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Mercedes-Benz Introduces New Generation of Four-Cylinder Diesel Engines

10 April 2008

Merc4
The new four-cylinder diesel family offers improved performance, torque, emission properties and fuel economy. Click to enlarge.

Mercedes-Benz has introduced a new generation of four-cylinder diesel engines with improved performance, torque, emission properties and fuel economy. The new engine family will supersede four different powerplants. The new engine will debut in the C-Class this fall, but will eventually be fitted in a number of variants across a wide range of model series, including the Mercedes-Benz Sprinter. Mercedes-Benz says it also earmarking the engine family for use in hybrid vehicles.

In its most powerful variant, the new 2,143 cc four-cylinder unit delivers up to 150 kW (204 hp)—about 20% more power than the engine it replaces. Peak torque has risen from 400 Nm (295 lb-ft) to 500 Nm (369 lb-ft)—an increase of 25%. Despite the 25 kW increase in output, the new four-cylinder diesel burns less fuel than its predecessor, and reduces CO2 emissions by up to 13%. The new engine is Euro-5 compliant.

Poweroutput
Power output graph for the 150 kW variant. Click to enlarge.

The power-to-displacement and torque-to-displacement ratios of the new engine are 70 kW (95.2 hp) and 233.3 Nm per liter respectively, compared to 58.2 kW (79.2 hp) and 186.2 Nm per liter of displacement for the earlier unit.

When fitted in the C-Class, the new 150 kW unit consumes 5.4 liters per 100 kilometers (NEDC) (43.6 mpg US), 0.5 liters less than previously. When powered by a new 125 kW (170 hp) variant, the C-Class consumes 5.1 L/100 km (46.1 mpg US).

As a consequence, CO2 emissions are reduced by 8% and 13% respectively to 143 g/km and 136 g/km.

Engine-out emissions are reduced to the point where even without an active denoxification process, the new four-cylinder diesel already meets the future Euro 5 emissions standard. Further reductions will be made with BlueTec aftertreatment systems.

Three different variants are initially planned for use in passenger cars.

New 4-Cylinder Mercedes Diesels
Parameter 250 CDI220 CDI 200 CDI
Cylinders 4
Valves/cylinder 4
Displacement [cc] 2.143
Bore/stroke [mm] 83.0/99.0
Compression ratio 16.2:1
Output [kW/hp] 150/204
@ 4200 rpm
125/170
@ 3200 - 4800 rpm
100/136
@ 3000 - 4600 rpm
Torque [Nm] 500
@ 1600 - 1800 rpm
400
@ 1400 - 2800 rpm
330
@ 1600 - 2800 rpm

Principal features of the new Mercedes diesel engine include:

  • Two-stage turbocharging to ensure high power output and optimum torque delivery. The compact two-stage turbocharging unit consists of a small high-pressure (HP) plus a large low-pressure (LP) turbocharger. Both comprise a turbine and a turbine-driven compressor, and are connected with one another in series.

    Mercturbo
    The two-stage turbo system. Click to enlarge.

    The HP turbine has a diameter of 38.5 mm and is positioned directly in the exhaust manifold. The flow of exhaust gases flows through this turbine first, causing it to rotate at speeds of up to 248,000 rpm.

    A bypass duct is integrated into the HP turbine housing. The duct can be opened or closed by means of a charge-pressure control flap triggered by an actuator. If the duct is closed, the entire exhaust stream flows through the HP turbine—i.e., all of the energy contained in the exhaust gases can be directed towards propelling the HP turbine only. In this way, the optimum charge pressure can be built up at low rev speeds.

    As the engine speed increases, the charge-pressure control flap opens to prevent the HP charger from becoming overloaded. A portion of the exhaust stream now flows through the bypass duct to relieve the load on the high-pressure stage.

    Downstream from the HP turbine, the two exhaust gas streams join up again, and any remaining exhaust energy drives the 50-millimeter LP turbine at a maximal speed of 185,000 rpm. To protect against overload, the LP turbine also features a bypass duct, which is opened and closed by means of an actuator-controlled flap—the wastegate.

    Once the engine reaches medium rev speeds, the HP turbine’s charge-pressure control flap is opened so wide that the HP turbine ceases to perform any appreciable work. This allows the full exhaust energy to be directed with low losses into the LP turbine, which then does all of the turbine work.

