appendix a - Velocidade

14
The effect of speed on noise, vibration and emissions
from vehicles
May 1998
the air-to-fuel ratio was maintained at the stoichiometric point. However, occasional
heavily-loaded conditions during the on-road testing led to richer than stoichiometric
operation.
During these brief enrichment events, which lasted up to 29 seconds, CO emissions were
increased by a factor of 2500 and HC by a factor of 40 over closed-loop stoichiometric
operation. NO emissions were similar during low-load stoichiometric and high-load
enrichment operation.”
Kelly and Groblicki went on to show that a single high power acceleration can produce more
CO than is emitted in the balance of a typical short trip (under 5 miles) in the USA.
Two results of two further real-world vehicle emission measurement trials have been
released in Europe. Schurmann and Staab (1990) describe an on-board exhaust emissions
measurement system which is capable of measuring CO, HC, NOx and CO2. The system was
developed at the headquarters of the Volkswagen car company. Vehicle characteristics such
as speed and engine rpm are also recorded. The system is small enough to be mounted in
cars such as the Volkswagen Golf. Limited results were published, probably because of the
commercial sensitivity of the results. De Vlieger (1997) tested the emissions of seven cars in
Belgium under calm, normal and aggressive driving conditions. De Vlieger describes
aggressive driving as sudden acceleration and heavy braking. Calm driving was anticipating
other drivers' movements and avoiding sudden acceleration. Normal driving had moderate
acceleration and deceleration. During all tests the speed limits were observed. It is not stated
in the report but is assumed that one driver or a team of specially trained drivers were used
to ensure comparability of results between the seven different vehicles tested.
The results of the comparison are shown below in Table 1.
The table clearly shows that the emissions from aggressive driving are not 2500 times those
found from normal driving but that in all but one case the aggressive driving emissions are
higher than the normal driving emissions. Schurmann and Staab (1989) suggest that on
board testing of emissions under real traffic conditions should be seen as complementary to
laboratory emission results.