GB/T 29125-2012Test methods for fuel consumption of CNG vehicles (English PDF)

3.1 Natural gas; NG

It refers to the methane-based complex hydrocarbon mixtures, usually containing ethane, propane and very small amounts of heavier hydrocarbons, as well as a number of incombustible gases such as nitrogen and carbon dioxide.

[GB/T 20604-2006, Definitions 2.1.1.1]

3.2 Dry natural gas

It refers to the natural gas for which the water vapor mole fraction is not more than 0.005% [50 × 10

-6 (mol)].

[GB/T 20604-2006, Definitions 2.1.1.9]

3.3 Combustion reference condition

It refers to the purely theoretical pressure and temperature conditions as specified for natural gas combustion.

[GB/T 20604-2006, Definition 2.6.1.1] […]

3.10 Inferior calorific value

It refers to, under the conditions that the pressure (p1) of the combustion reaction is kept constant AND all the combustion products other than water are returned to the gaseous state at the same temperature (T 1) as the reactant, the energy as released in the form of heat when a certain amount of fuel gas is completely burned in the air.

[GB/T 20604-2006, Definition 2.6.4.2]

4.1

The symbols, codes and abbreviations in Table 1 apply to this standard.

Table 1 Symbols, codes and abbreviations […]

5.1

Road test conditions shall comply with the provisions of GB/T 12534.

5.2

When using the chassis dynamometer test or carbon balance method, the

light vehicle test conditions shall comply with the provisions of GB/T 19233 and

GB18352.3; AND the heavy-duty vehicle test conditions shall comply with the provisions of GB/T 27840.

5.3

The natural gas fuel for the test of light vehicle and heavy vehicle shall respectively complies with the requirements of GB18352.3 and GB17691, OR the vehicle natural gas fuel complying with the provisions of GB 18047 may be used, with its components, density and heat and other parameters being known AND complying with the requirements of the automobile and engine manufacturers.

5.4

Lubricants for test purposes shall comply with the requirements of the enterprise AND shall be indicated in the test report.

6.1 Natural gas flowmeter

6.1.1 Allowable natural gas flowmeter type

6.1.1.1 Variable pressure mass flowmeter

an instrument using the Coriolis principle (or similar principle) to measure the mass flow.

6.1.1.2 Constant pressure volume flowmeter

an instrument used to measure the natural gas volume flow under certain test pressure (excluding the mass flow meter for constant pressure measurement), AND the test pressure can be adjusted and set by the regulator.

6.1.1.3 Low-pressure flowmeter

a fuel flowmeter for measurement in low-pressure piping installed between the pressure regulator and the engine.

6.1.1.4 High-pressure flowmeter

a fuel flowmeter for measurement in high-pressure piping installed between the compressed natural gas supply device (including vehicle CNG cylinders, fixed type CNG gas supply equipment and CNG storage cylinders, etc.) and the pressure regulator.

6.1.2 Natural gas flowmeter accuracy

Natural gas flowmeter accuracy shall be ± 0.5% of the measured value.

6.1.3 Installation of natural gas flowmeter

6.1.3.1

When using a high-pressure flowmeter for measurement, it shall install a relief valve in the pipeline to release the air pressure from the pipeline before disassembling the flowmeter.

6.1.3.2

The high-pressure flowmeter shall be connected using high-pressure pipe.

6.1.3.3

For fixed pressure type high-pressure flowmeter, it shall install an upstream pressure regulator; AND the outlet pressure of the regulator shall be set at the specified value of the flowmeter.

6.1.3.4

When using the low-pressure flowmeter for measurement, it shall install such devices as regulator box between the flowmeter and the engine, in order to eliminate the fuel pressure pulsation.

6.1.3.5

The installation of devices such as regulator box between the flowmeter and the engine shall not affect the normal operation of the engine.

6.1.3.6

In order to ensure the normal function of the fuel flowmeter, the flowmeter and accessories shall be arranged, connected and installed reasonably, AND not be loosened or disengaged in the test. It is not allowed for all connection pipelines and connection parts to have any leakage.

