Jump to content
Mechanical Engineering Community

Blogs

 

Blogging Event at mechanical engineering

dear fellow professional engineers, professors & students/ We invite you to take part in mechanical Engineering Blogging event. You need to create a blog on mechanical engineering with one of your favorite topic. http://mechanical-engineering.in/forum/ind...hp?autocom=blog The topic need to be related to mechanical engineering. key points to evaluate Content Presentation Regards Mechanical Engineering We are also looking for sponsors for this and coming future events.

admin

admin

 

Publish your engineering thoughts on mechanical-engineering.in

We have come up with Blogs section for mechanical engineers http://mechanical-engineering.in/forum/ind...hp?autocom=blog We invite all mechanical engineers, professors, Readers, and students to create your free blog and make best use of this free service. Whenever you start publishing your posts Make sure 1. Create Friendly URL of your blog 2. Activate Ping Service This will help other users to find your blog in search engines Both feature are in Blog Settings options Thanks and Regards http://mechanical-engineering.in/forum/ind...hp?autocom=blog

admin

admin

 

To Connect mechanical engineers and engineering students

Dear Mechanical Enginers and engineering students, Smart application has been added on http://mechanical-engineering.in/forum/ to connect mechanical engineers and engineers students. You can join this application. the basic premise is that you can login with your Google (or Yahoo, AIM, OpenID) credentials on third-party applications without signing up for a separate account and can also invite other people to join from within the application, either by emailing them (you’ll see a list of your Google contacts) or sharing the links on MySpace or Facebook. looking forward to meet Thanks and Regards Mechanical Engineering Portal

admin

admin

 

Get ur email at mechanicalengineers.in webmail

Dear Engineers Now u can have ur own mechanicalengineers.in Webmail, Powered by Google. http://mail.mechanicalengineers.in/ Please note This email service is only for members of http://mechanical-engineering.in/forum/ This email is equivalent to gmail service Your username on http://mechanical-engineering.in/forum/ (forum) and mail username are two different things, though u can opt for same username also Same email can be used for using Google Talk For more details visit us at.. http://mechanical-engineering.in/forum/ind...p?showtopic=101

admin

admin

 

Hello mechanical Engineers and engineering students

Smart hello to mechanical engineers and engineering students across the globe. We invite you to be part mechanical-engineering portal designed for mechanical engineers. This portal has been created specially for mechanical engineers and engineering students. We look forward to grow on mechanical engineering portal Join us in mechanical engineering forum http://mechanical-engineering.in/forum/index.php?act=idx and also ask your friends to be part of mechanical engineering portal Cheers http://mechanical-engineering.in/forum/index.php?act=idx

admin

admin

 

Feedback needed

Smart Hii, the reason of writing here is to ask for suggestions on a portal http://mechanical-engineering.in designed by me. The idea here is to capture and share the formal and informal mechanical engineering knowledge used as an industrial practice.
to provide the communication portal for working engineers, engineering students and fresh young engineers.
to provide e-resources for students for enhancing their engineering skills and career opportunities
to provide the lattest technical and maagerial practices across the engineeirng world
For this I have designed the portal in three sections. (A) Forum http://mechanical-engineering.in/forum/ ( Gallery http://mechanical-engineering.in/forum/ind...autocom=gallery © Blogs http://mechanical-engineering.in/forum/ind...hp?autocom=blog One time user name has to be created for posting in the forum, gallery and blogs.. Readings can be done directly as a guests. Username can be created with a single form http://mechanical-engineering.in/forum/ind...Reg&CODE=00 The structure so far created for forum is as below Meet N Greet Mechanical Engineers http://mechanical-engineering.in/forum/ind...hp?showforum=31 Mechanical Engineering Basics http://mechanical-engineering.in/forum/ind...hp?showforum=34 Mechanical enginering Applications http://mechanical-engineering.in/forum/ind...hp?showforum=32 Computer Applications in Mechanical Engineering http://mechanical-engineering.in/forum/ind...hp?showforum=33 Career Enhancement as an Mechanical Engineer http://mechanical-engineering.in/forum/ind...hp?showforum=37 This is the so far structure created by me. I look forward for your suggestions and feedback. Your few minutes considerations will help me to go in right direction with smart approach. Thanks and Regards Er Saurabh Jain

admin

admin

 

Cad cam forum for cad cam lovers

Dear Friends, http://mechanical-engineering.in/forum/ has started CAD CAM Technology forum and Software Talks forum Mastery of complex http://mechanical-engineering.in/forum/ind...hp?showtopic=33 List of Softwares used by mechanical engineers http://mechanical-engineering.in/forum/ind...hp?showtopic=48 Cad Cam technology http://mechanical-engineering.in/forum/ind...hp?showforum=12 Software Talks http://mechanical-engineering.in/forum/ind...hp?showforum=13 Thanks and Regards Saurabh jain

admin

admin

 

How Our Four Stroke Spark Ignition Engine Works?

