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Driving conditions critical to bus emissions
A new research report published by TNO, the Dutch research agency, shows that bus buyers should not rely solely on generic emissions claims when assessing different buses. They should also analyse the real-life driving conditions of the buses in order to get an accurate picture on emissions.
Real world driving conditions affect emissions
The TNO report VDL Ambassador diesel EEV bus: emission
measurements and comparison with other buses, shows that diesel buses can be more effective than CNG buses in reducing CO2 emissions in certain driving environments.
Surprising results...
In results that may surprise many supporters of CNG, TNO’s tests on an EEV (Enhanced Environmentally-friendly Vehicle) VDL Ambassador SB 200 bus (fitted with an SCR system and an oxidation catalyst with diesel particulate or soot filter) revealed that the SB 200 emitted only slightly more NOx and NO2 emissions and less CO2, particulate matter, CO and hydrocarbon emissions.
... from real world testing
TNO tested the bus using the Helsinki 3 and Braunschweig tests. These simulate ‘real world’ scenarios, rather than relying on generic European Steady-state Cycle (ESC) and the European Transient Cycle (ETC) emissions standards. Helsinki 3 simulates rural and suburban use, with an average speed of 39.5 km/h. Braunschweig simulates city and urban use, with an average speed of 22.4 km/h.
As Gerrit Kadijk, leader of the TNO research team, explains: “City bus driving patterns are very specific and differ from ESC/ETC driving patterns. Our results show that for both diesel and CNG buses, emissions vary greatly in practice from type approval tests such as ESC and ETC. For an accurate judgment on emissions, it is necessary to measure buses in their specific driving conditions.”
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