Pos. |
Designation |
|
Valve |
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Spark plug |
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Piston |
Normal Combustion
The figure shows the desired type of combustion of the gas/air mixture in the combustion chamber. The ignition spark ignites the gas/air mixture. The flame front spreads out evenly in the combustion chamber with the specific laminar flame speed of the gas/air mixture. The cylinder pressure increases slightly during combustion.
Knocking Combustion
Knocking combustion arises if the gas/air mixture self-ignites before the actual flame front, but after the ignition pulse . This system does not detect so-called pre-ignition.
The reason for this is an excessive increase in pressure and temperature of the as yet non-combusted mixture due to the pressure and temperature fronts preceding the normal flame front. The pressure and temperature fronts arising from the self-ignition, in turn, make further self-ignitions possible. High-frequency pressure waves arise in the combustion chamber, which are introduced into the engine structure via the walls of the combustion chamber and released as air-borne noise into the environment. The knocking becomes audible in this way .
Compared to normal combustion, significantly higher peak pressures arise, which may lead to major engine damage in addition to the higher thermal load.
Detonation Controller – System Overview (Example)
Pos. |
Designation |
Pos. |
Designation |
---|---|---|---|
DetCon detonation controller |
Binary outputs (alarm, load reduction and engine stop) |
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Detonation sensor wiring |
Power supply 9 V DC at 36 V DC |
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Detonation sensor |
PowerView3 HMI module* |
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Wiring rail (ignition) |
ALL-IN-ONE generator & CHP control system* |
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MIC ignition controller |
Computer |
*Visualization via the MOTORTECH PowerView3, alternatively via the MOTORTECH ALL-IN-ONE generator & CHP control system
Detonation Controller
The function of the DetCon detonation controller is to prevent engine from damage caused by knocking combustion.
Vibration occurs in the engine compartment during the combustion process. These have a frequency which is characteristic for the engine type. The DetCon measures the vibratory energy within a narrow frequency range which is typical for the respective engine. The energy measured is proportional to the knocking level.
The measurement is only carried out within operating cycles in which combustion is possible. This increases the sensitivity of the measurement and minimizes the reaction to random noises. The operating cycles are determined according to application and the ignition controller used via an auxiliary synchronization output (ASO), an ignition sensor unit (ISU) or a camshaft sensor.
The following diagram and the description below it illustrate the basic control process of the system:
Term used in diagram |
Description |
---|---|
Knocking Level |
Example of the progression of knocking energy |
Immediate stop limit |
The maximum value at which the engine is stopped. |
Ignition reduction limit |
The maximum value at which an ignition timing adjustment is performed. |
Engine Knocking (binary output) |
Signal at the binary output indicating knocking. |
Load Reduction (binary output) |
Signal at the binary output effecting load reduction. |
Trip (binary output) |
Signal at the binary output indicating that the Immediate stop limit has been exceeded or a defective sensor detected. |
Timing Reduction (analog output) |
Curve of the analog signal for ignition timing adjustment |
Max. level of analog output |
Maximum value of the ignition timing adjustment |
Timing reduction gain |
Speed of the ignition timing adjustment |
Decrease ramp |
Speed of reduction of the ignition timing adjustment |
Delay after load reduction |
Delay time after a load reduction |
The measured knocking energy (Knocking Level curve) is compared in every cycle with an preset maximum value (Ignition reduction limit). If this maximum value is reached, the binary output Engine Knocking is activated. At the same time, the analog outputs change their values (Timing Reduction curve). The rate at which the value of the signal changes is specified by the setting Timing reduction gain. The analog signals are transmitted to the ignition controller, thus adjusting the ignition timing. If this causes the knocking energy to fall below the maximum value, the value at the analog outputs is also reduced. The rate of this reduction is adjusted according to the preset value Decrease ramp.
If the ignition timing adjustment can no longer be corrected via the analog outputs and the engine is still knocking, the binary output for load reduction (Load Reduction) is activated. A master control system (e.g. ALL-IN-ONE) can control load reduction via this output.
The load reduction (Load Reduction) is deactivated again if the engine knocking stops. However, the analog outputs remain active for a further period which is set via the function Delay after load reduction. This period has to be longer than required for reaching full load.
The binary output Trip is activated when the knocking exceeds the maximum value Immediate stop limit. This can be used as an emergency stop signal to force the engine to stop.
Checkbox Enable bad sensor detect Activate the checkbox so that defective detonation sensors are indicated via the status display BAD SENSOR. This function only detects sensors which provide faulty signals. If a wire has ruptured or a sensor gives no signals for some other reason, it is not indicated on this display. If a defective sensor is detected, the binary output Trip is also activated. |