    The two compressors are likewise connected in series and are in addition connected to a bypass duct. The combustion air from the air cleaner first flows through the LP compressor (diameter 56.1 mm) where it is compressed as a function of the LP turbine’s operating energy input. This pre-compressed air now passes into the HP compressor (diameter 41 mm) that is coupled to the HP turbine, where it undergoes further compression. The result is a genuine two-stage turbocharging process.

    Once the engine reaches a medium rev speed, the HP compressor can no longer handle the flow of air, meaning that the combustion air would heat up too much. To avoid this, the bypass duct opens to carry the combustion air past the HP compressor and directly to the intercooler for cooling. In this case, the charge-pressure control flap is completely open too, meaning that the HP turbine is no longer performing any work. This is the equivalent of single-stage turbocharging.

    The benefits of this elaborate, needs-driven control of the combustion air feed with the aid of two turbochargers are improved cylinder charging (for high output) with abundant torque even from low rev speeds. Fuel consumption is lowered also.

  • Optimized intercooler and exhaust gas recirculation. The intercooler has been enlarged compared to the previous series-production version and now lowers the temperature of the air by around 140°C, allowing a greater volume of air to enter the combustion chambers.

    After the intercooler, an electrically controlled flap ensures precise regulation of the fresh air and recirculated exhaust gas. To optimize the quantity of exhaust gas recirculated and thereby achieve high recirculation rates, the exhaust gases are cooled down as required in a heat exchanger with a large cross-sectional area.

    This combines with the HFM (hot-film air-mass sensor) modules, which are integrated into the fresh-air supply and provide the engine management unit with exact information on the current fresh air mass, to bring about a substantial reduction in nitrogen oxide emissions.

  • Intake port shut-off for optimum air supply. The combustion air subsequently flows into the charge-air distributor module, which supplies air to each cylinder in a uniform manner. Built into the distributor module is an electrically controlled intake port shut-off which allows the cross-sectional area of each cylinder’s intake port to be smoothly reduced in size. This alters the swirl of the combustion air in such a way as to guarantee that the charge movement in the cylinders is set for optimum combustion and exhaust emissions over the full spectrum of engine loads and rev speeds.

  • Fourth-generation common-rail technology with a rail pressure of 2,000 bar—an increase of 400 bar—plus a new piezoelectric injector concept featuring direct injector needle control. The system enables more flexible injection timing, leading to smoother engine running, lower fuel consumption and reduced emissions.

    Mercinj
    Fuel injection system. Click to enlarge.

    New piezoelectric injectors are one of the key components in the fourth-generation CDI technology. The new injectors are fitted with a piezo stack, basically made up of piezoelectric elements connected in series. In contrast to the customary systems used to date, the movement of these elements controls the injector needle directly and enables even greater alterations in volume that are accurate to within a few thousandths of a millimeter.

    This enables an increase in the available injection volume as well as particularly fine and fast metering of the injection quantities. In turn, this enables the fuel injection process to be adapted to the momentary engine load and rev speed with greater exactness, with concomitant positive impacts on emissions, consumption and combustion noise.

    Injector operation is also completely leak free. This dispenses with the need for a leak oil line to return the negligible quantities of fuel that used to accumulate unavoidably in the system on account of the operating principle. This improves the injection system’s thermal circuit to such an extent that, even at a rail pressure of 2,000 bar, fuel cooling is superfluous. This reduces the high-pressure pump’s operating energy input by around one kilowatt at high engine loads.

  • Maximum ignition pressure of 200 bar and optimized combustion chamber. The fuel is injected into a combustion chamber with a geometrical form that includes precision-calculated recesses in the piston crowns. Compared to the engine it replaces, the combustion chamber has been made flatter and the diameter somewhat larger. The compression ratio was reduced from 17.5:1 to 16.2: 1.

    This optimizes the combustion process by achieving a lasting reduction in engine-out emissions—NOx levels in particular have been cut.

    To guarantee spontaneous starting, the engine is fitted with ceramic glow plugs which attain a temperature approximately 200°C higher than metallic glow plugs (1,250°C as opposed to 1,050°C) and are virtually wear-free. Mercedes-Benz put these glow plugs into series production for the first time in the predecessor diesel engine.

  • Controllable water and oil pumps. Electrically controllable water and oil pumps can be activated in accordance with requirements. Piston cooling is taken care of by an oil pump with a central valve for controlling all four piston-cooling sprayer units with large oil-spray nozzles. The result is identical basic thermal conditions for all cylinders. The larger nozzles provide optimum piston cooling, even when operating under full load, guaranteeing a long service life in the process. The oil pump’s controllable design additionally reduces the oil flow rate and therefore fuel consumption.

