Comparative Particulate Trap Performance Using Fischer-Tropsch and Conventional Diesel Fuels in a Modern CI Engine

Increasingly stringent emissions regulations aimed at drastically reducing particulate emissions from diesel engines pose one of the greatest challenges to diesel engine development today. Furthermore, engine manufacturers are finding it more and more difficult to comply with these new regulations through in-cylinder optimization alone. As a result, exhaust after-treatment systems, namely diesel particulate traps, present additional means for meeting these strict requirements. A previous study demonstrated the potential for diesel particulate emissions reduction using neat Fischer-Tropsch (F-T) fuel and blends. The absence of sulfur in F-T fuels permits the use of more aggressively catalyzed traps, as sulfur poisoning is not an issue. Furthermore, the reduced particulate emissions of F-T fuels leads to increased time between trap regenerations, which in conjunction with advanced catalyst formulations reducing the temperatures required to initiate regeneration, may provide substantial improvements in trap durability and performance. However, the deposition of particulates from F-T fuels on the trap substrates and loading and regeneration of the trap with F-T particulates and F-T fuel have not been adequately addressed. In this study a 2002, six-cylinder, 5.9 liter, Cummins ISB 300 diesel engine, outfitted with a fully instrumented particulate trap, was subjected to a subset of the Euro III 13-mode test cycle under steady-state operating conditions. In order to investigate the fundamental fuel effects on particulate trap loading characteristics, un-catalyzed Cordierite substrates were loaded with particulates generated from neat F-T diesel and a low sulfur diesel (LSD). Trap temperature, pressure drop, particulate emissions, and gaseous exhaust composition were monitored before and after the trap. The use of F-T fuel significantly extended the trapping period and reduced the regeneration frequency as compared to the LSD. Based on the differences in emissions and fuel composition, explanations for the observed differences in the trap performance were developed.