Many of us may know about two stroke or four stroke engine.Those who are from mechanical or automobile field must have to familiar with this term.Actually two stroke or four stroke is the cycle of any reciprocating engine.When only two stroke required to complete the reciprocating engine cycle then that engine is known as two stroke engine,and when four stroke required to complete the cycle then it is known as four stroke engine. In four stroke engine the work is obtained only during one stroke out of these for a single cylinder engine or for every cylinder individually for multicylinder engine.If you have any automobile vehicle or machine,then you better know the above terms.But ever you know,which are these strokes and how it perform? Interested to go deep in topic? Read below description. 01)Suction Stroke. This is first stroke of your engine.During this stroke the piston is moved downward from Top Dead Centre by means of crankshaft which is rotate by electric motor.This movement increases the size of combustion space thereby reducing the pressure inside the cylinder,as the result,the higher pressure of the outside atmosphere forces the air into combustion space through suction valve.The exhaust valve remain closed in this stroke. A carburettor is put in the passage of incoming air which supplies a controlled quantity of fuel to this air.This air-fuel mixture thus comes in engine cylinder. 02)Compression Stroke. This is second stroke of your engine.The air-fuel mixture is compressed during this upward stroke.The compression,forces the fuel into closer combination with air.Heat is produced due to compression aids the combustion of fuel.Just a little before the end of compression stroke the mixture is ignited by a spark produced by spark plug.During this stroke suction and exhaust valve remain closed. 03)Power Stroke. This is third stroke of your engine.You may call it as Expansion Stroke also.The air-fuel mixture which burns at the end of compression stroke expands due to heat of combustion.This expansion of burnt air-fuel mixture exerts pressure in the cylinder and on the piston,and under this impulse the piston moves downward thus doing useful work.Suction and exhaust valve remain closed during this stroke. 04)Exhaust Stroke. This is last stroke of your engine.During this stroke the suction valve remain closed while the exhaust valve opens.The greater part of burnt gases escape because of their own expansion.The upward movement of piston pushes the remaining gases out of the open exhaust valve.Thus complete the exhaust stroke and one cycle of engine. Number of cycles are depend upon the rotation per minute of your engine.Higher the R.P.M.,higher the workdone carried out by engine.I hope,this information will better help you to understand the working of your four stroke engine.

saurabhjain

saurabhjain

 

Welcome @ mechanical Engineers Portal

Dear All Engineers and engineering students This portal has been created to promote mechanical engineering activities and developments We invite you to be part of portal. This portal is divided in three sections Blogs Gallery Forum Your contributions will be highly appreciated.. Thx and Regards Mechanical Engineering team

admin

admin

 

fuel cells down the road?

