Working Paper

Real-world emissions performance of a Bharat Stage VI truck and bus

In-service conformity (ISC) tests for heavy-duty vehicles (HDVs) are being introduced for the first time in India with the Bharat Stage (BS) VI regulation. Such tests are meant to make manufacturers more accountable for in-use emissions and to bridge the gap between lab-based emissions and real-world emissions. While the ISC tests are not mandatory until April 2023, the requirements for testing and data processing have been established in Part IV of AIS 137 and the BS VI in-use portable emissions measurement system (PEMS) test will be performed to demonstrate compliance. At present there is little public information about the real-world emissions performance of HDVs in India, and this work aims to address that gap by conducting PEMS tests on two BS VI vehicles, one truck and one bus. ICCT conducted this work with testing partner HORIBA India.

In addition to evaluating emissions based on Part IV of India’s AIS 137 and the Euro VI-D and E provisions, researchers conducted a comprehensive, no-exclusions-based assessment at different engine loads and speeds. Both the truck and the bus were found to be well under the limits for nitrogen oxides (NOx) emissions using India’s AIS provisions. When the Euro provisions were applied, however, the NOx emissions increased for both vehicles and more so for the bus, which showed emissions 1.75 to 2.2 times higher than the WHTC limit, depending on the test parameters (see figure). The opposite was found for particle number (PN) emissions, as the bus had lower PN emissions than the truck on all routes. Note, though, that India’s AIS requirements do not currently include a conformity factor (CF) for PN and the red line in the figure is reflective of a recommended CF of 1.5, which is the same as the CF for NOx.

Overall, results show that India’s AIS provisions have some large gaps to cover when compared with the latest Euro VI-E provisions and do not capture emissions during cold start or urban operations well. For ISC testing in India to capture all emissions from real-world driving, the findings suggest that: (1) the power threshold needs to be lowered to 5%; (2) all cold-start emissions must be included; and (3) the percentile for data evaluations should be increased to 100%.