We use the digital holographic interferometry (DHI) technique to display the early ignition process for a butane-air mixture flame Because such an event occurs in a short time (few milliseconds), a fast CCD camera is used to study the event As more detail is required for monitoring the temporal evolution of the process, less light coming from the combustion is captured by the CCD camera, resulting in a deficient and underexposed image Therefore, the CCD's direct observation of the combustion process is limited (down to 1000 frames per second) To overcome this drawback, we propose the use of DHI along with a high power laser in order to supply enough light to increase the speed capture, thus improving the visualization of the phenomenon in the initial moments An experimental optical setup based on DHI is used to obtain a large sequence of phase maps that allows us to observe two transitory stages in the ignition process: a first explosion which slightly emits visible light, and a second stage induced by variations in temperature when the flame is emerging While the last stage can be directly monitored by the CCD camera, the first stage is hardly detected by direct observation, and DHI clearly evidences this process Furthermore, our method can be easily adapted for visualizing other types of fast processes

Digital holographic interferometry applied to the investigation of ignition process.

Premixed burners have been widely used in many applications for both industrial and household appliances. For this reason, it is very important to enhance the combustion and emission efficiency of premixed burners because of their strong position in the global dimension. On the other hand, the addition of hydrogen to various fuels has been a research topic in the last decade due to its environmental and economic positive effects. In this study, the effect of hydrogen addition to different gaseous fuels at different rates has been investigated in a premixed burner. A numerical parametric study has been carried out using a commercial CFD code. The gaseous fuels namely; methane, propane, LPG and natural gas have been enriched by different hydrogen addition rates with a 10% increment. Moreover, the results of pure hydrogen have been presented. The results reveal that the combustion efficiency for all fuels has been affected positively with hydrogen enrichment except for certain gas compositions. Furthermore, this study has shown that the hydrogen addition in general, decreases the unburnt HC and CO emissions.

Combustion performance of hydrogen-enriched fuels in a premixed burner.

We examine the propagation of the Yarnell Hill Fire in Arizona, June 28 -- July 3, 2013 to assess the nature of its complexity We identify the critical fire growth that starts about 35 hours after the fire initiation In a time span of three hours, the fire area is doubled Within the following four hours, the direction of fire turns by about 180 degrees An hour later, a pyrocumulonimbus cloud is observed above the fire area To monitor complex fires, we propose implementation of an IR instrument to scrutinize fire remotely for behaviors, such as vortices and rotation, arising from combustion events, terrain characteristics, and outside influences We propose a small reconnaissance plane circling to the side and above the fire area to search for anomalies in fire propagation and atmosphere during the fire consolidation during the initial 45 hours Ideally, the observing instrument would be sensitive in IR region at about 45 microns where carbon oxide emits and water transmits the radiation

Analysis of propagation of complex fire: case of the Yarnell Hill Fire 1

We describe a bispectral, 1000-frames per second imaging instrument working simultaneously in two spectral bands. These bands may be selected for a specific application; however, we implement a pair centered at 4.3 μm and 4.66 μm. Synchronization is accomplished by employing a single focal plane array. To demonstrate the performance of the bispectral imager, we apply it to the methane flame of a Bunsen burner in a near conjugate configuration with flame image length subtending at about 200 pixels. The instrument detects bispectral puffing at 2 Hz, pulsations, and bispectral radiation oscillations, first reported here in two spectral intervals. The period of oscillatory spectral components in two bands is the same, about 3 Hz for this flame, with delay of a quarter period between them, first reported here. With 1-ms integration time, we detect significant formation of turbulence and vortices, especially pronounced in the region where the flame transitions into a plume. We display bispectral ratioed images of flames in near-real time with either the laboratory or the field device.

High-resolution bispectral imager at 1000 frames per second.

We propose a novel model for the fire evolution, applicable to its spread in mountains, with low-height fuel. Fire propagates along contours of equal elevation on steep terrains. The wind outside the mountain does not conserve on the inside slopes at fuel height. The local wind depends on micro-climatic environment, influenced additionally by the fire itself.

M.K. Scholl

Papers

Combustion initiation and evolution during the first 400 ms in a gas burner at 10 μm