UC Riverside

Heavy duty on-road vehicles represent one of the largest sources of NOx emissions and fuel consumption in North America. Heavy duty vehicles are predominantly fueled with diesel, with the recent interest in natural gas (NG) systems. As emissions and greenhouse gas regulations continue to tighten new opportunities for advanced fleet specific heavy duty vehicles are becoming available with improved fuel economy. NOx emissions have dropped 90% for heavy duty vehicles with the recent 2010 certification limit. Additional NOx reductions of another 90% are desired for the South Coast Air basin to meet its 2023 NOx inventory requirements and the California optional low NOx standard in 2015.

One of the difficulties in quantifying NOx emissions at the levels proposed in this research (90% of the 2010 certification level ~ 0.02 g/bhp-hr) is the measurement methods are approaching their detection limit to sufficiently quantify NOx emissions. Three upgraded NOx measurement methods were considered which include a raw NOx measurement integrated with real time exhaust flow, a real-time ambient correction approach, and a trace level ambient analyzer for accurate bag analysis. In summary the improved methods varied in their success where the raw sampling approach showed to be the most accurate and precise over the rage of conditions tested.

The ISL G NZ 8.9 liter NG engine met and exceeded the target NOx emissions of 0.02 g/bhp-hr. This engine significantly reduced 97%-100% of NOx emissions compared with previous ISL G 8.9 engines. The NOx emissions decreased as the duty cycle was decreased which was the opposite trend for the diesel vehicles. It is expected NG vehicles could play a role in the reduction of the south coast NOx inventory problem given their near zero emission factors demonstrated.