Ionization Signal Knock Detection in Lean-Burn Engines

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Solution Overview

Problem

Existing knock detection systems in spark-ignition engines, particularly in lean-burn operations, struggle to reliably detect incipient knock due to high noise susceptibility and low ionized species concentration, leading to inefficient engine operation and potential damage from engine knock.

Innovation Solution

A system and method utilizing a spark plug with an electrical circuit to detect ionization signals during the thermal-ionization phase, allowing for closed-loop ignition timing control to prevent incipient knock by monitoring and adjusting the crank angle to avoid knock frequencies, thereby maintaining optimal engine efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If ion sensors are used for knock detection in lean-burn engines, then cost is reduced compared to in-cylinder pressure sensors, but measurement precision deteriorates due to low ionized species concentration and high noise levels

Engineering Contradiction:

Improvesensor costVSAvoidknock detection precision

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The system performs preliminary integration of the ion signal over a predetermined time period before knock detection. This preliminary action accumulates the weak ion signal energy, making it sufficient for reliable knock detection in lean-burn conditions where ionized species concentration is low.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses the integrated ion signal to provide feedback for controlling the ignition system. This feedback loop allows the control system to adjust ignition timing based on actual knock conditions detected by the ion sensor, optimizing engine performance while preventing knock damage.

Inventive Principle:

Principle #23Feedback

2Device complexity

If accelerometer-based knock sensors are used, then device complexity is reduced, but reliability deteriorates due to susceptibility to electrical noise and mechanical vibrations

Engineering Contradiction:

Improvesensor structureVSAvoidknock sensing reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent replaces the mechanical accelerometer-based knock sensing system with an electrical ion signal detection system. The ion sensor detects ionized species directly in the combustion chamber, providing electrical signal-based knock detection that is immune to mechanical vibrations and external electrical noise interference.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Speed

If ion sensors are used without signal integration, then response time is reduced, but measurement precision deteriorates due to low signal magnitude

Engineering Contradiction:

Improvedetection response timeVSAvoidion signal magnitude

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

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

This approach effectively detects incipient knock and prevents engine knock, enhancing thermal efficiency and extending the safe operating regime of lean-burn engines by accurately adjusting ignition timing based on ion current measurements.

Implementation Method 1

detecting an ionization signal within a combustion chamber of the SI engine that is indicative of incipient knock

Methodology Applied

Scientific EffectIonization: Ionisation

Implementation Method 2

provide a second voltage to the electrode to create a spark and initiate a combustion process within the combustion chamber

Methodology Applied

Scientific EffectElectric Spark: Electric Spark

Data Source

PatentUS7798124B2Method and system for closed loop combustion control of a lean-burn reciprocating engine using ionization detection

Publication Date: 2010.09.21 WOODWARD INC

AI summary

A system and method for controlling knock in a lean burn internal combustion (IC) engine includes a spark plug having an electrode, an electrical circuit, and a controller. The electrical circuit is configured to provide a first voltage to the electrode and detect an ion current during a thermal-ionization phase of the combustion process, and provide a second voltage to the electrode to create a spark and initiate a combustion process within the combustion chamber. The controller is configured to monitor the ion current for a knock condition that includes at least an incipient knock condition, determine a crank angle of the IC engine where the incipient knock occurs, and adjust timing of the IC engine to operate at a crank angle that does not exceed a threshold level beyond inception of incipient knock.