ISO 6855-1:2012

INTERNATIONAL ISO
STANDARD 6855-1
First edition
2012-09-15
Mopeds — Measurement method for
gaseous exhaust emissions and fuel
consumption —
Part 1:
General test requirements
Cyclomoteurs — Méthode de mesure des émissions de gaz polluants et
de consommation de combustible —
Partie 1: Exigences générales d’essai
Reference number
©
ISO 2012
© ISO 2012
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Published in Switzerland
ii © ISO 2012 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Standard reference conditions . 4
6 Tests . 4
6.1 Measurement of gaseous exhaust emissions . 4
6.2 Measurement of fuel consumption . 5
7 Measurement equipment . 5
7.1 Chassis dynamometer . 5
7.2 Gas-collection equipment . 5
7.3 Analytical equipment . 6
7.4 Cooling equipment. 6
7.5 Fuel consumption measurement . 7
7.6 Accuracy of instruments and measurements . 7
8 Preparing the test . 8
8.1 Engine fuel and lubricants . 8
8.2 Description of the test moped. 8
8.3 Conditioning/preparation of the test moped . 8
8.4 Adjustment of the analytical apparatus . . 8
9 System check procedure . 9
9.1 Accuracy of the CVS system . 9
9.2 Metering a constant flow of pure gas (CO or C H ) using a critical flow orifice . 9
3 8
9.3 Metering a limited quantity of pure gas (CO or C H ) by means of a
3 8
gravimetric technique . 9
10 Procedure for sampling, analysing and measuring the volume of gaseous
exhaust emissions . 9
10.1 Operations to be carried out before the moped start up . 9
10.2 Beginning of sampling and volume measurement .12
10.3 End of sampling and volume measurement .12
10.4 Analysis.12
10.5 Measuring the driving distance .13
10.6 Open type CVS system .13
11 Determination of the quantity of gaseous exhaust emissions .13
11.1 Total diluted exhaust mixture volume corrected to the standard reference conditions .13
11.2 Exhaust gas sampling and the dilution factor .14
11.3 Mass of the gaseous exhaust emissions .14
12 Determination of the fuel consumption .16
12.1 Carbon balance method .16
12.2 Fuel flow measurement method .17
12.3 Calculation of results in litres per 100 km .18
12.4 Criteria of the statistical accuracy for the fuel consumption measurements .18
Annex A (normative) Method and equipment for measuring fuel consumption by the fuel flow
measurement method .19
Annex B (informative) Example for record form of test fuel specifications .30
Annex C (informative) Exhaust gas leakage check procedure for the open type CVS system.31
Annex D (informative) Determination of the dilution factor .36
Annex E (informative) Principle of the carbon balance method .44
Annex F (informative) Simplified determination method of the atom number ratio of hydrogen
and carbon, and that of oxygen and carbon in gasoline .47
Annex G (normative) Fuel consumption for two-stroke engines .49
Annex H (informative) Criteria of the statistical accuracy for the fuel
consumption measurements .50
Bibliography .52
iv © ISO 2012 – All rights reserved

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International
Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies
casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 6855-1 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 23, Mopeds.
ISO 6855-1 cancels and replaces ISO 6855:1983 and ISO 7859:2000, both of which have been
technically revised.
ISO 6855 consists of the following parts, under the general title Mopeds — Measurement method for
gaseous exhaust emissions and fuel consumption:
— Part 1: General test requirements
— Part 2: Test cycles and specific test conditions
— Part 3: Fuel consumption measurement at a constant speed
Introduction
For measurement of moped fuel consumption, the carbon balance method, where the fuel consumption
is calculated from analysis of the carbon quantity in the exhaust gas, is now widely used in addition to
the conventional fuel flow measurement. Therefore, the measurement of exhaust gas and that of fuel
consumption are inseparably related to each other.
ISO 6855 now covers in one single series of standards the two subjects that were previously covered
separately by ISO 6855:1983 and by ISO 7859:2000. This part of ISO 6855 defines fundamental elements
such as the measurement accuracy, test vehicle conditions and the details of the carbon balance method.
