Alfa Romeo Twin Spark engine

Infobox Automobile engine


name=Alfa Romeo TwinSpark engine
manufacturer=Alfa Romeo
production=1986–
type=DOHC 2/4-valve I4
predecessor=Alfa Romeo Twin Cam
successor=
displacement=1.4 L
1.6 L
1.7 L
1.8 L
2.0 L
power = 76 kW (103 PS) - 114 kW (155 PS)
block =aluminium alloy
and cast-iron
head =aluminium alloy

Alfa Romeo Twin Spark (TS) technology was used first time in Alfa Romeo Grand Prix car in 1914.Cite web|url=http://www.ukcar.com/history/Alfa%20Romeo/index.html|title=Alfa Romeo Cars|accessdate=2007-07-05|work=ukcar.com] In the early 1960s it was used 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 engines installed in Alfa Romeo cars. Initially appearing in Alfa Romeo 75 model and then used in Alfa Romeo 164, 155, 145, 146, 156, 147 , 166 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.

The two sparks on the 8V Alfa Twin Spark engines fire at the same time per cylinder and this makes the fuel mixture burn faster than single plug ignition because it is fired from 2 different places simultaneously. So less ignition advance could be used and also leaner mixtures could be burned. The 8V engine also has 8 identical spark plugs. They are symmetrically located at opposite sides of the combustion chamber. There is no room for a center positioned spark plug because the 2L version of the 8V engine use a 44mm intake valve and the two spark plug holes are on the sides of the 2 valves.

On 16V engines there is room for a spark plug in the middle of the cylinder as in all 4-valve configuration engines, but also a second smaller plug is installed as well to keep the name Twin Spark. Both of the plugs fire on compression and on the 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 comes with reversed polarity and requires decreased breakdown voltage. On the later (CF3) 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 common 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 100000 kilometres, or 60000 miles. 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 on the later (plastic cam cover) 1.8 and 2.0 litre versions. On lower rpms the intake length is increased which increases the intake air speed and promotes better combustion and mixing under these conditions, also changes the intake resonance frequencies.

The advancing of the inlet camshaft by 30 degrees (or 15 camshaft degrees) which makes the intake valves open and close earlier, when the predetermined rpm and load range is reached, makes the compression phase of the combustion process to begin earlier than when the camshaft is not in its advanced state and in this way the dynamic effective compression ratio is increased which produces more torque at the given engine speed. Also as the intake valve is also opened earlier the valve overlap is also increased at that mode.On some similar inlet cam phasing systems like BMW VANOS the phasing is returned to the retarded state at higher rpm.

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 5cylinder engine, some Fiat Bravo/Marea engines, Fiat Baracheta, Fiat Coupe 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.

The notable effect that these two devices have is that the engine will have a linear power deilivery from low RPM up until the red line, without the lack of torque at low RPM, and a kick in power at higher RPM, that is typical of multivalve engines as they come "On cam".

In the lower RPM mode the air path is longer which increases the intake air speed and improves mixing, combustion, emissions and low rpm torque.

It is a type of Variable Length Intake Manifold

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 adviseable 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.

2 valve Twin Spark engines

*1.7 L 1749 cc 84 kW (115 PS) @6000 rpm, 146 N·m (108 ft·lbf) @3500 rpm
*1.8 L 1773 cc 98 kW (129 PS) @6000 rpm, 165 N·m (122 ft·lbf) @5000 rpm
*2.0 L 1962 cc 109 kW (148 PS)@5800 rpm, 186 N·m (137 ft·lbf) @3000 rpm
*2.0 L 1995 cc 104 kW (143 PS) @6000 rpm, 187 N·m (138 ft·lbf) @5000 rpm (cat.)

applications:
*Alfa Romeo 75
*Alfa Romeo 155
*Alfa Romeo 164

4 valve Twin Spark engines

*1.4 L 1370 cc 76 kW (103 PS) 6300 rpm, 124 N·m (91 ft·lbf) @4600 rpm
*1.6 L 1598 cc 77-88 kW (105-120 PS) @5600-6200 rpm, 140-146 N·m (103-108 ft·lbf) @4200-4500 rpm
*1.8 L 1747 cc 103-106 kW (140-144 PS) @6500 rpm, 163-169 N·m (120-125 ft·lbf) @3500-3900 rpm
*2.0 L 1970 cc 110-114 kW (150-155 PS) @6400 rpm, 181-187 N·m (133-138 ft·lbf) @3500-3800 rpm

applications:
*Alfa Romeo 145
*Alfa Romeo 146
*Alfa Romeo 155
*Alfa Romeo 164
*Alfa Romeo GTV (Type 916)
*Alfa Romeo Spider (Type 916)
*Alfa Romeo 156
*Alfa Romeo 147
*Alfa Romeo 166

ee also

* Alfa Romeo Twin Cam engine
* Fiat Twin Cam engine

Footnotes