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Audi reduces fuel consumption 21% in new direct injection 1.8L TFSI; indirect injection in part-load range

4 August 2011

18tfsi
Audi A5 1.8 liter TFSI engine. Click to enlarge.

Audi’s base gasoline engine in the updated A5 family—the 1.8 liter TFSI—incorporates new solutions in fuel injection and other technologies to deliver its 125 kW (170 hp) and 320 N·m (236 lb-ft) torque, with 5.7 liters per 100 km fuel consumption (41 mpg US), corresponding to 134 grams of CO2/km (215.65 g/mile).

Fuel consumption in the new 1.8 TFSI has been reduced by 21% compared with the previous model engine.

The four-cylinder engine displaces 1,798 cm3 and delivers its 320 N·m torque between 1,400 and 3,700 rpm. Peak output of 125 kW is achieved at 3,800 rpm. With a manual transmission, the 1.8 TFSI accelerates the Audi A5 Coupé from zero to 100 km/h; top speed is 230 km/h (142.92 mph).

Combustion behavior was a particular focus of the development work. In addition to FSI direct injection, the 1.8 TFSI also uses indirect injection in the part-load range. This system injects the fuel at the end of the intake manifold near the tumble valves, where it is swirled intensively with the air.

The rail pressure of the FSI system has been increased from 150 to 200 bar. The direct injection system is active when starting off and at higher loads. It can perform two or three individual injection operations per work cycle.

The injection system reduces fuel consumption and particulate emissions to such an extent that the four-cylinder engine complies with the limits of the future Euro 6 standard.

To further optimize gas exchange, the valve control system has been given greater operating freedom. The Audi valvelift system, which adjusts the lift of the valves in two stages, is active on the exhaust side. The two camshafts can be adjusted through 30 or 60 degrees of crankshaft angle.

The thermal management of the four-cylinder engine features a new fully electronic coolant regulation system. Two fast-switching, rotating cores, which are consolidated in a module and driven by an electric motor via a screw drive, control the flow of coolant. One of their primary objectives is to bring the motor oil up to operating temperature as quickly as possible following a cold start. This is done by keeping the coolant in the crankcase for a relatively long time.

The cabin heating runs off of a separate loop in the cylinder head. The main radiator, which dissipates the heat to the environment, does not come into play until the latest possible moment.

The new rotating core module can set the water temperature between 85 and 107 °C as a function of load and rpm to always achieve the best compromise between minimal internal friction and thermodynamic efficiency. Switchable valves throughout the cooling system manage heat flows between the engine, the heat exchanger for the transmission and the cabin. All together, the thermal management system reduces the CO2 emissions of the 1.8 TFSI by around 2.5 g per 100 km (4 g/mile).

This concept benefited from the integration of the exhaust manifold into the water-cooled cylinder head. Because this also reduces the exhaust gas temperature, it is not necessary with the 1.8 TFSI to enrich the mixture at full load, which reduces fuel consumption significantly when driving sportily.

The turbocharger in the 1.8 TFSI is also an all-new design that develops the high relative boost pressure of up to 1.3 bar very systematically. Key features include a turbine wheel made from a new alloy that can withstand exhaust temperatures of up to 980 °C, the oxygen sensor mounted directly upstream of the turbine wheel, a pulsation damper, a compressor wheel machined from a solid blank and an electric wastegate actuator that adjusts the boost pressure particularly quickly and precisely to further reduce fuel consumption.

Engine weight has been reduced from 135 to 131.5 kilograms (298 to 290 lb). The new turbocharger/cylinder head module, a new casting process for the gray cast iron crankcase that reduces wall thickness to roughly three millimeters (0.12 in) and the crankshaft with four rather than eight counterweights and reduced main bearing diameters all contributed to this weight reduction. The pistons are made of new, high-strength alloy. Lightweight polymers are used for the oil pan, and many screws are made of aluminum.

Internal friction has also been significantly reduced by the use of an novel coating on the piston skirts and by mounting the two balance shafts that counteract the second-order inertial forces in roller bearings. The regulated oil pump requires little energy itself, and the oil-jet cooling for the piston heads is controlled via a high-precision electric system.

