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.