⛽ Motor octane number (MON) of motor and aviation gasoline — CFR engine with variable compression ratio, comparison with isooctane / n-heptane primary reference fuel blends; PN-EN ISO 5163

Petrochemistry PN-EN ISO 5163

Overview

WHAT THE STANDARD COVERS. ISO 5163:2014 (clause 1) establishes the rating of liquid spark-ignition engine fuel on an arbitrary octane number scale, using a standardized single-cylinder, four-stroke CFR engine with a carburettor and variable compression ratio, running at constant speed. The motor octane number (MON) is a measure of the knock resistance of motor fuels in automotive engines under severe conditions; for aviation fuels for piston engines it is used — through a correlation equation — to obtain the octane number by the aviation method or the performance number (lean-mixture rating). The standard covers the whole scale 0–120 MON, but the working range is 40–120 MON; typical motor gasolines lie within 80–90 MON, aviation fuels within 98–102 MON. It applies to fuels containing oxygenates with oxygen up to 4.0 % (m/m) and to gasolines with ethanol up to 25 % (V/V); note 1 adds that 25 % (V/V) of ethanol is approximately 9 % (m/m) of oxygen and that full applicability for such an oxygen content has been verified only for gasoline-type fuels, note 2 — that work is under way on gasolines with ethanol up to 85 % (V/V). The "Scope" field of the PKN card of PN-EN ISO 5163:2014-08 (Polish version), fragment: "The motor octane number (MON) is a measure of the knock resistance of fuels for motor vehicles with spark-ignition engines at high engine loads. (…) This International Standard can be used over the whole determination range from 0 MON to 120 MON, but its working range covers from 40 MON to 120 MON. The typical range is from 80 MON to 90 MON. The typical range for aviation fuels is from 98 MON to 102 MON" (our translation).

PRINCIPLE AND MATERIALS (ISO 5163:2014, clauses 4–7). A fuel sample, run in the engine at the fuel-air ratio giving maximum knock, is compared with primary reference fuel blends, looking for the one which — also at the ratio giving maximum knock — gives the same standard knock intensity at the same compression ratio; the volumetric composition of that blend defines its octane number and the octane number of the sample. Reference fuels: isooctane (2,2,4-trimethylpentane) with a purity of at least 99.75 % (V/V), with not more than 0.10 % (V/V) of heptane and 0.5 mg/l of lead (= 100 MON); n-heptane with a purity of at least 99.75 % (V/V), with not more than 0.10 % (V/V) of isooctane and 0.5 mg/l of lead (= 0 MON); an 80-octane blend with 80 % ± 0.1 % (V/V) of isooctane; above 100 MON — millilitre additions of dilute tetraethyllead to 400 ml of isooctane (antiknock compound with 18.23 % ± 0.05 % (m/m) of tetraethyllead); toluene with a purity of at least 99.5 % (V/V) for toluene standardization fuel blends (TSF) and check fuels with an assigned MON value. Cylinder jacket coolant — water of grade 3 according to ISO 3696, boiling at the laboratory location at 100 °C ± 1.5 °C (laboratories at higher altitude — with added glycol); engine oil SAE 30 with a kinematic viscosity of 9.3–12.5 mm²/s at 100 °C and a viscosity index of at least 85, not multigrade and without viscosity-index improvers. Apparatus: CFR engine unit (a single manufacturer, according to the standard), electronic detonation meter (analogue or digital) with a pickup and knock indicator, burettes or volumetric vessels of 200–500 ml capacity with a tolerance of ±0.2 % (delivery rate not more than 400 ml/min, drainage from the tip after closing not more than 0.5 ml); blends may be prepared by mass with the same tolerance of 0.2 %. Samples are taken according to ISO 3170 or ISO 3171, cooled to 2–10 °C before the container is opened and protected from light (opaque container).

RELATION TO ASTM D2700. According to the introduction, ISO 5163:2014 is the ASTM D2700-12 method rewritten according to ISO rules; carrying it out requires the annexes and appendices of ASTM D2700-12 (equipment, critical settings, tables), which the ISO standard does not contain, and the CFR engine is built in inches — which is why some settings are given in inch units. The fourth edition (2014) replaced ISO 5163:2005 together with corrigendum Cor.1:2008 and allowed a digital detonation meter alongside the analogue one; according to the introduction, a comparison of both systems showed no statistically observable shift of results for MON.

