⛽ Gum content in gasoline

Petrochemistry PN-EN ISO 6246

Overview

STATUS (as of 02.11.2026). PN-EN ISO 6246:2017-05 — Polish version, published 17.04.2019, implements EN ISO 6246:2017 and ISO 6246:2017 [IDT]; it replaced PN-EN ISO 6246:2001. The PKN catalogue card has no withdrawal note; it states that the corrections made concern only the French language version. Amendment PN-EN ISO 6246:2017-05/A1:2020-03 (English version, published 11.03.2020; implements EN ISO 6246:2017/A1:2019 and ISO 6246:2017/Amd 1:2019) changes the purity requirement for n-heptane. ISO 6246:2017 is the third edition: it replaced ISO 6246:1995 with Corrigendum Cor 1:1998 and was technically revised and aligned with ASTM D381 — modern methods of temperature measurement were introduced, measurement limits were clarified, rounding steps were added and new precision from a 1997 joint ASTM/EI study was included; unwashed and washed gum results for non-aviation fuels can be expressed to the nearest 0.5 mg/100 ml, and the scope was broadened to modern gasolines and their blends (foreword).

SCOPE (clause 1). Determination of the existent gum content of aviation fuels and the gum content of motor gasoline and other volatile distillates, including products containing ethanol (up to 85 % (V/V)), ether-type oxygenates and deposit control additives; no precision data are available for automotive ethanol fuel E85. For non-aviation fuels, the standard also describes the determination of the heptane-insoluble portion of the residue. The method is not intended for testing gasoline components, particularly those with a high percentage of low-boiling unsaturated compounds, as they can cause explosions during evaporation.

SIGNIFICANCE OF THE TEST (introduction). The true significance of determining gum in motor gasoline is not firmly established: high gum content can cause induction-system deposits and sticking of intake valves, and low gum content usually ensures the absence of such difficulties, but the test is not of itself correlative to induction-system deposits. The primary purpose of the test applied to motor gasoline is to measure the oxidation products formed in the sample before or during the comparatively mild conditions of the test. Because non-volatile oils and additives are purposely blended into gasolines, the heptane extraction removes them from the residue so that the deleterious material — gum — can be determined. In aviation turbine fuels, large quantities of gum indicate contamination of the fuel by higher-boiling oils or particulate matter and generally reflect poor handling practices in distribution downstream of the refinery.

HOW THE TEST PROCEEDS — ACCORDING TO THE 1995 EDITION (ISO 6246:1995; the 2017 edition changed, among other things, temperature measurement, measurement limits, rounding and precision, and its procedure is not known to us). 50 ml of sample is poured into each pre-weighed 100 ml beaker (tall form, permanently marked; one of them is the tare beaker) and evaporated in a jet bath for 30 min: aviation and motor gasolines in a jet of air (bath 160–165 °C, well temperature 150–160 °C), aircraft turbine fuels in a jet of steam (bath 232–246 °C, well 229–235 °C); the flow from each jet at the test temperature is 1,000 ml/s ± 150 ml/s. A sample containing suspended or settled matter is first filtered through a sintered glass funnel (pores 150–250 µm), and the result is reported as filtered. The beakers are cooled for at least 2 h in a tightly covered vessel near the balance (a drying agent is not recommended) and weighed to the nearest 0.1 mg. To determine the heptane-insoluble portion, 25 ml of heptane is added to the residue, the beaker is swirled for 30 s, left to stand for 10 min and the solution is decanted; the extraction is repeated a second time, and a third time if the extract is coloured. The beakers are dried for 5 min in the bath at 160–165 °C, cooled for at least 2 h and weighed. The gum content in mg/100 ml is calculated from the increase in beaker mass, corrected for the change in mass of the tare beaker (clauses 4–11).

LEGAL REQUIREMENTS. Motor petrols: existent gum content (solvent washed) at most 5 mg/100 ml (Regulation of the Minister of Climate and Environment of 26.06.2024 on quality requirements for liquid fuels, Journal of Laws 2024, item 1018, Annexes 1 and 2 item 8). The regulation on test methods for the quality of liquid fuels (Journal of Laws 2024, item 1058, Annex Part I point 7) describes the method — evaporation of a measured volume of sample in a jet of air under controlled conditions of temperature and flow, washing of the residue with a solvent and weighing — and refers to the standard implementing EN ISO 6246.

