ASTM D8251-23

Standard Practice for Determining Compressor Oil Carryover in Compressed Natural Gas Used as a Natural Gas Motor Vehicle Fuel

SIGNIFICANCE AND USE
5.1 Uncontrolled oil carryover from lubricated natural gas compressors can adversely affect natural gas vehicle (NGV) performance. In some instances, small amounts of oil will accumulate in vehicle pressure regulators and slow their response. It can also affect other components of the engine fueling system. Erratic engine performance, under fueling, or engine shutdown can occur. Such incidents have been reported by operators of NGV fueling stations and vehicles.  
5.2 There is some vaporization of the lubrication (lube) oil that occurs due to compression of the gas. The oil vapor in CNG can be collected using a sorbent tube and quantified. Along with quantification of lube oil, this procedure can collect solids present in the gas.  
5.3 These methods do not separate any solids including siloxane from the compressor oil carryover or vapor.  
5.4 This practice can be applied to other gaseous samples requiring determination of compressor oil carryover provided the user’s data quality objectives are satisfied.
SCOPE
1.1 This standard practice is intended for gravimetric determination of compressor oil carryover as aerosols using either a coalescing filter method or sorbent tube method.  
1.2 The method using coalescing filters is applicable to analysis of compressor or lube oil carryover as a liquid and is intended for long term monitoring of a compressed natural gas (CNG) dispenser system.  
1.3 The method using a sorbent tube is applicable to analysis of compressor or lube oil carryover as a vapor and liquid in CNG dispenser systems present at 1 mg/kg to 500 mg/kg in a sample volume of 0.2 m3 to 0.6 m3. This method is applicable to a measurement intended to replicate the filling of a vehicle.  
1.4 This standard shall be applicable to natural gas, biogas, or renewable natural gas (RNG) that is compressed for use as a fuel for internal combustion engines in motor vehicles.  
1.5 This standard shall be applicable to natural gas, biogas, or renewable natural gas when they have been blended with hydrogen and have been compressed for use as a fuel for internal combustion engines in motor vehicles.  
1.6 The user shall determine if the volumetric measuring elements of the dispensing system are adjusted for the composition of gaseous fuel blends being delivered and those volumetric measuring elements correctly calculate the volume of fuel delivered. The users shall apply appropriate correction factors if necessary.  
1.7 Units—The values stated in SI units are to be regarded as standard.  
1.8 Mention of trade names or organizations in this standard does not constitute endorsement or recommendation. Other manufacturers of equipment or equipment models can be used.  
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.10 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-May-2023
• ICS: 75.060 - Natural gas
• Technical Committee: D03 - Gaseous Fuels
• Drafting Committee: D03.06 - Analysis of Constituents in Gaseous Fuels

Relations

• Refers: ASTM E617-23 - Standard Specification for Laboratory Weights and Precision Mass Standards
• Effective Date: 15-Aug-2023
• Refers: ASTM D4150-19 - Standard Terminology Relating to Gaseous Fuels
• Effective Date: 15-Dec-2019
• Refers: ASTM E617-18 - Standard Specification for Laboratory Weights and Precision Mass Standards
• Effective Date: 01-Oct-2018
• Refers: ASTM D4150-08(2016) - Standard Terminology Relating to Gaseous Fuels
• Effective Date: 01-Jul-2016
• Refers: ASTM D3588-98(2011) - Standard Practice for Calculating Heat Value, Compressibility Factor, and Relative Density of Gaseous Fuels
• Effective Date: 01-Nov-2011
• Refers: ASTM D1070-03(2010) - Standard Test Methods for Relative Density of Gaseous Fuels
• Effective Date: 01-May-2010
• Refers: ASTM E617-97(2008) - Standard Specification for Laboratory Weights And Precision Mass Standards
• Effective Date: 01-Dec-2008
• Refers: ASTM D4150-08 - Standard Terminology Relating to Gaseous Fuels
• Effective Date: 01-Dec-2008
• Refers: ASTM D4150-03 - Standard Terminology Relating to Gaseous Fuels
• Effective Date: 10-Aug-2003
• Refers: ASTM D1070-03 - Standard Test Methods for Relative Density of Gaseous Fuels
• Effective Date: 10-May-2003
• Refers: ASTM D3588-98(2003) - Standard Practice for Calculating Heat Value, Compressibility Factor, and Relative Density of Gaseous Fuels
• Effective Date: 10-May-2003
• Refers: ASTM D4150-00 - Standard Terminology Relating to Gaseous Fuels
• Effective Date: 10-Jun-2000
• Refers: ASTM D1070-85(1998) - Standard Test Methods for Relative Density of Gaseous Fuels
• Effective Date: 10-Nov-1998
• Refers: ASTM D3588-98 - Standard Practice for Calculating Heat Value, Compressibility Factor, and Relative Density of Gaseous Fuels
• Effective Date: 10-May-1998
• Refers: ASTM E617-97 - Standard Specification for Laboratory Weights And Precision Mass Standards
• Effective Date: 10-Nov-1997

