Spark Plug Ionization Current Signal Separation for Combustion Pressure Estimation
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Solution Overview
Problem
Existing methods for monitoring ionization current in spark ignition engines face challenges in discriminating ignition discharge current from ionization current, especially during initial flame propagation, leading to unexploited information and unreliable diagnostics.
Innovation Solution
A method involving a resistive element connected to the spark plug's ground electrode, allowing current sensing and voltage measurement to filter out high-frequency noise, with data processing to extract features like time delay and amplitude from the ionization current waveform, correlated with combustion chamber pressure using a mathematical model and look-up table.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inductive ignition system is used to generate spark discharge current, then reliable ignition is achieved, but ionization current is masked by the large discharge current during initial flame propagation
Solution Approach 1:
The patent segments the current measurement into two distinct components: the high-frequency spark discharge current and the low-frequency ionization current. By using a current sensor to detect the total current and then applying signal processing techniques (bandpass filtering, Hilbert transform), the system separates these components in the frequency domain, allowing accurate detection of ionization current despite the presence of the much larger spark discharge current.
Solution Approach 2:
The patent introduces an intermediary signal processing system that acts as a mediator between the raw current sensor output and the ionization current measurement. The bandpass filter (5-500 Hz) and Hilbert transform serve as intermediaries that extract the ionization current component from the composite signal, enabling accurate measurement without requiring separate physical sensors.
2Loss of information
If high frequency components of current are allowed to circulate in ignition coil windings, then complete current measurement is achieved, but information is lost due to dissipation as waste heat in magnetic core
Solution Approach 1:
The patent replaces the traditional approach of allowing high-frequency current to physically circulate through the ignition coil with an electrical field-based measurement approach. The current sensor measures the high-frequency discharge current as an electrical signal, and the information is extracted and processed electronically without requiring the energy to be dissipated in the magnetic core. This substitution preserves both information and energy.
3Measurement precision
If additional electrodes are added inside combustion chamber to detect ionization current during initial spark phases, then detection capability is improved, but device complexity increases
Solution Approach 1:
The patent makes the existing spark plug electrodes multi-functional: they serve both their primary function of generating the spark discharge for ignition and their secondary function of sensing the ionization current during flame propagation. The same electrode structure that creates the spark also detects the ionization current, eliminating the need for additional dedicated sensing electrodes inside the combustion chamber.
Solution Approach 2:
The spark plug system serves itself by using its own electrodes to detect the ionization current. The electrodes that generate the spark also function as the sensing elements, allowing the system to monitor its own combustion process without requiring external or additional sensing components inside the combustion chamber.
4Measurement precision
If Blind Source Separation method is used to discriminate ignition spark discharge current from ionization current, then signal separation is achieved, but effectiveness is reduced in case of significantly corrupted current signals
Solution Approach 1:
The patent applies preliminary signal processing actions before attempting to separate the signal components. A bandpass filter (5-500 Hz) is applied first to remove high-frequency noise and interference, and a Hilbert transform is applied to obtain the analytic signal and extract instantaneous amplitude and phase information. These preliminary actions prepare the corrupted signal for more reliable separation and analysis, improving robustness against signal corruption.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables reliable real-time evaluation of combustion chamber pressure and other parameters without additional sensors, enhancing diagnostic accuracy and robustness by filtering noise and correlating waveform features with environmental conditions.
Implementation Method 1
providing a resistive element connected to the ground electrode of the spark plug, such that when the spark plug is mounted in a SI engine combustion chamber, the ground electrode of the spark plug becomes electrically connected to the engine body through a resistive element interposed therebetween in the flow path of the ionization current
Implementation Method 2
ionization current diagnostics has proven itself to be an effective approach in investigating the mechanism of fuel combustion
Data Source
AI summary
The pressure in the combustion chamber of an electronically controlled spark plug ignition engine may be estimated in real time mode without specific sensors by processing sensed ionization current data to calculate features of the current waveform proven to be correlated to the pressure inside the engine cylinders and correlating them on the basis of a look up table of time invariant correlation coefficients generated through a calibration campaign of tests on a test engine purposely equipped with sensors. A mathematical model of the electrical and physical spark plug ignition system and combustion chamber of the engine is refined during calibration by iteratively testing the interactive performance of correlation coefficients of related terms of a mathematical expression of the model and comparing the expressed pressure value with the real pressure value as measured by a sensor.