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Risky Particles
The progress made in engine design the last years has exhausted the smoke-opacity measurement using current
procedures. Now the introduction of a newly offered measurement technology is being called for.
MAHA Maschinenbau Haldenwang GmbH & Co. KG., Hoyen 20, 87490 Haldenwang (Germany)
Mr. Multari, Phone: +49 (0) 8374 / 585-123, [email protected]
Workshop Technology Diagnosis
Particle Measurement
Risky Particles
The progress made in engine design the last years has exhausted the smokeopacity measurement using current procedures. Now the introduction of a
newly offered measurement technology is being called for.
W
e have all been in this situation.
An old taxi equipped with one
of the first Common Rail diesel
engines is in front of us. The driver accelerates and in a split second you feel like
you are driving into a black wall. The case
is clear. Worn injectors cause too much
diesel fuel to be injected at acceleration,
the mixture is much too heavy and leads
to heavy soot build up during combustion.
Those of us driving behind this kind of
vehicle secretly hope that this environmental scoundrel gets his due at the next
official emission inspection.
Invisible Danger
Instinctively one reaches for the air circulation knob on the car’s ventilation system
so as not to also inhale all this unhealthy
exhaust. Fact is, the modern diesel vehicles
of the latest design, which might be driving
right next to the taxi, pose much greater
health risks, but they are invisible. Modern
diesel vehicles emit particles so tiny that
they can no longer be seen. The ever
higher pressures in Common Rail Injection
systems in effect atomize the fuel, which
leads to extremely fine soot particles. These
typical particles can have a diameter of 250
nm making lung entry easy and opening a
path into a person’s bloodstream. Once
there they have a toxic effect. Because of
the high danger these particles represent,
particle filters have been developed which
can contain a major portion of these particles. Diesel vehicles have also been
equipped for some time now with OBD
systems (On-Board Diagnostics) which
monitor the adherence to permissible
pollutant emission levels. And the periodic
emission inspections are also a guarantee
that proper levels of pollutant emissions
are not exceeded.
However, the described measures to
reduce the particle emission have shown
to have some weak points. A national
program was initiated, for example, to
support vehicle upgrading with particle
filters. Environmentally-minded vehicle
drivers took great advantage of the offer,
but then the incomprehensible occurred.
Thousands of useless particle filters
had been thrown onto the market with
fraudulent intentions. The scandal shattered vehicle driver’s trust in the workshops, although they were in no way
responsible for the fraud. The discussion
dominated the headlines for months. The
emission properties of diesel vehicles
have been inspected since the inception
of emission inspection (AU) in 1993. For
this, the smoke opacity co-efficient, the
so-called k-value, is evaluated from
Details such as a missing monitor probe on a new car with
Otto-motor sometimes nourish doubts about the OBD.
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Photographs: Archives, MAHA
multiple sequential gas thrusts without
load. This measurement variable is
determined by an opacimeter which in
turn determines the smoke-opacity via
light penetration. The opacimeter has an
exact fixed-length measurement pipe
through which emission is channelled. A
light source is located on one end of the
measurement pipe and a light-sensitive
sensor on the other side. Now when heavy
sooted emission is channelled through
the measurement pipe, the sensor receives
less light which corresponds with a
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higher k-value. On the contrary, if a large
light quantity penetrates the emission,
this corresponds with a small k-value.
This long proven measurement procedure
is based on the principle that soot particles are visible. However, fine soot particles remain invisible using this measurement technology. With modern vehicles
then, the k-value measured in the framework of the official diesel emission
inspection lies below the resolution
capacity of this opacimeter. After the filter
scandal passed, this aspect was the focus
of consumer magazine discussions for a
short period, alleging unnecessary fee
collections from automobile drivers.
Automobile Manufacturers
Swear by OBD
The automobile manufacturers have been
of the opinion for some time now that the
OBD is much more effective than the
official emission inspection and would
therefore like to see it abolished. The fact
is, the OBD as vehicle supported diagnosAUTO SERVICE PRAXIS
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Workshop
Technology Diagnosis
OBD system is only checked intensively at
the homologation of a vehicle before
serial production starts. Whatever follows
is exclusively in the hands of the automobile manufacturer.
