Post-Injection Dedicated EGR Cylinder H2 Production
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Solution Overview
Problem
Conventional exhaust gas recirculation (EGR) systems in internal combustion engines are limited in increasing hydrogen (H2) and carbon monoxide (CO) concentrations in exhaust gases, which restricts combustion efficiency and knock tolerance, especially in dedicated EGR systems where maximum H2 concentration is capped at approximately 4% due to combustion instabilities at higher equivalence ratios.
Innovation Solution
Implementing a post fuel injection strategy in a dedicated EGR cylinder with direct injection of fuel after the majority of combustion has occurred, combined with a water-gas shift catalyst to enhance H2 and CO production, and optimizing the air-fuel ratio to exceed conventional flammability limits, thereby increasing the quality and quantity of EGR gas for improved combustion across all engine cylinders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the air-fuel ratio is increased to enhance H2 and CO concentrations in exhaust gases, then combustion efficiency and knock tolerance improve, but combustion instabilities occur at higher equivalence ratios limiting H2 concentration to approximately 4%
Solution Approach 1:
The exhaust system is segmented into dedicated EGR cylinders that operate independently to produce H2 and CO-rich exhaust gases. These dedicated cylinders are separated from the main combustion cylinders, allowing the EGR cylinders to run at rich air-fuel ratios (producing high H2 and CO) without causing combustion instabilities in the main cylinders that operate at normal equivalence ratios.
Solution Approach 2:
A water-gas shift catalyst is introduced as an intermediary component in the EGR system. This catalyst facilitates the water-gas shift reaction (CO + H2O → CO2 + H2), converting CO and H2O in the exhaust gases to produce additional H2, thereby enhancing the H2 concentration beyond what direct combustion could achieve while maintaining combustion stability.
2Quantity of substance
If post fuel injection is implemented after majority combustion to enhance H2 and CO production, then EGR gas quality improves, but additional fuel consumption occurs
Solution Approach 1:
Fuel is injected in advance during the main combustion stroke to establish normal combustion, then a second post-injection is performed after majority combustion has occurred. This preliminary main injection ensures stable combustion while the subsequent post-injection utilizes the remaining oxygen and high temperature conditions to generate H2 and CO through partial combustion and reforming reactions in the exhaust stream.
Solution Approach 2:
The air-fuel ratio in dedicated EGR cylinders is changed to operate at rich conditions (excess fuel), and post-injection timing is optimized to occur after main combustion when cylinder temperature and pressure are still high but oxygen is depleted. These parameter changes maximize H2 and CO production while minimizing additional fuel consumption by utilizing waste heat and unburned oxygen.
3Quantity of substance
If dedicated EGR cylinders operate at rich air-fuel ratios to maximize H2 production, then EGR effectiveness increases, but combustion efficiency in individual EGR cylinders decreases
Solution Approach 1:
The exhaust streams from multiple dedicated EGR cylinders operating at rich air-fuel ratios are merged and combined with exhaust from conventional cylinders operating at stoichiometric or lean conditions. This merging creates a blended EGR gas composition that has high H2 and CO content while maintaining overall combustion efficiency across the entire engine system, as the conventional cylinders compensate for the low efficiency of rich-running EGR cylinders.
Solution Approach 2:
The dedicated EGR cylinders serve multiple functions: they generate H2 and CO-rich exhaust gases for EGR, provide thermal energy to the exhaust stream, and enable the water-gas shift reaction to occur. By making these cylinders multi-functional, the system achieves high H2 production without sacrificing overall engine productivity, as the EGR gases improve combustion in the main cylinders.
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 significantly enhances H2 and CO concentrations, improving combustion efficiency, knock tolerance, and overall engine performance without compromising the effectiveness of three-way catalysts, allowing for higher engine efficiency and reduced ignition energy requirements.
Implementation Method 1
combined with a water-gas shift catalyst to enhance H2 and CO production
Implementation Method 2
post fuel injection strategy in a dedicated EGR cylinder with direct injection of fuel after the majority of combustion has occurred
Data Source
AI summary
A method using exhaust gas recirculation (EGR) in an internal combustion engine. The engine has at least one “dedicated EGR cylinder”, whose entire exhaust is recirculated back to all the engine cylinders. The dedicated EGR cylinder is operated at a rich air-fuel ratio, and the other cylinders are operated stoichiometrically so that a conventional three way catalyst may be used to treat the exhaust. A fuel injector is used to inject fuel into the combustion chamber of the dedicated EGR cylinder after initiation of the main combustion event. This post injection method overcomes flammability limits of a dedicated EGR cylinder, and increases the hydrogen (H2) and carbon monoxide (CO) in its exhaust.