Big leap for fusion: more energy produced than spent igniting fuel

Researchers in the US have overcome a key barrier to making nuclear fusion reactors a reality. In results published in Nature, scientists have shown that they can now produce more energy than put into igniting fuel, at least on an experimental scale. The use of fusion as a source of energy remains a long way off, but the latest development is an important step toward that goal.

Nuclear fusion is the process that powers the Sun and billions of other stars in the Universe. If mastered, it could provide an unlimited source of clean energy because the raw materials are plentiful and the operation produces no carbon emissions.

During the fusion process, smaller atoms fuse into larger ones, releasing huge amounts of energy. To achieve this on Earth, scientists have to create conditions similar to those at the center of the Sun, which involves creating very high pressures and temperatures.

There are two ways to achieve this: one uses lasers and is called inertial confinement fusion (ICF), another deploys magnets and is called magnetic confinement fusion (MCF). Omar Hurricane and colleagues at the Lawrence Livermore National Laboratory opted for ICF, with the help of 192 high-energy lasers at the National Ignition Facility in the US, which was designed specifically to boost fusion research.

A typical fusion reaction at the facility takes weeks of preparation. But the reaction is completed in an instant (150 picoseconds, to be precise, which is less than a billionth of a second). In that moment, at the core of the reaction, the pressure is 150 billion times atmospheric pressure. The density and temperature of the plasma created is nearly three times that at the center of the Sun.

The most critical part of the reaction, and one that had been a real concern for Hurricane’s team, is the shape of the fuel capsule. The capsule is made from a polymer and is about 2mm in diameter (about the size of a pinhead). On the inside it is coated with deuterium and tritium—isotopes of hydrogen—that are frozen to a solid state.

This capsule is placed inside a gold cylinder, when the 192 lasers are fired, they hit the capsule and indirectly cause a fusion reaction. The lasers hit the gold container, which emit X-rays that heat the pellet and make it implode, causing a fusion reaction. According to Debbie Callahan, a co-author of the study: “When the lasers are fired, the capsule is compressed 35 times. That is like compressing a basketball to the size of a pea.”

The compression produces immense pressure and temperature, leading to a fusion reaction. Problems with the process were overcome last September, when, for the first time, Hurricane was able to produce more energy output from a fusion reaction than the lasers put into it. Since then, he has been able to repeat the experiment.

Hurricane’s current output, although more than the hydrogen fuel put into the reaction, hasn’t yet reached the stated goal to achieve “ignition," where nuclear fusion generates as much energy as the lasers supply. At that point it might be possible to make a sustainable power plant based on the technology.

In plasma physics, the energy produced by a fusion reaction increases exponentially with the pressure applied to the system. According to Hurricane, they only need to double the pressure to achieve ignition. His other achievement is that, with these experiments, he has been able to show that computer simulations can predict experimental results.

Scientists have been trying to tame fusion power for more than 50 years with little success. Although the National Ignition Facility, a $3.5-billion operation, was built for classified government research, half of its laser time was devoted to fusion with an aim to accelerate research. Zulfikar Najmudin, a plasma physicist at Imperial College, said: “These results will come as a huge relief to scientists at NIF, who were very sure they could have achieved this a few years ago.”

With laser-mediated ICF showing positive results, the obvious question is how does it compare with magnet-mediated fusion? According to Stephen Cowley, director of Culham Centre for Fusion Energy, there isn’t a precise way of comparing the two technologies. But if a comparison has to be made, MCF still is ahead of ICF because a 1997 experiment by the European fusion leaders Joint European Torus achieved near break-even when they produced 16MW (megawatt) of energy for 24MW of input.

“We have waited 60 years to get close to controlled fusion. We are now close in both magnetic and inertial. The engineering milestone is when the whole plant produces more energy than it consumes,” Cowley said. That may happen at the fusion reactor ITER, under construction in France, which is expected to be the first power plant that produces more energy than it consumes to sustain a fusion reaction.

Nature, 2014. DOI: 10.1038/nature13008  (About DOIs).

This article was originally published on The Conversation.

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Is it time to move away from silicon-based solar?

CHICAGO—Currently, the world has the capacity to manufacture over 40 Gigawatts of solar panels each year, the vast majority of them silicon-based. And it's easy to see why: our expertise with processing the material has led to a staggering drop in costs, making photovoltaics (PVs) much more cost-competitive than just about anyone had predicted.

But that manufacturing innovation hasn't been matched on the basic research side; it's been over a decade since the last time anyone set a new efficiency record for silicon cells. And, even as manufacturing costs have dropped, the cost of support equipment and installation has remained stubbornly high and is an ever-increasing slice of the total price of PV systems.

That's got people thinking that it might be time that we get more power out of each installation. At the meeting of the American Association for the Advancement of Science, two researchers spelled out how they were finding ways to take an expensive material and make it cheap enough to be deployed on the same scale as silicon.

The material in question is gallium arsenide, which can be fashioned into solar cells with efficiencies twice those of silicon. The high cost of the material, however, has limited its use to applications like satellites. But two research groups have come up with ways to get much more out of GaAs.

Gallium goes thin

Both teams have figured out how to make extremely thin layers of GaAs. Harry Atwater's group at Caltech has developed a process that allows them to peel hundreds of thin layers off a large aggregate of the material, much like individual graphene sheets can be peeled off a block of graphite. The end result is an extremely thin film of GaAs (he passed some samples around to the audience).

John Rodgers, who works at the University of Illinois at Urbana-Champaign, grows thin layers of GaAs separated by a thin sacrificial layer. When the sacrificial layer is etched away, you're left with a collection of thin GaAs chips; the silicon wafer they were grown on can then be recycled, cutting down on the costs significantly. A plastic stamp can then pick up the chips and "print" them onto just about any surface, including one pre-patterned with wiring.

In the rare cases where GaAs chips are used here on Earth, they're typically used in what's called a concentrated solar system, where lenses pump as many photons into the chips as they can manage without melting. But these tracking and focusing systems add significantly to the cost of these systems. Both groups are thinking of doing some focusing, but going about it in different ways.

