ASTM D6890 Standard Test Method for Determination of Ignition Delay and Derived Cetane Number (DCN) of Diesel Fuel Oils by Combustion in a Constant Volume Chamber
9. Sampling and Test Specimen Preparation
9.1 Sampling:
9.1.1 Collect diesel fuel oil samples in accordance with Practices D4057 or D4177.
9.1.1.1 Collect and store diesel fuel samples in a suitable container such as a dark brown bottle, a metal can, or a minimally reactive plastic container to minimize exposure to UV emissions.
9.1.2 Refer to Practice D5854 for appropriate information relating to the mixing and handling of diesel fuel oil samples.
9.2 Test Specimen Preparation:
9.2.1 Sample Fuel Temperature - Condition the diesel fuel sample before opening the storage container, so that it is at room temperature, typically 18 °C to 32 °C.
9.2.2 Filtration - Prepare a test specimen by filtering diesel fuel oil of sufficient volume to complete the test method, including flushing, through a nominal 3 µm to 5 µm porosity filter element using a positive pressure delivery device such as a glass syringe or a glass-lined metal syringe.
9.2.2.1 Collect the specimen in a dark brown bottle, metal can or minimally reactive plastic container.
10. Basic Apparatus Settings and Standard Operating Conditions
10.1 Installation of the apparatus requires placement on a level floor and connection of all utilities. Engineering and technical support for this function is required, and the user shall be responsible to comply with all local and national codes and installation requirements.
10.2 Operation of the combustion analyzer, associated equipment, instrumentation and computer system requires setting a series of testing variables to prescribed specifications. Some of these settings are established by component specifications, others are operating conditions that are monitored/controlled by the computer software or by operator adjustment.
10.3 Settings Based on Component Specifications:
10.3.1 Injector Nozzle Opening Pressure - Each time the nozzle assembly is reassembled or replaced, or both, set the pressure-adjusting nut to release fuel in conformance with the requirements in the manufacturer's equipment manual, using an injector nozzle tester. For additional details, refer to the instruction manual of the manufacturer.
10.3.2 Injector Nozzle Motion Sensor Position - Manually position the motion sensor while visually observing the nozzle needle movement signal on the computer monitor (see Fig. A4.1). The criteria for optimized setting are as follows:
10.3.2.1 The signal prior to the steep increase in needle lift is required to indicate some signal noise. If the signal trace is flat and constant, the motion sensor is too far away from the nozzle needle extension pin.
10.3.2.2 The peak of the steep increase in signal level is required to be visible on the computer monitor screen. If the signal peak is flat, the motion sensor is too close to the nozzle needle extension pin. For additional details, refer to the instruction manual of the manufacturer.
10.3.3 Injector Nozzle Coolant Passage Thermocouple Position - Proper positioning of the thermocouple in the injector nozzle coolant passage is set by installing a compression fitting nut and associated plastic ferrule on the stainless steel sheath of the thermocouple, using a specialized depth setting tool to establish the correct depth of penetration. Adjust the depth of penetration (in accordance with the instruction manual of the manufacturer) by repositioning the plastic ferrule on the stainless steel sheath of the thermocouple and tightening the nut to a snug level of tightness. For additional details, refer to the instruction manual of the manufacturer.
10.3.4 Charge Air Thermocouple Position - Proper positioning of the thermocouple in the combustion chamber is set by installing a compression fitting nut and associated ferrule on the stainless steel sheath of the thermocouple, crimping the ferrule on the sheath using a specialized depth setting tool to establish the correct depth of penetration. For additional details, refer to the instruction manual of the manufacturer.
10.3.5 Rate of Decrease of Combustion Chamber Pressure, less than 3.5 kPa/s, as measured during the check of the sealing integrity of the combustion chamber (see A3.5).
10.4 Standard Operating Conditions:
10.4.1 Charge Air Pressure (P2), 2.130 MPa to 2.144 MPa.
10.4.2 Charge Air Temperature (T4), 515 °C to 575 °C.
10.4.2.1 The difference in temperature (T4max - T4min) as determined and recorded by the computer, shall be less than 2.5 °C during a 32 combustion cycle measurement determination.
10.4.3 Combustion Chamber Outer Surface Temperature (T1) - Initially set by the manufacturer, the surface temperature is monitored and controlled by the computer. Operator adjustment of the controller set-point is required, in accordance with the calibration procedure.
10.4.4 Combustion Chamber Pressure Sensor Temperature (T3), 110. °C to 150. °C.
10.4.4.1 The difference in temperature (T3max - T3min) as determined and recorded by the computer, shall be less than 8.0 °C during a 32 combustion cycle measurement determination.
10.4.5 Coolant Return Temperature (T7), 30. °C to 50. °C.
10.4.6 Fuel Sample Reservoir Pressure (P5), 310. kPa to 380. kPa. Visually check the gage reading, as this parameter is not recorded by the data acquisition system.
10.4.7 Fuel Injection Pump Temperature (T2), 32 °C to 38 °C.
10.4.8 Injector Nozzle Coolant Passage Temperature (T6) - The maximum (T6max) and minimum (T6min) temperatures as determined and recorded by the computer, shall be within 46.0 °C +/- 54.0 °C during a 32 combustion cycle measurement determination.
