Emissions ‘significantly lower’ from retrofitted Euro III buses

Brighton study finds further evidence that Euro III buses retrofitted with SCR produce less air pollution than newer Euro V buses

Further evidence has emerged that older buses designed to meet Euro III emissions standards — which are then retrofitted with after-treatment technology — produce fewer exhaust emissions than newer Euro V standard buses, according to a study conducted in Brighton.

One of the test buses in Brighton fitted with PEMS equipment

Published yesterday (November 27) by consultancy Ricardo, the report is based on real-world testing of buses in Brighton and builds on another report from July, which demonstrated the emissions benefits from a range of buses of improving traffic flow (see airqualitynews.com story).

As a follow up to the traffic flow study, Ricardo has since carried out measurements on an older Euro III bus that has recently been retrofitted with a selective catalytic reduction (SCR) and continuously regenerating particulate trap system.

The research found that, when averaged across the bus route on which tests were taken, the total emissions results of the Euro III retrofitted bus were substantially below those of all of the other buses tested, including the Euro V hybrid vehicle.

Data also indicated that of the nitrogen oxides (NOx) remaining in the exhaust, the nitrogen dioxide (NO2) fraction was substantially lowered to below 10% of total NOx.

The findings follow similar suggestions regarding the benefits of modifying older Euro III buses made last year by Steve Rawson, head of retrofit engineering at exhaust technology firm Eminox (see airqualitynews.com story).

Averaged NOx measured vs emissions technology (click to enlarge)

EU Euro III emissions bus standards for carbon monoxide, hydrocarbon, oxides of nitrogen (NOx) and particulate matter came into force in 2000, while Euro V standards setting tougher emissions limits came into force in 2008. Tougher Euro VI standards for new buses came into force just under a year ago.

Warm up

However, the retrofitted after-treatment system required a ‘considerable’ period of warm-up before its full emissions control functionality could be achieved — typically 5-10 minutes from cold start, the Brighton study found.

According to Ricardo, this may have implications for bus operators with depots in, or close to, low emissions zones.

In addition, the firm said, scope was also seen both for “further optimization of the system calibration by improving the dosing of the SCR system in uphill stop-start traffic, and improving thermal management of the exhaust”.

Brighton test

For the study, the Euro III bus was tested on the number 7 bus route in the city, which traverses Brighton & Hove through the air pollution hotspot of North Street in the city centre and covers a total of 18km (9km in each direction) with ‘significant’ gradients throughout.

The bus was fitted with data measurement firm HORIBA’s advanced Portable Emissions Monitoring System (PEMS) equipment and artificially loaded with ballast representing a 70% passenger load. Multiple trips were conducted in normal traffic during business hours, stopping at regular bus stops in a similar manner to the normal passenger service.

Instrumentation of the exhaust systems was entirely within the vehicle profile for testing on public roads

Jon Andersson, manager of after-treatment and chemical analyses at Ricardo UK, said: “The results of this additional study challenge the conventional received wisdom that newer vehicles are always better in terms of their emissions.”

He also added that there was “some scope for improvement of the installed system” on the Euro III retrofit bus”.

Mr Andersson said: “As bus operators attempt to balance their fleet replacement cycles with the imperative to reduce pollution and hence improve urban air quality, the optimal use of retrofit clean technologies of this nature may be an attractive and highly effective alternative to the early replacement of older vehicles. Local authorities are examining the potential of such retrofit solutions in the rules governing future Low Emissions Zones, as these may provide a highly practical path to reducing emissions at source.”