Rodgers, who can print large arrays of tiny GaAs chips, is managing costs by keeping things simple: his team's process simply involves dropping a plastic sphere that acts as a lens on top of the chip. There are some ideas about how to manufacture more specialized spheres that focus the light more efficiently, but, for now, simplicity is the selling point.

Trapping the photons

Caltech's Atwater is making the focusing device a more central part of his system for reasons that focused on the physics of what happens inside the chips. When a photon is absorbed, it creates a free electron and a positively charged "hole." There are three things that can happen to this pair. One is that they end up at electrodes, producing a useful current. One is that they recombine uselessly, releasing the energy as heat. The third is that they recombine by releasing another photon.

For Atwater, the key to an efficient photovoltaic material is minimizing the wasteful recombination of electrons and holes. And that means getting them to re-emit a photon—in his view, a good photovoltaic material is also a good LED. In these materials, photons get absorbed and re-emitted a hundred times before being productively harvested, and the inside of the material is a sea of photons.

The danger here is that some of the photons escape back out of the material. To limit that, the GaAs can be put on a reflective backing that sends the stray photons right back into the chip. The front has to let sunlight in, but then keep photons from escaping. To do that, he's testing a system that looks a bit like two U's with their bottoms fused (technically, it's back-to-back parabolic lenses connected by a narrow aperture). This takes photons from a broad area and funnels them into the PV chip. The other end of the U acts like a reflective cap, making it very hard for a photon to escape from the chip without being reflected back into it.

Grab all the wavelengths

At this point, we're pumping lots of photons into the GaAs device and keeping them there until they're absorbed. The next way to up the efficiency is to have multiple independent photovoltaic devices, each tuned to different wavelengths. Traditionally, this has been done with layered devices, where each layer takes out a specific chunk of the spectrum.

And that's what Rodgers' team is already doing, by placing a standard triple-junction cell (which absorbs three different chunks of the spectrum) on top of a fourth cell that grabs yet another chunk. Atwater hopes to use the optic devices his team is working on to split the light into colors and direct them to independent photovoltaic devices.

Both of these faculty members have started companies to try to commercialize their work, and the devices they're making are already above the 40-percent efficiency mark—double that of silicon cells. Rodgers' company already has a 5MW capacity plant, and he said that scaling up production to an 80MW capacity plant would let them produce devices that are cost-competitive with coal.

Lots of great sounding technologies never make it past the demonstration phase, or they get caught up in market forces beyond their developers' control. But in this case, market forces are clearly working in the devices' favor. As installation costs become an ever larger fraction of the total cost of a solar installation, it's clear that getting more out of each installation is likely to be critical.

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Carbon dioxide from exhaust can now be used to make new chemicals

Carbon capture is yet to become energy-efficient, but uses of CO₂ are growing.

To limit climate change, most governments focus on reducing the amount of carbon dioxide (CO₂) put into the atmosphere. But there are indications that such action won’t be enough—at some point, we will need to actively remove CO₂ from the air.

The removal of CO₂ is a big challenge, as it will require large amounts of renewable energy. For now, attention has focused on removing CO₂ from the exhaust of fossil fuel power plants, where it’s present in higher concentrations. Typically, that CO₂ is destined for carbon capture and storage (CCS), but another option is to skip the storage part—new research from Korea shows that it’s possible to take CO₂ directly from exhaust gases and make new chemicals.

Catch me if you can

CO₂ from an exhaust gas stream is often captured by nitrogen-containing compounds called amines. The reaction is reversible, as the products can be heated, allowing the CO₂ to be released. The gas can then be compressed, transported, and stored in geological features, such as depleted oil fields, or used as raw material in chemical factories.

Although trees and some microbes can capture CO₂ and incorporate it into more complex chemicals, humans have struggled to replicate the process on a large scale. Most chemical reactions involving CO₂ require expensive catalysts, high temperatures, or high pressures to make it react. The most common use of CO₂ as a chemical feedstock is in the formation of urea, which is found in around 90 percent of the world’s fertilisers.

In the new research, published in the journal Angewandte Chemie, Soon Hong and colleagues from the Institute for Basic Science in South Korea have caught CO₂ from exhaust gas and incorporated it into useful chemicals. One product is called alkynyl carboxylic acid, which has many uses, including making food additives. Another, cyclic carbonate, is used to make polymers for cars and electronics. Cyclic carbonates can also be used in place of phosgene, a very reactive and highly toxic chemical that is a starting material for a wide variety of useful products.

Hong compared these reactions to ones performed using highly pure CO₂, which is sold at a high price and requires lots of energy to make, in the same chemical reactions, but there was hardly any difference in the final yield.

As in CCS technologies, Hong passes exhaust fumes through a solution of amines, where CO₂ is captured and other gases pass unhindered. The resulting salt is then heated to yield pure CO₂ for chemical reactions. Hong can recycle the amine solution at least 55 times without a loss in yield.

Use me if you do

In another research paper just published in Nature Communications, Matthias Beller and colleagues at the University of Rostock in Germany show a new reaction that can use CO₂. Called alkene carbonylation, it usually requires the use of carbon monoxide (CO), which, as home detectors know well, is a highly toxic gas.

CO₂ has previously been used in the synthesis of carboxylic acids by using diethylzinc to drive the reaction. But diethylzinc is flammable in air. With the new reaction, Beller can make chemicals that are found in varnishes and paints with less risk of burning the lab down.

The researchers carried out a number of reactions and confirmed that the source of the newly formed C-O bonds was CO₂. This work shows that CO₂ can be used as a viable alternative to carbon monoxide in carbonylation reactions, which could increase the importance of CO₂ in the chemical industry.

While this is good news, energy is still needed to trap and use CO₂. But if researchers can increase the demand for CO₂ at industrial scale, they may also drive the development of some of the technologies needed for CCS.

