CBET Award Achievements
Notable Accomplishments from CBET Awards

Cleaning up Diesel Exhausts by Understanding Nanoreactivity

Andre Boehman, Pennsylvania State University

Background:  Diesel engines are notorious for producing sooty exhausts, forcing particulate filters to be required on all diesel cars, trucks and buses.  Diesel particulate filters are designed to filter the soot without hindering the exhaust flow, but as soot accumulates, air flow is reduced.  This effect requires filters either to be replaced or cleaned in place (regenerated).  Regeneration is more efficient because it allows continuous service.

To develop a more efficient regeneration process, this research focused on developing fundamental knowledge of the behavior of soot nanoparticles.  The research developed a fundamental understanding of how diesel smoke is affected by combustion conditions and fuel formulation, as well as how the resulting variations in nanoparticulate composition and structure then influence the chemistry of oxidative destruction.  With this knowledge, the researcher was able to develop a self-cleaning diesel particulate trap using lower exhaust temperatures to initiate regeneration, eliminating the need for active control of the particulate trap system.

Results:  In a major research advance, the PI determined how operating conditions can be modified to tailor the reactivity of diesel soot and enhance exhaust clean-up.  Perhaps even more importantly for further research and technological development, he also developed a technique for generating soot samples in small experiments that are similar to soot from large, practical devices, based on the uniform trends that have been detected across different combustion experiments.

The research showed that lowering combustion temperature via EGR provides greater disorder in the soot and thereby provides more active internal soot surface for oxidation, thus enhancing oxidation rates that must occur during filter regeneration.  Characteristics of soot samples were examined in detail from simulated and actual exhaust gas recirculation (EGR) conditions.  These samples were generated in very different systems: a laboratory ethylene diffusion flame; a single-cylinder, naturally aspirated, direct-injection diesel engine; and a four-cylinder, direct-injection, locomotive turbodiesel engine under simulated and real EGR conditions.  By controlling experimental conditions tightly, the researcher found the dilution, chemical, and thermal effects that exert the greatest influence on soot nanostructure and reactivity.  Electron microscopy showed burning within the particles, and measurements of engine-soot weight during oxidation confirmed the enhancement.  Trends in the surface area available for reaction were consistent regardless of the testing apparatus or system.

Andre Boehman Image A   Andre Boehman Image B

A.  Unreacted soot
      (dp = 30 nm)

B.  25% partially oxidized soot
      (dp = 29.28 nm)

Andre Boehman Image C   Andre Boehman Image D

C.  50% partially oxidized soot
      (dp = 26.73 nm)

D.  75% partially oxidized soot
      (dp = 25.74 nm)

Images Credit:  Khalid Al-Qurashi and André L. Boehman, Pennsylvania State University

Scientific Uniqueness:  This study used a unique combination of elementary flame studies, combustion studies in a practical engine, and extensive characterization of soot nanoparticles by electron microscopy and other techniques.  The linking of practical combustion conditions to nanoscale structural changes in diesel soot proved vital to understanding how diesel soot reactivity can be enhanced.

Work is notable because diesel particulate filters are required on all diesel cars, trucks and buses as of 2007.  This project is developing the science needed to improve this crucial emission control technology.

Work is broadly multidisciplinary: because it combines combustion engineering (internal combustion engines) with reaction engineering and materials science.

The research used characterization facilities of Penn State’s Materials Research Institute, home to the NSF-sponsored Nanofabrication Laboratory and the Materials Research Science & Engineering “Center on Collective Phenomena in Restricted Geometries.”

This project addresses the strategic outcome goals, as described in the NSF Strategic Plan 2006-2011, of:

(1) Discovery:  Because this project addresses an area of national importance that addresses energy and environmental technology and can provide valuable fundamental knowledge that can be immediately used by industry, this project directly addresses the strategic outcome goal of Discovery.

(2) LearningTwo graduate students are involved in conducting the research: Khalid Al-Qurashi and Kuen Yehliu.  Their participation provides substantive learning of research methods, analysis, and communication skills.

This Nugget represents transformative research.  The work points science in a new direction by showing that reactivity at the nanoscale can be modified by particle-formation conditions and that it impacts reactivity at the macroscale. Furthermore, by providing the supporting science to push through a technological barrier, the work is transformative technologically.

This Nugget represents Broadening Participation.  The co-PI is Angela Lueking, member of an underrepresented group (women).

Impact on Industry and/or Society:  Air quality of both streets and skies will be improved by making low-emission diesel vehicles possible.  More subtly, the higher efficiency of these vehicles will reduce both fuel usage and CO2 emissions, both of which are societally important.

Potential economic impact is high because fuel savings on diesel cars, buses and trucks will result from reducing the burden of regenerating diesel particulate filters.  By enhancing the reactivity of the diesel particulate matter, the fuel economy penalty associated with incorporation of diesel particulate filters may be reduced along with the complexity of the control system for regeneration.

Program Officer:   Phillip R. Westmoreland
NSF Award Number:   0553339
Award Title:   Using Fuel and Combustion Conditions to Alter the Nanostructure and Reactivity of Diesel Soot
PI Name:   Andre Boehman
Institution Name:   Pennsylvania State University
Program Element:   1407

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This Nugget was Approved by ENG on 15 April 2008.