Characterization of diesel particulate filters requires test methods that permit rapid and accurate assessment of important performance requirements. The operation of the filter is comprised of two primary functions, particle filtering and filter soot regeneration. One challenge facing implementation of diesel filter technology lies with the difficult process of regenerating the filter after accumulating a full complement of soot. This paper will primarily focus on laboratory bench testing methods developed to study the regeneration characteristics of filters under a variety of test conditions.
To rapidly assess the performance of many filters it was important to develop laboratory techniques that approximate engine exposure conditions. A simulated soot loading process and a well-controlled regeneration test method were developed. The simulated soot loading technique utilized carbon black that was entrained in a stream of compressed air passed through the filter to simulate engine soot deposition. The quantity of soot added to the filter was closely controlled in this process. The regeneration technique precisely controlled the inlet exhaust gas temperature, flow rate, and oxygen content to approximate various engine-operating conditions. With precise control over these loading and regeneration parameters, it was possible to experimentally study the response of the filter to various simulated engine-operating conditions. These test methods were meant to provide accurate screening of several filter candidates, and were meant to be a supplement to engine evaluation.
In this study the effect of exhaust gas inlet temperature, oxygen content, flow rate and soot concentration on maximum exotherm temperature and completeness of regeneration was studied. These studies were conducted on two varieties of wall flow filters. One of the filters studied was that of a cordierite material while the other was of a silicon carbide (SiC) composition. An objective of this experiment was to arrive at a set of severe regeneration conditions that could be used to assess filter regeneration durability.
Results indicate that there were many degrees of freedom that could be exercised to control the severity of an exothermic reaction propagating during regeneration. High flow rates, low oxygen contents, optimal inlet exhaust gas temperatures, and limited soot accumulation may all be used to control the severity of the regeneration process.