Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ignition”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13

Proactive Wildfire Management: A Remote Sensing and Multimodal CNN-MLP Architecture for Ignition Risk Forecasting

As the frequency and intensity of wildfires increase, with fire seasons now starting earlier and ending later than they have over the past decades, current monitoring systems, such as lookout towers and satellites, are hindered by cloud cover, low-resolution imagery, and static data gaps that fail to track vegetation moisture levels fast enough to catch rapid pre-ignition changes. This report proposes a Machine Learning-enabled Wildfire Ignition Prediction framework that combines satellite monitoring with dynamic and high-resolution remote sensing from Unmanned Aerial Vehicle (UAV) swarms. The method would use multispectral and thermal data from the Landsat program to create a baseline for vegetation health, calculating a two-band Enhanced Vegetation Index (EVI2) and the moisture content of the vegetation. These inputs will later be fused with microscale UAV weather data, including thermal hotspots found through thick canopies, hyperspectral chemical signatures of pre-visual combustion, and local weather streams. The multispectral satellite, multispectral Light Detection and Ranging (LiDAR), and thermal data would then be processed through a Convolutional Neural Network (CNN), alongside a Multilayer Perceptron (MLP) for the micro-weather telemetry. The outputs of these networks would be fused into a single feature representation and passed through a final prediction network to generate real-time ignition risk scores and hotspot alerts. Model performance would be assessed using standard classification metrics, including a Receiver Operating Characteristic - Area Under the Curve (ROC AUC) and F1 score. This system would allow first responders to identify high-risk zones and intervene before ignition occurs, improving emergency response time compared to current approaches.

machine learning↗

Effect of spark repetition rate on the ignition limits of a single tubular combustor /Hampton H. Foster

The effect of spark repitition rate on the altitude ignition limits of a single tubular (turbojet engine) combustor was investigated. An increase in sparking rate from 3 to 140 sparks per second reduced the ignition limiting combustor-inlet pressure about 2 to 4 inches of mercury for air-flow rates of 1.87 and 2.80 pounds per second per square foot.520::At 3.75 pounds pe At 3.75 pounds per second per square foot, the corresponding reduction was 4 to 12 inches of mercury. The trend was similar for both low-and high-volatility fuels and for two spark-energy levels.

IGNITION SYSTEMS - ENGINES, JET↗

Auto-ignition of hydrocarbons behind reflected shock waves.

The paper reports on the study of auto-ignition of hydrocarbon-oxygen mixtures behind reflected shock waves. Because of their bearing on the problem of knock in internal combustion engines, n-heptane and iso-octane were chosen as the combustible species. Their stoichiometric mixtures with oxygen had to be diluted with 70% argon to reduce the influence of the boundary layer. Photographic records demonstrated the existence of two different modes of ignition, as has been previously established for the hydrogen-oxygen system. The pressure-temperature limits between these regions of mild and strong ignition were determined. From the same experimental tests, induction time data were obtained over the pressure range of 1-4 atm and the temperature interval of 1200-1700 K.

Vermeer, D. J.↗

A fluidic sounding rocket motor ignition system.

Fluidic sounding rocket motor ignition has been found to be feasible using a system without stored energy and with the complete absence of electrical energy and wiring. The fluidic ignitor is based on a two component aerodynamic resonance heating device called the pneumatic match. Temperatures in excess of 600 C were generated in closed resonance tubes which were excited by a free air jet from a simple convergent nozzle. Using nitrocellulose interface material, ignition of boron potassium nitrate was accomplished with air supply pressures as low as 45 psi. This paper describes an analytical and experimental program which established a fluidic rocket motor ignition system concept incorporating a pneumatic match with a simple hand pump as the only energy source.

Marchese, V. P.↗

Spontaneous ignition temperature limits of jet A fuel in research-combustor segment

The effects of inlet-air pressure and reference velocity on the spontaneous-ignition temperature limits of Jet A fuel were determined in a combustor segment with a primary-zone length of 0.076 m (3 in.). At a constant reference velocity of 21.4 m/sec (170 ft/sec), increasing the inlet-air pressure from 21 to 207 N/sq cm decreased the spontaneous-ignition temperature limit from approximately 700 to 555 K. At a constant inlet-air pressure of 41 N/sq cm, increasing the reference velocity from 12.2 to 30.5 m/sec increased the spontaneous-ignition temperature limit from approximately 575 to 800 K. Results are compared with other data in the literature.

