Antiknock quality

An octane rating scale was devised for fuels to quantify their knock resistance. Further research led to cataloguing the antiknock qualities of the myriad individual hydrocarbon species found in gasoline. 

Catalytic reforming rearranging hydrocarbon molecules in a gasoline-boiling-range feedstock to produce other hydrocarbons having a higher antiknock quality isomerization of paraffins, cyclization of paraffins to naphthenes (g.v.), dehy-drocyclization of paraffins to aromatics (g.v.). 

High Volatility. The problem preceding that of antiknock quality was concerned with fuels of low volatility. Volatility again became a problem in the early thirties as a result, in part, of extended thermal operations to make higher octane nmn-... 

Figure 7. Average Antiknock Quality of Regular and Premium Grade Motor Gasolines...

Figures 6 and 7 illustrate the trends to high-compression engines and high gasoline antiknock quality for the past 25 years. These trends may be expected to continue, except as modified temporarily by restrictions imposed by national defense needs, shortages of materials, etc.

If we consider the typical 1950 gasolines mentioned above, with and without tetraethyllead, any reasonable method of estimation shows that the cost of the increased antiknock quality obtained by tetraethyllead is substantially less than the cost would have been for the same increase by refining operations. The almost universal use of tetraethyllead in gasoline is in itself a demonstration of its economy. Furthermore, its use permits flexibility in day-to-day refinery operations required to make gasoline of a given specification. 

Exhaust Gas Recirculation. In one method of NO emission control, exhaust gas is fed back into the inlet manifold and mixed with the fuel and inlet air. The resultant mixture upon combustion in the cylinder results in lower peak combustion temperature and lower NO formation because the reaction of N2 + 0-, — NOx is strongly dependent on the combustion flame temperature (99,109—112). The degree of NO depression is dependent on the amount of exhaust gas recirculation (EGR) as shown in Figure 13. EGR provides a diluent gas having high molecular weight and C02 which absorbs heat. Also, EGR affects the flame speed of the mixture, and thus provides a certain antiknock quality to the combustion process. The impact of EGR on engine parameters has been detailed (113). 

Tetraethyl lead (TEL) an organic compound of lead, Pb(CH3)4, which, when added in small amounts, increases the antiknock quality of gasoline. 

Thermal reforming a process using heat (but no catalyst) to effect molecular rearrangement of low-octane naphtha into gasoline of higher antiknock quality. 

Octane number is the important property in gasoline. Octane number measures the resistance offered by the fuel to compression. A higher octane implies higher resistance to compression (to promote high antiknock quality, ease of starting, quick warm-up, low tendency... 

F. Avella, A. Girelli, M. Famiglietti and F. Cattaneo, Evaluation of Antiknock Quality of Gasolines by the Energetic Criterion , Commission of the European Communities Report, EUR 12742 EN, 1990. 

The higher grades of fuel are thus classified by their specified antiknock ratings under both sets of test conditions. For example, 100/130 grade fuel has an antiknock quality of 100 minimum by the weak mixture test procedure and 130 minimum by the rich mixture procedure. Octane numbers are used to specify ratings of 100 and below, whereas performance numbers are used above 100. 

Over the past three decades catalytic reforming has evolved very rapidly. It is now one of the most important industrial applications of catalysis. The reforming process was originally developed to produce gasoline components of high antiknock quality to meet the fuel requirements of high compression ratio automobile engines. 

The liquid product, known as reformate, consists essentially of C5 through about C,0 hydrocarbons. Aromatic hydrocarbons in the liquid product are typically present in amounts in the range of 60-70 wt%, the actual amount depending on the reaction conditions. The antiknock quality of the liquid reformate increases with increasing aromatics content. 

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