The Transonic fuel injector represents the latest in supercritical fuel management that might finally enable the internal combustion engine achieve its efficiency potential.   Image Source: tscombustion.com

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Transonic, a relatively new company on the automotive technology scene, is working hard to help solve one of the world’s greatest issues: energy efficiency within the internal combustion engine (ICE). Their mission is to inject super fuel efficiency technology into global vehicle fleets that transform their energy foundation into a low-carbon future.

As the ailing automotive industry deals with a struggling economy and growing climate concerns, this company’s R&D is in the advance stage of commercialization of their innovative efficiency technology that can transform the internal combustion engine into a lean and cleaner process.

So far, a number of top automotive and engine manufacturers from Japan, Germany and America have engaged Transonic in an attempt to advance their own powertrain plans. Each country has an interest in radically shifting the technology base of the automotive industry by utilizing supercritical fuel injection.

Why? Battery technology is not ready for prime time, and the the masses can't afford it without government subsidies. 

The goal of Transonics is to radically shift the technological benefits of the automotive internal combustion engine, at least until battery technology comes of age; and there are many obstacles to overcome, like cost.

That is why you are seeing major improvements in gas mileage these days, but in a doled out manner. Fact is the final technology is still not in production, but the target goal is 2014. And you thought the IC engine was going away tomorrow!

TSCi(TM) Fuel Injection

By utilizing the supercritical-state of fuel, Transonic achieves lean combustion and ultra-high efficiency. It operates on modern high-compression engines, incorporating precise ignition timing and carefully minimizing waste-heat generation.

The specific details of Transonic’s patented technology are highly proprietary and reviewable only under Non Disclosure Agreement. All I could muster were terms like "fast mix, temperature and pressure to achieve critical state of fuel, and lean burn." However, there are several key features revealed on their website, tscombustion.com

Supercritical fluids have unusual physical properties that Transonic is harnessing for internal combustion engine efficiency. Supercritical fuel injection literally facilitates short ignition delay and fast combustion, which precisely controls the combustion that minimizes crevice burn and partial combustion near the cylinder walls; and that prevents droplet diffusion burn.

These are areas where gasoline energy and our money have been lost. Point is there is not a single drop of liquid entering the combustion chamber with this technology, because the fuel is in the supercritical state that I can only assume is gaseous.

This could not be achieved ten or twenty years ago without modern, engine-control software that facilitates the extremely fast combustion, enabled by advanced micro-processing technology. Their injection system can now supplement efficiency with advanced thermal management, exhaust gas recovery, electronic valves, and advanced combustion chamber geometries.

According to their website, the Transonic fuel system efficiently supports engine operation over the full range of conditions – from stoichiometric air-to-fuel ratios at full power to lean 80:1 air-to-fuel ratios at cruise, with engine-out Nox (nitrous-oxide emissions) at just 50% of comparable standard engines. Bottom line is their real-time programmable control of combustion heat release results in dramatically increased efficiency.

According to company reports, 3 patents (#7444230, #7546826, #7657363) have been issued to Transonic from the U.S. Patent and Trademark Office related to their technology, with another 14 patents still pending.

Examiner Commentary

This technology reminds me in many ways of GM’s HCCI technology. Perhaps Transonics is where they got it, but nobody is talking (See update below). For sure, the GM Research Lab has the talent to develop this on their own. However, GM often works with universities, the military and private enterprises to develop new technologies. My last visit to the GM Heritage Center in Sterling Heights is testament to such alliances over the years.

Recall that energy loss is the core of automotive inefficiency. The fundamental problem is that on average only about 15% of the energy from the gasoline you put into your tank gets used to move your car down the road (Source: U.S. Department of Transportation: Transportation Research Board). The rest of the energy is lost to engine and driveline inefficiencies and idling which causes the rest of the energy to be lost in various forms of heat.

The engine is where most thermal efficiency losses take place. Traditional combustion has resulted in large amounts of waste heat escaping through the cylinder walls and as unrecoverable exhaust energy.