6.1.3.7

The high-pressure gas pipeline for flowmeter connection shall comply with the provisions of QC/T 746.

6.1.3.8

When testing on a chassis dynamometer, if using the natural gas fuel flowmeter to measure the consumption of natural gas, the installation of the flow meter shall comply with the provisions of Appendix A.

6.1.3.9

When the test on the chassis dynamometer is supplied with gas by the on-board CNG cylinder, the installation of the natural gas fuel flowmeter shall comply with the provisions of Figure A.1, Figure A.2, or Figure A.3.

6.1.3.10

When the test on the chassis dynamometer is supplied with gas by the fixed type CNG supply equipment, the installation of the natural gas fuel flowmeter shall comply with the provisions of Figure A.4, Figure A.5 or Figure

A.6.

6.1.3.11

During the road test, the installation of the natural gas fuel flowmeter shall comply with the provisions of Figure A.1, Figure A.2 or Figure A.3 of

Appendix A.

6.1.4 Other equipment

7.2.3

Natural gas fuel consumption may be measured by flowmeter through

carbon balance method.

7.2.4

If using the flowmeter to measure the natural gas consumption, it shall simultaneously measure and record the travel time and travel distance.

7.2.5

When using the volume flowmeter to measure the natural gas consumption, it shall, at the same time, measure the temperature and pressure at the flowmeter inlet or outlet, in order to correct the fuel flow.

7.2.6

When using the carbon balance method, it shall, in accordance with the relevant requirements, measure the emissions such as CO 2 , CO and THC (or

CH4 and NMHC).

7.3 Test of compressed natural gas vehicle using gasoline starting

7.3.1

As for the compressed natural gas single gas fuels and dual purpose fuel vehicles operated with gasoline starting and then switching to gaseous fuel operation, the manufacturer shall provide a control strategy for the engine starting process. When conducting the fuel consumption test using the operating condition method as specified in the standard GB/T 19233 or GB/T 27840, it shall comply with the provisions of 7.3.2 and 7.3.3.

7.3.2

When using the carbon balance method, if the time from the engine start with gasoline to switch to gaseous fuel operation is not more than 60 s, it may, based on the measured emission of CO, CO 2 and THC (or CH4 + NMHC) in accordance with the requirements of GB/T19233 or GB/T 27840, use the equation (1) of 8.1 to calculate the natural gas consumption.

7.3.3

When using the natural gas flowmeter for measurement, it shall convert the gasoline consumed in the startup process into the natural gas consumption,

AND include it into the total consumption of the natural gas.

8.1 Carbon balance method

8.1.1

When using the carbon balance method, the natural gas density is the average (0.654 kg/m

3

) of G20 and G 23 under standard reference conditions (288.15 K, 101.325 kPa).

8.1.2

Natural gas consumption can be calculated in accordance with equation (1) based on the measured CO, CO 2 and THC (or CH 4 + NMHC) emissions:

8.4 Corrected to reference natural gas consumption

8.4.1

When using the flowmeter to measure the vehicle natural gas

consumption, if it is required to correct the test result into the reference natural gas consumption, it shall conduct calculation in accordance with the method as specified in 8.4.2 and 8.4.3.

8.4.2

During chassis dynamometer test, USE the equation (7) to correct it into the reference natural gas consumption.

Where:

FC0 - Reference natural gas consumption (15 °C, 101.325 kPa), m

3

/100 km;

FCr - Test natural gas consumption under standard reference conditions (15 °C, 101.325 kPa), m

3

/100 km;

HG20 - Inferior calorific value of reference fuel G 20 (15 °C, 101.325 kPa),

MJ/m

3

;

HG23 - Inferior calorific value of reference fuel G 23 (15 °C, 101.325 kPa),

MJ/m

3

;

HNG, low - Inferior calorific value of test natural gas (15 °C, 101.325 kPa),

MJ/m

3

;

8.4.3

During road test, USE the equation (8) to correct it into the reference natural gas consumption:

B.1 Overview

This appendix specifies the calculation method of natural gas density and calorific value.

