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

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.

Comments

clett

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

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

ToppaTom

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?

Engineer-Poet

And diesel-like torque, too.

Thomas Pedersen

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!

A D

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.

Peter_XX

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.

ExDemo

PeterXX,

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

3PeaceSweet

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

Peter_XX

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…

HarveyD

A demonstration of what can be done.

Thomas Pedersen

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.

Peter_XX

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.

ExDemo

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.

CelsoS

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 ?

Peter_XX

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.

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