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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.
·
Work cooperatively to develop a
worldwide-accepted test method for intake valve, combustion chamber, and
injector deposits in Direct Injection Spark Ignition (DISI) engines.
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 was 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 and is posted to the CRC website. 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, some rig-to-rig variation and also variation in the same rig
have been observed. The group is exploring the cause of the variations.
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 will be 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 the Phase 1. Preliminary study results were presented to the committee
in April 2007 and additional statistical analyses will be conducted to identify
sulfur specie contributions. 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 sensors. A comparison of fuel level sensor failures with ASTM silver
corrosion test methods will be made.
CRC/CEC/OACIS International Deposit Cooperative Research
CRC worked cooperatively with OACIS and CEC on a
program to develop a worldwide-accepted test method for IVD, CCD, and Injector
Deposits in DISI engines. Tests have been run with the three proposed engines
for injector, intake valve, and combustion chamber deposit evaluation. Testing
was done on a base mid-range fuel from the Japanese market, a high T90 and high
aromatic, a low T90 and high aromatic, a low T90 and low aromatic and a Japanese
Base + detergent (PBA), plus one fuel each from the U.S. and from Europe. Based
on Phase I tests, OACIS selected the Mitsubishi engine to use for future cycle
development. Ten U.S., Japanese, and European companies and organizations
participated in the test development program and installed the Mitsubishi GDI
engine. Evaluation of candidate test cycles was conducted. The fuels and
engine cycles investigated to date have not produced sufficient fuel injector
fouling, although a recent "low T90" fuel has shown more promise. Test cycle
studies were completed. No independent test program by CRC was carried out, but
rather CRC monitored the progress of the program. CEC recently announced they
will be concluding their efforts on this study and the CRC Performance Committee
approved a plan to summarize the test program results in a Final Report to
document the results and lessons learned from this cooperative international
program. The Final Report was released for publication in April 2007 and is
available on the CRC website.
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