Version: 0.1-0
Date: 2026-03-28
Title: Calorific Values and Properties of Natural Gas per ISO 6976:2016
Depends: R (≥ 3.5.0)
LinkingTo: Rcpp
Imports: Rcpp (≥ 1.0), R6
Suggests: knitr, lintr, rmarkdown, testthat (≥ 3.0.0)
Encoding: UTF-8
LazyData: false
ByteCompile: true
Description: Calculates calorific values (gross and net), density, relative density, and Wobbe indices together with their standard uncertainties from natural gas composition, implementing the method of ISO 6976:2016 "Natural Gas — Calculation of calorific values, density, relative density and Wobbe indices from composition". Uncertainty propagation follows Annex B of that standard. Reference: International Organization for Standardization (2016) https://www.iso.org/standard/55842.html.
License: GPL (≥ 3)
URL: https://github.com/RuedigerForster/ISO_6976
BugReports: https://github.com/RuedigerForster/ISO_6976/issues
RoxygenNote: 7.3.2
VignetteBuilder: knitr
NeedsCompilation: yes
Packaged: 2026-04-03 17:25:49 UTC; WinUser
Author: Rüdiger Forster [aut, cre]
Maintainer: Rüdiger Forster <meticulous.measurements@gmail.com>
Repository: CRAN
Date/Publication: 2026-04-09 09:00:46 UTC

ISO6976.2016: Calorific Values and Properties of Natural Gas per ISO 6976:2016

Description

Calculates calorific values (gross and net, molar, mass and volumetric bases), density, relative density, and Wobbe indices together with their standard uncertainties from natural gas composition, following ISO 6976:2016 "Natural Gas — Calculation of calorific values, density, relative density and Wobbe indices from composition".

Details

Uncertainty propagation is implemented according to Annex B of that standard (variance-covariance method).

**Application restrictions (ISO 6976:2016 §5):** * Combustion temperature: 0, 15, 15.55 (60 °F), 20, or 25 °C. * Volume reference temperature: 0, 15, 15.55 (60 °F), or 20 °C. * Reference pressure: 90–110 kPa. * Compression factor Z must be > 0.9.

Author(s)

Rüdiger Forster meticulous.measurements@gmail.com

References

ISO 6976:2016 "Natural Gas — Calculation of calorific values, density, relative density and Wobbe indices from composition".

See Also

Useful links:

R6 class for natural gas composition input

Description

R6 class for natural gas composition input

R6 class for natural gas composition input

Details

GasComponents holds the mole fractions, their standard uncertainties, and the inter-component correlation matrix for a natural gas mixture. All three quantities are required as input to calculateProperties.

Components are identified either by their integer index (1–60, matching ISO 6976:2016 Table A.2) or by English name (see componentNames).

Public fields

fractions

Numeric vector (length 60) of mole fractions [mol/mol].

uncertainties

Numeric vector (length 60) of standard uncertainties.

correlations

60x60 correlation matrix (default: identity matrix).

Methods

Public methods

Method new()

Create a new GasComponents object. Initialises fractions and uncertainties to zero and correlations to the 60x60 identity matrix.

Usage
GasComponents$new()

Method getFraction()

Get the mole fraction of a single component.

Usage
GasComponents$getFraction(name)
Arguments
name

Component name (English) or integer index 1–60.

Returns

Numeric scalar.

Method getUncertainty()

Get the standard uncertainty of a single component.

Usage
GasComponents$getUncertainty(name)
Arguments
name

Component name (English) or integer index 1–60.

Returns

Numeric scalar.

Method getCorrelation()

Get the correlation between two components.

Usage
GasComponents$getCorrelation(name1, name2)
Arguments
name1

First component name or index.

name2

Second component name or index.

Returns

Numeric scalar in \[-1, 1\].

Method setFraction()

Set the mole fraction of a single component.

