To know the detailed working of fuel processors, you must first know more about fuel cells. To know about fuel cells click o the link below.

TAKE A LOOK : WORKING OF FUEL CELLS

In the blog post on fuel cells I have explained the way hydrogen and oxygen react to produce electricity with water as a by-product. There also some disadvantages with this method. The problems include the improper storing and distribution of hydrogen.

What is a fuel processor?

When comparing a hydrogen fuel cell to that of a gasoline fuel, the density of hydrogen is lesser. Meaning, it has a very less energy/unit volume compared to gasoline. This makes it practically impossible to store enough hydrogen and process it and hence make it drive a car to a maximum distance. Though this problem can be solved by using liquid hydrogen, which has a density more than normal hydrogen it has problems regarding its storing temperature. The storing temperature of liquid hydrogen is extremely low and also needs a high pressure. This problem makes the cost of production higher and also a difficulty in the mode of transportation.

Another important note about hydrogen is that its molecular structure is present in all natural gases like methanol, ethanol, and gasoline and so on. If these molecular structures could be easily removed from these natural fuels and thus used for making a fuel cell, all the above said problems could be solved.

Thus, a fuel processor, commonly known as a steam reformer is used to produce hydrogen from natural fuels. This is carried out by a device called reformer. This device is used to react the natural fuel along with steam at very high temperatures.

Need for Fuel Processors

We speak about using fuel cells because they do not create pollution in any way. They are also highly efficient. So, if the hydrogen is readily available for the fuel cells, it will turn out to be one of the biggest innovations of this century. So, the fuel processor is needed to provide pure hydrogen to make it practically applicable in fuel cells. By making the fuel processor possible, the transportation and storage will also become easier.

For this, the fuel processors should be highly efficient. Otherwise there will be no profit in replacing gasoline fuel with fuel cells.

Other than hydrogen experiments with methanol is also been carried out. Since methanol can be stored as a liquid fuel, it is easy to store in cars. It clearly replaces large tanks that are used for carrying gasoline.

The natural fuel called propane is also applicable for use in homes.  Nowadays many houses have direct pipelines coming from propane tanks.

Working of a Fuel Processor / Steam Reformer

Steam reformers are mainly of two types. They are

1. Methanol Reformer

In a methanol reformer, methanol [CH3OH] is mixed with water at a very high temperature such that they vaporize. This vaporized mixture is later sent to a high temperature chamber and mixed with a catalyst. This process is carried out so as to extract as much hydrogen as possible and at the same time reduce the emission of pollutants like carbon monoxide [CO] as much as possible.

Both the hydrogen and carbon monoxide are produced in the heated chamber. Out of this the carbon monoxide is reacts with oxygen to form carbon-dioxide. Oxygen is formed by splitting water vapour into hydrogen and oxygen.

The chemical equation of the entire reaction is shown below.

CH₃OH – CO + 2H₂

H₂O + CO – CO₂ + H₂

Methanol – CH3OH

Hydrogen – H₂

Carbon Monoxide – CO

Water – H₂O

2. Methane Reformer

Natural gases contain molecules of methane. This methane is extracted and then a similar process like a methane reformer is carried out. The methane present in the natural gas is extracted and then reacted with water vapour to get carbon monoxide and hydrogen. Then the carbon monoxide is converted to carbon dioxide like the methanol reformer. The reactions taking place in the process is shown below.

CH₄ + H₂O – CO + 3H₂

H₂O + CO – CO₂ + H₂

Methane – CH₄

Water – H₂O

Carbon Monoxide – CO

Hydrogen – H₂

Combination of fuel cells and fuel processors

As the fuel cells have to provide the electricity constantly, the fuel processors have to work in parallel with it.

Suppose you want to drive a car that is powered with fuel cells. When the accelerator is pressed, the controller of the motor supplies current to the electric motor. This helps the electric motor in generating more torque. For the controller to supply power, the fuel call has to work in order to make electricity. When the amount of hydrogen becomes less, the fuel processor starts its mechanism and extracts the hydrogen from methanol. Though such a system has never been adapted properly, we can expect this to happen soon.

Drawbacks of Fuel Processors

Though the amount of carbon dioxide is not emitted as much as other technologies, it is still considered a threat to global warming. As fuel processors are used to provide the hydrogen, the emission of CO₂ is sure. If the pure hydrogen could be used this disadvantage would not have happened.

Though the efficiency of the fuel processor is less, the overall efficiency when connected to a fuel cell is very less. Most of the energy is wasted in the form of heat and high pressure.

