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Abstract : It is very interesting to know about complete combustion in automobile engineering. Because in actual practice ,perfect combustion is not at all possible due to various losses in the combustion chamber as well as design of the internal combustion engine. An alternate solution to it is by making the combustion of fuel as fast as possible. This can be done by using two spark plugs which spark alternatively at a certain time interval so as to increase the diameter of the flame and burn the flame instantaneously. This system is called DTSI (Digital Twin Spark Ignition). In this system, due to twin sparks, combustion will be complete. Spark ignition is one of the most vital systems of an engine. Any variation in the spark timing and number of sparks per minute affects the engine performance severely. Thus a good design and control of the system parameters becomes most essential for optimum performance of an engine. Due to Digital Twin Spark Ignition system it is possible to combine strong performance and higher fuel efficiency. DTSI offers many advantages over conventional mechanical spark ignition system. This paper represents the working of digital twin spark ignition system, how twin sparks are produced at 20,000 volts, their timings, efficiency, advantages and disadvantages, diameter of the flame, how complete combustion is possible and how to decrease smoke and exhausts from the exhaust pipe using twin spark plug.
INTRODUCTION
One of the requirements of an efficient engine is the correct amount of heat shock, delivered at the right time. This requirement is the responsibility of the ignition systems. The ignition system supplies properly timed high voltage surge to spark plugs. These voltage surges cause combustion inside the cylinder. The ignition system must create a spark or current flow across the each pair of spark plug electrodes at the proper instant, under all engine-operating conditions. This may sound relatively simple, but when one consider number of spark plug firing required and extreme variations in engine operating condition, it is easy to understand why ignition system so complex.[5] If a 6-cylinder engine is running at 4000rpm, the ignition system must supply 12,000 sparks per minutes because ignition system must fire three spark plugs per revolution. These plugs firing must also occur at the correct time and generate correct amount of heat. If the ignition system fails to these things, fuel economy, engine performance, and emission level will be adversely affected.[1]
Purpose of ignition system: For each cylinder in an engine system has three main jobs. It must generate an electric spark they has enough heat to ignite the air/fuel mixture in the combustion chamber. It must maintain the spark long enough to allow for the combustion of all the air and fuel in the cylinder. It must deliver the spark to each cylinder so combustion can begin at the right time during the compression stork to each cylinder.[3]
Ignition timing: Ignition timing is very important, since the charge is to be ignited just before (few degrees before TDC) the end of compression, since when the charge is ignited, it will take some time to come to the required rate of burning.[1] All ignition-timing changes are made in response to following primary factors. . Engine R P M
. Engine load
Engine RPM: At higher rpms, the crankshaft turns through more degrees in a given period of time. If combustion is to be completed by 10 degrees TDC, ignition timing must occur sooner or be advanced. However, air/fuel mixture turbulence increases with rpm. This causes the mixture inside the cylinder to turn faster. Increased turbulence requires that ignition must occur slightly later. Therefore, while the ignition timing must be advanced as engine speed increases , the amount of advance must be decreased some to compensate for the increased turbulence.[3]
Engine load: The load on engine is related to the work it must do. Driving up hills or pulling extra weight increases engine load. Under load, there is resistance on the crankshaft
therefore the piston have a harder time moving through their stroke. This is evident by low measure vacuum during the heavy loads. Under heavy loads, when the throttle is opened fully, a larger mass of air/fuel mixture can be drawn in, and the vacuum in the manifold is low. This results in high combustion pressure and rapid burning . In such a case, the ignition timing must be retarded to prevent complete burning from occurring before 10 degrees TDC.[2]
Ignition advance: The purpose of spark advance mechanism is to assure that under every condition of engine operation, ignition takes place at the most favorable instant in time i.e. . most favorable from a standpoint of engine power, fuel economy and minimum exhaust dilution. By means of these mechanisms the advance angle is accurately set so that ignition occurs before TDC point of the piston. The engine speed and the engine load are the control quantities required for the automatic adjustment of the ignition timing. Most of the engines are fitted with mechanisms which are integral with the distributor and automatically regulate the optimum spark advance to account for change of speed and load. . The two mechanisms used are :
(a) Centrifugal advance mechanism.
