Mazda6 MZR-CD Turbo Diesel

10 November 2009 · posted by JMC

Mazda’s new MZR-CD 2.2-litre turbodiesel is one of the quietest and most powerful in its class.

With a class-leading 136kW of power and 400Nm of torque, and a combined cycle fuel economy figure of 5.9L/100km in hatch form, the new-generation Mazda6 Diesel offers great performance that is unrivalled for the price range.

To realise this kind of power and torque with 2.2 litres of displacement, the MZR-CD 2.2-litre employs a highly efficient variable-geometry turbocharger (VGT) with curved (instead of straight) vanes on the turbine (exhaust) side.

Mazda6 Turbo Diesel

This increases maximum available torque at both low and high engine speeds while also increasing all-important low-end response (as low as 1,800rpm with a flat torque curve that continues until 3,000rpm) that contributes to a smooth and powerful driving feel.

When combined with an abradable seal on the compressor side (intake side), which reduces the clearance between the blade and the compressor housing, these attributes deliver superior turbocharger response at just about all engine speeds.

Converting the engine’s combustion energy into this much engine torque meant the pistons had to be designed to take the resulting high combustion pressure and temperatures. As a consequence, the pistons are made of an aluminium alloy with improved high-temperature fatigue strength.

A half-Keystone cross-section top-ring with improved carbon scavenging abilities is used, and the groove for the top ring is made more durable with the adoption of a cooled ring carrier that increases the groove’s cooling capability.

Mazda engineers also increased the fuel injection pressure to 200MPa (by comparison, the previous generation MZR-CD 2.0-litre turbodiesel uses 180MPa). They realised this by making functional improvements to the high-pressure pump, among other improvements, and by new injectors featuring 10 spray holes per injector (instead of the six for the MZR-CD 2.0-litre) that are smaller (reduced from 0.13mm to just 0.119mm).

These changes enable more precise injection timing, and an increase in the number of times of injection and injection amount. And it allowed the fuel injection patterns at transitional states to be more precisely controlled.

As a result, the Mazda6 Diesel 2.2-litre engine provides superior acceleration in those situations you need it most, like entering a highway. It also surpasses its competitors in lower-speed acceleration. Third gear from 50-100km/h, for example, is 1.7 seconds faster than the previous generation Mazda6 MZR-CD 2.0-litre.

Low Fuel Consumption
This new diesel engine meets the requirements of Mazda’s Sustainable Zoom-Zoom plan by being frugal at the pump. It uses 5.9L/100km (hatch) and 6.0L/100km (wagon) on the combined cycle.

It achieves this by employing highly responsive solenoids for the common-rail injection system that achieve a minimum injection interval of just 0.2ms (the MZR-CD 2.0 is 0.3ms), which speeds up the minimum injection interval by about 30 per cent, improves its responsiveness and lowers fuel usage.

Fuel is also saved by lowering the compression ratio to 16.3:1 and utilising the temperature cooling effect this causes, which secures more mixing time until ignition, and allows a more precise fuel-injection pattern. As a result, fuel consumption is a low 5.9L/100km (hatch) with CO2 emissions of just 156g/km (hatch).

In fact, the MZR-CD 2.2-litre offers substantially higher power and torque than the previous-generation MZR-CD 2.0-litre, while delivering equal levels of fuel consumption and CO2 emissions.

Low Emissions – Particulate Filter with World’s First Ceramic Support Matrix Structure
Mazda engineers not only made the new 2.2-litre turbodiesel powerful and lowered fuel consumption, they also lowered the amount of raw emissions and raised the efficiency of its after-treatment technologies.

The engine’s highly responsive fuel-injection technologies have new injectors that yield better atomised spray characteristics. These are combined with an exhaust gas recirculation (EGR) system with a cooler bypass structure – that decreases unburned gases and NOx – and the high-response solenoids described previously, to realise superior emissions performance without sacrificing power.

Emissions are then treated by a diesel particulate filter that uses a unique Mazda-developed, ceramic support matrix structure, which is the first of its kind to go into production in the world.

Previous diesel particulate filters converted particulate matter (PM) into CO2 by reacting the PM with the oxygen in the exhaust gas at the surface of the catalytic particle. This meant that the time needed for filter regeneration was determined by the amount of oxygen on the surface of the catalyst. When the temperature of the exhaust gas is raised to quicken the regeneration time, then technological issues – like higher fuel usage or the ceramics exceeding their thermal resistance limit – can occur.

Mazda solved these issues by using highly thermal resistant material for the ceramic monolith of its new diesel particulate filter, and designing the internal structure of the ceramic support matrix with passages for oxygen to enable a large amount of oxygen to be utilised for PM combustion.

With this, Mazda has succeeded in significantly increasing the PM combustion speed. As a result, the number of times the diesel particulate filter has to regenerate (in combined mode) is cut in half, and the time necessary for each regeneration phase is shortened by one third.

For owners of the new Mazda6 2.2-litre turbodiesel, this means worry-free filter regeneration and, because fewer regeneration phases are required, each takes less time resulting in less fuel consumption overall.

Running Quiet
The new Mazda6 Diesel 2.2-litre common-rail turbodiesel not only offers superior output, fuel economy and emissions performance, it is also one of the quietest engines in its segment with this amount of torque. This ensures a driving experience that is one of the segment’s most exclusive.

To achieve this, the new engine has a lower block with a very rigid aluminium-alloy structure, with the bottom of the cylinder block skirt and the cylinder block’s main bearing caps bolted to the lower block at 18 separate locations. This high structural rigidity is combined with a front chain-driven cassette-type balancer shaft to suppress booming noise and lower radiated noise, and to deliver optimised pedal response and engine sound for a refined acceleration feel.

Packaging and Weight Management
Keeping the new MZR-CD 2.2-litre turbodiesel as close as possible in size and weight to that of the MZR-CD 2.0-litre was a key factor in ensuring exhilarating performance combined with fuel efficiency and low emissions.

Some of the newly adopted technologies, such as the balancer shaft and DOHC, result in increased size and weight. Nonetheless, numerous innovations were added to manage size and weight increases, with the goal of maintaining packaging and keeping the weight increase within just 6.0kg of the previous MZR-CD 2.0-litre turbodiesel.

Due to the increase in displacement, the stroke of the MZR-CD 2.2-litre is 8mm longer compared to the MZR-CD 2.0-litre. At the same time, the overall length of the connecting rod was shortened by optimising their design. As a result, their weight remains at the same level as in the MZR-CD 2.0-litre.

The adoption of a balancer shaft that decreases vibration caused by reciprocating motion made a thinner cylinder block with fewer ribs possible – hypothetically, if the MZR-CD 2.2-litre had no balancer shaft, the cylinder block would have been 1.9kg heavier than that of MZR-CD 2.0-litre, and its crankshaft 1.3kg heavier.

Furthermore, decrease in size and weight was achieved by making the balancer housing, oil pump housing, and the oil suction pipe a single structure. To achieve even more weight reduction, while increasing the cooling capability of the new engine, the oil cooler is made of aluminium (-0.6 kg). The weight of the cam cover is also reduced by making it out of plastic (-1.0 kg).

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