Ember Generator for Fire Behavior Research
|Ember Generator Design
|University of Idaho College of Natural Resources
|Easy Ember Team
|Fall 2020 - Spring 2021
|Doug Hardman & Alistair Smith / College of Natural Resources
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[edit | edit source]
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[edit | edit source]
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[edit | edit source]
Wildfires cost the United States billions of dollars in damage and human lives every year. A better understanding of how these fires interact with materials is needed in order to prevent or mitigate damage. It has been difficult to replicate wildfire scenarios in a lab setting in the past. Our ember generator was designed to output firebrands at a flux equivalent to that seen in wildfires. This will enable researchers in the College of Natural Resources to study how embers interact with different materials in a safe and controlled lab setting.
Deliverables[edit | edit source]
The end product of this project is a fully functional ember generator capable of outputting a steady stream of embers for 15 minutes without refueling. In addition, we will deliver a final report that details our design process, several presentations, prototype drawing to our client, a tutorial video on how to use the ember generator, an expo presentation, and this Wikipage.
Specifications[edit | edit source]The criteria shown in the table are the agreed upon project specifications from our first client interview.
Design Considerations[edit | edit source]
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, measures to prevent multiple airflows to reduce possible fire paths, and an emergency shutdown system.
Woodchip Feed System[edit | edit source]
The initial design for the woodchip feeding system was a motorized shaft with four metal pegs which held silicon fins that filled the diameter of the square hole between a hopper that contained the woodchips and the stove pipe that led to the propane flame. Silicon was chosen because it is heat resistant and flexible, reducing clogging from larger woodchips.
Upon further consideration and testing, we found that the motorized wheel system became jammed frequently and decided to pursue a entirely different design. In the final design, a hopper funnels woodchips onto a horizontal 18" long auger that drops the the woodchips onto the mesh. The auger is powered by a 12 VDC 4-8rpm 40in-lb gear motor. The hopper and motorized auger are both capped to prevent airflow that could cause the fire to move toward the woodchip feed. The hopper holds enough woodchips to feed the fire for 15 minutes with the auger set at 4 rpm.
Project Learning[edit | edit source]
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.
Fall 2020 Testing[edit | edit source]Our first test was a simple proof of concept that embers could be blown vertically up a stove pipe. We built a wooden frame that held a small propane torch. We added a 7" diameter stove pipe above the torch, which we outfitted with an internal steel mesh to hold woodchips. We loaded the woodchips from the top of the pipe and turned on the propane. After a fire was started, we moved the stove pipe from the flame to above a fan, to see if embers could be lifted out of the pipe without extinguishing first.
Embers were successfully lifted into the air. Our next step would be to create a stand that allowed for air to be blown through the system while the flame from the propane torch was still on.
Spring 2021 Testing[edit | edit source]
In the spring we built the frame on the ember generator. 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, in all measuring 48"x16"x40".
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. Upon further testing with a 12 rpm motor, it was decided that a smaller rpm motor would work better, so a 4-8rpm motor was purchased. Tuning the auger at 4 rpm with a full hopper of woodchips allowed for a continuous stream of embers for 15 minutes.
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.
Design Evolution[edit | edit source]
Our initial design, based partially on the NIST Baby Dragon, had a hopper with a motorized wheel to feed woodchips to a mesh holder. A propane flame ignited the woodchips from below and a blower attached to the side of the flame lifted the embers up the vertical stove pipe. An additional blower or wind tunnel could be attached to the top of the set up to blow embers horizontally downwind.
Upon testing, we discovered the second blower was unnecessary and simplified the design to an 'S' shape made of stove pipe with a multivariable blower connected to the bottom inlet. A propane torch is attached just above the first 90 degree bend with a circular mesh above the flame which held woodchips fed from a hopper attached to the side of the 'S' shape structure. Embers were lifted from the burning woodchips by the air from the blower out the top outlet and blown horizontally. A frame made to 80-20 t-slots is used to hold the structure in place.
Over winter break, the woodchip feed system was redesigned to a funneled hopper that output woodchips downward onto a horizontal motorized auger. The frame was redesigned to reduce cost, weight, and overdesign. The new frame is made of 1.5" x 1.5" perf steel railing. The stovepipe is composed of stainless and galvanized steel. The mesh used in previous designs was not durable enough, so expanded steel was used with a finer stainless steel mesh on top to prevent woodchips from falling though.
Additional testing showed the need to seal the hopper/auger system to prevent airflow that could cause the fire path to flow through the feed system. Electrical components were added to that the ember generator could be operated remotely.
Final Design[edit | edit source]
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.
1 - propane tank
2 - propane torch entrance
3 - expanded steel and mesh, to hold woodchips
4 - 4" diameter auger, 18" length
5 - 4-8 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
9 - Control box
→ This box has a 25 foot chord enabling a use to control the auger, blower, and propane shut off from afar. On the left, is the motor control which sets the speed of the auger. The dial changes the speed from 4 to 8 rpm. In the middle is the propane shut off switch. To the right is the blower speed control.
The stovepipe shown in blue-gray is stainless steel. These areas experience heat up to 1600 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.
We had a $3,100 budget to complete this project, of which we spent $1979.60.
Validation[edit | edit source]
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 was validated based on the key requirements of the ember generator:
- ember steam lasts for 15 minutes without refueling
→ Ideal conditions for the ember generator were found through testing. At an auger speed of 4 rpm, a low blower speed, and a low propane flow, the ember generator produces a steady stream of embers for 15 minutes when the hopper was completely filled with woodchips. Additional volume can be added to the hopper, to allow the system to run for a longer period of time if needed. - entire system can be shut down, with embers stopping within 2 minutes
→ Our propane shut off switch turns off the propane touch immediately. The auger needs to be switched off as well to cut the fuel source from any existing fire in the combustion chamber. By cutting both the propane and auger, embers cease within 2 minutes. - embers flow in one direction, horizontally out of the output extended stovepipe
→ After mitigating airflow to the feed system and covering small gaps in the stove pipe with header wrap, airflow is mostly in the intended direction. Embers are blown horizontally out the stovepipe outlet with various speed, based on the blower speed setting. - embers are projected past flames
→ Embers typically fall 4 to 6 feet from the flame. We proved this by placing straw at 4, 6, and 8 foot intervals from the outlet and visually observed the 4 and 6 foot piles catch fire from the embers.
- embers are capable of catching materials on fire
→ Embers caught straw on fire, as seen in the photos above.
Team Members[edit | edit source]
Major: Biological Engineering
Hometown: Boise, ID
Responsibility: Project Manager
Major: Biological Engineering
Hometown: Boise, ID
Responsibility: Documentation, Prototyping
Major: Mechanical Engineering
Hometown: Caldwell, ID
Responsibility: Scheduling, modeling
Major: Mechanical Engineering
Hometown: Emmett, ID
Responsibility: Client Contact, Communication
Major: Mechanical Engineering
Hometown: Genesee, ID
Responsibility: Budget, Purchasing, Prototyping
Additional Documentation[edit | edit source]
Easy Ember Meeting Agendas/Minutes
File:EasyEmber2021 Snapshot Day 3 Presentation.pdf
File:Easy Ember - Expo Technical Presentation.pdf