Ingebo, R. D.↗

Electrostatic-discharge ignition

Electrode in cylinder permits charge to transfer during top dead center compression stroke in modified Otto-cycle engine. Charge transfer produces spark which causes ignition of droplets without resorting to other ignition devices which are incapable of igniting ultralean mixtures.

Stephens, J. B.↗

Ignitability of some insulation and building materials

A variety of insulation and building materials were evaluated for ignitability, using a screening test method developed at the University of San Francisco. Ignitability tended to be greater with the more efficient insulation materials because the insulating qualities resulted in a more rapid rise in temperature at the exposed surface. The use of a noncombustible facing material is recommended to provide protection from surface ignition.

Hilado, C. J.↗

Shock wave ignition of magnesium powders

The paper is concerned with magnesium powder ignition caused by the interaction of powder with incident shock wave-induced flows. Experimentally observed ignition delays are correlated with predicted times for particle melting and the onset of thermal erosion, and a good agreement is found between experiment and theory. Ignition delays were measured as functions of particle screening, cloud concentration, incident shock strength, initial pressure, and oxygen concentration (diluted with nitrogen). An expression for the Nusselt number in the Reynolds number range 0-10,000 and the Mach number range 0-6 is proposed. The expression, when applied to predict particle behavior, provides results in agreement with experimental data for M/Re less than 0.5.

Fox, T. W.↗

Ignition characteristics of some aircraft interior fabrics

Six samples of aircraft interior fabrics were evaluated with regard to resistance to ignition by radiant heat. Five samples were aircraft seat upholstery fabrics and one sample was an aircraft curtain fabric. The aircraft seat fabrics were 100% wool (2 samples), 83% wool/17% nylon, 49% wool/51% polyvinyl chloride, and 100% rayon. The aircraft curtain fabric was 92% modacrylic/8% polyester. The five samples of aircraft seat upholstery fabrics were also evaluated with regard to resistance to ignition by a smoldering cigarette. The four samples of wool-containing aircraft seat fabrics appeared to be superior to the sample of rayon seat fabric in resistance to ignition, both by radiant heat and by a smoldering cigarette.

Hilado, C. J.↗

Resonance-tube ignition of aluminum

An experimental program was carried out to determine whether spontaneous fluid-dynamic oscillations could create a hazard in gaseous oxygen flow systems by igniting metal contaminants. The particular fluid-dynamic oscillation studied was the resonance-tube phenomenon as it was excited in a tee-shaped configuration representative of configurations found in many industrial flow systems. Pure aluminum was chosen as the candidate material for ignition. The oscillations in the tee-shaped configuration were compared with oscillations driven by choked convergent nozzles and were found to differ markedly. The temperatures generated at the base of the resonance tube were well in excess of 1000 F for both gaseous oxygen and nitrogen. The effect of inert particulate matter introduced into the resonance tube was to increase significantly the measured temperatures. Aluminum in both powder and fiber form was readily ignited within the resonance tube at pressures less than 1200 psia. At higher pressures, the aluminum-oxygen mixture exploded. This investigation confirms the hazardous nature of resonance-tube oscillations as generated in typical piping configurations that use high-pressure oxygen.

Phillips, B. R.↗

Development, qualification, and delivery of a hydrogen burnoff igniter

The hydrogen burnoff igniter, a pyrotechnic device used to burn off excess hydrogen gas near the Space Shuttle Main Engine (SSME) nozzle, was designed, fabricated, and qualified. Characteristics of the burnoff igniter include a function time of 8 + or - 2 seconds, a minimum three foot flame length at maximum output, and hot particles projected 15 feet when fired directly into or perpendicular to a 34.5 knot wind. The three foot flame length was considered to be of questionable importance, since the hot particles are the media for igniting the hydrogen. Flame temperature is greater than 1500 F.

Ray, D.↗

Chemical kinetic analysis of hydrogen-air ignition and reaction times

An anaytical study of hydrogen air kinetics was performed. Calculations were made over a range of pressure from 0.2 to 4.0 atm, temperatures from 850 to 2000 K, and mixture equivalence ratios from 0.2 to 2.0. The finite rate chemistry model included 60 reactions in 20 species of the H2-O2-N2 system. The calculations also included an assessment of how small amounts of the chemicals H2O, NOx, H2O2, and O3 in the initial mixture affect ignition and reaction times, and how the variation of the third body efficiency of H2O relative of N2 in certain key reactions may affect reaction time. The results indicate that for mixture equivalence ratios between 0.5 and 1.7, ignition times are nearly constant; however, the presence of H2O and NO can have significant effects on ignition times, depending on the mixture temperature. Reaction time is dominantly influenced by pressure but is nearly independent of initial temperature, equivalence ratio, and the addition of chemicals. Effects of kinetics on reaction at supersonic combustor conditions are discussed.

