ASTM D6421 Test Method for Evaluating Automotive Spark-Ignition Engine Fuel
ASTM D6421 Standard Test Method for Evaluating Automotive Spark-Ignition Engine Fuel for Electronic Port Fuel Injector Fouling by Bench Procedure
4. Summary of Test Method
4.1 This test method describes a procedure for evaluating the formation of deposits in PFIs. The test method includes a bench test procedure that has been shown to rapidly form deposits in fuel injectors and a procedure for determining resultant flow loss.
4.2 This test method uses a simulated fuel system consisting of a fuel pump, filter, pressure regulator, fuel rail, and fuel injectors. A heat source is applied to the fuel injectors to simulate the hot-soak portion of the vehicle test (see Test Method D5598).
4.3 Each test begins with screened injectors that are known to foul. The tips of these four clean fuel injectors are placed in an aluminum block. A stainless-steel internal reservoir is filled with 2 L of the test fuel.
4.4 During one 60-min test cycle, the fuel injectors are pulsed for 15 s, followed by a 50-min hot-soak interval in which the injector aluminum block temperature controller is set at a temperature of 160°C (320°F) and the fuel pressure is regulated to 263 kPa (38 psig), followed by a 10-min cool down period. Flow measurements for each of the injectors are taken at the beginning of the test, after 22 cycles, and at the end of the test at 44 cycles.
4.5 The change in the rate of flow for each injector from the start to the end of the test is used to determine the fouling percentage of each injector.
5. Significance and Use
5.1 Driveability problems in PFI automobiles were first reported in 1984. Deposits are prone to form on the metering surfaces of pintle type electronic fuel injectors. These deposits reduce fuel flow through the metering orifices. Reductions in metered fuel flow result in an upset in the air-fuel ratio, which can affect emissions and driveability. When heavy enough, these deposits can lead to driveability symptoms, such as hesitation, hard starting, or loss of power, or combination thereof, that are easily noticed by the average driver and that lead to customer complaints. The mechanism of the formation of deposits is not completely understood. It is believed to be influenced by many factors, including driving cycle, engine and injector design, and composition of the fuel. The procedure in this test method has been found to build deposits in PFIs on a consistent basis. This procedure can be used to evaluate differences in base fuels and fuel additives. A study of PFI fouling was conducted in both the bench test and the vehicle test procedures to obtain a correlation. The vehicle tests were conducted as described in Test Method D5598. The tests were conducted on several base gasolines, with and without additives blended into these base fuels. The PFI bench test proved to be reliable, repeatable, and a good predictor of PFI fouling in test vehicles.
5.1.1 State and Federal Legislative and Regulatory Action - Legislative and regulatory activity, primarily by the state of California (see 2.3) and the federal government (see 2.4), necessitate the acceptance of a standard test method to evaluate the PFI deposit-forming tendency of an automotive spark-ignition engine fuel.
5.1.2 Relevance of Results - The operating conditions and design of the laboratory apparatus used in this test method may not be representative of a current vehicle fuel system. These factors must be considered when interpreting results.
5.2 Test Validity:
5.2.1 Procedural Compliance - The test results are not considered valid unless the test is completed in compliance with all requirements of this test method. Deviations from the parameter limits presented in Section 10 will result in an invalid test. Engineering judgment shall be applied during conduct of the test method when assessing any anomalies to ensure validity of the test results.
