All about the ignition system part 1

Different types of Ignition System 

  The engine is a concert off all subsystems: Air intake, EGR, Camshaft etc...All for the sake of a most powerful, most efficient combustion that brings torque and power and delivers less pollution possible to the environment. Ignition system is one of the most important engine subsystem that all other systems are timed together to deliver: a spark.

Remember the good old mechanical distributor? Everything is there: Ignition switch, Battery, Ballast resistor, Primary & secondary coils, The Rolling Distributor and all the spark-plugs, and don't forget the old-tech vacuum advance. The goal of the WHOLE thing is to create a spark, through a small gap on the spark plug right? Well if this is the kind of circuit you'd want to build to make your dream come true, lets go back to physic 101, 3 theory lessons: 
1. How induction works?
2. What is a transformer?
3. And Explain why lightning happens?

Lets start with the ignition switch, you switch on to start the engine also mean you are starting the ignition system. Ignition switch opens the path for battery to reach the primary coil. The ground side of the primary is through the Breaker point mechanism, which is brought connected, disconnected by a rotor cam lobe.

On the secondary side, its job is to deliver the Induced High Current Voltage (from 20000V up to 100000V) thought the spark plugs. A current with a voltage that enormous will easily "jump" the gap on the spark plugs to engine's ground, thus a spark to ignite the combustion is created.
Where do we get that amazingly high voltage? One word: Induction. The coils & Breaker points mechanism are the key for this miracle to happen. In a circuit where battery voltage is to power a coil, its maximum current does not immediately reached. And while it takes a little time for the current to build up on a coil, it induces a voltage so called Electromotive Force (EMF). Next, imagine if you have another coil nearby positioned appropriately, that voltage will get induced into it, we call it "mutual inductance". This law of physic is also applied in the invention of the transformer - namely our primary and secondary coil.
    

 Through the core, a sudden change in current in primary leads to a huge change in magnetic flux and travels to the secondary winding and gets amplified into multiple times larger. As a result, a very short but enormous voltage discharge from 20000V+ through the gap of the spark plug. Yet, this voltage would never be achieved without what had mentioned: a sudden change of current/ magnetic flux. It seems that the time it takes to maximize the current in primary is not as small as the time it collapses. And the less time it takes for change, the more voltage induced. A conventional mechanism that was very good at this is the Breaker Point with its Cam Follower. Each cam lobe angle(no. angle = no. cylinder) rotate to open/close the primary grounding, leading to the build-ups and collapses. 

Yet, the timing is a BIG issue. For best compression/power output/emission, the spark must be at the right places when it comes different engine condition. Hence we had vacuum advance, and centrifugal advance to overcome this in the past. Sure fuel burns @ roughly constant rate, but as RPM increases there is less time to burn, so spark is advanced. And when at lean idle/ low load cruise, mixture doesn't burn as fast as rich mixture so timing also needs to be advanced, so there is more burn time. And when the engine runs rich on cold starting, in low RPM, fuel burns even quicker than engine speed so retarding the timing is also necessary. Vacuum advance does advance the spark when there is high vacuum in the intake so it is made for idle/ cruising speed but lean mixture, while centrifugal advance is does more advancing at higher speed.

  Nowadays that we have electronic/ distributorless/ integrated ignition systems, the principal of delivering the spark is virtually exactly the same, after about 80 years of "evolution". Instead of having a rotor that spins around all the time to distribute very high voltage/material corrosive spark, why not having ECU ground each single spark plug at the exact time we want? Why bother having a spinning cam follower that pushes on the point breaker suffering the spark and corrosion, when we can use ECU to switch on, off the primary etc... Virtually, making mechanism to handle electrical function is mostly not the best idea, but using electrical processor and circuitry itself, and that the way engineers have been thinking.

    Last but not least about the theory, you ever wonder how electricity can "jump" a gap? It is as simple as the natural lightning phenomenon.