Overview

ASTM D8251-23 is the international standard developed by ASTM for determining compressor oil carryover in compressed natural gas (CNG) used as a fuel for natural gas motor vehicles (NGVs). This standard practice is essential for assessing the amount of compressor or lubrication oil present in CNG, biogas, renewable natural gas (RNG), or blends with hydrogen, which are used in internal combustion engines for vehicles. Oil carryover from natural gas compressors can have significant impacts on vehicle performance, fuel dispensing equipment, and overall system reliability.

By providing methods for gravimetric determination of oil as aerosols-using either a coalescing filter or a sorbent tube-this standard enables fuel providers and operators of NGV stations to monitor and control oil levels, reducing the risk of equipment malfunction and erratic vehicle operation.

Key Topics

• Compressor Oil Carryover in CNG Dispenser Systems: The standard addresses both liquid and vapor phases of lubrication oil resulting from gas compression. Oil vapor and associated solids can be collected and quantified.
• Gravimetric Determination Methods:
  • Coalescing Filter Method: Designed for long-term monitoring of compressor or lube oil in its liquid state within CNG dispensing systems.
  • Sorbent Tube Method: Suitable for quantifying compressor oil carryover as both vapor and liquid, specifically during fuel delivery simulations. Applicable for concentrations ranging from 1 mg/kg to 500 mg/kg within specified sample volumes.
• Scope of Applicability: The procedures are effective for natural gas, biogas, RNG, and their blends with hydrogen when used as motor vehicle fuels.
• System Adjustments: Emphasizes the importance of adjusting or correcting volumetric measuring instruments based on the composition of the gaseous fuel blend to ensure accurate delivered fuel measurements.
• Data Quality and Safety: Requires users to ensure data quality objectives are met and to implement stringent safety, health, and environmental protections when handling CNG and associated solvent materials.
• Limitations: Methods do not differentiate between solids (such as siloxanes) and compressor oil, capturing all gravimetrically.

Applications

ASTM D8251-23 provides practical value in several key areas:

• NGV Fueling Stations: Monitoring compressor oil carryover ensures optimal vehicle operation, preventing issues such as regulator fouling, slow response, engine underfueling, and unplanned shutdowns.
• Vehicle Fleet Operators: Enables regular analysis to detect oil accumulation in vehicle fuel systems, supporting predictive maintenance and reliable fleet operations.
• Gas Dispenser System Manufacturers: Essential for the design and validation of oil separation and filtration systems within CNG dispensers.
• Quality Assurance and Compliance: Fulfills regulatory and internal quality control requirements for fuel cleanliness in CNG, biogas, or RNG infrastructure.
• Broader Applications: The practice can be adapted for any gaseous fuel sample where compressor oil carryover is a concern, provided data quality standards are maintained.

Related Standards

For comprehensive management of natural gas properties and measurement, the following standards are referenced or may be relevant when implementing ASTM D8251-23:

• ASTM D1070: Test Methods for Relative Density of Gaseous Fuels
• ASTM D3588: Practice for Calculating Heat Value, Compressibility Factor, and Relative Density of Gaseous Fuels
• ASTM D4150: Terminology Relating to Gaseous Fuels
• ASTM E617: Specification for Laboratory Weights and Precision Mass Standards
• ISO 15970:2008: Natural Gas-Measurement of Properties-Volumetric Properties: Density, Pressure, Temperature, and Compression Factor

By aligning with these related standards, fuel providers and station operators ensure the highest quality, safety, and performance when monitoring and managing compressor oil levels in CNG and renewable gaseous fuels for vehicles.

