ISO 7536:1994

Overview

ISO 7536:1994 specifies the induction period method for determining the oxidation stability of gasoline. The test oxidizes a finished aviation or motor gasoline sample in a sealed pressure bomb filled with oxygen and heated; the time to a defined pressure breakpoint is recorded as the induction period. Results are reported as the induction period at 100 °C (IP100), calculated from the observed induction period at test temperature.

Key topics and requirements

• Scope: Applies only to finished aviation and motor gasolines (not individual components).
• Test principle: Oxidize 50 ml ±1 ml of sample in a pressure bomb filled with oxygen (commercial extra-dry, ≥99% purity) at 690 kPa, heat in a boiling water bath and monitor pressure until the breakpoint is reached.
• Temperature: Bath maintained between 98 °C and 102 °C; thermometer and bath specifications in Annex B.
• Breakpoint definition: Point in the pressure–time curve preceded by a pressure drop of exactly 14 kPa within 15 minutes and followed by a drop of not less than 14 kPa in 15 minutes.
• Recording: Continuous pressure recording or readings at intervals ≤15 minutes.
• Sample & apparatus: Glass sample container (50 ml), corrosion‑resistant steel pressure bomb (specification in Annex A), needle valve, pressure gauge (to at least 1 380 kPa) and a stainless steel burst‑disc assembly (rupture >1 530 kPa) for safety.
• Result calculation: Convert observed induction period IPt (minutes) to IP100 using formulas:
  • If test T > 100 °C: IP100 = IPt × [1 + 0.101 (T − 100)]
  • If test T < 100 °C: IP100 = IPt / [1 + 0.101 (100 − T)]
• Precision: Repeatability ~5% (single operator), reproducibility ~10% (inter-lab).
• Safety: Standard warns of explosion risk; use a safety shield, and follow chemical handling and disposal procedures.

Applications and users

• Quality control in refineries and fuel blending plants to monitor gasoline tendency to form gums during storage.
• Fuel laboratories in aviation and automotive fuel certification to verify oxidation stability and compliance.
• R&D teams developing additives or stabilizers to improve storage life.
• Regulatory and inspection bodies assessing fuel stability characteristics for safety and performance. Note: users should be aware the method is not suitable for testing individual volatile or highly unsaturated components.

Related standards

• Prepared by ISO/TC 28 (Petroleum products and lubricants). For complementary guidance, consult industry methods and historical Institute of Petroleum publications referenced in the standard for additional context and practice.

Keywords: ISO 7536, oxidation stability of gasoline, induction period method, pressure bomb, gasoline gum, aviation gasoline, motor gasoline, IP100, fuel quality control.