Nature Communications, 2014. DOI: 10.1038/ncomms4091 and Angewandte Chemie, 2014. DOI: 10.1002/anie.201308341 (About DOIs).

This article was originally published on The Conversation

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A way to double the efficiency of solar cells is about to go mainstream

SUNLIGHT is free, but that is no reason to waste it. Yet even the best silicon solar cells—by far the most common sort—convert only a quarter of the light that falls on them. Silicon has the merit of being cheap: manufacturing improvements have brought its price to a point where it is snapping at the heels of fossil fuels. But many scientists would like to replace it with something fundamentally better.

John Rogers, of the University of Illinois, Urbana-Champaign, is one. The cells he has devised (and which are being made, packaged into panels and deployed in pilot projects by Semprius, a firm based in North Carolina) are indeed better. By themselves, he told this year’s meeting of the American Association for the Advancement of Science, they convert 42.5% of sunlight. Even when surrounded by the paraphernalia of a panel they manage 35%. Suitably tweaked, Dr Rogers reckons, their efficiency could rise to 50%. Their secret is that they are actually not one cell, but four, stacked one on top of another.

Dr Rogers gets round this by using a different material for each layer of the stack. He chooses his materials so that the bottom of the band gap of the top layer matches the top of the band gap of the one underneath, and so on down the stack. Each layer thus chops off part of the spectrum, converts it efficiently into electrical energy and passes the rest on.Solar cells are made of semiconductors, and every type of semiconductor has a property called a band gap that is different from that of other semiconductors. The band gap defines the longest wavelength of light a semiconductor can absorb (it is transparent to longer wavelengths). It also fixes the maximum amount of energy that can be captured from photons of shorter wavelength. The result is that long-wavelength photons are lost and short-wave ones incompletely utilised.

The problem is that the materials needed to make these semiconductors (including arsenic, gallium and indium) are costly. But Dr Rogers has devised a way to overcome this. Normal solar-cell modules are completely covered by semiconductor, but in his only 0.1% of the surface is so covered. The semiconducting stacks, each half a millimetre square, are scattered over that surface as a matrix of dots, meaning that a panel with an area of 125 square metres has half a million of them. Each stack then has a pair of cheap glass lenses mounted over it. These focus the sun’s light onto the stack, meaning that all incident light meets a semiconductor.

The semiconductor stacks themselves are printed onto a cell one layer at a time by a rubber stamp, which picks them up from a crystal wafer of the appropriate material. This wafer has been grown as a series of layers, separated by a substance which can easily be dissolved away. By scoring a chequerboard of cuts through the layers to create squares of the correct size, and then dissolving the filler, layer after layer of semiconductor squares are created, which the rubber stamp peels away and places on the cell. Repeat the process with the other three semiconductors, and package the whole thing with electrical connectors and a transparent protective coat, and—presto!—you have a highly efficient solar panel.

Semprius’s panels are now being tested at 14 sites around the world. How much they will cost to make when manufacturing is running at full tilt is not yet clear, but Dr Rogers said that Siemens, a big German firm which is one of Semprius’s investors, reckons that they have the potential to produce cheaper electricity than coal-fired generators can. Solar energy obviously cannot replace fossil fuels completely until the problem of banking some of what is collected during the day, for use at night, is solved. But at this sort of cost it can make a useful (and unsubsidised) contribution.

The new panels have aesthetic advantages, too. The 99.9% of them not covered by stacks can be used for art. Seen from the sun’s point of view (ie, straight ahead), they appear black because the lenses are focused on the stacks, which absorb all the light falling on them. Viewed obliquely, however, their foci are on other parts of the panel. The result, as the picture shows, can be quite pleasing—and certainly prettier than a coal-fired power station.

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Who needs sunlight? In Arizona, solar power never sleeps

GILA BEND, ARIZONA—Every afternoon during the summer, millions of people across the American Southwest come home from work and switch on their air conditioners, straining the power grid in states like Arizona. Traditional solar power—although perfectly suited to the sunny climes of this region—can’t meet this demand since the surge in use peaks just as the day’s sun is disappearing.

That’s why most power suppliers diversify, using electricity from different sources to meet local needs. Solar power is abundant in the middle of sunny, clear days, but energy from other sources—coal, nuclear, or hydroelectric power for example—is necessary at night or when the weather is bad.

But increasingly efficient technology is allowing solar plants to contribute for a longer period of time each day and produce energy even in cloudy conditions. The key is a design that allows them to store the sun’s energy to be used later. And new facilities, such as the Solana power plant that recently came online in Gila Bend, Arizona, are increasing solar energy’s niche by producing electricity several hours after the sun sets.

Decked out in a too-large hard hat, neon yellow vest, and some very trendy safety goggles, Ars recently had the opportunity to visit Solana and find out precisely how these plants power cities after dark.

A solar primer

Unlike traditional photovoltaic systems, which directly convert the sun’s energy to electricity by liberating electrons, these new plants use “concentrated solar power,” or CSP. As the name suggests, CSP relies on either mirrors or lenses to collect and focus the sun’s heat, which is then used to generate power.

CSP isn’t exactly novel. According to legend, Archimedes used giant hexagonal mirrors to create a “death ray” to set fire to Roman ships, saving the city of Syracuse from invasion more than 2,000 years ago (whether or not this scenario actually happened is hotly debated). In a more recent era, I remember watching my brother perform small-scale mass murder with a magnifying glass, concentrating the sun’s rays onto the delicate bodies of insects.

But in recent years, CSP technology has blossomed. Its first large-scale test was the Department of Energy-funded Solar One, built in California in 1982. Solar One was a “power tower” plant, in which mirrors are arranged in a circular pattern around a central tower. The mirrors concentrate and direct energy onto a receiver at the top of the tower, which heats synthetic oil inside. The hot fluid is then used to boil water in a traditional steam turbine.

