LTC Engine SCR System Valve Overlap Control

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Solution Overview

Problem

Passive SCR systems face challenges in adjusting the air/fuel ratio to a rich setting while maintaining positive valve overlap, leading to high combustion noise and unstable combustion, and adjusting to a rich setting with negative valve overlap, which increases carbon monoxide emissions.

Innovation Solution

The system adjusts the air/fuel ratio to a rich setting only during positive valve overlap, minimizing the duration of rich operation to reduce carbon monoxide emissions and improve fuel efficiency, and uses throttle closure to reduce air mass while adjusting spark and fuel injection timing for stable combustion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If the air/fuel ratio is adjusted to rich to increase ammonia storage levels in the SCR catalyst, then ammonia storage increases, but combustion noise increases and combustion stability deteriorates when operating with positive valve overlap

Engineering Contradiction:

Improveammonia storage levelsVSAvoidcombustion noise

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

The system implements periodic switching between rich and lean air/fuel ratios during positive valve overlap operation. The combustion mode module switches the LTC engine between SI mode and PVO mode, creating periodic enrichment events that accumulate ammonia in the SCR catalyst over time while allowing combustion to return to stable lean operation between enrichment cycles.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system performs preliminary rich operation before transitioning to lean operation. By switching to PVO mode with rich A/F ratio first, the system pre-conditions the exhaust gas composition to ensure sufficient ammonia is available in the SCR catalyst before entering sustained lean combustion, preventing ammonia depletion during subsequent lean phases.

Inventive Principle:

Principle #10Preliminary action

2Quantity of substance

If the air/fuel ratio is adjusted to rich to increase ammonia storage levels in the SCR catalyst, then ammonia storage increases, but fuel economy deteriorates

Engineering Contradiction:

Improveammonia storage levelsVSAvoidfuel economy

Core Design Contradiction:

Quantity of substanceVSUse of energy by moving object

Solution Approach 1:

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system applies rich operation partially rather than continuously. By limiting rich operation to specific periods during PVO mode and using intermittent enrichment strategies, the system provides just enough ammonia to the SCR catalyst for effective NOx reduction while minimizing the fuel penalty associated with sustained rich combustion.

Inventive Principle:

Principle #16Partial or excessive action

3Quantity of substance

If the air/fuel ratio is adjusted to rich with negative valve overlap, then ammonia storage increases, but carbon monoxide emissions increase

Engineering Contradiction:

Improveammonia storage levelsVSAvoidcarbon monoxide emissions

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

The system inverts the conventional approach by using positive valve overlap instead of negative valve overlap for rich operation. This reversal allows the exhaust gas to mix with fresh charge during the overlap period, promoting more complete combustion and reducing CO emissions while still enabling ammonia generation in the SCR catalyst during the rich phase.

Inventive Principle:

Principle #13The other way round (Inversion)

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 reduces combustion noise, stabilizes combustion, minimizes carbon monoxide emissions, and enhances fuel efficiency by controlling valve overlap and adjusting fuel and spark timing during transitions.

Implementation Method 1

When an air/fuel ratio of the engine is rich or stoichiometric, the three-way catalyst reduces hydrocarbon, carbon monoxide, and nitrogen oxide and produces ammonia

Methodology Applied

Scientific EffectCatalysis: Catalysis

Implementation Method 2

the SCR catalyst stores the ammonia

Methodology Applied

Scientific EffectAbsorption: Absorption (physical)

Implementation Method 3

When the air/fuel ratio is lean, the three-way catalyst reduces hydrocarbon and carbon monoxide, and the ammonia stored in the SCR catalyst is used to reduce nitrogen oxide

Methodology Applied

Scientific EffectCatalysis: Catalysis

Implementation Method 4

The dosing agent breaks down to form ammonia that is stored in the SCR catalyst

Methodology Applied

Scientific EffectDecomposition: Decomposition (biological)

Data Source

PatentUS11459967B2Passive selective catalytic reduction (SCR) system and method for low-temperature combustion (LTC) engine

Publication Date: 2022.10.04 GM GLOBAL TECHNOLOGY OPERATIONS LLC

AI summary

A combustion mode module is configured to switch operation of a low-temperature combustion (LTC) engine between a spark ignition (SI) mode, a positive valve overlap (PVO) mode, and a negative valve overlap (NVO) mode. A spark control module is configured to control a spark plug to generate a spark in a cylinder of the LTC engine when the LTC engine is operating in the SI mode. A valve control module is configured to control intake and exhaust valves of the cylinder to yield a PVO and a NVO when the LTC engine is operating in the PVO mode and the NVO mode, respectively. An air/fuel (A/F) control module is configured to adjust a desired A/F ratio of the LTC engine to a rich A/F ratio when operation of the LTC engine is switched to the PVO mode from either one of the SI mode and the NVO mode.