade, the higher is the pressure drop


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PPee

PPmm ηMM

ηCC

PPcc

CompressorCompressor

IN

OUT

ElectricElectric MotorMotor

MeasurementMeasurement

devicedevice

1

2

Figure 11- Diagram for contaminants presence procedure

C.4 Test procedure

1. Install compressor/expander unit on bench test cell

2. Connect the compressor to the measurement device by means of inlet piping with free discharge

3. Set motor rotational speed at 50% maximum speed .

4. Let the compressor/expander unit operate for a reasonable11

time

5. Shut-off the compressor/expander unit and evaluate the presence of contaminants

6. Substitute a clean measurement ("filtration") device

7. Change motor speed up to its maximum value

8. Repeat steps 4 and 5

9. End of the test

C.5 Data Reporting

The section “Test results” of the final report shall include the indication of the presence of contaminants in thestream at the compressor outlet

11 Otherwise it would possible to identify a load cycle (on/off at a certain rotational speed) that the compressor has to follow, in order to

evaluate the influence of transients in the presence of contaminants in the air at the compressor outlet


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Annex D(Informative)

Compressor/expander sound emission test

D.1 Description

Compressor and expander are the most relevant device with rotating parts in the fuel cell system and for this

reason noise is an important issue in compressor/expander unit characterization.

This test consists of several measurements during discrete increasing of electric motor revolutions per minute to

change operative conditions of the air system.

Aim of sound emission test is to measure compressor/expander unit sound emission at different levels of rotating

speed from minimum to maximum. For this reason, with respect to scheme in Figure 4, no external piping isintroduced because it may alter the sound measurement from the components.

D.2 Reference

The following ISO Standard should be also included:

ISO 3745: Acoustics - Determination of sound power levels of noise sources – Precision method for anechoic

and semi-anechoic rooms

D.3 Equipment

The following instrumentation should be included to perform the measurement:

• condenser microphone cartridges (free-field type12);

• suitable microphone preamplifiers;

• DC power supply (for externally polarized microphones)

• FFT analyzer

D.4 Test procedure

In the following no preliminary operations with microphones are described because it is intended that

cartridges are already coupled with preamplifiers and that microphones are already calibrated.

1. Install compressor/expander unit on the bench in an anechoic test cell or in an ambient with low index of

reflection

12 With specially designed correctors on the cartridge, many free-field microphones may be practically independent of angle of incidence


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2. Turn on data acquisition system and check that no signal is given to the electric motor drive

3. (For externally polarized microphones) Turn on DC power supply

4. (For externally polarized microphones) Wait for a reasonable time (around one minute) to complete

charge of the backplate

5. Connect power supply to the electric motor drive

6. Set motor revolution per minute at minimum allowable value.

7. Measure compressor/expander unit sound emission (dBA)

8. Change motor speed with discrete increment

9. Repeat step 7 - 8 up to maximum allowable speed of the motor

D.5 Data analysis and mapping

Plot spectrum (dBA, Hz) and verify according to data sheet supplied by the manufacturer when available.


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Annex F(Informative)

Electric power supply instrumentation

F.1 General

The aim of this section is to give some issues of electric power supply devices, which are used for common

automotive applications17.

It must be remarked that, in most cases, automotive electric bus is at direct current, while electric energy, at

laboratories plugs, is available as a tri-phase alternate current. These devices must convert tri-phase alternatecurrent in a direct current suitable for automotive application.

F.2 Definitions

Constant current power supply: a device whose output current is constant when electric load changes

Constant voltage power supply: a device whose output voltage is constant when electric load changes

Load effect: variation of the stabilized value of voltage (constant voltage power supply) or current (constant

current power supply) when load is increased from 0 to 100%

Source effect: variation of stabilized voltage or current due to a variation in input voltage

Load effect transient recovery time: required time to stabilize voltage or current under a change in the applied

load

F.3 Requirements

Requirements for this device are:

• Continuous power supply able to sustain both nominal and peak loads

•Variation in output voltage, when stabilized, should not exceed 0.01% of nominal value (taking intoconsideration load and source effect)

• Load effect transient recovery time below 50 µs

17 It is possible to identify also a series of accumulators as a power supply device, but for test field activity a stabilized power supply

device is a preferable solution


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Annex G(Informative)

Analysis of uncertainty of measurement

Due to the nature of measurements, it is impossible to measure a physical quantity without error. The quality of a

test is well estimated if analysis of uncertainties of measurement is carried out (in order to achieve the aim of

coherence within international standards, see normative reference ISO 5168).

It is possible to calculate a deviation of the measured value in order to have a criterion of the accuracy of the

measurement.

In general the procedure to follow in this analysis involves the following steps:

• list of possible sources of error;

• calculation of the value of error for each source;

• separated combination of every measure with various methods (root of the sum of squares or index of precision);

• separate setting for each measure parameter of the index of precision;

• calculate uncertainties for each parameter;

• fix the interval of uncertainty for each parameter.

The results report must contain for each parameter (possibly in a table):

• the test value;

• the index of precision and the associated freedom degree;

• the band of systematic error;

• the uncertainty based on 95% of deviation map.

testprocedure compressor expander

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