⛽ Research Octane Number (RON)
In short
Determination of the research octane number (RON) of spark-ignition engine fuels in a standardized single-cylinder CFR engine of variable compression ratio, run at constant speed, by comparing the knock intensity with blends of reference fuels. The test is performed according to PN-EN ISO 5164:2014-08; Range: scale 0–120 RON; working range 40–120 RON; typical fuels 88–101 RON (clause 1). The procedure comprises 4 steps; it is used for: Unleaded petrols 95 and 98 — RON at least 95.0 and 98.0 after subtracting k = 0.2 (Journal of Laws 2024, item 1018, Annexes 1 and 2), Fuels with oxygenates up to 4.0 % (m/m) oxygen and petrol with up to 25 % (V/V) ethanol (clause 1), Petrol components and process streams in the working range 40–120 RON (clause 1; ASTM D2699).
At a glance
- Standard: PN-EN ISO 5164:2014-08
- Category: Petrochemistry
- Procedure steps: 4
- Range: scale 0–120 RON; working range 40–120 RON; typical fuels 88–101 RON (clause 1)
- Engine: single-cylinder, four-stroke, carburetted CFR engine with variable compression ratio (clause 1, 6.1)
- Engine speed: 600 ± 6 r/min when firing (8.2)
Overview
STATUS (as of 30.10.2026). PN-EN ISO 5164:2014-08 — Polish version, published 14.06.2016, implements EN ISO 5164:2014 and ISO 5164:2014 [IDT]; it replaced PN-EN ISO 5164:2007. The PKN catalogue card has no withdrawal note — the standard is current; Polish title according to the card: “Przetwory naftowe — Oznaczanie odporności benzyny samochodowej na spalanie stukowe — Metoda badawcza”. ISO 5164:2014 (fourth edition) replaced ISO 5164:2005 and introduced the digital detonation meter alongside the former analogue one.
ASTM D2699 METHOD (introduction). The standard gives ISO status to the ASTM D2699-12 procedure and refers to its annexes and appendices: the equipment, component settings and working tables are not in the ISO text but in ASTM D2699-12.
SCOPE (clause 1). Rating of liquid spark-ignition engine fuels on an arbitrary scale of octane numbers. RON is a measure of the knock characteristics of motor fuels in automotive engines under mild conditions of operation. The scale covers 0–120 RON, the working range is 40–120 RON, and typical motor fuels are in the range 88–101 RON. The standard applies to fuels containing oxygenates up to 4.0 % (m/m) oxygen and to petrol containing up to 25 % (V/V) ethanol; full applicability for that oxygen content has been checked only for petrol-type fuels.
PRINCIPLE (clause 4, definitions 3.6–3.17). The sample fuel, at the fuel-air ratio that maximizes its knock, is compared with blends of primary reference fuels (isooctane — 100 RON, n-heptane — 0 RON; above 100 — isooctane with dilute tetraethyl lead): the blend is sought that, at the same compression ratio, produces the same standard knock intensity. The volumetric composition of that blend defines its octane number and that of the sample. Knock is sensed by a magnetostrictive detonation pickup threaded into the cylinder; the signal is processed by a detonation meter (analogue or digital) and displayed by the knockmeter.
LEGAL REQUIREMENTS. Motor petrols: RON at least 95.0 for unleaded petrol 95 and 98.0 for 98; the final RON value is calculated by subtracting a correction factor k = 0.2 from the result of the determination (Journal of Laws 2024, item 1018, Annexes 1 and 2 item 1, footnote 3).
WHAT WE DO NOT GIVE HERE. The publicly available text of the standard ends with the engine speed (8.2). We do not give the other engine operating conditions (among others intake air and oil temperature, humidity), the engine check with toluene standardization fuel, the comparison procedures, the calculation of the result or the precision — in the standard they are in later clauses and in ASTM D2699-12.
