Octane rating

General

There are many materials, such as some aromatics, natural gas and LPG, which have an octane number greater than 100. Measuring technology, but they are difficult to detect, since the reference system is defined with isooctane only up to 100 octane. Octane numbers greater than 100 have to be extrapolated. The octane number over 100 RON / MON corresponds to the octane number of a mixture of iso- octane and tetraethyl lead (TEL ); The octane number of the mixture is associated with a given volume fraction of TEL in the iso - octane. This assignment is based on the 51756 part 1 specified in DIN table. You can not, as in the octane number to 100, be read directly from the mixing ratio of the reference fuel. In this context, the term octane blend is used; in aviation rather the figure of merit, last given as a two-part "break" such as 115/145, which means that the fuel used here with a lean mixture at a rich mixture has a capacity of 115, a figure of merit of 145. Isooctane is relatively anti-knock, n- heptane causes relatively quickly the so-called knocking at the engine. Reason for this is that the n- heptane uncontrolled fires already during the compression process by the heat of compression in the cylinder. Isooctane can be relatively highly compressed, without leading to auto-ignition. In a gasoline engine, the fuel -air mixture to be ignited by a spark and with a defined flame front to burn down ( in the further development of the gasoline engine with homogeneous charge compression ignition removes part of the spark ).

One can distinguish between different octane numbers:

• RON - Research Octane Number
• MON - Motor Octane Number
• SOZ - Roads octane number
• FOZ - front- octane, often also referred to as ROZ100 ° C.

Octane and Efficiency

The increase in the octane number was accompanied by the development of internal combustion engines. Earlier it was the raw gasoline / naphtha, such as is obtained in the primary distillation, used as fuel. The developed after the Second World War motors require tighter fuel knock. Due to stronger compression, the efficiency of the engine increase, and therefore the specific power.

From 1924, in the U.S. or in Germany in 1936 to 1996 petrol tetraethyl lead was added to increase the octane number. The lead, inter alia, as a radical scavenger prevents the uncontrolled spontaneous ignition of the fuel-air mixture during the compression. It also has a lubricating effect on the valve seats. Because lead and its compounds are highly toxic, the lead content of petrol was in the Federal Republic of Germany from 1971 limited by law, first at 0.4 g / l, later to 0.15 g / l In the 1980s, together with the catalytic converters unleaded gasoline was introduced because the lead additives would have made the Katalsysatoren ineffective. Finally, in 2000 leaded petrol in the European Union was generally forbidden on January 1. There were hardly any vehicles the valve seats were designed for lead in the fuel.

The different octane fuels available at gas stations is due to the different use of the produced in an oil refinery components. So premium gasoline contains more high-quality components than regular gasoline. The production of high quality components generally requires higher cost, high-octane gasoline are therefore more expensive.

It is also often methyl tertiary butyl ether ( MTBE) to improve resistance added, however, are allowed only up to 15 % vol. Due to poor degradability in water, MTBE is as hazardous to water (WGK 1 = slightly hazardous to water ) classified. In several states of the USA MTBE has already been back " banished " from the gasoline. Nowadays, more and more often resorted to ethyl tertiary butyl ether ( ETBE). ETBE compared with MTBE offers due to its higher boiling point and some advantages, since it is gained from bio- ethanol, fiscally interesting as a fuel component. As MTBE and ETBE has the disadvantage that it can only degrade in groundwater bad.

History

Since about 1912, the irregular firing was observed in engines. The noise is referred to as "tapping ", which also destroyed the motor relatively rapidly. First, the new battery-powered electric ignition systems were adopted as the cause. For more detailed studies, it was found that knocking was related to the compression ratio, which increased the engine specialists to achieve better performance ( connection between ignition temperature of the fuel and the temperature increase of the fuel during the reduction of the volume during compaction. Refer to Boyle's Law). Various methods were tried, due to the many variables ( fuel composition, ignition timing, compression, engine temperature, cylinder design ... ) but continued none the measurement procedures.