Measurement of gaseous exhaust gas emissions and fuel consumption of test cycles can be conducted
with this part of ISO 6855 and ISO 6855-2. Together with ISO 6855-3, they also give details of those
measurements at a constant speed.
While the most up-to-date technologies are reflected in the ISO 6855 series, further technical
development in the following aspects will be necessary in the future, when measurement of exhaust gas
at a lower level is required:
— cleaning of the background air (i.e the air in the test room which is used for the dilution air);
— heating of the sampling line;
— control of the test room humidity;
— the exhaust gas analysis system for low-level emissions;
— consideration for the evaporated fuel from the test moped.
In addition to the above future issues, the chassis dynamometer with electrically simulated inertia is
at the stage of practical application. Standardization of the verification method and the allowance of
simulated inertia would be necessary for this recent development.
vi © ISO 2012 – All rights reserved

INTERNATIONAL STANDARD ISO 6855-1:2012(E)
Mopeds — Measurement method for gaseous exhaust
emissions and fuel consumption —
Part 1:
General test requirements
1 Scope
This part of ISO 6855 specifies the general test requirements for measurement for the gaseous exhaust
emissions from mopeds, and for determining the fuel consumption of mopeds as defined in ISO 3833. It
is applicable to mopeds equipped with a spark ignition engine (four-stroke engine, two-stroke engine or
rotary piston engine).
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 3833, Road vehicles — Types — Terms and definitions
ISO 6855-2:2012,Mopeds — Measurement method for gaseous exhaust emissions and fuel consumption —
Part 2: Test cycles and specific test conditions
ISO 6855-3:2012, Mopeds — Measurement method for gaseous exhaust emissions and fuel consumption —
Part 3: Fuel consumption measurement at a constant speed
ISO 28981, Mopeds — Methods for setting the running resistance on a chassis dynamometer
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3833 and the following apply.
3.1
moped kerb mass
dry mass of the moped to which is added the mass of the following:
— fuel: tank filled at least to 90 % of the capacity specified by the manufacturer;
— auxiliary equipment usually supplied by the manufacturer in addition to that necessary for normal
operation [tool-kit, carrier(s), windscreen(s), protective equipment, etc.]
3.2
reference mass of the moped
kerb mass of the moped increased by a uniform figure of 75 kg, which represents the mass of a rider
3.3
equivalent inertia
total inertia of the rotating masses of the test bench, determined with respect to the reference mass of
the moped
3.4
gaseous exhaust emissions
carbon monoxide, hydrocarbons, nitrogen oxides (gaseous pollutants) and carbon dioxide emitted from
mopeds
4 Symbols
Table 1 — Symbols
a
Symbols Definition Unit
a mixing ratio of lubrication oil and fuel ─
c carbon monoxide concentration in the dilution air ppm
CO,d
c carbon monoxide concentration in the dilution air with the water vapour and carbon ppm
CO,dm
dioxide absorbent
c carbon monoxide concentration in the diluted exhaust mixture ppm
CO,e
c volumetric concentration of carbon monoxide in the diluted exhaust mixture, cor- ppm
CO,ec
rected to take account of carbon monoxide in the dilution air
c carbon monoxide concentration in the diluted exhaust mixture with the water ppm
CO,em
vapour and carbon dioxide absorbent
c carbon dioxide concentration in the dilution air %
CO2,d
c carbon dioxide concentration in the diluted exhaust mixture %
CO2,e
c volumetric concentration of carbon dioxide in the diluted exhaust mixture, corrected %
CO2,ec
to take account of carbon dioxide in the dilution air
c nitrogen oxides concentration in the dilution air ppm
NOx,d
c nitrogen oxides concentration in the diluted exhaust mixture ppm
NOx,e
c volumetric concentration of nitrogen oxides in the diluted exhaust mixture, cor- ppm
NOx,ec
rected to take account of nitrogen oxides in the dilution air
c oxygen concentration in the dilution air %
O2,d
c concentration of the pollutant i in the diluted exhaust mixture, corrected to take ppm
Pi,ec
account of the amount of the pollutant i contained in the dilution air
c hydrocarbon concentration in the dilution air as measured in parts per million car- ppmC
THC,d
bon equivalent
c hydrocarbon concentration in the diluted exhaust mixture as measured in parts per ppmC
THC,e
million carbon equivalent
c volumetric concentration, expressed in parts per million carbon equivalent, of ppmC
THC,ec
hydrocarbon in the diluted exhaust mixture, corrected to take account of hydrocar-
bon in the dilution air
D dilution factor ─
f
F specific fuel consumption km/L
c
F’ specific fuel consumption for lubrication oil mixed fuel km/L
c
F fuel consumption per 100 km L/100 km
c100
F lubrication oil consumption for the mixed fuel km/L
o
H absolute humidity in grams of water per kilogram of dry air ─
a
H relative humidity of dilution air %
d
H relative humidity in the test room %
r
H standard relative humidity %
a
ppm = parts per million.
