β½ Research Octane Number (RON)
Determination of gasoline Research Octane Number (RON) on CFR engine by comparing knock intensity with reference fuel blends.
Overview
Research Octane Number (RON) is the basic quality parameter of motor gasoline, determining its resistance to knock combustion (detonation) in spark-ignition engines. The higher the octane number, the more resistant the fuel is to uncontrolled self-ignition of the fuel-air mixture, which manifests as characteristic metallic knocking and can lead to engine damage.
The RON research method according to ISO 5164 (equivalent to ASTM D2699) uses a standardized single-cylinder CFR (Cooperative Fuel Research) engine with variable compression ratio, operating at 600 rpm. The test fuel is compared with Primary Reference Fuel (PRF) blends: isooctane (2,2,4-trimethylpentane, RON = 100) and n-heptane (RON = 0). The fuel's RON corresponds to the percentage of isooctane in the PRF blend that gives the same knock intensity as the test gasoline.
According to PN-EN 228, unleaded gasoline in Poland must have RON β₯ 95.0 (E95) or β₯ 98.0 (E98). The requirement also applies to gasoline with biocomponents (ethanol up to 10% V/V). RON determination is the most expensive and complex test in fuel laboratories β it requires a specialized CFR engine costing several hundred thousand zlotys and a qualified operator.
The research method (RON) simulates gentle city driving conditions (low speed, frequent acceleration), as opposed to the motor method (MON, ISO 5163), which simulates highway driving under full load.
Method principle
Test gasoline is burned in a single-cylinder CFR engine with variable compression ratio at 600 rpm and intake mixture temperature of 52Β°C. Knock intensity is measured with a piezoelectric sensor (knockmeter). Then two PRF blends (isooctane + n-heptane) are selected β one giving slightly stronger knock and one giving slightly weaker knock than the test fuel β at the same compression ratio. RON is calculated by linear interpolation between the RON of two PRF blends, proportional to knockmeter readings.
Applications
- Quality certificate of unleaded gasoline E95 and E98 (PN-EN 228) β RON β₯ 95.0 / β₯ 98.0
- Aviation gasoline quality control (AVGAS 100LL)
- Testing effect of biocomponents (ethanol, ETBE) on octane number
- Refinery component assessment (reformate, alkylate, isomerate)
- R&D research β optimization of gasoline formulations
- Customs control and commercial inspection of gasoline
- Quality monitoring at storage depots
Key parameters
| Parameter | Value |
|---|---|
| Measurement range | 0β120 RON (typically 88β101 RON) |
| CFR engine speed | 600 rpm |
| Intake mixture temperature | 52Β°C Β± 1Β°C |
| Reference fuels (PRF) | Isooctane (RON=100) + n-heptane (RON=0) |
| Repeatability | 0.2 RON (at RON ~95) |
| Reproducibility | 0.7 RON (at RON ~95) |
Standard
- Standard number
- PN-EN ISO 5164:2014
- Title (PL)
- Przetwory naftowe β Oznaczanie wΕaΕciwoΕci przeciwstukowych paliw silnikowych β Metoda badawcza
- Title (EN)
- Petroleum products β Determination of knock characteristics of motor fuels β Research method
Step-by-step procedure
1. CFR engine warm-up
Start CFR engine and warm up to stable operating conditions. Coolant temperature 100Β°C, oil 57Β°C, intake air 52Β°C. Warm-up time: 30β60 min.
2. Knockmeter calibration
Check knockmeter sensitivity and zeroing. Perform test with control fuel (toluene) β result should be within tolerance limits.
3. Preliminary sample testing
Introduce test gasoline to carburetor. Set compression ratio at which knock intensity is approx. 50 knockmeter divisions. Read compression value.
4. PRF blend selection
Based on preliminary reading, prepare two PRF blends (isooctane+n-heptane) with RON 1β2 units above and below expected RON.
5. Sample and PRF measurement
At same compression ratio, measure knock intensity sequentially: lower PRF β sample β higher PRF β sample. Repeat cycle 3 times.
6. Mixture composition adjustment
For each fuel, set A/F ratio for maximum knock (worst conditions). Use carburetor adjustment.
7. RON calculation
Calculate average knockmeter readings for sample and both PRFs. Interpolate linearly: RON = RON_lower + [(reading_sample β reading_lower) / (reading_higher β reading_lower)] Γ (RON_higher β RON_lower).
8. Result verification
Check if duplicate difference β€0.2 RON (repeatability). Compare result with standard requirement (β₯95.0 or β₯98.0).
9. Engine shutdown
After measurement series completion, flush fuel system with isooctane. Shut down engine according to manufacturer procedure.
10. Result recording
Record RON, atmospheric conditions (pressure, humidity), temperature and PRF series number. Complete CFR engine logbook.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| CFR F1/F2 engine | Waukesha CFR F1/F2 Combination Unit, SINPAR FTC-M1 | 400 000β900 000 PLN |
| Knockmeter (detonation sensor) | Waukesha XCP Technology (integrated with engine) | included with engine |
| Four-ball carburetor | CFR carburetor with A/F mixture adjustment | included with engine |
| PRF reference fuels | Isooctane + n-heptane, purity β₯99.75%, Chevron Phillips / Haltermann | 3 000β8 000 PLN / 5 L |
| Air humidity control system | Dehumidifier/humidifier, maintaining 25β50 grains/lb dry air | 10 000β30 000 PLN |
| Laboratory barometer and hygrometer | Digital barometer Β±0.1 kPa, hygrometer Β±2% RH | 2 000β5 000 PLN |
| Certified thermometers | ASTM thermometers for CFR engine (intake, coolant, oil) | 500β2 000 PLN / set |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Isooctane (2,2,4-trimethylpentane) | 540-84-1 | Reference fuel RON=100, purity β₯99.75%, certified |
| n-Heptane | 142-82-5 | Reference fuel RON=0, purity β₯99.75%, certified |
| Toluene (control fuel) | 108-88-3 | Reference toluene for CFR engine operation verification (known RON) |
| SAE 30 engine oil | β | Lubricating oil for CFR engine, change every 50β100 h operation |
| Coolant | β | Water/glycol mixture for CFR engine cooling system |
Health and safety (OHS)
- Gasoline and reference fuels β highly flammable, work in room with explosion-proof ventilation (ATEX)
- CFR engine β hot surfaces (>100Β°C), moving parts, noise >85 dB β use hearing protection
- Exhaust gases β toxic (CO, NOx), vent outside building through exhaust system
- N-heptane β highly flammable, irritating, toxic when inhaled
- Isooctane β highly flammable, store in fire-resistant cabinet
- Mandatory: hearing protection, glasses, gloves, coat, fire extinguisher within reach