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Given that the traditional four-stroke Otto-cycle engine piston engine only has a thermal efficiency of 25-30 percent, there is clearly still plenty of room for improvement. While most of the green automobile attention in recent years has been focused on electrification, liquid fuels still have about 100 times the energy density of today's best lithium-ion batteries, a difference that probably won't change significantly any time in the near future.

With that in mind, there is still plenty of effort being expended on improving the humble internal combustion engine. These efforts range from completely different architectures like EcoMotors' opposed piston opposed cylinder (OPOC) to new combustion processes such as homogeneous charge compression ignition (HCCI). One of the more interesting combustion-related developments comes from a California-based startup known as Transonic Combustion. In 2007, the company was claiming it could get an ICE vehicle to 100 miles per gallon. A lot has happened since then, and we finally have a better idea what the company's technology is. We sat down with CEO Brian Ahlborn to learn more about what the company is working on, and you can read all about it after the jump.






The heart of Transonic's technology is a new fuel delivery system conceived by company founder Mike Cheiky. Cheiky's idea was to get the liquid fuel into a supercritical state before injecting it into the combustion chamber. Traditionally, matter has been thought of as having three states, solid, liquid and gas and any given material can exist in one of those at any point in time depending on the temperature and pressure. Fuels like gasoline and diesel generally only burn after they are vaporized.


The supercritical state is essentially a fourth phase of matter that lies between liquid and gas that has properties of each as well as unique properties of its own. Achieving a supercritical state requires raising the temperature above the boiling point of the fluid while also increasing the pressure. According Ahlborn, the supercritical fluid can burn much faster than it can in a "normal" gaseous state, something that provides a number of advantages with respect to efficiency and emissions.

There are two major aspects to Transonic's technology, the fuel preparation and the direct injection system. The fuel delivery system is an evolution of current direction injection systems that use a common high-pressure (200-300 BAR) rail to deliver fuel directly to each each combustion chamber through individually controlled injectors. Before fuel is injected, the preparation system gets it into the supercritical state and this, according to Ahlborn, is where the "secret sauce" lies.

Ahlborn was reluctant to get into too many details of its proprietary system, but did reveal that the fuel temperature is increased from about "100 degrees centigrade to approximately 350-400." The fuel is also catalyzed, and although Ahlborn again declined to be specific about exactly what this means, he did respond to our query with, "I wouldn't necessarily draw the conclusion that we heat it in the presence of a catalyst." Ultimately, the goal is to have the fuel "be better prepared for an optimal combustion" says Ahlborn.

In a traditional piston engine, up to one-third of the energy of combustion is lost to heat transfer through the cylinder walls and into the coolant. One way to reduce some of this energy loss would be to have the actual combustion concentrated closer to the center of the cylinder and away from the walls. The claim from Transonic is that the faster burn rate of the supercritical fuel consumes the fuel before the flame front gets to the cylinder walls, thus reducing the heat transfer. In this way, more of the available chemical energy in the fuel can be transformed into mechanical energy to push the piston down.

With traditional fuel delivery systems, ignition typically occurs while the piston is still rising up in the cylinder, leading to pumping losses as the expanding gases push back against the piston. The faster burn rate of the supercritical fluid would make possible to delay ignition to either top dead center or afterwards, thus reducing those losses. Transonic's current prototype engines use compression ignition, like a diesel, while running on regular 87 octane gasoline. However, unlike homogeneous-charge-compression-ignition (HCCI) engines, they require no spark-plug or cylinder pressure sensor. As with many other details, Ahlborn declined to reveal the compression ratio being used in the prototype Transonic engines, although it's believed to be about 15:1.

The Transonic system also allows the engine to run at air-fuel ratios that are, in Ahlborn's words, "much leaner than conventional," going as high as 80:1. Normally, such lean air-fuel ratios can lead to combustion temperatures that rise above 600 degrees C, which in turn leads to the production of nitrogen-oxides. This is exactly what happened in modern diesel engines as the air-fuel ratios got leaner, in part to reduce particulate emissions. Ahlborn declined to get specific about the combustion temperature but acknowledged that it is below the NOx generation temperature and the engineers are doing some "neat tricks" to keep it there.

Transonic has consistently claimed that its engines are able to meet all current Tier 2 Bin 5 emissions limits without resorting to the expensive and bulky particulate filters and selective catalytic reduction systems required on contemporary diesel engines. The only after-treatment required by a Transonic-equipped engine is a conventional three-way catalytic converter. Supercritical fluid fuel injection is also claimed to be compatible with a range of fuels including gasoline, diesel, ethanol and butanol. While the engines have been tested with multiple fuels, most of the ongoing work is focused on optimizing for gasoline since the retail infrastructure is the most prevalent.

