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Spotlight: Adam Dempsey

One of the main objectives of HugYourEngine is to shine a spotlight on individuals who are helping make internal combustion engines cleaner and more efficient. This spotlight is on Professor Adam Dempsey.

Adam Dempsey is an Assistant Professor at Marquette University in the mechanical engineering department. Prior to joining Marquette, he was a senior research engineer at Caterpillar Inc. and a postdoctoral researcher at Oak Ridge National Laboratory. He received his bachelors and masters in mechanical engineering from Bradley University and his PhD in mechanical engineering from the University of Wisconsin-Madison in 2013. Dr. Dempsey’s expertise is in well controlled single- and multi-cylinder engine experiments, high-fidelity CFD spray and combustion modeling, and is branching into optical combustion imaging & measurements. These investigative tools are used to improve the sustainability of internal combustion engines through increased efficiency, reduced emissions, and optimal use of alternative fuels. He has published over 30 technical papers on engine combustion research and was recently awarded the ASME ICEF best technical conference paper for a manuscript on high quality cylinder pressure measurements in diesel engines.

Kelly Senecal (KS): When and why did you get started in combustion research?

Adam Dempsey (AD):My grandfather and uncle owned a farm when I was younger. My grandfather unfortunately passed away unexpectedly. My uncle desperately needed help on the farm. My father and I helped for many harvest seasons, starting when I was 10 years old. I could barely reach all the controls, but nevertheless was hauling grain with a John Deere 4640 tractor. From those days forward, I have always been infatuated with engines, particularly diesel engines.

My fascination with engines continued through my undergraduate and masters studies, where I found the thermal sciences to be my strongest subjects. My advisor at Bradley, Dr. Scott Post, encouraged me to pursue a PhD and said if you are interested in diesel engine research, there is only one place you need apply – the University of Wisconsin-Madison! He encouraged me to apply for a position in Professor Rolf Reitz’s research group. Professor Reitz generously offered me a position in his group as part of the Engine Research Center (ERC) to pursue my PhD and – as they say – the rest is history. My time as a PhD student really shape my interests. I had the opportunity to use CFD simulations and conduct engine experiments, which was unique, and I am grateful to have had that opportunity.

Engineering Hall at Marquette University. A 5-story, 115,000 ft2 building commissioned in 2011 to expand engineering research laboratory facilities.

KS: What are you working on now?

AD: As a new Assistant Professor at Marquette University, I am just starting to build my research program. My hope is that the major thrust of my research program will be on the optimal use of light fuels, such as gasoline, alcohols, and natural gas, in heavy-duty engines. Full electrification of a vehicle could potentially make sense in some transportation sectors, but certainly NOT heavy-duty commercial applications, such as long-haul trucks, construction equipment, marine, and distributed power generation. Thus, to reduce the environmental impact of these applications, the heavy-duty engines they use will need to be improved. It is my feeling that light fuels have the potential to increase efficiency, reduce emissions, and improve the sustainability of heavy-duty engines. The research I plan to conduct will revolve around a variety of investigative tools, namely a single-cylinder research engine capable of various combustion modes, High-Performance Computing (HPC) resources for doing detailed chemical kinetic and CFD simulations, and, through collaborations with Professor Casey Allen at Marquette, optical rapid compression machine (RCM) experiments investigating autoignition kinetics, lean-burn ignition technologies, and soot formation.

(Top) Engine research laboratory at Marquette University with double-ended AC dynamometer. Used for single- and multi-cylinder engine combustion research. (Bottom) Optical rapid compression machine (RCM) used by Casey Allen’s research group to study combustion chemistry.

KS: Describe your lab facilities.

AD: I am in the process of building my engine research lab at Marquette University, which will be a medium/heavy-duty single-cylinder research engine. The engine will be based on Caterpillar C9.3B diesel engine and converted to run as a single-cylinder capable of multiple combustion modes with various types of liquid and gaseous fuels. The engine was just recently donated to Marquette and are just now starting the process of installing it in the engine lab. The lab at Marquette has a double-ended AC dynamometer, so we can do single- and multi-cylinder research. The lab is equipped with National Instruments Powertrain Controls and data acquisition, as well as an FTIR for gaseous emission measurements. As we continue to build the engine research lab, we will be acquiring particulate measurement equipment as well as fuel systems capable of handling a variety of liquid and gaseous fuels.

My primary interest will be using this engine to develop advanced combustion strategies such that heavy-duty engines can efficiently use light fuels, such as gasoline, alcohols, and natural gas. There are challenges using these types of fuels in diesel engine applications, and I want my research to develop technologies to address those challenges. The combustion strategies used will likely be multi-mode strategies that could potential utilize advanced ignition systems, turbulent jet igniters (i.e., pre-chambers), low temperature volumetric combustion, and conventional mixing-controlled combustion.

In addition to the engine laboratory, my research program will use combustion simulations, primarily in-cylinder engine CFD simulations, but I am also interested in developing reduced order phenomenological models to describe the combustion process for model-based control strategies. Marquette is in the process of commissioning a brand-new computational cluster with ~8500 computational CPUs and a mix of GPUs, which will be very useful for the computational portion of my research program.