Before cars and buses can make their mark, some developers say the best economic case for fuel cell mobility applications may be found in the warehouse At a gathering of fuel cell developers at Germany's giant Hanover Fair this past April, Jacob Hansen talked about plans of his Danish startup, H2 Logic A/S, to launch the first of seven fuel cell-powered demonstration cars in Scandinavia this fall. Not possible, countered someone else close to the project, looking at a mockup of the vehicle across an aisle. Too much engineering remains, he said. No, replied another member of the H2 Logic team, the car will be ready. Fuel cells promise mass transit without the pollution, odor, or noise. While several cities operate prototype fuel cell buses, their range is limited and their costs aren't competitive with conventional engines. In popular perception, the automobile has become the poster child of the fuel cell revolution, but the exchange at Hanover underscores the rocky road to commercialization. Until there are service stations where a driver can pull in and buy hydrogen, the personal automobile is irrelevant. Municipal buses avoid that problem. They circulate within driving distance of a central fueling station. It could contain hydrogen as well as any other fuel. But there is another vehicle that is drawing attention for its possibilities in the fuel cell universe. It doesn't even go onto the public highway, so it stays close to its fuel supply. It isn't a toy, and in fact does essential work, and it is around these points that developers are trying to build a business case for it. According to several developers, the road to fuel cell buses and cars will be traveled first by the lowly forklift. Why forklifts? Fuel cell vehicles may dazzle with the claim of zero-emission performance, but somehow the wedding of technology and practical uses keeps getting pushed back. More than 30 years after fuel cells were touted as a solution to the original energy crisis, the global industry's research and development spending is still twice as high as its total sales, according to a survey by the U.S. Fuel Cell Council. Engineers have solved many of the issues that made real-world uses a receding target. Equally important, politicians responding to high oil prices and increasing concern over global warming have begun to pump money into alternative fuels. This past March, for example, Germany proclaimed that it would invest 500 million euros over the next 10 years and subsidize half the purchase cost of any fuel cell vehicle. The U.S. Department of Energy is ramping up spending, and the Federal Transit Administration recently set aside $49 million to test fuel cell buses. No wonder H2 Logic was at April's Hanover Fair with 130 other fuel cell exhibitors, 30 percent more than turned out in 2006. February's Fuel Cell Expo in Tokyo drew 462 exhibitors, up 50 percent from 2006, and 24,494 visitors from 53 countries. They are following the money, hoping that government funding will help close the cost gap between today's fuel cells and tomorrow's commercial vehicles. Yet even if the government picks up half the tab, it's not easy to find applications that make economic sense. Although fuel cell cars get lots of press—and nearly every major automaker and many smaller companies like H2 Logic have small fleets—they are essentially prototypes. Buses are more promising. "There is a real market in fuel cells for buses," said one exhibitor at Hanover. Yet fleets remain small. Europe's largest demonstration program involves 11 cities, if you include Perth, Australia, and about 27 buses. Berlin hopes to use German subsidies to launch a fleet of 14 buses. More typical is Sunline Transit Agency of Thousand Palms, Calif. It operates two hydrogen-powered vehicles, but only one uses a fuel cell. The other burns hydrogen in an internal combustion engine. In November 2006, Sunline received a $2.8 million grant to put a second fuel cell bus into operation in 2008. In the arguments of developers, economics set fuel cell forklifts apart from other vehicles. One of those arguments is offered by Mark Kammerer, head of business development for Hydrogenics Corp., a Mississauga, Ontario, developer of fuel cells that is partly owned by General Motors Corp. According to Kammerer, a large warehouse might operate a fleet of 200 or 300 forklifts. Each forklift battery operates for eight hours on a single charge. Most 24/7 warehouses need more than one battery for each forklift. While one powers the machine, the other recharges, and perhaps a third is kept as a backup. When the forklifts run low, they go back to the recharging station to swap out batteries. This is no simple operation. A very large forklift battery can weigh as much as 1.5 metric tons. A Nascar pit stop crew might be able to trade large batteries in as few as 10 minutes, but Kammerer estimates that 15 or 20 minutes is more common. Now imagine doing that for a fleet of 200 vehicles. If a crew can average four battery swaps per hour, it can do 32 swaps per day. It would take six or seven stations to service all 200 vehicles in a single shift, and 9 or 10 stations for a fleet of 300 vehicles. Companies must also pay for the costly disposal of hazardous spent lead-acid batteries. In addition to labor costs, Kammerer points to a cost in space. Most warehouses are searching desperately for more room. Many have raised their storage racks higher and higher, seeking every bit of available space. Most would be all too happy to reclaim the space now taken up by battery storage and swapping stations. Purolator Courier Ltd. has tested electric hybrid and fuel cell delivery vehicles. The vehicles combined hydrogen-based power plants with a battery to provide acceleration power. Purolator Courier Ltd. has tested electric hybrid and fuel cell delivery vehicles. The vehicles combined hydrogen-based power plants with a battery to provide acceleration power. Fuel cells address both issues, Kammerer said. Warehouse and factory managers can install a small hydrogen plant outside the building, a practice common among industrial gas users. Inside, fueling stations take up only a fraction of the room now housing batteries and service bays. Warehouses can reclaim that area. Refueling takes less than two minutes, and forklift operators can do it themselves, according to Benedikt Eska, CEO of Proton Motor Fuel Cell GmbH of Starnberg, Germany. This eliminates the need for dedicated "pit stop" teams to swap out batteries. Fuel cells also run about 12 hours between refueling, so fleets refuel two times per day instead of three. "We think we need to show the total cost of ownership before we can compete economically with battery-powered fuel cells," Eska said. That means not only