GMW GMW17149 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 long 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 driven for long periods of time, at conditions just above the freezing point and with high humidity, the probability of ice forming inside the throttle body, induction, or Positive Crankcase Ventilation (PCV) system increases. This is due to the airflow induced pressure drop through the induction system and throttle causing the temperature of the air entering the engine to drop below the freezing point. When the humidity of the intake air is high, the probability of ice forming is greater. Secondary sources of water vapor are 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.