Stoichiometric Dual-Fuel Compression Ignition for Knock Control
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Solution Overview
Problem
Gaseous-fuelled internal combustion engines face challenges in achieving efficient and cost-effective exhaust cleaning, particularly in maintaining stoichiometric conditions to comply with emissions standards without requiring complex and expensive aftertreatment subsystems, and in preventing combustion knock at higher compression ratios.
Innovation Solution
A method for operating a gaseous-fuelled stoichiometric compression ignition engine with pilot ignition, where the primary fuel is a gaseous fuel and the pilot fuel is more readily auto-ignited, with controlled injection timing and exhaust gas recirculation to maintain stoichiometric conditions and prevent combustion knock, using a combination of direct injection of gaseous fuel and pilot fuel, and variable valve actuation strategies to optimize engine efficiency and emissions treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If higher compression ratios are used in compression ignition engines, then power and efficiency are improved, but combustion knock occurs
Solution Approach 1:
The pilot fuel is injected during the compression stroke before the main combustion event, creating a preliminary combustion that prepares the charge for the main fuel ignition. This preliminary action allows the main fuel to burn more smoothly at higher compression ratios without knocking
Solution Approach 2:
The pilot fuel acts as an intermediary substance that facilitates the combustion of the main gaseous fuel. By introducing a small amount of easily ignitable pilot fuel, the system enables controlled combustion of the main fuel charge at higher compression ratios, mediating between the high compression ratio and the prevention of knock
2Object-generated harmful factors
If stoichiometric air/fuel ratio is maintained, then emissions compatibility with three-way catalyst is improved, but fuel efficiency decreases compared to lean burn
Solution Approach 1:
The system changes the operating parameters by using compression ignition instead of spark ignition, and by using a pilot fuel injection strategy. This allows the engine to operate at stoichiometric conditions while achieving better fuel efficiency through the high compression ratio and controlled combustion process
Solution Approach 2:
The patent replaces the traditional spark ignition system with a compression ignition system using pilot fuel injection. This substitution of the ignition mechanism enables the engine to achieve both stoichiometric operation and improved fuel efficiency that would not be possible with conventional spark ignition
3Object-generated harmful factors
If gaseous fuel is used instead of liquid fuel, then emissions are improved, but ignition difficulty increases
Solution Approach 1:
The pilot fuel serves as an intermediary that bridges the ignition difficulty of gaseous fuel. The easily ignitable pilot fuel initiates combustion, which then propagates to the main gaseous fuel charge, solving the ignition problem while maintaining the emission benefits of gaseous fuel
Solution Approach 2:
The pilot fuel injection creates a preliminary combustion event that prepares the gaseous fuel for ignition. This preliminary action occurs during the compression stroke, allowing the gaseous fuel to ignite reliably without requiring spark plugs or other complex ignition systems
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 allows for simpler and less expensive exhaust cleaning systems, improved fuel efficiency, reduced combustion knock, and compliance with emissions standards using a conventional three-way catalyst, while maintaining high engine performance and robustness.
Implementation Method 1
a charge consisting of gaseous fuel and air is difficult to ignite by compression alone without the use of an ignition assisting device, such as the ignition of a more readily ignited pilot fuel
Implementation Method 2
it uses relatively high rates of cooled exhaust gas recirculation (EGR) to reduce excess air and thereby reduce the production of NOx during combustion, while also lessening the likelihood of combustion knock
Implementation Method 3
the combustion products are compatible with modern three-way catalyst aftertreatment subsystems
Data Source
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AI summary
In a gaseous-fuelled stoichiometric compression ignition internal combustion engine, a pilot fuel is injected directly into the combustion chamber to help initiate a multi-point ignition. The engine provides performance improvements approaching those of high pressure direct injection engines but with less complexity because the gaseous fuel is introduced into the intake air subsystem at relatively low pressure and as a result of the stoichiometric combustion, the low oxygen content in the combustion products exiting the combustion chamber allows the use of a three-way catalyst instead of other after treatment arrangements normally associated with conventional compression ignition engines that require the addition of a reductant.