August 4, 2011 in Engines | Permalink | Comments (23) | TrackBack (0)

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"Peak output of 125 kW is achieved at 3,800 rpm"

That is one low-revving petrol engine, lower even than most diesels!

All very exciting - but complex.

Aluminum screws?
Exhaust routed within the head and cooled ahead of the turbocharger?
Multiple valves in the cooling system?

Is Audi durability better than when they last made cars for the American market?

And diesel-like torque, too.

While the article sounds like an expensive engineering tour-de-force, they are employing relative straightforward minor improvements, although at a seemingly higher pace than historically.

Amazing that this 1.8 litre gasoline engine has higher torque than their 2.0 diesel! I would not want to replace that turbo, though. It sounds horribly expensive.

Their improvements on engine thermal management are particularly intriguing since they only rely on an adjustable pump and some clever engine management software. I guess it also means that there is a great improvement in fuel economy for short trips and cold starts and less of an inprovement on long journeys. Most drive cycles incorporate a considerable amount of 'cold-start-driving'. Judging from the article, there is not too much improvement in highway fuel economy where the engine is humming quietly at low rev in high gear. Unless this is the load case where engine coolant temperature is allowed to increase to 107°C. If coupled with adjustable grille opening, there is an aerodynamic advantage to be achieved as well - not least when driving in hot conditions.

5.7 l/100km for a gasoline car of this size is very impressive indeed!

I knew that direct injection have not just advantages so they use both direct and indirect, that's a good engineering piece. The germans seams efficient these days with their audi windmills e-gas project, this engine and also the bmw i3, will they finally win the third world war( gasoline price at the pump) , they are on their way to eradicate the big oil cartel own and operated internationnally by swiss bankers with their secret black market private banks accounts. 2 world war for nothing, 1914-18 and 1939-45 for nothing because gasoline price is prohibitive and hack by this swiss corrupted internationnal petrol cartel. We don't need petrol except in old and actual cars. We need hydrogen cars, trucks, ships, electrical stations and airplanes and germany seam to tackle this tech better then usa,japan because these countrys financial elites are still casching petrol money in secret swiss bank accounts.

Thomas
The Audi engine does not have higher torque than a 2-liter diesel engine; not if you compare to a state-of-the-art diesel engine. The new BMW 2-liter engine (first used in the 525d) has 450 Nm, i.e. 40% higher. You can find many other 2-liter engines that produce a lot more than 320 Nm but you could, of course, also find engines with lower torque than that, as you can for gasoline engines, as well. Another comparison: the Fiat 1.6-liter diesel engine gives 320 Nm. The current leader in specific torque is actually the Mercedes 2.15-liter diesel engine that has been around for a while. It puts out 500 Nm and kind of dwarfs the Audi engine in this respect. It has the highest cylinder pressure (200 bar) as well as injection pressure (2000 bar) among contemporary diesel engines. Steel pistons (>>200 bar) and the next generation of common rail (2200 bar in first step) will be necessary for further increase of power and torque. Gasoline engine designers seem to struggle mostly with high temperatures in order to increase specific power and torque.

If one tries to make a “fair” and kind of “technology-neutral” comparison between power and torque for diesel and gasoline engines of same size using (among other features) DI and advanced turbocharging, it seems as the torque will be somewhat higher for the diesel and power somewhat higher for the gasoline engine. A simple explanation is that the diesel engine tolerates higher cylinder pressure (→torque) but the gasoline engine can achieve higher engine speed (→power). However, if fuel consumption is of highest priority, some limitation of engine speed (as shown by Audi) is a good idea also for gasoline engines.

Note that the Audi engine uses two injection systems, one for direct injection and the second for indirect injection. Expensive! It also illustrates the shortcomings of current injection systems.

Finally, the information in this article is not particularly new. The engine was already presented at the Vienna engine conference this spring and it has also been described in detail in a paper the MTZ journal.

PeterXX,

Where in the engine cycle is indirect injection superior to direct in-cylinder injection?

It's a good combination of technology but could it be more to go wrong?

The dual fuel injection might turn out to be a good move as you have some redundancy and could offer a path way to dual fueling using natural gas or low octane petrol with alcohol injection.