Description.
The circuit given here is of a 2 x 32 Watt stereo amplifier using the famous TDA2050V IC from ST Microelectronics. The TDA2050V is an integrated monolithic 32 watt class AB audio amplifier IC available in the Pentawatt package. The IC has lot of god features like low distortion, short circuit protection, thermal shut down etc.

Two TDA2050V ICs are used here, one for each channel. For each channel the input audio signal is fed to the non-inverting input of the IC through 1uF (Non-Polarized electrolytic) capacitor and this capacitor performs the job of DC decoupling. The ratio of the 22K and 680 ohm resistors determine the gain of each channel. The network comprising of 2.2 ohm resistor and the 0.47uF capacitor connected between the output of the amplifier and ground forms a Zobel network which represents the impedance of the speaker appear as a steady resistive load to the amplifier output and this dramatically increases the high frequency response.

Circuit diagram.

Notes.

• Assemble this circuit on a good quality PCB.
• Use 18V DC dual power supply for powering the circuit.
• Fit the ICs with adequate heat sinks.
• Connecting 10K POTs at input lines will serve as a volume control.
• For full output power the circuit require 200mVpp RMS input.

What is a Fuel Cell?

Fuel Cell is an electrochemical device that is used to convert an open source fuel into electricity. An electrolytic process has to take place inside a cell in which there is an open source fuel [hydrogen] and an oxidant [oxygen]. Both the fuel and oxidant reacts in the presence of an electrolyte. Both the fuel and oxidant are introduced into the cell, where they react and the output product is carried out of the cell and stored. The electrolyte is left as it is inside the cell. This process can take place non-stop for a long time as long as the flow of resources are maintained.

The result obtained by combining hydrogen and oxygen is water. As a result of this process, electricity is formed. Although batteries are also electrochemical devices, they are different from a fuel cell. They use reactants from an external source and the chemicals have to be stored inside the battery. These chemicals react to each other to produce the electricity. Thus they use closed source fuel. As the device stores the required energy in a chemical form, the battery has to be recharged at intervals or have to be replaced.

Other than hydrogen the other types of fuels commonly used are hydrocarbons and even alcohol. The most commonly used oxidants are oxygen, chlorine and also chlorine dioxide.

Need of Fuel Cells

The main reason for the use of fuel cell is the increasing dependency on the use of fossil fuels. The whole world has burnt so much fossil fuel like oil to such an extent that they have become one of the main reasons for the pollution. This pollution has eventually resulted in the global warming and extreme climate change. Other than the environmental problems, the use of oil has become large enough that the sources of production have become less. As a result more challenging expeditions will have to be made for oil deposits which results in a very high oil price.

Fuel cells are surely an alternative to the above said problems. They are a clear solution to the dependency of fossil fuels. The best feature of fuel cells is that they produce pure water as the by-product. As a result they are pollution free as well.

As a part of making hydrogen fuel cell dependent vehicles possible in the most efficient and cheapest way, American president George Bush announced the Hydrogen Fuel Initiative program (HFI) in the year 2003. The country has also spent nearly one billion dollars for the research of better fuel cells. The technology will surely become practical soon and thus bring a solution to the rising oil problems.

Basic design and Working of a Fuel Cell

For any type of fuel cell, there are mainly three segments.

1. Anode
2. Cathode
3. Electrolyte

The type of electrolyte used is what defines the type of fuel cell used. Whatever may be the type of fuel cell, their basic operation is always the same.

With the combination of the three segments, two main chemical reactions take place. A catalyst will be present at the anode. This anode catalyst, mostly platinum powder, is used to oxidise the hydrogen fuel. Thus the hydrogen gas turns into ions and electrons. Out of these, the ions make way through the electrolyte to the cathode. As soon as they reach the cathode, they combine with the cathode and then react with the oxidant to produce water.  The electrons pass through a wire producing the electricity. Nickel is mostly used as the cathode catalyst. Thus the electricity is formed at the load and water is obtained as the by-product.

Though a fuel cell can normally produce only up to 0.7 volts at full load, the desired amount of voltage can be obtained by combining the fuel cells in series. For obtaining the desired amount of current, the fuel cells can be connected in parallel.

The fuel cell also has certain losses which causes a lesser amount of voltage to be produced at a higher current rate. Some of the losses are ohmic loss. Activation loss and also the loss due to the mass depletion of reactants called mass transport loss.

Different Types of Fuel Cells

The type of fuel cell differs mainly according to their operating temperature and the different electrolytes used. Some of the most common are given below.

