AM MAGAZINE SHELL - Australian Automotive Aftermarket Magazine

NEWS
HEAT RANGE TESTING OF SPARK PLUGS
If you ever wondered how spark plugs are tested to make sure they will continue to perform in harsh environments, here’s
some insight into how testing is conducted for the Australian and New Zealand markets.
When an engine is operating the spark plug
is heated by the combustion process.
Some of the heat that is absorbed by the
spark plug is transferred to the incoming air
fuel mixture, however most of the heat is
conducted to the cylinder head.
The working environment
There is a delicate balance between the
heat absorption and heat dissipation, with the
aim to get the insulator temperature to reach
the self cleaning temperature of about 500°C.
If the temperature drops below this level
there is a danger that soot and oil from
incomplete combustion will settle on the colder
areas of the spark plug.
This can form a shunting of the spark and
result in misfiring. Conversely if the insulator
temperature is too high (above 900°C) there
will be a dramatic increase in electrode wear
due to oxidation and hot gas erosion, or even
worse, destructive pre-ignition.
How is the heat range of a
spark plug tested?
Robert Bosch Australia carries out regular
heat range testing of vehicles in the Australian
and New Zealand car parcs.
This ensures the heat range listed in its
catalogues is correct for the region.
STOPPING THE INDUSTRY FOR 40 YEARS
Since its humble beginning in 1968 selling brakes and clutches to local trade workshops, Superstop has grown to
become one of the largest independent brake and clutch resellers in Victoria.
So what’s its secret? From its first ever
advertisement in The Free Press in 1979
Superstop has always valued the importance
of advertising.
“Keeping our customers up to date with
the latest products and world leading brands
helps them run a professional business and
helps us to stay ahead of our competitors,”
Superstop Director, Steve Kreti, explained.
Testing is carried out on local vehicles using
local fuels to replicate the driving conditions in
the region.
To do this Bosch uses a large chassis
dynometer at its site in Clayton, Melbourne to
produce the required vehicle loads.
Firstly, for every given vehicle the hottest
cylinder in the engine is found.
This is done using a special spark plug
equipped with a thermocouple that allows
Bosch to directly measure cylinder
temperature.
The hottest cylinder is found because it is
the weak link.
It is the one that will suffer from pre-ignition
at elevated combustion temperatures before
the other cylinder.
It is for this reason the heat range testing is
conducted in this cylinder.
Ionic Current Measurement
The Bosch Ionic Current measurement
procedure uses combustion characteristics to
determine the engine’s heat range
requirements.
The ionizing effect of the flames is used to
determine how combustion develops over time.
This is done by measuring the conductivity of
the spark gap.
Characteristic changes in combustion
Another secret to the success of
Superstop has been its staff.
Mick Cree started with Superstop in 1975
as an eager 21-year-old mechanic.
Thirty-four years later Mr Cree, who
manages the Mont Albert store, admits he
has seen many changes since he first started
as a young man with Superstop.
“In the late ‘70s and early ‘80s Superstop
used to re-bond its own brake shoes and
remanufacture its own clutches,” he said.
“Technology has changed and so have we,
but one thing remains the same - good old
fashion service backed with up to date expert
advice.”
Mr Kreti said Superstop has continued its
winning formula by opening its second store
in South Yarra, Melbourne.
“Distributing some of the world’s best
brands such as Mintex, Pagid, LUK, Exedy
and Boge shock absorbers has really
Bosch spark plugs undergoing heat range testing.
process due to increased thermal loading can
be detected using ionic current and is used in
the assessment of the auto ignition process.
In this way Bosch can make adaptions in
the plug design to prevent thermal ignition from
occurring.
So, when you purchase a Bosch Spark plug
you can be assured that there is an intensive
testing program behind the application found
in the Bosch spark plug recommendation in its
catalogue.
For more information on Bosch spark plugs, or
for a copy of the Bosch spark plug catalogue,
contact your local Bosch representative or call
Bosch Customer Service on 1300 30 70 40.
separated us from our competitors,” Mr Kreti
said.
“Quality is no exception and we will not
put our name behind a product if it’s not the
best.”
Superstop: proudly stopping the industry
for more than 40 years.
Contact Superstop Brake & Cultch on
03 9890 1924
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