Method principle
The CFR engine runs at 600 r/min. The sample fuel, at the fuel-air ratio that maximizes its knock, is compared with blends of primary reference fuels (isooctane and n-heptane) at the same compression ratio; the blend producing the same standard knock intensity defines — by its volumetric composition — the octane number of the sample. The knock intensity is measured by a magnetostrictive detonation pickup with a detonation meter (clause 4, definitions 3.6–3.7, 8.2).
Applications
- Unleaded petrols 95 and 98 — RON at least 95.0 and 98.0 after subtracting k = 0.2 (Journal of Laws 2024, item 1018, Annexes 1 and 2)
- Fuels with oxygenates up to 4.0 % (m/m) oxygen and petrol with up to 25 % (V/V) ethanol (clause 1)
- Petrol components and process streams in the working range 40–120 RON (clause 1; ASTM D2699)
Key parameters
| Parameter | Value |
|---|---|
| Range | scale 0–120 RON; working range 40–120 RON; typical fuels 88–101 RON (clause 1) |
| Engine | single-cylinder, four-stroke, carburetted CFR engine with variable compression ratio (clause 1, 6.1) |
| Engine speed | 600 ± 6 r/min when firing (8.2) |
| Reference fuels | isooctane — 100 RON, n-heptane — 0 RON, minimum purity 99.75 % (V/V) (5.4–5.5) |
| Cylinder jacket coolant | water of grade 3 according to ISO 3696, boiling temperature 100 ± 1.5 °C (5.1) |
| Requirement for petrol | at least 95.0 / 98.0 RON after subtracting k = 0.2 (Journal of Laws 2024, item 1018) |
Standard
- Standard number
- PN-EN ISO 5164:2014-08
- Title (PL)
- Przetwory naftowe — Oznaczanie odporności benzyny samochodowej na spalanie stukowe — Metoda badawcza
- Title (EN)
- Petroleum products — Determination of knock characteristics of motor fuels — Research method
Step-by-step procedure
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Sampling and sample preparation
According to ISO 3170 or ISO 3171; the sample is cooled to 2–10 °C in the container in which it was received, before the container is opened, protected from light and stored in an opaque container (clause 7).
-
Installation and engine speed
The engine is located where it is not affected by gases and fumes influencing the result; the speed when firing is 600 ± 6 r/min and not more than 3 r/min higher than when motoring without combustion (8.1–8.2).
-
Comparison with reference fuels
For the sample and the reference blends, the fuel-air ratio giving maximum knock intensity is set and the knock intensity is compared at the same compression ratio; the blend with the same standard knock intensity defines the RON of the sample (clause 4).
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Result
The comparison procedures, calculation of the result and precision are in later clauses of the standard and in ASTM D2699-12, outside the publicly available text. To assess petrol against the requirements, k = 0.2 is subtracted from the result (Journal of Laws 2024, item 1018).
