MZR-CD R2 2008: Mazda Diesel Engine

Introduction

The MZR-CD R2 2008 was a 2.2-litre turbo-diesel engine that was offered with a range of power outputs. For Australia, the MZR-CD R2 2008 diesel engine was first offered in the Mazda GH Mazda6 Diesel in 2008 and subsequently powered the Mazda CX-7 Diesel Sports andBL Mazda3 Diesel (see table below). The MZR-CD R2 2008 engine effectively replaced the MZR-CD RF 2005 diesel engine.

Cylinder block

The MZR-CD R2 2008 diesel engine had a cast iron cylinder block and aluminium-alloy lower block. For rigidity, the bottom of the cylinder block skirt and the main bearing caps were bolted to the lower block at eighteen (18) separate locations. The MZR-CD R2 2008 engine had 86.0 mm bores and a 94.0 mm stroke for a capacity of 2183 cc.

Unlike the MZR-CD RF 2005, the MZR-CD R2 2008 had a chain-driven, cassette type-balancer unit which consisted of two balancer shafts that rotated at twice the speed of the crankshaft to offset secondary inertia forces.

According to Mazda, the offset of inertial forces by the balancer shafts enabled the block to be made thinner and require fewer reinforcing ‘ribs’ than the MZR-CD RF 2005 engine. To minimise mass, the balancer shaft housing was integrated with the oil pump housing and oil suction pipe to form a single structure.

Pistons

For the MZR-CD R2 2008 engine, the pistons were of an aluminium alloy which had improved high-temperature fatigue strength compared to those in the MZR-CD RF 2005 engines. Furthermore,

• The top piston ring was changed to a half keystone ring for improved carbon scavenging abilities; and,
• The top piston ring adopted a hollow ring carrier to improve cooling.

Cylinder head

The MZR-CD R2 2008 engine had an aluminium alloy cylinder head with chain-driven double overhead camshafts (DOHC) that actuated four valves per cylinder via roller rocker arms. Based on the table below, the MZR-CD RF 2008 engine had valve overlap of 14 degrees, intake duration of 216 degrees and exhaust duration of 228 degrees.

Variable Geometry Turbocharger (VGT)

The MZR-CD R2 2008 diesel engine had a variable geometry turbocharger (VGT), though the size of the turbine differed according to power output. Variable geometry turbochargers have a set of vanes which are arranged in the path of the air flow and, by changing the angle of the vanes, the area of the turbine inlet is changed. At low engine speeds, when air flow through the engine is relatively low, the velocity of the air flow can be increased by partially closing the vanes, thereby increasing turbine speed.

Compared to the turbocharger for the MZR-CD RF 2005 engine, the turbocharger for the MZR-CD R2 2008 engine had curved vanes on the turbine (exhaust) side and an abradable seal on the compressor (intake) side to reduce the clearance between the blade and the compressor housing to develop boost pressure more quickly.

The Mazda GH Mazda6 initially had a 41.5 mm turbine impeller, though a smaller 36.0 mm impeller was introduced for the GH.II Mazda6 to reduce turbo lag (along with other changes to comply with Euro IV emissions standards).

Common-rail direct injection

The MZR-CD R2 2008 engine had a Denso HP3 common-rail injection system. Compared to the MZR-CD RF 2005 engine, the MZR-CD R2 2008 engine had:

• An upgraded high-pressure pump;
• ‘Highly-atomising’, ten-hole solenoid injectors (six-hole injectors for the RF 2005);
• Faster response solenoids which provided a minimum injection interval of 0.2 ms (0.3 ms for the RF 2005);
• Smaller injector holes (diameter reduced from 0.13 mm to 0.119 mm); and,
• Injection pressure up to 2000 bar (1800 bar for the RF 2005).

These changes enabled more precise injection timing, more frequent injection and increased injection volume.

The MZR-CD R2 2008 engine had a compression ratio of 16.3:1, compared to 16.7:1 for the RF 2005. Lower than comparable diesel engines, this low compression ratio reduced pumping losses, improved thermal efficiency and the lower combustion temperature reduced NOx formation.

Diesel Particulate Filter (DPF)

In contrast to conventional diesel particulate filters (DPFs) which converted particulate matter (PM) into CO₂ by reacting the PM with the oxygen in the exhaust gas at the surface of the catalytic particle, Mazda’s DPF for the MZR-CD R2 2008 used a highly thermal resistant material for the ceramic monolith of its DPF. Furthermore, the internal structure of the ceramic support matrix had oxygen passages so that oxygen could be used for PM combustion. According to Mazda, its DPF

• Signficantly decreased PM combustion speed;
• Halved the number of times the DPF had to regenerate by burning of collected PM particles; and,
• Reduced the duration of each regeneration phase by one third.

Mazda CX-7: AdBlue Selective Catalytic Reduction (SCR)

Unlike the BL Mazda3 and GH Mazda6, the diesel-powered Mazda ER CX-7 had an AdBlue Selective Catalytic Reduction (SCR) system which used AdBlue urea additive to convert NOx emissions into nitrogen and water. The AdBlue solution was stored in a temperature insulated 15.5 litre tank under the luggage compartment; the tank also had a protective cover. The SCR system injected small amounts of AdBlue at a pressure around 5 bar into exhaust gases as they exited the DPF. Heat from the exhaust gases would cause the urea to decompose into ammonia which would react with nitrous oxides in the exhaust gases to convert them into nitrogen and water.

Under normal driving conditions, the AdBlue solution lasted for 20,000 kilometres and was to be re-filled under the normal maintenance schedule. As the AdBlue solution was consumed, the driver would receive progressive warnings:

• A trochoid gear type oil pump, directly driven by the crankshaft;
• A Water-cooled type oil cooler;
• A spin-on type oil filter; and,
• Oil jet valves.

If the solution was exhausted while the vehicle was being driven, continued driving would be possible but the engine could not be restarted once it had been stopped. According to Mazda, the CX-7 was the first Australian passenger car to be fitted with this an AdBlue SCR system.

Mazda MZR-CD R2 2008 Diesel engine failure: oil starvation

For Mazda vehicles with 2.2-litre MZR-CD R2 2008 diesel engines, there have been reports of premature engine failures. For these engines, it is understood that the copper seals of the no.1 fuel injector could fail and cause combustion gases to heat the engine oil in the camshaft chambers, creating hard carbon deposits. Over time, these carbon deposits could get flushed into the oil sump and block the pick-up strainer/filter that is in the oil sump. At worst, the oil pump can become starved of oil, the oil warning light can illuminate due to the lack of oil pressure and the engine may seize. If the latter occurs, the engine must be replaced.

If the driver notices that the engine oil warning light illuminates, AustralianCar.Reviews recommends that the vehicle be stopped immediately and towed to a mechanic. It is understood that the low oil pressure warning light illuminates at around 6 psi, whereas normal oil pressure is 50-60 psi. As such, illumination of the engine oil warning light demonstrates seriously low oil pressure which poses an imminent risk of engine damage.

For owners, it is recommended that the strainer/filter be inspected when the oil is changed for any signs of blockage. Furthermore, AustralianCar.Reviews understands that since the oil strainer/filter sits low in the oil sump, it is not possible to completely drain the oil if the strainer/filter is blocked.