Onboard Hydrogen Generation for IC Engine Emissions Reduction

Abstract

Improvement of internal combustion engine emissions and performance by the introduction of a reducing gas such as hydrogen has been the subject of research in recent years. The approach reduces engine exhaust emissions and improves fuel consumption. The gas may be introduced into the engine intake or upstream of the exhaust catalyst for different effects. To date, the technique has not been implemented due to the need for onboard storage or generation of hydrogen that complies with suitability for automotive applications. In industrial processes and stationary applications, reforming reactors are well known, highly efficient, and durable means to convert liquid fuels such as diesel into hydrogen or other reducing gas mixtures (synthesis gas). Efficiency and durability for thousands of hours is required for these applications for economic viability. For an automotive application, however, in addition to the above features, fast transient response (e.g. during start up and turndown), compactness, and low cost are also required — while maintaining sufficient durability for the application. Also, the need for liquid water common to reactions such as steam reforming or auto-thermal reforming are impractical for automotive applications. A waterless catalytic partial oxidation approach avoids this shortcoming but is not without its own set of problems. Material durability, fuel/air mixing, coke avoidance and reliable ignition means are among the challenges for a practical automotive hydrogen production solution. The catalyst for reacting the fuel must be tolerant to sulfur content common to fuels in use today, and must have resistance to fouling by carbon formation. To overcome these challenges, Precision Combustion, Inc. (PCI) has developed a diesel-fueled waterless catalytic partial oxidation reformer with efficiency and size suitable for onboard synthesis gas production at low cost. The goal of the development effort was to produce a novel mechanical design with the high efficiency of stationary reformers in a small package which could be operated with low parasitic loss from balance of plant components to maintain high engine efficiency. The reactor design (size, form factor) is discussed, along with performance data showing transient and steady state response of the prototype reactor. Catalytic partial oxidation (CPOX) of heavy fuels such as diesel poses unique challenges, relating to coking and fuel conversion efficiency, which have been addressed and presented in this paper.