2 © ISO 2012 – All rights reserved

Table 1 (continued)
a
Symbols Definition Unit
K humidity correction factor used for the calculation of the mass emissions of nitrogen ─
H
oxides
K venturi correction factor ─
K ratio of pressure to temperature at the standard reference conditions ─
L running distance actually travelled km
m mass of carbon monoxide in the exhaust gas g/km
CO
m mass of carbon dioxide in the exhaust gas g/km
CO2
m fuel consumed g
f
m mass of nitrogen oxides in the exhaust gas g/km
NOx
m mass emission of the pollutant i g
Pi
m mass of hydrocarbon in the exhaust gas g/km
THC
N number of revolutions of positive displacement pump during the test while samples ─
are being collected
p mean barometric pressure during the test in the test room kPa
a
p saturated water vapour pressure during the test in the test room kPa
d
p diluted exhaust mixture absolute pressure at the inlet of positive displacement pump kPa
p
p absolute pressure at the venturi inlet kPa
V
p (t) absolute pressure of the diluted exhaust mixture at the venturi inlet kPa
V
p total barometric pressure at the standard reference conditions kPa
Q measured flow rate of venturi at ambient conditions L/s
a
Q measured flow rate of venturi using the other gas flowmeter L/s
cal
R atom number ratio of hydrogen and carbon in the exhaust gas ─
HC,ex
R’ atom number ratio of hydrogen and carbon in the exhaust gas for lubrication oil ─
HC,ex
mixed fuel
R atom number ratio of hydrogen and carbon in the fuel ─
HC,f
R atom number ratio of hydrogen and carbon in the lubrication oil ─
HC,o
R atom number ratio of oxygen and carbon in the exhaust gas ─
OC,ex
R’ atom number ratio of oxygen and carbon in the exhaust gas for lubrication oil mixed ─
OC,ex
fuel
R atom number ratio of oxygen and carbon in the fuel ─
OC,f
R atom number ratio of oxygen and carbon in the lubrication oil ─
OC,o
r relative air density at the standard reference conditions ─
t time s
t total test time s
test
T measured ambient temperature during the test in the test room K
a
T fuel temperature measured at the burette K
f
T temperature of diluted exhaust mixture at the positive displacement pump inlet dur- K
p
ing the test while samples are being collected
T temperature at the venturi inlet K
v
T (t) temperature of diluted exhaust mixture at the venturi inlet K
v
T air temperature at the standard reference conditions K
a
ppm = parts per million.
