1. introduction 1 Purpose of Ignition System

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 .High combustion pressure and rapid burning results. In such a case the ignition timing must be retarded to prevent complete burning from occurring before 10 degrees ATDC.

Digital ignition system is same as an electronic ignition system in which spark timing is controlled by a computer that continuously adjust ignition timing to obtain optimum combustion. The ignition system on the Twin spark is a digital system with static spark advance and no moving parts subject 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. This 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 mixtures 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 few four-stroke engines. The actual picture of Bajaj Pulsar Bike is - Moreover, such a system can adjust idling speed & 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; if necessary, it also prevents the upper rev limit from being exceeded. At low revs, 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.

Figure 3: Cut Section view of DTSi Engine of Pulsar 2 Valve DTSi engine

1. 
   Main Characteristics of DTSi System
   

1. 
   Digital electronic ignition with two plugs per cylinder and two ignition distributors; (in case of multi cylinder TS engine )
   
2. 
   Twin overhead cams with camshaft timing variation;(for 4 valve)
   
3. 
   Injection fuel feed with integrated electronic twin spark ignition;
   
4. 
   A high specific power;
   
5. 
   Compact design and Superior balance.
   

1. 
   Benefits of Twin Spark
   

1. 
   Improved thermodynamic efficiency.
   
2. 
   More effective combustion at yielding and low speed.
   
3. 
   Considerable reduction in specific fuel consumption.
   
4. 
   Reduction in exhaust emission.
   
5. 
   Less chance of ignition system failure
   

The construction of DTSi engine (here we are considering about Bajaj Pulsar 180 DTSi model) is same as that of the conventional 4-Stroke engine. It consists of following parts:

1. 
   • Piston • Cylinder • Crankshaft
   
2. 
   • Connecting rod • Carburetor • 2-sparkplug
   

• Position Sensors • A/D Converter • Camshaft

Here the only change made is that the 2 sparkplug placed at the two opposite end of the combustion chamber. The 180cc Pulsar DTSi engine sticks with the aluminum alloy cased 4 stroke cycle engines that are clearly based on the earlier tried and tested power plant. Its Single cylinder is air cooled % still displaces 178.6cc. Bajaj has used its patented DTSi technology, which ensures the engines twin plugs are set to ignite together in one instant according to need. This means the twin sparks travel to combust mixture from opposite ends of the combustion chamber and accelerate this process thereby delivering higher power output as improved fuel economy. The bike also employs ExhausTEC, or a resonance chamber sitting on the silencer that helps pack a healthy punch low in the bikes power band. This engine gives about 17.02bhp at 8500 rpm & torque of 14.22Nm@6500.

Here we all know about the conventional mechanical parts of engine so we can skip and go to important parts of DTSi engine system. In Pulsar 180 cc DTSi technology based engine is used and it has the technologies called TRICS III and CDI. It works on the DTSi technology, depending on Throttle load, Engine speed and Load, and according sends the signal getting from position sensors.

Figure 4: CAD view of Pulsar 180cc 4valve DTSi Engine

There are some advance technology used in DTSi engine which makes it more powerful than the conventional single sparkplug 4-stroke engine like

1. Tricks III technology

2. CDI technology

These above technologies are discussed below
4.1 CDI

The Intelligent Capacitor Discharge Ignition contains a microprocessor, which continuously senses different speeds and load on engine and responds by altering ignition timing. A Digital CDI with an 8 bit microprocessor chip handles the spark delivery. The programmed chip’s memory contains an optimum Ignition timing for any given engine rpm, thereby obtaining the best performance characteristics from the combustion chamber. Working together with the TRICSIII system, the microprocessor's memory provides optimum ignition timings for any given engine rpm, thereby obtaining the best combustion performance. It improves fuel-efficiency and reduces engine noise and vibration through smoother power delivery.

