Overview
SIST EN ISO 17507-2:2026 establishes the PKI (Propane Knock Index) method for the calculation of the methane number of gaseous fuels, using only their composition as input. This European standard is identical to ISO 17507-2:2025 and applies to natural gas, biomethane, and their admixtures with hydrogen, targeting the needs of reciprocating internal combustion engine applications.
As the gaseous fuel landscape evolves with the introduction of LNG, hydrogen, and renewable gases, accurate assessment of fuel knock resistance-the methane number-is essential for engine safety and efficiency. The PKI method offers a standardized approach to quantify this property, benefiting fuel suppliers, engine manufacturers, and operators across the energy sector.
Key Topics
- PKI Methodology: This standard defines a two-step polynomial function approach to calculate the propane knock index (PKI) and the methane number (MN) using only the normalized mole fraction composition of the gaseous fuel.
- Scope of Application: The PKI method covers a wide range of fuel compositions common in modern gas engine operations, including natural gas, biomethane, and significant hydrogen admixtures.
- Component Treatment: Provides detailed guidance on handling typical and atypical fuel components, with normalization instructions for components like argon, helium, oxygen, and water vapor as well as directions for non-listed components.
- Validity Boundaries: Specifies upper and lower limits for constituent gases to ensure the method’s reliability, supporting fuels ranging from nearly pure methane up to those with substantial hydrogen or higher hydrocarbons content.
- Expression & Integrity of Results: Requires results to be expressed as integer methane numbers, with method reference (e.g., "74 MN as per ISO 17507-2"), and recommends rounding per ISO 80000-1 for consistency.
Applications
- Reciprocating Internal Combustion Engines: The methane number calculated by the PKI method is critical for optimizing engine tuning, ensuring safe operation, and maintaining warranties in natural gas and biomethane-fueled engines.
- Gas Suppliers: Gas grid operators and LNG terminal managers can use the PKI method to validate fuel quality, accommodate variable feedstock, and ensure regulatory compliance.
- Engine Manufacturers: Supports original equipment manufacturers (OEMs) in specifying fuel parameters, benchmarking knock resistance, and communicating clear standards to customers.
- Measurement and Analysis Equipment Providers: Instrument and gas analyzer OEMs can implement the standardized PKI formulas in their product software to offer accurate, traceable methane number measurements.
- Consulting and Engineering Services: Facilitates transparent communication across the energy value chain when analyzing, specifying, or troubleshooting gaseous fuels for engine applications.
Related Standards
- ISO 17507-1: Covers another methodology for methane number calculation, allowing for comparative evaluation with the PKI approach.
- ISO 23306: Describes a PKI-based method specifically for LNG fuels.
- ISO 14532: Provides standardized vocabulary for natural gas sector applications, ensuring clarity in definitions.
- ISO 14912: Outlines procedures for the conversion of gas mixture composition data, essential for correct PKI method application where composition is reported in various units.
- ISO/IEC Guide 98-3: Addresses uncertainty of measurement, which underpins robust reporting of methane numbers using the PKI method.
By following SIST EN ISO 17507-2:2026, stakeholders ensure a harmonized, scientifically robust approach to fuel characterization, supporting engine protection, regulatory compliance, and efficient integration of renewable and alternative gases into the energy system. This standard is a key resource for the calculation and specification of methane number in modern gaseous fuels, ensuring consistent and reliable performance across diverse applications.