10.4.9 Injection Actuator Air Pressure (P3), 1.18 MPa to 1.24 MPa.
10.4.10 Inlet/Exhaust Valve Actuator Air Pressure (P4), 445 kPa to 515 kPa. Visually check the gage reading, as this parameter is not recorded by the data acquisition system.
11. Calibration and Quality Control Testing
11.1 Calibration - Calibrate the combustion analyzer for only the following reasons: (1) after it is installed and commissioned, (2) after replacement of critical parts or components of combustion chamber assembly (see A2.2), fuel injection system (see A2.3) or instrument sensors (see A2.4), (3) after calibration of the data acquisition board, injection actuator air pressure sensor or charge air pressure sensor, (4) whenever check standard or QC sample determinations are not in statistical control as determined by Practice D6299 or equivalent and the assignable causes for QC non-compliance have been suitably addressed.
11.2 Precalibration Procedures:
11.2.1 Clean the combustion chamber pressure sensor assembly (see A3.3 and A3.4).
11.2.2 If necessary, start and warm-up the combustion analyzer (see A3.1).
11.3 Calibration Procedure - Two filtered calibration reference materials are tested: (1) heptane to affirm that the combustion chamber charge air temperature setting produces ignition delay measurements for this material that are within specification limits and, (2) methylcyclohexane to affirm that the measurement sensitivity of the combustion analyzer produces ignition delay measurements for this material that are within specification limits.
11.3.1 Heptane Calibration Reference Material - Perform three consecutive ignition delay determinations.
11.3.1.1 The average of three acceptable ID results is required to be within 3.77 ms to 3.79 ms.
11.3.1.2 If the average ID is outside the limits, the combustion chamber outer surface temperature controller set-point requires adjustment to cause a change in the combustion chamber charge air temperature.
NOTE 4 - ID increases when the combustion chamber outer surface temperature decreases and vice versa.
11.3.1.3 If the temperature controller set-point adjustment from the previous setting, exceeds +/- 4 °C, a system malfunction is suspected and diagnostic procedures to determine and remedy the problem are recommended. Refer to the instructions provided by the manufacturer.
NOTE 5 - After a change of charge air cylinders that employ a blend of oxygen and nitrogen, a temperature controller set-point adjustment beyond 4 °C can accommodate the extreme limits of the 19.9 volume percent to 21.9 volume percent oxygen in the blend.
11.3.1.4 After a temperature controller set-point adjustment, wait at least 10. min before initiating a new calibration so that the combustion analyzer attains thermal equilibrium.
11.3.1.5 To be an acceptable data set, each single result is required to be within 3.72 ms to 3.84 ms.
11.3.1.6 If any of the three results is outside the limits, a system malfunction is suspected and diagnostic procedures to determine and remedy the problem are recommended before performing a new calibration. Refer to the instructions provided by the manufacturer.
11.3.2 Methylcyclohexane Calibration Reference Material - Perform two consecutive ignition delay determinations.
11.3.2.1 To be an acceptable data set, each single result is required to be within 9.9 ms to 10.9 ms and the average of the two results is required to be within 9.9 ms to 10.9 ms.
11.3.2.2 If either of the two single results or the average of the two results is outside the respective limits, system performance is unacceptable and it is recommended that diagnostic procedures be used to determine and remedy the problem before performing a new calibration. Refer to the instructions provided by the manufacturer.
11.3.3 The combustion analyzer calibration is complete when both heptane and methylcyclohexane data sets are acceptable.
11.4 Quality Control (QC Testing) - Conduct a regular statistical quality assurance (quality control) program in accordance with the techniques of Practice D6299 or equivalent.
11.4.1 This test method requires quality control testing at the beginning of each operating period by a single ignition delay determination for both the check standard (heptane) and one QC sample.
11.4.2 The QC sample is a typical diesel fuel oil having an ignition delay that represents the primary range of use for the combustion analyzer.
11.4.2.1 If the combustion analyzer is used for testing fuels having a very wide range of ignition delay, it may be useful to have a second QC sample of a different ignition delay.
11.4.3 For locations using blends of oxygen and nitrogen as the source for charge air, conduct a QC test whenever there is a change from one cylinder to another.
NOTE 6 - The oxygen content of the new oxygen and nitrogen blend may differ from that of the previous source and can have a significant effect on ID measurements.
11.5 Check Standard - Perform a single ignition delay determination for filtered heptane.
11.5.1 This determination is acceptable if it satisfies the limits protocol specified in Practice D6299 or equivalent.
11.5.2 Prior to having established ignition delay tolerances for heptane in accordance with Practice D6299 or equivalent, use warning limits of +/- 0.07 ms and action limits of +/- 0.106 ms, based on the average of the three acceptable ID results for heptane, as per 11.3.1.
NOTE 7 - The warning and action limits for heptane were determined by analysis of round robin test data.
11.6 QC Sample - Perform a single ignition delay determination for the filtered QC sample.
11.6.1 This determination is acceptable if it satisfies the limits protocol specified in Practice D6299 or equivalent.
11.7 The combustion analyzer is fit-for-use when both the check standard (heptane) and the QC sample ignition delay determinations are acceptable. If the ignition delay determination for either material is not acceptable, conduct a new calibration before performing further ignition delay determinations.