Method and system of measuring cetane values for middle distillate fuels

A method for calculating derived cetane number values comprising the steps of:

• combusting a calibration sample having a known cetane number value in the constant volume combustion chamber apparatus to produce a calibration pressure versus time combustion profile,
• selecting at least one calibration data point from the calibration profile,
• computing a derived cetane number values from a power series expansion equation expanded about the selected calibration data points and/or ratios of the selected calibration data points,
• adjusting expansion coefficients in the equation to minimize a difference between the known cetane number value and the derived cetane number value to obtain a set of optimized expansion coefficients,
• obtaining a pressure versus time combustion profile of a sample using the constant volume combustion chamber apparatus capable of yielding a sample pressure versus time combustion profile,
• selecting at least one sample data point from the sample profile, and
• calculating a derived cetane number values from a power series expansion equation expanded about the selected sample data points and/or ratios of the selected calibration data points using the optimized expansion coefficients.

A method for calculating derived cetane number values comprising the steps of:

• 2 combusting a calibration sample having a known cetane number value in the constant volume combustion chamber apparatus to produce a calibration pressure versus time combustion profile,
• selecting at least one data point from the calibration profile,
• computing a derived cetane number values from a power series expansion equation expanded about the selected data points,
• adjusting expansion coefficients in the equation to minimize a difference between the known cetane number value and the derived cetane number value to obtain a set of optimized expansion coefficients,
• burning a middle distillate sample in a constant volume combustion chamber apparatus,
• measuring and storing a pressure versus time combustion profile of the sample, where the profile has a first region corresponding to sample components having earlier ignition temperatures and a second region corresponding to sample components having later ignition temperatures,
• selecting at least one sample data point from the first region from the profile, and
• calculating a derived cetane number values from a power series expansion equation expanded about the selected sample data points using the optimized expansion coefficients.

A method for determining coefficients of a series expansion equation for calculating derived cetane number values comprising the step of:

• combusting a sample having a known cetane number value in a constant volume combustion chamber apparatus under controlled conditions to obtain pressure versus time combustion data,
• selecting at least one point from the profile,
• computing a derived cetane number value using the series expansion equation about the selected points with a set of initial coefficients, and
• adjusting coefficients of the series expansion equation so that a difference between the cetane number and the derived cetane number value is minimized.