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The Alfa-Romeo 1.9 and 2.4 JTD Multijet

by François Dovat

At the 2002 Paris Motor Show Alfa Romeo presented a new version of the 4-in line JTD of 1910 cc with common rail direct injection on the 156 and 147. Thanks to a new cylinder head with 4 valves per cylinder and to an advanced electronic management of the injection, the performances of this engine are up-rated to the level of the former 2.4 liters 5 cylinders JTD. The announced maximum torque is exactly identical at 305 Nm (225 ft-lbs) while the power is indicated at 140 hp instead of 150 for the previous version of the 5 cylinders. But the weight saving of 80 kg almost compensates for the lost 10 hp, even more so as a 6th ratio has been added to the gearbox. But in June 2003 the 5 cylinder has been updated also and now produces 175 hp. Let's the guys of the FIAT group the pleasure to enlighten us:

"The secret of the Multijet engine lies in the control unit that governs the electric injector opening and closure system (and also in the injectors themselves). The crucial part of the engine is the electronic control unit itself, due to its ability to deliver a series of very closely-spaced injections.

Fiat Auto's researchers developed the part (together with the injectors) especially for this application. It is designed to deliver the multiple injections that assure the designer more accurate control of pressures and temperatures developed inside the combustion chamber and also more efficient use of air taken into the cylinders. This enables further goals to be achieved: quieter combustion reduced emissions and increased performance.

The Multijet system is underpinned by long years of research. Our engineers began by resolving the problem of limits imposed by the control units. Then they went on to map the benefits they could achieve by plotting different multiple injection sequences (two secondary injections very close to the main injection; one secondary injection not too close to the main injection plus two closely-spaced secondary injections; one secondary injection and then two main injections close together after a certain period etc.) against different engine service conditions; in the idling region; with low loads and low rpm; with high rpm and moderate load; with low rpm and high load etc.

The study revealed the potential of the system and showed that great benefits are achievable in all cases, though these tend to focus on one field or another according to the type of sequence chosen and the engine service area targeted. In some cases, for example, the priority is to reduce start-up times and fume levels, in other cases it is to increase torque and reduce noise while in others it is to reduce emissions and ensure a quieter drive.

And now this research strand has led to the creation of the first Multijet engine: another first for the Fiat Group in the diesel engine field. All this has been possible because we have been building up know-how in this field since 1986, the date that marked the arrival of the Croma TDI, the first direct injection diesel vehicle in the world.

At that time, this represented a true engineering breakthrough that was later adopted by other manufacturers. Direct diesel injection engines offered better performance and lower fuel consumption but failed to resolve the problem of excessive engine noise at low rpms and while speeding up or slowing down. So work began on a more advanced direct injection system and a few years later this led to the development of the Common Rail principle and the Unijet system.

The idea first came from the Zurich University research laboratories where scientists were working on an injection system that had never before been applied to a vehicle, i.e. the Common Rail system. The idea is simple yet elegant: if you continue to push diesel into a tank, the pressure inside will rise and the tank itself will become a hydraulic accumulator (or rail), i.e. a reserve of pressurized fuel ready for use.

Three years later, in 1990, the Unijet system developed by Magneti Marelli, Fiat Research Centre and Elasis on the Common Rail principle entered the pre-production stage. In 1994, when this stage was complete, Fiat Auto started to look for a partner with superlative knowledge of diesel engine injection systems. The final phase of the project, i.e. completion of development and industrial production, was thus eventually entrusted to the Robert Bosch company.

Now our story has reached 1997 and the launch date of the Alfa 156 JTD with its revolutionary turbodiesel engine. Compared to conventional diesel power units (with swirl chamber – note of FD), the JTD guarantees an average improvement in performance of 12% together with a 15% reduction in fuel consumption. These results meant that cars fitted with the engine were an immediate hit."

According to the revs and ambient temperature, the new versions also provides between 3 to 6 decibels reduction of the sound levels in the heating phase.


If the bore and stroke remain 82 x 90.4 mm, the new cylinder head has twin camshafts lifting the valves by roller levers and motionless hydraulic lifters, as well as new manifolds. The pistons are cooled by an internal oil circuit; the oil and water pumps are new and an oil cooler was adopted. Other modifications relate to the crankshaft-connecting rod assembly and cooled EGR system with electronic regulation. The injection pressure has been increased from 1300 to 1400 bars and the Garrett turbocharger is now fitted with variable pitch turbine inlet stator blades, vacuum controlled (picture below).


The 1.9 147 accelerates from 80 to 120 km/h in 9 seconds (in 5th) and from 0 to 160 km/h (100mph) in 26 sec.

The 1.9 156 reaches a top speed of 209 km/h, accelerates from 0 to 100 km/h in 9.3 sec and cuts down the km standing start in 31 sec.

At stabilized speed in 6th gear, the fuel consumption is remarkably low:


4,5 l/100 km à 90 km/h;

5,9 l/100 km à 120 km/h;

7,3 l/100 km à 150 km/h.


The axle ratio has been lowered from 3.35 to 3.56 and the first 5 ratios are unchanged, the 6th increasing the overall span to 6,23:

3,8 - 2,235 - 1,36 - 0,971 - 0,763 - 0,61

With 185/65R15 tires, the two cars get 52 km/h per 1000 rpm in 6th so that the top speed correspond quite exactly with the engine max power revs of 4000 rpm.

The peak mean effective pressure of 20.2 bars is attained at 2000 rpm for a torque of 305 Nm, an increase of 24% when the rpm drop from 4000 to 2000.

The 156 with the latest 175 hp 5 cylinders has a top speed of 225 km/h, reaches 100 km/h in 8.3 sec and needs 8.2 sec only to pick up from 80 to 120 km/h in 5th gear. A compact new transmission with 3 shafts and synchronized reverse has been designed to handle the 385 Nm of torque.

(© François Dovat)
#124

Technical files

Idée & conception © 1999-2011 van Damme Stéphane.


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