Bosch BEA 055 Originalbetriebsanleitung Seite 19

3.7 Exhaust measurements for 2 cycle
engines
Vehicles with two cycle engines have higher HC emis-
sions and also deposit oil compared to vehicles with four
cycle engines. Oil mainly consists of hydrocarbons (HC).
This forms deposits on the walls of the gas path (ex-
haust extraction probe, exhaust extraction hose, filter) if
no precautions are taken.
These deposits result in an HC concentration display
(residual value display), even if no exhaust measure-
ment was performed, thus the actual value of this
residual value is adulterated (increased) during an HC
measurement.
This affect, known as "hang up" by experts, appears in
all exhaust instruments, and is not related to the prod-
uct. It is only visible in instruments that measure HC.
These deposits can mostly be prevented by inserting
activated carbon filters. These filters bind and neutral-
ize the greatest part of oil and volatile hydrocarbons.
This type of filter has a limited service life.
!
Always use an activated carbon filter when measur-
ing exhaust in 2 cycle engines. This activated carbon
filter must be inserted behind the rough filter in the
gas path.
i
We recommend always using a separate, second
outer gas path (exhaust extraction probe, exhaust
extraction hose, GF1 filter and activated carbon
filter) when measuring exhaust in 2 cycle engines.
All necessary parts required for this are contained in
the 2 cycle set 1 687 001 283.
Robert Bosch GmbH
Product description | BEA 055 | 19
!
The exhaust extraction hose in this 2 cycle set is
made of silicon. However, exhaust extraction hoses
made of silicon and activated carbon filter can only
be used for CO measurements, not for HC and
Lambda measurements.
5 4
Fig. 2: AMM with 2 cycle set 687 001 283 to measure exhausts
in 2 cycle engines
1 Silicon exhaust extraction hose 7.5 m
2 Activated carbon filter
3 GF1 rough filter
4 Viton exhaust extraction hose 30 cm
5 Exhaust extraction probe
i
Any possible deposits can quickly be removed after
measurements by blowing out the removed hose
with compressed air.
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1 689 989 181 2016-12-14