Alfa Romeo Twin Spark engine

Alfa Romeo TwinSpark engine
Alfa Romeo TwinSpark engine
	Alfa Romeo Twin Spark engine
Overview
Manufacturer	Alfa Romeo
Production	1986–2009
Layout
Configuration	DOHC 2/4-valve I4
Displacement	1.4 L; 1.6 L; 1.7 L; 1.8 L; 2.0 L
Cylinder block material	aluminium alloy; and cast-iron
Cylinder head material	aluminium alloy
Output
Power output	76 kW (103 PS) - 114 kW (155 PS)
Chronology
Predecessor	Alfa Romeo Twin Cam
Successor	Alfa Romeo JTS engine

Alfa Romeo Twin Spark (TS) technology was used first time in Alfa Romeo Grand Prix car in 1914.^[1] In the early 1960s it was used in their race cars (GTA, TZ) to enable it to achieve a higher power output from its engines. And in the early and middle 1980s, Alfa Romeo incorporated this technology into their road cars to enhance their performance and to comply with stricter emission controls.

The 'Twin Spark'

Twin Spark name usually refers to the dual ignition engines installed in Alfa Romeo cars. The 8-valve engine was fitted initially to the Alfa Romeo 75 but also the Alfa Romeo 164 and Alfa Romeo 155. The 16-valve engines appeared in the Alfa Romeo 145, Alfa Romeo 146, Alfa Romeo 155, Alfa Romeo 156, Alfa Romeo 147, Alfa Romeo 166, Alfa Romeo GTV & Spider and even Alfa Romeo GT models.

The TS series engines are all '4-cylinder inline' with twin cam (DOHC) shafts. The original 8-valve engine featured a light alloy (Si enhanced alu alloy) block + head, wet-cooled iron cylinder liners and the camshafts were driven by double row timing chains (long and short). Similar design to the earlier and famous Alfa Romeo DOHC engines, but with narrower valve angle on this model.

The later 16-valve engines had a heavier cast-iron block engine, with an alloy head, and the camshafts were belt driven. The Twin Spark name comes from the fact that there are two spark plugs per cylinder. The block was Fiat sourced. It was cast iron for its higher beam strength, less complexity and hence lower production costs. When new, these engines were notable for their high efficiency as demonstrated by the BMEP (brake mean effective pressures) exerted upon the piston crowns.

The two sparks on the 8V Alfa Twin Spark engines do not fire at exactly the same time (true at least of the 75 which uses traditional ignition coils with king leads and distributors). This was deliberate to avoid the most powerful part of the flame fronts meeting at the centre (weakest part) of the piston. As there are 2 symmetrically placed sparks plugs, the flame front must travel less distance which allows less ignition advance to be used and it is accepted ignition timing can be closer to optimal than a single spark plug would allow. Also, leaner mixtures can also be tolerated for better fuel economy. The 8V engine also has 8 identical spark plugs. There is no room for a centrally positioned spark plug due to the 2-valve design which uses a 44 mm diameter inlet valve on the 2.0 engine.

On 16V engines there is room for a spark plug in the centre of the cylinder as in all 4-valve configuration engines, but also a second smaller plug (off to the side on the axis) is installed. Both of the plugs fire at exactly the same time on compression and exhaust stroke, due to the way in which the coils are paired (1&4 and 2&3). This production economy allows the use of 4 coils, instead of eight, which would normally be required to fire eight plugs, and is common practice called "wasted spark" system. (used also in Ford EDIS system as well as in some Alfa Romeo V6 engines 3 coils for the 6 cylinders). The main reason for the wasted spark system is cost. As both plugs are connected to the same coil the spark one of them operates with reversed polarity and requires decreased breakdown voltage. On the later CF3 (2001 on Euro 3 emissions standard) 16v TS the four coils fire the same cylinder spark plugs (so not 1 and 4 and 2 and 3 as pairs but coil #1 fires the big and small plug of cylinder 1, and so on). The TS 16V engines, 1.6, 1.8 and 2.0, all use a 10 mm diameter and a 14 mm diameter long life platinum electrode spark plug per cylinder. The spark plugs have a replacement interval of 100,000 kilometres (62,000 mi). The operation of the Twin spark engine has been subject to much debate but this is the general theory of operation, as described by Auto Italia magazine.

The engines also incorporate two other devices to enhance the performance under operation, the Camshaft Phase Variator and the Variable Intake Length Control (or Modular Inlet Manifold in Alfaspeak) on the later (plastic cam cover) 1.8- and 2.0-litre versions. Where both these variable systems are deployed they are controlled in tandem by the Bosch Motronic Engine Management ECU in response to rpm, load, and throttle position. According Fiat Auto S.p.A DTE electronic service documentation for the Alfa Romeo 156 Twinspark (1.8/2.0)...