WHAT WE DO NOT GIVE HERE. From the 2017 edition, the foreword, introduction, scope and normative references are publicly available. We do not give the test procedure, calibration, calculation and rounding of the result (clauses 7–13) or the precision values (clause 14) according to that edition, and we do not carry over the precision of the 1995 edition, because the new edition replaced it. The content of Amendment A1:2019 (purity requirement for n-heptane) is not known to us — only its title.

Method principle

A measured portion of fuel is evaporated under controlled conditions of temperature and flow of air or steam. The evaporation residue is weighed; it may be further washed with heptane and weighed again (clause 4 of the 1995 edition).

Existent gum (aviation fuels) is the evaporation residue without further treatment. In non-aviation fuels, unwashed gum is the evaporation residue, and solvent-washed gum is the residue remaining after washing with heptane and discarding the washings (definitions 3.1–3.4 of the 1995 edition).

Applications

• Motor petrols — existent gum content (solvent washed) at most 5 mg/100 ml (Journal of Laws 2024, item 1018, Annexes 1 and 2 item 8); method according to Journal of Laws 2024, item 1058, Annex Part I point 7
• Aviation fuels — existent gum content (clause 1)
• Motor gasolines and other volatile distillates, including those with up to 85 % (V/V) ethanol, ethers and deposit control additives; no precision data for E85 (clause 1)
• Aviation turbine fuels — high gum content indicates contamination with higher-boiling oils or particulate matter (introduction)

Key parameters

Standard

Standard number

PN-EN ISO 6246:2017-05

Title (PL)

Przetwory naftowe — Zawartość żywic w paliwach — Metoda odparowania w strumieniu

Title (EN)

Petroleum products — Gum content of fuels — Jet evaporation method

Step-by-step procedure

1. Cleaning the beakers

   1995 edition: the beakers (including the tare) are washed with gum solvent, rinsed with water and immersed in a detergent cleaning solution (conditions established by the laboratory; criterion — cleanliness matching chromic acid cleaning), then handled only with forceps, rinsed with tap water and grade 3 water, dried for at least 1 h at 150 °C and cooled for at least 2 h in the cooling vessel near the balance (10.1).

2. Setting up the bath

   1995 edition, Table 1: air — bath 160–165 °C, well 150–160 °C (aviation and motor gasolines); steam — bath 232–246 °C, well 229–235 °C (aircraft turbine fuels); the flow is set according to clause 7 or 8 (10.2).

3. Weighing the beakers

   1995 edition: the beakers are weighed against the tare beaker to the nearest 0.1 mg (10.3).

4. Evaporation

   1995 edition: a sample with suspended or settled matter is first filtered through the sintered glass funnel. 50 ml of sample is added with a cylinder to each beaker except the tare, the beakers are placed in the bath, the jets are centred above the liquid, splashing is avoided and the portions are evaporated for 30 min (10.4–10.5).

5. Cooling and weighing

   1995 edition: the beakers are transferred to the cooling vessel, cooled for at least 2 h near the balance and weighed (10.6).

6. Heptane extraction

   1995 edition, non-aviation fuels: 25 ml of heptane is added to the beakers (and the tare), swirled for 30 s, left to stand for 10 min and the solution decanted without loss of residue; the extraction is repeated a second time, and a third time if the extract is coloured (10.8–10.10).

7. Drying after extraction

   1995 edition: the beakers are dried for 5 min in the bath at 160–165 °C without the jets fitted, cooled for at least 2 h near the balance and weighed (10.11–10.12).

8. Calculation

   1995 edition: gum content [mg/100 ml] = 2,000 × [(mass of beaker with residue − mass of tare beaker after treatment) − (mass of empty beaker − mass of tare beaker before treatment)], masses in grams (11.1). Rounding rules of the 2017 edition — clauses 12–13, outside the available text.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The standard does not address all hazards associated with its use — safety measures are established by the user (warning in the standard)
• Gasoline components with a high percentage of low-boiling unsaturated compounds can explode during evaporation — the method is not intended for them (clause 1)
• Chromic acid (the cleanliness reference for cleaning beakers) is toxic, carcinogenic (Cr(VI) compounds) and highly corrosive; used solution is not poured down the drain (1995 edition, warning in 10.1)
• Gasolines, heptane, toluene and acetone are flammable — precautions according to the safety data sheets

Frequently asked questions