A huge solar facility called Ivanpah recently went online in California’s Mojave Desert. It consists of three separate plants with massive power towers—each 46 stories tall—with a combined capacity of nearly 400 megawatts. It's currently the largest solar thermal facility in the world.

Today, CSP’s popularity is exploding. Nearly 1.3 gigawatts of CSP power came online in 2012 or will debut this year; that’s enough to power about a million homes (or one time-traveling DeLorean). Huge new plants are currently under construction in South Africa, Chile, China, Morocco, Israel, and elsewhere.

The major advantage of CSP is the potential for storage. Since the sun’s energy is already being converted to heat, it’s relatively straightforward to store some of this heat to create electricity later. A variety of storage media are used, including oil and beds of packed rock, but the most common is molten salt. These salts are highly effective at retaining thermal energy and can be heated to very high temperatures (over 1000 degrees Fahrenheit), making storage extremely efficient.

With thermal storage, these plants can either produce at maximum efficiency during the day or store some of the energy as heat to convert later when the sun isn’t shining. This adds not only flexibility to the power system—since the production curve can be tailored to match the demand curve—but also stability in case of cloudy or stormy conditions.

A field full of mirrors

The view from the top of Solana's cooling towers is impressive: row upon row of shiny mirrors stretch out in all directions, tilted toward the sun like thousands of soldiers standing at attention. It's clear from this vantage point that Solana is in a league of its own.

When this CSP plant went online in October of 2013, it became the largest working parabolic trough plant in the world (although Spanish parent company Abengoa is currently building an even bigger version in the Mojave Desert). Solana covers more than 1,900 acres in southern Arizona—that’s the equivalent of more than 1,400 football fields packed with mirrors and power equipment.

Abstractly, the concept behind a parabolic trough plant is the same as that in a power tower plant: concentrate the sun’s energy to heat fluid, which then boils water to create steam. However, the details differ pretty significantly.

In a parabolic trough plant like Solana, the mirrors are curved inward, with a glass tube running along the deepest point, or trough, of each mirror. The tube is full of synthetic oil (also known as heat transfer fluid, or HTF). The concave mirrors concentrate light onto this HTF, heating it to 740 degrees Fahrenheit. The system is extremely efficient in collecting heat and concentrating it to a blistering level; when I asked what would happen if I touched the tube, the reply was a curt "Trust me, you definitely don't want to do that."

Once the oil is up to temperature, about 270 miles of pipe transport it to the power block, where the HTF takes one of two pathways, depending on Solana’s current needs.

In the most direct route, the HTF is simply sent to the steam generator to boil water and create steam to drive two 140-megawatt turbines, just like a traditional power plant. This is the more efficient of the two pathways, since virtually no energy is lost between collection and conversion.

Huge overflow tanks allow for the expansion of the hot synthetic oil.

Alternatively, to store this energy for later production, the HTF can instead be sent to one of 12 giant salt tanks at Solana, where hot oil heats molten salt. Each tank can hold 12,000 tons of salt (the salt mixture used at Solana is 40 percent sodium nitrate and 60 percent potassium nitrate). The tanks function just like huge thermoses, holding the heat from the HTF for up to six hours. When electricity is needed, the hot salt is transferred into another holding tank, passing through a heat exchanger on the way. Cold HTF then passes through the heat exchanger in the opposite direction, picks up the heat, and travels to the steam generator in the power block to generate electricity.

Arizona Public Service, the state’s largest electric utility, has agreed to purchase all the power generated by Solana for 30 years. On a daily basis, APS determines how Solana should produce and store its energy in order to best meet local demand. Abengoa estimates that under optimal conditions, Solana can produce enough electricity to power 70,000 homes.

One traditional measure of a power plant’s utility is its capacity factor. A facility’s capacity factor is the ratio of the energy it produces over a certain amount of time compared to the potential energy the plant could produce if it could operate at full capacity the entire time. Plants converting renewable energy generally have low capacity factors because resources like wind and sunlight aren’t always available. But thanks to thermal storage, facilities like Solana have capacity factors of more than forty percent—that's twice as good as plants using photovoltaic technology.

In many ways, Solana’s system is highly automated. Each mirror assembly is outfitted with temperature and pressure sensors, as well as a hydraulic sun-tracking system to maximize the heat captured.

Maintaining this giant solar field, however, is complicated. The mirrors need to be kept virtually spotless, because the cleaner they are, the more quickly the HTF is heated to the optimal temperature. To keep all 3,200 mirrored collectors bright and shiny, the company has a fleet of trucks that spray and scrub each mirror either on a bi-weekly basis or as needed. Breakage is minimal, since the mirrors are tempered glass—just like car windshields—but Solana officials estimate that about one percent of mirrors require replacement each year.

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Nitrous Oxide Injected Engine

Nitrous oxide (N₂O) is a chemical compound used as an oxidizing agent to increase an internal combustion engine's power output by allowing more fuel to be burned than would normally be the case by introducing a high amount of oxygen into the fuel mixture

When nitrous oxide decomposes, a single mole (a mole is a common scientific term for a specified number of atoms, or in this case, molecules), will release 1/2 mole of O2 molecules (oxygen gas), and one mole of N2 molecules (nitrogen gas). This decomposition allows an oxygen saturation of 33% to be reached (the produced nitrogen gas is non-combustible and does not support combustion). Air, which contains only 21% oxygen, the rest being nitrogen and other equally non-combustible and non-combustion-supporting gasses, permits a 12 percentage point lower maximum oxygen saturation than that of nitrous oxide. This oxygen is the gas which supports combustion, in that it alone combines with hydrocarbons such as gasoline, alcohol, and diesel fuelto produce carbon dioxide and water vapor, and heat, which causes these two products of combustion to expand and to exert pressure on pistons, driving the engine.

Nitrous oxide is stored as a liquid in tanks, but because of its low boiling point it vaporizes easily when released to atmosphere. When injected into an inlet manifold, this characteristic causes a reduction in air/fuel charge temperature with an associated increase in density, thereby increasing the cylinder's volumetric efficiency.