Would like to see the end of the belt and replacement with combined motor / generator and small battery, and they can just be plugged into the water cooling system

ExDemo
Where in the engine cycle? I am not sure I understand your question but I will give some background… The engine has 4 strokes, in two engine revs, i.e. 720°. Injection timing is completely different for both types of injection systems and has to be so. With indirect injection, much longer time is available for air/fuel preparation if injection is early in relation to the combustion stroke. This gives more homogenous mixture, which is advantageous under some operating conditions (e.g. low engine load). On the other hand, injection during the induction stroke alone is problematic regarding homogenization. Likewise, fuel deposition in the inlet system is not easy to control during transients. Direct injection makes use of the so-called “charge cooling” effect and can utilize higher compression ratio without knock, with lower fuel consumption as a benefit. Charge stratification can also be used to get a lean mixture – or more exhaust gas recirculation – for reducing fuel consumption but the former alternative has not been used by Audi, probably due to NOx control problems. With DI, the “window” for injection (in crank angle degrees) is much smaller and must be timed with regard also to both piston position and air movement, which cannot all the time be optimized. Thus, indirect injection can be better under some operating conditions. However, if direct injection could be made “perfect” under all operating conditions, there would be no need for two injection systems. Some researchers have started to investigate high injection pressures, i.e. in the 500 to 1000 bar range (compared to current state-of-the-art level of 200 bar).

Besides the theoretical aspects listed above, the statements by Audi in the papers I mentioned are important, although they do not discuss the topic thoroughly. Indirect injection is used by Audi at low engine loads; direct injection is used at high load and during engine starts. One advantage mentioned is lower particle emissions (mass and number) with indirect injection. Recall the more homogenous air/fuel mixture with indirect injection, as I mentioned above, which reduce soot formation. Thus, Audi states that the engine will be able to fulfill the (proposed) Euro 6 limit for particle number emissions. It now appears that a much higher level for number of particles will be allowed for gasoline cars than for diesel cars and meeting this limit without a gasoline particle filter (GPF) could justify two injection systems. If only direct injection would be used, a GPF might have to be fitted with a significant cost increase as the result.

If you want more detailed information about the benefits of double injection systems, I recall that Toyota has provided much more on this topic in a paper on one engine (V8) that also use this feature. I have to look for that paper myself, since it was a long time ago when I read it…

A demonstration of what can be done.

PeterXX,

You misunderstood, or did not read what I wrote. I said that is has more (specific) torque than *their* 2.0 L diesel. I am well aware that VW/Audi are behind the curve regarding 2.0 diesels, even though their 2.0 has been upgraded to 177 hp in the new Audi A6.

Diesels still allow higher torque than gasoline engines because of higher compression ratio, and slower combustion, which allows the maximum cylinder pressure to be maintained for a longer period. However, compression ratio is just one way to ensure high cylinder pressure (torque). A decent charge air cooler will deliver the incoming air at the same temperature regardless of the charge air pressure. So with a good turbo (or supercharger), the cylinder pressure before ignition can be the same in a gasoline engine as in a diesel. This effect is exactly what we see in this engine, made possible by new turbine alloys and more expensive construction of the compressor wheel.

I would like to add to Peter's comment about gasoline injection pressure that while state-of-the-art diesel injection pressure is now around 2000 bar, gasoline has extremely poor lubrication properties (much worse than water), making it difficult to increase pressure in a pump that is both economical and durable.

I would also like to add that I fail to see how direct injection accoplishes more charge cooling than indirect injection..? Unless it is about local temperature rather than cylinder average temperature.

Thomas
I know the VW/Audi engines, although I consider the comparisons I made more relevant. The VW group has several 2-liter engines with higher torque than 320 Nm. So, you are simply wrong. Please check data first.

