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Nissan Releases the New-Look 2002 Navara
With a Powerful ZD30 Diesel Engine

December 6 2001

Nissan's hard-working Navara ute range received a significant upgrade with the launch of a new model line-up, highlighted by the introduction of a 3.0-litre turbo diesel engine in all four-wheel drive models.

The new-look Navara range gets a comprehensive update with revisions to the suspension tuning, improved noise, vibration and harshness levels, updated interior trim and a substantial exterior upgrade.

However, the highlight of the new Navara range is fitment of Nissan's ZD30 power plant. This lightweight, compact DOHC four-cylinder displaces 2953cc and features the M-Fire combustion system.

Delivering 110kW of power at 3400rpm and 314Nm of torque at 2000rpm, the ZD30 engine enhances Navara's already impressive performance and towing capacity - now up to a class-leading 3000kgs (trailer with brakes).

The new ZD30 engine will be available in 4x4 Single and Dual Cab models. The standard transmission is a five-speed manual with double-cone synchronisers on first and second gears. Standard suspension across the range is double-wishbone front with an anti-roll bar and leaf rear suspension. Revisions to the suspension have improved ride comfort and handling.

Ventilated front disc brakes and rear drums comfortably handle Navara's stopping requirements, even when fully loaded or towing.

According to Nissan Australia's Marketing Manager for Commercial Vehicles, Mr Andrew Dimsey, the new 3.0-litre diesel is a significant step forward in the commercial vehicle range.

"The Navara 3.0-litre turbo-diesel will be the class-leader in its segment and like its predecessors will maintain Nissan's commitment to offering the best value for money proposition in each market," Mr Dimsey said.

Engine
Nissan's new ZD30 DOHC direct injection turbo-diesel engine has been designed to deliver petrol-engine type performance with quietness, fuel economy and reduced exhaust emissions.

The new power plant making its debut in the Navara range delivers a lusty 110kW of power (44 per cent more than the superseded QD32 engine) and 314Nm of torque (42 per cent more than the QD32). Nissan's ZD30 engine generates greater power, operates more quietly, reduces soot and NOx emissions while maintaining the excellent fuel economy of conventional direct-injection engines. It does so by achieving premixed combustion at a low temperature.

M-Fire Combustion System
Efforts to improve diesel engines have so far tended to focus on improved diffusion combustion. Nissan reasoned that NOx and soot could be reduced simultaneously if premixed combustion - which is inherently less likely to produce soot - could be accomplished at a low temperature. This is what M-Fire combustion achieves.

Gasoline engines produce little soot because the fuel and air are first thoroughly mixed and then ignited and burned - a process called premixed combustion. But when this process is attempted in a diesel engine, combustion takes place all at once, raising the combustion temperature and causing the formation of large quantities of NOx. To avoid that, diesel engines burn the mixture in a diffusion combustion process - since the mixture is combusted as the fuel is injected, premixed combustion is controlled.

In order to prevent the mixture from burning instantaneously in this process, the combustion temperature is kept low, which works to suppress NOx formation. However, because the fuel is ignited before it is fully vaporised, some places in the cylinder lack a sufficient supply of oxygen, resulting in the formation of soot that causes black smoke in the exhaust.

The measures adopted to accomplish M-Fire combustion include:

  • optimisation of fuel injection timing;
  • application of heavy exhaust gas recirculation (EGR); and
  • generation of strong fuel swirl.

In diesel engines, fuel has traditionally been injected at a point considerably before the piston reaches top dead centre (TDC) of the compression stroke.

In the ZD30 engine, the injection timing has been changed so that the fuel is injected closer to TDC of the stroke, allowing compressed air to enter the expansion stroke, thus combustion occurs after the pressure has started to drop meaning lower pressure at the onset of combustion.

As well, injecting fuel at this point allows ample time for fuel to evaporate - because it is not ignited immediately after being injected - making it possible to accomplish premixed combustion.

In designing the ZD30 engine, Nissan engineers increased the Exhaust Gas Recirculation (EGR) rate. This results in a gradual combustion process in which the mixture does not burn instantaneously following ignition, which keeps the combustion temperature from rising.

And a helical port is used to generate strong swirl motion to improve mixture formation and promote stable combustion.

High pressure distributor-type fuel injection pump
A high-pressure fuel injection pump is used which generates high injection pressure of approximately 100MPa (conventional direct injection diesels have a maximum injection pressure of less than 70MPa).

The higher injection pressure promotes better fuel spray atomisation, making the fuel more combustible resulting in greater power and combustion characteristics less likely to produce exhaust soot.

The control unit has been partially integrated with the pump to enable variation in pumping pressure to be adjusted at each individual pump - making it possible to achieve high fuel injection precision for greater efficiency and improved combustion.

Additionally, Nissan engineers ensured friction inside the pump was minimised which, together with increased efficiency in the compressed fuel line, enables the pump to generate high injection pressure with minimal energy.

16-Valve DOHC
Four valves per cylinder is proven to improve induction efficiency. Additionally, the fuel injection nozzle is positioned vertically in the centre of the combustion chamber which - along with the strong swirl motion - allows extremely efficient use of the air in the combustion chamber, contributing to a combustion process which reduces soot production. Variable Swirl Mechanism
In the ZD30 engine, Nissan's variable swirl mechanism consists of the tangential port, helical port and swirl control valve but in normal engine speed range, the swirl valve is closed and air is inducted only through the helical port - which works to generate powerful swirl for stable combustion. At high engine speeds, the swirl control valve is opened and air is also taken in through the tangential port - increasing the intake air quantity in proportion to the larger amount of injected fuel to achieve thorough combustion characterised by little exhaust soot.

Styling
The new Navara model line-up will be hard to miss thanks to a comprehensive exterior update. All Navara models pick up new front bumpers and grilles that ensure they look as rugged as the car itself. The new Navara range also bear the company's distinctive new brand identity badge.

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