Fuel Efficients Engines


rednuslura
06-30-2010, 12:54 PM
Hydrogen-boosted gasoline engine- The Best Efficiency Boosting Technology
Hydrogen-boosted gasoline engine technology or Hydrogen boost energy technology is new and just now beginning to emerge from the laboratory. It offers the prospect of an economic way to produce a small amount of hydrogen from gasoline with an on-board system designed to do so. Invented by scientists at the Massachusetts Institute of Technology, and being perfected by auto industry supplier ArvinMeritor in cooperation with the German automotive engineering firm IAV, this system may provide a cost-effective alternative to fuel-cell technology and traditional gasoline- and diesel-combustion engines. It's possible that hydrogen-boosted engines could bridge the gap between today's gasoline-powered vehicles and the fuel-cell vehicles of the future.

While fuel-cell vehicles may hold long-term promise, the reality is that they are years away from mass production. Critics cite the high cost of fuel-cell stacks, hydrogen fuel mass-production issues, and general fueling problems as key stumbling blocks. Some believe it may be decades before fuel-cell vehicles become widely available. European automakers have already turned to more expensive diesels but their cost and related complexity is increasing with stiff new emissions requirements for control of particulate matter and NOx emissions.

HYDROGEN BOOST OR HYDROGEN ENHANCEMENT

A potential way in which the lean misfire limit can be extended is through hydrogen enhancement. Hydrogen- enhanced combustion refers to the addition of a pure hydrogen or hydrogen-rich mixture to an engine running on gasoline in order to improve the combustion characteristics. The pure hydrogen or hydrogen-rich mixture, typically accounts for anywhere from 0 to 45% of the total energy flowing into the engine. The gasoline and the hydrogen-rich mixture can mix in the intake manifold or in the combustion chamber prior to combustion. Hydrogen-rich mixtures are typically produced from reformed gasoline, and ideally consist of 25% H2, 26% CO, and 49% N2 on a molar basis. For the addition of pure hydrogen into the engine, the most commonly used method in the vehicle is the electrolysis of water and for the addition of hydrogen-rich gas, the plasmatron fuel reformer is used. Because the partial oxidation undergone in the plasmatron is exothermic and therefore some of the fuel energy is released as heat, this reforming method has thermodynamic losses on the order of 15-20%. With its higher laminar flame speed, hydrogen speeds up combustion and extends the location of the peak efficiency as well as the location of the lean limit. In SI engines, hydrogen is inducted along with gasoline, compressed and ignited by a spark. In CI engines, hydrogen can be added in two ways, either by introducing hydrogen with air and using a spray of diesel oil to ignite the mixture or by introducing hydrogen directly into the cylinder at the end of compression.

HYDROGEN BOOST ENERGY

In this, hydrogen is not used as a fuel but as a combustion stimulant. Hydrogen burns more rapidly than hydrocarbon fuels because it is smaller and enters combustion reactions at higher velocity, has lower activation energy, and incurs more molecular collisions than heavier molecules. These characteristics make it possible to use mixtures of hydrogen with conventional hydrocarbon fuels such as gasoline, diesel and propane to reduce emissions of unburned hydrocarbons. Mixing hydrogen with hydrocarbon fuels provides combustion stimulation by increasing the rate of molecular-cracking processes in which large hydrocarbons are broken into smaller fragments. Expediting production of smaller molecular fragments is beneficial in increasing the surface-to-volume ratio and consequent exposure to oxygen for completion of the combustion process. PRODUCTION OF HYDROGEN The hydrogen can be obtained through many thermo chemical methods utilizing natural gas, coal (by process known as coal gasification) liquefied petroleum gas, biomass (biomass gasification) by a process called thermolysis, or as a microbial waste product called Biohydrogen or Biological hydrogen production. Most of today's hydrogen produced is using fossil fuel resources. Hydrogen can also be produced from water by electrolysis or by chemical reduction using hydrides or aluminium.
At present, hydrogen gas required for the enhancement of fuel is produced in the vehicle itself by the following two methods.
1. Electrolysis of water (Electrolysis unit)
2. Partial oxidation of fuel (Plasmatron fuel reformer)

ELECTROLYSIS UNIT

An Oxygen molecule has its lower orbital filled with two electrons, however it naturally occurs with only 6 electrons in its outer orbital. Since atoms always seek to have their orbitals filled to capacity, the Oxygen is seeking two more electrons.
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Hydrogen has only one proton and one electron. This means that because it has only one electron in one orbital, it seeks another electron so its orbital is at its maximum capacity of two electrons.