When traditional combustion engines run with rich air-to-fuel ratios, fuel is trapped in the crevices as well as partially combusting near the cylinder walls. Thus the potential to improve fuel efficiency with advanced internal combustion engine technologies is enormous.

There are seven advantages associated with this technology, including: improved fuel efficiency, multi-fuel compatibility, economical OEM power train integration, near-term adoption, global auto industry sustainability and energy independence. In my opinion, economics and near-term adoption provide the greatest appeal for this technology to achieve energy independence while cutting air pollution. Now all we need is for that Ford laser ignition to officially kill the antiquated spark plug.

Ford is indeed proving it has a better idea. This time the company is collaborating and researching the use of laser power in the near infra-red spectrum to replace spark plugs for igniting combustion in its engines.

Upon further investigation, Ford's collaboration with the University of Liverpool is paying off. According to Research Intelligence, a webpage at the university, the technology’s feasibility is real and subject to patent protection. In fact, you will find there are quite a few benefits for automobiles. Perhaps that includes split hybrids which use direct-drive, internal combustion engines. Benefits include:

1) Variable power levels for improved cold-weather starting2) Better fuel recognition based on vapor signature (Flex Fuels)3) Multiple ignition points for more thorough burning of fuel and less emissions4) Feedback on conditions within the combustion chamber to the ECU

In other words, the ECU (Engine Control Unit) would now have every aspect of combustion monitored for precise ignition control. For example, some flex fuels like ethanol have a lower energy per volume content than gasoline. That means it burns slower. With a standard spark plug, the only controllable variable has been fuel-to-air mixture and ignition timing. A laser would allow the ignition power level to be truly variable, perhaps for the first time in automotive history.

Examiner Comments

Special thanks to my friend and hot-rodder, Glenn Weathers, for bringing this one to my attention. I couldn’t just report on it from an email attachment, though, unless I first proved the source.

In my opinion, this technology reads as a great enhancement to the ICE (internal combustion engine). That’s not only great news for Ford, but for the entire auto industry; not to mention the environment. A laser ignition system, based on its feedback, would precisely adapt its ignition points and temperatures in order to maximize fuel-burn efficiency, especially with lean mixtures. That alone would increase engine power output, increase mileage and reduce emissions.

In concert with other engine technologies already on the table, like Ford's EcoBoost and GM’s Ecotec technology (GM's HCCI is a compression-ignition process), this LI (laser ignition) system could literally advance the auto industry's use of the internal combustion engine to a new efficiency level; and all without really upsetting the present fuel distribution system. Are we headed toward super-mileage IC Engines? It would seem so. In addition, the cost might provide less payback time than what’s required now for some larger hybrids.

Expect more from Ford and the University of Liverpool as their team refines this technology for a production model.

Fast Ignition

University of California at San Diego researchers participate in experiments on the Titan laser at the Jupiter Laser Facility to study fast ignition.

The approach being taken by the National Ignition Facility to achieve thermonuclear ignition and burn is called the "central hot spot" scenario, which relies on simultaneous compression and ignition of a spherical fuel capsule in an implosion, much like in a diesel

engine (see How to Make a Star). Although the hot spot approach has a high probability for success, there is considerable interest in a modified approach called fast ignition (FI), in which compression is separated from the ignition phase. Fast ignition uses the same hardware as the hot spot approach but adds a high-intensity, ultrashort-pulse laser as the "spark" that achieves ignition. A deuterium-tritium target is first compressed to high density by lasers, and then the short-pulse laser beam delivers energy to ignite the compressed core – analogous to a sparkplug in an internal combustion engine.

An advantage of the FI approach is that the density and pressure are less than in central hot spot ignition, so in principle fast ignition will allow some relaxation of the requirement for maintaining precise, spherical symmetry of the imploding fuel capsule. In addition, FI uses a much smaller mass ignition region, resulting in reduced energy input, yet an improved energy gain estimated to be as much as a factor of 10 to 20 over the central hot spot approach. With reduced laser-driver energy, substantially increased fusion energy gain – as much as 300 times the energy input – and lower capsule symmetry requirements, the fast ignition approach promises an easier development pathway toward an eventual inertial fusion energy power plant.

