Development of Model-Based OBDII-Compliant Evaporative Emissions Leak Detection Systems

The paper presents the main results obtained by developing and critically comparing different evaporative emissions leak detection diagnostic systems. Three different leak detection methods have been analyzed and developed by using a model-based approach: depressurization, air and fuel vapor compression, and natural vacuum pressure evolution. The methods have been developed to comply with the latest OBD II requirement for 0.5 mm leak detection. Detailed grey-box models of both the system (fuel tank, connecting pipes, canister module, engine intake system) and the components needed to perform the diagnostic test (air compressor or vacuum pump) have been used to analyze in a simulation environment the critical aspects of each of the three methods, and to develop “optimal” diagnostic model-based algorithms. Experiments have been initially carried out in a laboratory environment to identify both the main model unknown parameters and the main disturbances, and to acquire data that could be used to validate the simulation results. During a subsequent phase of the project, a prototype vehicle has been setup with various sensors and actuators, and several experiments have been conducted to test the three leak detection model-based methods, while varying environmental and in-vehicle conditions. The critical aspects of each methodology have thus been isolated and compared, also by taking into account actual and possibly future European and North American on-board diagnostic regulations.