When N₂O breaks down in the engine's combustion phase, there is an additional benefit to performance: the oxygen atoms in N2O, as they are freed from their bond to the nitrogen atoms release heat in an exothermic reaction, i.e. one producing more heat than was required to initiate the breakdown; contributing to the overall power increase. The additional amount of heat produced, like that achieved above by increasing the charge of fuel allowed, by use of "nitro," similarly increases engine efficiency and performance, which is directly related to the difference in temperature between the unburned fuel mixture and the hot combustion gasses produced in the cylinders.

Nitrous systems can increase power by as little as 0.5 hp (0.37 kW) or as much as 3,000 hp (2,200 kW), depending on the engine type and nitrous system type. In many applications torque gains are even greater as increased fuel is burnt at a lower rpm range and is what causes the significant improvement in acceleration. All systems are based on a single stage kit, but these kits can be used in multiples (called 2, 3 or even 4 stage). The most advanced systems are controlled by an electronic progressive delivery unit that allows a single kit to perform better than multiple kits can. Most Pro Mod and some Pro Street drag race cars use three stages for additional power, but more and more are switching to pulsed progressive technology. Progressive systems have the advantage of utilizing a larger amount of nitrous (and fuel) to produce even greater power increases as the additional power and torque is gradually introduced as opposed to being applied to the engine and transmission immediately, reducing the risk of mechanical stress and consequently damage.

Spectators can easily identify nitrous-equipped cars at the track by the fact that most will "purge" the delivery system prior to reaching the starting line. A separate electrically operated valve is used to release air and gaseous nitrous oxide trapped in the delivery system. This brings liquid nitrous oxide all the way up through the plumbing from the storage tank to the solenoid valve or valves that will release it into the engine's intake tract. When the purge system is activated, one or more plumes of nitrous oxide will be visible for a moment as the liquid flashes to vapor as it is released. The purpose of a nitrous purge is to ensure that the correct amount of nitrous oxide is delivered the moment the system is activated as nitrous and fuel jets are sized to produce correct air / fuel ratios, and as liquid nitrous is denser than gaseous nitrous, any nitrous vapor in the lines will cause the car to "bog" for an instant (as the ratio of nitrous / fuel will be too rich) until liquid nitrous oxide reaches the intake.

Types of nitrous systems

There are two main categories of nitrous systems: dry & wet. A nitrous system is primarily concerned with introducing fuel and nitrous into the engine's cylinders, and combining them for more efficient combustion.

Wet versus Dry

I'm sure you've heard the terms "wet kit" and "dry kit." Actually, let me start with a rant on the "kit" part. A kit is a bunch of nitrous components packaged together by any of the usual vendors, and sold as one item. Typically, these are completely devoid of safety devices, so that they can be sold at a cheap price. This is where the "$600 nitrous kit" idea comes from. While these are fine for getting lots of the basic parts, they are horrible from a safety perspective, and can easily damage your motor. Get the appropriate safety devices and add them to your kit, if you go that way. I'll be calling a complete setup a "system" here.

On to the wet and dry discussion. A "wet system" is a nitrous system which mixes nitrous and fuel, and feeds it (in a "fog") into the intake. A "dry system" only feeds nitrous into the intake, and tricks the existing fuel system to add the fuel. In an LS1 car, this is done via the MAF sensing the colder intake temperature as nitrous is fed through it. In an LT1 car, a dry system typically adds adds about  50 psi of pressure to the vacuum nipple of the stock fuel pressure regulator, increasing the fuel pressure to about 90 psi, and driving more fuel through (hopefully upgraded) fuel injectors via the muscle of the add-on fuel pump. 

Either wet or dry system can be made to work, of course, so how do you decide which to use? Here's a chart f some pro's and con's with each to help you decide:

Feature	Wet	Dry
Nitrous	Plumbed and wired by you, into any of the various delivery mechanisms	Same as the wet system
Fuel	Plumbed, wired and jetted by you. You have complete control over the fuel system, typically making the nitrous system easier to tune. Stock pump and injectors are typically fine.	Uses the stock fuel delivery, via raising the fuel pressure by tricking the regulator. Must have good quality fuel injectors that won't fail on high pressure, and must have a fuel pump that can supply the pressure (ie, not the stock injectors or pump).
Tuning	Done by adjusting the fuel and nitrous jets, using O2 sensors to measure the a/f ratio.	On an LT1, this is done by adjusting the "fuel" and nitrous jets, the "fuel" jet actually being a jet that connects to the fuel pressure regulator to raise and lower fuel pressure. Not completely flexible, as the FPR can only support a certain range of pressure. On an LS1, nitrous is sprayed through the MAF, which is able to tell the PCM to adjust the injector pulses to compensate with extra fuel.

Delivery Mechanisms

As I mentioned, there are several ways to feed the nitrous and fuel into your motor. Here are brief descriptions of them.

Throttle Body Plate

This is a 1/2" thick plate that's mounted between your throttle body and intake manifold. Both nitrous and fuel lines are connected to it (so it's a wet setup) and the plate combines them and sprays them into the intake.

Fogger Nozzle

A nozzle can support either a single line for nitrous, or a pair of lines for nitrous and fuel, and sprays them in a fine mist into the intake.

Direct Port

The ultimate setup, a port is tapped and threaded specifically for each cylinder, running eight nitrous and eight fuel lines to spray directly into the cylinders. This setup is typically used above about 250hp, to allow accurate tuning for each cylinder. At left is the Agostino Racing direct port LT1 manifold.

Triggering the System

Of course, you don't want the system to be running all the time - a 10lb bottle will last you less than a minute, if it's open. Typically, you want the system triggered on while you're at the track, at WOT (wide open throttle), and at relatively high rpm's (see "Safety" for why). To make that happen, you'll typically want to wire, in sequence, several switches. I won't describe the specific wiring here, but you'll have some or all of the following:

• A Master On/Off switch
• A WOT switch, which is installed on the actual throttle, that closes the circuit only when your foot is on the floorboard
• A pushbutton in the car, probably on the shifter
• A "window switch" (see "Safety" for details) that closes the circuit only when the engine RPM is between a certain range (like 3000-6000) that you decide is acceptable
• A fuel pressure switch

What Can Go Wrong?