Keywords: ASTM D8251-23, compressor oil carryover, CNG, compressed natural gas, NGV, natural gas vehicle, oil contamination, fuel quality, biogas, renewable natural gas, RNG, hydrogen blends, fueling stations, gravimetric analysis, filter method, sorbent tube method.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D8251 − 23
Standard Practice for
Determining Compressor Oil Carryover in Compressed
Natural Gas Used as a Natural Gas Motor Vehicle Fuel
This standard is issued under the fixed designation D8251; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
1.1 This standard practice is intended for gravimetric deter-
mine the applicability of regulatory limitations prior to use.
mination of compressor oil carryover as aerosols using either a
1.10 This international standard was developed in accor-
coalescing filter method or sorbent tube method.
dance with internationally recognized principles on standard-
1.2 The method using coalescing filters is applicable to
ization established in the Decision on Principles for the
analysis of compressor or lube oil carryover as a liquid and is
Development of International Standards, Guides and Recom-
intended for long term monitoring of a compressed natural gas
mendations issued by the World Trade Organization Technical
(CNG) dispenser system.
Barriers to Trade (TBT) Committee.
1.3 The method using a sorbent tube is applicable to
2. Referenced Documents
analysis of compressor or lube oil carryover as a vapor and
2.1 ASTM Standards:
liquid in CNG dispenser systems present at 1 mg ⁄kg to
3 3
D1070 Test Methods for Relative Density of Gaseous Fuels
500 mg ⁄kg in a sample volume of 0.2 m to 0.6 m . This
D3588 Practice for Calculating Heat Value, Compressibility
method is applicable to a measurement intended to replicate the
Factor, and Relative Density of Gaseous Fuels
filling of a vehicle.
D4150 Terminology Relating to Gaseous Fuels
1.4 This standard shall be applicable to natural gas, biogas,
E617 Specification for Laboratory Weights and Precision
or renewable natural gas (RNG) that is compressed for use as
Mass Standards
a fuel for internal combustion engines in motor vehicles.
2.2 ISO Standard:
1.5 This standard shall be applicable to natural gas, biogas,
ISO 15970:2008 Natural gas—Measurement of properties—
or renewable natural gas when they have been blended with
Volumetric properties: density, pressure, temperature, and
hydrogen and have been compressed for use as a fuel for
compression factor
internal combustion engines in motor vehicles.
3. Terminology
1.6 The user shall determine if the volumetric measuring
3.1 For definitions of terms used D03 Gaseous Fuels
elements of the dispensing system are adjusted for the compo-
standards, refer to Terminology D4150.
sition of gaseous fuel blends being delivered and those
volumetric measuring elements correctly calculate the volume
3.2 Definitions of Terms Specific to This Standard:
of fuel delivered. The users shall apply appropriate correction
3.2.1 natural gas vehicle (NGV), n—vehicle designed to
factors if necessary.
operate on compressed natural gas (CNG), liquefied natural gas
(LNG), or renewable natural gas (RNG).
1.7 Units—The values stated in SI units are to be regarded
as standard.
4. Summary of Practice
1.8 Mention of trade names or organizations in this standard
4.1 This practice describes construction of an apparatus for
does not constitute endorsement or recommendation. Other
collecting compressor oil contained in CNG as well as a
manufacturers of equipment or equipment models can be used.
procedure for collecting and gravimetrically measuring com-
1.9 This standard does not purport to address all of the
pressor oil in CNG.
safety concerns, if any, associated with its use. It is the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
This practice is under the jurisdiction of ASTM Committee D03 on Gaseous Standards volume information, refer to the standard’s Document Summary page on
Fuels and is the direct responsibility of Subcommittee D03.06 on Analysis of the ASTM website.
Constituents in Gaseous Fuels. Available from International Organization for Standardization (ISO), ISO
Current edition approved June 1, 2023. Published July 2023. DOI: 10.1520/ Central Secretariat, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