“…the cylinder pressure before ignition can be the same.” Save your combustion theories for another forum. The cylinder pressure before ignition in a gasoline engine is nowhere near the level in a diesel engine. Do you really believe yourself what you have written? I do not bother to comment on your other statements in that paragraph…

Yes, it is possible to use high injection pressure also with gasoline if the right measures are taken, although I would not go for as high as 2000 bar, if a lower level is sufficient. This is why up to 1000 bar is under research. We also have examples from the history that proves the point. The Detroit Diesel methanol bus engine with high-pressure injection (EUI) could also be fueled with gasoline. In fact, methanol (and ethanol) is worse than gasoline in this respect. However, hardware (common rail) for very high gasoline injection pressures is simply not commercially available yet.

The merits and theory behind charge cooling with direct injection is an established fact that is recognized in the field. Heat for evaporation with indirect injection is mostly taken from hot surfaces, not from the air, as with direct injection. I do not have to explain that in more detail, I hope. You can find information about this in many scientific publications, so why not start by studying such literature.

Peter XX,

Thanks for your explanation.

As I thought, only with very cheap first generation DI is there any possibility of indirect injection being superior for portions of the fueling cycle, and engine operation.

A modern high pressure direct injection setup with multiple and controlled injection events in a cycle such as FIAT uses in its "Multi" Air or "Multi" Jet approaches for Otto and Diesel ICEs respectively, eliminates the necessity for a dual, and redundant second complete set of indirect injection equipment.

IOW, this Audi engine is a kludge; and a hodge podge of old ideas, producing little comparable HP, with a very limited rev range, while costing an excessive amount of money and componentry to construct.

PeterXX,

There´s no need to be harsh on people as you did with Thomas. This is neither an SAE or DEER conference nor some kind of beauty context. Here, we´re just exchanging ideas. Be assured I almost always appreciate your comments. Let´s make more friends than enemies.


ExDemo,

IMO, the two different fuel injection methods (PFI and DI) allow them a kind of control of the fuel mixture and temperature in chamber that would be very difficult otherwise.

You might want to read the thesis behind PPC (Lund University´s Partially Premixed Combustion). (Some tests where done with a GM 2.0L 4cyl block). (http://www.greencarcongress.com/2010/09/ppc-20100928.html, http://www.energy.lth.se/fileadmin/energivetenskaper/Avhandlingar/Gasoline_PPC_07062010.pdf)

PFI injected fuel will be homogeneous while DI could be stratified. A greater control of reactivity; peak temperature and NOx formation; combustion stability might be achieved.

There is another point not mentioned here about the relation of the demanded dynamic range from the injectors and it´s metering and atomizing abilities. Some companies even try using two (PFI) injector per cylinder just to keep atomization and metering precise over the whole load range. (http://www.greencarcongress.com/2009/07/nissan-dual-20090714.html)

Fiat´s "Multi-Air" is a clever design that promises higher control than VVT and VVL at an acceptable cost, while "Multi-Jet" is related to control of combustion event(s) on a CI (diesel) engine. Related, but not exactly the same.

As a last thought, for the price premium VW charges for Audi labeled vehicles, there is no problem over designing them with all those degrees of freedom as a platform to test in the real world the upper bound of what can be expected from it, even if some of this won´t be ever mass produced. Remember the double-boosted 1.4L supercharged and turbocharged ?

It might sound that I express a negative position but the Fiat multi-air, BMW valvetronic or any other gimmick today cannot “fix” the shortcomings of current gasoline direct injection. That is, if we want good enough atomization and mixing at molecular level to achieve the low solid particle number (SPN) emission level that we get with particle filters (DPF) on diesel engines (but without a filter in the gasoline case). If we want to achieve that SPN level, the contemporary solution would be to revert to indirect injection, with higher fuel consumption as a result (which nobody wants). However, considerable progress has been demonstrated by optimization of the injection event (multiple injections, timing, etc.), such as in a recent publication by the consultant company AVL. It is also up to the EU to set the SPN limits. If they would set a similar limit for SPN as for diesel cars, it is simply not possible to meet that level with DI. If the limit is set at a higher level (e.g. up to 10x diesel), optimization of the DI might be sufficient to meet that limit. Dual injection system, such as in the Audi case, will provide much more freedom in optimization and will achieve an even lower level (as indicated by Audi) but still not as good as a diesel with DPF. As current information suggest, EU will set a higher limit for gasoline cars than for diesel cars but, in this case, I do not have any inside information about the exact level to be proposed. However, on the long term, it cannot be “fair” to allow much higher SPN emission level from gasoline cars than from diesel cars, so I presume that the level will become more stringent in later regulations (e.g. Euro 7, 8…). This will be a driving force for further development of direct injection systems; it will not stop at 200 bar, which engineers refer to as second generation (1st @120 bar). I have hard to believe that double injection systems will be the preferred solution in the long run. I do not think manufacturers will revert to indirect injection alone either, so there is a good opportunity for fuel injection suppliers to continue development in this field. The gasoline particle filter (GPF) is not as efficient as the DPF counterpart (I will leave the explanation out this time) and will add to the cost considerably. However, I would not completely rule out this solution either. With very tough SPN limits (e.g. Euro 7…) and limits also for “off-cycle” driving conditions, a GPF might be necessary. It might also be possible to integrate the GPF function in the catalyst. If this could be accomplished at low incremental cost, GPF might even be an attractive solution in contrast to expensive injection solutions.