While Transonic's approach will obviously slash the cost of the exhaust after-treatment, it's unclear how much of a price premium the fuel pre-treatment will add. According to Ahlborn, the system is still being optimized for production and the engineers are continually reducing the part counts. As with many other aspects of the design, details were scarce.

Transonic has seven engine dynamometer cells at its Camarillo, CA facility and has purchased a number of engines from various automakers that have been modified with its fuel system. The engineers have been able to push the supercritical fuel system to a 25-30 percent improvement in fuel efficiency over the base gasoline engines. In order to validate its own internal test results, Transonic shipped several stock engines plus two modified engines from automakers to a third-party engineering test lab in Detroit earlier this year. The results from the un-named lab achieved a high degree of correlation with those from Transonic. In fact, Ahlborn says that the emissions results achieved both internally and at the outside lab were better than the initial predictions. Subsequent testing and analysis has allowed the engineers to better understand the properties of the supercritical fluid and why it achieved those results.

In addition to engineers and designers that are working on building and developing prototype hardware and control systems, Transonic has 10 PhDs working on mathematical models of supercritical fluids, the fuel preparation components and the injectors. These highly sophisticated models are needed for up-front analysis of component sizing, flows and calibration before prototype parts are produced. So far, Transonic has built and tested between 500 and 1,000 injectors from which they have collected data for the modeling process. Ultimately, using the simulation models should cut the lead time for new product applications from two or three years down to just six months.



While the bulk of the development work has occurred in its own labs and independent of customers, Transonic is working with three different automakers to test prototypes based on modern current-generation engines that have sufficient real-world data to provide a good baseline. Ahlborn explains that he is trying to keep his team focused on the the R&D required to get a viable, robust product to market as soon as possible. However, keeping some potential customers in the loop will also provide a sanity check on their work to make sure that what they create is commercially suitable from a cost, performance and packaging standpoint for different applications. There is always a risk when sharing too much information too early, but Ahlborn feels that the potential benefits in this case are worth it.

Ahlborn's self-proclaimed "big-hairy-audacious-goal" is to have Transonic go into business as a supplier of fuel systems to the auto industry by the 2014-15 time-frame. Given the three to five year lead times required to bring a product to market in this industry, that doesn't leave a lot of time for an automaker to commit to a program with Transonic. Ahlborn is well aware of the difficulty of meeting his target, but he believes the internal combustion engine, "is a long-term product for many decades still to come" and says, "we believe there is a quantum leap breakthrough in what we're doing" and that, "there will be a lot going on commercially next year (2011)."


Evidently Ahlborn is not alone in that belief. Transonic has been able to attract a substantial amount of venture funding from Vinod Khosla and, in May of this year, the company enticed retired General Motors executives Bob Lutz and Don Runkle to join its board of directors. Runkle's presence is particularly interesting since he also currently serves as the CEO of Ecomotors. There's been no public discussion of combining supercritical fluid injection with the Ecomotors OPOC architecture, but there doesn't seem to be any reason it couldn't be done.

Transonic Combustion still has a long road ahead of it to prove that it can beat the fuel efficiency of a diesel engine with cleaner emissions and a lower cost. Much more detail and public testing will be required to validate the company's claims, but this seems like one to watch.


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    • 1 Second Ago
  • 57 Comments
      • 5 Months Ago
      Wow. A lot of bad info in here about diesel as usual. There are three main reasons for Diesel fuel mileage gains over gas:

      Higher btu content

      Higher compression ratio

      Longer stroke

      This tech is awesome if it proves out. I do not smell snake oil. They have a lot to prove though. I'll invest if it plays out. And no, my fine Utopian friends, we can't just wave our hands and make dino-juice go bye bye next week because you say so.
      • 5 Months Ago
      I agree with the last comment submitted by Snowdog .boiler replacement
      • 5 Months Ago
      Seem like a viable direction, but not sure why we would need to invest in yet another new engine technology when we already have advanced diesel and rotary. The issue is the fuel. We and nearly 100 business partners are gearing up to produce over 25B gallons of biodiesel year. This is more fuel than the US currently buys from OPEC.

      EV's and Hybrids are not our future and no idea why people are still driving gasoline powered cars. GM just announced they will be offering a diesel powered car in the US next year. Maybe this is a turning point.

      etcgreen.com Are you driving your last gasoline powered car?



