Exhaust emissions of a H_2-enriched heavy-duty diesel engine equipped with cooled EGR and variable geometry turbocharger

摘要

This paper investigates the impact of hydrogen (H_2) addition on the exhaust emissions of a 2004 Mack MP7 355E heavy-duty diesel engine. As expected, the addition of H_2 reduced substantially the emissions of paniculate matter (PM), unburned hydrocarbon (HC), and carbon dioxide (CO_2). However, the effects of H_2 addition on the emissions of carbon monoxide (CO) and oxides of nitrogen (NO_x) depended on the amount of H_2 added and engine load. For measurements using the 13-mode European Stationary Cycle (ESC), the addition of 2% and 4% H_2 (vol.% in intake mixture) increased substantially the nitrogen dioxide (NO_2) emissions but reduced the emissions of nitric oxide (NO). The addition of H_2 only minimally affected NO_x emissions. The detailed effects of H_2 addition on the exhaust emissions were investigated for various loads at 1200 rpm. The addition of H_2 at low load mildly influenced NO_x emissions, with the exception of 10% load. Adding over 4% H_2 at 10% load began to reduce NO_x emissions. When operated at medium to high loads, the addition of a relatively small amount of H_2 slightly reduced NO_x emissions. The expected increase in NO_x emissions was observed only with the addition of a large amount of H_2 at medium to high loads. When operated at full load, the addition of H_2 had a negligible effect on NO_x emis sions. In a few cases, a minor change in H_2 flow rate suddenly increased NO_x emissions. By further increasing or reducing the amount of H_2 added, NO_x emissions resumed to the expected values. This dis crepancy was attributed to the unexpected change in the flow rate of the recirculated exhaust gas. Based on the data obtained, it seems infeasible to substantially reduce the exhaust emissions of this diesel engine through the addition of a small amount of H_2 such as that produced on-board using a small H_2O electrolyzer, or diesel fuel reformer.