Hybrid Engine Two-Stroke Mode for Catalyst Heating
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Solution Overview
Problem
Hybrid vehicles face increased engine emissions and longer catalyst heating times during cold starts due to low catalyst efficiency and higher engine feed gas emissions, which can be attributed to the engine being shut off and then restarted, leading to inefficient combustion modes.
Innovation Solution
Operating the engine in a two-stroke mode before the catalyst reaches light-off temperature, where some cylinders combust fuel while others pump air and fuel to the catalyst, increasing mass flow rate and reducing energy loss, thereby accelerating catalyst heating and reducing emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the engine is operated in four stroke mode during cold start, then the engine can generate torque to rotate itself, but the mass flow rate to the catalyst is insufficient and catalyst heating time is extended
Solution Approach 1:
The engine dynamically switches between four-stroke and two-stroke modes based on operating conditions. During cold start, the controller transitions from four-stroke mode (which generates torque) to two-stroke mode (which maximizes mass flow rate to the catalyst), allowing the system to adapt its breathing characteristics to the specific requirement of rapid catalyst heating.
Solution Approach 2:
The valve timing parameters are modified during cold start operation to enable two-stroke mode. Specifically, the intake valve remains open longer and the exhaust valve opens earlier, creating a breathing pattern that maximizes fresh charge flow through the engine and to the catalyst, thereby increasing the mass flow rate and accelerating catalyst light-off.
2Power
If the engine operates in two stroke mode with all cylinders combusting fuel, then torque output is increased, but energy is lost to engine heating rather than catalyst heating
Solution Approach 1:
The engine cylinders are segmented into two groups: a first group that combusts fuel to generate torque, and a second group that pumps fresh charge to the catalyst without combustion. This segmentation allows the engine to simultaneously produce the torque needed to rotate the engine while maximizing the mass flow rate of unburned fuel and oxygen to the catalyst for rapid heating.
Solution Approach 2:
Different cylinders are assigned different functions based on local requirements. Cylinders in the first group are optimized for combustion and torque generation, while cylinders in the second group are optimized for pumping fresh charge to the catalyst. This local differentiation of cylinder function allows the engine to achieve both torque output and rapid catalyst heating efficiently.
3Power
If the engine is restarted after being shut off, then powertrain torque output is increased, but engine emissions increase due to low catalyst efficiency
Solution Approach 1:
The engine performs preliminary action by operating in two-stroke mode immediately upon restart to rapidly heat the catalyst before normal combustion begins. This preliminary two-stroke operation delivers a high mass flow rate of unburned fuel and oxygen to the catalyst, raising its temperature quickly so that when combustion is initiated, the catalyst is already active and can immediately convert harmful emissions.
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 tailpipe emissions by increasing catalyst efficiency, shortening catalyst heating time, and providing additional energy to heat the catalyst without generating torque, thus improving overall engine performance during cold starts.
Implementation Method 1
a catalyst may reach a catalyst light off temperature (e.g., a temperature at which the catalyst efficiency for converting exhaust gases (e.g., HC, CO, NOx) may exceed a threshold efficiency (e.g., 50%))
Implementation Method 2
combusting fuel in a first group of cylinders of the engine
Data Source
AI summary
Systems and methods for operating an internal combustion engine that is included in a hybrid vehicle are described. In one example, the internal combustion engine is operated in a two stroke mode during cold starting to increase mass flow to an electrically heated catalyst so that engine emissions may be reduced.