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BMW Emphasizes Improved Efficiency of New 4-Cylinder Engines; Gasoline Direct Injection and Diesel

New 2.0-liter diesel with Variable Twin Turbo and 2,000-bar injection. Particulate filter is the cylinder at left rear. Click to enlarge.

At its recent Innovation Day 2007 in Germany, BMW emphasized the role its new families of four-cylinder diesel and gasoline engines will play in increasing fuel economy while still delivering power and performance. BMW views its diesels in particular as a core technology in its strategy to reduce CO2 emissions.

The new gasoline direct injection engines and the next-generation diesel engines, already being applied in new models, all offer lower weight, more power, greater fuel economy, and optimized emissions. In addition to the various improvements and modifications within the different engines, BMW is also adding auto stop start, regenerative braking, electrical power steering and improved on-demand ancillaries control to reduce fuel consumption. (Earlier post.)

BMW High Precision Injection cutaway. Click to enlarge.

High Precision Injection gasoline engines. The new series of four-cylinder gasoline engines features second-generation direct fuel injection: BMW’s High Precision Injection, allowing lean burn operation of the engine throughout a wide range of engine speed thus helping to significantly reduce fuel consumption in everyday traffic despite increases in engine power.

Applied in the new 120i, the engine offers a 14% reduction in fuel consumption to 6.4 l/100km (37 mpg US) compared to its predecessor, while increasing power by 15 kW. The engine in the new 118i decreases fuel consumption by 19% to 5.9 l/100km (40 mpg US) while increasing power by 10 kW.

BMW introduced High Precision Injection for the first time in the 225 kW/306 hp straight-six power unit with Twin Turbo technology featured in the BMW 335i Coupé. (Earlier post.)

The HPI engines can operate in lean-burn mode (lambda >1) throughout a wide operating range.  Piezo-injectors positioned directly next to the spark plugs support stratified charging and combustion, with the exact composition of the fuel:air mixture varying from one layer to the other.

Within the common fuel rail, the high-pressure pump generates 200 bar of pressure for the four injectors delivering fuel to the combustion chambers. The piezo-injectors allow up to six injection processes in each operating stroke.

The piezo-injectors form a stable, conical injection jet within the combustion chamber. The jet-guided process ensures a much faster and more efficient fuel/air mixing process in the direct vicinity of the spark plug, without any loss otherwise caused by fuel resting on the walls of the cylinder as in wall-guided injection.

This provides exactly the right conditions for a stratified cylinder charge characteristic of lean burn operation: various, intersecting zones of differently composed fuel-air mixtures forming within the combustion chamber. In the process the share of fuel in the mixture decreases consistently with an increasing distance from the spark plug, a rich, ignitable fuel/air mixture being maintained only in the direct vicinity of the spark plug.  As soon as this richer mixture is ignited, the leaner layers further away from the spark plug will also start burning in a clean, smooth and consistent process.

This serves to maintain fuel-efficient lean burn operation throughout a very wide range of engine speeds and loads.

To support lean burn operation with a stratified cylinder charge, BMW redesigned the cylinder to support the positioning of the piezo-injectors. A highly efficient charge cycle within the cylinders is ensured by conventional valve drive with two overhead camshafts and roller-type drag arms optimized for minimum friction. Compared with engine variants featuring VALVETRONIC, this type of valve management allows a significant increase in engine speed by 800 rpm to 7,000 rpm.

To maintain a beefy torque curve throughout the entire engine speed range, both camshafts come with double-VANOS for infinite adjustment of valve opening times. In order to build up high torque as soon as possible at low engine speeds, in turn, the engine also incorporates a special intake system with variable manifold length (DISA technology).

The new lean burn engine comes with a main catalyst close to the engine itself and storage catalysts further down the line to reduce NOx emissions. BMW is initially introducing its new family of four-cylinder gasoline HPI engines only in the European markets.