Well, a lot can go wrong, but hopefully you'll have adequate safety mechanisms built in to protect your motor when it does. The main thing that can go wrong is adding nitrous into your engine without compensating fuel. This extreme lean condition is disaster for the engine, and you're not likely to get a second chance - at least with the same engine. Conversely, adding extra fuel without nitrous is not particularly bad for the engine, so you can imagine, it's safer to start with the car running rich (too much fuel), then lean it back from there. Some examples of problems you might encounter include:

Fuel pump fails	A failed pump will lose pressure immediately, causing an extreme lean condition
Fuel injector failure or lockup	Using stock fuel injectors with a dry nitrous kit can cause the injectors to lock up and not flow fuel
Solenoid failure	A failed fuel or nitrous solenoid can cause serious damage

Ignition RPM limiter

On a stock LT1 or LS1 computer, the rev limiter is implemented by cutting the signal to the fuel injectors so the cylinders have no combustion. If you're running a dry system, which depends on the fuel injectors to provide compensating fuel for the nitrous, losing fuel this way is the ultimate disaster. An aftermarket ignition will typically implement the rev limit by cutting off spark rather than fuel, which is a much safer implementation of the rev limit. Typically, you'd get your stock PCM programmed to set the rev limit up higher than you'll ever expect to go (like 7000RPM), and use the setting on the aftermarket ignition as your actual rev limit.

Window Switch

This electrical device provides an open or closed circuit based on the engine being between two RPM values (hence "window") that you chose, so that you'll only flow nitrous in this range. Why would you do that? Well, for two very different reasons.

At low RPM, think about what's going on: you're spraying nitrous into the intake at a constant flow. That is, the nitrous bottle and solenoids have no idea what RPM you're at, and they're just pushing it into the intake at a constant volume. Inside the engine, though, the nitrous and fuel combination is being sucked into the cylinders during every stroke. The net result is that at low RPM, you're getting far more of the mixture into the cylinders. At 3000 RPM, for example, you're getting twice the amount as at 6000 RPM. So, you can imagine that running nitrous at, say 1000 RPM, is far more stressful on the motor as at 3000 RPM, and typically causes a "nitrous backfire" - meaning that the nitrous/fuel combination can explode in the intake manifold (rather than the cylinders) - a bad thing. So that's why you don't want the system triggered at low RPM.

At high RPM, the situation is easier to explain. Given the discussion of the rev limit above, you may just want the nitrous system to cut off before hitting that rev limit. If you've got a stock LT1 or LS1 ignition, you certainly want a window switch. If your rev limit is implemented by an aftermarket ignition, it's perfectly safe for the motor to run nitrous during the rev limit. It's not particularly easy though, on your transmission or clutch to have all that power during the shift, which may be a reason to keep the window switch set a bit before you shift. 

Fuel Pressure Safety Switch (FPSS)

This is a device that's plumbed into the fuel system, and provides an open or closed circuit based on availability of fuel pressure. It can be used in the triggering circuit to make sure the system isn't on when you've got a fuel problem. Typically, you only use it to switch off the nitrous solenoid; turning off the fuel solenoid as well can start a cycle of switching the solenoids on and off while the pressure raises and drops in the fuel system when you're switching the solenoid on and off. Let the pressure build up in the fuel lines when you open that solenoid, and when it's high enough, the nitrous solenoid will open. The switch can be used whether you've got a wet or a dry system. You can adjust the pressure at which it triggers by using an allen wrench on the back of the switch (loosen the screw lowers the pressure threshold).

You want to set the pressure on the FPSS, such that if the pressure drops about 10psi the nitrous system will shut off. On a wet LT1 system, this will be around 33psi, and on a dry system I'd leave the switch just above stock, say 45psi.

To set the threshold pressure, you've got a few options"

1. Connect enough plumbing so that you can have the FPSS installed at the same time as a fuel pressure gauge. Turn the key on to pressurize the fuel system, then turn it off. As the fuel pressure bleeds down, monitor the continuity across the FPSS contacts (disconnect them from the rest of the nitrous system) and when the pressure reaches the level you're interested in, adjust the screw on the back so it just balances back and forth between the continuity signal.
2. You could use an air compressor, with the appropriate fitting for the FPSS. Remove the FPSS from the car, and thread it onto the compressor. Set the compressor for the pressure of interest, and measure continuity as above.
3. If you can't do option #1 above because you don't have two available ports, first thread in the pressure gauge, and cycle the key. Then time how long it takes for the pressure to bleed down to the correct level. Then disconnect the pressure gauge, install the FPSS, and do the process against the clock rather than the pressure.

Timing Retard

A nitrous/fuel mixture increases the burn rate in the cylinder, and typically adding a few degrees of timing retard is recommended for safety. A rule of thumb is two degrees per 50hp of nitrous, but this will also reduce the power generated. When I tune my system, I monitor engine knock, and retard the timing only enough to eliminate the knock, which is usually about one degree per 50hp. At the track, under harder conditions (actually pulling the weight of the car, possibly higher outdoor temperatures, etc) I'll add a degree of retard.

The LT4 Knock Module is a common modification to 4th generation f-bodies. This device dulls the sensitivity of the knock sensor readings, which allows the PCM to avoid seeing noises from headers, exhaust and loud valvetrain parts incorrectly as knock. The net result is that the overall timing of the engine is advanced a bit, and the PCM is a bit less sensitive to all knock, whether real or false. Unfortunately, knock when running nitrous has more of a chance of doing damage, and it's not at all clear that using a LT4 KM while running nitrous would be a good thing. Personally, since I tune my nitrous while watching knock, and retard my timing as well, I do use the LT4 KM. Once again, though, it's your call on all these safety issues.