    Just like the controllable oil sprayer units, the water pump also helps to quickly warm up both the combustion chamber and the friction partners, at the same time lowering fuel consumption and untreated emissions.

  • Rear-mounted camshaft drive. The rear-mounted camshaft drive allows statutory pedestrian protection requirements to be fulfilled when the engine is installed lengthways. The vibration stimuli originating from the crankshaft are furthermore lower on the rear face of the engine than at the front, which benefits the engine’s smooth running.

    The valve timing mechanism is another new development and reduces friction at the 16 intake and exhaust valves, which are controlled by one overhead intake shaft and one overhead exhaust shaft acting via cam followers featuring hydraulic valve clearance compensation. The camshaft, Lanchester balancer as well as the ancillary assemblies are driven by a combination of gearwheels and just a very short chain drive.

  • The engine block is made from cast iron, the cylinder head from aluminium.

  • Two water jackets guarantee maximum cooling even at the points of greatest thermal radiation; it is this that enables a ignition pressure of 200 bar and such a high power-to-displacement ratio.

  • The aluminium pistons slide up and down in cast-iron barrels for minimum frictional resistance.

  • The connecting rods are made from forged steel, and their weight has been optimized.

  • In the interests of vibrational comfort, the forged crankshaft with its eight counterweights turns supported by five bearings. The radii of the crankpins are rolled for high strength.

  • To compensate for the free vibration moments which are inherent to four-cylinder inline engines, there are two Lanchester balancer shafts at the bottom of the engine block running in low-friction roller bearings rather than conventional plain bearings.

  • A two-mass flywheel, featuring a primary flywheel mass fixed to the crankshaft that is connected to the secondary flywheel mass on the transmission by means of springs (spring-mass system), isolates the crankshaft’s vibration stimuli from the drivetrain, thereby contributing to the engine’s excellent smoothness.

Mercedes says that it is continuing to work on the possibilities offered by ultra-flexible injection timing with a view to reducing engine-out emissions even further.

April 10, 2008 in Diesel, Engines | Permalink | Comments (31) | TrackBack (0)

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Comments

A modern design featuring sequential turbos to deliver the same rated power as BMW's current inline four 2L diesel used in the 1 series in Europe.

Note Mercedes' use of a rear-mounted camshaft drive for the sake of pedestrian crash safety - an expensive solution. However, I'm fairly sure that 2000 bar common rail system is even pricier.

The technical complexity and sophistication of modern ICEs is impressive. What are all the highly-trained MEs going to do once improved battery technology makes such a tour-de-force into an anachronism?

I appreciate the engineering work here even thought I'm not an ME. Maybe I'm missing something here: But why would you want to produce such an expensive engine for use in a hybrid in the U.S.?, especially when PHEVs are coming on and companies like GM are planning small gensets to act as range extenders. The only application I can think of is european diesel cars. I look at the torque curve and I'm amazed at the high narrow rpm range peak torque curve. It seems to me that it would take a 10 gear transmission to keep it in the acceleration section of the torque curve.

work at mcdonalds :)

Good job MB- now offer these options in your US line-up.

I'm all for reducing oil consumption, and diesel, while not perfect, provides yet another way to help us tell OPEC to pack sand.

I would prefer MB' new 4-cyl than their present 6cyl Bluetec diesel engine offered here in the US. The 204bhp and 369lb-ft output of the 4 cyl is close enough to the 210bhp and 400lb-ft of the costlier, larger, heavier and more complex 6 cyl- without the added fuel consumption!

Perhaps this engine offering could reduce the entry price of any of the Bluetec diesels by $3000-$5000?

Additionally, the smaller 4-cyl engine could lop off a couple hundred pounds off the front end of any of MB's Bluetec CDI's- while extending driving range from ~700 miles/tank to nearly 1,000 miles per tank! Try that in a Prius!

Seems like a simple marketing decision for MBUSA, now make it so!

Good job MB- now offer these options in your US line-up.

I'm all for reducing oil consumption, and diesel, while not perfect, provides yet another way to help us tell OPEC to pack sand.

I would prefer MB' new 4-cyl than their present 6cyl Bluetec diesel engine offered here in the US. The 204bhp and 369lb-ft output of the 4 cyl is close enough to the 210bhp and 400lb-ft of the costlier, larger, heavier and more complex 6 cyl- without the added fuel consumption!

Perhaps this engine offering could reduce the entry price of any of the Bluetec diesels by $3000-$5000?