REGULATIONS. Regulation of the Minister of Climate and Environment of 26 June 2024 on test methods for the quality of liquid fuels (Journal of Laws 2024 item 1058, amended by Journal of Laws 2024 item 1966; "in force" in the ELI database of the Sejm, read on 27.10.2026), annex, part I points 2–2.3: MON is determined with a standardized test engine under standardized conditions, and the procedure, apparatus, reagents, calculations and precision are specified by standard PN-EN ISO 5163. Regulation of the Minister of Climate and Environment of 26 June 2024 on quality requirements for liquid fuels (Journal of Laws 2024 item 1018), Annex No 1, item 2: MON at least 85.0 for unleaded gasoline 95 and 88.0 for unleaded gasoline 98; footnote 3: "The final value of RON and MON is calculated by subtracting the correction factor k = 0.2 from the result of the determination of MON and RON by the appropriate method" (our translation); footnote 2 refers the interpretation of results to PN-EN ISO 4259-2.

STATUS (PKN card as of 27.10.2026). The card of PN-EN ISO 5163:2014-08 (Polish version) has no withdrawal label: publication 14-06-2016, 36 pages, Chemistry Sector, KT 222/PK 1 Liquid Fuels, "Adopts: EN ISO 5163:2014 [IDT], ISO 5163:2014 [IDT]", "Replaces: PN-EN ISO 5163:2007/AC:2009 - Polish version, PN-EN ISO 5163:2007 - Polish version", ICS 75.160.20. PKN search, search term "ISO 5163" (27.10.2026): alongside it there is the English version PN-EN ISO 5163:2014-08, and PN-EN ISO 5163:2006 (English version) and PN-EN ISO 5163:2007 (Polish version) are withdrawn. In the iTeh catalogue (read on 27.10.2026) ISO 5163:2014 has the status "Published" and the review stage "9093 – International Standard confirmed", and EN ISO 5163:2014 — "Published".

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database refreshed from the production server on 27.10.2026 and current PCA documents downloaded on that day). Number 5163 appears in 14 records at 6 Polish laboratories: AB 009, AB 297, AB 387, AB 474, AB 484, AB 773. The current PCA documents confirm the standard at five of them; AB 474 (ORLEN Laboratorium, Gdańsk Refinery Laboratory, accreditation valid until 16-12-2027) has no scope document on the PCA website on 27.10.2026, so its entries could not be compared. No entry with this standard is suspended. Forms: "PN-EN ISO 5163:2014-08" (AB 474, AB 484, AB 297 — the last one "excluding point 7.1"), "PN-EN ISO 5163" (AB 387, AB 773), "PN EN ISO 5163" (AB 009). AB 297 also has "ASTM D 2700-24c Procedure A excluding point 9.1" in the same entry. The "Laboratories" tab ("PN-EN ISO 5163") shows 8 laboratories: these 6 Polish ones and 2 Czech ones (tab query on labcoda.pl, 27.10.2026).

WHAT THE LABORATORIES TEST (database copy and PCA documents). All entries are the engine method. Unleaded gasoline — at all of them; ranges: 80.0–95.0 (AB 009, also biohydrocarbons for spark-ignition engines and gasoline with bioethanol), 80.0–110 (AB 297, also ethanol fuel E85, aviation gasoline and gasoline components), 40.0–100.0 (AB 474 and the Instrumental Laboratory of AB 484), 70–107 (AB 484, Fuels and Aromatics Laboratory, also fractions with boiling points of 30–250 °C), 60–100 (AB 484, Jedlicze), 84.0–90.0 (AB 484, Ostrów Wielkopolski), 80.0–90.0 (AB 484 in Lublin, Olsztyn, Warsaw and Wrocław and AB 773 in Bydgoszcz); AB 387 (Koluszki, Boronów) gives no range.

