Test Sequence

The testing sequence for the FIT follows ASTM D7170 exactly[1]. The test standard defines pertinent values, such as the injection period, derived cetane number, and ignition delay. The test standard also defines the testing conditions, including

temperature parameters, pressure parameters, and acceptance criteria. ASTM D7170 was last updated in 2014. The test method involves direct fuel injection into a temperature-controlled constant volume chamber filled with heated, compressed air. The ignition delay is measured and converted to a derived cetane number (DCN). ASTM D7170 is applicable for fuels in the range of 35.0-59.6 DCN (ignition delay from 4.89 ms to 2.87 ms, respectively). Each test requires 220 mL of fuel and, under ideal operating conditions

in a fit-for-use instrument, 20 minutes. A schematic of the FIT system is shown in Figure 6.

Figure 6: FIT schematic including components, sensors, and analysis system[1]

Before the start of testing, D7170 requires calibration of the apparatus using n-heptane with a minimum purity of 99.5 volume percent. The combustion chamber leakage rate cannot exceed 2.0 kPa/s. This leakage rate is tested by an automated check conducted by the system. The standard operating conditions of the chamber are defined in Table 1. All values in Table 1 indicated by an asterisk after the variable are based on an average of 25 combustion cycles.

Table 1: Standard operating conditions of FIT given by ASTM D7170

Variable Description Value Range Units

P0* Chamber static pressure 2.40 + 0.02 MPa

T1 Chamber charge air temperature 510 + 50 °C

T2max Max chamber inner wall temperature 595 °C

T2max-T2min Difference in temperatures 2.5 °C

T3 Fuel injection pump temperature 35 + 2 °C

T4 Injector nozzle coolant temperature 30 + 0.5 °C P2 Injection actuator air pressure 0.75 + 0.05 MPa

IP* Injection period 5.00 + 0.25 ms

IP Individual injection period for each cycle 5.00 + 1.00 ms

3.2.1 Calibration Testing

Two reference materials should be tested: heptane and methylcyclohexane.

Heptane affirms that the combustion chamber air temperature setting produces ignition delay results that satisfy the specification limit of three averaged ignition delay results be

equal to 3.15 + 0.02 ms. If the results are not within this limit, the temperature setpoint must be adjusted. If the result is less than the desired value, the temperature of the

chamber should be increased. If the result is more than the desired value, the temperature of the chamber should be decreased. The ID increases when the combustion chamber temperature decreases. Three more ID measurements should then be taken. If the average of the three ID measurements is not within the specification limit and the temperature change was greater than + 4 °C from the last setpoint, testing cannot continue. If the calibration setpoint value cannot be obtained, reliable results for ID with other fuels cannot be obtained.

Methylcyclohexane should then be tested in a series of two consecutive ID

determinations. The results from each test must be between 10.1 + 0.6 ms. The average of the two sequential results must be within 10.1 + 0.5 ms. As before, if either of those conditions is not met, testing cannot continue without diagnostic procedures being preformed on the device, as it is likely that there is a system malfunction. If the heptane and methylcyclohexane calibration results are all within the acceptable values, testing can continue in the device with other fuels.

At any point, if it suspected that ID results from the device are not acceptable, a single quality check can be done with heptane and with a quality control sample of known ID within the standard range. For this case, a single ID determination is

acceptable for each fuel and the results must be within the limits of ASTM D6299, the Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measurement System Performance.

3.2.2 Operating Procedure

3.2.2.1 Preliminary setup

Before an official test cycle can begin, the following should be conducted.

i) Ensure that the regulator for the charge air is set to provide an acceptable pressure.

ii) Turn on the computer, the coolant circulator pump, and the air supply for the fuel pump.

iii) Initiate the warm-up sequence.

iv) Perform a quality control test as described in Calibration Testing.

If the device is found to be fit-for-use, procedure to the test procedure.

3.2.2.2 Test Procedure

i) Fill fuel reservoir with the test specimen, ensuring that the reservoir cap is reinstalled and is hand tight.

ii) Flush the entirety of the test specimen through the fuel injection system.

iii) Remove he fuel reservoir cap and refill the reservoir with the test specimen, again ensuring that the reservoir cap is reinstalled and is hand tight.

iv) Flush the test specimen through the system for approximately 3 seconds.

v) Conduct two pre-injection tests.

(1) Inject the test specimen two times.

(2) Evaluate the injection duration to confirm that the duration is within 5.00 + 0.25 ms.

(3) If the injection duration does not match this criterion, the fuel pump needs to be adjusted according to the instructions provided in the manufacturer instruction manual.

vi) If all pre-testing conditions are met, proceed to conduct 25 combustion tests vii) The results from the 25 combustion tests will be provided by the automated

testing system, which will list the ID result as an average of the 25 cycles and the DCN as determined by the mean ID.

viii) Once testing is completed, flush the remainder of the test specimen through the system until the reservoir is empty.

To test another specimen, repeat the procedure listed above.

3.2.3 Diagnostic Equipment

The diagnostic equipment utilized by the FIT apparatus includes a static pressure sensor, a dynamic pressure sensor, type K thermocouples, a needle-lift sensor, PT100 temperature sensors, and a microprocessor-controlled system that is connected to the device.

The static pressure sensor measures the static pressure within the chamber before and after each combustion cycle (P0). The dynamic pressure sensor records the pressure within the combustion chamber during each combustion cycle (P1).

This pressure sensor is also equipped with a temperature sensor that records the temperature at the sensor (T3). The type K thermocouples measure the

temperatures at the internal surface of the chamber and of the gas at the center of the chamber (T2 and T1, respectively). The PT100 temperature sensors measure

the temperatures of the fuel injection pump and of the coolant flowing through the coolant passage (T4 and T5, respectively).