Saab has unveiled its new 9-3 Convertible 1.9 TiD turbo diesel variant at the Brussels International Motor Show.

The introduction of this powerful yet frugal turbo diesel engine substantially broadens the appeal of the Saab 9-3 Convertible range. Available in Linear and Vector specifications, the 150 bhp, 16-valve 1.9 TiD unit is offered with a choice of six-speed manual or optional automatic transmissions.

This common rail, direct and multiple injection engine, successfully launched already in the Saab 9-3 Sport Saloon and SportWagon ranges, is distinguished by a level of refinement as impressive as its strong performance. An advanced, maintenance-free, exhaust particulate filter is fitted as standard.

In the Saab 9-3 Convertible, this engine is offered only in its most powerful configuration. That means 150 bhp maximum power generated at 4,000 rpm. But, even more importantly, it offers a wide spread of strong pulling power, with 90% of maximum torque available all the way from 1,750 to 3,250 rpm. The maximum value of 320 Nm, between 2,000 and 2,750 rpm, is exceeded only by the 350 Nm of the top-of-the-range, 250 bhp, 2.8 V6 Turbo petrol engine.

On the road performance is equally impressive, with the engine’s distinctly sporty character further narrowing any perceptible difference between diesel and petrol performance levels – except in the frequency of visits to the filling station.

In-gear acceleration, most important for everyday driving, is on a par with the 210 bhp petrol engine (50 to 70 mph in fifth gear taking 8.7 seconds, vs. 9.3 seconds), while the zero to 60 mph dash is accomplished in just 10.0 seconds (11.2 seconds for the automatic).

The driving experience is notable for a level of smoothness and refinement, together with a progressive torque build-up, that belies the presence of compression ignition. Calibrating the movement of the electronic throttle to deliver a response similar to Saab’s petrol engines had helped achieve this. And the process is optimised by a low-inertia Garrett turbocharger, operating at 1.35 bar boost, with variable vane geometry (VNT), allowing the pitch of the turbine blades to be electronically adjusted for a quick pick-up at low engine speeds.

With combined cycle fuel consumption of 44.8 mpg (6.3 litre/100 km)(automatic 38.2 mpg; 7.4 litre/100 km) showing a 25 per cent gain over the 150 bhp, 1.8t petrol engine, the new Convertible 1.9 TiD offers an appealing combination of performance, refinement and economy. CO2 levels are a low 169 g/km for the 6-speed manual, and 199 g/km for the automatic.

The 1.9 TiD engine consists of a four cylinder, cast-iron block and an alloy cylinder head, accommodating two, chain-driven, overhead camshafts with hydraulic tappets. It has a steel crankshaft and connecting rods, a dual-mass flywheel, a weight-saving pressure cast aluminium intake manifold and electronically-controlled exhaust gas re-circulation (EGR) for quick warm-up and low emissions.

Common rail technology provides consistently high injection nozzle pressures of 1,600 bar, independent of the prevailing engine speed or load. This allows the use of small, multiple injections of fuel, between two and five, to release as much energy as possible from a given amount of fuel.

The Bosch ECM continually adjusts the number, frequency and size of the injections according to three main parameters: current engine speed, the requested throttle setting and engine coolant temperature. Each injection pulse may be separated by as little as 150 microseconds, delivering a quantity of fuel as tiny as one cubic millimetre.

This extremely efficient combustion process pays dividends in a number of key areas. Apart from improving fuel consumption, emissions and power, it is crucial in helping to iron out the strong vibrations traditionally associated with compression ignition.

Low levels of NVH (noise, vibration and harshness) inside the car are due to the engine’s advanced combustion technology as much as its careful chassis installation. This includes the adoption of an electro/hydraulic power steering system, for improved fuel consumption, and additional tuning of the front suspension and wheel angles.

The high level of driving satisfaction is reflected in the standard fitment of a close-ratio, six gear manual gearbox that encourages driver involvement, complementing the sporty nature of the 1.9 TiD engine and the Convertible’s chassis, with its unique ReAxs rear wheel steer characteristic.

The optional six-speed Aisin AW automatic transmission is a smooth and adaptive unit, responsive to changes in engine load, road gradient or altitude, and quickly finds the ‘right’ gear without any irritating ‘hunting’. The driver can also switch to manual control by using a sequential floor shift or optional steering wheel-mounted buttons. It features a lock-up in all forward ratios, except first.

The 1.9 TiD powertrain includes the most advanced diesel particulate filter on the market. Unlike other particulate traps, it is maintenance-free and self-cleaning, requiring no additives or periodic replacement.

Located in the exhaust system downstream of the close-coupled catalyst, the housing for the filter also includes a secondary oxidation catalyst to remove residual hydrocarbons (HC). The exhaust gases pass through this first, before entering the filter’s ceramic core, made from a honeycomb of silicon carbide. This is perforated along its length by a matrix of microscopic channels, which collect the particulates as deposits from the exhaust.

In order to clean the filter and keep the exhaust gas flow as free as possible, these deposits are periodically burnt off by short pulses of over-fuelling. These briefly raise exhaust temperatures to the required level of 600º C. The process is automatically initiated when back pressure in the exhaust system reaches a certain level and it is completely undetectable by the driver.

This innovative solution has been made possible through the fuelling flexibility provided by the engine’s multiple injection strategy. The self-cleaning process takes place whenever necessary, irrespective of throttle load or engine temperature.

British deliveries of the new Saab 9-3 Convertible 1.9 TiD models commence in late February, with on-the-road prices ranging from a competitive £25,370 for the Linear model, to £27,664 for the sporting Vector derivative. The special metallic blue 20th anniversary Cerulean edition is also temporarily available in Vector form at £28,439.

The UK market for four seater premium diesel convertibles is expanding rapidly, and Saab’s new entry into this sector is certain to ensure continued growth. Saab forecasts the new 1.9 TiD will account for at least 20 per cent of all 9-3 Convertible sales in 2006.