Emissions Test On Two-Stroke Engines - Bosch BEA 750 Original Instructions Manual

6.9

Emissions test on two-stroke engines

!
When performing an emissions test on 2-stroke
engines, always use a separate, second, external
gas path (exhaust gas sampling probe, exhaust gas
sampling hose of silicone, coarse filter GF1 and
active carbon filter 1 687 432 025).
!
When performing emissions tests on two-stroke
engines, always use the active carbon filter
1 687 432 025. This active carbon filter must be
inserted in the gas path downstream of the coarse
filter GF1. The active carbon filter 1 687 432 014 is
not to be used for two-stroke measurements.
!
Silicone exhaust gas sampling hoses and the active
carbon filter 1 687 432 025 may, however, be used
for CO measurements only, not for HC and Lambda
measurements.
i
The two-stroke set 1 687 001 283 includes silicone
hoses (1 x 7.5 m and 2 x 0.3 m) and the active
carbon filter 1 687 432 025.
5 4
Fig. 5: Emissions test on two-stroke engines
1 Silicone exhaust gas sampling hose, 7.5 m
2 Active carbon filter (1 687 432 025)
3 Coarse filter GF1
1)
4 Silicone exhaust gas sampling hose, 30 cm
5 Exhaust gas sampling probe
not included in two-stroke set 1 687 001 283
1)
Robert Bosch GmbH
3 4
2 1
1)
Operation | BEA 750 | 27
As compared to vehicles with four-stroke engines,
vehicles with two-stroke engines have a higher HC
emission level and additionally emit oil. Oil consists
essentially of hydrocarbons (HC). Hydrocarbons collect
on the walls of the external gas path (exhaust gas
sampling probe, exhaust gas sampling hose, filter).
These HC deposits result in an HC concentration
display (residual value display), even when no exhaust
emissions test is being performed, i.e. the actual value
for an HC measurement will be biased (increased) by
this residual value.
This effect, known to technicians as "Hang-up", occurs
with all exhaust gas analyzers and is not specific to any
particular make. It only becomes apparent with exhaust
gas analyzers for measuring HC.
The HC deposits are minimized through use of an
active carbon filter. Active carbon filters bind most of
the hydrocarbons. Active carbon filters have a limited
service life and must be replaced regularly.
i
HC deposits can be removed quickly after a
measurement by blowing compressed air through
the detached hose in the opposite direction to the
intake flow.
en
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1 689 989 339 2017-12-12