Vi H. Rapp, PhD

We present a method for systematically selecting molecular descriptor features and developing interpretable machine learning models without sacrificing accuracy. Our method simplifies the process of selecting features by reducing feature multicollinearity and enables discoveries of new relationships between global properties and molecular descriptors. To demonstrate our approach, we developed models for predicting melting point, boiling point, flash point, yield sooting index, and net heat of combustion with the help of the Tree-based Pipeline Optimization Tool (TPOT).

This research explores 3 potential sorghum derived jet fuel molecules from 4 different production routes, hydro-processed esters and fatty acids (HEFA), and Jet A, to identify how blends including these fuels could offer improved performance (MJ/kg, MJ/L) and improved emissions (gCO2/MJ) while minimizing costs.

We conducted a cluster-randomized stepped-wedge trial. The primary aim was to assess the effect on overall euthermia rates of introducing the warmer compared to standard of care in rural Rwandan hospitals. The secondary aims were to assess effects of warmer introduction on mortality, as well as the safety and feasibility of the warmer.

We use a modular cookstove platform to experimentally quantify the practical secondary air injection design requirements to reduce harmful emissions by at least 90% relative to a traditional cooking fire.

This research parametrically investigates the effect of secondary air injection on the mass and size distribution of PM emitted during solid biomass combustion using a modular, experimental wood-burning cookstove platform.

The efficacy of a low-cost, re-usable, and non-electric infant warmer is evaluated in a hospital setting to prevent neonatal hypothermia. It is capable of maintaining 37 C for approximately six hours when a parent is not available for skin-to-skin care.

This paper investigates the effect of air injection on cooking performance, PM and gaseous emissions, and PM size distribution and number concentration. Although air injection can decrease total PM mass emitted, it is unclear if it reduces the number concentration of all PM emission sizes uniformly or concurrently increase the number of ultrafine particles per mass of fuel burned, which may be more harmful to human health.

This study presents a comprehensive review of standardized wood heater test methods to identify fundamental experimental objectives and regulated performance metrics. Using the results of this review, recommendations are provided to make the test methods more accessible and representative of residential performance, while generating actionable data to motivate heater design improvements. This study elucidates the current state of standard test methods, and the developments needed to advance clean wood heater technologies and public policies.

District energy systems (DES) have the potential to meet building power, heating and cooling needs efficiently and reliably, but further research is needed to understand their coupling with local renewable energy sources such as biomass. Here we assess the cost and greenhouse gas implications of using bioenergy from local organic waste to power DES in California communities.

In this paper, we used CHP operating data and determined annual and monthly availability of the installed CHP capacity from various sectors (e.g., utility, independent power producer, commercial, and industrial) in all seven U.S. independent system operators and regional transmission organizations.

We report the synthesis of large-area, wafer- scale arrays of porous silicon nanowires with ultra-thin Si crystallite size of ~4 nm. Concurrent measurements of thermal conductivity (κ), electrical conductivity (σ), and Seebeck coefficient (S) on the same nanowire show a ZT of 0.71 at 700 K, which is more than ~18 times higher than bulk Si. This ZT value is more than two times higher than any nanostructured Si-based thermoelectrics reported in the literature at 700 K.

To understand the emissions and impacts from vaporizable cannabis concentrates, we evaluated mixtures containing different proportions of 12 VCC terpenoids and high MW compounds. Terpenoids, thermal degradation byproducts, and ultrafine particles were quantified from all samples.

This paper investigates the anti-knock properties of biofuels that can be produced from microorganism metabolic processes. The biofuels are rated using Research Octane Number (RON) and Blending Research Octane Number (BRON), which determine their potential as additives for fuel in spark ignition (SI) engines.

The performance of primary alcohols was experimentally determined using the research octane number (RON) and the blending research octane number (BRON). The primary alcohol mixture, or “AlcoMix,” consists of 75% ethanol, 11% 1-propanol, 8% 1-butanol, and 6% 1-pentanol and was approved by the U.S. EPA for use in blending with gasoline.

The purpose of this research is to investigate the impact of fuel composition on auto-ignition in homogeneous charge compression ignition (HCCI) engines in order to develop a future metric for predicting fuel performance in future HCCI engine technology.

A microwave-assisted spark plug was used to extend the lean operating limit (lean limit) and reduce emissions of an engine burning methane-air. In-cylinder pressure data were collected at normalized air-fuel ratios of 1.46, 1.51, 1.57 1.68, and 1.75.

We investigated the extension of the lean stability limits of gasoline-air mixtures using a microwave-assisted spark plug. Experiments are conducted on a 1200 RPM single-cylinder Waukesha Cooperative Fuel Research (CFR) engine at two compression ratios: 7:1 and 9:1; and four different levels of microwave energy input per cycle.

We investigate the role of both the compression ratio and the specific heat ratio on engine efficiency by conducting experiments comparing operation of a single-cylinder variable-compression-ratio engine with both hydrogen-air and hydrogen-oxygen-argon mixtures.

A 28-species reduced chemistry mechanism for Dimethyl Ether (DME) combustion is developed on the basis of a recent detailed mechanism by Zhao et al. (2008).

We estimate postmeter methane (CH4) emissions from California’s residential natural gas (NG) system using measurements and analysis from a sample of homes and appliances.

The purpose of this article is to assess VENT-II’s ability to predict combustion gas spillage events due to house depressurization by comparing VENT-II simulated results with experimental data for four appliance configurations.

We propose a new framework that determines the minimum thermal energy required to keep building occupants comfortable. This framework provides benchmarks and is used to highlight opportunities that go beyond energy efficient technology and designs.

A mobile and affordable, miniature wind tunnel to aid students in studying high-speed compressible flows was constructed and tested. Millimeter-sized nozzles of different contours were fabricated to produce supersonic flows at Mach 2.