"To optimise the quantity of air drawn into the engine the control unit checks: inlet timing on two angle positions (and) geometry of inlet ducts at two lengths (only 1.8/2.0 TS). At maximum torque speed the control unit sets the "open" phase: cam advanced by 25°, inlet casing long ducts (Only 1.8/2.0 TS). At the maximum power speed the control unit sets the "closed" phase: cam in normal position, inlet box short ducts. At idle speed the control unit sets the "closed" phase: cam in normal position and inlet box short ducts. In the other engine operating conditions, the control unit selects the most suitable configuration to optimise performance - consumption - emissions. During overrunning, the inlet ducts of the box are always short."^[2]

The advancing of the inlet camshaft by 25 crankshaft degrees (or 12.5 camshaft degrees) opens and closes the intake valves earlier in the inlet cycle. This allows the filling of the cylinders with air/fuel mix to begin earlier, and by closing sooner trap more of the fuel/air mix for the compression phase of the combustion process. On 1.8 and 2.0 16V Twinsparks the longer inlet ducts deployed in conjunction with the advanced inlet cam, are of a tuned length that assists cylinder filling by harnessing the harmonic pressure wave present in the lnlet duct. In this way the dynamic effective compression ratio is increased which produces more torque at the given engine speed. As the intake valve is also opened earlier in relation to the exhaust valves, the valve overlap (the period both inlet and exhaust valves are simultaneously open) is also increased at this mode. This promotes the scavenging effect of the exiting exhaust which causes a partial vacuum in the cylinder to further assist in filling the cylinder with a fresh charge.

As with similar inlet cam phasing systems like BMW VANOS the phasing is returned to the retarded state at higher rpm to improve power and effiency as inlet gas dynamics change with rpm. The short inlet ducts being tuned to the higher frequency and thus shorter inlet duct pressure wave.

On 8V engines the valve overlap and intake open duration are quite big. These engines hardly idle with the variator at On position so on these models it had the meaning also to enhance lower speed operation. On the newer 16V engines the camshaft variator is used to enhance the performance/emissions but also might be the source to the common 'diesel noise' problem often seen on high mileage used models which used the earlier internals of the variator. The same variator system is also used in many Fiat/Lancia engines like one used in Lancia Kappa 5-cylinder engine, some Fiat Bravo/Fiat Marea engines, Fiat Barchetta, Fiat Coupe, Fiat Stilo etc. models.

Variable Inlet Control

The Variable Inlet Control causes the air intake (plenum) to shorten its path from the intake trumpet to the valve bores, again when the engine reaches a pre-defined RPM. This works on the principle that the air intake length is a tuned pipe that when operating at its ideal frequency-in tune with the valves, will allow a smooth and even air flow, and will assist with filling the cylinders efficiently. This works in a similar method to the tuned exhaust system on all modern cars, where the exhaust system creates back pressure to pull spent gasses from the cylinder bores. The variable intake system uses the cone inside the airbox to reflect negative pressure waves back down the inlet. These waves are used to assist in filling of the cylinders. The variable inlet allows this to take place at different engine speeds.

Variable valve timing

Variable valve timing gave the Twin Spark engine very good performance for its cubic capacity, but it is one of the weaker areas of the 16-valve engine. The variator that controls the cam timing is prone to wear or jam. Symptoms are a slight loss of performance and a diesel type rattle from the top of the engine, which appears at startup and gradually lasts for longer. It is therefore advisable to get the variator changed regardless of its apparent condition at the 36,000 mile (60,000 km) cambelt replacement. The variator problem is not often seen in the earlier 8V Twin Spark version, as these use a different type of cam timing variator system, this is also the case for later 16v versions used in the Alfa Romeo 156 and the 147 where the weak variator was addressed.

8-valve Twin Spark engines

1.7 L 1,749 cc 84 kW (115 PS) @6000 rpm, 146 N·m (108 ft·lbf) @3500 rpm
1.8 L 1,773 cc 98 kW (129 PS) @6000 rpm, 165 N·m (122 ft·lbf) @5000 rpm
2.0 L 1,962 cc 109 kW (148 PS)@5800 rpm, 186 N·m (137 ft·lbf) @3000 rpm
2.0 L 1,995 cc 104 kW (143 PS) @6000 rpm, 187 N·m (138 ft·lbf) @5000 rpm (cat.)

applications:

16-valve Twin Spark engines

1.4 L 1,370 cc 76 kW (103 PS) 6300 rpm, 124 N·m (91 ft·lbf) @4600 rpm
1.6 L 1,598 cc 77-88 kW (105-120 PS) @5600-6200 rpm, 140-146 N·m (103–108 ft·lbf) @4200-4500 rpm
1.8 L 1,747 cc 103-106 kW (140-144 PS) @6500 rpm, 163-169 N·m (120–125 ft·lbf) @3500-3900 rpm
2.0 L 1,970 cc 110-114 kW (150-155 PS) @6400 rpm, 181-187 N·m (133–138 ft·lbf) @3500-3800 rpm