Alfa Romeo Twin Spark engine
From Wikipedia, the free encyclopedia
| Alfa Romeo TwinSpark engine | |
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| Manufacturer | Alfa Romeo |
| Type: | DOHC 2/4-valve I4 |
| Production: | 1986– |
| Predecessor: | Alfa Romeo Twin Cam |
| Displacement: | 1.4 L 1.6 L 1.7 L 1.8 L 2.0 L |
| Block alloy: | aluminium alloy and cast-iron |
| Head alloy: | aluminium alloy |
| Power output: | 76 kW (103 PS) - 114 kW (155 PS) |
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 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.
Contents |
[edit] The 'Twin Spark'
Twin Spark name refers usually engines made after 1986 when the 164 Twin Spark was introduced. The TS series engines are all '4 cylinder inline' with twin cam (DOHC) shafts, and are developed first with 8 valves (an all alloy wet-liner engine, chain driven) and later with 16 valves (a modern iron block engine with alloy head, belt driven). All cars featuring the Twin Spark engines since the Alfa Romeo 155 (which originally also came with the 8V unit) use the 16 valve models over the 8V ones. The Twin Spark name comes from the fact that there are two spark plugs per cylinder.
The two sparks on the Alfa twin spark engines fire one after the other on the power stroke causing higher compression as the flame front travels across the combustion chamber. The second spark fires in the extra compressed mix, ensuring a cleaner burn and less unburnt fuel in the exhaust as well as a higher thermodynamic efficiency. The 8V units have 8 identical spark plugs, while the 16V ones have a larger and a smaller plug in each cylinder. On the later 16v TS there are 4 independent 8-ampere coils, connected to plugs; 1a and 4a, 1b and 4b, 2a and 3a, 2b and 3b. This arrangement facilitates the separate firing of the spark plugs in each combustion chamber, and also saves parts by utilising a "wasted spark" system, where - between the exhaust and inlet stroke of each pistons "partner" - a useless spark occurs, this may improve emissions very slightly, but the intention is to reduce cost. The common TS 16V engines, 1.6, 1.8 and 2.0, all use a 10 mm diameter and a 14 mm diameter platinum electrode spark plug per cylinder.
The spark plugs of the 8V TS Alfa Romeo engine are symmetrically located in the upper part of the chamber to the sides of the line passing from the opposing intake and exhaust valves and this allows the usage of larger intake valves due to the missing central spark. Thus the 2L version of the 8V engine uses 44mm intake valve. By firing the spark plugs at the same time and considering their location the burning lasts shorter time (faster burn) because the mixture is ignited simultaneously from 2 different locations. This allows usage of less ignition advance than when using single spark ignition.
The engines also incorporate two devices to improve the performance under normal operation, the Camshaft Phase Variator and the air intake Variable Inlet Control on the later (plastic cam cover) 1.8 and 2.0 litre versions.
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 VANOS the phasing is returned to the retarded state at higher rpm.
[edit] 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. Modifying this tuned system in any way and failing to re-tune it will create performance drops.
The notable effect that these two devices have is that the engine will surge powerfully forward on hitting the ~4300 rpm mark, right up to the RPM limiter.
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
[edit] Variable valve timing
Variable valve timing gave the Twin Spark engine very good performance for its cubic capacity it is one of the weaker areas of the 16 valve engine. The variator solenoid 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.
[edit] 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:
[edit] 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
[edit] See also
[edit] Footnotes
- ^ Alfa Romeo Cars. ukcar.com. Retrieved on 2007-07-05.