The OBD Should be Monitored
The technology for measurement of the tiniest particles is ready
for serial production. Now its introduction is being called for.
tic system monitors a engine during the
complete operation. As soon as a malfunction occurs, the driver is informed when
the malfunction lamp MIL (malfunction
indicator lamp) lights up. However, the
At OBD introduction there were a series of
massive irregularities such as OBD sockets,
missing software not installed and similar
things. Just recently a major serial model
with Otto motor appeared on the market
which no longer had a monitor probe after
the catalytic converter. That may function,
but does not correspond with the original
regulations. Test series conducted by the
task force Emission 2010 determined that
several emission-relevant malfunctions on
diesel vehicles equipped with OBD did
not lead to MIL lamp light up. And in addi-
Invisible Danger
tion to this, the particle filter was not
checked by any of the systems because this
is not stipulated. Hence, the experts are of
unanimous opinion that the OBD is a
sensible supplement to the tail pipe inspection, but cannot replace it. Last year at the
Official Emission Inspection Guideline 4
introduction, many users were surprised
that under certain conditions it omitted an
end pipe measurement on vehicles if all
readiness codes signalized test readiness.
Even as good as the OBD system may be,
who actually inspects it? An end pipe test
every two years can certainly not be amiss
and provides neutral clarity about the entire
system consisting of engine, OBD and emission gas further treatment.
For some time now the laser light scattered photometry measurement procedure
has been in serial production and offers a
functional, workshop suitable alternative to
solve the described problem of measuring
the tiniest soot particles.
New Measurement Technology in
Serial Production
In order to understand the depth of danger that the smallest particles in diesel
engine emission represent, we need to try to think in the tiniest dimensions. The
most common measure of comparison is the human hair. It measures 70,000 nm in
diameter. A typical diesel particle measures only 250 nm diameter. More than a
million of these particles can be found in a volume of cm3 which corresponds with
a normal concentration. When inhaling, particles in the range of 5,000 to 10,000 nm
get into the nose and throat with smaller particles between 3,000 and 5,000 nm
reaching into the air pipe. Even smaller particles with a diameter of 2,000 to 3,000
nm can advance forward into the bronchial tubes. Particles with a diameter of 1,000
to 2,000 nm can reach the bronchiole area. And the smallest diesel particles with a
diameter of only 100 to 1,000 nm attack the pulmonary alveoli in the lungs. This then
opens the path for particles to enter the bloodstream. It does not take all too much
fantasy to imagine the damage that they can cause there. For this reason it is of
paramount importance that vehicles with heavy particle emission be identified in
the framework of the official emission inspection using state-of-the-art measurement
technology. Our health also depends on this.
The laser light scattered photometry
measurement procedure functions in
principle similar to a flashlight in whose
light cone a dustcloth has been shaken
out. Even the tiniest particle is visible in
this light beam and can be caught by
detectors. The MAHA MPM4 is already
available and measures the particle
mass concentration which is issued in
mg/m3 and converted to the k-value.
MAHA already supplies this device to
research and development institutes,
universities and laboratories involved
with fuel research. The introduction of
this technology means that the emission
inspection for diesel engines is now stateof-the-art. Comprehensive test series have
proven that there is a strong correlation
between particle concentration and the
k-value. Efforts are currently underway
to receive an approval of the new technology as opacimeter from the PTB.
Worldwide, on the national and international level, task forces are striving for
further development of the tail pipe test in
the framework of the emission inspection.
The ASA Association also demands the
clear preservation of the general end pipe
measurement and the quickest possible
introduction of the new measurement
technology for the official diesel emission
Bernd Reich
inspection. Human hair has a diameter of
70,000 nm.
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© Andreas Schäfer - Fotolia.com
Diesel Particle
Typical diesel particles are much smaller than the diameter of a human hair.
Extremely fine diesel particles can enter
the bloodstream through the lungs.
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