The neqsim.standards package calculates gas- and oil-quality properties from a NeqSim fluid. These calculations support engineering screening and contract workflows; they do not replace representative sampling, validated composition analysis, a certified laboratory method, or the governing contract.

Choose a calculation

Need NeqSim class Guide
Calorific value, relative density, and Wobbe index Standard_ISO6976 or Standard_ISO6976_2016 ISO 6976
LNG density from composition Standard_ISO6578 ISO 6578
Water or hydrocarbon dew point Draft_ISO18453 or BestPracticeHydrocarbonDewPoint Dew-point methods
CNG methane number and motor octane number Standard_ISO15403 ISO 15403
Simulated crude-oil vapour pressure Standard_ASTM_D6377 ASTM D6377
Other simulated oil-quality properties Classes in neqsim.standards.oilquality Oil-quality methods
Delivery-point specification checks BaseContract and ContractSpecification Sales contracts

Use the edition and reference conditions named by the applicable contract or regulation. A class name identifies the implemented calculation route; it is not by itself evidence that the complete measurement system is compliant.

ISO 6976 gas-quality quick start

The example reports superior calorific value and superior Wobbe index on a real-gas volumetric basis. Volume reference temperature is 0°C and combustion-energy reference temperature is 15.55°C (60°F).

import neqsim.standards.gasquality.Standard_ISO6976;
import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;
import neqsim.thermodynamicoperations.ThermodynamicOperations;

SystemInterface gas = new SystemSrkEos(293.15, 1.0);
gas.addComponent("methane", 0.931819);
gas.addComponent("ethane", 0.025618);
gas.addComponent("nitrogen", 0.010335);
gas.addComponent("CO2", 0.015391);
gas.setMixingRule("classic");
new ThermodynamicOperations(gas).TPflash();

Standard_ISO6976 iso6976 =
    new Standard_ISO6976(gas, 0.0, 15.55, "volume");
iso6976.setReferenceState("real");
iso6976.calculate();

double gcvMJPerNm3 = iso6976.getValue("GCV") / 1000.0;
double wobbeMJPerNm3 =
    iso6976.getValue("SuperiorWobbeIndex") / 1000.0;
double relativeDensity = iso6976.getValue("RelativeDensity");

Expected values for this fixture are approximately 39.615 MJ/Nm³, 51.701 MJ/Nm³, and 0.5871. Report both reference temperatures, reference state, and basis with every result. Supported combustion-energy reference temperatures are 0, 15, 15.55, 20, and 25°C. Although checkReferenceCondition() currently accepts 25°C as a volume reference temperature, volume-dependent corrections are implemented only for 0, 15, 15.55, and 20°C; use one of those four values.

GCV and LCV are aliases for SuperiorCalorificValue and InferiorCalorificValue. WI and WobbeIndex are aliases for SuperiorWobbeIndex. StandardInterface declares the generic getValue(...) methods, but each concrete standard defines which parameter names and units it supports.

ISO 6578 LNG-density quick start

ISO 6578 uses the liquid temperature and molar composition. The supported component set and temperature range are method limits, so screen the input before using the result.

import neqsim.standards.gasquality.Standard_ISO6578;
import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;

SystemInterface lng = new SystemSrkEos(113.15, 1.0);
lng.addComponent("nitrogen", 0.006538);
lng.addComponent("methane", 0.918630);
lng.addComponent("ethane", 0.058382);
lng.addComponent("propane", 0.011993);
lng.addComponent("n-butane", 0.003255);
lng.addComponent("i-pentane", 0.000657);
lng.addComponent("n-pentane", 0.000545);
lng.setMixingRule("classic");
lng.init(0);

Standard_ISO6578 iso6578 = new Standard_ISO6578(lng);
iso6578.calculate();
double densityKgPerM3 = iso6578.getValue("density");

The calculation is composition-based. Confirm that the sample is a single, representative LNG liquid and disclose uncertainty from composition, temperature, and sampling.

ASTM D6377 simulation quick start

Use the type-safe RvpMethod enum so that the selected calculation route is explicit. The result is a thermodynamic simulation of the NeqSim fluid, not a claim that a laboratory apparatus or sampling procedure conforms to ASTM D6377.

import neqsim.standards.oilquality.Standard_ASTM_D6377;
import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;

SystemInterface oil = new SystemSrkEos(275.15, 1.0);
oil.addComponent("methane", 0.0006538);
oil.addComponent("ethane", 0.006538);
oil.addComponent("propane", 0.065380);
oil.addComponent("n-pentane", 0.154500);
oil.addComponent("nC10", 0.545000);
oil.setMixingRule(2);
oil.init(0);

Standard_ASTM_D6377 vapourPressure = new Standard_ASTM_D6377(oil);
vapourPressure.setReferenceTemperature(37.8, "C");
vapourPressure.setMethodRVP(
    Standard_ASTM_D6377.RvpMethod.RVP_ASTM_D6377);
vapourPressure.calculate();

double rvpBara = vapourPressure.getValue("RVP", "bara");
double tvpBara = vapourPressure.getValue("TVP", "bara");

For this fixture, RVP_ASTM_D6377 gives approximately 0.965 bara simulated RVP and 1.666 bara TVP. The alternative VPCR4 route gives approximately 1.157 bara for the same fluid; always report the selected route with the result. Preserve light ends when constructing the fluid; flashing or stabilizing the sample before this calculation changes the vapour pressure.

Contracts and isOnSpec()

BaseContract(system, terminal, country) loads specifications from the gascontractspecifications data set. A terminal name is therefore data-dependent, not a portable built-in guarantee. BaseContract.display() opens a Swing window and should not be used in headless services; use runCheck() and getResultTable() for programmatic reporting.

Do not treat isOnSpec() as a universal compliance engine. In the current implementation, calculation-only classes such as Standard_ISO6976 and Standard_ISO6578 return true unconditionally. Standards with implemented contract logic, such as Draft_ISO18453, compare against their attached contract. For auditable checks, evaluate each calculated value against an explicit, version-controlled ContractSpecification and record its basis, limits, units, reference conditions, and uncertainty.

Input and reporting checks

Before calculation:

  1. Confirm the governing standard edition and contractual reference conditions.
  2. Use molar composition and preserve trace components relevant to the property.
  3. Normalize or otherwise document the composition basis.
  4. Check that every component and temperature lies within the method’s coverage.
  5. Characterize heavy ends before hydrocarbon-dew-point or oil-volatility work.

After calculation:

  1. Record the NeqSim version, class, edition, method, and reference conditions.
  2. State whether the result is molar, mass-based, ideal-volume, or real-volume.
  3. Review getComponentsNotDefinedByStandard() for ISO 6976. The implementation substitutes generic component data for unsupported species, so the result is not equivalent to explicit coverage by the standard.
  4. Compare important results with certified measurements or another validated method before fiscal, contractual, or design use.

References