Vahid Motevalli

Flame Length Measurements of Burning Fuel Puffs

Abstract An experimental study of burning of natural gas puffs generated by a fully modulated jet, has been conducted. The present study concentrated on the effects of duty-cycle and puff volume, or equivalently the injection time, on the flame length. It is observed that when individual puffs are well-separated, considerably shorter flame lengths, by as much as a factor of four, are obtained compared to a steady jet flame. Furthermore, the flame length of individual puffs scales with the initial volume of puff, in agreement with the previous studies of buoyant puffs in aqueous media. For a given puff volume, as the duty-cycle is increased beyond a given value, the flame length tends to rise rapidly due to the interaction among neighboring puffs. A dimensionless parameter is found which indicates the transition of puff characteristics.

Material Pyrolysis Properties, Part II: Methodology for the Derivation of Pyrolysis Properties for Charring Materials

ABSTRACT A methodology for deriving material pyrolysis properties is proposed and validated by using three charring materials (pure cellulose, and two different particle boards designated as N and F). The methodology uses experimental data obtained in a pyrolysis apparatus together with an accurate integral thermal pyrolysis model for the charring pyrolysis process (see CST, 88, 309-328, 1993). The effects of various parameters on pyrolysis rates and surface temperatures are investigated by applying the integral pyrolysis model. This analysis shows that, in addition to the unpyrolyzed (virgin) material thermal properties, char conductivity (kc) and heat of pyrolysis (L) are adequate to describe the transient pyrolysis process for a charring material. The thermal capacity of char is shown to have negligible effects on the pyrolysis process because surface radiation loss from the hot char surface is the dominant mechanism causing the reduction of pyrolysis rates in charring materials. This result, which is ...

Numerical prediction of ceiling jet temperature profiles during ceiling heating using empirical velocity profiles and turbulent continuity and energy equations

Abstract Transient development of temperature profiles of an unconfined ceiling jet, induced by a constant fire source, are modeled using the Favre-averaged turbulent continuity and energy equations using Prandtl mixing length along with the equation of state. The primary motivation is to examine if one can use existing empirical velocity profiles to obtain temperature profiles, during the transient heating, as well as the vertical component of velocity of the ceiling jet and thus use these transient ceiling jet temperature profiles in room fire models. The numerical predictions show that the approach is promising, however, the agreement with the experimental data (two different heights of 1·0 and 0·5 m) suffers near the ceiling. The numerical results generally under-predict the 1·0 m case and over-predict the 0·5 m case.

Positive ion chemistry related to hydrocarbon flames doped with CF3 Br

Abstract Reactions of positive ions known to be present in hydrocarbon flames have been studied for their reactivity toward the fire suppressant CF3Br (Halon 1301) at 300 and 525 K. Rate constants and product branching percentages were measured at the two temperatures. The ions HCO+, CH+3, and CH+5 reacted rapidly with CF3Br producing CF+3 and CF2Br+ in all three cases. For CH+5, proton transfer was also observed at 300K. The ions H2COH+, H3COH+2, and H3O+ were unreactive with CF3Br at 300 and 525 K, and at ≈0.5 eV of collision energy supplied by a drift tube at 300 K. The product ions CF+3 and CF2Br+ were studied in separate experiments for reactivity toward selected hydrocarbons, and rate constants and branching percentages were determined. The hydrocarbons CH4, C2H6, C3H8, C2 H4, C3 H6, and C2H2 were selected for study (CF2] Br+ was studied with CH4, C2 H6, C2 H4, and C2H2 only). Neither CF+3 nor CF2Br+ reacted with CH4, but both ions reacted with other hydrocarbons. Hydrogen fluoride was among the inferred neutral reaction products in the reactions of CF+3 with C2H4 and C3H6. We found no evidence for any ionic process which could release Br atoms, any other free radicals, or the CF3Br+ molecular ion, and therefore no evidence was found to indicate that ions play a role in flame inhibition by CF3Br.