Isn't it when electricity can't get through air, then a huge voltage one just might do it for fractions of a second? Isn't it lightning is just simple as so many positive charges trying to get down to its grounding? Obviously if lightning can make a 10Mega Volt up to 120k Amps jumping a "gap" of sky high in just 30 nanoseconds, then we might as well can create a spark of just 40kV jumping a few milimeters. But why some engine sparks just 20000V while some spark even up to 100000V? Will it affect the burn rate of the mixture? Or make the exhaust gas hotter? etc... One thing for sure, engines that run higher Octane fuel will need bigger Voltage sparks, because they require hotter sparks to ignite.

  Also, we can't forget the condenser, which is actually a coil of wire that "catches" any voltage spike or surges when the breaker point opens and closes. This little device is very important because the real "spike" that we want belongs to the 2nd winding, not the intermittent, lousy surge that residue after primary collapses, which will gradually destroy the points. Plus, all that surges are stored and sent back to the primary when the dwell period starts( points close) again, results in longer, hotter spark, which is better for performance of course.

   

 Enough about level 3 Physics, lets move on to the real deal: more advanced ignition systems. But before we do, I need to address that the conventional ignition system is not just another method of delivering a spark, it is actually THE ONLY WAY yet to deliver a spark. Even if we have some fancy Coil-on plugs, Wasted spark, or Electronic etc...the circuit's principal stays the same, especially there are as many FUNCTIONS, or PROCESSES in the conventional as there are many in either Distributor less, Wasted Spark or Electronic etc... My point is the new ignition systems is just new materials, new modifications, not new methods, NOT a car with a N/A engine and a hybrid car calling themselves a real difference.

  Lets review all the "compulsory" functions inside any ignition system: battery supplying, current-controlled ballast resisting, points contact closing: Dwell period, opening: EMF discharged, residual voltage spike absorbing(Condenser), the amplification and inductance of 2 coils, and finally, the spark grounding(delivering) for each cylinder(simultaneous; grouped; sequential). These are must-occur processes, if one of these fails, the spark is considered malfunction, that means the engine will NOT run properly. And each and every single one of these processes will occur one way or another inside the other types of ignition system.

  

Electronic Ignition System

  Oops! Where is the Breaker points and it's Condenser? Instead, this system has a power transistor inside a module that receives converted digital ON/OFF signal from the ECU, (or from distributor). The reason the ECU can decide when to switch ON or OFF the power transistor WITHOUT a Breaker point mechanism is that it receives signals from NE(speed sensor) and G(crank position sensor) and process it to work out the right cylinder and the right time, using its intricate microprocessor.

  The main difference in structure between electronic and mechanical is the Ignition module or so called "IGniter". When the On/OFF signal is sent, the power transistor will get turn on or off, allowing primary current to build up and cut it, leading to voltage inductance into secondary coil. The picture above shows the earliest Electronic Ignition System, which only replaced the Mechanical by its Breaker points mechanism. And still, it received Digital Signal from a mechanis (Pickups Coil, Hall-effect, Photo sensitive etc...)

The fact that this small change was called Electronic Ignition makes it sounds like there is a WHOLE new way of delivering spark. But really, this is just a new way to switch between building up and collapsing primary current. The rest of the system: 100% similar to the Conventional.

Disadvantages started to disappear as there is less mechanical part, hence destruction from voltage spikes to Points is eliminated, enduring the performance and reliability of components.

But the BIGGEST advantage of electronic Ignition is the fact that ADDONS are now easier to develop because instead of being considered as an additional device of chunky mechanical pieces, it is only a matter of a little bit more programing, chip, circuitry etc...which might be more sophisticated in development but production, installment and maintenance are much more comfortable and reliable to achieve.

For example, would we need a vacuum advance and a mechanical advance anymore when the computer is deciding when to spark? and it is not only an open loop computer it is closed loop: it means all the sensors' data is continuously fed and processed to give out best actuation...ALL the time. Ignition timing can be compacted into just some additional circuitry, like the ESA  or integrated chip- VAST from Toyota:

 Also, circuit breaker/ protector like the Darlington's circuit; Primary & Secondary coils etc... can also be integrated into 1 unit, making it easier for installment & replacement. And we call these Integrated Electronic Ignition system. It's really nothing but a more convenient Electronic Ignition System. But still, these system compares to the Electronic Ignition System with no computerized switch signal, is a real big leap.

