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The selection and testing of compression seal and chamber coating materials for the pivotal engine™.

Wear and friction tests were conducted on a rotational tribometer to identify material
couples for compression seals and chamber coatings to extend the service life of the
Pivotal Engine™. Potential materials were identified based on reports in the literature
of successful use in similar environments. From the rotational tribometer tests, the
best material couple was found to be reaction bonded silicon nitride against a Sulzer
Metco F4301 plasma sprayed coating followed by a Total Seal TiN coated seal
against the F4301 coating. However, the performance predicted by the rotational
tribometer was not realised in a fired engine, where the TiN coated seal wore almost
as fast as an uncoated seal. This discrepancy was due to the large differences in
operating conditions between the rotational tribometer and the fired engine,
particularly the reciprocating motion of the engine. The different operating conditions
mean that the results from the rotational tribometer have little or no relevance actual
performance in the engine.
To overcome the limitations of the rotational tribometer a reciprocating tribometer
was designed and built. The performance predicted by the reciprocating tribometer
was much closer to the observed wear rates from the engine, particularly with the
Total Seal TiN coated seals. Some of the results from the reciprocating tribometer
were a direct-contradiction to those obtained on the rotational tribometer. When tested
on the rotational tribometer the nitrided stainless steel seal wear rate was lower than
that of the Mazda cast iron seal. However, on the reciprocating tribometer the Mazda
cast iron seal had a lower wear rate than the nitrided stainless steel seal. From the
testing conducted on the reciprocating tribometer the best material couple was found
to be Total Seal TiN coated seals on the F4301 chamber coating. However, this
material couple cannot be recommended to increase the seal life in the Pivotal
Engine™ because at the conclusion of a twenty hour test the Total Seal TiN coating
had worn through to the substrate. In addition to testing different materials, different
oils were tested while keeping the wear couple constant. The oil that offered the best
wear protection to both the seal and chamber coating was Castrol A747. These tests
showed that different oils have as much effect as different materials.

Even with the best material combinations (Total Seal TiN seal, F4301 chamber
coating) the seal wear rates in the Pivotal Engine™ are much higher than would be
expected in other engines. This leads to the hypothesis that the origin of high seal
wear in the Pivotal Engine™ is not due to material properties, but to design issues.
The most likely problem is distortion of the chamber, which causes high localised seal
loadings, and in turn causing high seal wear.
Date January 2006
CreatorsMiller, David J
PublisherUniversity of Canterbury. Mechanical Engineering
Source SetsUniversity of Canterbury
Detected LanguageEnglish
TypeElectronic thesis or dissertation, Text
RightsCopyright David J Miller,

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