Ocatane Info links

[Guest head_tech]

This is a collection of info on Octane I have collected over the years most is copyed, hope its of interest to you

Octane

The octane quality of a gasoline is its ability to resist detonation, a form of abnormal combustion. Detonation occurs when the air-fuel mixture reaches a temperature and/or pressure at which it can no longer keep from self igniting. Two types of abnormal combustion are common: the first is detonation as previously mentioned and the other is preignition.

Detonation occurs after the spark plug has ignited the air-fuel mixture and the flame front is moving smoothly across the combustion chamber. If, during this burning process, the unburned air-fuel mixture reaches a temperature and/or pressure at which it is no longer stable, it burns very rapidly causing a new flame front to collide with the one that originated at the spark plug. Maximum pressure in the cylinder occurs before the piston reaches top dead center (TDC) and that pressure try's to push the piston down before it is ready to go down. Piston burning and rod bearing damage are the result.

Preignition is the other bad actor and is usually started by a hot spot in the combustion chamber which causes the mixture to ignite before the plug fires. Under wide open throttle conditions, preignition will destroy pistons in seconds.

Research Octane Number (RON)

RON is determined in a single cylinder variable compression ratio engine that operates at 600 rpm with a 125 degree inlet air temperature at standard barometric pressure. Spark advance is fixed at 13 degrees btdc. In a real world engine, RON is necessary to satisfy part throttle knock problems.

A good quality racing gasoline has a RON in the range of 110 to 115. The difference in the spread of RON is not very important to racing engines.

The test and hardware were originally developed in 1931. The hardware was revised in 1946 with procedural changes made until the late 1960's.

Motor Octane Number (MON)

MON is determined in a single cylinder engine similar to the RON engine with a few changes that make operating conditions more severe and therefore the octane numbers are lower. The MON engine runs at 900 rpm with a 300 degree mixture temperature. Spark advance varies with compression ratio. In a real world engine, MON is necessary to satisfy octane demands at wide open throttle. This is a very important number for racing engines since they spend a high percentage of their lives under high speed and high load conditions. Racing engines cannot afford to be short on octane quality, since detonation or preignition will quickly reduce a racing engine to junk.

The motor octane appetite of an engine with 13:1 compression ratio and a four inch bore varies with operating conditions but is normally around 101. Good quality racing gasolines have MON in the range of 100 to 115. If your engine requires a 101 MON, it is of no value to use a gasoline that has a 115 MON. To cover yourself for extreme conditions, it is wise to have an octane cushion but there is no advantage to using a very high octane quality product if you do not need it.

The MON test was originally developed in 1932. Major hardware changes were made in 1948 with procedural changes made until the late 1960's.

(R+M)/2

This is the average of RON and MON. It is sometimes referred to as the aki or anti-knock index. By law this number must be posted on the dispensing pump at retail outlets in most states. It is the most commonly used octane reference today. It was developed about 20 years ago as a compromise between RON and MON for advertising purposes and also to keep from confusing the consumer with too many different terms. It has erroneously been referred to as road octane number.

Observed Road Octane Number (RdON)

This is derived from testing gasolines in real world multi-cylinder engines, normally at wide open throttle. It was developed about 70 years ago but is still reliable today because engines are the test tools so we are able to take immediate advantage of current technology. The original testing was done in cars on the road but as technology developed the testing was moved to chassis dynamometers. this eliminated a lot of variables and some people have since built very elaborate chassis dynamometers with environmental controls to improve consistency.

Here is some links with info on a octane engine etc.

http://www.geocities.com/runyardj/octane1.html

http://www.europeancarweb.com/tech/0503 ... rs_tested/

http://en.wikipedia.org/wiki/Octane_rating

Significance of RON and MON

For clarity it is useful to provide a general overview of an octane number. An octane number is a quantitative, but imprecise measure of the maximum compression ratio at which a particular fuel can be utilized in an engine without some of the fuel /air mixture "knocking" or self igniting. This self ignition of the air/fuel mixture in the cylinder results in a loss of peak power. Directionally as the compression ratio of the engine increases so does the required octane number of the gasoline if engine knocking is to be avoided.

The performance of an engine is dependent upon many factors, one of which is the severity of operation. Accordingly the performance of a fuel is also dependent upon engine severity. To account for differences in the performance quality of a fuel two engine octane numbers are routinely used. Thc Research Octane Number (RON, or F1) simulates fuel performance under low severity engine operation. The Motor Octane Number (MON, or F2) simulates more severe operation that might be incurred at high speed or high load. In practice the octane of a gasoline is reported as the average of RON and MON or R+M/2.

