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Fuel & battery technology

Thảo luận trong 'Tiếng Anh chuyên ngành' bắt đầu bởi binhminhbkhn, 1/2/10.

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    Alternative fuels
    Alternative fuel sources are used as a way of reducing the operating cost of vehicles, or to reduce pollution from vehicle emissions, or both.
    Some alternative fuels can be mixed with gasoline as a fuel additive to reduce the total amount of gasoline used, others are a complete fuel alternative which may require some modifications to the vehicle.
    Ethanol is usually derived from an organic process such as the fermentation of sugar cane, and is therefore referred to as a bio-fuel. It is normally used in the ratio of 9:1 or 9 parts gasoline to 1 part ethanol and is primarily used to reduce the negative emission effects of gasoline.
    Methanol is produced from wood or other organic materials. Its calorific value, or burn rate, is not as high as that of gasoline fuel and cannot be used in conventional vehicles without significant modifications.
    Liquefied Petroleum Gas or LPG is a petroleum derived colorless gas, and has been used for many years to power specially modified gasoline engine vehicles. It is the third most common fuel and emits much fewer harmful emissions than gasoline. It is generally cheaper than gasoline and is non-toxic and non-poisonous with a very small flammability range. It is popular with high-mileage applications such as taxis, where the cost of vehicle modification can be recouped over time more easily through lower fuel costs.
    Compressed Natural Gas or CNG is being used as an alternative fuel in vehicles such as light-duty passenger vehicles, delivery trucks and buses. CNG powered vehicles use natural gas stored in cylinders at pressures of 2,000 to 3,500 pounds per square inch or 140 to 240 Bar.
    Liquefied Natural Gas or LNG is being used in heavy-duty diesel powered vehicles such as long-haul trucks, delivery trucks and buses. LNG is almost pure methane and has an energy storage density much closer to gasolinethan CNG, but for the gas to become a more compact and easily stored liquid it has to be cooled to an extremely low temperature, minus 263.2 degrees Fahrenheit, or minus 164 degrees Celsius. The need to keep the liquid very cold at all times limits the more widespread use of LNG.
    Natural gas, whether liquified or compressed, is less expensive than diesel and natural gas vehicles are substantially cleaner than comparable diesel vehicles.

    Fuel cells
    Fuel cell technology has been used for a number of years in the space industry. Recent improvements in technology and the need to seek alternative fuel technologies for the automotive industry have seen a number of manufacturers develop fuel cell technology for use in automobiles. In a vehicle powered by a fuel cell, the electrical motor is powered by electricity generated by the fuel cell.
    A fuel cell is an electro chemical device that combines hydrogen and oxygen to produce water and in the process it produces electricity and heat. Fuel cells operate without combustion so they are virtually pollution free.
    Another electrochemical device you are already familiar with is the vehicle battery. In a battery all the chemicals are stored inside, and it converts those chemical into electricity. This means the battery eventually becomes discharged until you recharge it.
    In a fuel cell, the chemicals oxygen and hydrogen constantly flow through the cell, like fuel through an engine, so it continues to produce electricity as long as fuel is available.
    There are four basic elements to a fuel cell, the anode, the cathode, the electrolyte and the catalyst.
    Pressurized hydrogen flows into the fuel cell anode. The platinum coating on the anode helps to separate the gas into protons (hydrogen ions) and electrons. The electrolyte in the center allows only the protons to pass through to the cathode side of the fuel cell. The electrons cannot pass through this electrolyte and flow through an external circuit in the form of electric current.
    At the same time, oxygen flows into the fuel cell cathode where another platinum coating helps the oxygen, protons, and electrons combine to produce pure water and heat.
    A fuel cell only produces a voltage of about 0.7 volts. To get the required voltage for automotive applications a fuel cell stack is created. The number of fuel cells in the stack determines the total voltage, and the surface area of the cells determines the total current.
    Fuel cells use hydrogen and oxygen to produce electricity. The oxygen can come from the air, however hydrogen it is not readily available. Hydrogen is difficult to store and distribute. To address this problem in automotive applications, an additional device called a reformer is used.
    The reformer turns hydrocarbon or alcohol fuels into hydrogen. So to make fuel cells practical for automotive applications car manufacturers are developing better fuel cell systems and technology to improve the efficiency of the system while using readily obtainable fuels.

    Electric motors
    Vehicles that include electric drive motors have many advantages over the traditional vehicle. Lower noise and gas emissions are among the major benefits.
    While other benefits include, fewer moving parts, less maintenance requirements and, increased reliability.
    Power for the electric drive motor is obtained from either rechargeable storage batteries or a generator via an electrical inverter/converter.
    The most popular types of electric motors used are brushless, multi-phase, synchronous and permanent magnet motors.
    The meanings of these terms are:

    • Brushless: Brushes and commutators are not used
    • Multi-phase:The stator contains more than one winding, usually three
    • Synchronous: The speed of the rotor is synchronized to the frequency of current flowing through the stator windings. This design maintains excellent power and efficiency characteristics even at low speeds
    • Permanent Magnet:The rotor is made from very powerful rare earth permanent magnet alloys. Typically neodymium-iron-boron or samarium-cobalt.
    Basic Operation
    The computer controls the direction, frequency, order and amplitude of current flowing through the stator windings. The magnetic field produced by this current reacts with the permanent magnets of the rotor. This causes the rotor to rotate. It is important to note that these systems operate on dangerously high voltages typically 500 volts.
    The electric motor is connected to road wheels via gears, chains, or shafts.
    Vehicle braking and current flow back into the battery The electric motor can also be used as a generator to provide partial recharging of batteries whilst braking or during over-run.

    Biodiesel is a processed fuel derived from vegetable oils, such as rapeseed/canola, that can be readily used in diesel-engine vehicles. Some modified diesel engines can run on straight vegetable oils (SVO) or waste vegetable oils (WVO), but processed biodiesel fuels can run in any diesel engine designed for petroleum-based fuels. Although biodiesel runs in unmodified diesel engines and can be distributed through normal channels, it is generally more expensive to produce than petroleum diesel, although because of taxes and subsidies in some countries, such as Germany, biodiesel can actually be cheaper to buy than regular diesel fuel.
    Biodiesel is biodegradable and non-toxic, and has significantly fewer emissions than petroleum-based diesel. It also has a higher lubricity index than petrodiesel fuels which can help to prolong the life of fuel injectors. Biodiesel is a better solvent than petrodiesel, so it helps to clean the fuel system, and it can break down and flush out residue deposits in vehicles that have been running on petrodiesel. Switching over to biodiesel fuel will therefore quickly clog up the fuel filter in older and dirty engines, so this will need to be changed after the lines have been cleaned by the fuel.
    Biodiesel is oil-based so it does not mix with water, but it is hygroscopic, which means that it attracts water from the atmosphere. Contamination with moisture can corrode fuel system components such as pumps or injectors, it can make the engine harder to start and produce less power and more smoke, and it can encourage the growth of microbes in the vegetable-based fuel. The fuel will also degrade rubber gaskets and hoses, although it does not affect synthetic rubber, from which most components are now made.
    Biodiesel is a light yellow to dark yellow liquid, and it has a viscosity similar to petrodiesel. It can be used by itself or mixed with regular diesel in any concentration as an additive. The 'B' rating of the fuel indicates the amount of biodiesel in any fuel mix. Fuel containing 20% biodiesel is therefore labeled B20. Pure biodiesel is labeled B100.

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