Octane number (RON, MOZ) & knock resistance

The octane number (OZ) is a key figure for the knock resistance of gasoline, which varies between 0 and 100. It provides information about the combustion behavior of the fuel in the engine, whereby a distinction is made between the research octane number (RON) and the engine octane number (MOZ).

Definition
The octane number describes the ability of a petrol fuel to resist premature, uncontrolled self-ignition during compression. A higher octane number value indicates a higher knock resistance, which is crucial for optimum engine performance with adjusted parameters.

Background / Origin
Octane number is a key characteristic for evaluating gasoline fuels and is categorized into two main types: research octane number (RON) and engine octane number (MOZ). The RON is determined under simulated conditions at a lower temperature and speed and is the more common measurement used at filling stations. According to DIN EN 228, the minimum requirement for a super gasoline fuel is a RON of at least 95.0 and 98.0 for super-plus gasoline.

In contrast, the MOZ describes the behavior of the fuel at higher temperatures and speeds, such as those encountered when driving on the freeway. Although the MOZ is less well known to the consumer and is not indicated at filling stations, the minimum values according to DIN EN 228 are 85.0 for super gasoline and 88.0 for super plus gasoline.

The knock resistance is a defined measure to ensure that the air-fuel mixture in the engine does not self-ignite in an uncontrolled manner, but only through the ignition spark or compression. Misfilling the tank with diesel fuel can lower the octane rating and lead to serious operating problems, which underlines the everyday importance of the octane rating.

Properties
The octane number is a measure of knock resistance and influences engine performance. When determining octane numbers, a comparison is made with one or more specific fuels in the laboratory. The CFR test engine, a 4-stroke gasoline engine with adjustable compression, is often used for this purpose. It owes its name to the Cooperative Fuel Research Committee, which developed the test procedure.

Composition
- The octane number is determined by a mixture of reference fuels.

Physical characteristics
- Octane numbers vary between 0 and 100.

Differences in quality
- In practice, RON and MOZ are usually above the minimum values required by DIN EN 228.

Chemical characteristics
- The knock resistance is strongly dependent on the specific fuel and its chemical properties.

Application and importance on the market
Gasoline fuels with a high octane rating can increase engine performance if the engine parameters are adjusted accordingly. This is particularly relevant for high-performance engines and sporty driving styles.

The development and availability of gasoline with different octane numbers shows international differences in fuel quality and use. In Germany, the Rohs information is defined by the continuous indication of the RON at the fuel pumps, as well as by the European standards, which set minimum requirements for RON and MOZ.

Differentiation from similar terms
- Research octane number (RON): Measures the behavior at lower temperature and speed.
- Engine octane number (MOZ): Measures the behavior at higher speed and temperature.
- Front octane number (FOZ): A special designation, also known as RON 100, which is less commonly used.

Summary
The octane number is a key figure for the knock resistance of gasoline, with a scale from 0 to 100. It is divided into research octane number (RON) and engine octane number (MOZ), which reflect different operating conditions. A high octane number is important for engine performance, road safety and fuel quality. Misunderstandings when refueling, especially diesel fuel contamination, can have a serious impact on driving performance. The demanding standards and test procedures, such as the use of the CFR test engine, protect the quality standard of the fuel market.