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ASSESSING THE QUALITY OF FUTURE EUROPEAN FUELS.

Cel

TO FIND OUT THE BASIS FOR NEW RATING METHODS, MAINLY BASED ON HIGHER KNOCKING INTENSITY LEVEL, WHICH WOULD BETTER FIT THE REQUIREMENTS OF THE FUTURE UNLEADED, HIGH OCTANE GASOLINES.
The need arose to characterize motor fuels with respect to knock. To do so, a standard engine is normally used with a variable volumetric ratio, called the CFR engine, with standard methods. These methods have undergone constant developments over the years under the impetus of technical progress and a critical analysis of the methods to classify motor fuels according to their antiknock capacity is s apressing matter, owing to the sweeping changes of the legislation in force.
The extraordinary evolution of electronics and information processing in recent years now offers access to tools that are more appropriate than ever to characterize combustion in engines.

Whereas the method to measure the octane number is reliable, sensitive and reporoducible over a wide operating range, one is justified in questioning the significance of the results.
The study quanitified the influence of the engine parameters on the measurement of the octane number, and also, above all, the great influence of the choice of the definition of knock on this value, that could cause a variation up to 15 points.
The choice of thecriteria to characterize the knock intensity resulted from the observation of the signal generated by a pressure sensor placed in the combustion chamber. This approach enabled identification of the differences in rate of energy release associated with autoignition as a function of the type of fuel and the test conditions.

The method could be improved in 3 different ways:
changing in the standard knock intensity to take the measurement at constant knock irrespective of prevailing octane level (this would increase the repeatability of the measurements);
a change in the characterization of knock to compare motor fuels with a more physical criterion;
a change in the equipment and the measurement methodology in order to facilitate the operator's tasks, increase the accuracy, and decrease the cost of the measurement.
The study has enabled the indentification of the co nsiderable effect of the chemical composition of the fuel on the knock intensity. In the light of these results, it seems indispensible to investigate the process of autoignition more throroughly.
CONVENTIONAL ASTM METHODS FOR OCTANE INDEX DETERMINATION FAIL SOMETIMES IN DISTINGUISH AUTHENTIC KNOCKING PHENOMENA FROM PRESSURE OSCILLATIONS DUE TO A QUICK BUT NORMAL COMBUSTION. THIS IS ESPECIALLY TRUE WITH AROMATIC-RICH FUELS. THE ASSESSMENT OF THE QUALITY OF PRESENT AND FUTURE EUROPEAN FUELS REQUIRES MORE ADVANCED METHODS. A CRITERION FOR FUEL CLASSIFICATION BASED ON THE CALCULATION OF SPECIFIC ENERGY ASSOCIATED WITH THE PRESSURE WAVES (" ROSSINI PROCEDURE ") HAS BEEN PROPOSED BY STAZIONE SPERIMENTALE PER I COMBUSTIBILI (SSIC) OF MILANO, WHICH ON THESE GROUND WILL DEVELOP A NEW INSTRUMENTAL TESTING METHOD (SEE CONTARCT EN3V005400).

A CRITICAL INVESTIGATION OF ASTM METHODS AND A SEARCH FOR OPERATING CONDITIONS MORE APPROPRIATE TO MODERN FUELS WILL BE CONDUCTED WITHIN THE PRESENT CONTRACT, USING THE CONVENTIONAL INSTRUMENTATION.
FIVE KINDS OF UNLEADED GASOLINES WILL BE PREPARED ACCORDING TO THE CORC PROCEDURES. WITHIN EACH TYPE, THE ANTIKNOCK CHARACTERISTICS WILL BE CONTINUOUSLY VARIED BY CHANGING THE RATIO BETWEEN 2 CONSTITUENTS OF HIGH AND LOW OCTANE INDEX.

1.- HIGHLY PARAFFINIC: ABSENCE OF OLEFINS AND OXYGENATES, LOW AROMATIC CONTENT

2.- HIGH OLEFINIC CONTENT (20%): ABSENCE OF OXYGENATES

3.- HIGH AROMATIC CONTENT (40%): ABSENCE OF OXYGENATES

4.- 10% MTBE; MEDIUM CONTENT OF OTHER CONSTITUENTS

5.- 3% METHANOL + 2% TBA; MEDIUM CONTENT OF OTHER CONSTITUENTS.

FOR TWO GASOLINE TYPES, CHOSEN AMONG THE MOST REPRESENTATIVE GROUPS (NUNBER 2 AND 3), THE " OCTANE INDEX " EVOLUTION AS A FUNCTION OF KNOCKING INTENSITY READ ON THE KNOCK METER WILL BE DETERMINED.

TWO LEVELS OF " EXPERIMENTAL " INTENSITY WILL BE SELECTED AFTER THE EASINESS AND PRECISION OF MEASUREMENT HAVE BEEN EXAMINED OVER THESE DIFFERENT OPERATING CONDITIONS. THESE LEVELS WILL BE KEPT ALONG THE REMAINDER OF THE MEASUREMENTS CONDUCTED ON THE WHOLE SERIES OF THE AFOREMENTIONED GASOLINES.
THE INTERPRETATION OF THE RESULTS, WHICH WILL BE MADE IN CO-OPERATION WITH SSIC, WILL START BY COMPARING THE DATA SO OBTAINED WITH THOSE FROM THE NORMALIZED PROCEDURE. SHOULD A DISTINCT BEHAVIOUR APPEAR FOR THE DIFFERENT GASOLINE TYPES, THEN A NOVEL KNOCKING STANDARD INTENSITY WOULD BE CONSIDERED. A NEW RATING METHOD MIGHT RESULT ALLOWING DISCRIMINATIONS TO BE MADE AMONG GASOLINES IN THE HIGH OCTANE INDEX RANGE (RON > 100). A COMPARISON WITH DATA FROM ROSSINI METHOD COULD BE MADE.

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