Spark-Ignition Engine Cold-Start Fuel Injection Strategy
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Solution Overview
Problem
Spark-ignition 4-stroke internal combustion engines face challenges in achieving rapid heating of the exhaust gas catalytic converter during cold-start operations, leading to inefficient emission conversion and increased operational costs due to the need for additional components like secondary air pumps and complex control systems.
Innovation Solution
A method involving multiple fuel injections, including a lean intake stroke injection, a compression stroke injection to form a rich mixture, and a stratified injection timed close to ignition, which creates a rich fuel/air mixture locally at the spark plug for rapid combustion and heat transfer to the catalytic converter, eliminating the need for secondary air and reducing operational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rich mixture charge is used during cold-running operation to ensure reliable combustion and smooth engine operation, then the exhaust gas catalytic converter can be heated up, but high proportions of unburnt fuel are produced in the exhaust gas and additional components (secondary air pump, switching valves) are required
Solution Approach 1:
The fuel injection process is segmented into three distinct phases: intake stroke injection (lean mixture), compression stroke injection (additional fuel for rich mixture), and exhaust stroke injection (secondary air injection). This segmentation allows the system to achieve the benefits of rich mixture combustion while eliminating the need for complex external secondary air pumping systems by utilizing the engine's own pneumatic cycles
Solution Approach 2:
The engine system uses its own pneumatic resources (intake air, compression air, exhaust air) to provide the secondary air needed for complete combustion and catalytic converter heating. The fuel injection system and existing pneumatic pathways serve multiple functions, eliminating the need for separate secondary air pumps and reducing system complexity
2Reliability
If a late ignition time is used during cold-running operation to ensure smooth engine operation, then combustion is more complete, but the combustibility of the mixture is limited and engine operating noise increases
Solution Approach 1:
The air-fuel ratio is dynamically changed throughout the combustion cycle by injecting fuel at different stages. The mixture transitions from lean (intake stroke) to rich (compression stroke) to extremely rich (exhaust stroke near ignition), allowing late ignition timing to be used without compromising combustibility or increasing noise, as the locally rich mixture near the spark plug ensures reliable ignition even at late timing
3Productivity
If conventional fuel injection methods are used during cold start, then the engine can start, but the exhaust gas catalytic converter cannot be heated up quickly and emissions remain high
Solution Approach 1:
Fuel is injected during the compression stroke before ignition occurs, creating a rich mixture that will produce high temperatures during combustion. This preliminary preparation of the fuel-air mixture ensures that when ignition occurs, the resulting combustion generates sufficient heat to quickly warm the catalytic converter and reduce emissions
Solution Approach 2:
The method utilizes the oxygen present in the cylinder during the exhaust stroke (after power stroke and before intake stroke) to create a rich oxygen environment. When combined with the injected fuel during this phase, it enables complete combustion and thermal post-combustion in the exhaust system, rapidly heating the catalytic converter and accelerating the oxidation of 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 ensures rapid heating of the exhaust gas catalytic converter to its light-off temperature within seconds, achieving low emissions and smooth engine operation without the need for additional air supply or complex control systems.
Implementation Method 1
A fuel/air mixture is formed with fresh air which is sucked into the cylinder, and said fuel/air mixture is ignited at a predefined time by means of a spark plug in order to initiate a combustion process
Implementation Method 2
The exhaust gas which is produced contains portions of hydrocarbons, carbon monoxide and nitrogen oxides, for the conversion of which into substances which are more compatible with the environment an exhaust gas catalytic converter is connected downstream in the exhaust gas system
Implementation Method 3
By adding secondary air to the exhaust gas, a thermal post-combustion can be obtained, the reaction heat of which accelerates the heating-up of the exhaust gas catalytic converter
Data Source
AI summary
In a method for cold-running or warm-up operation of a spark-ignition, direct-injection 4-stroke internal combustion engine having an exhaust gas catalytic converter, wherein fuel is injected into the cylinders of the internal combustion engine by means of injectors and is externally ignited by means of spark plugs, in an intake stroke fuel injection a lean, combustible but non-ignitable lean mixture is produced in the cylinders, in a compression stroke fuel injection following the intake stroke injection, by a compression stroke fuel injection, a combustible and ignitable fuel/air mixture is formed in the combustible but non-ignitable lean mixture in the cylinders and, subsequently, in a stratified fuel injection which is close in timing to an ignition time, a rich fuel/air mixture is locally formed in the region of the spark plug and is then ignited by the spark plug so as to provide for rapid heat up of the cold exhaust gas catalytic converter with reliable combustion and smooth engine operation.