Development of an "On-Board On-Demand" Fuel Reformer for Diesel Exhaust

Aftertreatment and Other Applications

Background

Passenger car Tier 1 suppliers have manufacturing capacity 30% over demand. An alternative to closing plants is to apply core competencies and manufacturing capabilities to new products and new markets. To this end ArvinMeritor will apply their automotive sector exhaust emissions control expertise to diesel truck emissions after-treatment.

Diesel truck emissions after-treatment is a highly promising market segment because 2007 federal regulations significantly reduce allowable emissions of NOx andparticulate matter requiring after-treatment devices similar to catalytic converters. One promisingtechnology is using plasma to reform diesel fuel for regenerating NOx traps.

Plasma technology hasquick response times to handle transient operating conditions, provides effective NOx conversion atthe lower temperatures typical of diesel engine exhaust, and is more fuel efficient than other technologies. Working with PurdueUniversity to improve the fuel spray mixing and combustionprocesses, ArvinMeritor will complete the final development of a plasma fuel reformer anddemonstrate the superiority of this technology on vehicles operating in various duty cycles.

The fuel reformer consists of an air-blast atomizer located on the axis, and at the upstream end, of a plenum. A flow of air is fed into the plenum, also at its upstream end. The spray and air flows travel down the plenum until they interact with a high-voltage, non-thermal plasma. The interaction of the plasma with the air-fuel mixture initiates fuel reforming reactions using a partial oxidation process resulting in the production of H2 and CO.

Current computational codes developed at Purdue allow accurate simulation of the swirling, burning flow field. These codes require comprehensive data that describes the droplet and surrounding gas fields as inputs. In particular, drop size distributions, local gas-phase velocities, and local vapor-phase concentrations are necessary for accurate simulations. The goal of this aspect of the research is to supply that experimental data.

Experimental spray research

The experimental data will take three forms: drop size distributions, location of the vapor boundary at the edge of the spray, and gas-phase flow field mapping outside the spray.

Drop size distribution measurements will be made using a commercial forward-light scattering (diffraction) instrument—a Malvern 2600 Spray Analyzer. This type of instrument has been used by 18 graduate and 5 undergraduate students in the PIs laboratory over the past 20 years and provides ensemble averaged drop size distribution data obtained along a line-of-sight through the spray. Results can be reported as either an average over a plane perpendicular to the spray symmetry axis or, in the case of axisymmetric sprays, as a radial distribution by deconvoluting the line-of-sight measurements using standard mathematical techniques (the so-called Abel inversion).

Measurements will be made at a number of radial locations at each of several axial stations downstream of the atomizer, and then compared to model predictions. Instrument spatial resolution will be adjusted by decreasing the Malvern laser beam diameter from the typical 9 to 1 mm, as was done by Miles et al [1990]. In addition, if significant evaporation is present the correction techniques developed by the PI and his students at Purdue will be employed [Miles et al., 1990; Pietsch et al., 1992].

The location of the vapor boundary produced when fuel droplets evaporate will be determined using schlieren photography and shadowgraphy. Both techniques locate variations in the index of refraction of a system, and are therefore sensitive to compositional (fuel-air) variations at the spray perimeter. This approach has been used by the PI in several studies, most notably by Richards et al. [1987], Richards and Sojka [1990], Jardine et al., [1990], Buckner et al. [1991], and Stapleton and Sojka [1991]. Again, results can be reported as either line-of-sight data, or can be deconvoluted in the case of axisymmetric sprays to yield radial variations, prior to comparison with model predictions, after which they are compared to model predictions.

The gas flow field will be mapped using particle image velocimetry (PIV). PIV provides complete (planar) pictures of the flow field surrounding a spray at any instant in time. It is therefore useful when determining velocity fields and structural features. Recent examples of data acquired using this instrumentation include Pande et al. , Plesniak et al. [2002], and Shu et al. [2002]. Results will be provided at various planes throughout the spray such that the full three-dimensional velocity field can be compared to computational predictions.

References

Buckner, H.N., Jardine, K..J., and Sojka, P.E., "Effervescent Atomization of Highly Viscous, Multiphase non-Newtonian Fluids," 1991 International Fine Particle Research Institute Annual Meeting, Albuquerque, NM (June 1991).

Jardine, K.J., Buckner, H.N., and Sojka, P.E., "Spray Formation via Effervescent Atomization," 1990 International Fine Particle Research Institute Annual Meeting, Karlsruhe, West Germany (May 1990).

Miles, B.H., Sojka, P.E., and King, G.B., "Malvern particle size measurements in media with time varying index of refraction gradients," Applied Optics, 29(31), 4563-4573 (1990).

Pande, A., S.H. Frankel, M.W. Plesniak, and P.E. Sojka, “Numerical Modeling and Simulation of Paint Spray Transfer Efficiency,”

Pietsch, R.A., King, G.B., and Sojka, P.E., "Correcting Malvern Particle Size Measurements for Phase Distortion," Atomization and Sprays,2(2), 73-85 (1992).

Plesniak, M.W., F. Shu, P.E. Sojka, S.H. Frankel, "Flow Control and Design of Environmentally Benign Spray Systems,” (invited paper) Technology for a Sustainable Environment (TSE) session, Annual American Institute of Chemical Engineers (AIChE) 2002 Conference, November 3 – 8, 2002, Indianapolis, Indiana, 2002.

Richards, G.A., Sojka, P.E., Lefebvre, A.H., "Heterogeneous Flame Speeds with Hydrogen Addition," paper no. 67, Central States Section Combustion Institute Conference, Argonne, IL (May 1987).

Richards, G.A. and Sojka, P.E., "A Model of H2-Enhanced Spray Combustion," Combustion and Flame, 79, 319-332 (1990).

Stapleton, S.E. and Sojka, P.E., "The Effect of Shock Structure on the Performance of an Effervescent Atomizer," poster session paper no. 35, Fifth International Conference on Liquid Atomization and Spray Systems, Gaithersburg, MD (July 1991).

Shu, F., M. W. Plesniak, and P.E. Sojka, "Structure of an Impinging Jet Issuing from a Nozzle of Indeterminate Origin with Applications to Improving Transfer Efficiency for Spray Systems,” 2002 Painting Technology Workshop (PTW2002), LexingtonKY, June 25-26, 2002.