FACTfile - Alfa GTV – Page 3

The New Engines

The true heart and soul of every Alfa Romeo model is its engine. The Alfa Spider and Alfa GTV are no exception. The new models' attractive, personality-packed looks conceal a diverse range of outstanding high-tech power units that all offer superlative performance.

First up, the legendary 3.2 V6 24V unit delivers a power output of 176 kW at 6200 rpm and boasts a torque figure of 289 Nm at 4800 rpm for exhilarating performance on a sporty run but also during everyday use. More specifically, a GTV equipped with this engine reaches 255 kmh, a performance that makes this the fastest road car in Alfa Romeo's history. The second power unit available for the new models is the 121 kW 2.0 JTS. This is the first direct injection petrol engine with a specific power rating higher than 60 kW/l (82 bhp/l) and a specific torque greater than 100 Nm/l. Two manual gearboxes are also available: a six speed unit for the 3.2 V6 24v and a five-speed unit for the 2.0 JTS versions.

The 176 kW 3.2 V6 24V engine
The top-of-the-range power unit for the new sports cars is the scintillating 3.2 V6 24V unit already adopted on GTA versions of Alfa 156 and Alfa 147. Derived from the now classic three litre V6 24 valve unit - also fitted to the Alfa GTV - the mighty 3.2 is a vigorous and well-rounded power unit. Compared to the 3.0 litre V6 it replaces, Alfa's engineers changed the crankshaft and pistons to increase the cylinder capacity to 3.2 litres and lengthened the stroke to 78 millimetres. This change speaks volumes about the type of performance required because the power could simply have been increased by adjusting the timing, fuel system and electronics.

The fact that cylinder capacity has been increased by lengthening the stroke means that the aim was not simply to obtain out-and-out performance coupled with high power and torque peaks but also an even, gradual power delivery from the lowest speeds - as befits a car capable of thrilling performance that is suited for driving on ordinary roads as well as on the track.

The increase in cylinder capacity is naturally accompanied by a whole set of changes. The intake and exhaust ports have been tuned by applying a new timing pattern, the control unit software has been rewritten and the cooling system has been upgraded with the addition of an engine oil radiator. The result? Power output is 176 kW at 6200 rpm with a maximum torque of no less than 289 Nm at 4800 rpm. These figures are all it takes to achieve exciting performances and are complemented by a torque curve that permits high values at low speeds. The car can also travel in sixth gear at less than 2000 rpm and unleash extreme performance without changing gear. Extremely satisfying behaviour, therefore, even during daily use. The self-confessed goal of the Alfa GTV and Alfa Spider is this: to offer sensations unique to a racing car yet still be perfectly serviceable for everyday use.

The 121 kW 2.0 JTS engine
The 2.0 JTS is a top-performing power unit that owes its name of JTS (Jet Thrust Stoichiometric) to its combustion system. As far as the customer is concerned, this means a two litre car that already meets tough Euro 4 emission limits; does not need low sulphur petrol but is able to use normal petrol. The 2.0 JTS thus represents a true technological leap for Alfa Romeo, its first petrol engine with injectors that work directly inside the combustion chamber. It achieves its end by interpreting the principles of stratified charge and the creation of motion in the mixture inside the cylinder in an entirely original way.

Lean burn, but not too lean
The possibility of injecting petrol directly into the combustion chamber instead of the intake duct has been known since Nikolaus Otto (who took out a patent in 1877) and has been applied for two different purposes over the years - on racing cars in the Fifties and Sixties to increase engine power - more recently (since 1996) to reduce fuel consumption. Recently, manufacturers have devoted all their efforts in this latter direction and gratifying results have been achieved with the stratified charge method. The principle is simple: instead of injecting all the petrol required to maintain the normal air-fuel ratio of 14.7:1 (stoichiometric) throughout the combustion chamber, only a small amount of fuel is injected that mixes with the air to form a core of almost stoichiometric composition about the spark plug. The resulting mixture is stratified or layered because it is richer where the ignition spark ignites and increasingly lean (more air and less fuel) as it approaches the outside of the chamber.

So far the benefits of this lean burn system, usually applied in the rpm band up to 3000 rpm by other car makers, have amounted to a fuel saving of some 10%. The disadvantages of their systems may be summarised as follows:

1. a drop in performance when the car is required to deliver full power (because the ducts and pistons are shaped in a certain way that is essential to reduce fuel consumption at low speeds);
2. the need to use sulphur-free fuel;
3. the requirement for costly, delicate exhaust gas treatment methods (DENox) to reduce the higher nitrogen oxide emissions generated by the leaner burn

It goes without saying that Alfa Romeo's approach to the new technology had to be quite different. Category-topping performance and irrepressible driving behaviour have always been essential requirements for all Alfa models. But what was to stop Alfa from using direct injection to increase engine power and torque in keeping with the sporty applications of this technology. Then, Alfa reasoned, the engine could bring in the stratified charge system to reduce fuel consumption within a restricted rpm band around idle speed.

