Browse Publications Technical Papers 2019-01-0751
2019-04-02

ULTRA-LOW NOX MEASUREMENT AND EMISSION FACTORS EVALUATION OF TWO COMPRESSED NATURAL GAS (CNG) HEAVY-DUTY ENGINES 2019-01-0751

Heavy duty on-road vehicles represent one of the largest sources of NOx emissions and fuel consumption in North America. NOx emissions dropped 90% for heavy duty engines with the 2010 certification limit, but it is expected that additional NOx reductions of another 90% are needed in the Los Angeles area to meet its 2023 NOx inventory requirements, which led to a California optional low NOx standard of 0.02 g/bhp-hr in 2015. Recently there has been increased interest in natural gas (NG) engines as a strategy to reduce emissions, particularly at the 0.02 g/bhp-hr NOx level. The emissions of two heavy-duty vehicles equipped with 0.02 g/bhp-hr low NOx NG engines were evaluated on a chassis dynamometer. This included a refuse hauler and a transit city bus, each with a 0.02 g/bhp-hr ISL G NZ 8.9 NG engine. The vehicles were tested over a variety of different cycles, including the Urban Dynamometer Driving Schedule (UDDS), drayage cycles, transit bus cycles, and a refuse truck cycle. For both vehicles, the NOx emissions results were below the 0.02 g/bhp-hr level for most cycles, with the exception of some tests during the cold start mode. For the refuse hauler, NOx emissions averaged between 0.014 and 0.002 g/bhp-hr for the hot start tests, and from 0.043 to 0.014 g/bhp-hr for the cold start tests. This represented NOx emissions reductions from 97%-100% of compared with previous ISL G 8.9 engines. For the transit bus, the NOx emissions ranged from 0.0007 g/bhp-hr to 0.0042 g/bhp-hr for the warm tests and up to 0.04 g/bhp-hr for the cold start test. The NOx results are 99% lower than the existing 2010 NOx diesel standard (0.2 g/bhp-hr) and 90% lower than the optional low NOx standard (0.02 g/bhp-h). In contrast, some elevation of NH3 were observed for both vehicles, due to the presence of the three way catalyst. Overall, the results suggest that ultralow NOx NG engines could play an important role in reducing emissions from heavy-duty vehicles towards near zero levels in urban areas.

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