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| CFR F-1 octane rating unit | single-cylinder engine with compression ratio adjustable while operating, thermal-siphon jacket cooling, multiple fuel tanks with selector valving, intake air system with controlled temperature and humidity; belted to an electric motor that starts it and absorbs power at constant speed; the sole manufacturer is Waukesha (6.1, introduction) | — |
| Knock measuring instrumentation | detonation pickup, detonation meter and knockmeter — analogue or digital (6.2, definitions 3.6–3.13) | — |
| Burettes for reference fuels | capacity 200–500 ml, volumetric tolerance ± 0.2 %, verified according to ISO 4787; tip discharge after shut-off up to 0.5 ml, delivery rate up to 400 ml/min; gravimetric blending permitted (6.3–6.4) | — |
| Tetraethyl lead dispensing equipment | calibrated burette or pipette of up to 4.0 ml, for dispensing into 400 ml of isooctane (6.5) | — |
| Special maintenance tools | speciality tools and measuring instruments for maintaining the engine (6.6) | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Isooctane (2,2,4-trimethylpentane) | 540-84-1 | primary reference fuel 100 RON; minimum purity 99.75 % (V/V), heptane up to 0.10 % (V/V), lead up to 0.5 mg/l (5.4) |
| n-Heptane | 142-82-5 | primary reference fuel 0 RON; minimum purity 99.75 % (V/V), isooctane up to 0.10 % (V/V), lead up to 0.5 mg/l (5.5) |
| 80-octane reference fuel blend | — | isooctane with n-heptane, 80 % (V/V) ± 0.1 % (V/V) isooctane (5.6) |
| Dilute tetraethyl lead | — | for reference fuel blends above 100 RON (millilitre additions to 400 ml of isooctane); the antiknock compound contains 18.23 % (m/m) ± 0.05 % (m/m) tetraethyl lead, the diluent is xylene with n-heptane (5.7–5.8) |
| Toluene | 108-88-3 | reference fuel grade — at least 99.5 % (V/V), peroxide number up to 5 mg/kg, water up to 200 mg/kg; for toluene standardization fuel (TSF) blends (5.9, definition 3.19) |
| Check fuels | — | typical fuels with a RON accepted reference value, low volatility and good long-term stability (5.10) |
| Crankcase lubricating oil | — | SAE 30, API SF/CE or better, with detergent additive, viscosity 9.3–12.5 mm²/s at 100 °C, viscosity index at least 85; no viscosity index improvers, not multigrade (5.3) |
| Cylinder jacket coolant | — | water of grade 3 according to ISO 3696; where the laboratory altitude requires it — with glycol-based antifreeze (5.1) |
Health and safety (OHS)
- The standard warns that its use may involve hazardous materials, operations and equipment, and that the user establishes the safety and health practices (warning before clause 1)
- Isooctane and n-heptane are flammable, their vapours are harmful and may cause flash fire (5.4–5.5)
- Tetraethyl lead is poisonous and flammable; it may be harmful or fatal if inhaled, swallowed or absorbed through the skin (5.7)
- The engine is installed in compliance with local and national codes (8.1)
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 5164:2014-08 — “Petroleum products — Determination of knock characteristics of motor fuels — Research method”.
How does this method work?
The CFR engine runs at 600 r/min. The sample fuel, at the fuel-air ratio that maximizes its knock, is compared with blends of primary reference fuels (isooctane and n-heptane) at the same compression ratio; the blend producing the same standard knock intensity defines — by its volumetric composition — the octane number of the sample.
What is the measuring range and accuracy?
Range: scale 0–120 RON; working range 40–120 RON; typical fuels 88–101 RON (clause 1); Engine: single-cylinder, four-stroke, carburetted CFR engine with variable compression ratio (clause 1, 6.1); Engine speed: 600 ± 6 r/min when firing (8.2); Reference fuels: isooctane — 100 RON, n-heptane — 0 RON, minimum purity 99.75 % (V/V) (5.4–5.5).
How long does the test take?
The procedure comprises 4 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
CFR F-1 octane rating unit, Knock measuring instrumentation, Burettes for reference fuels, Tetraethyl lead dispensing equipment, Special maintenance tools.
Where is this test used?
Unleaded petrols 95 and 98 — RON at least 95.0 and 98.0 after subtracting k = 0.2 (Journal of Laws 2024, item 1018, Annexes 1 and 2); Fuels with oxygenates up to 4.0 % (m/m) oxygen and petrol with up to 25 % (V/V) ethanol (clause 1); Petrol components and process streams in the working range 40–120 RON (clause 1; ASTM D2699).
What safety precautions apply?
The standard warns that its use may involve hazardous materials, operations and equipment, and that the user establishes the safety and health practices (warning before clause 1); Isooctane and n-heptane are flammable, their vapours are harmful and may cause flash fire (5.4–5.5); Tetraethyl lead is poisonous and flammable; it may be harmful or fatal if inhaled, swallowed or absorbed through the skin (5.7); The engine is installed in compliance with local and national codes (8.1).
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 5164.