Presspley.com was an Australian company who specialised in simulation and analysis.
The investigation was interesting but disappeared when Presspley went bust.
So here it is again in all its glory (with some of the poor English and grammar sorted).
FAILURE INVESTIGATION OF
EXHAUST MANIFOLD TURBOCHARGER UNIT
to around 40mpg, with no difference in vehicle use.
Smart Centre, and have them try to
persisting, the vehicle was serviced at a Mercedes Benz dealer. The exhaust
manifold/turbocharger unit was found to be cracked in two places.
unit being investigated is a Garrett GT12 turbo with part number: A 160 096 0599
to be in good condition except for the two large cracks in between the 3 cylinders.
The extent of the cracking can be seen in the photographs.
These were then progressively ground before final polishing with 0.05mm colloidal silica
suspension, to give a scratch-free surface and reveal the true grain structure.
again at magnifications up to x1000.
out by swabbing the polished surface with 5% Nital solution.
throughout the section of the casting, however it is not considered to be excessive.
using an lnstron 5582 tensile testing machlne. Results are shown below.
UTS (MPa) = 467
Elongation (%) = 16.5
Results can be seen in the table below.
Manganese, Mn = 0.581
Nickel, Ni = 34.065
Copper, Cu = 0.086
Chromium, Cr = 1.852
Sulphur, S = 0.002
Molybdenum, Mo = 0.125
The chemical composition is similar to that of a Ni-Resist cast iron.
(980-1040°C) for 3 to 5 hours and air-cooling. This breaks down some of the
carbides and most of those remaining will be spheroidised.
very hot, then the engine left to cool; heat treatment mechanisms could have taken place.
internal residual stresses which could have lead to crack initiation.
the gaps between the shrinkage. Shrinkage is caused by poor casting design and technique.
shock loading from undulating road surface not being fully considered.
the manifold based on the change of section of manifold, exhaust gas temperature
within the manifold, and method of attaching to cylinder head.
at the design or manufacturing level, is yet another factor that cannot really be
commented on. Incorrect ignition advance is one such example.
modem vehicle. The use of modem computational analysis programmes such as Ansys
that can calculate combined thermal and mechanical stresses should (with suitable safety
factors) eliminate this - again assuming the
issue. Note that the cracks are propagating at the points around the manifold fixings.
It appears all bolt holes are the same size also. I would expect a greater hole size in the
fixings at either end of the manifold to allow the manifold and head to expand & contract
relative to each other, maintaining its position with the centre studs.
along its length. The end furthest from the turbine housing has one cylinders worth of exhaust
gasses (and heat). The second cylinder experiences two cylinders worth, whilst the third has one
cylinders worth but is closest to the compressor housing – the hottest part of any turbocharger.
imposed by American. Japanese. and European legislation. To meet future HC and CO
limits, and to improve fuel economy, automotive engine manufacturers are looking towards
running air to fuel ratios near lambda = 1 for full load engine conditions.
improve maximum engine power output and maintain engine durability. The excess fuel under
these conditions has a cooling effect on the exhaust temperature and has allowed engines
to be below 1000°C in exhaust temperature. The move towards lambda = 1 will remove
this fuel cooling effect and will yield exhaust temperatures up to 1050°C.
gasoline applications. This has been a delicate balance of design, material technology,
and cost. The move to 1050°C exhaust temperatures has prompted the Garrett Turbocharging Group to redefine this balance for turbochargers.
Close up of cracking.
Close up shot of crack 1, as received.
Close up shot of crack 2, as received.
Showing complete penetration to inner face of manifold at crack 1.
Showing complete penetration to inner face of manifold at crack 2.
x100 magnification micro-section in the as polished condition.
Structure shows small graphite nodules with columnar cementite.