  

Integrated Electronic Ignition System

Any Ignition System that uses the same method of delivering spark but is more advanced in structure layouts, circuitry, modification etc... can all be considered an Integrated Electronic Ignition System. With Integrated, there is mainly no DIY modification on the system to improve any sort of performance but the spark plugs. It is in fact most manufacturers' intention to integrate all the important components into 1 unit for ease of manufacturing, reducing cost, maintenance and usage. This also means that if there is a fault in the ignition system for which doesn't deliver a spark in just 1 cylinder, I'm afraid you will have to replace the WHOLE unit, as well as you will be fine if you have insurance for the unit. IF you are keen for a little bit of science, stick around a little bit more because there are still some disclosures from manufacturers, wanting to explain to their auto electricians how their magic boxes work so they don't look ridiculous in front of customers.

Distributor-less Ignition 

There are 2 common types of distributor-less Ignition System: Wasted-Spark EIS and Coil-on Plugs EIS, which of course don't have any distributor-like mechanism. Instead, they can fire induced voltage directly from secondary coil to the right spark plug, at the right time. How?

Wasted-spark  

This is quite a special lay-out, can only be used on engines with even number of cylinders, preferably 6. The main components are consist of: CAM or Crank sensor; Igniter, and The Coils...and there are 3 coil packs inside since there are 6 cylinders. 

The key operation of this type lies in the sophisticated Igniter and the "Discharge circuit".

The Igniter, in this case for 6 cylinders, will have 3 Drive circuits each responsible for "driving" 2 spark plugs, giving that the positions of the chosen pair gives the engine the best vibration balance: 1-6; 3-4; 2-5 etc...The rest of the control circuit is still controlled by the ECU. There are 4 types of signal that makes this EIS a complete Closed-Loop Ignition system: 

   IGdA & IGdB for the 3 "spark-driving" circuits: these 2 give the Cylinder Identification Circuit some sort of Binary codes to work out which is the right cylinder to fire. For example, from 0 and 1, there are 4 "permutation" possible like 00, 01,10,11. So for each out come, the CIC will tell which drive circuit will fire. However, IGdA is out-of-phase with IGdB so that they will never give out "11", because that means 2 drive circuits will fire at the same time- impossible for the crankshaft position to be right.

  The discharge circuit is what defines Waste Spark Ignition. For each pair of spark plug for eg: 1 and 6, they are in series so that when the first one fires, the spark travels through ground and goes back to the companion spark plug, creating another spark. This is timed so that one fires @ TDC of compression one fires at TDC of the exhaust stroke. This has an advantage of burning off unburnt fuel from the main combustion, creating a little more power when the piston is about to go down.

Coil-on Plugs(COP)

 The latest advance in Electronic Ignition, the COP system minimizes mechanical appearance at maximum level:

No distributor, no condenser, no Breaker Points, and very very short secondary HIGH TENSION CORD.

Because, everything that makes the COP looks mystical, sophisticated but surprisingly & extremely reliable: The Igniter and coils pack and all the timing advance circuits are all CRAMPED, in other word, integrated into one single unit, and each cylinder has 1 unit that we call this is the Direct Ignition System. 

   This is the most reliable, advanced set up of EIS that is popularly available on the market. Comparing to its friend, the Wasted Spark, the Igniter or Ignition Module are basically similar since all the basic process like Cylinder selection circuit, current limiting, Ignition Identification Feedback, Dwell Timing Advance circuit...But this time, each Spark plug will have its own Power transistor/ Darlington, and coils pack, this means there is a big leap from the Wasted spark here. Not only the Waste spark "wastes" a spark on Exhaust stroke, which can bring a small benefit but it is mainly a disadvantage. As spark plug gets damaged faster, the high tension cord will get corroded faster leading to current leak, which in time will weaken the spark. And yes, there are still quite a length of secondary high voltage delivering cord here, so Electrical 101, less wire length, less resistance, less time travel. 

  Talking about timing, if high voltage takes less to get to the spark plug, it means there is more time for spark "saturation", thus more powerful spark is achieved making it possible for the engine to run leaner with significantly less chance of miss-firing, all in the favor of having a few micro seconds more.

  Still, this is a mortal's creation which is not 100% immune to all the ignition problems, but its capability of narrowing all trouble down to 1% keeping us moving forward.