initial costs, operating costs, and product life, but also maintenance costs and up-time reliability. "We think we need to show fuel cell lifespans of 5,000 hours to compete with a forklift with a one-battery set and 10,000 hours with a forklift with a two-battery set." Until he has more field experience with long-term service costs, it's hard to mount a believable economic argument. Fuel cells also pose a more easily solved problem. Although they take up as much space as lead-acid batteries, they weigh much less. The cell packs are so light that a truck can tip over when lifting heavy loads. Of course, the problem is easily solved by adding some lead or other weights under the fuel cell system. Several companies have already invested in small fuel cell forklift fleets. Hydrogenics, for example, is planning a two-year test of 19 fuel cell forklifts at General Motors in Oshawa, Ontario. Proton Motor, Nuvera Fuel Cells (a Cambridge, Mass., supplier owned by Hess Corp., Renault S.A., and Gruppo De Nora), and General Hydrogen (Canada) Corp. in Richmond, British Columbia, have smaller tests or development alliances under way. Fuel cells remain a work in progress, however. They have yet to reach the 5,000-to-10,000-hour lifespan Eska estimates they need to compete with batteries. Thanks to materials, designs, and filters, both Eska and Kammerer expect cells to last about 3,000 hours in a forklift. That is equivalent to one-third of a year in a facility running 24/7. Both men say their companies have bench-tested fuel cells that last 5,000 to 8,000 hours, but Eska warns that those results are for cells, not complete systems. Nickels and Dimes Catalysts are another sore point. They are made of platinum, a metal associated with jewelry when gold is just not expensive enough. No matter how thin a coating developers use, platinum is a major cost. Developers try to circumvent the problem by recovering platinum from spent fuel cells. Hydrogenics, for example, recovers about 98 percent of its catalyst, Kammerer said. Yet recovery remains costly. Those 2 percent losses also add up: A fleet of 20 forklifts running 24/7 would lose the equivalent of 1.2 fuel cells' worth of platinum every year. Critics note that there isn't enough platinum in the ground to serve potential fuel cell markets. Several companies are investigating other catalysts, most notably nickel-based nanoparticles. Although nickel has lower catalytic activity than platinum, nanoparticles have a much higher surface area per unit volume than conventional platinum coatings. Researchers hope the sheer number of catalytic sites on nanoparticles will enable them to achieve the same amount of activity as an equivalent area of platinum. The key to using nanoparticles is finding a way to make all that surface area available. Several companies are attacking the problem. In Crespina, Italy, for example, Acta S.p.A. bonds nickel and other metal nanoparticles to polymers, which it then coats onto cheap and highly porous carbon black. Heating the carbon black vaporizes the coating, leaving nickel nanoparticles applied evenly over all the pores. "The key is the size of the particles and how you deposit them," said Antonio Filpi, an Acta scientist. Acta estimates that it can supply 1 metric ton per month of catalyst at about 5 euros per gram, about one-fourth the cost of a similar volume of platinum. In order to circumvent hydrogen infrastructure issues, developers have proposed converting hydrocarbons into hydrogen inside the fuel cell itself. That has been questioned as possibly being less efficient than burning the hydrocarbons directly. Two potential sources of hydrogen, natural gas and propane, already have distribution infrastructure systems in place. Two others, methanol and ethanol, are alcohols that could possibly use existing pipelines, delivery trucks, and storage tanks. Powered by a Hydrogenics Corp. fuel cell, this airport tow tractor can generate enough power to pull a jetliner into its gate. The company plans a two-year test of 19 fuel cell forklifts. Methanol has attracted the most attention as a possible fuel. Just a few years ago, the only economical way to re-form methanol was in refinery-sized chemical plants. Today, several companies can do it with fist-size systems that simplify processing and take only a few moments to reach operating temperatures. Germany's Jülich Institute of Energy Research has unveiled its first forklift powered by a direct methanol fuel cell. Detlef Stolten, the lab's director, said, "With this prototype, we are now only a small step away from the commercialization of our fuel cell technology." Some direct methanol fuel cells have already broken into the market. Michael Tausch, European key account manager of IdaTech LLC in Bend, Ore., said his company has installed several direct methanol fuel cells for backup power in telecommunications facilities. The application is smart for all the right reasons. According to Tausch, a single 30-gallon barrel of methanol-water mixture replaces 18 cylinders of compressed hydrogen. "No hydrogen provider delivers to some of these remote facilities, but liquid is a lot easier and safer to transport and almost anyone can do it," he said. Meanwhile, Protonex Technology Corp. of Southborough, Mass., expects to release a small, 250-watt direct methanol fuel cell for backup power, boating, and camping later this year. Forklifts may take advantage of direct methanol. By eliminating the need to build on-site hydrogen plants, the technology would quickly improve fuel cell competitiveness. So would new processes designed to purify hydrogen. The typical fuel cell requires hydrogen that is four to six nines (99.99 to 99.9999 percent) pure, explained Jeffrey Altman, president and CEO of Hy9 Corp. of Hopkinton, Mass. Industrial grade hydrogen, which sells for $28 per cylinder, is only 2-nines pure. Hydrogen costs $206 per cylinder for 4-nines and $320 for 6-nines purity. The company has a membrane-based purifier that would enable fuel cells to run on cheaper grades of fuel. It would also give small hydrogen plants a more economical way of producing highly purified fuels. It is hard to predict how the fuel cell future will evolve. Perhaps better and cheaper catalysts or direct methanol or natural gas technologies may bring fuel cells within reach of ordinary drivers. In the meantime, though, developers are still testing technology and economics. This can take place only in the real world, where people make decisions based on returns on their investments. Because forklifts make the best economic case for any fuel cell mobility application, they're likely to provide answers that may lead to the fuel cell cars and buses of the future. Or warn us to take another direction.

