Plenary Lectures

André Boehman is a Professor of Mechanical Engineering at the University of Michigan.  He joined U-M in 2012 after serving for 18 years at Penn State as a Professor of Fuel Science. At U-M, Prof. Boehman serves as the Director of the Walter E. Lay Automotive Laboratory.  He holds degrees in Mechanical Engineering: a BS from the University of Dayton (1986) and an MS (1987) and PhD (1993) from Stanford University.  He served as the Editor in Chief of the journal Fuel Processing Technology from 2007-2011, and as an Associate Editor for Energy & Fuels from 2016-2019. He is a Fellow of the Society of Automotive Engineers, the American Chemical Society, the American Society of Mechanical Engineers and the Combustion Institute. He received the 2009 John Johnson Award for Outstanding Research in Diesel Engines and the 2009 Arch T. Colwell Merit Award from the Society of Automotive Engineers. He received the 2018 Achievement Award from the U-M Mechanical Engineering Department and both the 2021 Monroe-Brown Foundation Service Excellence Award and 2023 David E. Liddle Research Excellence Award from the U-M College of Engineering.  He also received the 2020 ASME Internal Combustion Engine Award.

Reducing GHG Emissions via Low Carbon Fuels: Challenges and Opportunities

In this talk, we will address the role that low carbon fuels (not strictly “carbon free” fuels, but those with low carbon intensity) can and should play in reducing greenhouse gas emissions.  To some, it seems a foregone conclusion that the days of the internal combustion engine are nearing an end, and that the fastest path to “zero carbon emissions” is through adoption of electric vehicles.  But bringing down fossil carbon emissions immediately can yield tremendous improvements with regard to the climate crisis, in contrast with waiting for electric vehicles to penetrate the market, and electricity production to be deeply de-carbonized.  Widespread and immediate adoption of low carbon intensity renewable fuels can provide dramatic carbon intensity reductions, overnight, when used in the vehicles we drive today.  But both the pursuit of electrification of the transportation sector and adoption of low carbon fuels runs into a major practical challenge – achieving major reductions in reducing fossil carbon emissions at scale.  Replacing 20 million barrels a day of petroleum presents a daunting barrier to addressing the climate crisis.  We will take a realistic look at these questions, and recommend a path forward that uses both strategies.

Professor Rogak is an expert on aerosol measurements and emissions, and over the years his group has investigatged on-road measurements of traffic emissions, particle deposition in diverse environments (from HVAC equipment to supercritical water), and the in-room transport of particles produced by human coughs and sneezes. However, over 3 decades, he has always returned to the topic of the formation and structure of solid nanoparticles that exhibit fractal structures- especially soot. Recent work has focused on the discovery that soot seems to retain structures that correspond to inhomogeneous regions within flames, and this leads to some important enhancements to the decades-old fractal model that is commonly used to model soot. When he is not working on this, he is probably developing teaching labs at UBC or preparing his sailboat for Race to Alaska.

Updates to the Fractal Model of Soot Aggregates

About 15 years ago, my group has noticed that large soot aggregates tend to be composed of large primary particles, and small aggregates are composed of small primary particles.  In the last decade, we have examined this more carefully for thousands of TEM images from a half dozen combustion sources (all non-premixed flames). Most recently, with colleagues from the University of Alberta and the National Research Council of Canada, we investigated the question that perhaps these observations related to morphology affect the optical properties of soot. This work was summarized in work with Jason Olfert,

 https://www.tandfonline.com/doi/full/10.1080/02786826.2019.1577949

The key ideas behind the External Mixing Hypothesis (EMH) described there are that:

1. Most of the coagulation giving rise to the fractal structure occurs over very small spatial and temporal scales and for relatively uniform formation and oxidation conditions.
2. Aggregates from different regions of the flame tend to have different primary particle and aggregate sizes, and the degree of maturity may differ.
3. In the exhaust stream where emissions are typically sampled, the particles from different regions of the flame are mixed within the gas stream but for the most part do not coagulate ie they are “externally mixed”.

 The EMH has implications for the measurement and structural modelling of soot, and probably also for the formation process, although that is not tackled in this talk.  Here, I will review some fundamentals of the fractal models used over 40 years to model soot, then describe updates to the model (from other groups as well as our own), attempting to highlight areas were there still appears to be controversy or work to be done (for example, cases where the EMH probably breaks down).   The material for this talk is gratefully taken from a review article in preparation with Tim Sipkens, Rajan Chakrabarty, Adam Boies, Jason Olfert, Joel Corbin and me.

Sandeep Jella has been a member of the combustion group at Siemens Energy (formerly Rolls-Royce Canada) since 2008, contributing to the design and troubleshooting of injector systems. His focus is on increasing the fidelity of modeling-driven design of low-emissions gas turbine combustion systems. His main research question in any given combustion issue: “Which combustion fundamental did we break?”.

Scientific Engineering Challenges for Industrial Gas Turbines Modeling Acoustics and Autoignition – A Fuel’s Errand?

The energy business is in a state of great excitement over low/no-carbon fuels for gas turbines. In this author’s opinion, much of this excitement focuses on the fuel itself – its low-cost production, renewability, storage, distribution, and geopolitical implications. In this talk, we divert focus to the response to fuel changes via two well-known phenomena that have haunted gas turbine design. Eliminating carbon is just the beginning.
This talk will focus on modeling complex combustion effects in real systems, but the unique role of both lab-scale experiments and direct numerical simulations will be highlighted. Regardless of which decarbonised cocktail is poured into the engine; the system mostly experiences it as a modification of the heat release rate and its oscillation amplitudes. In addition, for some engines such as the low emissions, premixed type – the propensity to spontaneously ignite in the unshielded mixing chamber increases strongly. Higher fidelity models employed to study these effects in full systems are assumed to be a “niche-market” in the industry. We will attempt to destroy this assumption, using two recent case studies from Siemens Energy and provide a retrospective for interested researchers. The first study focuses on high frequency thermoacoustic instabilities in two different systems, the second one focuses on modeling ignition kernels in a high pressure premixer when highly reactive fuels (di-methyl ether being representative) are introduced. In both studies, the theme of scientific engineering is drawn out.