      • 5 Months Ago
      20 bucks, the three automakers in question are Ford, GM, and BMW.
      • 5 Months Ago
      The ICE is not going away. Hydrocarbon based fuels are plentiful and will be so for another 20-30 years. So the best approach is to squeze as much efficiency as possible out of the ICE and marry it to micro-battery technologies. This will keep the cost of innovation within reach of the millions of new car buyers each year. Eventually as battery technology gets better- and manufacturers scale up production- the micro technology will give way to fuller apps for electric propulsion (i.e. the chevy Volt) that will be within reach of more consumers.

      One thing that would be useful to clarify in your article is just how efficient the transcom tech is. I read about prototypes that get 100+ mpg. At the same time, your article talks about a 20-30% improvement in mpg. The technology is exciting but you should at least attempt to reconcile these two very different estimated results.
      • 5 Months Ago
      There's a lot of problems with this post.

      First, there's this:

      Given that the traditional four-stroke Otto-cycle engine piston engine only has a thermal efficiency of 25-30 percent, there is clearly still plenty of room for improvement.

      Not according to the Second Law of Thermodynamics. The temperatures of operation limit a heat engine to well below 100%; and this is only for an idealized engine that operates infinitely slowly. A real engine, even one with no friction, will perform significantly worse.

      Secondly, we have this:

      Traditionally, matter has been thought of as having three states, solid, liquid and gas and any given material can exist in one of those at any point in time depending on the temperature and pressure....The supercritical state is essentially a fourth phase of matter that lies between liquid and gas that has properties of each as well as unique properties of its own. Achieving a supercritical state requires raising the temperature above the boiling point of the fluid while also increasing the pressure.

      The supercritical "phase" is NOT a fourth phase of matter--it's simply a fluid, which can be more like a gas or more like a liquid, depending on temperature and pressure. It can be turned into a liquid or a gas without ever changing its phase. It is NOT a new thing, and it's been known about for almost two hundred years. It involves raising temperature and pressure beyond the CRITICAL point, not the "boiling point".

      All this is stuff that could be easily learned from Wikipedia.
      • 5 Months Ago
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      • 4 Years Ago
      Look! Battery operated self charging when in motion systems will propel driving a car from much more simplistic fueless designs that practically cost US slaves to things very little! That's almost godly! This way boys! It's not as complex as injection systems from studies like Transonic hooked on conventional fuels any time in the future. Think of fuel from oil like a demon that needs to be cast out and exorsized! My suggestion is to forget fuel based cars and start thinking Lithiulm such as in a conversion package like AFS Trinity already proven to reach 150 mpg. using much less lithium than Volt!
      Stick that in your pipe & smoke it!

      Simplicity is the greatest sophistication! Wake up or get left behind!
        • 5 Months Ago
        Stringing words together doesn't necessarily produce meaning!

        Your "Battery operated self charging when in motion"
        is what all cars with regen do when braking, or a physical impossibility due to the conservation of energy, or a garbled misrepresentation of AFS Trinity's vaporware serial hybrid. The AFS Trinity will only get over 50 mpg when you recharge it by plugging it in, regardless of what ultracapacitor secret sauce they add, and adding that takes away any claim of "simplicity".

        "receiving much more synergy out"
        Lucky for you there's no conservation of B.S. when using buzzwords :-)
      • 4 Years Ago
      The fuel injection system appears comparable to diesel common-rail systems but with lower injection pressure, which makes life easier, but apparently with some sort of heating system built into the injectors.

      It's not quite the same as current gasoline direct injection systems. Those normally squirt fuel in well before the end of the compression stroke, and combustion happens with the air and fuel "pre-mixed". This system appears to be injecting the fuel near top-dead-center on compression stroke, like diesels do.

      Thermodynamically, this should have comparable efficiency to a diesel engine, but if they can get the combustion system right, it shouldn't have the RPM limitations of normal diesel engines. If they can get the air/fuel mixing fast enough and the combustion process fast enough, it might even be able to beat diesel efficiency, by having combustion occur faster (closer to TDC with a higher rate of pressure rise).

      High combustion pressure rise also means combustion noise ... something the diesel engineers have been trying to deal with by *slowing down* the initial combustion phase. If you want the high efficiency, you're probably going to hear it!

      I don't mind the clattering sound of a diesel ... in moderation, of course.

      I wonder how they're initiating combustion. Gasoline is specifically designed to *not* self-ignite with compression pressure and temperature and have a long ignition delay when exposed to such conditions. Diesel fuel is designed to ignite with compression pressure and temperature and *not* have a long delay under those conditions. Octane rating (gasoline) and cetane rating (diesel) act oppositely to each other.
      • 4 Years Ago
      "liquid fuels still have about 100 times the energy density of today's best lithium-ion batteries, a difference that probably won't change significantly any time in the near future."