saurabhjain

saurabhjain

 

A Welding of Plasma and MIG

Developers of a new commercial hybrid technology say it could double the speed of some of the most common industrial welding systems, even while it produces deeper welds and reduces splatter and heat distortion. Developed by former researchers from Ukraine's Paton Welding Institute, the technology is called Super-MIG and marries two welding technologies: plasma arc and metal inert gas, generally known as MIG, a variant of gas metal arc welding. Super-MIG was designed to work with such available MIG welding systems as Lincoln, Miller, Panasonic, OCT, and ESAB. "If you already have a standard robotic welding cell, for approximately $50,000 you could add the system and run most operations nearly twice as fast," according to Ray Davis, sales and marketing manager of Welding Solutions Inc., the technology's North American sales agent. This hybrid welding robot combines a conventional metal inert gas head with a plasma arc welder. Super-MIG speeds welding because plasma and MIG share the load. MIG is often called "short circuit welding" because the weld wire and the workpiece carry opposite charges. When they touch, the weld wire expels metal from the workpiece. This carves a crater, which fills with molten metal and melted weld wire that cool to form the weld. "A single weld wire has a lot of functions," Davis said. "We take away half that work by using plasma." Plasma is exceptionally good at making deep cuts into metal. Super-MIG aims its plasma ahead of the MIG welder. Like a plow, the plasma slices through the workpiece, creating a deep crater and a pool of molten metal before the MIG head gets there. The MIG head then slices into the workpiece through the bottom of this "keyhole," penetrating three to four times deeper than MIG alone. "We've been successful welding 12-13 millimeters into steel," Davis said. "Standard MIG can do that, but you have to really slow the process down." According to Davis, the process is very good for heavy structural welds, the types used in beams, heavy truck suspensions and frames, tube-to-tube welding, boilers, and heavy axle components. Super-MIG has also produced true overlapping welds. They bond two or three pieces of flat steel plate to one another by welding together their centers. "Other systems say they can do it, but they'll put a slot or hole or some sort of joint preparation in the part and weld through that. We go right through the center without it. The only other systems that can do this are lasers," Davis said. Lasers, however, cost upward of $1 million for starter systems, and require highly skilled operators and expensive consumables like optics. Super-MIG, Davis said, is for companies that may not need or cannot afford a laser, but want to run at faster speeds. -------------------------------------------------------------------------------- Metal or Plastic? Take Both To introduce a new type of composite based on nanocrystalline metal cladding over a plastic core, DuPont Co. is partnering with Toronto-based Integran Technologies Inc. Potential uses range from under-hood and powertrain automotive parts to sporting goods. According to Integran's president, Gino Palumbo, the composite combines the best properties of polymers and metals. Polymers are lightweight and easy to mold into intricate shapes that can consolidate a complex metal assembly into a single component. However, all but the most advanced and expensive polymers are prone to break down under abrasion and high temperatures. Metals, on the other hand, can be strong, hard, and heat-resistant, but also heavy and relatively hard to form into complex shapes. MetaFuse composites combine the formability and light weight of plastics with the hardness and thermal conductivity of their nanocrystalline metal coating. The new MetaFuse hybrids are billed as combining the strengths of metals and plastics while minimizing their weaknesses. Engineers can mold plastics into intricate, lightweight shapes. Coating them with nanocrystalline metals makes them much harder. It also boosts thermal conductivity, enabling MetaFuse parts to transport heat away from the plastic core and to extend their heat range. Certainly, many companies have coated plastics with metal before. According to Palumbo, what makes MetaFuse different is the nanoscale nature of the coatings. Metals are made up of tiny crystalline grains. They deform (bend or break) when forces collide at weak points where the crystals are not aligned. These dislocations then move through the metal like a ripple running along the length of a carpet. "You can push a ripple along a carpet more easily than lifting the entire carpet and moving it," Palumbo said. The smaller size of nanocrystals gives dislocations less room to move. "The strength goes up by a factor of five," he said. Hardness also increases. According to Palumbo, the nanometals deliver these properties without the usual sacrifice of ductility. As a result, a thin nanometal coating can provide a surprising boost in properties. Integran's first use of the technology came when it was a research group within the Canadian utility company Hydro Ottawa. It needed to resurface the interior of the water tubes running through its nuclear reactor without pulling them out. "Using a conventional sleeve would have affected flow," Palumbo said. "Our nanocoating let us do the repair with one-quarter to one-fifth the amount of material. Those tubes have been in service for 15 years without a problem." Palumbo expects his collaboration with DuPont to lead to many more applications in the near future. One of the most promising is automotive injector rails, which deliver pressurized fuel to the fuel injector. Affordable polymers cannot take the heat, and gasoline tends to permeate through them. MetaFuse's metal cladding dissipates heat before it weakens the polymer core and also prevents permeation. Metal also could harden glass-filled nylon, making it competitive in powertrain components as well as in wheel hubs and door handles subject to stone chip damage and abrasion. DuPont and Integran are also working on sporting goods, such as bicycles and ski equipment, and on other consumer products. The process itself doesn't use nanoparticles, obviating the potential health questions they raise. Instead, Integran deposits the coating from a solution at rates of 0.004 inch an hour. That sounds slow, but many applications require only 0.001 inch of coating (although others may use 0.03-0.04 inch or more). Still, as Palumbo notes, he can coat thousands of components in a single batch run.

saurabhjain

saurabhjain

 

With a new standard, CNC machines can read CAD and CAM files directly.

