Engine Cylinder Segmentation for NOx Reduction
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Solution Overview
Problem
Three-way catalysts used in exhaust aftertreatment systems are ineffective in decomposing NOx gases under lean engine operation conditions, limiting fuel efficiency improvements and increasing costs with the use of urea-water solution (UWS) injection in selective catalytic reduction (SCR) technology.
Innovation Solution
Operating a subset of engine cylinders under lean conditions and another subset under rich conditions, with exhaust gases from the rich cylinders passing through an ammonia generating catalyst to produce ammonia for NOx reduction, decoupling the mass flow rates and maintaining a balanced NOx to ammonia ratio for efficient SCR system operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a three-way catalyst is used for exhaust aftertreatment, then NOx decomposition efficiency is improved under stoichiometric conditions, but fuel efficiency deteriorates due to the narrow air/fuel ratio operating band
Solution Approach 1:
The engine is divided into multiple cylinders with different air/fuel ratios. Some cylinders operate under rich conditions to generate reductant (ammonia), while others operate under lean conditions for efficient fuel combustion. This segmentation allows the system to simultaneously achieve high fuel efficiency and effective NOx treatment without being constrained to a narrow stoichiometric operating band.
2Reliability
If UWS injection with SCR technology is used for lean engine operation, then NOx decomposition efficiency is improved, but system cost and control complexity increase
Solution Approach 1:
The system generates its own reductant (ammonia) internally through rich combustion in dedicated cylinders, eliminating the need for external UWS storage tanks, injection systems, and associated control mechanisms. The engine itself serves as the reductant production facility, significantly simplifying the overall system architecture while maintaining effective NOx decomposition capability.
3Use of energy by moving object
If the engine operates under lean conditions to maximize fuel efficiency, then fuel consumption is reduced, but NOx decomposition efficiency deteriorates
Solution Approach 1:
Different regions (cylinders) of the engine are assigned different air/fuel ratios optimized for their specific functions. Lean-operating cylinders prioritize fuel efficiency and produce minimal NOx, while rich-operating cylinders prioritize reductant generation. This local differentiation allows the overall system to achieve both high fuel efficiency and effective NOx treatment simultaneously.
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 enhances engine fuel efficiency, extends the engine's operating range, reduces combustion temperatures, and maintains the efficiency of the aftertreatment system for NOx decomposition without the need for additional reductants, thereby improving fuel efficiency and reducing emissions.
Implementation Method 1
an ammonia generating catalyst positioned downstream of and in fluidic communication with the second set of cylinders. The ammonia generating catalyst receives only the exhaust gas second portion and converts NOx gases included in the exhaust gas second portion to ammonia
Implementation Method 2
A selective catalytic reduction system is positioned downstream of the plurality of cylinders. The selective catalytic reduction system receives the exhaust gas first portion and the exhaust gas second portion containing ammonia therewithin
Data Source
AI summary
A system comprises an engine including a plurality of cylinders. A first intake throttle is positioned upstream of a first set of cylinders of the plurality of cylinders. The first intake throttle provides air at a first flow rate to the first set of cylinders so as to produce a lean air/fuel mixture in the first set of cylinders. A second intake throttle is positioned upstream of a second set of cylinders included in the plurality of cylinders and in parallel of the first intake throttle. The second intake throttle provides air at a second flow rate to the second set of cylinders so as to produce a rich air/fuel mixture in the second set of cylinders.