Twin Spark Technology

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 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.
16 valve Twin Spark with older cover.

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 barchetta, Fiat Coupe, Fiat Stilo etc models.
Variable Inlet Control
16 valve Twin Spark

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

[edit] 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.

[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:

* Alfa Romeo 75
* Alfa Romeo 155
* Alfa Romeo 164

[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 and Spider (Type 916)
* Alfa Romeo 156
* Alfa Romeo 147
* Alfa Romeo 166

Royal Enfield Twinspark Technology

If you think that buying a Royal Enfield Bullet comes with oil leaks, high maintenance costs and unknown reliability, think again, there is
good news.
Royal Enfield Motorcycles, one of the oldest bike companies, has developed a twin-spark technology and has come out with a new engine architecture called unit construction engine (UCE) which is aimed at providing riders better fuel efficiency, higher reliability and lower maintenance costs, while retaining the styling and appeal of a Bullet.
The company has come out with two engine platforms, which are seen as future growth drivers. While UCE 350 cc twin-spark platform has been developed for the domestic market, the UCE 500 cc electric fuel injection (EFI), which is Euro-III compliant, is meant for export markets.
Leading two-wheeler makers TVS Motor and Bajaj Auto have been fighting over ownership of patent for twin-spark technology. Nevertheless, Siddhartha Lal, managing director and chief executive officer, Eicher Motors, said the company examined everything while developing its technology and there is no issue of infringement.
R L Ravichandran, chief executive officer, Royal Enfield, said the development of new engine platforms is part of company’s strategy to boost Bullet’s sales through product quality enhancement and new products.
While the company launched the Thunderbird Twinspark 350 cc, featuring an UCE, on Wednesday for the Indian market, it has already started test marketing the Electra model, featuring UCE 500 EFI, for the overseas markets. Thunderbird Twinspark 350 cc comes with a price tag of Rs 1.03 lakh.
Royal Enfield, a division of Eicher Motors, plans to launch three more models — one for domestic and two for export markets — over the next
two-three years.
Armed with new engine platforms and a few launches in the pipeline, the company expects to maintain a growth rate of 15-20 per cent annually in the coming years.
Royal Enfield sold over 39,000 units, including exports of over 2,500 units in 2007-08, as against 32,000 plus units in 2006-07, despite the slowdown in the two-wheeler industry.
With new UCE 500cc technology, Lal expects huge growth in export markets such as the US, Europe, Japan and Australia. “Traditionally, we have been exporting an Indian bike dressed up for export markets. However, this new UCE 500 cc EFI has been developed specifically to meet customer requirements in export markets,” he added.
Royal Enfield has chalked out an investment budget of Rs 25 crore to scale up its vehicle production capacity to 60,000 units by 2010 from the present 40,000 units a year at its Tiruvottriyur factory near Chennai.

Fuel Injection Technology

A Dose of Injection

First the Glamour, now the Pulsar. Fuel injection is like the flu and it’s only going to spread. We simplify this technology.

India’s ever-tightening emission norms are gradually coaxing bike-makers into cleaner and superior technology. Years ago, these rules forced the two-stroke cycle engine into retirement, and today, most of our inherently cleaner four-stroke bikes have to use air injection systems or supplementary catalytic converters to help stay on the greener side of the line. However, this will all soon be passé, as electronic fuel injection or EFI starts to deliver its magic to us.

New Pulsar DTS-Fi combines Bajaj's proven twin spark plugs with new fuel injection technology.

An internal combustion engine runs on a mixture of air and fuel. However, the precise air and fuel ratio needed by an engine varies depending on infinitely variable conditions. With a carburettor, one can adjust the blend to within a zone where the engine gets its approximate ‘fix.’
However, making rapid changes to the mixture to suit every possible riding situation is well nigh impossible, prohibitively expensive and awfully complicated. EFI eliminates the carburettor and simplifies the game, while also offering lightning quick, and really precise metering.

In an EFI-equipped bike, fuel is stored in the conventional manner within the motorcycle tank. From here, a pump sucks up the precious fluid and force-feeds it to an injector. A regulating system works hard to ensure that a constant, predetermined pressure is always on hand for the injector.

Fuel injection relies on a batch of inputs from various sensors that supply their information to a central brain — the electronic control unit or ECU. Throttle position, airflow, engine temperature, intake air temperature, intake pressure, and engine speed are a few commonly used factors taken into account by the ECU. Guided by these sensors, the ECU decides the precise fuel ratio needed by the engine for any given condition and orders the injector to deliver the same.

The fuel injector itself is a valve capable of opening or shutting within the blink of an eye. The actual opening and shutting is performed by an electromagnet. When activated, pressure forces fuel to be spurted through a narrow orifice, so designed to atomise fuel into a fine spray that is easily combusted.

This fuel mist is delivered into the intake manifold, ready to be sucked past the intake valve/s by the cylinder vacuum. Fuel amount offered is directly controlled by the period the fuel injector is kept open by the ECU.

Most EFI systems incorporate safety cut-offs that kick in when they sense their engine has died or tilted beyond a safe limit — in the event of a crash. At these moments, the fuel pump immediately shuts down its supply.
EFI negates the need for a manual choke, or riding with the choke on till engine operation temperature is obtained. It manages this via the ECU delivering a richer cocktail to the cylinder when the engine is cold, thus allowing hassle-free starts and glitch-free riding during the first few kilometres of the day.

Carburettors are simply no match for an EFI system and Indian bikes will do well to switch to the latter. One added negative carb effect is that air needs to pass through the bottle neck in a venturi at all times. At high engine speeds, this sometimes limits the amount of air that can be shovelled through. EFI-equipped engines do not have to deal with this as the air channel does not need to have any restriction.

Greener emissions, higher and smoother power output and better fuel economy are all benefits to be allied with electronic fuel injection. So while some may lament the loss of the long-lived and successful carburettor, it might soon be time to stash them away as valuable bits of India’s unique motorcycling history.