DEPOSITS

CRC Project No. CM-136

Leader:       J. T. Joseph

Scope and Objective

The objectives of CRC Project No. CM-136 are to:

• Develop test procedures for the objective evaluation of fuel and fuel additive contributions to combustion chamber deposits (CCD).
• Determine the extent of fuel injector fouling in a specific region of the U.S. and adequacy of current deposit control additive dosages to prevent injector fouling.
• Establish the relationship of vehicle fuel level sensor failures and concentrations of corrosive sulfur gasoline species.

Current Status and Future Programs

Port Fueling Injector Fouling Survey

Auto companies reported deposit-related Port Fuel Injector (PFI) plugging problems in cars, with a high incidence rate in Florida. The Deposit Group formed a Panel to determine the extent of fuel injector fouling in this region of the U.S. and the adequacy of current deposit control additive dosages to prevent injector fouling.

The program approach was to sample gasoline from 10 major marketers in Tampa and Miami, analyze the fuel composition, assess PFI fouling tendencies with the CRC PFI bench rig using ASTM D 6421, and compare fouling tendency of Honda and GM injectors with standard Chrysler rig injectors.  GM provided injectors from Florida that have been known to cause fouling problems.  Twenty commercial fuels were collected in Florida, analyzed, and tested in the PFI bench rig.  Six of the twenty fuels were shown to be deposit-prone.  There appeared to be no correlation between apparent deposit severity and fuel properties or additive dosage.  This raises the question of whether the PFI bench test is representative or too severe.

In a second phase of the program, the tendency of OEM and ASTM injectors to foul was compared.  All showed fouling in the PFI bench rig. The effectiveness of several detergents and dosage was also evaluated and varying degrees of effectiveness were observed in the PFI bench rig.

The Panel then compared the bench rig with the Chrysler PFI fouling vehicle test.  Poor correlation was observed with the bench rig being more severe. Of the six fuels passing the ASTM D 5598 Chrysler vehicle test, four fouled by 11 to 41% in the bench rig.  CRC Report No. 646, “Port Fuel Injector Fouling Using the PFI Bench Rig – Evaluation of Florida Gasoline, OEM Injectors, and Deposit Control Additives,” was issued in September 2005. A proposal for the next phase of testing was circulated to the group members for comment and was approved.  Additional bench test evaluations are underway at SwRI assessing deposit levels with test temperatures.  While general trends have been demonstrated, rig-to-rig variation and also variation in the same rig have been observed.  The group is exploring the cause of the variations and is working closely with SwRI who has offered to resolve the rig performance problems before further work is attempted.  A decision was made at the Spring 2008 Performance Committee meeting to discontinue efforts with the old injectors, and now the Committee recommends finding a more modern injector test article that will allow testing in the longer term.

Silver Fuel Level Sensor Corrosion

There have been field reports of fuel level sensor failure due to corrosion of silver contacts by reactive sulfur species.  The objective of this study is to establish the relationship of vehicle fuel level sensor failures and concentrations of corrosive gasoline sulfur species.  These data will assist ASTM in establishing a sound basis for pass/fail criteria. 

The study is being conducted in two phases.  In the first phase, the fundamental effects of elemental sulfur, H2S, and mercaptans have been determined.  CRC issued a request for proposal to characterize the response of pertinent levels of sulfur, H2S, and mercaptans and their interactions using two laboratory test methods (ASTM modified silver corrosion and the new PetroCanada silver wool test).  Three proposals were reviewed by the project panel leaders and SwRI was selected to conduct Phase 1.  Study results were presented to the committee in April 2007 and additional statistical analyses were conducted and presented in October 2007 to characterize and identify sulfur specie contributions.  A final report on the Phase 1 effort is expected in the near future.  In Phase 2, a correlation study of fuel sensors durability and corrosion test methods will be conducted.  The study includes a matrix of test fuels with increasing corrosivity to be tested on sensitive fuel level sensor components.  A comparison of fuel level sensor failures with ASTM silver corrosion test methods is the main objective of this study.

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