Table 1 (continued)
a
Symbols Definition Unit
T mean dry bulb temperature during the test in the test room K
T mean wet bulb temperature during the test in the test room K
V measured volume of fuel consumed L
V dilution air volume L
d
V volume of the diluted exhaust mixture expressed corrected to the standard refer- L/km
e
ence conditions
V exhaust gas volume L
ex
V fuel volume of lubrication oil mixed fuel L
f
V volume of the diluted exhaust mixture in one test under the standard reference con- L
i,e
ditions
V lubrication oil volume of lubrication oil mixed fuel L
o
V diluted exhaust mixture volume pumped by the positive displacement pump per one L
p
revolution
V total diluted exhaust mixture volume during one test L
s
−1
α coefficient of volumetric expansion for the fuel K
ρ carbon monoxide density at the standard reference conditions g/L
CO
ρ carbon dioxide density at the standard reference conditions g/L
CO2
ρ fuel density at 293,15 K g/L
f
ρ nitrogen oxides density under the standard reference conditions, expressed in g/L
NOx
equivalent NO
ρ lubrication oil density at 293,15 K g/L
o
ρ density of the pollutant i under the standard reference conditions g/L
Pi
ρ hydrocarbon density at the standard reference conditions g/L
THC
ρ air volumetric mass at the standard reference conditions kg/m
a
ppm = parts per million.
5 Standard reference conditions
The standard reference conditions shall be as follows:
a) total barometric pressure, p : 101,325 kPa;
b) air temperature, T : 293,15 K;
c) relative humidity, H : 65 %;
d) air volumetric mass, ρ : 1,205 kg/m ;
e) relative air density, r : 0,931 9.
6 Tests
6.1 Measurement of gaseous exhaust emissions
6.1.1 Average gaseous exhaust emissions during conventional test cycles
The test shall be carried out in accordance with the method described in ISO 6855-2.
4 © ISO 2012 – All rights reserved

6.1.2 The gaseous exhaust emissions measurement at an idling speed
The test shall be carried out in accordance with the procedure described in ISO 6855-2.
6.2 Measurement of fuel consumption
6.2.1 Average fuel consumption during conventional test cycles
The test shall be carried out in accordance with the procedure described in ISO 6855-2.
6.2.2 Fuel consumption at a constant speed
The test shall be carried out in accordance with the procedure describedin ISO 6855-3.
7 Measurement equipment
Irrespective of the provisions specified below, any measurement system(s) may be used when the
performance of the equipment is proven by the equipment manufacturer to be equivalent to CVS
(constant volume sampling) system.
7.1 Chassis dynamometer
The chassis dynamometer shall be set in accordance with ISO 28981.
7.2 Gas-collection equipment
7.2.1 The gas-collection device, shall be a closed type device that can collect all exhaust gases at
the moped exhaust outlet(s) while maintaining atmospheric pressure at the exhaust outlet(s). An open
system may be used as well if it is confirmed that all the exhaust gases are collected. The gas collection
shall be such that there is no condensation, which could appreciably modify the nature of exhaust gases
at the test temperature.
7.2.2 A connecting tube, between the device and the exhaust gas sampling system. This tube, and the
device, shall be made of stainless steel, or of some other material which does not affect the composition
of the gases collected, and which withstands the temperature of these gases.
7.2.3 A heat exchanger, capable of limiting the temperature variation of the diluted exhaust mixture in the
pump intake to ± 5 K throughout the test. This exchanger shall be equipped with a preheating system capable
of bringing the exchanger to its operating temperature (with the tolerance of ± 5 K) before the test begins.
7.2.4 A positive displacement pump (PDP), to draw in the diluted exhaust mixture. This pump is
equipped with a motor having several strictly controlled uniform speeds. The pump capacity shall be
large enough to ensure the intake of all the exhaust gases.
7.2.5 A critical flow venturi (CFV) may also be used.
7.2.6 A device to allow continuous recording of the temperature of diluted exhaust mixture entering
the pump.
7.2.7 Two gauges:
— one to ensure the pressure depression of the diluted exhaust mixture entering the pump, relative to
atmospheric pressure;
— one to measure the dynamic pressure variation of the positive displacement pump.
7.2.8 A probe, located near to but outside the gas-collecting device, to collect, through a pump, a filter
and a flowmeter, samples of the dilution air stream, at constant flow rates, throughout the test.
7.2.9 A sample probe, pointed upstream into the diluted exhaust mixture flow, upstream of the positive
displacement pump or the critical flow venturi to collect, through a pump, a filter and a flowmeter, samples
of the diluted exhaust mixture, at constant flow rates, throughout the test.
The minimum sample flow rate in the two sampling devices described in 7.2.8 and 7.2.9 shall be 150 L/h.
