Rogak, Steven

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Research Interests

Aerosols are liquid or solid particles suspended in a gas. Solid nanoparticles (ie., diameters much less than 1 micron) are produced by combustion processes (eg., diesel engines), and as an atmospheric contaminant, they can have a major impact on climate forcing as well as on human health. It is important to understand the impact of these particles, and more importantly, reduce concentrations of these particles in the indoor and outdoor environments. This overall motivation for my research has taken me and my students down several interconnected paths.

• The first path has been to understand how particle morphology of solid, fractal-like particles (such as soot) affects the transport properties and measurement of the particles. This is an essential component of conducting experimental research on fractal nanoparticles, and an important ingredient in models of particle formation in engines. A related research project has sought to characterize the difference in real particle morphology as a function of engine operating conditions.
• A second path has been the development of new fuel injectors and injection strategies to minimize particle formation in compression ignition engines. This work, done in collaboration with Westport Innovations has been applied and experimental, but my group is working on new phenomenological models of particle formation in engines.
• A third stream of research aims to reduce aerosol concentrations where people spend most of their time – inside buildings. Here the challenge is to remove harmful nanoparticles using filtration systems that do not require excessive energy consumption.

Research Projects

• Soot and nanoparticles: Our long-term research objective is to understand how formation conditions control particle structure, which in turn controls how the particles can be measured and their impact on the environment. Recently we have found that not only do fuel and operating conditions affect soot structure, but inhomogeneity within the combustion device produces particles with diverse structures. Recently we have found an important but previously overlooked feature of soot structure: real soot is formed non-uniform combustion zones, but often there is minimal coagulation of particles from different zones, so that the final structures show “externally mixed” primary particle polydispersivity. That is, primary particle size is uniform within aggregates, but differs greatly from aggregate to aggregate.
• Engine Emissions: We are working with Westport Innovations to develop better fuel injection methods and combustion strategies for heavy duty engines. To support this, we are developing novel diagnostic techniques, including a new soot sensor to resolve the differences in emissions from one engine cycle to the next. The engines group at UBC has investigated a wide range of injection conditions and practices, and with Westport have found a variety of methods of reducing engine-out soot emissions by 80-90%. An benefit of the project has been the development of the Injector Visualization Chamber (IVC, at right), which can determine injector flow and spray characteristics at realistic fuel and background pressures. Initially, fouling of the IVC windows prevented us from imaging injections at steady state. Some early (spectacularly bad) atomization is visible below for injections NOT at steady state.
• Energy and Aerosols in Buildings: The Energy and Aerosols Laboratory is tackling one part of the challenge to design better buildings: ventilation. Recent work with Green and Montgomery found optimal (health vs energy) strategies for the use of filters in buildings. Currently we are working with CORE Energy Solutions (formerly dPoint Technologies) to improve energy recovery ventilators. This work provides practical information on when (and how) air pollution may degrade the performance of energy recovery ventilators (ERV).