ALONGSIDE THIS STANDARD (database copy, 27.10.2026). The motor octane number is given in the scopes of 10 Polish laboratories; apart from this standard — for liquefied petroleum gas LPG — as a value "calculated" according to Annex B of the product standard PN-EN 589 (AB 079, AB 103, AB 1275, AB 474, AB 484 with the form "PN-EN 589:2024-08", AB 1278 without the year), i.e. without an engine. The research octane number (RON) is tested by the same laboratories according to PN-EN ISO 5164 (separate entry of this database), AB 297 also according to ASTM D 2699.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — the correction from the regulation: for comparison with the requirement of 85.0 (gasoline 95) or 88.0 (gasoline 98) the result of the determination reduced by 0.2 is taken; a result of 85.1 gives a final value of 84.9, below the requirement (numerical example ours). Second — scope of application: the standard covers gasolines with ethanol up to 25 % (V/V) and fuels with oxygen up to 4.0 % (m/m); ethanol fuel E85, which AB 297 has in its scope, lies outside the confirmed scope of application (according to note 2, work on ethanol up to 85 % was ongoing when the standard was issued). Third — sample: the standard requires it to be cooled to 2–10 °C before the container is opened and protected from light, because light can change the properties of the fuel (points 7.2–7.3). Fourth — MON and RON are two different tests with separate requirements; the result of one does not replace the other. Fifth — the reference to ASTM is dated: the ISO standard requires the annexes and appendices of ASTM D2700-12, not of later editions; AB 297 also has ASTM D 2700-24c in the same entry.

WHAT WE DO NOT GIVE. The fragment of ISO 5163:2014 we read ends at point 8.1. We do not give the engine settings and operating conditions (clause 8: engine speed, timing, temperatures, humidity, cylinder height, fuel-air ratio), engine qualification (clause 9), the course of the determination (clause 10), calculations, how the result is expressed or precision (clauses 11–13).

Method principle

A fuel sample is burned in a CFR engine with variable compression ratio at the fuel-air ratio giving maximum knock and is compared with primary reference fuel blends (isooctane = 100 MON, n-heptane = 0 MON, above 100 MON isooctane with added dilute tetraethyllead), also at the ratio giving maximum knock. The MON of the sample is the octane number of the reference blend which at the same compression ratio gives the same standard knock intensity (ISO 5163:2014, clause 4). WE DO NOT GIVE the engine settings and the course of the determination.

Applications

• Motor gasolines for spark-ignition engines, also with ethanol up to 25 % (V/V) and fuels with oxygen up to 4.0 % (m/m) (ISO 5163:2014, clause 1)
• Aviation fuels for piston engines — through a correlation equation with the octane number by the aviation method (ISO 5163:2014, clause 1)
• Quality control of gasolines placed on the market: method cited in Journal of Laws 2024 item 1058, requirement MON ≥ 85.0 (95) and ≥ 88.0 (98) in Journal of Laws 2024 item 1018
• In accreditation scopes: 6 Polish laboratories, all by the engine method; ranges from 40.0–100.0 to 80.0–110 MON

Key parameters

Standard

Standard number

PN-EN ISO 5163:2014-08 (wersja polska i wersja angielska; wprowadza EN ISO 5163:2014 i ISO 5163:2014 [IDT])

Title (PL)

Przetwory naftowe — Oznaczanie odporności benzyny samochodowej i benzyny lotniczej na spalanie stukowe — Metoda motorowa

Title (EN)

Petroleum products — Determination of knock characteristics of motor and aviation fuels — Motor method

Step-by-step procedure

1. Sampling and storage

   Sampling according to ISO 3170 or ISO 3171; cooling to 2–10 °C before the container is opened; protection from light, opaque container (clause 7).

2. Engine preparation

   Installation and basic settings according to clause 8 and the annexes of ASTM D2700-12; engine qualification on check fuels and TSF blends according to clause 9. WE DO NOT GIVE the settings.

3. Determination

   Sample and reference blends at the fuel-air ratio giving maximum knock; the blend giving the same standard knock intensity at the same compression ratio is sought (clause 4). WE DO NOT GIVE the course from clause 10.

4. Result and assessment

   MON according to clauses 11–12; for comparison with the requirement of Journal of Laws 2024 item 1018, 0.2 is subtracted from the result. PN-EN ISO 5163:2014-08 — current (PKN card as of 27.10.2026).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Isooctane and n-heptane are flammable, their vapours harmful; the vapours can ignite (warnings in points 5.4–5.5)
• Tetraethyllead is toxic and flammable — harmful or fatal if inhaled, swallowed or absorbed through the skin (point 5.7)
• The engine is placed where gases and vapours from the surroundings do not affect the result (point 8.1)
• TECHNICAL NOTE: result for comparison with the requirement of the regulation = result of the determination − 0.2

Frequently asked questions