Classically, both numbers are measured with a standardized single cylinder, variable compression ratio engine. For both RON and MON, the engine is operated at a constant speed (RPM's) and the compression ratio is increased until the onset of knocking. For RON engine speed is set at 600 rpm and MON is at 900 rpm.

MON and RON Depend on Gasoline Composition

The octane number measured is not an absolute number but rather a relative value based on accepted standards. By definition, n-heptane has an octane number (RON and MON) of 0, while iso-octane (2,2,4-trimethyl pentane) is 100. Linear combinations of these two components are used to measure the octane number of a particular fuel. A 90%/10% blend of iso-octane/n-heptane has an octane value of 90. Any fuel knocking at the same compression ratio as this mixture is said to have an octane number of 90.

In general, RON values are never less than MON, although exceptions to this rule exist. For pure compounds the differences between RON and MON range from 0 to more than 15 numbers. Typical values for gasoline range hydrocarbons having boiling points between 30° and 350° F go from less than 0 to greater than 100 with the extreme values being generated by extrapolation. Table 1 summarizes actual RON and MON values for a variety of pure hydrocarbons.

In practice octane numbers do not blend linearly. To accommodate this, complex blending calculations employing blending octane numbers as opposed to the values for pure hydrocarbons are routinely employed. There is no universal blending program used industry wide. In fact, for a given oil company, blending calculations that are refinery specific are not uncommon. As an improvement over octane numbers of pure compounds, there are tabulations of blending octane numbers for both RON and MON. Summarized in Table 1, these numbers are measured by blending 20 vol.% of the specific hydrocarbon in 80 vol.% of a 60/40 iso-octane/n-heptane mixture. Although still not exactly indicative of the actual blending octane number for a specific gasoline composition, the blending octane numbers are more representative. In general, the blending octane numbers are greater than the corresponding pure octane number.

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Octane in FCC Gasoline

Discussions of the source of octane in FCC gasoline are numerous. For the most part these discussions focus on RON and avoid the discussion of MON. For RON it is well known that increasing the aromatic, iso-/normal ratio and olefin content of gasoline results in significant increases in octane. Current catalyst technology requires that the hydrogen transfer activity of the catalyst be low if RON is to be increased. Most FCC octane catalysts make RON by increasing the olefin content of the gasoline rather than making aromatics. The use of Z-100™ catalyst for increasing RON relies on cracking of low octane N-paraffins to generate olefins and concentrate the aromatic content. In fact it can be said that Z-100™ catalyst does not make gasoline octane, but rather it concentrates it. A source of increased aromatic content can come from selective bottoms cracking. Selective bottoms cracking implies that substituted aromatic hydrocarbons boiling outside the gasoline range (>400°F) have their boiling point reduced to below 400°F by selective cracking of large substituent side chains. These can be either long chain paraffins or naphthenic rings. The saturated substituent will crack while the aromatic core cannot. Bottoms cracking of this type may most likely be achieved through improved understanding of the role of the matrix.

Improving the RON of FCC gasoline as discussed is for the most part well understood. The same cannot be said for MON. Although it is true that increasing the RON of gasoline does increase its MON, the incremental increase in MON is typically only 33-50% of the RON. Referring to Table 1, MON values (either actual or blending) are always less than RON except for highly branched paraffins. Increasing the weight fraction of isoparaffins in the gasoline should result in an increased MON/RON ratio although overall R+M/2 could in fact decrease. This is due to the fact that although isoparaffins have higher MON values than RON, their absolute values are generally less than their olefin counterparts.

Another approach to increase the MON / RON ratio of gasoline may result from increasing the weight fraction of those hydrocarbons having blending MON's nearly equivalent to the blending RON's. Examples include propyl or isopropyl-benzene, C-5 and substituted C-5 naphthenes and highly branched olefins like 4-methyl 2 pentene. The ability to selectively increase the concentration of these hydrocarbons may be more a feedstock property than anything that current catalyst technology can do.

If motor octane is to be increased to a greater extent than research octane it appears that the specific hydrocarbon types must be selectively produced or concentrated. Directionally, the degree of highly branched isomers, either paraffinic or olefinic, must be increased with emphasis on the degree of internal branching. Although aromatics have a large effect on both RON and MON, alkylbenzenes such as propyl or isopropyl benzene may effect MON to a greater extent than RON. To fully understand the factors effecting MON, detailed chemical characterizations of a variety of gasolines should be studied.

[Guest head_tech]

There was a table of octane's of hydrocarbons included that has not shown up in my post, if anyone one can tell me how to included this table I'll post it also, it was copyed and pasted from a word .doc