Modern-day computer numerically controlled machines are no longer modern enough. The 50-year-old G and M codes that drive those machines can't transfer valuable geometric information from CAD and CAM systems, according to a group of experts who are advocating for widespread use of the recently approved STEP-NC standard. With the new standard, CAD and CAM applications have the capability to send product information to CNC machines. But getting equipment and software suppliers on board with the new standard might take a while, the experts add. Still, if universally adopted, the standard could make subcontracting of machining across many manufacturing industries much easier. Today's global engineering companies commonly pass CAD files back and forth. There are a number of ways for suppliers to translate their own CAD files into a format that original equipment manufacturers can read. Although the system is not always effective, suppliers and OEMs can almost get by. But engineering organizations can sometimes perceive CNC machines as the weak link that holds back a data stream that flows seamlessly from design to manufacturing, said Xun Xu, an associate professor of mechanical engineering at the University of Auckland in New Zealand. Now comes STEP-NC, the machine-language standard first published by the International Organization for Standardization in 2003. Ten years in the making, STEP-NC includes tolerance and process planning capabilities that G and M codes can't accommodate, Xu said. He's looking at how STEP-NC can be adapted to all machining environments. With the standard, a cutting tool is driven by geometric representation of the part to be made, said Martin Hardwick, president of STEP Tools Inc. of Troy, N.Y. His company sells software libraries that help companies write STEP-translation programs. It now sells similar tools for STEP-NC applications. A machine tool creates a metal part. With the STEP-NC standard, the tool could read geometrical data from both CAD and CAM files. Just as STEP has standardized the description of product data, allowing it to be passed with translation between varied CAD and CAM systems, STEP-NC is expected to streamline the passing of vital product data as well as geometric information across a global manufacturing chain, Xu said. With STEP-NC, a machine tool can receive a file with extended product data, know what it means, and proceed to mill the piece without any more instructions. No more programming the machine tool for each job. "Really, today, the guy on the CAM system generates codes for one specific CNC machine in his plant that he understands well," Hardwick said. "With geometric representation that machining program could be sent anywhere in the world and they could make it on their machine." In terms of interoperability, the new standard promises to do for CNC tools what STEP and IGES have done for computer-aided design and computer-aided manufacturing, Hardwick said. The ISO standard STEP, which stands for the "standard for the exchange of product model data," allows all CAD and CAM systems to exchange information, regardless of file format. The U.S. National Institute of Standards and Technology has a standard called initial graphics exchange specification—usually shortened to IGES—which also functions as a translator. According to Hardwick, machine shops using the STEP-NC standard could reduce setup times by as much as 35 percent by seamlessly reading the 3-D product geometry and manufacturing instructions supplied by their customers. Original equipment manufacturers could reduce the time they spend preparing data for suppliers by 75 percent because they could share the design and manufacturing data straight from their databases. A STEP-NC converted CAD file can whiz via Internet from a New York OEM to a California machine shop, which can then immediately start milling the part, Hard- wick said. Adoption Obstacles Given all these benefits, manufacturers and vendors should be lining up for STEP-NC, right? Not yet. Experts generally agree adoption isn't around the corner. It will happen eventually, although no one can yet say how long it will take. Hardwick expects adoption of STEP-NC to mirror that of STEP, which users have been slow to accept. STEP for CAD became an ISO standard in 1995. Three years later, the large manufacturers—the early adopters, who saw the business case for STEP—began using the standard. "In 2001 other enterprises started using it, and in 2003 all the complaints and whining disappeared as people realized what it did," Hardwick said. "There's a tremendous amount of resistance when these standards come out." But more than users' reluctance holds back full-fledged adoption. CAM vendors will need to add system interfaces that write STEP-NC data while CNC machine makers will have to add interfaces to read data. Without significant customer demand for STEP-NC, vendors are hesitant to make the necessary investment in their systems, said John Callen, vice president of marketing at Gibbs and Associates of Moorpark, Calif., which sells CAM and NC programming software. Callen has partic-ipated in the STEP standards community and was a member of the STEP-NC industry review board for STEP Tools. Vendors could also start making CNC machine tools that could read STEP-NC files. But the manufacturing world isn't exactly clamoring for those machines, so companies haven't stepped up to produce them. "The audience that STEP-NC addresses is extremely conservative," Callen said. "Manufacturers say, if it ain't broke don't fix it. If they've got a system that works, they're not interested in jeopardizing that. "A lot of them have spent years getting their operating procedures to the point they're fairly canned," he added. "Introduce STEP-NC and that throws a significant wrench in the works that they have to modify their system around. Most manufacturers will go, 'I want to do this why?' " Gibbs and Associates' customers aren't yet asking for systems that can output to the new STEP-NC format, he added. When they do, Gibbs will provide them. For his part, Hardwick thinks more companies will create their own postprocessors, based on STEP-NC libraries like those his company provides. These types of postprocessors offer a STEP-NC interface between CAM and CNC systems. So STEP-NC proponents must lead the way by making the business case for the CNC standard. Boeing has taken a point position here, Callen said. Representatives from the aircraft company have been part of STEP-NC deliberations and recent prototype demonstrations. An aircraft manufacturer has been particularly interested in a CNC-language standard because its CAM systems generate APT CL language, an intermediate file format that—when sent through a postprocessor—automatically generates machine-specific G codes, Callen said. STEP-NC files could include information that APT CL files can't handle, such as part-model geometry, part dimensions, and tolerances, as well as machine probing commands. The manufacturer would like to work with the new standard on the company's next-generation aircraft. Still Lost in Translation? Should STEP-NC follow STEP's customer acceptance model as Hardwick predicts, it will likely face some adoption impediments along the way. OEMs, well aware of STEP's limitations, don't make widespread STEP use easy, Callen said. "In our industry, we see a lot of doublespeak when it comes to using STEP," he said. A number of big players give lip service to STEP, he said. They agree the translation standard can be used to pass information from supplier to OEM. But, in reality, these large manufacturers require that suppliers use the same CAD system the OEM uses to avoid loss of data during translation. "They're saying one thing and requiring something entirely different," Callen said. "Many say something about STEP in the contract, but suppliers are encouraged to adopt the same CAD system the OEM uses." So STEP itself still isn't an optimal interoperability format and that'll likely be the case with STEP-NC, said Ken Tashiro, vice president and chief operating officer at Elysium Inc. of Southfield, Mich. The company sells CAD translators that Tashiro said can ease the headache that engineers face when translating STEP or IGES files. The STEP and IGES translation programs have the same problems as human translators. Sometimes, there just isn't a one-to-one correlation between words or, in the case of CAD systems, pieces of product data, like geometry features or attributes. And there's another issue as well. IGES and STEP standards have to evolve as fast as today's engineering technologies are evolving. And a slow-moving standards committee can't keep up. Specialized translators like the ones Elysium makes are specifically written to translate files from one brand of software to another such as, say, UGS to Catia. Engineers who rely only on STEP or IGES as their translation tool of choice rather than on specialized translators can lose data in the translation process, Tashiro said. Translators like Elysium's have been programmed to understand the characteristics of each of the supported CAD systems, keep on top of them, and make the required adjustments and corrections required for any data conversion, Tashiro said. Elysium's STEP product is based on STEP tools. "STEP Tools tells us how to build something, so we conform with STEP, and we add our own spice," Tashiro said. "If we know that some CAD format has something weird, like it calls a cylinder a truncated cone, but every other format calls it a cylinder, we know we should pop it into STEP as a cylinder." Down the line, Tashiro expects to see specialized STEP-NC readers similar to the enhanced translators his company provides. For his part, Xu is working to develop portable STEP-NC data that can be adapted to different machining environments. The key to this is to capture the information about machining tasks unambiguously and leave the decision on machining methods until the last moment when a machine tool is chosen. So why don't software vendors get together and agree upon standard language? That way, a fillet would be a fillet— whatever CAD system it originated in, whatever CNC machine eventually machines the part. The answer is easy, Tashiro said. For competitive reasons, vendors simply aren't willing to reveal their algorithms. That makes it impossible to transfer both files and codes among unlike systems without the use of a translator, whether STEP, or a spiced-up STEP. Hardwick is hopeful that when manufacturers see STEP-NC in action, they'll get behind the new stan-dard. Next month in Dallas, STEP Tools will help to demonstrate the new standard for participants from Airbus, Lockheed Martin, Boeing, and Sandvik, among others. "It'll be a fairly big demonstration to show the CAD/CAM vendors and hardware control vendors that all these people are interested in doing STEP-NC and to get them to move forward," Hardwick said. "But we still need to put forth more effort and get more vendors jumping in." The road toward STEP-NC has been long and often filled with setbacks. But Callen said he hopes talk of the newly approved standard sparks user interest. "We're getting there," he said. "We need to keep it in perspective, though. But I don't want to lose sight of the real benefits of STEP-NC and what it's done as far as making people aware of the type of product infor- mation that's required for next-generation manufacturing systems."