(b) vacuum advance mechanism.
Firing order: The order or sequence in which the firing takes place, in different cylinders of a multi cylinder engine is called Firing Order. In case of SI engines the distributor connects the spark plugs of different cylinders according to Engine Firing Order. The firing order is arranged to reduce rocking and imbalance problems. Because the potential for this rocking is determined by the design and construction of the engine, the firing order varies from engine to engine. Vehicle manufacturers simplify cylinder identification by numbering each cylinder
ENGINE CONSTRUCTION
The engine used on the Alfa 164T. spark is a four in line cylinder unit whose weight has been considerably reduced with all aluminium-alloy engine block, cylinder head, oil sump and tappet covers.
Eight counterweights ensure optimal balancing of the high strength nitride steel crankshaft.
The pressed in cast iron cylinder liners feature wet mounting for mare effective heat dissipation.[6]
Constructional detail: The construction of DTSI engine is same as that of the conventional 4-stroke engine. It consists of following parts:
• Piston
• Cylinder
• Crankshaft
• Connecting rod
• Fly wheel
• Carburetor
• 2-sparkplug
• 2-ports
• 2-valves
Here the only change made is that the 2 spark plug placed at the two opposite end of the combustion chamber are at 90 degree to each other. [6]
MAIN CHARACTERISTICS
• Digital electronic ignition with two plugs per cylinder and two ignition distributors;
• Twin overhead cams with camshaft timing variation;
• Injection fuel fed with integrated electronic twin spark ignition;
• A high specific power;
• Compact design and superior balance;
This power unit, equipping the naturally aspirated 2-litre used on the Alfa 164, is a direct dilative of the engine fitted on the 2.0 twin spark version of the Alfa 75, a recent addition to the Alfa car range. It includes a number of exclusive engineering solutions resulting in superior power output and exceptional peak torque for this cylinder capacity. Its main characteristics are:
• Digital electronic ignition with two plugs per cylinder and two ignition distributors;
• Twin overhead cams with camshaft timing variation;
• Injection fuel fed with integrated electronic twin spark ignition;
WORKING
DTSI Engine has two spark plugs located at opposite ends of the combustion chamber and hence fast and efficient combustion is obtained. The benefits of this efficient combustion process can be felt in terms of better fuel efficiency and lower emissions. The ignition system on the twin spark is a digital system with static spark advance and no moving parts subjected to wear. It is mapped by the integrated digital electronic control box which also handles fuel injection and valve timing. It features two plugs per cylinder.
The innovative solution, also entailing a special configuration of the hemispherical combustion chambers and piston heads, ensures a fast, wide flame front when the air fuel mixture is ignited, and therefore less ignition advance, enabling, moreover, relatively lean mixture to be used. This technology provides a combination of the light weight and twice the power offered by two stroke engines with a significant power boost, i.e. a considerable power to weight ratio compared to quite a four stroke engines.
Moreover, such a system can adjust idling speed and even cuts off fuel feed when the accelerator pedal is released, and meters the enrichment of the air fuel mixture for cold starting and accelerating purposes, it necessary it also prevents the upper rev limit from being exceeded. At low revolutions, the over boost is mostly used when overtaking, and this is why it cuts out automatically. At higher speeds the over boost will enhance full power delivery and will stay on as long as the driver exercises maximum pressure on the accelerator.
CONCLUSION
Hence it can be concluded that the application of these technologies in the present day automobiles will give the present generation what they want i.e. power bikes with fuel efficiency. Since these technologies also minimize the fuel consumption and harmful emission levels, they can also be considered as one of the solutions for increasing fuel costs and increasing effect of global warming. The perfect Combustion in Internal Combustion engine is not possible. So for the instantaneous burning of fuels in I.C. engine twin spark system can be used which producing twin sparks at regular interval can help to complete the combustion. Thus, it is better in all areas like power, speed, efficiency and clean emission and hence it has brought a new evolution in automobile industry.