Enhanced TFSI Debuts in a 1.8-Liter Engine; New Engine Family for Audi
04 December 2006
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| The 1.8 TFSI is Audi’s first four-cylinder engine. Click to enlarge. |
Audi has introduced a new turbocharged four-cylinder FSI engine with a displacement of 1.8 liters for the Audi A3 and A3 Sportback. The 1.8 TFSI is the first in a new family of engines and combines the evolution of the TFSI concept with an entirely new basic engine.
The TFSI concept brings together the advantages of gasoline direct injection and turbocharging, delivering better performance with reduced fuel usage and emissions. The 1.8-liter TFSI develops 118 kW (160 hp) of power and high peak torque of 250 Nm (184 lb-ft).
Audi refined its existing TFSI concept—represented by the 2.0 TFSI engine, available since September 2004—for the 1.8 TFSI by increasing the injection pressure to 150 bar and applying new six-hole injectors to guarantee highly homogeneous mixture preparation and efficient combustion.
A new type of high-pressure pump supplies this injection pressure. The pump is driven by a four-fold cam on the exhaust camshaft. This reduces the operating forces required and boosts precision, thus improving the emissions.
The high-pressure lines through which the fuel reaches the injectors at maximum pressure are made entirely from stainless steel. Dual injection—the distribution of the fuel quantity between the admission stroke and the compression stroke—brings further advantages for the homogenization of the mixture and heating of the catalytic converters after a cold start.
The integrated turbocharger and a new engine management system bring a further improvement in responsiveness and help the torque to build up even more smoothly.
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| Power/torque curves for the 1.8 TFSI. Click to enlarge. |
The watercooled turbocharger K03, from Borg Warner, maintains optimum cylinder filling. An optimized turbine wheel improves the aerodynamics inside the charger, as a result of which responsiveness lower down the engine range is further enhanced. In the intake system, the redesigned charge movement flap reduces flow losses and simultaneously assures a very homogeneous distribution of the mixture.
Audi also re-engineered the continuous adjusting mechanism of the intake camshaft; this vane-type system now responds much more swiftly than previous concepts and promotes a spontaneous response from the engine even starting at low engine speeds.
The peak torque of 250 Nm is available across a very wide engine speed range extending from just 1,500 rpm all the way to 4,200 rpm.
The new engine is available initially in the A3 and A3 Sportback, both in combination with the six-speed manual gearbox and with the optional S tronic, the dual-clutch gearbox for lightning-fast gearshifts without any perceptible interruptions to the flow of power.
With a top speed of 220 kph (137 mph) and acceleration from a standstill to 100 kph in 7.8 seconds for the 3-door A3 with S tronic, the A3 with the 1.8 TFSI consumes 7.3 liters per 100 km of fuel (32 mpg US).
By comparison, the A3 2.0 FSI model uses a 2.0-liter engine that develops 115 kW/150 hp at 6,000 rpm and maximum torque of 200 Nm at 3,500 rpm, and accelerates from 0 – 100 kph in 8.9, all with the same fuel consumption (7.3 l/100 km) as the more powerful and smaller 1.8 TFSI.
The first 1.8 TFSI-equipped vehicles will be available in January 2007.
Audi's first 4-cyclinder? I'm pretty sure my '99 A4 was a 4-cyclinder, not a five or six. Wasn't the Audi 4000 a four as well? The Audi Wiki says their very first car was a four-cylinder.
Posted by: Steve Patterson | 04 December 2006 at 08:56 AM
Hmm. Audi says the 1.8 is their first four cylinder. I'll remove the sentence until I can confirm.
Posted by: Mike | 04 December 2006 at 09:23 AM
Hmmm...in the US we only get a TFSI version of the 2.0 (200hp and ~200ft-lbs torque) with fuel economy of 25 city 32 highway. We never received a non-turbo direct injected version of the 2.0L so I doubt they will bring this 1.8L engine over here. I personally would prefer this 1.8L Turbo motor over the 2.0L turbo they use right now...but previously they were using a 150-180hp turbo 1.8L (multi-port injection).
Posted by: Patrick | 04 December 2006 at 09:31 AM
I wonder if all the fours Audi has used up to this point have been share with VW, and aren't considered to be Audi's engine per say.
Posted by: yesplease | 04 December 2006 at 11:09 AM
I had an Audi 4000 that had a 1.6 liter 4 cylinder. It was similar to the 1.8 liter GTI I had at the same time. If memory serves correct the used the same basic engine block. I was able to pull the 1.6 out of the Audi and replace it with a GTI 1.8.
Posted by: Andy | 04 December 2006 at 11:54 AM
Again we see incredible engineering effort going into the ICE. When will similar effort be applied to plug-in hybrids and electric cars?
Posted by: JN2 | 04 December 2006 at 12:02 PM
Gents -
of course this isn't Audi's first four-banger, I don't know what gave you that idea. It's just their first one to feature charge motion control, homogenous GDI, a turbocharger and an intake cam phaser all in one package. That combination delivers a lot of fuel economy improvement for modest investment, comparatively speaking. For comfort, they added compensation shafts.
