Knocking characteristics

Octane rating (Section 2 16) The capacity of a sample of gasoline to resist knocking expressed as a number equal to the percentage of 2 2 4 trimethylpentane ( isooctane ) in an isooctane-heptane mixture that has the same knocking characteristics... 

Knocking Characteristics of Pure Hydrocarbons, ASTM Special Pubhcation No. 225, American Society of Testing Materials, Philadelphia, 1958. 

Gasoline-air mixtures tend to ignite prematurely, or knock, rather than bum smoothly. The octane number of a gasoline is a measure of its resistance to knock. It is determined by comparing the knocking characteristics of a gasoline sample with those of isooctane (the common name of one of the isomers of octane) and heptane ... 

Research Octane Number is a measure of the knocking characteristics of gasoline in a laboratory engine and can be used to characterize gasoline quality. The best linear regression model to predict RON for catalyst A has the form ... 

The following year Ricardo 27) published the results of investigations on the highest useful compression ratio of a number of hydrocarbons and found a wide variation among different fuels in this respect. Since that time the relations between physical properties of hydrocarbons and their molecular structure on the one hand, and the knocking characteristics of the same hydrocarbons and their molecular structure on the other, have received more intensive study. 

The petroleum refiner, by the mid-thirties, was faced with two problems (a) What hydrocarbon constituents did his gasolines and low boiling naphthas contain and (b) What were the knocking characteristics of each of these constituents ... 

Both the physical properties and the knocking characteristics of pure hydrocarbons are strongly dependent upon the length of uninterrupted chain fragment. 

Structural Factors Determining Knocking Characteristics of Pure Hydrocarbons... 

Knocking characteristics of pure hydrocarbons and observed correlations between structure and knock have been summarized by Lovell (117). Work of American Petroleum Institute Project 45 (2, 3) represents a large fraction of this information. The reasons for these relationships have not been as adequately reviewed. 

HAWTHORNE AND SCOTT—KNOCKING CHARACTERISTICS OF PURE HYDROCARBONS... 

Other Properties. THERMAL STABILITY. Several attempts have been made to correlate knock resistance with thermal stability. Petrov (162) attempted to account for the knock characteristics of various gasoline fractions in terms of their cracking products. Rice (177) showed that a parallelism existed between yields of cracking products and knock tendency. Estradgre (60) did not find a direct relation between temperature for initial cracking and detonation characteristics. 

A large number of experimental engine techniques have been developed in the course of investigating the knock phenomenon. Highly instrumented, precision knock-rating engines have been used in studying the knock characteristics of various hydrocarbon... 

The knock characteristics of hydrogen and carbon monoxide provide an insight into... 

Figure 7. Knock characteristics of hydrogen, n-heptane, and iso-octane...

Octane Number—The octane rating of a motor fuel is defined in terms of its knocking characteristics relative to those of blends of isooctane (2.3,4-trimethylpentane) and n-heptane. and a rating of 100 to isooctane, The octane number of an unknown fuel is numerically equal to the volume percent ot isooctane in a blend with -heptane which has the same knocking tendency as the unknown fuel when both the unknown and the reference blend are run in a standard single-cylinder engine operated at specified conditions. Motor Method octane numbe-is are measured at moie- severe engine conditions and are numerically lower than those determined by the milder Research Method. The difference between the two numbers is termed sensitivity. 

Octane number a number indicating the anti-knock characteristics of gasoline. 

G. Edgar, Measurement of Knock Characteristics of Gasoline in Terms of Standard Fuel, Ind. Eng. Chem. 19 (1927) 145. 

Anon Knocking Characteristics of Pure Hydrocarbons, API Research Project 45, American Society for Testing Materials (1958). 

P.D. Ronney, M. Shoda, S.T. Waida, C.K. Westbrook and W.J. Pitz, Knock Characteristics of Liquid and Gaseous Fuels in Lean Mixtures, SAE Technical Paper 912311 (1991). 

The reader will be particularly interested in the portion of the Boord-Lovell paper devoted to the synthesis of low molecular weight hydrocarbons in the various series of hydrocarbons such as the paraffins, the olefins, the cycloparaffins, and the aromatics. Some of our best information on the engine knocking characteristics of various hydrocarbons has come from the work of this project. The lessons learned, and the relation between structure and knock, are very ably brought out in their paper. Another important phase of this work is the study of blends of hydrocarbons with respect to knocking. This study is an important part of the future program of the project. The paper is concluded by a list of 27 literature references pertinent to the work of APIRP 45. 

For natural gasoline, the primary criteria are volatility (vapor pressure) and knock performance. Determination of the vapor pressure (ASTM D-323, ASTM D-4953, ASTM D-5190,ASTM D-5191) and distillation profile (ASTM D-216, IP 191) is essential. Knock performance is determined by rating in knock test engines by both the motor method (ASTM D-2700, IP 236) and the research method (ATSM-2699, IP 237). The knock characteristics of liquefied petroleum gases can also be determined (IP 238). 

The knock rating of a gasoline is expressed as octane number and is the percentage by volume of o-octane (octane number 100, by definition) in admixture with normal heptane (octane number 0, by definition) that has the same knock characteristics as the gasoline being assessed. 

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