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Description / Abstract:
Introduction
Note: Nothing in this standard supercedes
applicable laws and regulations.
Note: In the event of conflict between the
English and domestic language, the English language shall take
precedence.
Purpose. To evaluate the susceptibility of a
vehicle to powertrain icing under short drive conditions.
Applicability. Passenger cars and light duty
trucks equipped with mono-fuel or bi-fuel systems. The gaseous fuel
can be Compressed Natural Gas (CNG) or Liquefied Petroleum Gas
(LPG).
Remarks. When vehicles are started and run for
only short periods of time in cold weather, the probability of ice
forming inside the throttle body, induction system, or Positive
Crankcase Ventilation (PCV) system increases. The ice is formed
when water vapor, formed as a combustion by-product or ingested
into the engine from the intake air, does not have time to leave
the engine system and instead condenses out as the engine cools.
The common sources for water vapor are the intake air, the engine
blow-by through the PCV system and from the Exhaust Gas
Recirculation (EGR) system. The throttle body area is susceptible
for two reasons; it is located close to the exit point for both PCV
and EGR, and due to interior airflow, it is normally cooler than
surrounding parts. Vehicles operating on CNG and LPG are more
sensitive to icing because gaseous fuels produce more water vapor
during combustion compared to gasoline.