Additionally, the smaller 4-cyl engine could lop off a couple hundred pounds off the front end of any of MB's Bluetec CDI's- while extending driving range from ~700 miles/tank to nearly 1,000 miles per tank! Try that in a Prius!

Seems like a simple marketing decision for MBUSA, now make it so!

I believe that Mercedes-Benz will install a full BlueTec emissions control system to make the engines fully Euro 6 compliant, which means only minor changes are needed to meet even the stringent EPA 2009 emission regulations on light-duty diesel engines. In short, the C250CDI could arrive in the USA as early as spring 2009 as a 2010 model.

Can some one enlighten me. The following:

"The rear-mounted camshaft drive allows statutory pedestrian protection requirements to be fulfilled..."

...leaves me scratching my head. What does the location of the camshaft drive have to do with pedestrian safety? I must be missing something.

Haven't finished reading the whole article, but I thought I'd note that sometimes, even if I think the development might be leading down the wrong path, the sheer technological triumph and engineering mastery simply impresses the heck out of me. Sounds like a heck of a nice job of engineering, and until perfection comes anything that boosts output by 25 percent while cutting emissions 13 percent and trimming fuel use is impressive. Given the age of diesel technology that there are still improvements on this scale to be wrung from it is fascinating. Anyone know how close to the maximum possible efficiency of this sort of engine we have gotten?

Now, how cool is that - even when this engine is idling, it provides 50 kW - about twice the power you need to cruising along a highway at 120 kph (provided you are not sitting in a brick with a cd of 1)...

Just think of all the fuel wasted going around town (avg. power requirement 10-15 kW peak).

I have to agree with Nick on this one...

Pedestrian safety:

I think they try to avoid bits sticking up above the engine, so that when a person is hit, and hits the bonnet (hood), the metal can deflect down further before it hits solid metal (the engine).

Thus, if it can deflect 100mm, the bonnet (hood) can absorb more energy than if it can only deflect 40mm. Thus the pedestrian is injured less.

The idea is to have a vertical "crumple zone" between the hood and engine, without making the hood any higher ( as has been done in the latest Toyota Yaris ) which spoils the line of the car.

The people buying a Yaris might not care too much about the hood line, but the people buying a Mercedes certainly do.

This is my understanding. More technical people might correct or refine it.

In General:
Wow impressive - how much extra will it cost in the new cars ?

It would also be nice to see it with a stop/start system for urban use - mainly to reduce local pollution.

Note that the 125 KW version generates 136 gm CO2 - getting very near the Euro 130 gms limit!

Not at all bad for a car of the size of a C Class.
(But still not as good as a BMW 320 @ 128 !).

"The technical complexity and sophistication of modern ICEs is impressive. What are all the highly-trained MEs going to do once improved battery technology makes such a tour-de-force into an anachronism?"

BEV's are practically a religion on this website, so such an arrogant comment is not surprising. but consider that much less than 1% of the world's passenger vehicles employ any kind of battery technology in the drivetrain at all (aside from using it to power the starter motor and the headlights); heaven forbid we can wring yet more improvements out of ICE's, when everyone knows hybrids and BEV's are the future.....aren't they?

long story short, don't be so cocksure about the triumph of BEV's, they're not even at the same stage of their evolution as the model T a hundred years ago (ie zero penetration of the mass market).

Now, how cool is that - even when this engine is idling, it provides 50 kW

Realarms, you know that statement is not even remotely true. 50 kW is at low RPM but full throttle. Idle power output is near 0 kW.

"Now, how cool is that - even when this engine is idling, it provides 50 kW - about twice the power you need to cruising along a highway at 120 kph (provided you are not sitting in a brick with a cd of 1)..."

Allow me to explain a couple of things:

1) Car engines typically idle (after warmup) around 600-800rpm, not the ~1100rpm of the graph
2) The graph shows the "full throttle" response of the engine, so this is the maximum that the engine can put out at a certain rpm. The power output at 1100rpm at lighter throttle settings would be significantly less

Good job MB- now offer these options in your US line-up.
US diesel fuel has a lower cetane rating than European fuel. This may make it impossible to offer the same engine with its lower compression ratio.

'The new engine family will supersede four different powerplants'

I think they just saved a lot of time and effort for a lot of engineers, never mind customers, by eliminating the point of choosing a (larger) petrol engine.

If the electronics in the ECU decides the power output 136-204bhp, and all the mechanicals are the same, then how can you cahrge more for the 204bhp version over the base? Is it that it will come with more options and you are paying for those things?

