Check “Petroleum Refining Technology and Economics” by Gary, J. and Handwerk, G. (1984). In the book, refer to chapter 13 (Catalytic Reforming and Isomerization); there some simple yield correlations showing the relationship between RON and reformate (a main constituent of conventional gasoline) composition. Good luck!

you can take octane as the formula for analysis(C8H18)

I agree with the posters. If you have absolutely no further indication e.g. due to analysis, you could imply your gasoline consists of RON-% iso-octane and (100-RON)-% n-heptane, since this is in relation to the definition of the RON. You could improve your estimates by using literature data from the petroleum refining sector (as the one named by Bolaji). The best results should be available from analysis of actual petroleum.

Anyways, for your calculations, you must be aware that gasoline of a certain RON can (and usually will) be of different composition, and you should consider that e.g. in a sensitivity analysis for your model.

I highly appreciate your answers

What I want exactly to know is the relation between changing in octane numbers of gasoline types in commercial markets and corresponding change in exhaust emissions for a certain type of 4 stroke SI engine.

So,  in part of theoretical study; I have to form chemical equations for gasoline types in different ON numbers in order to calculate the products of the equations. Then, I will test many gasoline samples in my department laboratory at which it's easy to calculate the results: exhaust emissions, torque, power ... etc.

considering your answers means that is impossible to form chemical equation based only on octane number. So, I'm wondering whether there is a way to link between ON numbers and chemical equations, especially that I can get the specifications of samples from the refinery.

The octane number of unleaded motor gasoline is in fact a function of its chemical composition where a significant correlation exists between the octane number and the aromatic and naphthenic content of gasoline. Basing the calculation of the octane number on the detailed composition of gasoline is, however, complicated and impractical for a variety of reasons, but it was possible instead to demonstrate a significant correlation between the research octane number and a factor that combines the effects of both the aromatic and naphthenic components of gasoline, which are the chief contributors to its overall octane number. The following equation was derived based on a survey of different types of unleaded gasolines:

RON = 37.4954 + 0.4724 (N + 2 A)

where N is the weight percentage of naphthenes and A the weight percentage of aromatics in gasoline. The correlation factor for this equation was 0.90. Better correlation was also obtained but the resulting equation was much more complicated. (Ref. Correlation between the chemical composition of motor gasoline and its anti-knock characteristics (In Arabic), Oil and Arab Cooperation, vol. 24, Issue 84, 1998, pp. 89–107).

Fuels have been developed which have a higher anti-knock rating than iso-octane.There is a relationship between octane number (ON) and performance number (PN). ON above 100 = 100 +(PN-100)/3. With higher compression ratio engines other phenomena are observed and obtained. You need to carry out chemical combustion equation involving hydrocarbon and oxygen. Determine the air-fuel ratio from the orsat analysis and proximate analysis. You will get good results. You may refer to thermodynamics textbook.

Octane number has little discernable impact on the emissions of modern gasoline-fueled automobiles equipped with three-way catalysts under most driving conditions.  Once catalyst light-off is achieved, NOx reduction and oxidation of NMOG and other VOC's is often greater than 99%.  Fuel components that impact catalyst effiency have far greater effects on exhaust emissions.  For example, reducing gasoline sulfur in unleaded gasoline from 350 ppm to 10 ppm can more than halve NMOG and NOx emissions even from older U.S. Tier 1 or global Euro4 vehicles equipped with three-way catalysts once sulfur is purged from catalytic surfaces. Emissions improvements with reducing fuel sulfur content are even greater with lower emissions vehicles (Euro 5, Tier 2, LEV II, etc.).

The only manner in which increased octane can improve catalyst efficiency is during very high-load operation.  If enrichment is used along with spark retard to prevent knocking combustion, and if the engine is equipped with knock detection and is calibrated to use less enrichment if knock is not encountered, then the engine's closed-loop, stoichiometric operation can be extended at larger throttle openings and higher loads.  Most urban driving and freeway cruise conditions do not encounter open-loop fuel enrichment, so any emissions advantage would only occur during fairly aggressive or very high-speed or high-load driving conditions and only if the vehicle has the hardware and engine calibration to take advantage of the increased octane content.

Probably you will interest the computer program “Euroxtest”. It allows to calculate the total aromatics and the total oxygen in finished gasoline (type "Petrol"). The program uses as the source data - index of refraction nD20, determined at yellow D-line of Na-spectrum, and density of gasoline d20 (g/cm3) which are measured at 20ºС. Using the calculated values of the total aromatics and the total oxygen the program “Euroxtest” chooses a class of Euro which corresponds to your gasoline, Euro-2, Euro-3 or Euro-4/5. In the program the research octane number (RON) is roughly sized up (discretely). The program algorithm is described in article of journal Fuel, DOI: 10.1016/j.fuel.2014.10.042 (http://dx.doi.org/10.1016/j.fuel.2014.10.042)

Бензины представляют собой смесь углеводородов, состоящий из предельных - 25-61%

непредельных-13-45%

нафтеновых - 9.7%

ароматических- 4-16%

марку бензина, определяет октановое число