A new method to calculate instantaneous vehicle emissions using OBD data

The actual type approval procedure of vehicles, based on a fixed driving cycle for all the vehicles (NEDC), is not representative of their real on-road usage: the driving style and its influence on consumption and emissions cannot be neglected. The on road impact of vehicles on their real use is not known and it is difficult to measure (the PEMS are expensive, have big volume and mass and need continuous maintenance); the objective of this work is to develop a methodology to calculate in real time the energy and environmental impact of spark ignition vehicles, using the onboard sensors of the vehicle and emissions models to calculate them. An onboard instrumentation able to communicate with the electronic system of the vehicle (OBD/CAN) was developed to collect all the sensor data installed on a vehicle: those values are used as input values to the emissions models of CO2, CO, HC and NOx developed in the present work. The CO2 and CO have been calculated using a chemical equilibrium combustion model with 6 combustion products, with the equilibrium temperature used as a calibration constant. HC and NOx, produced during transients, are assumed to be dependent from the accelerator pedal gradient, but during engine cold start also from the catalyst temperature. To validate the models, a spark ignition hybrid vehicle, the Honda Civic Hybrid has been tested on a chassis dynamometer running the three Artemis driving cycles. The emissions have been measured with the CVS (taken as reference) and with a portable emission analyzer, (Horiba OBS 1300), used for comparison with the models. The results shows that the values calculated by the models are comparable with those measured by OBS, but for HC and NOx are better because the OBS gave inaccuracies due to its high minimum resolution.