B.2 Calculation of compression factor

Taking into account the non-ideal nature of the real gas, when calculating the volume calorific value, density, and other parameters, it shall correct the gas volume.

The correction of volume non-ideal nature is conducted by the compression factor Z mix. Under the metering reference conditions (temperature t 2 , pressure p2 ), the compression factor Zmix is calculated using the equation (B.1) as below:

Where:

- Summation factor.

Table B.2 provides the values of the summation factors for the natural components of the natural gas under the three metrological reference conditions, AND the compression factor Z j of each pure component, wherein the relationship between b j and Zj is: bj = 1 - Z j .

B.3 Density calculation

B.3.1 Ideal gas

The ideal gas density is calculated in accordance with the equation (B.2):

Where:

- The density of ideal gas (temperature t, pressure p);

R - Molar gas constant (R = 8.314510 J·mol

-1

·K

-1

);

T - Absolute temperature (T = t + 273.15), K;

xj - The molar fraction of component j in the mixture;

M j - The molar mass of component j in the mixture.

Table B.1 provides the molar mass of each component in natural gas.

B.3.2 Real gas

The real gas density is calculated in accordance with the equation (B.3):

Where:

rho (t, p) - Real gas density (temperature t, pressure p);

- Ideal gas density (temperature t, pressure p);

Zmix (t, p) - Gas compression factor (temperature t, pressure p).

B.4 Calculation of calorific value

B.4.1 Calculation of molar calorific value

B.4.1.1 Ideal gas

The molar calorific value of the known composition mixture under the temperature t 1 is calculated in accordance with the equation (B.4):

Where:

- The ideal molar calorific value (superior or inferior) of the mixture;

B.4.2.2 Real gas

In this standard, the actual gas mass calorific value and the ideal gas mass calorific value are regarded as equivalent in value.

B.4.3 Calculation of volume calorific value

B.4.3.1 Ideal gas

The ideal gas volume calorific value of the mixture of known composition under the combustion temperature t 1 , metering temperature t 2 and the pressure p 2 is calculated in accordance with the equation (B.8):

Where:

- The ideal gas volume calorific value of the mixture (superior or inferior);

- The ideal molar calorific value (superior or inferior) of the mixture;

R - Molar gas constant;

T2 - Absolute temperature (T2 = t 2 + 273.15), K.

In addition, the ideal gas volume calorific value can also be calculated using the equation (B.9):

Where:

- The ideal gas volume calorific value of the component j in the mixture (superior or inferior);

Table B.5 provides the ideal gas volume calorific value for each component of natural gas under different combustion reference conditions.

B.4.3.2 Real gas

The real gas volume calorific value of the gas mixture under the combustion temperature t 1 and pressure p 1 AND the metering temperature t 2 and the pressure p2 is calculated in accordance with the equation (B.10):

Where:

- The real gas volume calorific value of the mixture (superior or inferior);

- The ideal gas volume calorific value of the mixture (superior or inferior);

Zmix (t 2 , p2 ) - The compression factor under the metering reference condition.

Table B.1 Molar mass of each component of natural gas […]

C.1 Brand (product name of the manufacturer)

C.2 General description on type and product

C.3 Type identification method

C.4 Type of vehicle

C.5 Production date

C.6 Vehicle identification number (VIN)

C.7 Odometer reading (km)

C.8 Manufacturer name and address

C.9 Chassis model and production enterprises (heavy duty)

C.10 Address of the assembly plant (light duty)

C.11 Maximum design speed (km/h)

C.12 Windward area (m

2

)

C.13 Air resistance coefficient

C.14 Vehicle mass (light duty)

C.15 Vehicle mass and shaft load (heavy duty)

C.16 Maximum design total mass (light duty)

C.17 Maximum design total mass and shaft load (heavy duty)