When an Oxygen atom meets a Hydrogen atom, both decide to share an electron. This means the Hydrogen now has the two electrons it desires, but the Oxygen still is short by one electron. Along comes another Hydrogen who wants to share with the Oxygen. Both Hydrogens now have two electrons in their orbital and the oxygen has its outer orbital filled to its capacity with eight electrons. The atoms are now have what is termed a' covalent' (or electron-sharing) bond between them. Now that all the atoms are content, we have a water molecule.
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When we apply electricity to this covalent bond, its breaks. This procedure is called electrolysis. As the covalent bond is broken, the Oxygen naturally migrates to the positive electrode. When enough Oxygen atoms arrive at the positive electrode, they combine in pairs and form Oxygen gas. The same happens to the Hydrogen atoms arriving at the negative terminal, the atoms pair and form hydrogen gas.

2H2O(l)+ electricity 2H2(g) + O2(g)

Electrolysis of water can be observed by passing direct current from a battery or other DC power supply through a cup of water (in practice a salt water solution increases the reaction intensity making it easier to observe). Using platinum electrodes, hydrogen gas will be seen to bubble up at the cathode, and oxygen will bubble at the anode. If other metals are used as the anode, there is a chance that the oxygen will react with the anode instead of being released as a gas, or that the anode will dissolve. For example, using iron electrodes in a sodium chloride solution electrolyte, iron oxides will be produced at the anode. With zinc electrodes in a sodium chloride electrolyte, the anode will dissolve, producing zinc ions (Zn2+) in the solution, and no oxygen will be formed. When producing large quantities of hydrogen, the use of reactive metal electrodes can significantly contaminate the electrolytic cell-which is why iron electrodes are not usually used for commercial electrolysis. Electrodes made of stainless steel can be used because they will not react with the oxygen.

The energy efficiency of water electrolysis varies widely. The efficiency is a measure of what fraction of electrical energy used is actually contained within the hydrogen. Some of the electrical energy used is converted to heat, a useless by-product. Some reports quote efficiencies between 50% and 70%. This efficiency is based on the calorific value of Hydrogen.

PLASMATRON FUEL REFORMER

A plasmatron is a reformer that converts various fuels to synthesis gas containing abundant hydrogen by applying partial oxidation reforming. The heat of the plasma itself and the internal reaction heat due to partial oxidation are used during the reforming in a plasmatron. Because of its fast starting and response times within a few seconds, it is applicable to a wide range of flow rates, and is particularly useful for the small scale systems, such as the reformer in a residual fuel cell, which needs fast response characteristics.
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The reaction in a partial oxidation plasmatron is

CmHn + (O2 + N2) mCO + H2 +. N2

Plasmatron fuel converters operate through the generation of a continuous discharge where fuel is undergone a partial oxidation process. The discharge generates numerous localized regions of intense heating (even through the resulting spatially averaged temperature increase can be quite modest), as well as large number of radicals that promote the reaction. The discharge and the subsequent exothermic reactions generate enough energy for the gasification of the remaining liquid fuel. The plasmatron induced turbulence also improves the mixing of the air fuel mixture as well as mixing of those regions where partial oxidation has started with those regions where conversion has yet to begin. Thus reactions occur over essentially the entire reformer volume facilitating high conversion efficiency, in a device with small volume. Rapid heating of the fuel and good air fuel mixing are also helpful in the minimization of soot production. In some circumstances, the plasma energy can be used to provide additional enthalpy increase of the air fuel mixture. This capability can be utilized to meet demanding requirements, such as rapid startup and quick transient performance.
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Introduction of hydrogen into the combustion process has been shown to:

1. Increase thermal efficiency and decrease fuel consumption.

2. Decrease carbon monoxide and unburned hydrocarbon emissions.

3. Increase NOx emissions unless proper timing and mixture adjustments are used.

4. The challenge to using hydrogen as a supplemental fuel is the storage and generation of hydrogen.

5. Use of electrolysis of water to create hydrogen to enrich combustion should be completely experimentally investigated before dismissing it as ineffective.

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