Throttle Responsive Ignition Control System 3rd generation. It is a means of controlling the Ignition by operating the Throttle. Depending on the needs of the Rider whether it be cruising, acceleration or max speed, the ignition requirements constantly change. Based on a particular amount of Throttle opening, the Magnetic field generated by the Magnet opens or closes the Reed switch. The Reed switch is connected to the Digital CDI, which signals the CDI to change/switch, the desired Ignition Advance Timing Maps. This helps in achieving a good balance between drivability and Optimum Ignition Spark advance, resulting in an almost perfect Ignition Spark advance for every Throttle opening and Engine rpm. Throttle Responsive Ignition Control System - III is an intelligent system which can quickly adapt ignition timing to suit different riding characteristics.

TRICS III helps in achieving a good balance between low-to-mid range torque and top-end power. This helps to ride easily in different conditions like flyovers, hilly areas, dense traffic and highway cruising

5. ADVANTAGES OF DTSI SYSTEM
5.1 Performance

There is a new feel to the power, strong yet not daunting in the least, torque and smooth in its delivery. For 180 DTSi 0 to 80 comes up in 6.8 sec. while 0 to 100 kmph is attained in 14.66 seconds. It is not just raw speeds and times that are impressive but the manner in which the engine just spews the forth the juices in manner in which is thoroughly intoxicating. The pulsar 150 benefits with DTSi technology with all round gains in acceleration and maximum speeds.

Due to DTSi system it is possible to combine strong performance and fuel efficiency. The improved engine efficiency modes have also resulted in lowered fuel consumption. Taking the 180 pulsar first, fuel consumption in city was averaged 43.3 kmph. However she went better in steady speed 80 kmph highway mode she recorded 46 km/l as company noted. Pulsar delivers shattering performance and high levels of actual on road fuel efficiency but that both bikes meet the Government of India’s emission norms for 2005 right now itself without use of any secondary devices.

Figure 5: Comparison of Power of Old Pulsar 180 & New DTSi Pulsar 180

For the number crunches the power output and torque outputs have increased. The graph shows the comparison between original pulsar & pulsar DTSi. The gains are not just in peak power and torque but also in lowering the torque peak and torque spread even better across the rev range. What the DTSi system does is to overcome the problem on a small capacity four stroke engines in a very elegant manner with the use of two spark plugs placed diametrically opposite to each other in the combustion chamber, normal to the valve plane. The initiation of two flame fronts, invoked instantaneously combustion, reduced the required flame travel length required to burn the charge.

The Coefficient of variance of indicated mean effective pressure at part throttle has improved by 50%. For a given fuel ratio when running in part throttle condition the indicated mean effective pressure has gone up by 15% in the Pulsar 180.

This further helped the Bajaj bowfins to mote run the high compression ratio 9.6:1 of the original but with a leaner air furl mixture which its reward in enhanced fuel efficiency without stunting the power & torque produced. Data supplied by Bajaj auto (indicating BSFC- brake specific fuel consumption being reduced by 10% in 150cc & 1.7% in 180cc) & experienced in our tests on both road & track confirmed the enhanced efficiency fuel bits & also bring a smile to the faces of those who forever revel in wringing the throttle wide open. Add to that the virtual absence of knock & one has an engine which many would kill for just to put their names plates on.
At last we can enlist these advantages as follows:

1. 
   Less vibrations and noise
   
2. 
   Long life of the engine parts such as piston rings and valve stem.
   
3. 
   Decrease in the specific fuel consumption
   
4. 
   No over heating & better work output
   
5. 
   Increase the Thermal Efficiency of the Engine & even bear high loads on it.
   
6. 
   Better starting of engine even in winter season & cold climatic conditions or at very low temperatures because of increased Compression ratio.
   
7. 
   Because of twin Sparks the diameter of the flame increases rapidly that would result in instantaneous burning of fuels. Thus force exerted on the piston would increase leading to better work output.
   