Polymer Electrolyte Membrane Fuel Cell (PEMFC)

Polymer Electrolyte Membrane Fuel Cell (PEMFC) uses electro-chemical reaction to react both hydrogen and oxygen to form water as a by-product and also electricity. The device is said to be completely pollution free and with an efficiency of more than 50%. As the name suggests, in between the anode and cathode terminals is a sandwiched membrane called the proton-exchange polymer membrane. This will act as the electrolyte. This membrane can conduct only positive charged ions and stops electrons from passing through. To use this electrolyte in this device, the membrane should be in the hydrated form so as to be in the stable form.

The anode, a cathode and the membrane are together called as the Membrane Electrode Assembly [MEA]. The earlier mentioned catalysts are used here as well. But the anode catalyst will be assembled in a carbon fibre substrate.

In the anode, the hydrogen gas reacts with the anode catalyst causing it to split into protons and electrons. The protons are then carried to the oxidant region where they react together form multi-facilitated proton membranes. The electrons travel through another wire and react with the oxygen as well as protons and thus water is produced. When the electron travels through the external circuit, electricity is also produced. Take a look at the diagram given below.

As usual the voltage produced will be very low [0.5 volts to 1 volt]. The wanted voltage can be obtained by adding fuel cells in series. This device is mostly efficient at low temperatures from 50 to 70 degree Celsius and also a high power density.

Alkaline fuel cell (AFC)

This type of fuel cell was been introduced since the early 1960’s. As the electrolyte used for this device is aqueous alkaline solution like potassium hydroxide, the procedure for electricity consumption is rather expensive.

Direct Methanol Fuel Cell (DMFC)

This device has somewhat the same characteristics as that of a Polymer Electrolyte Membrane Fuel Cell (PEMFC). But the only difference is in the percentage of efficiency. It has lesser efficiency [<30%] and also needs a huge amount of anode catalyst and thus highly expensive. The device uses Polymer membrane, mostly ionomer as the electrolyte.

Molten-Carbonate Fuel Cell (MCFC)

Molten alkaline carbonate like sodium bicarbonate is used as the electrolyte. They can produce high powers up to 100 Mega Watts. Thus they can be used as high power generators. They can also be operated at high temperatures up to 650 degree Celsius. They are not so expensive in production and hence can be used for commercial uses.  It has an efficiency of almost 55%.

Phosphoric Acid Fuel Cell

Molten phosphoric acid is the electrolyte used in this type of fuel cell. It operates at high temperature up to 200 degree Celsius. It has an efficiency of up to 55%. This type of fuel cell is most commonly used in commercial cars.

Solid oxide Fuel Cell (SOFC)

This is one of the most commercially used fuel cell as they have the highest operating life. It has a very high operating temperature of 1,000 degrees Celsius. But other parts of the fuel cell may not be able to withstand at this temperature making it highly unstable. But, when used in a continuous state they can be highly reliable. At high temperatures the device can produce water in the form of steam which can be easily transported through steam turbines to produce more electricity, thus increasing the efficiency of the system. This device is also special in the case where a wide variety of fuels can be used. Most of the petroleum products can be used as the fuel. The electrolyte used in the cell is called yttria stabilized zirconia (YSZ). This electrolyte is good for large scale power generation and has the same characteristics as all the other electrolytes.

As the device has a very high operating temperature, there are some disadvantages as well. There may be unwanted number of reactions taking place inside the cell due t the high temperature. As a result of these reactions carbon dust and also graphite may be built up on the anode making it insufficient from reacting with the catalyst.

Fuel Cells – Advantages

• It is compact, light weight and has no moving parts. Thus it is 99.9% reliable.
• Pollution is reduced by 99%. This is the lowest pollution rate when compared to batteries as well as gasoline powered devices.
• If the device is used to power cars, it means that the efficiency level of all the three components will be different. Though the basic components of the car like tyre, transmission and so on are the same the efficiency is define on the power produced and the power converted to mechanical power. In the beginning almost 80% efficiency is produced by converting hydrogen into electricity. When this electricity is converted to mechanical energy to run the device, motor/motors and also an inverter will be needed. This will also have a efficiency of 80%. Thus the overall efficiency will be almost 65%, which is a high efficiency when compared to battery and gasoline. The overall efficiency of a battery is considered to be 60% and that of a gasoline powered vehicle is 40%.

Fuel Cells –Disadvantages

1. Cost

The overall production cost of a fuel cell is very costly. The anode catalysts like platinum and also gas diffusion layers almost hold up to 75% of the total cost. When compared to batteries and gasoline powered vehicles, they tend to be the costliest. If a kilowatt of power produced by the fuel cell comes around $35 to $40, it can be used. Currently, it costs up to $75. This can be done only by extensive research in replacing platinum with some other cheaper substance.