Density and temperature profiles of a conventional central hot spot inertial confinement fusion target and a fast ignition target.

How Fast Ignition Works

In the compression stage, X-rays generated by laser irradiation of the hohlraum wall deposit their energy onto the outside of a spherical shell, the ablator shell, that rapidly heats and expands outward. This drives the remaining shell inward, compressing the fuel to form a uniform dense assembly.

To ignite the fuel assembly, it is necessary to deposit about 20 kilojoules of energy into a 35-micrometer spot in a few picoseconds, heating the fuel to the ignition temperature and initiating thermonuclear burn. The leading approach to FI uses a hollow cone of high-density material inserted into the fuel capsule so as to allow clean entry of this second laser beam to the compressed fuel assembly (see Stages of Fast Ignition).

The physics basis of FI, however, is not currently as mature as that of the central hot spot approach. The coupling efficiency from a short-pulse laser to the FI hot spot is a critical parameter dependent on very challenging and novel physics. Fast ignition researchers must resolve these physics problems to justify advancement to the next stage. Success in demonstrating efficient transport of a high-energy pulse into dense plasma, development of a target design for the compression phase and definition of a power plant concept could perhaps lead to a new energy source for the nation and world.

Laser Car Ignition Dream Sparks Multiple ApproachesLaura Marshall, Managing Editor, laura.marshall@photonics.comLaser car ignition systems promise better fuel efficiency and lower pollution than conventional ones – as long as the technology continues to develop.

As calls for improved energy efficiency and reduced auto emissions grow ever louder, lasers are being investigated as possible replacements for the conventional spark plug. But there’s another reason, too.

Laser car ignition technology could lead to improved energy efficiency and reduced auto emissions. Here, a laser spark is emitted at the end of the National Energy Technology Laboratory laser spark plug.

“Every laser jock wants to run an engine with laser ignition,” said Dr. Steven D. Woodruff, a research chemist at the US Department of Energy’s National Energy Technology Laboratory (NETL) in Morgantown, W.Va. “I became involved with a team working on new ignition systems for natural gas reciprocating engines, and this was a natural fit.”

Woodruff’s focus at NETL is on laser spectroscopic diagnostics in combustion, and his current

projects include developing a laser spark plug for natural gas-fueled engines. He also serves as an adjunct professor in the Mechanical and Aerospace Engineering Department at West Virginia University, also in Morgantown.

Dr. Steven D. Woodruff makes lab-bench adjustments on the National Energy Technology Laboratory (NETL) prototype laser spark plug. The team has lab-tested its laser ignition system on a single-cylinder engine.

His colleague Dr. Dustin L. McIntyre wrote his 2007 doctoral dissertation on a laser spark plug ignition system for stationary lean-burn natural gas engines. McIntyre continues to develop intellectual property related to lasers, laser diagnostics and laser ignition systems, and has more than 10 years of experience in ignition-system and high-energy-laser design.

“As a graduate student, I developed an interest in novel ignition systems and worked to develop a microwave plasma ignition system for my master’s degree,” McIntyre said. “When the opportunity became available for me to study laser ignition for my continued graduate work, I felt that it aligned perfectly with my interests and prior experience.

Conventional spark plugs such as these could someday be replaced by laser-based ignition systems, thanks to ongoing research.

“There was also the whole coolness factor, but, primarily, I was interested in moving a helpful and needed technology to market, where it could do some good in improving efficiencies and reducing exhaust emissions.”

Feeling the lean burn

Lean-burn operation is vital for low NOx emissions in natural-gas-fueled engines, Woodruff noted. “Lean burn” means that the air-fuel ratio in an engine is high, so the engine is using less fuel.

“However, lean burn means less fuel in the cylinder unless you increase the compression ratio,” Woodruff added. “Increasing the compression ratio means high pressure, and standard spark plugs then need much more energy to spark. But laser plugs can do with less. Because more current passes through standard spark plugs, the electrodes wear more quickly, requiring early replacement at over $100 each.