The result was an entirely original Alfa Romeo approach to applying direct injection in petrol engines. A solution that offered a compromise between the two methods pursued to date. The 2.0 JTS works using a lean burn approach up to around 1500 rpm and this saves fuel, although not as much as on other lean GDI engines. Above this engine speed, the engine burns a stoichiometric air-fuel mixture, i.e. with a normal 14.7:1 ratio between both components. All this means outstanding performance and much better than would be obtained using a normal indirect injection petrol unit.

Firstly, because petrol is injected directly into the combustion chamber instead of the duct it cools intake air to increase the engine's volumetric efficiency. As temperature drops, the gases increase in density and their volume therefore decreases: this means that more air can be introduced into the combustion chamber. Power unit susceptibility to knock is also reduced by chamber cooling. It is therefore possible to increase the compression ratio - in this case from 10:1 for the 2.0 T. Spark to 11.3:1 for the 2.0 JTS. This means more power for the new Alfa Romeo engine that is, moreover, able to deliver its power unhindered because the exhaust gas treatment system used on Alfa Romeo models does not generate the strong counterpressures typical of the Nox absorbers used by lean GDIs. Direct introduction of petrol into the chamber improves power unit response speed to the accelerator control because it is faster overall than a conventional petrol engine.

Benefits = higher performance and lower fuel consumption. Compared to the current 2.0 T. Spark unit and other currently-available direct injection petrol engines, this 2.0 JTS unit offers slightly lower fuel consumption and a generous increase in power and - above all - torque. + 15 bhp and + 25 Nm. To sum up, the 2.0 JTS develops a maximum power of 121 kW at 6400 rpm and a maximum torque of 206 Nm at 3250 rpm. And all this is achieved using petrol currently on sale and current catalytic converters.

A new combustion chamber principle - the new JTS combustion system displays two distinctive features:

1. the principle followed to generate the movement that propels the air and fuel mixture toward the spark plug inside the cylinder
2. the range of rotation speeds within which the engine works using a lean burn system

In other GDI engines, the air's force drags the fuel spray into the area where the ignition spark ignites. This option is determined by a desire to achieve a very lean mixture (up to 60:1) and thus consistent fuel savings. But it brings a need to change the air's motion within the combustion chamber (charge motion) according to rpm level and this complicates the air input mechanisms (throttles, duct closure systems etc).

In the 2.0 JTS, however, the force of the fuel spray (Jet Thrust) propels the fuel toward the spark plug as it mixes with the air. In this way, we achieve a charge that is less lean overall (the ratio remains constant at all speeds and is 25:1) and less fuel is consequently saved. But the engine's internal mechanism is far less complicated because it lacks systems for altering the air's motion.

The same process of simplification also guarantees the limitation of lean burn technology to rpm levels around idle speed (up to 1500 rpm). GDI engines that use stratified charge within a broader speed band (up to 3000 rpm) must employ modified piston and duct profiles. The resulting shape does not allow power to be optimised at high speeds. The use of stratified charge only up to 1500 rpm, however, means that the pistons and ducts on the Alfa Romeo 2.0 JTS are hardly altered. Because their shape is more similar to those of current indirect injection engines, they are able to exploit all available power at high speeds.

The addition of an exhaust gas treatment system (Nox absorber) to remove nitrogen oxides is also only required when the lean burn range is extended up to 3000 rpm. This also dictates the use of sulphur-free fuel, i.e. the only type that will not damage the catalytic converter. The use of stratified charge only at speeds around idle speed, however, allows the 2.0 JTS unit to use a conventional catalytic converter system. This result is also made possible by a more extensive use of exhaust gas recirculation, which reduces the production of nitrogen oxides (NOx). Because Alfa Romeo engines are fitted with variable valve timing, exhaust gas is recirculated to the intake on the 2.0 JTS directly between the intake and exhaust valves (internal EGR).

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Engineering

What changes

The main engineering changes on the 2.0 JTS compared to the corresponding Twin Spark engine affect the cylinder head with Bosch injectors fitted in the chamber, pistons, camshafts and exhaust system. All these components are completely new. The intake ports are high performance; the fuel manifold is high pressure (common rail type); piston compression ratio is higher - and the exhaust - built to Euro 4 standards - is cascade type.

The exhaust gas treatment system works conventionally despite an unconventional layout: the system no longer consists of a preconverter and a main converter located under the body. Instead it comprises two main catalytic converters built into the manifold (each connected to a double branch that leads to two cylinders). This frees up the space under the body for a silencer that is more permeable and thus more able to reduce counterpressure for fuller engine power delivery.

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