1927 Graham Edgar came up with the idea that you could use pure substances and reference systems. They needed two substances ( a strong throbbing low ignition temperature and a high octane with high ignition temperature ), which could be prepared in high purity and sufficient quantities. Furthermore, these two substances should rather similar properties ( melting and boiling point, density, and evaporation characteristics ). n- heptane was obtained by distillation of high purity and had very bad knock properties. 2,2,4- trimethylpentane ( " isooctane " ) was synthesized by addition of isobutene to isobutane and be purified by distillation and had very good knock properties.

The fuels available at that time had knocking behavior, represented by mixtures of 40:60 to 60:40 of i - octane: n -heptane were shown. They could be well characterized with this system so. Then the normal gasoline car had before 1930 octane number of 40 to 60, but could by high additions of " potato fuel " or benzene or adjuncts of " tetraethyl lead " or iron carbonyls " compression- resistant " are made.

Octane numbers

In Europe, only the RON is specified at the gas stations in the U.S., the " gas pumps Octane Number " ( AON - Average Octane Number) is mostly associated with (RON MON): calculated 2. Most providers in Europe, however, advertise the research octane number, as these values ​​are to be determined later and simpler than the motor octane number.

Researched ( Explored ) octane number ( RON)

The RON is determined by the single-cylinder CFR test methods.

Both MON and RON are the ( OZ = 100 ) and Normalheptan (OZ = 0) determined in the CFR engine (variable compression ratio ) by comparison with a reference fuel from isooctane. The volume fraction of isooctane of the reference fuel which has the same knock intensity as the test fuel is the octane rating. The MOZ is usually lower than the RON, since it is determined at a higher speed and Gemischvorwärmung to about 149 ° C.

The Research on the Method ( DIN EN ISO 5164 ) determined RON is intended to describe the knocking behavior at low engine load and low engine speeds.

Motor Octane Number ( MON)

The engine with the method (DIN EN ISO 5163 ) identified "Motor Octane Number " to describe the behavior at high engine load and high thermal stress. Here tougher conditions will be used in the standard motor, namely instead of 600 now 900 revolutions per minute, an automatically adjustable ignition timing and a Gemischvorwärmung at least 149 ° C. Characterized the MOZ is always less than or equal to RON.

Will octane numbers in the CFR engine or BASF engine by comparison with a reference fuel from isooctane (OZ = 100) and Normalheptan (OZ = 0 ) is determined. The volume fraction of iso-octane reference fuel which has the same knock intensity as the test fuel is the octane rating.

The difference between RON and MON is referred to as " sensitivity " ( sensitivity ), and brings the temperature dependence of the octane number for expression. A high sensitivity means that the fuel is sensitive to higher thermal stress.

Road octane number ( SCO )

The comparative figures are measured under realistic conditions on the road. This one goes to the limit of the fuel: consistently high speed at full throttle. Thus, the SCO - value is comparable, it is subject to a standard.

Front - octane ( FOZ )

The FOZ describes the octane rating of up to 100 ° C boiling components of the fuel. It is doing the research octane number of up to 100 ° C vaporized components of the fuel determined ( hence the name ROZ100 ° C). The FOZ thus describes the behavior of the fuel at low engine temperatures shortly after starting the engine ( cold cranking amps ).

Octane numbers of some pure substances

Octane requirement of a gasoline engine

The octane requirement describes the need for knock resistance of the fuel of an engine, so that no unwanted pre-ignition. The octane requirement depends on the engine operating conditions (speed, temperature, combustion chamber geometry, compression ratio, mixture composition, pressure, humidity, ignition timing, deposits, etc.). Thus, the engine is working correctly, so the octane number range of the fuel must be so high that the octane requirement of the engine is still fulfilled even in the most unfavorable operating conditions - for example, the octane requirement of an engine at full throttle can 10 octane numbers higher than idle. The use of lying above the motor octane specification does not bring any benefits normally. Modern engines with electronic -map ignition in combination with knock sensors can be operated with different octane numbers at reduced power.

Octane number of petrol

In Austria, OMV AG has introduced in 2004 Super Plus 100 RON per year, in Switzerland, you will also BP Super Plus with a 100 RON. This has already been set in Germany in many cases, in addition Ultimate102 is now out there.