Rogers, R. C.↗

A Chemical Kinetic Mechanism for the Ignition of Silane/Hydrogen Mixtures

A chemical kinetic reaction mechanism for the oxidation of silane/hydrogen mixtures is presented and discussed. Shock-tube ignition delay time data were used to evaluate and refine the mechanism. Good agreement between experimental results and the results predicted by the mechanism was obtained by adjusting the rate coefficient for the reaction SiH3 + O2 yields SiH2O + OH. The reaction mechanism was used to theoretically investigate the ignition characteristics of silane/hydrogen mixtures. The results revealed that over the entire range of temperature examined (800 K to 1200 K), substantial reduction in ignition delay times is obtained when silane is added to hydrogen.

Jachimowski, C. J.↗

Development of space shuttle ignition overpressure environment and correlation with flight data

The Space Transportation (STS) launch vehicles are more complex than other launch vehicles. A comprehensive analysis of the lift-off event is required so that the responses of the vehicle and payloads can be predicted. The transient overpressure induced by ignition of the solid rocket motors (SRM's) is one of the critical design factors assessed for lift-off. The STS-1 ignition overpressure design environment was developed from 6.4-percent scale-model tests in which the Tomahawk solid rocket motors were used to simulate the start-up process of the SRM's. The overpressures measured during STS-1 lift-off were much more severe than predicted. The reasons for this anomaly are discussed in this paper. The 6.4-percent scale model was redesigned and used as a tool to develop an effective ignition overpressure suppression system for STS-2 and subsequent flights. Also presented are advancements in subscale-model simulation and theoretical understanding of this transient overpressure phenomenon that led to the successful development of the fix.

Lai, S.↗

Theoretical studies of the ignition and combustion of silane-hydrogen-air mixtures

A chemical kinetic mechanism is proposed for the combustion of silane-hydrogen-oxygen-nitrogen mixtures in the initial temperature range from 800K to 1250K and pressure range from 0.5 to 1.35 atm. The mechanism yields results which are in agreement with published ignition delay times obtained from shock tube experiments. Comparisons between the results obtained using the proposed mechanism and that of an alternative mechanism reveal that the former predicts appreciably shorter ignition delay times, but a flame blowout envelope which is shifted so as to decrease the stable flame region. Over much of the thermodynamic range examined, the mechanism predicts long reaction times. A three step global mechanism is proposed which closely models the ignition phase of SiH4 - H2 - air combustion; however, the reaction phase is less well reproduced by the global model. The necessity for additional experimental data to further assess the proposed models is stressed.

Chinitz, W.↗

Near-infrared two-color pyrometer for determining ignition temperatures of metals and metal alloys

A two-color pyrometer has been designed, constructed, and used to measure the ignition temperatures of metals and metal alloys. Cylindrical metal and metal alloy specimens were ignited by a focused cw CO2 laser beam in a cool, static, pure oxygen environment. The pyrometer operates in the near-infrared at two narrow spectral regions, with a nominal bandwidth of 10 nm centered at 0.9051 and 1.06 micron, and has a temperature range from 1000 to 4000 K. In the present design the temperature of a spot, about 0.5 mm in diameter, can be recorded with a maximum time resolution of 25 microseconds and with an accuracy of a few percent. Results of CO2 laser ignition of cylindrical specimens of 6061 aluminum alloy and 302 SS in a pure oxygen environment were obtained from the two-color pyrometer and were compared with those obtained from a thermocouple placed inside the specimen near the laser-irradiated surface.

Nguyen, K.↗

Ignition System for Gaseous Propellants

Installation of spark plug in fuel-injection manifold of coaxial injector promotes more efficient cooling of combustor walls in rocket and turbine engines. After ignition occurs in fuel injector, combustion maintained in cooled main combustor leaving spark-plug tip in cool, clean environment. Eighteen tests have proven this injector design; no ignition failures occurred in 8,000 seconds of operation with gaseous oxygen and hydrogen. System also used with other propellants gaseous in ignition phase.

Pieron, R. A.↗