One of the most challenging issues for building sustainable cities is the improvement of municipal solid waste (MSW) management, which requires a substantial effort to reduce its production and improve its collection, transport and treatment systems.
Modern (Euro VI) heavy-duty vehicles have significantly lower emissions compared to older vehicles. However, there are still concerns regarding the emissions of refuse collection vehicles in cities, because they use engines designed for long haulage trucks and consequently not optimised for low speed stop and start driving. The very low average speeds and the frequent stops represent difficult conditions to cope with from the emission reduction perspective. In fact, for short periods, where the exhaust gas temperature is low for the aftertreatment devices (cold start, some city conditions), the emissions are relatively high.
In an effort to provide insight on the optimal future planning and renewal of the Milan waste collection vehicle fleet, the Joint Research Centre (JRC) of the European Commission (EC), in collaboration with the Azienda Milanese Servizi Ambientali (AMSA), initiated an on-road emission testing campaign. The aim of this extensive experimental study, performed both under real and laboratory controlled operating conditions was to identify the actual emission levels of the waste collection vehicles, comparing two different engine technologies (diesel and natural gas fuelled engines) and assess the environmental efficiency of the different engines solutions.
For this purpose, we tested a Diesel Euro VI step C and a Compressed Natural Gas (CNG) Euro VI step C refuse collection heavy-duty vehicle both in the laboratory and on the road using a cycle similar to the in-service conformity (ISC) trips for this type of vehicles (N3). The vehicles were also tested using actual refuse collection cycles. The idea was to directly compared the two vehicles’ engine technology to evaluate the performance and the pollutant emissions under realistic and controlled operating conditions in order to support a fleet renewal initiative in the city of Milan. Particle and gaseous pollutants were measured using a Portable Emissions Measurement System (PEMS). Additionally, in the laboratory we used laboratory grade gaseous, particle number and FTIR (Fourier-transform infrared spectroscopy) systems to measure the emissions and check the proper operation of the PEMS.
The present work summarizes the results of the aforementioned experimental activity lead on two vehicles (one Diesel and one Compressed Natural Gas), which were tested in three different phases using a portable emission measurement system. The first phase included a similar In-Service Conformity test (ISC_LIKE) and a city simulation cycle (CITY_SIM), the second part involved real world operation in the city of Milan, whilst a third phase was dedicated to the comparison lab test in confined conditions. This report will address only the road comparison, while the laboratory tests and the relative comparison together with the real world findings will be object of a future report.
Focusing on CITY_MILAN cycle, which is the most representative of the real in-use conditions, THC calculated emission factors were two orders of magnitude lower in Diesel engine (0.79 mg/kWh) than in CNG (73.49 mg/kWh), even if we have to consider a different limit for CNG engines. Continuing with the analysis of “Urban” routes, CNG truck showed NOX emission nearly 4 times higher than the Diesel (755.31 mg/kWh vs 157.10 mg/kWh), exceeding the reference limits. The CNG engine PN levels were 3 times higher than in Diesel one. Including also the regeneration events in the Diesel vehicle, the emissions increased the PN significantly, but it still remained below the limit of 6×10^11 particle/kWh. In the metropolitan cycle (CITY_MILAN) CNG truck has a CO emission reduction of -85 % compared to the Diesel one, with respectively 40.92 and 320.30 mg/kWh. Nevertheless, CO emissions of both tested vehicles appear to be at very low levels, abundantly below the reference limits (4000 mg/kWh). This trends did not vary significantly among the different routes.
In general, Diesel technology presented important advantages with regards to the NOX, PN, CO2 emissions as compared to the CNG engine, while the CNG vehicle provided a better CO emission behaviour.
This trade off needs to be carefully analysed prior to decide if a fleet should be shifted towards either technology, mainly because is based only to a limited comparison between the two considered vehicles. Therefore, the conclusions drawn in this report are only valid for the tested vehicles and they cannot be extrapolated or generalised for a larger fleet of vehicles.JRC.C.4 - Sustainable Transpor
