Skip to main content

VALUATION OF ANTIKNOCK QUALITY OF GASOLINES BY THE " ENERGY CRITERION ".

Objective

TO DEVELOP AN ADVANCED COMMERCIAL METHOD FOR GASOLINE RATING, ESPECIALLY IN VIEW OF THE SUBSTITUTION OF ALKYL-LEAD, ALLOWING THE OPTIMIZATION OF THE GASOLINE COMPOSITION FOR OPTIMAL ENGINE-FUEL ADAPTATION.
The empiric concept of octane number, on which 2 standard test methods have been developed and universally applied in practice, is considered inadequate to value correctly the antiknock performance of gasolines. This is particularly true for the European gasolines, whose composition is changing in connection with the recent phaseout of lead alkyls. The Energetic Criterion (EC) a simple mathematical model of the knock combustion in an internal combustion engine constitutes a suitable principle on which to develop a rational test method to value the antiknock characteristics of gasolines.

The EC considers that the energy released by detonation can be expressed in terms of specific (by volume or mass) energy (or power) of the overpressure wave generated by the autoignition of the end gas.

Under research conditions, the EC detected antiknock performance from aromatics: aromatic fuels, CORC fuels series 01 high sensitivity (H) and CORC fuels series 04H all contain more than 24% of aromatics and give a different knock response, expressed in terms of the Energetic Index (IE) (Wm{-3}) than the corresponding primary reference fuels (PRF) under the same operating conditions.

The apparent contrast with the above statement observed with the CORC fuels 01 low sensitivity (L) and CORC fuels series 04L (which have about the same aromatic content as the CORC 04H fuel but an equal knock performance with the corresponding PRF) is probably due to the high content of n-paraffins in these former gasolines.

Under motor conditions, both aromatic hydrocarbons and isoparaffinic hydrocarbons could be better rated by the EC. This assertion is confirmed by the differnt response, in terms of measured knock energy (IE), observed in the tests with the 2 unleaded gasolines and the 2 high sensitivity CORC fuels with respect to the American Standard for Testing Materials (ASTM) ratings.

These observations are coherent with the well known divergences observed between the laboratory rat ing by the conventional ASTM methods and the road tests. This study has shown that a simple test procedure based on the IE measurement can be developed to monitor more accurately the knock resistance of the commercial gasolines. The improved knowledge of antiknock performance of motor fuels will allow both engine manufacturers and refinery industries to find solutions for energy savings and environmental pollution.
A NEW METHOD OF EVALUATION OF THE ANTOKNOCK CHARACTERISTICS OF GASOLINES WILL BE DEVELOPED BASED ON A SIMPLE MATHEMATICAL MODEL OF THE KNOCKING PHENOMENA. THE UNDERLYING CONCEPT IS THE ABSOLUTE MEASUREMENT OF THE ENERGY RELEASED DURING THE ABNORMAL COMBUSTION IN ITS EFFECTIVE PERIOD (20-40 C A D), IE OF THE SPECIFIC POWER ASSOCIATED WITH THE PERTURBATION OF THE COMBUSTION PRESSURE.
AN INSTRUMENTAL CHAIN WILL BE DEVELOPED BY CISE, TO PICK UP, ANALYSE AND PROCESS THE PRESSURE SIGNALS DURING THE TRANSIENT IN THE COMBUSTION CHAMBER.

SUCH A CHAIN WILL BE MADE UP OF: A PRESSURE TRANSDUCER (PIEZOELECTRIC TYPE, NATURAL FREQUENCY 125 KHZ, A CHARGE AMPLIFIER FOR THE SIGNAL CONDITIONING OF THE PRESSURE TRANSDUCER, AN EXTERNAL TRIGGER FOR ANGULAR SYNCHRONISM WITH THE CRANKSHAFT, AN ANALOG DIGITAL CONVERTER (12 BIT, 15 MHZ), A COMPUTER FOR THE WAVEFORM ANALYSIS AND DATA PROCESSING, TOGETHER WITH THE RELEVANT SOFTWARE.

THE CFR ENGINE, TO WHICH THE CHAIN WILL BE CONNECTED, WILL BE EQUIPPED ALSO WITH AN EXHAUST-GAS ANALYSER FOR AIR/FUEL RATIO DETERMINATION AND WITH THERMOCOUPLES FOR INTAKE AIR AND AIR/FUEL MIXTURE TEMPERATURE MEASUREMENT.
DURING THE CHECKING OF THE SYSTEM UNDER ASTM CONDITIONS THE MAIN PARAMETERS FOR EVALUATING E.I VIS FREQUENCY BAND, CRANKSHAFT ANGULAR POSITION AND THE CONSTANT OF CALIBRATION K' WILL BE OPTIMIZED. FIRST THE SUITABLE OPERATING CONDITIONS WILL BE DEFINED BY INVESTIGATING THE RESPONSE OF UNLEADED GASOLINES WITHOUT AND WITH OXYGENATES AND OF CORC FUELS OF HIGH AND LOW SENSITIVITIES TO: COMPRESSION RATIO, SPARK ADVANCE, AIR/FUEL RATIO, INTAKE AIR AND AIR/FUEL MIXTURE TEMPERATURES.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Stazione Sperimentale per i Combustibili SpA
Address
Via G. Galilei 1
20097 San Donato Milanese
Italy

Participants (1)

CISE - Centro Informazioni Studi ed Esperienze SpA
Italy
Address
Via Reggio Emilia 39
20090 Segrate Milano