Marquette has a growing group of combustion research faculty members in the mechanical engineering department, which is now up to four and includes Dr. Casey Allen, Dr. Simcha Singer, Dr. Somesh Roy, and me (Dr. Adam Dempsey). Dr. Allen is an expert in fuel ignition chemistry and mainly utilizes an optical rapid compression machine (RCM) for his research. Dr. Simcha Singer and Dr. Somesh Roy are both focused on fundamental model development for combustion related simulations. Dr. Singer’s focus is on multi-component droplet vaporization and the gasification/pyrolysis of solid fuels, such as biomass. Dr. Roy’s group is working on soot formation and radiative heat transfer modeling for combustion applications. With my focus being on engine research, you can see how Marquette’s combustion research group has come full circle from fundamental science to engine application.

KS: What’s your favorite type of flame?

AD: Turbulent Mixing-Controlled Diffusion Flame! My passion for engine research is rooted in my love for diesel engines. The conventional mode of combustion in a diesel engine is a diffusion flame, in which the rate of combustion is controlled by turbulent mixing. This is my favorite type of flame for two reasons:

First, they are beautiful! The combination of chemiluminescence and soot incandescence in the visible wavelength range reveals magnificent blue and orange colors. Also, the turbulent nature of the flame is fascinating to watch as the flame is stretched and advected.

Second, it is my belief that the highest efficiency reciprocating IC engines will use mixing-controlled diffusion combustion for some portion of its operating space. The keys to high efficiency are high compression ratio and lean operation (i.e., high ratio of specific heats of the working fluid). Mixing-controlled combustion is the best way to use these two key ingredients for high efficiency engines, without the fear of knock, pre-ignition, high cyclic variability, or lack of a control mechanism.

KS: What’s your favorite fuel?

AD: I think I am expected to say diesel fuel, but I think my favorite fuels are the alcohols, such as methanol and ethanol. Fundamentally, they are extremely clean burning (low NOx, particulate matter, and little residue/deposits), have high laminar flame speeds, are resistant to autoignition, and have very high latent heat of vaporization. Thus, they are fantastic SI engine fuels right out of box and, with some research, have the potential to be promising fuels for heavy-duty engines as well. When you consider the challenge that we are facing of reducing the environmental impact of transportation, it is paramount that we consider the full life cycle, which is another reason why I like alcohol fuels. They can be made renewably from almost any biomass material and are a very practical energy carriers when produced from sequestered atmospheric CO2, water, and clean electricity. Energy carries need to be energy dense and easy to transport. Liquid fuels fit that bill much better than hydrogen or batteries in my opinion.

Faculty members from the Department of Mechanical Engineering at Marquette University, all of whom are involved in combustion research. (From Left to Right) Adam Dempsey, Casey Allen, Simcha Singer, and Somesh Roy.

KS: What advice would you give students thinking about going into combustion research?

AD: Humans have been using combustion for thousands of years to do many useful things. It is very unlikely that this will all end abruptly anytime soon. There are still many things that we don’t understand about combustion, ranging from the fundamental sciences of chemistry and fluid mechanics to the applications of engines. So, I would say that if you are passionate about the topic of combustion, jump in headfirst and have confidence that it is a subject that will be around for a long time.

KS: Is the IC Engine dead?

AD: Absolutely not. I am not anti-electrification, but I am pro-arithmetic. There are certainly niche applications where a fully battery electric vehicle makes sense and almost all segments of transportation could benefit from some form of electrification via a hybrid powertrain. Hybrids have efficiency benefits and can reduce CO2 emissions. However, due to the sheer scale of transportation around the globe, full electrification can’t be adopted. The increase in the amount of electricity that would need to be produced in a clean fashion is mind blowing and scaling up battery production, which tends to use rare earth metals, to fully electrify all forms of transportation is nonsense. There are simply not enough raw materials.

For these reasons, almost all energy agencies are predicting that in the year 2050, only ~10% of global transportation energy demand will come from electricity. The remaining 90% will come from petroleum or bio-renewable fuels used in IC engines. Today, electricity only accounts for ~1% of global transportation energy demand. Thus, full battery electric vehicles are certainly growing, but it does not seem plausible that they will completely replace the IC engine, and most experts seem to agree on this.

Caterpillar C9.3B diesel engine that was recently donated to Marquette University, which will be converted into a single-cylinder research engine for investigating the use of light fuels in heavy-duty engines.

KS: How is your work helping improve fuel efficiency or reduce emissions?

AD: My research program is focused on improving the efficiency and reducing emissions from medium- and heavy-duty engines by using lighter fuels, such as gasoline, alcohols, or natural gas. There is a lot of potential for these to be clean burning fuels in heavy-duty engines, but there are certainly challenges that need to be addressed, so, I feel it is a ripe area to be working in. Commercial transportation, off-road equipment, and marine vessels, all of which use heavy-duty engines, are not threatened by batteries in my opinion due to their sheer power output. Thus, the most compelling way to reduce the environmental impact of these applications is through innovative improvements of engines by developing high efficiency, clean combustion strategies. This is what I am setting out to do!

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