D8251-23. Switzerland, https://www.iso.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8251 − 23
5. Significance and Use 6.1.7 Safety glasses.
6.1.8 Oven capable of maintaining a temperature of 250 °C
5.1 Uncontrolled oil carryover from lubricated natural gas
6 1 °C.
compressors can adversely affect natural gas vehicle (NGV)
6.1.9 Analytical balance with a minimum capacity of 200 g
performance. In some instances, small amounts of oil will
at a minimum resolution of 0.1 mg.
accumulate in vehicle pressure regulators and slow their
6.1.10 Tongs.
response. It can also affect other components of the engine
fueling system. Erratic engine performance, under fueling, or
6.2 Tube Method:
engine shutdown can occur. Such incidents have been reported
6.2.1 Stainless steel tubing, 316.
by operators of NGV fueling stations and vehicles.
6.2.2 Sampling apparatus as per Fig. 2.
6.2.3 Chromosorb® P NAW, 60/80 mesh or equivalent.
5.2 There is some vaporization of the lubrication (lube) oil
6.2.4 Glass wool.
that occurs due to compression of the gas. The oil vapor in
6.2.5 Analytical balance with a minimum capacity of 200 g
CNG can be collected using a sorbent tube and quantified.
at a minimum resolution of 0.1 mg.
Along with quantification of lube oil, this procedure can collect
6.2.6 Oven capable of maintaining a temperature of 250 °C
solids present in the gas.
6 1 °C.
5.3 These methods do not separate any solids including
6.2.7 Dessicator.
siloxane from the compressor oil carryover or vapor.
6.2.8 Dessicant.
5.4 This practice can be applied to other gaseous samples
6.2.9 Gloves compatible with the solvent used and/or tongs.
requiring determination of compressor oil carryover provided
6.2.10 Acetone, Certified ACS Grade.
the user’s data quality objectives are satisfied.
6.2.11 Plastic bags.
6.2.12 Stainless steel needle valve.
6. Materials
6.2.13 Particulate filter, 0.5 micron (as needed).
6.1 Filter Method:
6.2.14 Drying tube (as needed).
6.1.1 Filter test assembly (Fig. 1).
6.2.15 Hydrocarbon filter (as needed).
6.1.1.1 Coalescing filter elements 0.1 micron.
6.2.16 Compressed nitrogen. Purity consisting of total hy-
6.1.1.2 Coalescing filter housings without auto drain fea-
drocarbons less than 0.5 ppm(v) and water less than 1 ppm(v).
ture.
7. Hazards
NOTE 1—The filter selected should not be affected by the solvent used
to wash it. The filters used should be verified that any binder material is
7.1 CNG is a highly flammable gas. Care should be taken to
not soluble in the solvent.
avoid hazards associated with gas leaks during sampling.
6.1.2 Cleaned and pre-weighed glass jars for liquids.
Redundant safety measures such as gas leak monitors are
6.1.3 Two glass jars (100 mL) for filter elements.
recommended to ensure that potentially combustible gas mix-
6.1.4 Solvent: Petroleum ether or Acetone; certified ACS
tures do not come in contact with any ignition sources.
grade.
7.2 Improper handling of CNG can result in fire and/or
6.1.5 O-rings for filter housings, compatible with selected
explosion.
solvent.
6.1.6 Gloves compatible with the solvent(s) used. 7.3 Rapid release CNG can result in asphyxiation.
FIG. 1 Filter Test Assembly
D8251 − 23
NOTE 1—Source: Czachorski, M. & Kina, R., 1998. Validation Testing of a Gravimetric Method to Measure CNG Compressor Oil Carryover, Illinois:
Institute of Gas Technology. (GRI-98/0228)
FIG. 2 Compressor Oil Carryover Sampling Apparatus
8. Procedure 8.1.2.5 Place filters in a clean glass jar. Label the jar with the
filter tare-weight.
8.1 Filter Method:
8.1.3 Filter Housing Installation:
8.1.1 Cleaning and Pre-weighing Glass Jar:
8.1.3.1 The filter housings must be rated for the CNG
8.1.1.1 When handling the glass jar, always wear gloves.
fueling pressure. For example, a CNG fueling pressure of
Several glass jars may be cleaned and weighed at one time. The
24 800 kPag (3600 psig) requires a filter housing rating of at
jars are labelled with the pre-weight on the jar lids and stored
least 27 700 kPag (4000 psig). All tubing and valves, in this
until needed.
case, must be rated for 34 600 kPag (5000 psig). Ball valves
8.1.1.2 Wipe the outside of a 100 mL glass jar with a soft,
