Science Fair Project Encyclopedia
Alfa Romeo Twin Spark engine
The Alfa Romeo Twin Spark (TS) engine was developed in the mid '90s to enable it to achieve a higher power output from its engines, incorporate newly developed technology and most importantly for cleaner emissions.
The TS engines are all '4 in line' with twin cam (DOHC) shafts, and are developed with either 8 or 16 valves. All newer models since the Alfa Romeo 155 use the 16 valve models. The Twin Spark name comes from the fact that there are two spark plugs per cylinder, but contrary to popular belief, the second (and smaller) plug only serves to act as an emissions control, igniting leftover fuel on the exhaust stroke. The common TS engines, 1.6, 1.8 and 2.0, all use a 10mm and a 14mm plug per cylinder.
The engines also incorporate two devices to improve the performance under normal operation, the Camshaft Phase Variator and the air intake Variable Inlet Control.
The Phase Variator (aka 'Variator') adjusts the angle (or 'phase') of the air intake camshaft to allow the valve open and close time to advance when the engine RPM exceeds 4300 RPM. This a similar process to that used in Honda's VTec and Toyota's VVT-i technology.
The Variable Inlet Control causes the air intake (plenum) to shorten it's path from the intake trumpet to the valve bores, again when the engine reaches a pre-defined RPM. This works on the principal that the air intake length is a tuned pipe that when operating at it's 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 spend 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.
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details