7.2.10 Three way valves, on the sampling system, described in 7.2.8 and 7.2.9, to direct the samples
either to their respective bags or to the outside throughout the test.
7.2.11 Gas-tight collection bags, for dilution air and diluted exhaust mixture of sufficient capacity
so as not to impede normal sample flow and which will not change the nature of the gaseous exhaust
emissions concerned.
The bags shall have an automatic self-locking device, and shall be easily and tightly fastened either to the
sampling system or the analysing system at the end of the test.
7.2.12 A revolution counter, to count the revolutions of the positive displacement pump throughout the
test.
Good care shall be taken with the connecting method and the material or configuration of the connecting
parts because there is a possibility that each section (e.g. the adapter and the coupler) of the sampling
system will become very hot. If the measurement cannot be performed normally due to heat-damages of
the sampling system, an auxiliary cooling device may be used as long as the exhaust gases are not affected.
NOTE 1 With open type devices, there is a risk of incomplete gas collection and gas leakage into the test room,
so it is important to make sure that there is no leakage throughout the sampling period.
NOTE 2 If a constant CVS flow rate is used throughout the test cycle that includes low and high speeds all in
one, it is advisable that special attention be paid because of higher risk of water condensation in high speed range.
7.3 Analytical equipment
7.3.1 The sample probe shall consist of a sampling tube leading into the collecting bags, or of a drainage
tube. This sample probe shall be made of stainless steel or of some other material that will not adversely
affect the composition of the gases to be analysed. The sample probe as well as the tube taking the gases
to the analyser shall be at ambient temperature.
7.3.2 Analysers shall be of the following types:
a) non-dispersive type with absorption in the infrared for carbon monoxide and carbon dioxide;
b) flame ionization type for total hydrocarbons (diluted measurements);
c) non-dispersive type with absorption in the infrared for hydrocarbons (direct measurements);
d) chemiluminescence type for nitrogen oxides.
7.4 Cooling equipment
Throughout the test, a variable speed cooling blower shall be positioned in front of the moped, so as to
direct the cooling air to the moped in a manner which simulates actual operating conditions. The blower
speed shall be such that, within the operating range of 10 to 50 km/h, the linear velocity of the air at the
blower outlet is within ± 5 km/h of the corresponding roller speed. At roller speeds of less than 10 km/h,
air velocity may be zero.
6 © ISO 2012 – All rights reserved

As far as possible, the air speed shall be constant across the whole outlet section.
The blower outlet shall have a cross-section area of at least 0,2 m and the bottom of the blower outlet
shall be between 5 cm and 20 cm above floor level. The blower outlet shall be perpendicular to the
longitudinal axis of the moped between 30 cm and 45 cm in front of its front wheel. The device used to
measure the linear velocity of the air shall be located at between 0 cm and 20 cm from the air outlet.
7.5 Fuel consumption measurement
7.5.1 One of the following methods shall be used to measure the fuel consumption, depending on
the characteristics of each method and on the type of test to be performed (conventional test cycle or
constant speed):
a) carbon balance method;
b) volumetric method;
c) gravimetric method;
d) flowmeter method.
The carbon balance method shall be applied in accordance with 12.1.
Other methods may be used if it can be proved that the results given are equivalent.
7.5.2 Fuel shall be supplied to the engine by a device capable of measuring the quantity of fuel supplied
with an accuracy of ± 2 % in accordance with Annex A, and which does not interfere with the supply of
fuel to the engine. When the measuring system is volumetric, the temperature of the fuel in the device or
in the device outlet shall be measured.
Switching from the normal supply system to the measuring supply system shall be done by a valve
system and shall take no more than 0,2 s.
7.5.3 Annex A gives the description and the methods of use of the appropriate devices for fuel flow
measurement.
7.6 Accuracy of instruments and measurements
7.6.1 The distance travelled by the moped shall be measured with an accuracy of ± 1 %.
7.6.2 The speed of the moped shall be measured with an accuracy of ± 1 % to the resolution of 0,1 km/h.
For speeds less than 10 km/h, the speed shall be measured to the resolution of 0,1 km/h.
