Testing the pollutant emissions and fuel efficiency of a commercial bus in India
As part of ICCT’s ongoing effort to better understand the real-world performance of heavy-duty vehicles (HDVs) in India, we designed and managed a testing program of an HDV engine and chassis at the International Centre for Automotive Technology in Gurgaon, India, between fall 2016 and spring 2018. The 7.5-tonne Bharat Stage (BS) IV commercial bus selected is a top-seller in its segment, and the vehicle’s 3.8-liter diesel engine is the second most prevalent engine displacement size in the on-road commercial vehicle market in India.
As this working paper details, tests showed lower aftertreatment system efficiencies for hydrocarbons, carbon monoxide, and particulate matter (PM) conversion during the cold start tests as compared to hot start tests. These characteristics are mostly attributable to manufacturer calibration strategy, and that strategy is expected to change significantly when vehicles are calibrated for BS VI standards, where cold start emissions are weighted 14%. Regarding emissions of nitrogen oxides (NOx), rates from the transient chassis dynamometer runs ranged from 4.3 to 5.4 grams (g)/kilowatt hour (kWh), and that is similar to what was observed from the engine-based results, 3.9 to 5.6 g/kWh. Thus results from both the engine (European Stationary Cycle and European Transient Cycle only) and chassis testing, which are illustrated in the figure below, suggest the vehicle’s real-world NOx emissions are up to 15% and 55% higher, respectively, than what would be expected if the engine was fully compliant with BS IV standards. Given that this new, low-hour engine showed such variability in repeated transient tests on the chassis dynamometer, there are concerns about the effects of the dynamic conditions such as grade, weather, and traffic that are encountered in use.
To comply with the more advanced BS VI standards, most manufacturers will introduce entirely new aftertreatment technologies for controlling NOx and PM emissions. For regulators, this makes the need for independent testing that much more acute. The tests need to examine a wide range of engine models and sizes across the heavy-duty spectrum in India to better understand the distribution of emission levels and how emission control systems are performing under real-world conditions. This is especially important when it comes to measuring NOx emissions.