“Laser plugs have no electrodes. Assuming replacement every 500 hours, this is $16,000 per year just in spark plug costs, compared to approximately $10,000 for the laser diode array. The usual advertised lifetime for laser diodes is over 10,000 hours, and, since the duty factor is 10 to 20 percent, they can potentially last for much longer.”

Removing the electrodes from the system has a big impact. “The impetus behind the work was spark plug erosion, emissions reduction through lean-burn operation and efficiency improvement in large-bore stationary natural gas engines used for pipeline pumping and distributed electrical power generation,” McIntyre said. “A laser ignition system allows for the spark plug electrodes to be completely removed from the combustion chamber, and it optically produces a larger spark kernel within the fuel/air mixture to initiate combustion.”

The NETL prototype laser spark plug is mounted onto a research engine fueled by natural gas or a natural gas/hydrogen mixture. The laser is pumped via optical fiber by a 225-µs pulse from a 200-W diode laser at 810 nm, resulting in a 10 mJ, 2.5-ns Q-switched pulse with 1-µs jitter.

The engine as a whole also can work at a higher pressure level with laser ignition. “This has two primary advantages,” McIntyre said. “The increase in the operating pressure improves the thermal efficiency by reducing the pumping losses of the engine, and, secondly, according to Paschen’s law, as gas pressure increases, the voltage potential required to initiate a breakdown between two electrodes increases significantly.

“In other words, more and more insulators – air and fuel molecules – are being crammed between the electrodes, making an electrical discharge more difficult. As the pressure increases, the voltage and the spark energy must also increase dramatically, which shortens the spark plug lifetime because the electrodes are basically being eroded away one spark at a time.”

A spark plug’s electrodes also “steal” a good deal of energy from the ignition spark, McIntyre added, which means that the spark must achieve much higher energy just to maintain normal combustion. “For a laser spark discharge, the optical breakdown threshold falls dramatically as the pressure increases because more optical absorbers – air and fuel molecules – are being crammed into the focal volume,” he said. “Therefore, laser ignition becomes much easier as the pressure is increased.”

Laser spark plugs in action

The high laser power needed to create a laser spark has been a challenge for laser distribution through optical fibers, which would be damaged by such high power, but NETL’s laser spark plug met that challenge by locating a compact Q-switched laser at the engine cylinder; this is pumped by a diode laser from one end through an optical fiber. This setup allows the laser power to be low enough that it does not damage fiber.

“Our system delivers low peak power – less than 1 kW – to a miniature passively Q-switched laser that it converts to a high peak power output of a few megawatts suitable to be focused down to approximately 100 GW/cm2 to create a laser spark,” McIntyre said.

This pump energy excites the laser, and the output that results is released in a high-peak-power pulse with a width of 2 to 3 ns. “The high-peak-power pulse is then directed into the combustion chamber so that the focal intensity exceeds the breakdown threshold of the fuel/air mixture,” McIntyre said.

The team has lab-tested its end-pumped laser spark plug system on a single-cylinder engine fueled by natural gas and also by natural gas with 20 percent hydrogen by volume. Over three days, the engine ran smoothly through various conditions as well as multiple shutdowns and startups.

“Our laser spark plug is a passively Q-switched Nd:YAG laser, 1 in. long, pumped coaxially by a

diode laser source through a fiber optic,” Woodruff said. “The laser pulse is aimed through a thick fused-silica lens that also serves as the pressure barrier. With diode laser pumping, the energy cost is very similar to an electric spark system.”

“We currently hold a patent on the optical delivery system, which could be used to reach multiple cylinders on an engine with the proper timing,” McIntyre added.

Multiple approaches

The NETL team collaborated with an industry-academic consortium from 2002 to 2008, McIntyre said, to produce data that would validate the idea of laser ignition as an appropriate avenue. Each collaborator also developed its own intellectual property over those years, he noted.

“Others have investigated using a high-peak-output laser to simply deliver the high-peak-power pulse through an optical fiber or other type of waveguide,” McIntyre said. “Some have considered actuated mirrors that swing in and out of the laser path to redirect it to different locations.