And could you buy the base 136bhp and re-map the ECU, there are a lot of chipping companies around with the hardware, could they do it for you?

RealityCzech-

Always the optimist:)

When MB updated their previous 3.2 liter I6 diesel offering in their E320 CDI to the current 3.0 liter Bluetec V6 diesel in the US market compression ratio was decreased from 18:1 to 16.5:1 (as is the CR for this new 4-cyl). The Bluetec V6 CDI appears to have no issues with our US diesel fuel.

Seeing this V6 powerplant is the only 50-state legal diesel in currently on the US market- I don't see why MB's new 4-cyl would be limited by cetane ratings either.

It appears the fuel issue has been overcome seeing
VW, Honda (Acura), Nissan, BMW, and even Hyundai are all due to flood the US market with clean diesel powerplants within the next 3-4 years.

Am I missing something?

@lad,

Your comment about needing ten speed transmissions is very apt.

This is a technological tour-de-force. It will be an expensive engine to build with the inter-cooled, dual turbo-compounding, but MB has the price point umbrella to fit it under. Not many do.

Still this is a very peaky engine that will probably prove to be an unsatisfactory to drive vehicle, in practice. Unless the 8-10 speed transmissions are very seamless.

@ Raymond,

EU 5 or even EU 6 is no big deal. Were it proposed here in the US, its almost a standard to laugh at, as environmental organizations went to court to object to the fake "standard".

Even with EU6 compliance, never mind the easier EU5, the NOx standard will STILL be 800% worse than T2B5.

You would have to get to a mythical, not even proposed standard for Europe, perhaps in the post 2030 time frame, to achieve the NOx cleanliness of T2B5.

Note that MB chose to make the engine run richer as a cheap way to meet EU5. I suspect that the US version will achieve better mileage when leaned out and full Blue Tec technology is applied.

mahoni:

Ah, that makes sense; thanks for the explanation.

eric:

My comment was snarky and hyperbolic, true, but the point I was trying to make is that this engine seems like an almost baroque refinement of the existing ICE paradigm. A paradigm shift in automotive technology will (I hope!) eventually turn such machines into technically fascinating anachronisms. With luck, future observers will marvel at the complex, expensive means we once employed in order to get around. In the mean time, it's definitely a cool machine to contemplate for those who are fascinated by such things (including me).

10 speed trans? You guys are clueless!

The power curve (not torque) is what you should look at. If you compare it to a gasser power curve with same peak power, you will find it has more power at lower speeds, meaning less reving required for the same acceleration. This is one of the little known advantages turbo-diesels have in city driving which saves fuel much more than the highway advantage.

Also the 50kw near idle does not impact efficiency. Diesels have 1/3 the fuel consumption of a gasser at idle.

These comments just remind me that few people realize how much better diesels are than gassers.

@ Nick -

what mahonj said. The US doesn't have pedestrian crash safety rules but Europe now does. This has forced designers to significantly raise vehicle beltlines, which makes the whole thing look chunky instead of sleek.

Jaguar solved the problem by placing explosive charges under the hood, launching it upward to meet the oncoming pedestrian in mid-air several inches above where impact would otherwise have occurred. It's an expensive system, though, because that hood offers significant inertial and aerodynamic resistance to the rapid upward acceleration required - i.e. you need to safely pack quite a large charge rather close to the hot engine.

@ Lad, Stas Peterson -

the torque curves of most diesel engines feature flat tops because they are artificially limited to protect the transmission. Mercedes simply chose not to do that so drivers could achieve excellent acceleration at low-to-medium vehicle speeds while still keeping the engine below 2500 RPM. That makes it both efficient and quiet. And yes, Mercedes uses 7-speed ATs. The objectives here are comfort and fuel economy, not race car performance.

@stan and lad: This engine is not "peaky", for passenger car use. It has huge amounts of torque (over 300Nm) across the whole rpm range. That's enormous. If it were put in use in a heavy truck, it would need ample gears to function optimally. But in a passenger car, it has torque in excess. Anyway, MB automatics have seven speeds now, and their manuals six, not that you would need it.

I agree with Larry on the accomplishment of adding a good deal of power while raising gas mileage substantially.

I think that this is a perfect setup, so long as it's got an added hybrid boost option to both power and fuel economy to take it from good to impressive. I don't want to see a motor like this as a gen set, I want to see it as in a more prius-like parallel hybrid form so it can still be enjoyed. Turbo + Diesel + Hybrid = : )

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