Carlos Fernandez-Pello

Bio: Carlos Fernandez-Pello is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: Flame spread & Ignition system. The author has an hindex of 20, co-authored 79 publications receiving 1795 citations.

Generalized pyrolysis model for combustible solids

Abstract: This paper presents a generalized pyrolysis model that can be used to simulate the gasification of a variety of combustible solids encountered in fires. The model, Gpyro, can be applied to noncharring polymers, charring solids, intumescent coatings, and smolder in porous media. Temperature, species, and pressure distributions inside a thermally stimulated solid are determined by solving conservation equations for the gaseous and condensed phases. Diffusion of species from the ambient into the solid is calculated with a convective–diffusive solver, providing the capability to calculate the flux and composition of volatiles escaping from the solid. To aid in determining the required material properties, Gpyro is coupled to a genetic algorithm that can be used to estimate the model input parameters from bench-scale fire tests or thermogravimetric (TG) analysis. Model calculations are compared to experimental data for the thermo-oxidative decomposition of a noncharring solid (PMMA), thermal pyrolysis of a charring solid (white pine), gasification and swelling of an intumescent coating, and smolder in polyurethane foam. Agreement between model calculations and experimental data is favorable, especially when one considers the complexity of the problems simulated.

The application of a genetic algorithm to estimate material properties for fire modeling from bench-scale fire test data

Abstract: A methodology based on an automated optimization technique that uses a genetic algorithm (GA) is developed to estimate the material properties needed for CFD-based fire growth modeling from bench-scale fire test data. The proposed methodology involves simulating a bench-scale fire test with a theoretical model, and using a GA to locate a set of model parameters (material properties) that provide optimal agreement between the model predictions and the experimental data. Specifically, a GA based on the processes of natural selection and mutation is developed and integrated with the NIST FDS v4.0 pyrolysis model for thick solid fuels. The combined GA/pyrolysis model is used with cone calorimeter data for surface temperature and mass loss rate histories to estimate the material properties of two charring materials (redwood and red oak) and one thermoplastic material (polypropylene). This is done by finding the parameter sets that provide near-optimal agreement between the model predictions and experimental data, given the constraints imposed by the underlying physical model and the accuracy with which the boundary and initial conditions can be specified. The methodology is demonstrated here with the FDS pyrolysis model and cone calorimeter data, but it is general and can be used with several existing fire tests and almost any pyrolysis model. Although the proposed methodology is intended for use in CFD-based prediction of large-scale fire development, such calculations are not performed here and are recommended for future work.

A model for the oxidative pyrolysis of wood

Abstract: A generalized pyrolysis model (Gpyro) is applied to simulate the oxidative pyrolysis of white pine slabs irradiated under nonflaming conditions. Conservation equations for gaseous and solid mass, energy, species, and gaseous momentum (Darcy’s law approximation) inside the decomposing solid are solved to calculate profiles of temperature, mass fractions, and pressure inside the decomposing wood. The condensed phase consists of four species, and the gas that fills the voids inside the decomposing solid consists of seven species. Four heterogeneous (gas/solid) reactions and two homogeneous (gas/gas) reactions are included. Diffusion of oxygen from the ambient into the decomposing solid and its effect on local reactions occurring therein is explicitly modeled. A genetic algorithm is used to extract the required material properties from experimental data at 25 kW/m 2 and 40 kW/m 2 irradiance and ambient oxygen concentrations of 0%, 10.5% and 21% by volume. Optimized model calculations for mass loss rate, surface temperature, and in-depth temperatures reproduce well the experimental data, including the experimentally observed increase in temperature and mass loss rate with increasing oxygen concentration.