Supercritical fuel injection avoids the entire issue of fuel evaporation. Perhaps Transonic Combustion is the company to watch.

Sure, there are other options...

"Peak output of 125 kW is achieved at 3,800 rpm"

What's not mentioned in the text is captured in the Audi photo: max power is there from 3800 - 6200 rpm... revs just fine

Peter_XX,

My mistake - the latest Audi A6 2.0 diesel has a specific torque of 190 N·m/litre, versus 177 for this gasoline. I was referring to the Audi/VW 2.0 diesels with either 320 or 350 Nm, both lower than this new gas engine and still the bread and butter of their sales.

Regarding initial pressure before ignition in gasoline versus diesel: While I find your tone offensive, I would still like you to comment on while it is not possible. I am not an automotive combustion engineer, so I do not have access to detailed autoignition curves (usually hidden behind '$20 firewall'). With the limited time I have had to research the issue, I have not been able to fine any pressure dependence, nor understand where it comes from. Autoignition is obviously strongly dependent on chemical composition and temperature, but I have not been able to see where the pressure dependence comes from. Perhaps you could educate us?

I was stating that turbo/supercharging, followed by intercooling and then compression with low compression ratio can achieve the same pressure before ignition as in a diesel, without exceeding autoignition temperature.

Whether that would be feasible is a whole other matter... But as a possible way for gas engines to catch up to diesels, I find it interesting, although it relies on expensive turbos, as in the case of this Audi 1.8 engine.

PS, thanks for the explanation about charge cooling of indirect injection being eaten by hot surfaces. That makes sense.

PPS. Since gas engines have higher Max/ave pressure than diesels during the expansion stroke (isochoric vs isobaric combustion), might this engine have higher maximum pressure than contemporary diesels?

@Thomas
VW group have 2.0-litre diesel engines not only at the torque levels you mentioned but also 380 and 400 Nm. BMW recently increased torque from 400 to 450 Nm but specific torque is still lower than the Mercedes engine I mentioned. One could also mention the 1.9-liter Fiat engine at 400 Nm that has been around for a couple of years.

We do not have any pressure traces from cylinder pressure for the engines under discussion for a direct comparison of measurement data. However, it is quite easy to estimate the pressure before combustion (or actually at top dead center) with some simple assumptions. If I use reasonable values for charge pressure (1.9 and 2.6 bar abs), compression ratios of 9.6:1 and 16:1 respectively and finally, a polytropic exponent of 1.35, I get cylinder pressure of ~110 bar for a diesel and ~40 bar for a gasoline engine. Presumably, the actual level could be a somewhat higher in each case (higher charge pressure) but hardly any higher than 130 and 50 bar, respectively. It does not matter which set of numbers we use, this is still more than a factor of 2.5 higher for the diesel engine. This tells me that you must have very little or no experience from assessing cylinder pressure curves. Furthermore, you must realize that 1) the diesel has higher maximum combustion pressure and 2) the gasoline pressure increase due to combustion is greater in relative terms, so the pressure before combustion should have been lower even if the maximum pressure would have been the same. Thus, your theory that one could get similar pressure before combustion in gasoline and diesel engines does not make any sense to me. The most basic insight will tell you that these pressure levels cannot be at the same magnitude. Offensive or not, you cannot change such facts very much. When your hypothesis was wrong in the first place, why should I bother to comment on you argumentation?