Usage
GasComponents$setFraction(name, value)
Arguments
name

Component name or index.

value

Mole fraction [mol/mol].

Method setUncertainty()

Set the standard uncertainty of a single component.

Usage
GasComponents$setUncertainty(name, value)
Arguments
name

Component name or index.

value

Standard uncertainty.

Method setCorrelation()

Set the correlation between two components.

Usage
GasComponents$setCorrelation(name1, name2, value)
Arguments
name1

First component name or index.

name2

Second component name or index.

value

Correlation coefficient in \[-1, 1\].

Method setFractionArray()

Set all mole fractions at once.

Usage
GasComponents$setFractionArray(x)
Arguments
x

Numeric vector of length 60.

Method setUncertaintyArray()

Set all uncertainties at once.

Usage
GasComponents$setUncertaintyArray(u)
Arguments
u

Numeric vector of length 60.

Method setCorrelationMatrix()

Set the full correlation matrix.

Usage
GasComponents$setCorrelationMatrix(r)
Arguments
r

60x60 numeric matrix; values must lie in \[-1, 1\].

Method clone()

The objects of this class are cloneable with this method.

Usage
GasComponents$clone(deep = FALSE)
Arguments
deep

Whether to make a deep clone.

Calculate natural gas properties per ISO 6976:2016

Description

Computes all combustion and volumetric properties of a natural gas mixture together with their standard (or expanded) uncertainties, following the method and tables of ISO 6976:2016 and the uncertainty propagation formulae of its Annex B.

Usage

calculateProperties(
  compositionArray,
  uncertaintyArray,
  correlationMatrix,
  combustionTemperature = 25,
  volumeTemperature = 15,
  pressure = 101.325,
  coverage = 1
)

Arguments

compositionArray

Numeric vector of length 60: mole fractions \[mol/mol\] in the component order of ISO 6976:2016 Table A.2. See componentNames for the ordering. If values are given in mol%, divide by 100 before passing them here.

uncertaintyArray

Numeric vector of length 60: standard uncertainties of the mole fractions (same units as compositionArray).

correlationMatrix

60x60 numeric matrix of correlation coefficients between component mole fractions. Use diag(60) when correlations are unknown or assumed to be zero.

combustionTemperature

Combustion reference temperature in °C. Permitted values: 0, 15, 15.55, 20, 25. Default: 25.

volumeTemperature

Volume reference temperature in °C. Permitted values: 0, 15, 15.55, 20. Default: 15.

pressure

Reference pressure in kPa. Must be in \[90, 110\]. Default: 101.325.

coverage

Coverage factor k; uncertainties are multiplied by k before being returned. Default: 1 (standard uncertainty).

Value

A named list with the following elements (all numeric scalars):

| Name | Description | Unit | |———–|—————————————————–|————| | M | Molar mass | kg/kmol | | Z | Compression factor | — | | G_o | Ideal-gas relative density | — | | D_o | Ideal-gas density | kg/m³ | | G, u_G | Real-gas relative density and uncertainty | — | | D, u_D | Real-gas density and uncertainty | kg/m³ | | Hcg, u_Hcg| Molar gross calorific value and uncertainty | kJ/mol | | Hcn, u_Hcn| Molar net calorific value and uncertainty | kJ/mol | | Hmg, u_Hmg| Mass-basis gross calorific value and uncertainty | MJ/kg | | Hmn, u_Hmn| Mass-basis net calorific value and uncertainty | MJ/kg | | Hvg_o, u_Hvg_o | Ideal-gas vol. gross CV and uncertainty | MJ/m³ | | Hvn_o, u_Hvn_o | Ideal-gas vol. net CV and uncertainty | MJ/m³ | | Hvg, u_Hvg| Real-gas vol. gross CV and uncertainty | MJ/m³ | | Hvn, u_Hvn| Real-gas vol. net CV and uncertainty | MJ/m³ | | Wg_o | Ideal-gas gross Wobbe index | MJ/m³ | | Wn_o | Ideal-gas net Wobbe index | MJ/m³ | | Wg, u_Wg | Real-gas gross Wobbe index and uncertainty | MJ/m³ | | Wn, u_Wn | Real-gas net Wobbe index and uncertainty | MJ/m³ |