Design and fabrication of a silicon-based mems rotary engine

Abstract: Design and fabrication of a Silicon-based MEMS rotary engine are discussed in this paper. This work is part of an effort currently underway to develop a portable, autonomous power generation system potentially capable of having an order of magnitude improvement in energy density over alkaline or lithium-ion batteries. Central to the development of this power generation system are small-scale rotary internal combustion engines fueled by high energy density liquid hydrocarbons capable of delivering power on the order of milli-Watts. The rotary (Wankei-type) engine is well suited for MEMS fabrication due to its planar geometry, high specific power, and self-valving operation with a minimal number of moving parts. The smallest "micro-rotary" engine currently being fabricated has an epitrochoidalshaped housing under 1 mm 3 in size and with a rotor swept volume of 0.08 mm 3. This paper discusses some of the fabrication issues unique to MEMS fabrication of a rotary engine at this small scale. High precision, high aspect ratio structures are necessary to provide adequate sealing for high compression ratios. Effects such as footing and lateral to vertical etch rates must be minimized for proper engine operation. A fabrication process is necessary for the complex, multiheight geometry of the housing and rotor assembly. Finally, a repeatable and simple assembly technique must be developed in order to mass-produce these engines. Fabrication of a Silicon-based micro-rotary engine is being conducted in U.C. Berkeley's Microfabrication Laboratory. The engine system is composed of three main components: rotor, housing, and shaft. The engine and rotor housing mast be entirely fabricated from Silicon without embedded oxide to prevent thermal mismatch or structural weakness at the Si-oxide interface. In order to meet this requirement, the fabrication processes for the housing consists of a two-mask two-etch process of a solid Silicon wafer. The fabrication of the rotor follows a similar process, utilizing deposited oxide as a release layer. Using Silicon Dioxide and photoresist for masking, housing and rotor structures are etched from solid Silicon using timed Deep Reactive Ion Etching (DRIE). A unique feature of these processes is the self-masking of the spur gear in the housing and the shaft thru hole in the rotor during the second DRIE steps, which give the necessary multi-level, cross-sectional profile.

Micropower generation using combustion: Issues and approaches

Abstract: The push toward the miniaturization of electro-mechanical devices and the resulting need for micro-power generation (milli-watts to watts) with low-weight, long-life devices has led to the recent development of the field of micro-scale combustion. The concept behind this new field is that since batteries have low specific energy, and liquid hydrocarbon fuels have a very high specific energy, a miniaturized power generating device, even with a relatively inefficient conversion of hydrocarbon fuels to power would result in increased lifetime and/or reduced weight of an electronic or mechanical system that currently requires batteries for power. In addition to the interest in miniaturization, the field is also driven by the potential fabrication of the devices using Micro Electro Mechanical Systems (MEMS) or rapid prototyping techniques, with their favorable characteristics for mass production and low cost. The micro-power generation field is very young, and still is in most cases in the feasibility stage. However, considering that it is a new frontier of technological development, and that only a few projects have been funded, it can be said that significant progress has been made to date. Currently there is consensus, at least among those working in the field, that combustion in the micro-scale is possible with proper thermal and chemical management. Several meso-scale and micro-scale combustors have been developed that appear to operate with good combustion efficiency. Some of these combustors have been applied to energize thermoelectric systems to produce electrical power, although with low overall efficiency. Several turbines/engines have also been, or are being, developed, some of them currently producing positive power, also with low efficiency to date. Micro-rockets using solid or liquid fuels have been built and shown to produce thrust. Hydrogen-based micro size fuel cells have been successfully developed, and there is a need to develop reliable reformers (or direct-conversion fuel cells) for liquid hydrocarbons so that the fuel cells become competitive with batteries. In this work, some of the technological issues related to meso and micro-scale combustion and the operation of thermochemical devices for power generation will be discussed. Some of the systems currently being developed will be presented and described.

Climate-induced variations in global wildfire danger from 1979-2013

Abstract: Climate strongly influences global wildfire activity, and recent wildfire surges may signal fire weather-induced pyrogeographic shifts. Here we use three daily global climate data sets and three fire danger indices to develop a simple annual metric of fire weather season length, and map spatio-temporal trends from 1979 to 2013. We show that fire weather seasons have lengthened across 29.6 million km2 (25.3%) of the Earth's vegetated surface, resulting in an 18.7% increase in global mean fire weather season length. We also show a doubling (108.1% increase) of global burnable area affected by long fire weather seasons (>1.0 σ above the historical mean) and an increased global frequency of long fire weather seasons across 62.4 million km2 (53.4%) during the second half of the study period. If these fire weather changes are coupled with ignition sources and available fuel, they could markedly impact global ecosystems, societies, economies and climate.