Audi and VW still maintain separate engine design teams, in the spirit of internal competition. The new CEO, Martin Winterkorn (previously responsible only for the Audi, Seat & Lamborghini brands) is rumored to be mulling a reorganization into value and premium brands. Note that Audi already builds a lot of VW engines in Hungary.
JN2 -
actually, a lot of effort is going into HEV designs at many manufacturers (Audi commissioned a concept study with FEV) but it's naive to believe everyone will stop building ICEs overnight. Only about 2% of new car registrations in the US were for hybrids this year, up from last year but still a tiny market share. Besides, the lead time for revising an engine design is 30-36 months and the general public usually doesn't get to hear what's in the R&D pipeline. Stay tuned.
Posted by: Rafael Seidl | 04 December 2006 at 03:21 PM
It was always a problem in GDI stratified charge engines to assure complete combustion of extremely lean mixture in “fuel cloud” boundary layer. The solution appears to be to divide fuel injection in two phases: one early on intake stroke to form very lean, but homogenous charge in all cylinder volume, and second injection - late in compression stroke to form rich “fuel cloud” around spark plug. In order to assure function of cat converter, overall mixture is stoichiometric. As you remember, Toyota on their last hybrid Lexus sedan employed GDI engine with two sets of injectors: regular port injectors and direct gasoline injectors. It is very important news, that Audi managed one set of DG injectors to perform both two functions.
Posted by: Andrey | 04 December 2006 at 11:31 PM
JN2 -
smart companies invest money where they expect to find returns. for Germany, hybrids are not worth the effort because they don't improve steady-state efficiency significantly (the prius is more effient on the highway primarily because of aerodynamics, narrow wheels, and atkins cycle engines, not hybrid electronics). hybrids make the biggest improvement for stop and go driving, not for cruising the bahn at 120 mph.
so, a company that sells mostly in Germany should invest in technology that increases efficiency for their real life situation, not for fictional US EPA standards.
Japan, because of tax laws that favor smaller engines, a low national speed limit, a virtual lack of diesel engines, and high gas prices should invest in hybrid tech.
the US consumer on the other hand currently has no economic reason to bother with either more efficient compact turbo engines of hybrids. the US in general would obviously be best served in the long run by a focus on improved fuel efficiency, but personal economies are not significantly impacted by fuel efficiency, especially when comparing new vehicles, so vehicles are bought based on desire and image rather than efficiency.
Posted by: shaun mann | 05 December 2006 at 12:05 AM
Andrey -
this particular engine uses homogenous GDI to avoid the expensive NOx aftertreatment and PM formation. The fuel injector is still arranged laterally between the intake valves. VW/Audi abandoned "fuel stratified injection" some time ago but their marketing depts. retained the FSI moniker regardless. TFSI "just" adds a turbo.
Mercedes and BMW have both developed spray-guided GDI, in which the injector and the spark plug are arranged next to each other at the apex of the combustion chamber. The distance and angle are subject to tight tolerances. Geometrically, this arrangement is only feasible in designs featuring relatively large-bore cylinders. However, it does permit sufficiently complete stratified combustion in part load, eliminating or at least substantially reducing throttling losses. Unfortunately, as long as there is a flame front there is no way around an NOx store cat or SCR if your global lambda is greater than one.
Shaun -
considering the simultaneous drop of SUV and rise of compact car market share in 2005 and 2006, I think it may not be accurate to assert that "personal economies are not significantly impacted by fuel efficiency" in the US. While true of the well-off, evidently there are also many people in the US who can ill afford gas at $3 a gallon. While seasonal variations in prices at the pump are much stronger than in the Europe, the average trend has been firmly upwards for several years now. This is likely to continue as long as the world economy continues to grow and the Middle East remains a region in turmoil and, many US consumers are implictly acknowledging this reality.
In addition, the US dollar is now falling rapidly because even the Japanese and the Chinese cannot afford to prop it up forever to safeguard their exports to the US. American debt levels, both public and private, are at all-time highs while the savings rate remains much lower than elsewhere in the developed world. In other words, the average American is really living above his financial means.
Posted by: Rafael Seidl | 05 December 2006 at 01:59 AM
Rafeal
You made two erroneous statements:
1. "homogeneous" GDI does not infer a Stoichiometric A/F ratio.
2. Ultra-lean pre-mixed combustion with a deflagration flame can achieve extremely low NOx if the A/F mixture is lean enough. I think you were suggesting that only flameless autoignition could achieve extremely low NOx values with lean mixtures - not correct.
Posted by: informer | 05 December 2006 at 01:19 PM
Informer -
technically, you are correct, it is possible to have a homogenized lean mixture. In the German GDI literature, at least, "homogenous" is used to refer to globally stoichiometric, homogenized charges - as opposed to globally lean, stratified charges.
