The invention relates to a method for evaluating a substance, especially a hydrocarbon fuel such as gasoline, diesel fuel, naphtha, jet fuel, kerosene and the like, to determine one or more parameters of the substance.
Accurate methods for measuring parameters of fuels such as gasoline are desirable. It is especially useful to obtain accurate measurements of parameters such as octane numbers, Reid vapor pressure and the like so that products can be supplied to customers which accurately meet the customers specifications.
Near infrared (NIR) spectroscopy has been found to be useful in evaluating certain substances because certain bands of the NIR signal are indicative of parameters of the substance. For example, U.S. Pat. No. 4,963,745 to Maggard discloses a process for measuring octane of gasoline using NIR spectroscopy and mathematical processing using derivatives. This method, sometimes referred to as multi-variate analysis, is useful in measuring some parameters. However, the method requires a high signal-to-noise ratio and long-term stability, and further requires a linear correlation between the NIR spectrum data obtained and the parameter to be determined.
In accordance with the foregoing, it is the principal object of the present invention to provide a method for evaluating desired parameters of a substance, particularly a hydrocarbon such as gasoline or other types of fuel using NIR spectroscopy wherein accurate readings are obtained despite non-linearity of the relation between the input NIR signal and the output parameter to be determined.
It is a further object of the invention to provide a method for evaluation which provides accurate determinations despite potentially large amounts of "noise" or corrupted data in the NIR signal.
It is still another object of the invention to provide a method for evaluation wherein measurements are obtained "on-line."
Other objects and advantages will appear herein below.