References

ISO 6976:2016 "Natural Gas — Calculation of calorific values, density, relative density and Wobbe indices from composition"

See Also

GasComponents, componentNames

Examples

data("example1")
res <- calculateProperties(example1$fractionArray, example1$uncertaintyArray,
                           example1$correlationMatrix,
                           combustionTemperature = 15, volumeTemperature = 15)
res$M      # molar mass [kg/kmol]
res$Hvg    # real-gas vol. gross CV [MJ/m^3]
res$u_Wg   # standard uncertainty of gross Wobbe index

Return the index of a gas component by name

Description

Return the index of a gas component by name

Usage

componentIndex(name)

Arguments

name

Character string: component name (English). See componentNames for the full list.

Value

Integer index (1–60) into the composition vector.

Return the name of a gas component by index

Description

Return the name of a gas component by index

Usage

componentName(index)

Arguments

index

Integer 1–60.

Value

Character string with the English component name.

Return the names of all 60 gas components

Description

Returns the ordered character vector of all 60 natural gas components recognised by ISO 6976:2016 (Table A.2). The position of each name corresponds to the index used in compositionArray, uncertaintyArray, and correlationMatrix.

Usage

componentNames()

Value

Character vector of length 60.

See Also

componentIndex, componentName

ISO 6976:2016 Annex D.2 — Example 1 (5-component mixture, 15/15 °C)

Description

A five-component natural gas mixture from Annex D.2 of ISO 6976:2016. Non-zero components: methane, ethane, propane, nitrogen, carbon dioxide.

Format

A named list with three elements:

fractionArray

Numeric vector (length 60) of mole fractions [mol/mol].

uncertaintyArray

Numeric vector (length 60) of standard uncertainties [mol/mol].

correlationMatrix

60×60 identity correlation matrix.

Source

ISO 6976:2016 Annex D.2, Table D.2.

ISO 6976:2016 Annex D.3 — Example 2 (mixture with water vapour, 15.55/15.55 °C)

Description

An eleven-component natural gas mixture including water vapour from Annex D.3 of ISO 6976:2016.

Format

A named list with three elements (same structure as example1).

Source

ISO 6976:2016 Annex D.3, Table D.3.

ISO 6976:2016 Annex D — Example 3 (11-component mixture, identity matrix)

Description

An eleven-component natural gas mixture from Annex D of ISO 6976:2016 with an identity correlation matrix (no inter-component correlations). Used to verify calculations at 15/15 °C and 25/0 °C.

Format

A named list with three elements (same structure as example1).

Source

ISO 6976:2016 Annex D.

ISO 6976:2016 Annex D — Example 3, full correlation matrix

Description

The same eleven-component mixture as example3 but with a full inter-component correlation matrix from a GC calibration covariance analysis, as given in Annex D of ISO 6976:2016.

Format

A named list with three elements (same structure as example1).

Source

ISO 6976:2016 Annex D (extended correlation case).

Calculate all ISO 6976:2016 properties and their uncertainties

Description

Calculate all ISO 6976:2016 properties and their uncertainties

Usage

iso6976_calc(x, u_x, r_x, t1, t2, p2, k = 1)

Arguments

x

Numeric vector of length 60: mole fractions [mol/mol]

u_x

Numeric vector of length 60: standard uncertainties

r_x

Numeric matrix 60x60: correlation matrix

t1

Combustion temperature [°C]: 0, 15, 15.55, 20, or 25

t2

Volume reference temperature [°C]: 0, 15, 15.55, or 20

p2

Reference pressure [kPa]: 90–110

k

Coverage factor (default 1)

Value

Named list of properties and uncertainties