Characterization of Smoke From Smoldering Combustion for the Evaluation of Light Scattering Type Smoke Detector Response

Experiments were performed to characterize smoke produced from smoldering materials using light scattering theory. A prototype Scattered Light Detection Instrument (SLDl) was developed to measure the intensity of light scattered at various angles by smoke parti cles. A Gallium Arsenide solid-state laser was used as the source, with photodiodes used as scattered light receivers. A smoke chamber (8.2 m3) was constructed in which to per form experiments using various fuels. Four different fuels — rubber, cotton, douglas fir (wood), and computer printer paper — were burned in the smoldering mode at various positions with respect to the SLDI within the smoke chamber. Experimental data obtained using a test aerosol of known optical properties indicated general agreement with results calculated using Mie scattering theory. Light scattered by smoke particles indicates that the intensity of scattered light at a given angle changes as the fuel changes, consistent with Mie scattering theory. This suggests that an ev...

Effect of Beams on Ceiling Jet Behavior and Heat Detector Operation

Effect of obstructions on an unconfined ceiling jet induced by a fire plume has been investigated using small-scale experimental simulations. Parallel beams placed on a ceiling with the ceiling height varied between 0.76 to 1.28 m resulted in a range of beam depth to ceiling height ratio of 0.048 to 0.19. The non-dimensional fire size ranged from 0.003 to 0.027, corresponding to a fire size range of 450 kW to 1160 kW for a 3.5 m ceiling. The results show that the ceiling jet velocity and temperature beyond the obstruction, when normalized by the smooth ceiling jet correlation, can be characterized as a simple function of the ratio of obstruction depth to the ceiling height. The data shows a nearly 80% reduction in the velocity and temperature of the ceiling jet flowing over an obstruction, when compared with the smooth unconfined case, for a beam depth equal to approximately 15% of the fire to ceiling height. It is also shown that a nearly corridor flow condition is attained when the obstruction approache...

A first approximation method for smoke detector placement based on design fire size, critical velocity, and detector aerosol entry lag time

An analog light-scattering-type smoke detector was tested in a wind tunnel at various low velocities. The air flow in the wind tunnel contained an aerosol concentration that resulted in a high ambient optical density, simulating smoke well above threshold optical detector density. The objective of this research was to determine the lag time to alarm, Δt, associated with difficulty of smoke entry into a detector. A “critical velocity” was identified for the smoke detector, below which the lag time increased exponentially with decreasing velocity. Increased lag time results in the detector responding unacceptably late—or not at all—even when ambient obscuration is well above limits defined in UL standard tests.A preliminary method for placing smoke detectors has been developed, based on a user-defined design fire size and the detector aerosol-entry lag time. The preliminary method applies only to flaming fires producing smoke, with the detector far from a wall and mounted on smooth ceilings. The critical velocity value used in the examples in this paper applies only to the smoke detector configuration tested in this work, at the evaluated sensitivity setting, with the optical densities reached using the generated artificial smoke. Any variation in detector housing, design, operation principle, or application with different aerosols requires specific tests to determine a different critical velocity.This paper provides the basis for further development of a smoke detector placement method based on a design fire size and the proposed detector critical velocity concept. It does not presume to report a unique “critical velocity” for all smoke detectors, but suggests that such a value may indeed exist, but with differing values among different smoke detectors.

Hybrid Electric Vehicle Powertrain Controller Development Using Hardware in the Loop Simulation

It is a time and cost consuming way to physically develop Hybrid Electric Vehicle (HEV) supervisor controller due to the increasing complexity of powertrain system. This study aims to investigate the HEV supervisor controller development process using dSPACE midsize Hardware in the Loop simulation system (HIL) for HEV powertrain control. The prototyping controller was developed on basis of MircoAutoBox II, and an HIL test bench was built on midsize HIL machine for the purpose of verification. The feasibility and capability of HIL were attested by the prototyping control strategy and fault modes simulation. The proposed approach was demonstrated its effectiveness and applicability to HEV supervisor controller development.