8. 
   Twin ignition tends to improve the engine’s fuel consumption under part load operating conditions.
   
9. 
   Twin ignition helps the ignition advance timing to be somewhat retarded which tends to improve the engines smoothness and response.
   

The following are the various statistics showing the advantages of application of DTSi & its derived technologies i.e. the comparison of various aspects of 150 cc category and 125 cc category bikes.

Figure 6: Comparison of various aspects in 150cc category

Figure 8: Comparison of various aspects in 125cc category

• 
  There is high NOx emission
  
• 
  If one spark plug get damaged then we have to replace both
  
• 
  The cost is relatively more
  
• 
  You spend double the amount on spark plugs when it is time to replace them.
  
• 
  The engine tends to overheat and loose power at higher speeds as compared to a single plug engine.
  
• 
  In case the Engine is kept unused for a long time soiling of spark plugs occur. Twin Spark system helps to reduce this problem.
  
• 
  It does not deliver any better mileage and acceleration than that derived from a single spark plug.
  

• 
  Digital Twin Spark – Swirl Induction (DTS - Si)
  

• 
  Digital Twin Spark – Fuel Injection (DTS - Fi)
  
• 
  Digital Triple Spark ignition
  

The DTS-I technology is the parent technology for this latest DTS-Si technology (Used in Bajaj XCD 125, XCD 135). Even though a faster rate of combustion is achieved by incorporating the DTS-I technology, there is a chance for further of improvement of rapid combustion process at lighter loads. When there is a sufficient or heavy load on the engine, the 4 – stroke cycle completes at a faster rate resulting in the faster combustion because of the twin sparks produced by the twin plugs. But when there exists a lighter load on the engine, the 4 – stroke cycle will not complete at a faster rate. Therefore even the incorporation of twin spark plugs cannot aid the faster combustion i.e. still a better rate of combustion can be achieved at lighter loads. Combustion efficiency in lean Air-Fuel mixture conditions can be further improved by generating high turbulence in the combustion chamber. Combustion chambers having low turbulence give rise to propagation of a flame front, which is akin to that of a gradually expanding balloon. This results in a slower rate of combustion and thus slower rate of pressure rise. End result is lower efficiency. When high turbulence is generated and combustion takes place, the surface of the ballooning flame front fragments itself, with projection like fingers, which increases its surface area, thereby improving combustion further. Here comes the Swirl Induction concept, which is meant for producing higher turbulence in the combustion chamber. Swirl Induction is nothing but imparting a swirling motion to the fresh charge that enters the combustion chamber. This can be done by making slight modifications in the ports positioning of engine.

The DTS-Si engine will have two spark plugs but it differs from the parent DTS-I engine in the design of position of the ports. The straight ports used in conventional engines have limitations in generating high swirl values due to their geometry. One of the ways to generate more swirl is to have a port configuration that promotes this phenomena. An offset port configuration was arrived upon and optimized to generate the required swirl numbers. Incorporated in the new engine, this results in a swirling motion of the incoming charge, which decays itself into turbulence as the piston moves in the Induction and Compression strokes. This results in the Air-Fuel mixture being more thoroughly mixed and spread around the combustion chamber. Sparks provided by the twin spark plugs ignite this highly turbulent and compressed Air-Fuel mixture, leading to a flame front with high surface area, resulting in a rapid rise of pressure due to rapid combustion. The values of turbulence achieved now, are substantially higher than that of a straight port cylinder head, such as in DTS-i. A combination of DTS-i and Swirl induction thus provides extremely rapid combustion, resulting in high efficiency.