7.6.3 The ambient temperatures and the temperatures considered in 7.2.3 and 7.2.6 shall be measured
with an accuracy of ± 2 K.
7.6.4 The atmospheric pressure shall be measured with an accuracy of ± 0,2 kPa.
7.6.5 The relative humidity of the ambient air shall be measured with an accuracy of ± 5 %.
7.6.6 The pressures considered in 7.2.7 shall be measured with an accuracy of ± 0,4 kPa.
7.6.7 The analysers shall have a measuring range compatible with the accuracy required to measure the
content of the various pollutants and carbon dioxide with an accuracy of ± 1 %, regardless of the accuracy
of the calibration gases. The overall response time of the analysing circuit shall be less than 1 min.
7.6.8 The cooling air speed shall be measured with an accuracy of ± 5 km/h.
7.6.9 The duration of cycles and gas collection shall be conducted with an accuracy of ± 1 s. These times
shall be measured with an accuracy of 0,1 s.
7.6.10 The total volume of the diluted exhaust mixture shall be measured with an accuracy of ± 3 %.
7.6.11 The total flow rate and the sampling flow rates shall be steady with an accuracy of ± 5 %.
7.6.12 The wind speed on the test road shall be measured with an accuracy of ± 5 % to the resolution of
0,1 m/s.
8 Preparing the test
8.1 Engine fuel and lubricants
The test fuel shall be selected in accordance with the manufacturer’s requirements and the specification
of test fuel shall be reported. An example of the record form is given in Annex B.
With regard to grade and quantity of oil, the lubrication of the engine shall comply with the manufacturer’s
recommendation.
8.2 Description of the test moped
The main specifications of the moped shall be provided in accordance with ISO 6855-2:2012, Annexes A
and B and with ISO 6855-3:2012, Annex B.
8.3 Conditioning/preparation of the test moped
8.3.1 The engine, transmission and moped shall be run in properly in accordance with the manufacturer’s
requirements.
8.3.2 The moped shall be adjusted in accordance with the manufacturer’s requirements (e.g. the viscosity
of the oils, tyre pressures) or, if there is any alteration, the full description shall be given in the test report.
8.3.3 The distribution of the load between the wheels shall be in conformity with the manufacturer’s
instructions.
8.4 Adjustment of the analytical apparatus
8.4.1 Calibration of the analysers
The calibration gas at the indicated pressure, compatible with the correct functioning of the equipment,
shall be passed through the analyser.
The curve of the analyser’s deviations shall be drawn as a function of the contents of the various gas
cylinders used.
8.4.2 Adjustment of the analysers
The adjustment of the analysers can then be carried out with only one calibration gas having an
established content.
8 © ISO 2012 – All rights reserved

8.4.3 Overall response time of the apparatus
The gas from the cylinder that contains the maximum concentration shall be introduced into the end
of the sampling probe. A check shall be made to ensure that the indicated value corresponding to the
maximum deviation is reached in less than 1 min. If this value is not reached, the analysing circuit shall
be inspected from end to end for leaks.
9 System check procedure
9.1 Accuracy of the CVS system
The total accuracy of the CVS system and analytical system shall be determined by introducing a known
mass of a pollutant gas into the system while it is being operated as if during a normal test and then
analysing and calculating the pollutant mass according to Formula (1).
−6
mV=×ρ ××c 10 (1)
Pi i,ePiPi,ec
There is no humidity correction for hydrocarbon and carbon monoxide.
The two techniques in 9.2 and 9.3 are known to give sufficient accuracy.
9.2 Metering a constant flow of pure gas (CO or C H) using a critical flow orifice
3 8
A known quantity of pure gas (CO or C H ) is fed into the CVS system through the calibrated critical
3 8
orifice. If the inlet pressure is high enough, the flow-rate (q), which is adjusted by means of the critical
flow orifice, is independent of orifice outlet pressure (critical flow). If deviations exceeding 5 % occur,
the cause of the malfunction shall be located and determined. The CVS system is operated as in a gaseous
exhaust emission test for about 5 to 10 min. The gas collected in the sampling bag is analysed by the usual
equipment and the result compared to the concentration of the gas samples which was known beforehand.