saurabhjain

saurabhjain

 

What Is a Fuel Cell ?

The recent success of fuel-cell-powered demonstration vehicles using the proton exchange membrane fuel cell developed by the Canadian company Ballard Power Systems, by DaimlerChrysler and many others, suggests that fuel cells have finally come of age. Elsewhere, Plug Power and a number of other developers are striving to bring their domestic grid-independent power supplies onto the market within the next couple of years. What has driven these developments? And what exactly is a fuel cell? 1.1 What Is a Fuel Cell? As early as 1839, William Grove discovered the basic operating principle of fuel cells by reversing water electrolysis to generate electricity from hydrogen and oxygen. The principle that he discovered remains unchanged today. A fuel cell is an electrochemical “device” that continuously converts chemical energy into electric energy (and some heat) for as long as fuel and oxidant are supplied. Fuel cells therefore bear similarities both to batteries, with which they share the electrochemical nature of the power generation process, and to engines which — unlike batteries — will work continuously consuming a fuel of some sort. Here is where the analogies stop, though. Unlike engines or batteries, a fuel cell does not need recharging, it operates quietly and efficiently, and — when hydrogen is used as fuel — it generates only power and drinking water. Thus, it is a so-called zero emission engine. The thermodynamics of the electrochemical power generation process are analyzed in Chapter 3, where fuel cells are compared to thermal engines. Thermodynamically, the most striking difference is that thermal engines are limited by the Carnot efficiency while fuel cells are not. Grove’s fuel cell was a fragile apparatus filled with dilute sulfuric acid into which platinum electrodes were dipped. From there to modern fuel cell technology has been an exciting but long and tortuous path, as outlined in Chapter 2. 1.2 Main Applications/The “Drivers” It was not until the beginnings of space travel that fuel cells saw their first practical application in generating electric power (and drinking water) in the Gemini and Apollo programs. Extensive research 1.2 Main Applications/The “Drivers” It was not until the beginnings of space travel that fuel cells saw their first practical application in generating electric power (and drinking water) in the Gemini and Apollo programs. Extensive research efforts were made in those days, and many results from that work are still perfectly valid and have been incorporated into modern fuel cell systems; others continue to inspire modern-day researchers. The work of the early fuel cell researchers has produced an awesome wealth of knowledge. Chapter 2 covers some of the spirit of their pioneering work. So, is there a road from messy bench experiments involving strong acids to clean, safe equipment suitable for use in homes and vehicles, and from “rocket science” to practical applications in everyday life? And why fuel cells in the first place? It now looks as though fuel cells will eventually come into widespread commercial use through three main applications: transportation, stationary power generation, and portable applications. We will see that the reasons for having fuel cells are rather different, at least in relative importance, in each of these three sectors. 1.2.1 Transportation In the transportation sector, fuel cells are probably the most serious contenders to compete with internal combustion engines (ICEs). They are highly efficient because they are electrochemical rather than thermal engines. Hence, they can help to reduce the consumption of primary energy and the emission of CO2. What makes fuel cells most attractive for transport applications is the fact that they emit zero or ultra-low emissions. And this is what mainly inspired automotive companies and other fuel cell developers in the 1980s and 1990s to start developing fuel-cell-powered cars and buses. Leading developers realized that although the introduction of the three-way catalytic converter had been a milestone, keeping up the pace in cleaning up car emissions further was going to be very tough indeed. After legislation such as California’s Zero Emission Mandate was passed, people initially saw battery-powered vehicles as the only solution to the problem of building zero emission vehicles. However, the storage capacity of batteries has turned out to be unacceptable for practical use because customers ask for the same drive range that they are accustomed to with internal combustion engines. In addition, the battery solution is unsatisfactory for another reason: With battery-powered cars the location where air pollution is generated is merely shifted back to the electric power plant that provides the electricity for charging. Once this was understood, people began to see fuel cells as the only viable technical solution to the problem of car-related pollution. Unfortunately, public perception of fuel cells subsequently became blurred, and all sorts of miracles were expected from this fledgling new motor. It was supposed to make us entirely independent of fossil fuels (since “it only needs hydrogen”), and undoubtedly many still believe that fuel-cell-powered cars will run on a tank full of water. When the first fuel-cell-powered buses rolled out of the labs of Ballard Power Systems, it soon became clear that buses would make the fastest entry into the market because the hydrogen storage problem already had been solved (compare Chapter 5). The prospects of fuel-cell-powered vehicles are fully discussed in Chapter 10; the fueling issue, particularly for cars, is covered in Chapter 5. Clearly, the automotive market is by far the largest potential market for fuel cells. When developers started doing their first cost calculations, they realized they were in for steep competition against improved internal combustion engines, hybrid cars, and other possible contenders. The main competitors of fuel-cell-powered cars are discussed in Chapter 11. Complete fuel chains, for both automotive and stationary systems, are analyzed in Chapter 12. 1.2.2 Stationary Power Cost targets were first seen as an opportunity. The reasoning was that when fuel cells met automotive cost targets, other applications, including stationary power, would benefit from this development, and a cheap multipurpose power source would become available. Stationary power generation is viewed as the leading market for fuel cell technology other than buses. The reduction of CO2 emissions is an important argument for the use of fuel cells in small stationary power systems, particularly in combined heat and power generation (CHP). In fact, fuel cells are currently the only practical engines for micro-CHP systems in the domestic environment (5–10 kW). The higher capital investment for a CHP system would be offset against savings in domestic energy supplies and — in more remote locations — against power distribution cost and complexity. In the 50- to 500-kW range, CHP systems will have to compete with spark or compression ignition engines modified to run on natural gas. So far, several hundred 200-kW phosphoric acid fuel cell plants manufactured by ONSI (IFC) now have UTC fuel cells been installed worldwide. The current range of stationary power systems is presented in Chapter 8. 1.2.3 Portable Power The portable market is less well defined, but a potential for quiet fuel cell power generation is seen in the 1-kW portable range and possibly, as ancillary supply in cars, so-called auxiliary power units (APUs). The term “portable fuel cells” often includes grid-independent applications such as camping, yachting, and traffic monitoring. The fuels under consideration vary from one application to another. In addition, the choice of fuel is not the only way in which these applications vary. Different fuel cells may be needed for each sub-sector in the portable market. Portable fuel cells are discussed in Chapter 9. 