New V6 diesel engine

The new direct injection V6 turbodiesel has been developed by the Renault Nissan Alliance to deliver high levels of performance with strong economy, competitive emissions and class-leading refinement.

The key element of the new V6 - with an unusual vee angle of 65 degrees - is the material chosen for the engine block. Alliance development engineers chose Compacted Graphite Iron (CGI), a material that offers all the benefits of cast iron, including high levels of stiffness and noise absorption, without the weight penalty. And while CGI is heavier than a pure alloy block there is no need to add stiffening ribs or extra sound deadening material so the weight gain is comparatively modest.

Using experience gained during the development of the Alliance 2.0-litre dCi engine - and carrying over some technology - accelerated development of the new V6, but number of significant changes have been made to the hardware for the V9X. The combustion chamber design, for example, has been optimised to improve the balance between emission levels and fuel efficiency.

The compression ratio has been lowered to 16:1 to benefit not just economy and emissions but also noise, vibration and harshness (NVH), while internal engine friction is reduced by the use of ultra smooth components such as the micro-finished forged steel used for the crankshaft.

Class leading levels of torque and highly competitive specific power outputs are delivered thanks to the adoption of a comparatively large single turbocharger, which is mounted within the vee of the engine, an intercooler, and the use of the latest generation of Bosch common-rail fuel injection. This system incorporates piezo injectors and operates at 1800 bar.

Power output is 170 kW (231PS) while the torque output of 550 Nm leads the class. Better still, peak torque is achieved from as low as 1,700 rpm and is available all the way to 2,500 rpm, while as much as 500 Nm is available from a mere 1,500 rpm. Idle speed is an exceptionally low 650 rpm with none of the vibrations and noise usually associated with a diesel.

The result is strong low-end performance with comfortably refined delivery and exemplary throttle response. In addition, the engine helps provide strong towing performance, the Nissan Pathfinder capable of towing a 3500 kg braked trailer with Nissan Navara having a 3000 kg limit.

Emissions and fuel efficiency targets included achieving Euro 5 compliance. In addition to the gains made by the changes to the combustion chamber, the V9X engine also incorporates a number of innovative features.

Among these is the adoption of an overcooled Exhaust Gas Recirculation (EGR) system which reduces NOx emissions. The system incorporates an integrated exhaust gas bypass in the EGR cooler which quickly helps to achieve the optimum temperature after start up so that the full cooling capacity can be used. This features a low temperature water circuit for the EGR cooler to reduce still further the temperature of the exhaust gas and lower carbon monoxide and hydro carbon emissions.

Equally significant is the treatment of the tailpipe emissions. The system comprises a metallic oxidation catalytic converter offering lower pressure loss compared to a ceramic system and an exothermic catalyst and a catalytic diesel particulate filter (DPF) in the same container. The latter arrangement works in conjunction with a seventh fuel injector which is positioned in the exhaust.

This is activated while the particulate filter is being regenerated - a process of which the driver is completely unaware - but significantly means the opportunity for unburnt fuel to pollute the engine oil is removed. It also allows the filter to be regenerated in low-load conditions, such as idling, and therefore achieves a high efficiency level under all driving conditions. It also helps stretch oil change intervals to 20,000 kms.

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