9.3 Metering a limited quantity of pure gas (CO or C H ) by means of a gravimetric
3 8
technique
The following gravimetric procedure may be used to verify the CVS system. The weight of a small cylinder
filled with either carbon monoxide or propane is determined with a precision of ± 0,01 g. For about 5 to
10 min, the CVS system is operated as in a normal gaseous exhaust emission test, while CO or propane
is injected into the system. The quantity of pure gas involved is determined by means of differential
weighing. The gas accumulated in the bag is then analysed by means of the equipment normally used for
exhaust-gas analysis. The results are then compared to the concentration figures computed previously.
10 Procedure for sampling, analysing and measuring the volume of gaseous ex-
haust emissions
10.1 Operations to be carried out before the moped start up
A schematic diagram is shown in Figure 1 for the representative closed type CVS system with CFV and
Figure 2 for the representative closed type CVS system with PDP.
Key
1 exhaust gas 11 pressure gauge
2 dilution air 12 calculator
3 dilution air filter 13 integrator
4 mixing chamber F , F filters
2 3
5 cyclone P , P pumps
2 3
6 diversion valve R , R flowmeters
2 3
7 sampling venturi S , S sampling bags
a b
8 continuous sampling probe S , S probes
2 3
9 blower T temperature gauge
10 main critical flow venturi V , V valves
2 3
a
To HFID; special sampling line when HFID is used.
b
To atmosphere.
c
To exhaust pump.
d
To analysing system.
Figure 1 — A schematic diagram for the representative closed type CVS system with CFV
10 © ISO 2012 – All rights reserved

Key
1 exhaust gas F , F filters
2 3
2 dilution air g , g pressure gauges
1 2
3 dilution air filter P positive displacement pump
4 mixing chamber P , P pumps
2 3
5 heating exchanger R , R flowmeters
2 3
6 diversion valve S , S sampling bags
a b
7 motor S , S probes
2 3
8 continuous sampling probe T temperature gauge
CT revolution counter V , V valves
2 3
a
To HFID; special sampling line when HFID is used.
b
To atmosphere.
c
To exhaust pump.
d
To analysing system.
Figure 2 — A schematic diagram for the representative closed type CVS system with PDP
10.1.1 The bags for collecting the samples (S and S ) are emptied and sealed.
a b
10.1.2 The positive displacement pump (P ) is activated without starting up the revolution counter.
10.1.3 The pumps (P and P ) for taking the samples are activated with the valves set to divert the gases
2 3
produced into the atmosphere; the flow through valves (V and V ) is regulated.
2 3
10.1.4 The following recording devices are put into operation: the temperature gauge (T) and the
pressure gauges (g and g ).
1 2
10.1.5 The revolution counter (CT) and the roller revolution counter are set to zero.
10.2 Beginning of sampling and volume measurement
10.2.1 The operations specified in 10.2.2 to 10.2.5 are performed simultaneously.
10.2.2 The diversion valves are set to collect the samples, which have previously been directed towards
the atmosphere, continuously through probes (S and S ) in bags (S and S ).
2 3 a b
10.2.3 The moment at which the test begins is indicated on the analogue graphs which record results
from the temperature gauge T and the differential pressure gauges (g and g ).
1 2
10.2.4 The counter which records the total number of revolutions of pump (P ) is started up.
10.2.5 The device which directs a flow of air at the moped, referred to in 7.4, is started up.
10.3 End of sampling and volume measurement
10.3.1 At the end of the test cycle, the operations described in 10.3.2 to 10.3.5 are performed
simultaneously.
10.3.2 The diversion valves shall be set to close bags (S and S ) and to discharge into the atmosphere
a b
the samples sucked in by pumps (P and P ) through probes (S and S ).