Development of a SIL, HIL and Vehicle Test-Bench for Model-Based Design and Validation of Hybrid Powertrain Control Strategies

Abstract Hybrid powertrains with multiple sources of power have generated new control challenges in the automotive industry. Purdue Universitys participation in EcoCAR 2, an Advanced Vehicle Technology Competition managed by the Argonne National Laboratories and sponsored by GM and DOE, has provided an exciting opportunity to create a comprehensive test-bench for the development and validation of advanced hybrid powertrain control strategies. As one of 15 competing university teams, the Purdue EcoMakers are re-engineering a donated 2013 Chevrolet Malibu into a plug-in parallel- through-the-road hybrid-electric vehicle, to reduce its environmental impact without compromising performance, safety or consumer acceptability.This paper describes the Purdue teams control development process for the EcoCAR 2 competition. It describes the teams efforts towards developing a complete vehicle model of a Parallel-through-the road PHEV which can leverage SIL and HIL simulation platforms for control development. A HIL test-bench was developed for real-time controller testing. The use of parameterized models, a prototyping controller and a unique interfacing philosophy allows the team to transition quickly between the SIL, HIL and vehicle platforms, thus providinga comprehensive test environment for the design and validation of various hybrid supervisory control strategies. Some preliminary data from the teams SIL and HIL simulations has also been presented.

Aviation Safety Priorities in Emerging Air Transport Systems

technologic, geographic, or regulatory attributes. This paper also discusses the validity of transferring priorities in aviation safety across industry segments (delineated by these same attributes), each of which may have unique hazard and vulnerability exposures. Collectively, this paper discusses the potential for identified aviation safety priorities (which may be biased toward dominant industry segments) to mask unique hazard and vulnerability exposures inherent in emerging aviation markets. This potential biasing of safety priorities becomes a more critical topic when viewed from the perspective of a future commercial aviation industry with a greater reliance on Part 135 commuter- and air-taxi-type operations using nontowered airports under a high-volume operations paradigm. I. Introduction T HIS paper has two purposes. The first is to demonstrate that priorities in aviation safety can be biased toward specific industry segments that may not be fully representative of other subsets of aviation. The second is to demonstrate that establishing safety priorities based on worldwide operations or specific segments of aviation may not be directly applicable to all subsets that cross regional (national or continental), regulatory (Code of Federal Regulations, or CFR, Title 14 Parts 121 and 135), or technological (jet, turboprop, large aircraft, small aircraft, etc.) boundaries. Specifically, this paper demonstrates that safety priorities in domestic commercial aviation operations have been biased to reflect the accident profile of international commercial operations. A metaanalysis of published safety summaries is used to demonstrate the limitations of any assumption that an accident profile of some subset within a global aviation market is correlated to global aviation in the aggregate. The authors consider this review of real vs perceived domestic commercial aviation safety priorities to be a critical factor in forming the perspective that emerging and nascent aircraft operations and aviation markets, such as high-volume operations (HVO) at nontowered airports and the burgeoning air-taxi industry using light and very light jets (VLJ), may have unique hazard and vulnerability exposures relative to more traditional commercial aviation markets. If these emerging industry sectors are not critically analyzed for sector-specific hazards and vulnerabilities, there is a potentialforincreasednumbersandratesofaccidentsasthesesectors grow. Any such increase could lead to subsequent delays in societal acceptance of HVO in the nontowered “community” airport environments and potential delays in the growth of these emerging aviation markets that would directly affect the capacity of the commercial air transport industry in the aggregate as the hub-andspoke infrastructure nears its maximum capacity. This paper first revisits an earlier work by the authors [1] that critically reviewed aviation accident data summaries compiled and released by various governmental, nongovernmental, and quasigovernmentalorganizations[2–6].Inthispreviouswork,theauthors