may be used for the inlet, outlet, and bypass test valves. Needle
clean cloth. Attach a label to the jar lid.
valves must be used for the drain valves. Installation of the test
8.1.1.3 Remove the lid and place the jar in an oven at 82 °C
assembly is usually done by the NGV station operator.
6 1 °C for one hour.
8.1.3.2 Install the test assembly shown in Fig. 1 downstream
8.1.1.4 Remove the jar from oven. Place it in a desiccator
of all coalescing filters in the system, and as close to the
and allow it to cool to room temperature.
dispenser as possible (Note 4). Make sure the filter housings
8.1.1.5 Weigh the jar to the nearest 0.1 mg (lid off). Record
are installed correctly (flow direction is specified by filter
the weight on the jar label.
manufacturer). The size of the tubing should be the same as the
NOTE 2—When removed from the desiccator, the jar should be weighed
size used near the installation location.
as soon as possible to minimize weight gain due to moisture from the air.
NOTE 4—Make sure that the test assembly is installed in a location
8.1.2 Cleaning and Pre-weighing Filter Element:
where the entire volume of compressed gas, as recorded by the meter,
passes through the filter housings. One exception is discharge side
NOTE 3—Filter elements used for testing are rinsed initially with either
petroleum ether or acetone to remove oils. Wear gloves and use tongs once-through dryers where the test assembly is installed between the
coalescing filter and dryer cartridges on one side of the dryer. In this case
when handling the filter elements. The filters are stored in glass jars
labelled with the jar tare-weight until needed. it is assumed that half of the total volume of gas passes through each side
of the dryer.
8.1.2.1 Submerge filter elements in a beaker of solvent. Let
8.1.3.3 Check the test assembly for leaks. Repair any leaks.
them soak for 1 min to 2 min.
8.1.3.4 Label the filter housings as filter #1 and #2 in the
8.1.2.2 Place filter elements on a glass tray. Place them
direction of the gas flow.
under a hood to allow ether to evaporate. Depending on the
8.1.3.5 Close both inlet and outlet valves to the test assem-
filter size this can be 3 h or more.
bly and open the bypass valve.
8.1.2.3 Once the solvent has evaporated, place the filters in
8.1.4 Filter Installation:
an oven at 82 °C 61 °C for 4 h.
8.1.2.4 Place filters in a desiccator and allow to cool to room 8.1.4.1 Make sure the bypass valve is open, and the inlet and
temperature. Remove and immediately (see Note 2) weigh outlet test valves are closed. Purge out any pressure in the filter
each filter to the nearest 0.1 mg. housings by slowly opening the drain valves.
D8251 − 23
8.1.4.2 Remove both filter housings. They should loosen 8.1.5.8 Wearing gloves, remove filter element #2, and place
without using a wrench. If not, use a wrench on the bottom of it in the original jar labelled filter #2. Record the removal date
the housing to loosen. on the label.
8.1.5.9 Hold the glass jar, with any liquid collected, under
8.1.4.3 Using tongs, install a filter element in each housing.
each filter housing, rinse the inside of the housing with solvent
Record the date of installation, location, and filter # on the label
until clean. Place the lid on the jar.
of each filter element jar, and in a data sheet.
8.1.5.10 If additional testing is needed, install a new filter
8.1.4.4 Record the meter reading, compressor hours (if
element in each housing. Record the date of installation,
available), filter #’s, and tare-weights in the data sheet.
location, and filter # on the label of each filter element jar.
8.1.4.5 Make sure the O-rings (if applicable) are in place
Record the filter # for each element on a new data sheet.
and tighten the filter housings and drain valves.
NOTE 6—If further testing is not needed, do not install new filter
8.1.4.6 Slowly, open the inlet test valve all the way. Caution,
elements. Replace O-rings and close the inlet and outlet test valves. Open
if a valve is opened too fast, filter elements may be damaged.
the bypass valve.
8.1.4.7 Slowly open the outlet test valve all the way.
8.1.6 Record the meter reading, compressor hours (if
8.1.4.8 Check for leaks.
available), glass jar tare-weight, and removal date in the data
...