Bus emission evaluation: 2002-2004 Summary report

Within 2002 – 2004, VTT measured altogether 34 different Euro 1 – EEV certified city buses. All measurements were made on VTT’s new chassis dynamometer. The output of the measurements is truthful emission factors in the form of g/km.

There were large variations in the regulated emissions. Diesel Euro 1 vehicles and EEV natural gas vehicles make up the extreme ends. The NO_x emission varied from some 20 g/km for Euro 1 diesel vehicles to around 2 g/km for the most advanced natural gas vehicles. For particulates, the spread was even greater, i.e., from 0.6 to 0.003 g/km, a difference of a factor of 200. Good news is that real-life emissions seem to be falling with advancements in Euro classes.
The work included PM emissions of low-emitting CRT diesel vehicles and natural gas vehicles. To stay operational, a CRT filter needs some service. Natural gas vehicles showed extremely low PM values independent of mileage. Older CNG vehicles show rather high THC or methane emissions. For a detailed diesel/natural gas bus comparison, seven modern buses, three diesel-driven and four CNG vehicles, were tested for emission performance. The measurements included regulated emission components and a number of speciality measurements. A CRT type particle filter improves the emission performance of a diesel vehicle in many ways. However, with current technology the best natural gas buses outperform the CRT diesel vehicle in most respects.