Abstract: According to the detection principle that asphaltene flocculent can be produced when heavy fuel oil samples are diluted with n-hexadecane, a set of instrument for measuring the P value of heavy oil products has been developed independently, and a pressure-light threshold method was developed for the determination of the P value of heavy oil products. Under the control of dropping rate and interval of n-hexadecane, the end point of detection was determined by the change of pressure, transmitted light transmittance and intensity of backscattered light caused by dropping n-hexadecane. The pressure-light threshold method could simplify the operation, ensure the accuracy of the test, and reduce the frequent preparation and detection times of samples and reagents. At the same time, the accuracy and precision of the detection results were guaranteed by using 3 kinds of parameters judgment modes.

Key words: P value, pressure-light threshold method, heavy fuel oil, stability