Four-cylinder diesel. BMW’s new 2.0-liter, four-cylinder diesels offer an all-aluminium crankcase; variable turbine geometry or variable twin turbo technology in the most powerful variant; third-generation common rail fuel injection, and diesel particulate filters placed close to the engine.

The variable twin turbo technology—also referred to as multistage turbocharging—gives the top-end unit maximum output of 150 kW/204 hp, making this the first all-aluminium diesel engine in the world to develop output of more than 100 hp per liter.

The distinction between the power and torque offerings of the three variants lies in the specific modification of the injection components and the turbocharger system. Developing maximum output of 105 kW/143 hp and peak torque of 300 Nm/221 lb-ft, even the basic version of the new diesel outperforms its predecessor by 15 kW/20 hp and, respectively, 20 Nm/15 lb-ft.

The most powerful version of the new engine develops maximum output of 150 kW/204 hp, 30 kW/41 hp more than the formerly most powerful four-cylinder diesel from BMW—and at 400 Nm/295 lb-ft, the engine’s peak torque is up by 60 Nm or 44 lb-ft. The middle engine in the four-cylinder diesel range is a 130 kW/177 hp power unit developing maximum torque of 350 Nm or 258 lb-ft.

Increased fuel efficiency accompanies the increased dynamics. Fuel consumption in the entry level 118d is down by approximately 16% versus the former model to 4.7 l/100km (50 mpg US) despite an increase in power by 15 kW to 105 kW/143 hp. The new BMW 120d, in turn, comes with an increase in output by 10 to 130 kW (177 hp) and an improvement in fuel economy of the same magnitude, the engine now making do with just 4.9 l/100km (48 mpg US).

The cylinder head with its intake ducts is a new design. The intake ducts are positioned at the side and designed as a spiral and tangential manifold. To reduce emissions to an absolute minimum, the spiral duct is electronically variable in an infinite process.

With their larger diameter, the valves facilitate the gas charge cycle and are now positioned upright, facing vertically into the combustion chambers. This avoids the need for extra cavities on the piston surface, which no longer requires separate valve pockets. The turbulence duct, in turn, gives the fresh air flowing into the engine a swirl motion improving the internal mixture formation process.

While the basic engine operates at an injection pressure of 1,600 bar and solenoid valves serve to supply the fuel in appropriate doses, the two more powerful engines inject diesel fuel at a pressure of 1,800 and 2,000 bar respectively through four piezo-injectors. The most powerful version of the new diesel is the first engine ever to use piezo-injectors operating at 2,000 bar.

To make the combustion process even more efficient, both the shape of the combustion chambers and the trough at the bottom of the piston have been modified and the compression ratio reduced to 16:1. Fuel is injected in up to three doses for each operating stroke of the engine.

The variable twin turbo unit (left). Click to enlarge.

The Variable Twin Turbo made its debut in the six-cylinder diesel featured in the BMW 535d. The turbocharger unit in the Variable Twin Turbo comprises  one small and one large exhaust gas turbocharger. The smaller turbocharger becomes active at low engine speeds just above idling. At higher speeds the larger turbocharger then also cuts in, developing extra power in the process.

This process eliminates lag, developing noticeable thrust and momentum even when the driver barely presses down the accelerator pedal. A turbine control flap distributes the flow of exhaust gases variably to the two turbochargers.

New engine electronics ensure smooth management in the transition phase between the two turbochargers and optimum interaction of the two units with one another. This sophisticated control concept coordinates the complete system of turbines, the turbine control flap, bypass and wastegate as a function of the engine’s operating conditions.

The lower-powered units each feature one exhaust gas turbocharger with variable turbine geometry. An electric step motor serves to adjust the turbine blades with supreme accuracy and minimum delay to the respective operating conditions and running requirements.

To keep the periphery of the engine as clear-cut and uncluttered as possible, the feed pipe for exhaust gas recirculation (EGR) is integrated in the cylinder head. The EGR valve is positioned on the hot side of the engine, the EGR radiator features a bypass serving to limit the emission of harmful substances while the engine is warming up. All versions of this new engine generation come with a diesel particulate filter fitted close to the engine as standard.