7.2 Digital Twin Spark – Fuel Injection (DTS - Fi)

DTS – Fi is another advancement of the parent DTS – i technology. This technology is the combination of both DTS– i and fuel injection. This technology is meant for increasing the fuel efficiency in power bikes. Generally in conventional 4-stroke engines, which use petrol as fuel, makes use of carburetor, which mixes the fuel and fresh air in required ratio and supplies the same to the combustion chamber. The process is similar for all loads. But the fuel consumption will be more when there is a heavy load on the engine and it is less when there is a light load on the engine. It is impossible for a conventional carburetor to take care of the fuel supply for these varying loads. Therefore there is a need for some intelligent device that controls the fuel supply according to the varying loads. That so wanted intelligent device is nothing but the Electronic Control Unit (ECU). The Electronic Control Unit is a microprocessor based system and can be regarded as the brain of the fuel injection system. It processes information sent by various sensors and instantly determines optimum fueling and spark timing for various engine-operating conditions. The ECU contains detailed information of the engine's characteristics from which it picks the necessary data for commanding both fueling & sparks timing.

At the heart of the new Pulsar is its cutting-edge engine which sets new benchmarks in performance, emission and incidentally also fuel efficiency. The DTS-i (Digital Twin Spark-ignition) technology launched in 2003 marked a unique first in the history of Indian Motoring. The new Pulsar takes this technology altogether to another level with a SOHC 4-valve Triple Spark engine controlled by an advanced Electronic Control Unit for an absolutely unmatched performance. To support this exhilarating heart-pumping performance the bike comes with liquid cooling and a six speed gear box. The Pulsar 200NS chassis comprises a pressed steel perimeter frame and a Rectangular tube section swing arm delivering over three times the lateral stiffness of a P220 frame. These deliver outstanding high speed handling and cornering stability. The centrally located muffler and the unique gas filled Nitrox mono suspension further improve the ride and handling of the bike due to low & centralized CG position. The Pulsar design character has evolved with the performance & dynamics. It's become stronger, more aggressive with a street fighter stance. The look just begs you to ride it. Once astride, the sporty Speedo console, triple-tree clip-ons, the signature clips and the illuminated switches evoke the design, fit and finish so far exclusively reserved for much more expensive super sports bikes. The new 200cc Pulsar is probably the most stunning sports bike in its class oozing raw muscular appeal. To make use of 3 spark plugs, the pulsar engine houses a pent roof combustion chamber which in turn allows housing 3 spark plugs in the engine chamber. Out of the three plugs, the primary plug is the center one and is mounted in an angle and enters the chamber at the top-center. The other two secondary plugs are mounted below, each opposite each other and one of them being vertically underneath the primary plug. The secondary plugs fires a bit after the primary one has fired and the timings are controlled by the ECU depending on various parameters like throttle position, engine revs, load on engine and much other stuff. According to Bajaj, these plugs gain an advantage in low-rev riding condition where it extracts the best economy.

• 
  Dr. Kirpal Singh, Automobile Engineering. Vol.2, Standard Publishers Distributors, 2009 Pg. No 516 to 607 Engine specifications
  
• 
  John b. Heywood, Internal Combustion Engine Fundamentals, McGraw-Hill Book Co., New Delhi, 2001.
  

• 
  Recent trends in Four-Stroke Internal Combustion Engines of Two-Wheelers Syed Moizuddin1, Naved Ahmad2, Mohammad (IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE) e-ISSN: 2278-1684, p-ISSN: 2320-334X PP 37-41)
  
• 
  Digital Twin Spark Ignition Using Mechatronics by Dattatrey Zambre1, Gaurav Shintre2, Bhagyashri Patil (IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE) e-ISSN: 2278-1684, p-ISSN: 2320-334X PP 73-78)
  
• 
  Comparative study of performance of dual plug and single plug SI engine at different compression ratios By Narasimha Bailkeri1, Krishna Prasad, Shrinivasa Rao (International Journal of Advanced Research in engineering technology Volume 4, Issue 5, July – August 2013, pp. 188-197)
  

• 
  OVERDRIVE –Vol. 6, No.1, September 2003. OVERDRIVE—Vol. 5, No 5, January 2003.
  
• 
  Pulsar DTSi Workshop manual
  
• 
  Auto-car India No. 509 Bajaj Pulsar 180cc DTSi Article
  

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