PIV ON THE FLOW IN A CATALYTIC CONVERTER

Transcription

1 PIV ON THE FLOW IN A CATALYTIC CONVERTER APPLICATION NOTE PIV-016 The study and optimization of the flow of exhaust through a catalytic converter is an area of research due to its potential in increasing engine performance and decreasing noxious pollutants released into the environment. Catalytic converters have proven to be reliable and effective in reducing noxious tailpipe emissions, and therefore most automobile spark-ignition engines in North America have been fitted with catalytic converters since 1975, and the technology used in non-automotive applications is generally based on automotive technology. The negative aspects of using catalytic converters are generally perceived to be suppressed vehicle performance and lower fuel economy. Having a better understanding of the exhaust flow within the converter can help designers optimize key parameters in order to maximize engine performance and fuel economy, while still decreasing the release of noxious chemicals. Particle Image Velocimetry (PIV) is one such technique that can be used to investigate the flow of gasses through the catalyst. Several tests were run on the flow through a catalytic converter. The first used stereopiv on a mock setup in the lab looking at the flow at the exit of the converter into the atmosphere. The second setup was 2D PIV and run on a transparent converter attached to a motorcycle that was actually running. Experimental Setup and Results (StereoPIV) Figure 1 shows an image of the experimental setup. The catalytic converter was mounted to a post with water vapor forced through it generated by an ultrasonic humidifier. The 4MP cameras were mounted in a Scheimpflug configuration approximately 300mm downstream of the outflow exit. The 200 mj Big Sky laser (not visible in Fig. 1) was to the left of the image, and the laser sheet illuminated droplets in the plane parallel to the exit of the converter. The model synchronizer can also be seen in the image and was used to control the timing of the laser pulses and camera image capture. The system was calibrated by putting a 2-plane calibration target aligned with the laser light sheet in the measurement region of interest. The cameras were focused and aligned on the target, and calibration images were taken and analyzed in order to establish a set of dewarping polynomials allowing the mapping of information from both cameras onto the same plane. Data was taken on 4 separate measurement planes; therefore the calibration was repeated 4 times, once for each measurement plane.

2 Fig. 1. Experimental setup for the stereopiv configuration. StereoPIV gives 3-components of velocity information in a plane, and 4 planes were taken: immediately after the exit, 25mm downstream, 50mm downstream, and 100mm downstream. Data from a set of captures can be seen in Fig. 2. Regions shown in red indicate higher velocity through the plane of measurement. In the case shown, a region of higher out-of-plane velocity can be seen in the upper left corner of the plots, as seen from downstream.

3 Fig. 2. Data shown is from the 4 planes in which measurements were taken. The coloring represents velocity out of the plane, with red indicating regions of higher velocity. Experimental Setup and Results (PIV) A motorcycle was modified in order to have an extended exhaust pipe from the engine to the catalytic converter which was cylindrical and had its center portion made of glass for optical viewing. The inlet tube and diffuser were steel and the modified parameter in these experiments was the diffusion angle of 15 and 60. A schematic representation of the two configurations can be seen in fig. 3. The green region represents the PIV field of view, which was just upstream of the mesh catalyst. After the catalyst, the walls converged again to enter the muffler. A 4MP camera, a 200 mj laser, and a TSI model# synchronizer were used for the PIV measurements. Seed particles were introduced into the flow using a TSI model# 9306 atomizer. The atomizer was filled with a 50/50 water/glycerine mixture, and 4 micron titanium dioxide seed particles (TSI model# 10086A) were added. The glycerine helped keep the titanium dioxide particles in suspension until they were atomized, and the titanium dioxide particles are very robust in order to survive the combustion process in the engine. The seeding was guided from the 9306 via Tygon tubing to the air inlet port of the engine.

4 Fig. 3. Schematic representation of the Field of View of the PIV camera (green), and location of the catalyst, as well as the diffuser geometry 60 (top), and 15 (bottom). The motorcycle was operating and firing at 50 km/hr during the testing, and phase-locked PIV measurements were made in steps of every 2 ms from top-dead-center (TDC). An instantaneous velocity field can be seen in fig. 4 from each of the two cases at a delay time of 6 ms from TDC. The color contour in the plots represents streamwise velocity, with red indicating high speed exhaust to the right, and blue indicating negative flow to the left. Vectors are overlaid on the contours, indicating the local flow direction. Fig. 4. Instantaneous velocity fields from the 60 case (left) and the 15 case (right) taken at 6 ms delay from TDC. Color represents stream-wise velocity, and the vectors show the local flow velocity. The striking difference between the 60 and 15 cases is the presence of a strong jet of exhaust at the center of the converter for the 60 case (left) that causes a large vortex ring to form. The peak velocity of the eshaust near the center exceeds 120 m/s, and there exists backflow of -20 m/s around the periphery. By contrast, the 15 case (right) shows more diffuse velocities, with peaks closer to the outer core of approximately 50 m/s, with little, if any, backflow. A further vector field can be seen in fig. 5 at a delay of 30 ms. This phase represents the highest velocity seen in the 15 case (right) of all the phases captured, which is about m/s in a small region of the flow near the center. As shown previously, the 60 case continues to exhibit velocities greater than 100 m/s near the center of the converter.

5 Fig. 5. Instantaneous velocity fields from the 60 case (left) and the 15 case (right) taken at 30 ms delay from TDC. Color represents stream-wise velocity, and the vectors show the local flow velocity. The results of the diffusion angle testing indicates that the more gradual diffuser angle of 15 allows for a more uniform velocity distribution across the cross-section of the converter as opposed to the 60 case, where the flow entering the converter is much more jet-like, creating a large velocity distribution across the field of view. The steep 60 angle causes flow separation along the walls of the converter resulting in back-flow and a less efficient flow pattern for passing exhaust through the catalyst and out of the system. TSI Incorporated Visit our website for more information. USA Tel: UK Tel: France Tel: Germany Tel: India Tel: China Tel: Singapore Tel: PIV-016 Rev. A 2012 TSI Incorporated Printed in U.S.A.