2 3 2 3
10.3.3 The moment at which the test finishes shall be indicated on the analogue graphs referred to in 10.2.3.
10.3.4 The pump (P ) revolution counter is stopped.
10.3.5 The device which directs a flow of air at the moped, referred to in 7.4, is stopped.
10.4 Analysis
10.4.1 The exhaust gases contained in the bag shall be analysed as soon as possible, unless otherwise
specified in ISO 6855-2.
10.4.2 Prior to each sample analysis, the analyser range to be used for each pollutant shall be set to zero
with the appropriate span gas.
10.4.3 The analysers shall then be set to the calibration curves by means of span gases of nominal
concentrations of 70 % to 100 % of the range.
10.4.4 The analysers’ zeros shall then be rechecked. If the reading differs by more than 2 % of the range
from that set in 10.4.2, the procedure is repeated.
10.4.5 The samples shall then be analysed.
10.4.6 After the analysis, zero and span points shall be rechecked using the same gases. If these rechecks
are within 2 % of those in 10.4.3, the analysis is considered acceptable.
10.4.7 At all points in this clause the flow rates and pressures of the various gases shall be the same as
those used during calibration of the analysers.
10.4.8 The figure adopted for the concentration of each gaseous exhaust emission is that read off after
stabilization of the measuring device.
12 © ISO 2012 – All rights reserved

10.5 Measuring the driving distance
The distance actually travelled, expressed in km, is obtained by multiplying the total number of
revolutions shown on the revolution counter by the size of the roller.
10.6 Open type CVS system
When the open type CVS system is used in the test facility, the exhaust gas shall not leak from the
connecting part of the sampling pipe(s) of CVS system and tailpipe(s) of test moped. The exhaust gas
leakage shall be checked.
NOTE The exhaust gas leakage check method is described in Annex C.
11 Determination of the quantity of gaseous exhaust emissions
11.1 Total diluted exhaust mixture volume corrected to the standard reference conditions
The total diluted exhaust mixture volume flowed into the CVS system during the test shall be calculated
and corrected to the standard reference conditions of temperature and pressure. In the case of the CVS
system equipped with the CFV the procedure in 11.1.1 shall be used, and for the CVS system equipped
with the PDP the procedure in 11.1.2 shall be used.
11.1.1 Total diluted exhaust mixture volume for the CVS system with CFV
The diluted exhaust mixture volume for the CVS system equipped with the CFV shall be obtained from
Formulae (2) and (3):
VV=× (2)
e s
L
t
test pt()
v
VK= dt (3)
s1
∫
Tt()
v
The venturi correction factor, K , shall be determined from the measured flow rate of venturi, Q ,
1 cal
using the other gas flowmeter (e.g. the laminar flowmeter) and the venturi correction factor shall be
calculated from Formulae (4) and (5):
T
v
KQ=× (4)
1cal
p
v
p
a
QK=×Q (5)
cal2 a
T
a
The ratio of pressure to temperature at the standard reference conditions, K , shall be
K = 293,15/101,325 = 2,893.
11.1.2 Total diluted exhaust mixture volume for the CVS system with PDP
The volume of diluted exhaust mixture pumped during the test, V , shall be calculated by Formula (6).
e
p
p
VK=×VN×× × (6)
e2 p
TL
p
The diluted exhaust mixture volume pumped by the PDP per one revolution, V , is dependent upon the
p
variation of dynamic pressure of the PDP.
The diluted exhaust mixture absolute pressure at the inlet of PDP, p , is the difference between
p
atmospheric pressure and the depression at the inlet to the PDP while samples are being collected.
11.2 Exhaust gas sampling and the dilution factor
11.2.1 Exhaust gas sampling
The whole exhaust gas emitted from the tail pipe of the test moped shall be flowed into the CVS system, and
the adequate volume to analyse the diluted exhaust mixture (e.g. 50 L −100 L) shall be collected in the bag.
11.2.2 Dilution factor
The dilution factor, D , shall be calculated by Formula (7). (Detailed information is given in Annex D.)
f
It is recommended that the amount of the dilution air be determined so that the dilution factor becomes
8 or more to prevent the water condensation in the CVS system.
The dilution fact
...