C.18 Maximum design static load (kg) for semi-trailers (heavy duty)

C.19 Maximum design traction mass (kg) (heavy duty)

C.20 Load mass utilization factor (heavy duty)

C.21 Maximum total mass of train (kg) (heavy duty)

C.22 Dimensions

L × W × H (mm) (heavy duty)

C.23 Rated number of passengers (light duty)

C.24 Rated number of passengers (including driver) (heavy duty)

C.25 Cab attendance (heavy duty)

C.26 Body type (light duty)

C.27 drive wheel: front, rear, 4 x 4 (light duty)

C.28 Drive Type (heavy duty)

C.29 Engine

C.29.1 Model and production enterprises

C.29.2 Type

C.29.3 Displacement (cm

3

)

C.29.4 Numbering

C.29.5 NG fuel supply system principle

mixer/jet

C.29.6 Maximum power (kW)

C.29.7 Maximum torque (Nm)

C.29.8 Idling speed (r/min)

C.29.9 Supercharger

Yes/No

C.29.10 Ignition system

conventional ignition/electronic ignition

1)

C.29.11 Recommended fuels by the manufacturer (NG)

C.29.12 CNG cylinder number and model

C.30 Transmission

C.30.1 Transmission model and production enterprises

C.30.2 Transmission type

manual/auto

C.30.3 Primary and secondary transmissions (heavy duty) (with/without)

C.30.4 Number of gears

C.30.5 Each gear ratio

C.30.6 Main reduction ratio

C.31 Tires

C.31.1 Tire production enterprises

C.31.2 Model/size/inflation pressure (front/rear)

C.31.3 Rolling perimeter under load (light duty)

C.31.4 Number of tires (heavy duty)

C.31.5 Rolling radius (heavy duty)

C.31.6 Rolling resistance coefficient (heavy duty)

C.31.7 Semi-trailer tire type, number and production enterprises (heavy duty)

C.31.8 Semi-trailer tire pressure (front/rear) (kPa) (heavy duty)

C.32 Lubricants

C.32.1 Brand

C.32.2 Model

C.33 Travel resistance

C.33.1 Determination method of travel resistance

C.33.2 If using the taxiing method, it shall attach the duplicated copy of the test report, calculation report, or other relevant data

C.34 Test results

C.34.1 Light duty vehicles

C.34.1.1 CO 2 emissions

C.34.1.1.1 Urban CO 2 emissions (g/100 km)

C.34.1.1.2 Suburb CO 2 emissions (g/100 km) […]

D.1 Overview

D.1.1 This Appendix describes the method of converting the natural gas vehicle consumption of compressed natural gas vehicle into the equivalent liquid fuel consumption such as gasoline or diesel.

D.1.2 The fuel consumption of natural gas fuel vehicles is generally expressed in m

3

/100 km, that is, the number of cubic meters of natural gas fuel consumed by vehicles traveling at 100 km distance. Petrol or diesel and other liquid fuel vehicle fuel consumption is generally expressed in L/100 km, that is, the number of liters of liquid fuel consumed by vehicles travelling at 100 km distance. In general, the calorific value per cubic meter of natural gas fuel is not equal to the calorific value per liter of liquid fuel. Therefore, it is not possible to simply compare the consumption of natural gas fuel with liquid fuel such as gasoline and diesel. Therefore, it must establish the relationship between the consumption of natural gas fuels and the consumption of liquid fuels such as gasoline or diesel. This Appendix is intended to establish a conversion relationship between natural gas fuel consumption and liquid fuel consumption such as gasoline and diesel.

D.2 Conversion method

D.2.1 CONDUCT conversion based on the equivalent relationship between the inferior calorific value of the natural gas fuel and the liquid fuel under standard reference conditions.

D.2.2 Determination of natural gas fuel components shall comply with the provisions of GB/T 13610.

D.2.3 Natural gas inferior calorific value shall be determined in accordance with the method specified in GB/T 22723 OR calculated by the method specified in Appendix B.