Regular gasoline has an ignition stability limit of lambda = 1.3-1.6 depending on engine design and your definition of smooth running. That isn't really all that spectacular compared to diesels or the limits for other spark ignition fuels, such as natural gas or hydrogen. A more common strategy for avoiding throttling losses is internal EGR control via cam phasers, because it permits the use of cheap three-way catalysts.
I have not heard of deflagration flames before. Do you have a link describing how this combustion concept can be applied to automotive engines at low load? The entire process of ignition and heat release must be executed extremely reliably and fairly predictably within ~45 degrees crankshaft (~3 milliseconds at 2400 RPM). For a typical combustion chamber geometry , that implies an average flame propagation velocity of ~16m/s.
Posted by: Rafael Seidl | 05 December 2006 at 05:06 PM
There is too much misconception in popular literature about “lean burn”, “GDI”, and alike. To put things simple, current automotive GDI works as follows:
1) on intake stroke part (about ½) of gasoline is injected and is homogenously mixed with air, filling all combustion volume.
2) On compression stroke second part of gasoline is injected and forms rich fuel cloud around spark plug.
Overall mixture is stoichiometric, so exhaust gases could be treated on three-way cat converter to comply with tight emission regulations in US and EU. As one familiar with theory of SI engines should know, rich mixture around spark plug allows higher compression ratio without risking detonation. On described Audi turbocharged engine compression ratio is very high – about 10. On recent naturally aspirated 2.8 liter 210 hp Audi engine with GDI it is 12. Together with VVT, it allows about 5% increase in torque and hp, and about 10% better fuel efficiency. No reduced pumping losses for this technology.
The reason why almost every automotive manufacturer continues to mess with GDI is very simple. When equipped with emerging NOx absorber, GDI engine will meet emission standards while working on overall substantially lean mixture. How it works is extensively covered in literature, and actually most of modern outboard gasoline engines on motorboats (subject to lenient emission regulation) use this tech. Such engines substantially reduces pumping and heat transfer losses. Fuel efficiency increases by no less than 20%. On full throttle stoichiometric or slightly rich mixture is used to develop max power from unit of engine displacement.
Most of popular publications describe lean GDI engines, which, once again, are not in compliance with emission regulations (varies to some degree in different countries). Paired with CVT or in microhybrid configuration, lean GDI can seamlessly step to stoichiometric mode to regenerate NOx absorber with minimal fuel loss, unlike NOx absorber regeneration on diesel engine.
Now, its basics, particular designs differ substantially.
Informer:
Ultra-lean high compression ratio combustion as you described is extensively used on NG SI diesel generators, with diesel-like thermal efficiency and very low emissions. Unfortunately, gasoline fuel never evaporates/mixes with charge air perfectly, which precludes high compression ratio. Without high compression ratio (about 16), extra-lean fuel mixture produces unreliable ignition and poor combustion.
Somehow I suspect you know this.
Posted by: Andrey | 05 December 2006 at 10:23 PM
Rafael:
Even in German literature "homogen" does not refer to the stoichiometry of the A/F mixture as much as in English literature. "Luftverhaeltnis" (A/F ratio) is always referenced be it Lambda =1, Fett (rich) or Mager (lean).
If you get a copy of a fundamental combustion text you can learn what deflagration flames are. Needless to say that irrespective of pre-mixed or non-premixed combustion, a deflagration flame is typical in IC engines. The exceptions are autoignition or the other flame type - detonation.
Andrey:
Even though gasoline must change phase to vapour, it actually mixes better with air than a gas can when injected into an air space. We should be careful here, because it all depends on the application. In-cylinder fuel preparation is a tricky subject and extremely large cylinder, slow revving engines have somewhat of an advantage over small cylinder high revving engines. In any event, modern gasoline engines have a very high combustion efficiency which indicates that most of the fuel is getting mixed and combusted.
Your statement about ignition of extra-lean mixtures being unreliable without high compression ratio sounds slightly off mark. Granted that a higher charge temperature will reduce the ignition energy requirement. But higher cylinder pressure before ignition requires higher breakdown voltage (see Paschen curve for reason). Ignition systems have serious challenges at increased C.R. However as you would understand, it is the flame development and successful completion which presents the greatest challenge with ultra-lean mixtures.
One more note. The ratio of specific heats of the working gas, which is influenced by the A/F ratio (not forgetting gas temperature and any participating gas compositions before and after combustion), is an important parameter in setting the upper bound on real engine efficiency. It is often forgotten that lean operation is more than just throttle and cylinder wall heat loss reduction. However as with compression ratio it too has a point of diminishing return in a real engine.
Posted by: informer | 06 December 2006 at 12:38 AM
Informer, thanks.
As I understand, modern high-voltage ignition systems and iridium-tipped spark plugs manage to resolve most of the problems. And yes, flame propagation and optimum swirl is very tricky to optimize, especially at varying loads. Plus variations in NG or, god forbid, LPG fuel compositions.
I hope you will continue your informative posts on GCC.
Posted by: Andrey | 06 December 2006 at 09:59 AM