Impact of Oxidation Catalyst Formulation and Space Velocity on Performance with Conventional and Renewable Fuels

Prior study with biodiesel and its blends with ultra-low sulfur diesel (ULSD) and renewable diesel (RD) showed that a commercial diesel oxidation catalyst (DOC) is unable to effectively oxidize neat biodiesel (B100) or high-level biodiesel blends injected into the exhaust of a diesel engine at challenging conditions of low temperature, high exhaust flow rate and high dosing rate. In steady-state performance tests, the performance of blends up to B50 in ULSD or RD was nearly equivalent to ULSD at the lowest exhaust flow rate or for exhaust temperature over 340°C for medium and high flows. ULSD blends above 50 vol% biodiesel exhibited reduced thermal efficiency and DOC outlet temperature with increasing dosing rate and required exhaust temperatures over 400°C to achieve similar performance as ULSD. For RD blends at higher flow rates and temperatures below 300°C even B10 blends showed some loss in performance at the highest dosing rates. Data showed an increase in lightoff temperature with an increase in biodiesel concentration in both the ULSD and RD blends. Here we conducted a limited study with higher catalyst volume and increased platinum group metal (PGM) loading to see if these factors would improve DOC performance with B100. ULSD, RD and B100 were run on steady-state performance test with the same DOC used previously. To assess the impact of PGM loading and catalyst volume we also used a three-way catalyst (TWC) for comparison to the DOC. The TWC consisted of two bricks and the test was run with one and both bricks to assess the impact of catalyst volume. The data showed that the single brick of TWC was marginally better than the DOC with better light off performance for B100 at low temperatures and exhaust flow rates. The entire TWC (two bricks) was significantly better than the DOC showing marginally better performance at low temperature and exhaust flow rate and significantly improved performance at low temperature and medium flow rate. The additional catalyst volume and higher overall catalyst loading produced better oxidation of B100 even at the most challenging conditions – with increased catalyst volume (increased residence time) have the largest effect.