High Octane Fuel

High octane gas (e.g. 100 or more, unleaded) will also slow the burn rate in the cylinder. This will provide another way, similar to retarding timing, to avoid knock. I only use nitrous on a 50/50 mix of 92 octane pump gas and 100 octane racing gas. Make sure it's unleaded, of course, or you'll destroy your O₂ sensors.

By the way, watch out for Octane Boost claims. Typical claims are "8-10 points of octane boost for a tank of gas." You should be aware that these "points" are tenths of a point of octane as you'd purchase at a gas station. So the above example will raise your octane from 92 to 92.8 or 93, not 100-102 as you might think.

Don't assume that if high octane fuel helps on nitrous motors, that it'll help your naturally aspirated motor too. A naturally aspirated motor is tuned for a particular octane of gas; adding more doesn't help one bit. Save your money.

Nitrous Filter

A simple part, but essential in any nitrous system. This filter is added in-line to your nitrous line, between the tank and the solenoid. Install it as close to the solenoid end as is convenient. It will trap any small particles that may come through the line, much like a fuel filter. A common solenoid failure is due to some particle jamming it open.

Fuel Systems

Your fuel system is the most important part of the system. As I hope is clear by now, the worst scenario in a nitrous system is a lean air/fuel mixture. The solutions to a good fuel system depend on the type of nitrous system you're using.

On a wet system, you simply need to ensure that your fuel system can supply adequate fuel, at standard (~45psi at WOT) pressure. A stock f-body fuel pump can usually supply enough fuel for around 450 total horsepower to the motor; any more and you want to get a larger pump. Much more than 650hp and you'll want larger fuel lines as well.

On a dry system, not only do you want adequate fuel like the wet system, but on an LT1 setup the fuel is added by raising the fuel pressure, which forces more gas through the injectors. In this scenario, it's typically recommended that you replace the stock fuel injectors with better quality (not higher rating, just better, like Bosch) injectors. These injectors are able to handle the increased fuel pressures necessary.

Spark Plugs

Generally you want to use copper spark plugs as opposed to the stock platinum ones. You also want to reduce the gap from the stock 0.050" down to 0.035"-0.040".  I've received a couple notes on why you use a smaller gap. "The reason you want a smaller gap is because of ionization.  If you change from the typical air (78%nitrogen, 21% oxygen)/fuel ratio, a given gap requires more energy to ionize the mixture, resulting in less energy in the spark, if you even get a spark. You could also increase the coil voltage instead of decreasing the gap, but I think using a smaller gap would be preferential since the spark time will be smaller." and also this message: "The reason that you will close the gap on your spark plugs is because when nitrous is added, it raises the cylinder pressure, much like a supercharger. Therefore "blowing" the spark out. When you close the gap it cannot put out the spark as easily."

Testing Solenoids

I mentioned failed fuel or nitrous solenoids doing damage. Some of the issues here may be hard to cover with only other safety devices. I recommend you wire your solenoids with spade clips, so you can easily disconnect them, and test them on a regular basis. Simply disconnect them from the rest of the wiring, then ground one side, and connect the other side to 12V, and listen for the click-click to make sure they open and close. Some folks will also use two nitrous solenoids, in-line, which will ensure that both would have to fail before the flow would fail to stop. Of course you still need to test this setup, to ensure one isn't stuck open.

Tuning

All of the kit systems will come with a couple tuning setups, labeled "50-shot", "100-shot", etc. These are tuned to provide 50, 100, or other horsepower amounts, usually measured at the crank (i.e., measured on a chassis dyno you'll get a bit less). I consider these a starting point, and certainly good for your first passes (hopefully you'll make these with the lowest power, until you tune the system up). Once you've got the system installed and functional, though, tuning it is paramount, before running any serious power through it. I really recommend you do this tuning right away, even though the temptation will be strong to just go out and enjoy the power. This is the time you're very likely to do some serious damage to the motor, so it's important to get it set up right.

The Mechanism

Collateral Damage

You can break tons of other parts on your car by running nitrous, or any other large power adder. Running slicks at the track will just accelerate the damage. Here are a few things to keep in mind.

Clutch

The huge torque spike at low rpm's is particularly hard on clutches. I had to buy a new clutch as soon as I made my first pass with nitrous on slicks. Keep in mind, on a manual transmission car, you're likely to need one too.

Rear End

Not unique to nitrous, but certainly a common failure on high horsepower cars, is the rear end. A 4th generation f-body, with a stock 10-bolt rear end, is not going to last long on nitrous. Plan for an expensive (~$2,000) upgrade at some point.

Tires

With all the extra power, you'll have trouble hooking up with any traction, especially on street tires. You'll probably have to use drag radials at least, or slicks if you're adding any significant power.

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Thorium: Proliferation warnings on nuclear 'wonder-fuel' % Developement of Thorium Nuclear Fuel.

Thorium is being touted as an ideal fuel for a new generation of nuclear power plants, but in a piece in this week's Nature, researchers suggest it may not be as benign as portrayed.

The element thorium, which many regard as a potential nuclear "wonder-fuel", could be a greater proliferation threat than previously thought, scientists have warned.

Writing in a Comment piece in the new issue of the journal, Nature, nuclear energy specialists from four British universities suggest that, although thorium has been promoted as a superior fuel for future nuclear energy generation, it should not be regarded as inherently proliferation resistant. The piece highlights ways in which small quantities of uranium-233, a material useable in nuclear weapons, could be produced covertly from thorium, by chemically separating another isotope, protactinium-233, during its formation.

The chemical processes that are needed for protactinium separation could possibly be undertaken using standard lab equipment, potentially allowing it to happen in secret, and beyond the oversight of organisations such as the International Atomic Energy Agency (IAEA), the paper says.

The authors note that, from previous experiments to separate protactinium-233, it is feasible that just 1.6 tonnes of thorium metal would be enough to produce 8kg of uranium-233 which is the minimum amount required for a nuclear weapon. Using the process identified in their paper, they add that this could be done "in less than a year."