      That's BS. There are lab-tested batteries with over 1kWh/L. If one gallon of gas has 36kWh energy that is about 9.7 kWh/L ( http://en.wikipedia.org/wiki/Gasoline). No more than ten times higher. Current best already in use lithium ion batteries have over 300Wh/L densities. That's about 33 times better energy density, nowhere near 100. And I just recently found an article about battery manufacturer that has over 700Wh/kg batteries, and because volumetric energy density is higher than gravimetric for traditional solid batteries that probably already is that 1kWh/L

      Because BEV overall efficiency is as high as it is you very soon can have a battery that is smaller than equal gas tank to get bigger range than ICE vehicle would. With near future batteries that will be several times bigger range. If best theoretical batteries get realized then you can have a BEV with 1000mile range using battery that is no larger than a suitcase.
        • 5 Months Ago
        Continuing that mind game:

        Volt has 340 mile range from which 300 is made using 9 gallon fuel tank.

        9 gallons is about 34 liters.

        For typical sedan sized BEV you can have about 300 mile range with about 80-90kWh battery. Lets say 90kWh. That means you need about 2.6 kWh/L battery to get that same range. Not yet there, but close. With 1kWh/L battery you need only 90liter battery to get that 300 miles. 90 liters sounds much but it is only about 170cm*30cm*18cm which fits nicely under the backseats.
      • 4 Years Ago
      I don't give a crap if they can get 1000 miles per gallon. The ICE is a 19th century technology that has too many moving parts and requires too much maintenance. Parts and service are way too expensive, it's time to move on.
        • 5 Months Ago
        Okay then, 1.5 gallons of gas ;p
        • 5 Months Ago
        And the battery predates the ICE, so doesn't that make it worse? I suppose you think we should get rid of the wheel as well, because that is clearly outdated... :rolleyes:
        • 5 Months Ago
        I had an idea some months ago about ice engines and batteries. it's a little ice of approximately 125 cc working as a little electric generator for a battery car . the ice work at constant speed with a highly precise efficient combustion in h.c.c.i or at least a very lean mixture, some water mist is introduced in the combustion chamber to increase the power output and the exhaust heat is used to heat a little compact boiler powering a second electric generator.

        Theses generators should be constructed by me or anyone else and putted starting in november into the leaf or volt. the main problem to take care of is to get rid of the exhaust carrefully to avoid been suffocated. It should return over 100 m.p.g in extended mode beatting the big volt generator in efficiency and giving the little leaf a way bigger range and an increase in security to avoid been stuck on the road with a car like the leaf at night or in the cold or into a crowded highway.
        • 5 Months Ago
        @The_R1_Kid
        Comparing only density is kind of misleading. The efficiency of the electric motor makes up for it. Right now we are starting with 100-200 mile BEVs, but I think is clear 300 is achievable in the near future.

        However, I agree the ICE will still be around for a long while and it makes sense to improve it as much as possible.
        • 5 Months Ago
        Yes, it's very complicated, expensive and unreliable! So much so, I don't think it's EVER going to get off the ground! It's sad that people like you are allowed to vote. =/
        • 5 Months Ago
        With what? MY 14kw/h battery pack has the same energy as a 1/2 gallon of gas. Batteries just aren't there yet. ICE is going to be around for quite some time might as well make it more efficient.
        • 5 Months Ago
        ICEs aren't the problem, it's what we're burning in them.
        • 5 Months Ago
        gorr, that doesn't work all that well.

        Adding a steam generator to your design is going to increase weight SIGNIFICANTLY. Water is heavy, and to have a boiler strong enough to hold all that pressure will require a highly dense material.

        Also, why are you adding water into the combustion chamber? I hope you like hydrolocking.
        • 5 Months Ago
        to be fair though, electric motors aren't all that new either. lest you forget electric cars were around at roughly the same time as gas cars were. Jay Leno has a couple in his 'museum' of a garage. Then I believe streetcars were also electric. So. that side of things isnt 21st century only tech, it's had some time in the history books too, just not in the spotlight like ICEs have. If there's room for improvement to the ICE, then by all means go for it since it's not likely that car buffs will gain the intelligence to move forward with car technology (still using pushrods and carburetors tsk tsk dinosaurs..) The rotor engine is actually where it's at IMHO since there's very little moving parts. Granted there's not much torque in one compared to a piston engine and it's fuel economy isn't all that hot yet but for it's displacement, it's impressive (Mazda 1.3 rotary roughly 200hp naturally aspirated -- most engines that size that use pistons need forced induction to reach that, or just very very good tuning and parts.) Hydrogen is still being touted as a silver bullet but I don't think it'll ever be the fuel of cars to come due to so many having issues about the manufacturing of it (power sources are fossil fuels for now, but can be cleaner like wind and solar if they just put some r&d into it)
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