Regarding the most powerful diesel version
(150 kw = 204 HP)
Does anyone know the RPM at which this engine delivers the 150 kw ?


HAHAHAHAHA a 4 cyl diesel BMW! What a stupid idea. While they are at it why not make a 2 stroke bmw that runs on bees wax. You people report some real BS stories. Does it have a built in flux capacitor? Mr Fusion maybe?


Useless comment chinaman, I hope an admin removes it.

Regarding BMW: I think that 204bhp is rather impressive especially considering it gets 40+mpg. I can only hope that BMW will bring it over to the states for my 2008.

Does anyone have the specifics (torque/hp curves)? Twin sequential turbo on an I-4 should make for some unusual graphs.

Harvey D.

Would it be un-american for GM + Ford + Chrysler to install BMW's aluminium, high performance, diesel engines in their cars, suvs and pick-up trucks?

It would be the quickest way to meet new CAFE regulations.


Does it come with a rainbow flag bumper sticker?


Forget diesel. GDI lean burn with NOx adsorption cat is the way to go. Fuel efficiency is close to diesel, with price comparable with regular gasoline engine. Plus full compatibility with hybrid drivetrain, including PHEV.

BMW rocks!

Rafael Seidl

Harvey D. -

BMW is partnering with Peugeot to achieve the economies of scale necessary in engines in the 1.6L class, with a slightly larger displacement family reportedly already in the works. BMW needed an engine upgrade for its Mini, but only 100,000 of the 1.6L class are destined for that vehicle. The other 900,000 are going into Peugeots. The new family will be used in a future release of the 1 series as well.

These engines include technologies such as full variable valve lift and phasing (Valvetronic) that BMW introduced in its higher-end engines a few years ago. Expect to see HPI, intelligent alternators, sequential turbos etc. to trickle down to the high-volume market in coming years.

@Andrey - Mercedes and (soon) BMW all have exactly the setup you recommend in selected vehicles, for the reasons you suggest. I believe Audi does as well. As I'm sure you know, NOx adsorption cats makes sense mostly for the smaller engine classes and are highly sensitive to sulfur in the fuel, which poisons the catalyst (necessitating a fuel-guzzling and slightly damaging purge process). For large displacement engines, which benefit most from globally lean combustion in part load, SCR may be a better option. Both NOx adsorption and SCR are quite expensive, though.

However, all of these companies view all of the things they are doing to improve the fuel economy of gasoline engines as complementary to their diesel offerings. Ultimately, that's because each barrel of crude oil yields a little of both fuels plus other products, with the proportions varying by source and the applied refinery technology.

Technically, diesel engines could be hybridized with electric systems as well. It's just that they are heavier and more expensive per rated horsepower and, they don't complement the torque curve of permanent-magnet synchronous electric motors as well. Still, the high cost of any electric drivetrain means hybrids will continue to feature few-frills gasoline engines for quite a while.


One thing that puzzles me. The article says that these enginess will have regenerative breaking. How is this used? What is being regenerated? Doesn't this imply that a battery is being regnerated? And if so, does this imply an electric motor? If not, how does this improve fuel economy?

As a person who used to own a bimmer back in 1983 and loved it, I am glad to see BMW join the better fuel economy parade.

Any evidence they would be bringing these diesels to the U.S.?


BMW + diesel = FLAMING!

If you are trying to come out of the closet why not just buy a pink Miata and get it over with. Cheaper than this diesel business.


Regen braking can be done pneumatically, hydraulically, with a spring, flywheel or many other means. It just says that the energy is stored for reuse at a later time. One method was to compress nitrogen gas and use that force to move the vehicle off a dead stop. Otis elevator is doing similar things in their Gen2 designs. Capturing energy on the way down, for the way up. Very clever ideas that could have been done ages ago, but were not because energy seemed cheap, abundant and almost limitless. Economics has a principle that says in effect, when something is cheap, it will be overused and perhaps misused in inefficient ways. This may be the nature of things so far but they are changing...because they have to.


