Characterizing emission rates of regulated and unregulated pollutants from two ultra-low NOx CNG heavy-duty vehicles

In this study, a goods movement vehicle equipped with the ISX12N 400 near-zero natural gas engine and a yard tractor equipped with the B6.7 N 240 near-zero natural engine were evaluated over different test cycles on a chassis dynamometer. Both vehicles were operated stoichiometrically and equipped with a three-way catalyst (TWC). Experiments emphasized on nitrogen oxide (NOx) emissions, greenhouse gases (GHGs), and particulate emissions. Results showed substantially low levels of NOx emissions of both vehicles and dramatic reductions of up to 90% compared to the 2010 certification standard. The cold-start period did not influence the overall NOx emissions, suggesting that real-world NOx formation during cold-start will not contribute to ground level ozone considering the vocations of these vehicles. Carbon monoxide (CO) emissions were found at relatively high levels. Solid particle number emissions from both vehicles were seen to be above the European particle number limit, indicating that current natural gas engines could be an important source of nanoparticles, especially those of the sub 23 nm range. Both vehicles demonstrated elevated methane (CH4) and ammonia (NH3) emissions. Nitrous oxide (N2O) and NH3 emissions were largely dependent of the cold-start fraction of the test cycles, showing greater concentrations compared to the hot-start tests.