ASTM method D 6421, “Standard Test Method for Evaluating Automotive Spark-Ignition Engine Fuel for Electric Port Fuel Injectors Fouling by Bench Procedure”, was developed by South West Research Institute (SWRI) and the procedure standardized by the Coordinating Research Council (CRC) in 1999. The method has the potential to be a cost-effective tool for evaluating additive and fuel effects on port fuel injector performance. However, the Bosch injectors specified in the test procedure are no longer commercially available and in practice, obtaining repeatable and reproducible results using Bosch injectors can be difficult.
This paper reports on bench test apparatus and test procedure modifications directed at obtaining better repeatability and responsiveness to fuels and additive chemistry. These modifications allow for better control of test-to-test injector tip temperature and keep the temperature closer to the injector soak temperature. Evaluation of injector-to-injector variability has led to the identification of Honda pintle style injectors as replacements for the Bosch injectors. Further study found that non-weeping injectors have fouling at test conditions. The initial injector flow rate, however, does not affect the injector fouling tendency
Use of different source of fuel injectors was determined to have advantages of not requiring pre-screening for fouling capability, improved test repeatability, and good response to base fuel and additive chemistries compared to using Bosch injectors specified in the standard test.