Two-Cycle Uniflow Diesel Modes with Exhaust Valve Deactivation
Solution Overview
Problem
Two-cycle uniflow-scavenged diesel engines experience low exhaust temperatures at low loads, which adversely affect catalyst-based exhaust aftertreatment systems, worsening fuel economy and increasing carbon dioxide emissions.
Innovation Solution
Implementing exhaust valve deactivation (EVD) strategies combined with fueling adjustments and compressor control to increase exhaust gas temperatures, including Air Spring and Internal EGR modes, and using variable turbocharger/supercharger configurations to optimize engine performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If exhaust valve deactivation is implemented to increase exhaust temperatures, then catalyst effectiveness is improved, but fuel economy deteriorates
Solution Approach 1:
The engine operation is segmented into different modes (standard mode and rebreathing mode) based on load conditions. Exhaust valve deactivation is applied selectively during low-load conditions when the engine is in rebreathing mode, while normal operation continues during high-load conditions. This segmentation allows the system to achieve adequate exhaust temperatures for catalyst effectiveness only when necessary, without sacrificing fuel economy during high-load operation.
Solution Approach 2:
The exhaust valve deactivation is implemented periodically through rebreathing cycles, where the exhaust valve is deactivated for a predetermined number of cycles followed by normal operation. This periodic action allows exhaust gases to accumulate and increase temperature in the aftertreatment system, while maintaining overall engine efficiency by returning to normal operation periodically.
2Temperature
If fuel is burned in the exhaust stream to increase exhaust temperatures, then catalyst effectiveness is improved, but carbon dioxide emissions increase
Solution Approach 1:
The invention extracts the exhaust valve deactivation function from the combustion process itself. Instead of adding fuel to the exhaust stream (which would increase CO2 emissions), the system extracts heat from the combustion chamber by controlling exhaust valve timing, allowing exhaust gases to retain more heat and increase temperature in the aftertreatment system without additional fuel combustion in the exhaust.
3Temperature
If electrical heating elements are used in the exhaust stream to increase exhaust temperatures, then catalyst effectiveness is improved, but fuel economy worsens
Solution Approach 1:
The exhaust aftertreatment system serves itself by utilizing the engine's own exhaust gases and thermal energy. The rebreathing mode allows exhaust gases to accumulate and self-heat within the system, eliminating the need for external electrical heating elements or additional fuel injection into the exhaust stream. The system uses its own operational characteristics to achieve the required temperature increase.
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
Enhances exhaust gas temperatures, improves fuel efficiency, and reduces emissions by optimizing engine operation across varying load conditions.
Implementation Method 1
A forced induction EMD engine uses a turbo-supercharger, which drives the forced induction system mechanically at low power operating modes. The gear-driven turbocharger provides the required air flow at idle and light-to-moderate loads
Implementation Method 2
Internal EGR modes, and using variable turbocharger/supercharger configurations to optimize engine performance
Data Source
AI summary
Methods of operating a two-cycle uniflow-scavenged engine, especially at lower loads. The exhaust valves of one or more of the engine's cylinders may undergo exhaust valve deactivation (EVD), that is, a cylinder's exhaust valve is activated with a frequency that is less frequent than every engine cycle. EVD may be combined with additional engine operating strategies, such as by using fewer than all cylinders as combusting cylinders and adjusting airflow and fueling to combusting cylinders.