EXPLANATION
The ignition delay (ID) and derived cetane number (DCN) values determined by this test method can provide a measure of the ignition characteristics of diesel fuel oil in compression ignition engines. The relationship of diesel fuel oil DCN determinations to the performance of full-scale, variable-speed, variable-load diesel engines is not completely understood. This test method is applicable to products typical of specification D975, Grades No. 1-D and 2-D regular and low-sulfur diesel fuel oils, European standard EN 590, and Canadian standard CAN/CGSB-3.517-2000 and 3.6-2000. This test method may be applied to nonconventional fuels. This test determines ignition characteristics and requires a sample of approximately 220 mL and a test time of approximately 20 min on a fit-for-use instrument. The method measures the ignition delay and utilizes a constant volume combustion chamber with direct fuel injection into heated, compressed air. An equation converts an ID derived determination to a DCN. This test method covers the ID range from 2.90 to 4.35 ms (60.0 to 40.0 DCN). The combustion analyzer can measure shorter and longer ignition delays but precision may be affected.
TEST METHOD SUMMARY
A small specimen of diesel fuel oil is injected into a heated, temperature-controlled constant volume chamber, which has been previously charged with compressed air. Each injection produces a single-shot, compression ignition combustion cycle. IDs measured using sensors that detect the start of fuel injection and the start of significant combustion for each cycle. A complete sequence comprises two preliminary cycles and 25 further cycles. The ID measurements for the last 25 cycles are averaged to produce the D result. An equation converts the ID result to a DCN value.
INTERFERENCES - Minimize exposure of sample fuels, calibration materials, QC samples, and check standard to sunlight or fluorescent lamp UV emissions to minimize induced chemical reactions that can affect ignition delay measurements. Exposure of these fuels and materials to UV wavelengths shorter than 550 nm for a short period of time can significantly affect ignition delay measurements. The formation of peroxide and radicals can affect ID measurement. These formations are minimized when the sample or material stored in the dark in a cold room at a temperature of less than 10° C and covered by a blanket of nitrogen.
TEST PRECISION
