Fuel Efficient Cooker Student Materials

"The Stingy Stove"

STUDENT

WHY DOES THIS PROBLEM MATTER?

Burning wood for warmth, light, and cooking accounts for more than 90% of the energy used by many third world countries. The use of wood as fuel is a major factor in the destruction of forests in these countries, and in the associated severe problems of soil loss by erosion, inability to grow food (no soil), and reduced water supply (it all runs off). The traditional three-stone fire of these countries is very inefficient (figure 1). Typically, less than 6% of the energy in the wood is applied to food being cooked.

Figure 1: A traditional three stone cooking fire.

Mechanical engineers design efficient boilers and engines for power plants and automobiles. Some engineers even design microwave ovens and different types of stoves that you find in homes. Using their knowledge about heat transfer, combustion, and materials, engineers can design a cheap, reliable, higher efficiency cooker that could have a major impact on reducing fuel wood consumption and on reducing the severe problems associated with the destruction of forests. This project gives you a chance to think about ways to design an improved cooker, to create candidate cookers, and to test your ideas.

WHAT ARE WE SUPPOSED TO DO?

Your basic task is to design, fabricate, and test a simple cooking system, which will boil water quickly while burning a minimum of fuel, using only the materials indicated below. Specifically, you are asked to design and fabricate a Fuel Stingy Cooker (FSC) which meets the following requirements:

1. bring 1/2 cup of water to boil,

2. use the smallest possible amount of fuel,

3. bring the water to boil in a minimum of time,

4. be reusable.

WHAT EQUIPMENT AND MATERIALS CAN WE USE?

Your actual FSC may involve use of no materials other than the following:

• aluminum foil (5 sq. ft.),

• aluminum soda cans (any number),

• tin cans (any number),

• metal wire (ten ft.),

• paper clips (12 each),

• bricks/rocks (four each),

• newspaper (for fuel). You will need to prepare the newspaper fuel in some way such as tearing it or crumpling it into balls.

The tools you may use include some or all of the following: a ruler, wire cutters, pliers, tin snips, an awl (metal punch), a hammer, and punch type can opener (church key).

HOW WILL WE KNOW HOW WELL WE HAVE SUCCEEDED?

The Basic Performance Requirement for your FSC is that it bring 1/2 cup of water from room temperature to a boil while using less than four pages (double, with fold in center) of newspaper for fuel. A FSC meeting this minimum requirement will be judged satisfactory. An Extra Performance Index (EPI) will be calculated for your FSC using the formula:

EPI = [# sheets of newspaper used]x[time to boil (seconds)]

The less fuel used and time taken to bring the water to boil indicate an efficient design. Thus, an FSC with a low EPI will be judged to have high performance. There is a trade-off to consider here. The trade-off is whether or not to increase the amount of fuel to lower the time taken to boil? You and your team must consider this dilemma.

WHAT ELSE MIGHT BE USEFUL TO KNOW?

When wood or paper burn the energy is released mainly in the form of very hot gasses (there is some energy radiation). Since these hot gasses are lighter than air, they tend to rise. The energy from the hot gasses is then transferred to a cooking container which in turn heats and thus cooks the food.

Good burning is primarily dependent on the surface area of the fuel, on a good supply of air (really oxygen), and on a free flow of the hot gasses away from the fire. The rate at which the energy is transferred from the hot gasses to a container depends largely on the volume and temperature of the gasses, on the surface area of the container that they contact, on the length of time the hot gasses contact the container (figure 2). Therefore, the cooker your team builds must take into account the following design aspects:

Figure 2: Typical wood cooking fire

1. A container for the water that will not leak.

2. A way to load fuel into your cooker.

3. Provide cool, oxygen-rich air to feed the fire.

4. Direct the hot gases around the water container.

5. Provide a way to remove the resulting carbon dioxide gases from the combustion chamber.

6. The preparation of the fuel.

7. Lighting the fuel.

You team must consider these and other issues when you plan, construct, and test your cooker. Remember that you are a team and to create a successful design requires teamwork. Teamwork will help you and your teammates to overcome unforeseen problems and to not become discouraged. The bottom line of all this is that you and your team will want to have a good fire and have your hot gasses flowing freely in such a way as to contact lots of surface area of your container.

SAFETY CONSIDERATIONS UNIQUE TO THIS PROJECT

First, don't set fire to anything! Be very careful where you build fires. Don't sit your cooker on a flammable base, and be careful there is nothing flammable around for the wind to carry sparks to. Outdoors in the middle of a concrete slab is a good idea. You might protect your slab with dry sand or perhaps test in a large sand box. Further, have a fire extinguisher handy, be sure it is fully charged, and know how to use it.

Second, don't burn yourself or anyone else. Move slowly and carefully, don't joke around, and remember that hot things take a long time to cool down. Some tongs, kitchen hot pads, or insulated gloves might help too. Of course, be careful during the fabrication of your FSC and don't cut yourself on sharp edges or with tools. Mainly, think ahead and be careful!

This project was developed by John Garcelon.