A Predictive Model for Feedgas Hydrocarbon Emissions: An Extension to Warm Engine Maps

Abstract

A feedgas hydrocarbon emissions model that extends the usefulness of fully-warmed steady-state engine maps to the cold transient regime was developed for use within a vehicle simulation program that focuses on the powertrain control system (Virtual Powertrain and Control System, VPACS). The formulation considers three main sources of hydrocarbon. The primary component originates from in-cylinder crevice effects which are correlated with engine coolant temperature. The second component includes the mass of fuel that enters the cylinder but remains unavailable for combustion (liquid phase) and subsequently vaporizes during the exhaust portion of the cycle. The third component includes any fuel that remains from a slow or incomplete burn as predicted by a crank angle resolved combustion model. The hydrocarbon model estimates the oxidized portion of these fuel sources according to a simplified empirical model incorporating exhaust port temperature predictions from a simple, heat transfer-based pipe model. Calibration of the hydrocarbon model to a base vehicle/powertrain/engine run allows estimates of feedgas hydrocarbons when changes are made to vehicle calibration, hardware, or external environment. Agreement between the hydrocarbon model prediction and vehicle data measurements for a range of vehicle calibrations is excellent.