Ember Generator for Fire Behavior Research

The goal of this project was to create an ember generating device which mimics the output of firebrands at the wildland urban interface during wildfires. This ember generator will be used by researchers and students at the University of Idaho's College of Natural Resources in fire behavior studies and testing of fire-resistant materials.

=Problem Definition= Ember generation is a byproduct of fires. Wildfires are expanded through the emission of embers which start spot fires downwind. Embers emitted from wildfires can cause structure fires at the wildland urban interface. Understanding how these embers interact with natural and human-made material is important in stopping the spread of wildfires and designing fire-resistant construction materials for buildings. Researchers need a way of observing and testing controlled ember-structure interactions that is realistic to wildfire scenarios and can be scaled down and made safe.

Background
The National Institute of Standards and Technology (NIST) developed a Standard Firebrand Generator (The Dragon) and later a Reduced‐Scale Continuous Feed Firebrand Generator (The Baby Dragon). We used their Baby Dragon schematic, shown here, as a starting point for our design but made key changes to meet our client's requirements including a more compact design that allowed for easy transportation and remote controls.

Value Proposition Statement
Wildfires are responsible billions of dollars in damage per year, but a better understanding of how these fires interact with materials could greatly limit these costs in the future. With the goal of better understanding of wildfires and their impact, an ember generator is being designed to output firebrands at a flux equivalent to that seen in wildfires. This will allow for testing and research of an accurate, scaled down wildland fire scenario. It has been shown to be difficult to accurately recreate these scenarios in a lab setting but having a system that can do this will be helpful in a further understanding of forest fire damage. Our group will design and build a working ember generator to meet the requirements needed for physical testing of wildfire impact on structural materials.

Deliverables
The end product will be a fully functional ember generator capable of outputting a steady stream of embers for 15 minutes without refueling.

Throughout the 2020-2021 academic year, our client requested a 35%, 65%, and 95% design. The 35% design is our initial design. After testing this prototype we will gather client feedback and redesign for the 65% benchmark and repeat this process for the 95% design. After building this model we will modify it to our client's specifications and deliver a final product.

Specifications
=Design Considerations= Our design was made to follow the specifications given to us by our clients, listed above. In the future, our ember generator will be connected to a wind generator, so our design kept that in mind. safety was an upmost concern, our design has several safeguards in place including heat resistant stainless steel stovepipe, propane leak detection, measures to prevent multiple airflows to reduce possible fire paths, and an emergency shutdown system.

Woodchip Feed System
The initial design for the wheel feeding system is a motorized shaft with four metal pegs which hold silicon fins that fill the diameter of the square hole between a hopper that holds the woodchips and the piping to the propane flame. Silicon was chosen because it is heat resistant and flexible, reducing clogging from larger woodchips.

=Project Learning= Our client gave us access to the Idaho Fire Lab, a concrete building used by the College of Natural Resources to study fire behavior, throughout the semester to test our designs for proper ember generation. We also had access to the Engineering Capstone Design Suites where we built our ember generator and tested different design features that weren't reliant on fire testing.

Spring 2021 Testing
In the spring we built the frame to our ember generator based on the desired dimensions given to us by our clients. The frame holds the propane tank and ember generator which consists of galvanized and stainless steel stove pipe, a blower, a motorized auger, a hopper that holds 7 lbs. of woodchips (enough to feed the fire for 15 minutes with an auger speed of 12rpm), and a propane torch connected to the propane tank.

The auger system was chosen after testing the wheel design over winter break at home and finding that it jammed easily. The funnel system in the hopper was chosen after testing different designs at the Design Suite using cardboard models. The funnel narrows the diameter of the hopper to 3 inches and allows the woodchips to fall continuously onto the auger without getting jammed, but slowly enough to allow the auger to carry woodchips evenly. The auger caught on the ridges of the stovepipe, so a smoother stove pipe insert was added under the auger. During testing it was also found that big woodchips caused the system to jam and took much longer to burn, so it was decided to only use small (1cm or less) woodchips.

The motor size was decided after testing in the Fire Lab, as shown in the picture. The auger was turned manually with attention to rpm as a set weight of woodchips was added to the system and burned. It was determined that the motor needed to have a 10-12rpm speed and 3.5ft-lb force.

Testing also showed that the hopper/auger system needed to be sealed to prevent airflow. When not sealed the additional airflow caused the fire to move up the auger to the hopper and through the hollow shaft of the auger which would damage the motor if connected. Additional measures to prevent fire in the feed area will also be taken, including narrowing the hole between the auger and the fire path in the vertical stovepipe.

=Final Design= Our final design is a compact ember generator, capable of holding 7 pounds of woodchips and producing a stream of embers for 15 minutes. The frame, made of 1.5"x1.5" perf steel railing and base plates holds the entire ember generator, with fuel, auger feed system, variable speed blower, and propane tank on 4 caster wheels for easy transport.

Figure key: 1 - propane tank 2 - propane torch entrance 3 - expanded steel and mesh, to hold woodchips 4 - 4" diameter auger, 18" length 5 - 12 RPM VDC motor 6 - funneled hopper, with a 7 lb woodchip volume capacity 7 - 10-35ft/s variable speed blower 8 - extended stovepipe for ember output

The stovepipe shown in blue-gray is stainless steel. These areas experience heat up to 1400 F. The stovepipe shown in gray is galvanized steel, a significantly less expensive material. These areas see less heat and therefore do not require stainless steel.

=Validation=

We have tested our prototypes throughout the semester to ensure proper ember generation, user friendly design, and that the design is safe to use.

Our design will be validated based on key requirements: - ember steam lasts for 15 minutes without refueling - entire system can be shut down, with embers stopping within 2 minutes - embers flow in one direction, horizontally out of the output extended stovepipe - embers are projected past flames - embers are capable of catching common building materials on fire

=Team Members=

=Additional Documentation=

Project Schedule Project Schedule

Meeting Minutes Minutes Folder

Presentations

Client Interview