1.3 Low- and Medium-Temperature Fuel Cells A whole family of fuel cells now exists that can be characterized by the electrolyte used — and by a related acronym as listed in Table 1.1. All of these fuel cells function in the same basic way. At the anode, a fuel (usually hydrogen) is oxidized into electrons and protons, and at the cathode, oxygen is reduced to oxide species. Depending on the electrolyte, either protons or oxide ions are transported through the ion-con­ducting but electronically insulating electrolyte to combine with oxide or protons to generate water and electric power. A more detailed analysis of the power generation process is presented in Chapters 3 and 4. Table 1.1 lists the fuel cells that are currently undergoing active development. Phosphoric acid fuel cells (PAFCs) operate at temperatures of 200°C, using molten H3PO4 as an electrolyte. The PAFC has been developed mainly for the medium-scale power generation market, and 200 kW demonstration units have now clocked up many thousands of hours of operation. However, in comparison with the two low-temperature fuel cells, alkaline and proton exchange membrane fuel cells (AFCs, PEMFCs), PAFCs achieve only moderate current densities. The alkaline fuel cell, AFC, has one of the longest histories of all fuel cell types, as it was first developed as a working system by fuel cell pioneer F.T. Bacon since the 1930s (compare Chapter 2). This technology was further developed for the Apollo space program and was key in getting people to the moon. The AFC suffers from one major problem in that the strongly alkaline electrolytes used (NaOH, KOH) adsorb CO2, which eventually reduces electrolyte conductivity. This means that impure H2 containing CO2 (reformate) cannot be used as a fuel, and air has to “scrubbed” free of CO2 prior to use as an oxidant in an AFC. Therefore, the AFC has so far only conquered niche markets, for example space applications (the electric power on board the space shuttle still comes from AFCs). Some commercial attempts has been made to change this. Most notably, ZETEK/ZEVCO started in the mid-1990s to reexamine the AFC technology developed by ELENCO, a Belgian fuel cell developer that had previously gone into bankruptcy. A number of ZETEK’s activities attracted extensive publicity. In the late 1990s, ZETEK presented a so-called fuel-cell-powered London taxi. Little is known about the technology of the engine in this vehicle. However, the AFC employed had a power range of only 5 kW, which means it cannot be the main source of power and merely served as a range extender to some on­board battery. Other recent activities based on AFC technology include the construction of trucks (by ZEVCO) and boats (etaing GmbH). A big advantage of the AFC is that it can be produced rather cheaply. This may help this technology penetrate the highly specialized market for indoor propulsion systems, such as airport carrier vehicles, and possibly a number of segments in the portable sector. The proton exchange membrane fuel cell, PEMFC, takes its name from the special plastic mem-brane1 that it uses as its electrolyte. Robust cation exchange membranes were originally developed Therefore, it is also known as a solid polymer fuel cell (SPFC). for the chlor-alkali industry by DuPont and have proved instrumental in combining all the key parts of a fuel cell, anode and cathode electrodes and the electrolyte, in a very compact unit. This membrane electrode assembly (MEA), not thicker than a few hundred microns, is the heart of a PEMFC and, when supplied with fuel and air, generates electric power at cell voltages up to 1 V and power densities of up to about 1 Wcm–2. The membrane relies on the presence of liquid water to be able to conduct protons effectively, and this limits the temperature up to which a PEMFC can be operated. Even when operated under pressure, operating temperatures are limited to below 100°C. Therefore, to achieve good performance, effective electrocatalyst technology (Chapter 6) is required. The catalysts form thin (several microns to several tens of microns) gas-porous electrode layers on either side of the membrane. Ionic contact with the membrane is often enhanced by coating the electrode layers using a liquid form of the membrane ionomer. The MEA is typically located between a pair of current collector plates with machined flow fields for distributing fuel and oxidant to anode and cathode, respectively (compare Fig. 4.2 in Chapter 4). A water jacket for cooling may be inserted at the back of each reactant flow field followed by a metallic current collector plate. The cell can also contain a humidification section for the reactant gases, which helps to keep the membrane electrolyte in a hydrated, proton-conduction form. The technology is given a more thorough discussion in Chapter 4 (compare Section 10.2.3). Having served as electric power supply in the Gemini space program, this type of fuel cell was brought back to life by the work of Ballard Power Systems. In the early 1990s, Ballard developed the Mark 5 fuel cell stack [Fig. 10.4(a)] generating 5 kW total power at a power density of 0.2 kW per liter of stack volume. With the Mark 900 stack [Fig. 10.4( ] jointly developed by Ballard and DaimlerChrysler in late 1990s, the power density had increased more than fivefold to over 1 kW/l. At a total power output of 75 kW, this stack meets the performance targets for transportation (compare Section 10.2.3). PEMFCs are also being developed for stationary applications. In the 250-kW range, Ballard Generation Systems is currently the only PEMFC-based developer. More recently, the micro-CHP range has been claimed by a wide range of developers. Here, high power density is not the most crucial issue. In a The MEA is typically located between a pair of current collector plates with machined flow fields for distributing fuel and oxidant to anode and cathode, respectively (compare Fig. 4.2 in Chapter 4). A water jacket for cooling may be inserted at the back of each reactant flow field followed by a metallic current collector plate. The cell can also contain a humidification section for the reactant gases, which helps to keep the membrane electrolyte in a hydrated, proton-conduction form. The technology is given a more thorough discussion in Chapter 4 (compare Section 10.2.3). Having served as electric power supply in the Gemini space program, this type of fuel cell was brought back to life by the work of Ballard Power Systems. In the early 1990s, Ballard developed the Mark 5 fuel cell stack [Fig. 10.4(a)] generating 5 kW total power at a power density of 0.2 kW per liter of stack volume. With the Mark 900 stack [Fig. 10.4( ] jointly developed by Ballard and DaimlerChrysler in late 1990s, the power density had increased more than fivefold to over 1 kW/l. At a total power output of 75 kW, this stack meets the performance targets for transportation (compare Section 10.2.3). PEMFCs are also being developed for stationary applications. In the 250-kW range, Ballard Generation Systems is currently the only PEMFC-based developer. More recently, the micro-CHP range has been claimed by a wide range of developers. Here, high power density is not the most crucial issue. In a (domestic) micro-CHP system, high electric efficiency and reliability count. The overall goal is the most economic use of the fuel employed, usually natural gas, in order to generate electric power and heat. 1.4 High-Temperature Fuel Cells Two high-temperature fuel cells, solid oxide and molten carbonate (SOFC and MCFC), have mainly been considered for large-scale (MW) stationary power generation. In these systems, the electrolytes consist of anionic transport materials, as O2– and CO23 – are the charge carriers. These two fuel cells have two major advantages over low-temperature types. First, they can achieve high electric efficiencies; prototypes have achieved over 45%, with over 60% currently targeted. This makes them particularly attractive for fuel-efficient stationary power generation. Second, the high operating temperatures allow direct internal processing of fuels such as natural gas. This reduces the system complexity compared with low-temper­ature power plants, which require hydrogen generation in an additional process step. The fact that high-temperature fuel cells cannot easily be turned off is acceptable in the stationary sector, but most likely only there. A full account of the technology and the merits of fuel cells in stationary power generation is given in Chapter 8. 1.5 Liquid Fuel: The Direct Methanol Fuel Cell No doubt one of the most elegant solutions to the fueling problem would be to make fuel cells operate on a liquid fuel. This is particularly so for transportation and the portable sector. The direct methanol fuel cell (DMFC), a liquid- or vapor-fed PEM fuel cell operating on a methanol/water mix and air, therefore deserves careful consideration. The main technological challenges are the formulation of better anode catalysts to lower the anode overpotentials (currently several hundred millivolts at practical current densities), and the improvement of membranes and cathode catalysts in order to overcome cathode poisoning and fuel losses by migration of methanol from anode to cathode. Current prototype DMFCs generate up to 0.2 Wcm–2 (based on the MEA area) of electric power, but not yet under practical operating conditions or with acceptable platinum loadings. However, the value is sufficiently close to what has been estimated to be competitive with conventional fuel cell systems including reformers and reformate cleanup stages.

admin

admin

  • Recently Browsing   0 members

    No registered users viewing this page.

  • Blog Statistics

    411
    Total Blogs
    753
    Total Entries


×