About PPS: There is some gain by speeding up the late part of combustion, which improves fuel consumption without virtually any “cost” in other areas. I made some calculation on that about 20 years ago and found a potential of about 5% but the exact number might be somewhat different with conditions today and a more thorough analysis (that I never have done in this case…). Less soot formation will decrease radiation losses but other issues related to heat transfer might be negative. Besides the mentioned positive effects, I am afraid that PPS will increase cylinder pressure compared to conventional diesel combustion under the condition that similar compression ratios and charge pressure is used in both cases. You do not get much “for free” in this business. Stronger engine structure or a reduction of the compression ratio, as Mazda has done recently (see another article at GCC), might be ways to handle this issue.

Peter_XX

It seems we are slowly converging to understanding each other...

The 177 hp Audi has 380 Nm (190 per litre). I was not aware there was a 400 Nm (200 per litre?) version as well. Which model?

I never meant to imply that contemporaty gasoline and diesel engines have the same pressure before combustion. I know better than that. My point was that it is theoretically possible (by higher turbo boost in the gasoline engines than in diesel engines), although gas engines have a long way to go.

In the case of this Audi engine, the absolute pressure would be 2.3 bar (multiplied by inlet suction factor) for the gasoline engine and I have no idea what a small diesel engine can achieve. I know the large ship engines can be equipped with turbos capably of up to 5 in pressure ratio (single stage with titatium compressor wheel), but I suspect car turbos are much less efficient. Since diesel exhaust is colder there is less potential for work. On the other hand, diesel exhaust pressure might be higher, and a colder turbine can run faster with better aerodynamic efficiency under real world conditions. You indicated 2.6 in pressure ratio and you are probably right since you obviously know more about this than I do.

I see now that PPS (max/ave pressure in expansion stroke) is perhaps the final limiting factor to raising cylinder pressure to diesel levels, notwithstanding other issues such as very high charging costs, control issues, etc.

So you are most likely right that pressure before ignition cannot be as high for gasoline engines as diesels, as I wrote. It is definitely unlikely that it would be feasible. I was wrong to state that and you are right that it has been a while since I have actually made calculations based on real figures. I am not an automotive engineer (like most of the posters on this forum), but enjoy reading and learning about engine technology on this site, since my career did not go into engine development. I suspect I am not the only one like that posting on this site. But cars are cool and reduced fossil fuel consumption in cars is important for the future - hence our interest.

Peter, I find your debate style a bit too harsh sometimes (not just with me), but I also acknowledge that I have learned something in our present discussions. And thank you for keep coming back to follow up. But please try to be patient with those of us who have not done engine research more than 20 years.

BR
Thomas

@Thomas
The 400 Nm engine is for the commercial van. It has bi-turbo that the 380 Nm engine does not have. Audi (VW), we are waiting…

I think 2.3 bar is not needed for the TSI engine, 2.1 bar might be a closer estimate but I have not seen any numbers. The 2.6 bar level I used was for a BMW single-turbo 6-cylinder engine. The bi-turbo BMW (or any competitor…) should have a somewhat higher pressure level, as I indicated.

Peter_XX,

Now that I think of it, I seem to remember having seen that VW model at a dealership about a year ago... But I forgot about it. I remember being worried about putting such a heavily tuned engine in a heavy vehicle. The engine will be operated at high load much more than in a passenger car, especially if driven by young guys late for work (I see that all the time on the motor ways here in Denmark - black smoke from the exhaust half of the time and brake lights the other half)... I hope they put in a heavy duty gearbox!

The article says in the third last paragraph that a boost pressure of 1.3 bar is developed - 2.3 bar absolute minus pressure loss from the compressor to the cylinder.

A friend of mine has a BMW 135i Coupe with that bi-turbo straigh six... VERY impressive engine. Driving on mountain roads it feels like it does not matter whether you drive it in 3rd, 4th or 5th gear - the acceleration is equally powerful. Oh, that is the gas engine. I have not tried the x35d engine, sadly.

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