Low-Pressure EGR System for Spark-Ignition Engine Knock Reduction

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Solution Overview

Problem

Spark-ignition engines face inefficiencies due to low compression ratios to prevent knock, which limits mechanical efficiency and increases emissions, making it desirable to control or minimize knock events.

Innovation Solution

A system incorporating a low-pressure exhaust gas recirculation (EGR) system, controlled by an electronic control unit (ECU), which adjusts EGR flow and temperature to reduce engine knock by managing intake and exhaust gas flows, and using variable valve timing to optimize combustion conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If compression ratio is increased to improve mechanical efficiency, then engine efficiency improves, but knock occurs causing engine damage

Engineering Contradiction:

Improvemechanical efficiencyVSAvoidengine damage from knock

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

Exhaust gas is introduced as an intermediary substance into the combustion chamber to modify the combustion environment. The exhaust gas acts as a buffer that suppresses knock while allowing higher compression ratios, thereby resolving the contradiction between mechanical efficiency and engine reliability

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The composition and temperature of the gas in the combustion chamber are changed by introducing exhaust gas. This parameter change allows the engine to operate at higher compression ratios without experiencing knock, simultaneously improving mechanical efficiency and preventing engine damage

Inventive Principle:

Principle #35Parameter changes

2Reliability

If compression ratio is kept low to prevent knock, then engine reliability is maintained, but mechanical efficiency decreases

Engineering Contradiction:

Improveknock preventionVSAvoidmechanical efficiency

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

Exhaust gas serves as a mediator that enables the engine to maintain reliability while improving efficiency. By controlling the amount and temperature of exhaust gas introduced, the system prevents knock without being constrained by low compression ratio limitations

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system dynamically adjusts the amount of exhaust gas introduced based on operating conditions. This dynamic control allows the engine to optimize the balance between knock prevention and mechanical efficiency across different operating regimes

Inventive Principle:

Principle #15Dynamics

3Productivity

If exhaust gas temperature is increased to improve combustion, then combustion efficiency improves, but knock likelihood increases

Engineering Contradiction:

Improvecombustion efficiencyVSAvoidknock occurrence

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The system changes the temperature parameter of the exhaust gas by introducing it at different stages and mixing it with intake air. This parameter control allows maintaining combustion efficiency while suppressing knock by optimizing the thermal state of the combustion chamber

Inventive Principle:

Principle #35Parameter changes

4Reliability

If more exhaust gas is recirculated to reduce knock, then knock is suppressed, but pumping losses increase

Engineering Contradiction:

Improveknock suppressionVSAvoidpumping losses

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

Instead of fully recirculating exhaust gas, the system introduces only the necessary amount to suppress knock. This partial action approach achieves knock suppression while minimizing the energy losses associated with excessive exhaust gas recirculation

Inventive Principle:

Principle #16Partial or excessive 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

Enables spark-ignition engines to operate at higher cylinder pressures with reduced knock likelihood, enhancing mechanical efficiency and minimizing emissions by effectively managing engine operational parameters.

Implementation Method 1

A low-pressure exhaust gas recirculation (EGR) system, controlled by an electronic control unit (ECU), which adjusts EGR flow and temperature to reduce engine knock by managing intake and exhaust gas flows

Methodology Applied

Scientific EffectExhaust gas recirculation:

Implementation Method 2

reducing an exhaust gas recirculation (EGR) gas temperature

Methodology Applied

Scientific EffectGas cooling: Cooling

Implementation Method 3

using variable valve timing to optimize combustion conditions

Methodology Applied

Scientific EffectVariable valve timing:

Implementation Method 4

a compressor coupled to an inlet of the intake system

Methodology Applied

Scientific EffectGas compression: Compression

Data Source

PatentUS11598277B2System and method for reducing engine knock

Publication Date: 2023.03.07 CUMMINS INC

AI summary

A method includes operating a spark ignition engine and flowing low pressure exhaust gas recirculation (EGR) from an exhaust to an inlet of the spark ignition engine. The method includes interpreting a parameter affecting an operation of the spark ignition engine, and determining a knock index value in response to the parameter. The method further includes reducing a likelihood of engine knock in response to the knock index value exceeding a knock threshold value.