"Thorium certainly has benefits, but we think that the public debate regarding its proliferation-resistance so far has been too one-sided," Dr Steve Ashley, from the Department of Engineering at the University of Cambridge and the paper's lead author, said.

"Small-scale chemical reprocessing of irradiated thorium can create an isotope of uranium – uranium-233 – that could be used in nuclear weapons. If nothing else, this raises a serious proliferation concern."

Thorium is widely seen as an alternative nuclear fuel source to uranium. It is thought to be three to four times more naturally abundant, with substantial deposits spread around the world. Some countries, including the United States and the United Kingdom, are exploring its potential use as fuel in civil nuclear energy programmes.

Alongside its abundance, one of thorium's most attractive features is its apparent resistance to nuclear proliferation, compared with uranium. This is because thorium-232, the most commonly found type of thorium, cannot sustain nuclear fission itself. Instead, it has to be broken down through several stages of radioactive decay. This is achieved by bombarding it with neutrons, so that it eventually decays into uranium-233, which can undergo fission.

As a by-product, the process also produces the highly radio toxic isotope uranium-232. Because of this, producing uranium-233 from thorium requires very careful handling, remote techniques and heavily-shielded containment chambers. That implies the use of facilities large enough to be monitored.

The paper suggests that this obstacle to developing uranium-233 from thorium could, in theory, be circumvented. The researchers point out that thorium's decay is a four-stage process: isotopically pure thorium-232 breaks down into thorium-233. After 22 minutes, this decays into protactinium-233. And after 27 days, it is this substance which decays into uranium-233, capable of undergoing nuclear fission.

Ashley and colleagues note from previously existing literature that protactinium-233 can be chemically separated from irradiated thorium. Once this has happened, the protactinium will decay into pure uranium-233 on its own, with little radiotoxic by-product.

"The problem is that the neutron irradiation of thorium-232 could take place in a small facility," Ashley said. "It could happen in a research reactor, of which there are about 500 worldwide, which may make it difficult to monitor."

The researchers note that from an early small-scale experiment to separate protactinium-233, approximately 200g of thorium metal could produce 1g of protactinium-233 (and therefore the same amount of uranium-233) if exposed to neutrons at the levels typically found in power reactors for a month. This means that 1.6 tonnes of thorium metal would be needed to produce 8kg of uranium-233. They also point out that protactinium separation already happens, as part of other chemical processes.

Given the need for access to a research or power reactor to irradiate thorium, the paper argues that the most likely security threat is from potential wilful proliferator states. As a result, the authors strongly recommend that appropriate monitoring of thorium-related nuclear technologies should be performed by organisations like the IAEA. The report also calls for steps to be taken to control the short-term irradiation of thorium-based materials with neutrons, and for in-plant reprocessing of thorium-based fuels to be avoided.

"The most important thing is to recognise that thorium is not a route to a nuclear future free from proliferation risks, as some people seem to believe," Ashley added. "The emergence of thorium technologies will bring problems as well as benefits. We need more debate on the associated risks, if we want a safer nuclear future."

The researchers are: Dr Stephen F. Ashley and Dr. Geoffrey T. Parks from the University of Cambridge; Professor William J. Nuttall from The Open University; Professor Colin Boxall from Lancaster University; Professor Robin W. Grimes from Imperial College London.

Copies of the comment piece in this week's Nature are available on request. Interviews with Dr Steve Ashley can also be arranged by contacting Tom Kirk.

Hans Blix calls on scientists to develop thorium nuclear fuel

Thorium-232 crystal, prepared by the van Arkel (chemical vapour transport) process. Credit: The Actinide Group, Institute for Transuranium Elements (via Wikipedia)

Call it the great thorium divide: Thorium supporters and thorium critics do not agree over claims that thorium is an alternative nuclear fuel that could ensure a better future for the planet. Nonetheless, interest continues in thorium as a safer and abundant alternative to uranium. On the side of thorium, the latest call for action has come from Hans Blix, the former UN weapons inspector and former Swedish foreign minister. Urging nuclear scientists to develop thorium as a new fuel, Blix also called on the nuclear industry to start powering reactors with thorium instead of uranium. Blix said that the radioactive element may prove much safer in reactors than uranium and it is also more difficult to use thorium for the production of nuclear weapons.

He believes efforts in turn should be made to develop thorium, as the world looks for future energy supplies. "I'm a lawyer not a scientist," Blix told the BBC News. He acknowledged there are many obstacles ahead in turning to thorium, but development efforts should be made.

Thorium is a radioactive element and there are thorium reserves in countries around the world. Scientists promoting thorium as an alternative nuclear fuel argue that is a safer, more economical way of generating nuclear power than uranium. It is also more difficult to use thorium for the production of nuclear weapons. To be sure, abundance has been a strong argument among supporters. Thorium is believed to be three times more plentiful than uranium.

Oystein Asphjell, chief executive of Thor Energy, told BBC News: "There is lots of thorium in the world, very well distributed all over the globe." As for nuclear waste, he said "we do not generate long lived waste."

As the BBC News report explained, when a uranium reactor overheats and the fuel rods can't contain the chain reaction, as happened at Fukushima, the crisis continues. This bears contrast to the case of thorium where, if something happened to a thorium reactor, technicians could switch off the stimulus which comes from uranium or plutonium in a small feeder plant. The thorium reaction would shut itself off without any human intervention. A number of countries have explored thorium as an alternative fuel. Led by Norwegian company Thor Energy, thorium is being tested at a site in Halden, Norway.

Nonetheless, critics warn that, if supporters say it is high time to turn to thorium, they say this is a poor time. Their concern is that developing new reactors could drain funds best applied elsewhere. Nils Bohmer, a nuclear physicist with Norwegian environmental NGO, Bellona, said thorium development was a distraction from the need to cut emissions immediately to stave off climate change. He called the advantages of thorium"purely theoretical," according to the BBC.

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