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The new V8 Power Unit for the BMW M3 - Ion Flow Technology and Spark Plugs

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The new V8 Power Unit for the BMW M3
High-speed engine
Formula1 foundry Engine block
Oil supply and Intake System
Dynamic Performance and Engine Management
Ion Flow Technology and Spark Plugs
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The highlight in engine management: ion flow technology
One of the highlights of the engine control unit is ion flow technology serving to determine the risk of the engine knocking as well as misfiring and miscombustion. This significant innovation from BMW was introduced as a standard feature for the first time on the V10 power unit in the BMW M5. Now, in its latest configuration, ion flow technology no longer requires an ion flow satellite, whose function has been integrated in the ignition coil.
“Knocking” is undesired selfignition of fuel in the cylinder. Engines without knock control have a lower compression ratio and their ignition point comes later (retarded ignition), since the engine would suffer from going beyond the knock limit. However, this “safety margin” costs fuel, engine power, and torque.
By contrast, active knock control allows the engine to run with optimum ignition timing and protects the engine from damage. It also offers the highest standard of efficiency.


With conventional anti-knock control sensors measuring body sound are fitted outside on the cylinder. But the ability of such sensors to detect knocking in the combustion process decreases with increasing engine speed and a growing number of cylinders – and particularly such accuracy and reliability is essential on a fast-revving eight-cylinder in order to optimise combustion quality in the cylinders and, as a result, the service life of the battery and the exhaust emissions. Hence, ion flow technology measures the risk of knocking exactly directly where this phenomenon occurs – within the combustion chamber.
In this process the system uses a physical phenomenon resulting from the high temperatures of up to 2,500 oC encountered in the combustion chamber during the combustion process. These high temperatures and the chemical reactions occurring during combustion serve to partially ionise the fuel/air mixture inside the combustion chamber, this gas becoming electrically conductive particularly along the flame front due to the generation of ions resulting from the separation and deposition of electrons (ionisation). The so-called ion flow generated in this way is measured between the electrodes by an electronic measurement unit electrically isolated from the cylinder head and interacting with engine management. This unit is inte-grated in the ignition coil and interacts with the spark plug electrode to which a specific direct current is applied to generate the signal required. This signal, in turn, depends on the degree of gas ionisation between the electrodes.
Measurement of ion flow thus provides information on the combustion pro-cess directly where combustion takes place. The electronic “brain” integrated in each ignition coil receives the signal from the spark plugs on all of the eight cylinders, reinforces the signal and conveys this data to the engine management unit. Analysing this incoming data, engine management then controls the cylinders as required, for example by adjusting the point of ignition ideally to the combustion process for the purpose of efficient knock management.
Using an innovative semi-conductor circuit to measure the control voltage required and reinforcing/multiplying the incoming signals in a variable process, the engineers at BMW M have raised ion flow technology to an even higher level in an important new step. And now this circuit control is integrated directly in the ignition coil together with the terminal stage of the ignition for the first time in the new BMW M3, detecting the ion flow signal even more directly within the combustion chamber, then reinforcing the signal and breaking it down into individual elements for even finer measurement.

Spark plugs taking on additional control functions
This technology thus uses the spark plug in each cylinder to sense and, if necessary, control the risk of knocking. At the same time it supervises the ignition and recognises any misfiring. In other words, the spark plug serves as a calculator for the ignition and as a sensor monitoring the entire combustion process, distinguishing between misfiring and mis-combustion. And precisely this dual function performed by the spark plug facilitates diagnostic processes in the maintenance and service of the car.



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