Hydrogen Generation from Plasmatron Reformers: a Promising Technology for Nox Adsorber Regeneration and Other Automotive Applications

Plasmatron reformers are being developed at MIT and ArvinMeritor [1]. In these reformers a special low power electrical discharge is used to promote partial oxidation conversion of hydrocarbon fuels into hydrogen and CO. The partial oxidation reaction of this very fuel rich mixture is difficult to initiate. The plasmatron provides continuous enhanced volume initiation. To minimize electrode erosion and electrical power requirements, a low current, high voltage discharge with wide area electrodes is used. The reformers operate at or slightly above atmospheric pressure. Plasmatron reformers provide the advantages of rapid startup and transient response; efficient conversion of the fuel to hydrogen rich gas; compact size; relaxation or elimination of reformer catalyst requirements; and capability to process difficult to reform fuels, such as diesel and bio-oils. These advantages facilitate use of onboard hydrogen-generation technology for diesel exhaust after-treatment. Plasma-enhanced reformer technology can provide substantial conversion even without the use of a catalyst. Recent progress includes a substantial decrease in electrical power consumption (to about 200 W), increased flow rate (above 1 g/s of diesel fuel corresponding to approximately 40 kW of chemical energy), soot suppression and improvements in other operational features.. Plasmatron reformer technology has been evaluated for regeneration of NOx adsorber after-treatment systems. At ArvinMeritor tests were performed on a dual-leg NOx adsorber system using a Cummins 8.3L diesel engine both in a test cell and on a vehicle. A NOx adsorber system was tested using the plasmatron reformer as a regenerator and without the reformer (i.e., with straight diesel fuel based regeneration as the baseline case. The plasmatron reformer was shown to improve NOx regeneration significantly compared to the baseline diesel case. The net result of these initial tests was a significant decrease in fuel penalty, roughly 50% at moderate adsorber temperatures. This fuel penalty improvement is accompanied by a dramatic drop in slipped hydrocarbon emissions, which decreased by 90% or more. Significant advantages are demonstrated across a wide range of engine conditions and temperatures. The study also indicated the potential to regenerate NOx adsorbers at low temperatures where diesel fuel based regeneration is not effective, such as those typical of idle conditions. Two vehicles, a bus and a light duty truck, have been equipped for plasmatron reformer NOx adsorber regeneration tests. INTRODUCTION In order to meet stringent US emissions regulations for 2007-2010 diesel vehicle model years, after-treatment technology is being developed. Both particulate and NOx emissions after-treatment technology will be necessary, as it seems that engine in-cylinder techniques alone will be unable to meet the regulations. The purpose of the present work is to develop hydrogen based technology for addressing after-treatment issues. In this paper recent developments in both the technology for on-board generation of hydrogen as well as applications to NOx aftertreatment issues will be discussed. Potential on-board generation of hydrogen from renewable energy biofuels for the transportation sector is also discussed.