GMW GMW17148 PDF

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.