2. Durability

Most of the fuel cells that are used in cars, like PEMFC does not operate well enough in higher temperatures. As a result they have less tolerance level and less stability under running conditions.

3. Bad infrastructure

In order to make vehicles with fuel cells enough amount of hydrogen has to be generated. After generation process, they must also be carefully transported from the generating plants. This can be done only by transportation or pipelines. For this a proper infrastructure has not yet been developed.

Fuel Cells – Applications

• Can be used as power sources in remote areas.
• Can be used to provide off-grid power supplies.
• Can be applicable in both hybrid and electric vehicles.

Sometimes you may be unable to find a particular inductor the market. This is actually a problem faced by most of the electronic hobbyists and the problem becomes more serious if your project is RF related. The inductors required for RF circuits (antenna, tuner, amplifier etc) are almost impossible to find in the market and the only solution is nothing other than home-brewing them.

With a little practice and patience you can construct almost all air cored inductors at home. The inductance of an air cored inductor can be represented using the simplified formula shown below and to calculate the inductance of an air-core inductor, the same equation may be used.

L  = [d² n²] / [18d + 40l]

• Where’ L ‘  is the inductance in Micro Henries [µH]
• ‘d’ is the diameter of the coil from one wire centre to another wire centre. It should be specifies in inches.
• ‘l’ is the length of the coil specified in inches.
• ‘n’ is the number of turns.

Notes :

• The length of the coil used in the inductor should be equal to or 0.4 times the diameter of the coil.
• As shown in the equation, inductance of the air-core inductor varies as the square of the number of turns.  Thus the value ‘l’ is multiplied four times if the value of ‘n’ is doubled.  The value of  ‘l’ is multiplied by two if the value of ‘n’ is increased up to 40%.

Winding the coil.

• The coil must be first wounded on a plastic former of the adequate diameter (equal to the required core diameter).
• The winding must be tight and adjacent turns must be as close as possible.
• After the winding is complete, slowly withdraw the core without disturbing the coil.
• Now apply a thin layer of epoxy over the coil surface for mechanical support.
• Remove the insulation from the coil ends.

Example

Suppose you want to make an inductor which produces an inductance of 10 μH. The diameter of the coil is 1 inch and the coil length is given by 1.25 inches. You will have to find the number of turns of the coil.

Thus substituting the values in the above equation t

L = 10 inches

d = 1inch

l = 1.25 inches

n = √{L [18d * 40l]} / d = 26

Thus, the number of turns of the coil will be 26.

Number of turns/inch = 20.8

Description.
A lot of electronic circuits in the domain of audio amplifiers are already been published here. This circuit is a little different because it is a four channel amplifier. Each channel of this amplifier can deliver an output of 15Watts into a 4 ohm speaker. The amplifier can be operated from a single 12V DC supply and this makes it possible to use this amplifier in car audio applications too.

The circuit is based on the 15W BTL X 2 channel audio power amplifier IC TA8215 from Toshiba. Even though chip is specifically designed for car audio applications it can be also used for home audio applications. Two TA8215 ICs are used here in order to obtain a 4 channel amplifier system. The circuit is designed almost exactly as per the application diagram in the ICs datasheet. Pins 7 and 19 are the Vcc pins of the ICs internal integrated power amplifier stages and these pins are connected to the positive supply. Pin 9 is the Vcc pin for ICs internal preamplifier and it is also connected to the positive supply. Pins 13 and 14 are the internal power amplifiers ground pins and they are tied together and connected to the ground. The internal preamplifier’s ground pin (pin5) is connected to the common ground through a 10 Ohm resistor which makes the input ground separated from the common ground by a resistance of 10 ohms and this improves the noise rejection. The 100uF capacitor works as a power supply de-coupler. The resistor networks connected to the output lines of each amplifier improves the high frequency stability. The variable resistors (R3, R4, R12 and R13) works as the volume controller for the corresponding channels.

Circuit diagram.

Notes.

• Assembling the circuit on a good quality PCB is a must for obtaining optimum sound quality.
• Use 12V DC for powering the circuit.
• The ICs must be fitted with adequately sized heat sinks.
• R3, R4, R12 and R13 serves as volume controllers.
• K1 to K4 can be 4 Ohm, 20W speakers.
• This amplifier circuit can be used in a variety of applications such as car audio systems, home theater systems, personal audio systems, public address systems etc.