“In the early development phase, most people in the consortium were using laboratory-scale high-peak-power lasers that were either directly connected to a single cylinder, or they were bouncing the laser beam across the room and into the combustion chamber.” This was carried out, he noted, mainly to obtain reliable data as other methods were being developed or considered.

“A Japanese group is working on ceramic Nd:YAG lasers, which may help lower the cost of the YAG component,” Woodruff said, “although the real high-cost component is the diode pump laser.”

He’s talking about the work of Dr. Takunori Taira and colleagues. Taira is an associate professor at the National Institutes of Natural Sciences, Institute for Molecular Science, and at the Department of Functional Molecular Science, The Graduate University for Advanced Studies (Sokendai), both in Okazaki, Japan. He also is an invited professor at Toyohashi University of Technology.

“Laser ignition allows us the ideal combustion,” Taira said. “As you know, the energy density of oil is two orders higher than [that of a] Li-ion battery. However, the conventional combustion is no longer the ideal situation. It requires [intense] ignition.”

Laser ignition was demonstrated back in 1974, he pointed out. “However, it was just basic research because the giant pulse lasers were so large, and [had such] poor efficiency and reliability for a long time.”

To make small, powerful lasers that could focus light to ~100 GW/cm2 with short pulses of more than 10 mJ each, Taira and colleagues at the National Institutes of Natural Sciences produced composite lasers from ceramic powders, heating them to fuse them into optically transparent

solids. They also embedded metal ions in the lasers for tunability. Ceramics tune optically more easily than conventional crystals and are stronger, more durable and more thermally conductive, so that they can dissipate an engine’s heat without breaking down.

Researchers at the National Institutes of Natural Sciences have made composite lasers for car ignition systems from ceramic powders, heating them to fuse into optically transparent solids.

Their laser, which they presented at CLEO 2011, is built from two yttrium aluminum gallium segments, one doped with chromium, the other with neodymium; the resulting laser is powerful despite its small size at only 11 mm long and 9 mm in diameter. It can produce two laser beams, which the researchers say can ignite engine fuel in two places at once, making a flame wall that grows more uniformly and quickly than one created by a lone beam.

This setup cannot yet ignite the leanest available fuel mixtures with only a single pulse, but it can ignite a lean fuel mixture completely using several 800-ps-long pulses.

Spark plugs of the future

The technology may be in development today, but several challenges must be overcome before laser spark plugs appear on commercially available vehicles. Taira’s research is supported in part by Denso Co. of Aichi, Japan, and he believes strongly that laser spark plugs will go commercial in the coming years. The field is so promising, he said, that he will chair the first Laser Ignition Conference in April 2013 (see sidebar for more details).

Woodruff and McIntyre reported no current serious interest in their work from automakers but said that the technology could appear someday on consumer cars. At present, McIntyre pointed out, “the technology only offers lean-burn operation advantages for gasoline powered engines. The cost of the current technology would greatly offset any gains in emissions or fuel efficiency.”

That cost-benefit ratio is possibly the biggest hurdle that laser ignition will have to overcome. “It is difficult to compete with a $4 spark plug that will last 100,000 miles,” Woodruff said. “Current automobile engines run on liquid fuels at stoichiometric fuel air ratios and do not require the very high compression ratios.”

And cars might not even be the initial target for laser spark plugs.

“The most likely place for laser ignition to be employed in commercial applications would be natural gas-fueled transit buses,” McIntyre said. “Stationary natural gas engines will probably be the first market to adopt any commercial embodiment of laser ignition, and this will probably be encouraged by regulations.

“Currently, the automotive market is able to meet their emissions and efficiency goals with stoichiometric combustion in conjunction with exhaust after-treatment. If automakers begin looking at lean combustion in a serious manner, then laser ignition may be an option for designers.”

There are technologies that need to be proved before laser spark plugs can realistically be adopted, Woodruff said. “First, the diode laser pump must demonstrate that it can operate continuously for 10,000 hours,” he said. “Second, will the pressure barrier window/lens stay clean for 10,000 hours? The window is self-cleaning to some extent, in that each laser pulse cleans the window. If it holds up over the duration, it will then be competitive with electric spark for natural gas-fueled engines.”

