EXHAUST EMISSIONS OF A H2-ENRICHED HEAVY-DUTY DIESEL ENGINE EQUIPPED WITH COOLED EGR AND VARIABLE GEOMETRY TURBOCHARGER

This paper investigated the effect of hydrogen (H-2) addition on the exhaust emissions of a 2004 Mack MP7 355E diesel engine. As expected, the addition of H-2 substantially reduced the emissions of particulate matter (PM), unburned hydrocarbon (HC), and carbon dioxide (CO2). However, the effect of H-2 addition on the emissions of carbon monoxide (CO) and nitrogen oxide (NOx) depended on the amount of H-2 added and the engine load. When preliminarily measured using the 13-mode European Stationary Cycle (ESC), the addition of 2% and 4% (vol. % in intake mixture) H-2 significantly increased nitrogen dioxide (NO2) emissions and slightly reduced nitric oxide (NO) emissions. In comparison, the H-2 addition only minimally affected NOx 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 emissions, with the exception of 10% load operation. Adding over 4% H-2 at 10% load began to reduce NOx emissions. When operated at medium to high load, the addition of a relatively small amount of H-2 slightly reduced NOx emissions. The expected increase in NOx emissions was observed only with the addition of a large amount of H-2. When operated at full load, the addition of H-2 had negligible effect on NOx emissions. In a few cases, a minor change in H-2 flow rate suddenly increased the emissions of NOx. By further increasing or reducing the amount of H-2 added, NOx emissions resumed to their expected values. This discrepancy was attributed to the unexpected change in EGR flow rate. Based on the data obtained, it seems infeasible to substantially reduce the exhaust emissions of diesel engine through the addition of a small amount of H-2 such as that produced on-board using a small H2O electrolyzer.