Hi Tom, as I read the story, the car mileage is also being improved by shift to electrically driven accessories, i.e. electric power steering, and start/stop technology. Therefore the energy from regen braking would via battery recovery and storage, drive the accessories and lower engine load.



Thank you for the explanation. But does anyone know what BMW is doing with this technology (regenerative breaking)?


The fix for all breaking is repair by the dealer, at least during the warranty period.


Looks excellent, good go BMW! My only small gripe is with 4 cylinders in general...why go through the expense and weight of balance shafts when with a 5 cylinder they are unnecessary?


not all 4 cylinders need balance shafts(and they are small because they are for 2nd order not 1st).only those that are over 2L in displacement and have high redline do. 4 cylinders are a better design than a 5 cylinders because id rather have 2nd order balance problems than 1st order. a five cyl still has 1st order balance problems, needs a large balance shaft and is a POOR design in general. 6 or more cyl is the only way to go.


I would love to see a small-medium pickup or crossover SUV with the diesel unit. With all that torque you could tow a reasonable boat when you needed to while having great mileage in daily driving. A 35-40 MPG minivan might be another possibility--no hybrid complexity required.

This approach is so practical and sensible. I hope it is emulated by other manufacturers.

Warren Heath

BMW seems to have a knack to come up with weird and unworkable ideas, going against the tide, which is the conversion of all vehicles to standard BEV's with the option of the series HEV version, for those who need it, or the compromise series PHEV version of the standard BEV chassis. Isn't BMW the same wacks that were heavily promoting their nutty Liquid Hydrogen vehicle? And where is BMW in making small high efficiency, high compression engines, fueled by ethanol, methanol & butanol for which >40% efficiency can readily be obtained, with much lower emissions.

In a series hybrid, methanol fueled engine, 43% efficiency can be obtained, in an engine that always operates in the most efficient region, regenerative braking is very efficient and easily obtained, and the engine can be about 1/3rd the size of the engine in the ICE powered vehicle. The scale economies of making the three versions, as well as a Fuel Cell generator version (in a decade or two) makes for huge scale economies, and far superior drivetrain reliability and low maintenance costs. Typical Electric Motor / Generator / PEM’s last the equivalent of over a million miles with zero maintenance. Maybe that’s why BMW (stands for Bullshit Makes us Wealthy) avoids the obvious like the plague.


BMW had the Turbosteamer, which was a novel approach to recovering waste heat. Maybe we need more of these companies taking the path less traveled to arrive at our destination on time.

Thomas Pedersen

BMW's flavour of regenerative braking is explained in the linked post of 15 January; they mostly engage the alternator during breaking and coasting (taking the foot off the gas).


Bosh developed and already produces both diesel and GDI fuel systems with applicable sensors and peripheral hardware, including standard set-ups for catalytic aftertreatment. These technologies are open to adaptation to any engine manufacturer. In near past half of the world, including Japanese and American manufacturers, used Bosh fuel injection systems. Conversion to GDI could be accomplished quite fast.

Mike Weindl

Chinaman and Warren Heath.. pls. find another forum where
you can post your senseless comments. Thanks..


These engines would sell nicely in the emerging Biodiesel markets in tropical countries. VW may have some competition.

Warren Heath

Mike Weindl please find another forum to post your absurd, senseless, and malicious comments. Thankyou very much.

Warren Heath

Nick, the series hybrid design is actually simpler than the complex diesel technology advocated by BMW. I cannot but see that as a mature technology the series hybrid drivetrain will be much more reliable and inexpensive than the ICE drivetrain it will replace. You can say the electronics is more complicated, but that is like saying the far more sophisticated $100 PC motherboard is an absurd nightmare of complexity.


A PC motherboard is an absurd nightmare of complexity...if that thing has a hardware failure there is no way I'm going to try to pull up a schematic and look for node voltages with a scope on one of those; I'll just buy a new one.

The hybrids should be more inexpensive...they just don't have the proper economies of scale for a single manufacturer yet.

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