Laser safety interlock systems are another must, McIntyre said. “The laser output can pose a serious eye safety hazard,” he noted. “Installed, the output is completely shielded and contained by the engine system.

“However, one concern is that an end user who is unfamiliar with high-peak-power lasers may tamper with a laser spark plug during operation. If the output were to strike someone in the eye, the eye would focus the high-peak-power pulse onto the retina, where it would cause irreparable damage. The person would most likely lose a considerable portion – if not all – of the vision in that eye. Therefore, work is being done to develop appropriate interlock systems that would disable one or more lasers if they were removed from their proper place of operation.”

There is still a spark of hope in the researchers’ eyes, and both continue to work on related research. “Our primary experimental work ended about four years ago, but I have continued to develop intellectual property as new technologies and new interests emerge,” McIntyre said. “Recently, I’ve been working with industry and academia to secure funding for further development and testing of an ignition system.”

Advanced Laser Ignition System (ALIS)

The primary constituent of natural gas is methane (>90%) which being a stable molecule is difficult to ignite.  For methane, both chain branching reactions, as well as, chain propagation reactions are highly constrained by the available radical pool.  As a result, ignition as well as flame propagation are difficult compared to other hydrocarbons.

With a view to comply with the ever stringent NOx emission standards, engine manufacturers have resorted to low-temperature combustion strategies such as lean-burn combustion and Exhaust Gas recirculation (EGR).  To offset the loss in specific power of the engine in such strategies the intake charge is boosted by turbocharging.  This along with the industry driven target to enhance typical engine BMEP ≈ 25 bar from the current values of BMEP ≈ 18 bar, results in extremely high in-cylinder charge densities across the spark plug electrodes that has an insulating effect.  The Capacitance Discharge Ignition (CDI)Systems capable of generating voltages up to 40 kV across the spark gap and used prominently in the industry are not capable of overcoming such insulating effects and result in misfires.  Additionally, at high spark gap voltages, the electrode erosion is accelerated to a point that spark plug life is highly compromised.  Though the ARES desirable spark plug life is 8000 hrs, modern plugs have a life of 1000-3000 hrs.

With the above problems in mind, laser ignition appears to be a promising alternative.  A series of tests were conducted by Argonne comparing the performance of conventional CDI ignition and laser ignition in a static chamber and a Rapid Compression Machine.  Such tests have shown that sparking becomes easier at higher pressures in the case of laser ignition.  Also, laser ignition is found to be capable of extending the lean-ignition limit all the way to the lean-combustion limit (flammability limit).  Alternately, laser ignition allowed use of higher rates of charge dilution with exhaust gases or inert gases.  Subsequent tests on a 11 liter displacement single-cylinder engine using laser ignition have shown lean-limit extension and accelerated combustion.  Such a behavior with optimal ignition timing results in NOx reductions up to 70% or efficiency improvements up to 3% points.  Additional performance improvements are possible through accelerated combustion resulting from placement of ignition kernel at the center of the combustion chamber and through multi-point ignition.

Encouraged by such results, efforts were pursued to develop a laser ignition system that has the functional blocks shown schematically below.  The pulse train from a high-power laser is multiplexed and distributed to individual cylinders via fiber optic cables.  At the distal end of the fiber optic cables, laser plugs – plugs with the same foot print as a conventional spark plug but containing a sapphire lens – refocus the laser energy to achieve sparking.  Though most of the functional elements have been designed successfully, reliable transmission using fiber optic cables has remained a challenge.  While efforts continue to develop better strategies for fiber-optic transmission, in the interim a system based on free-space laser transmission is being developed for use with a 6-cylinder engine.  Preliminary tests performed on a Cummins 6-cylinder engine offer promise for lean-operation as compared to other advanced ignition systems.

Schematic representation of Advanced Laser Ignition System (ALIS).A video showing prototype ALIS under

test.