Multi-Fuel Engine Air-Fuel Ratio Control via Closed-Loop Feedback
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Solution Overview
Problem
Conventional techniques fail to provide precise control of air-fuel ratio in throttled engines operating near stoichiometry, especially when a premixed charge of natural gas is ignited by a pilot fuel, particularly under conditions where fuel composition varies significantly between light and heavy loads.
Innovation Solution
A method and apparatus for controlling air-fuel ratio in multi-fuel internal combustion engines by determining a target air-fuel ratio based on engine operating conditions, adjusting the quantities of a liquid pilot fuel and a gaseous main fuel to maintain the ratio within a predetermined tolerance, using a closed-loop control system that incorporates proportional, integral, and derivative control modules to calculate fuel quantities dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional techniques are used to control air-fuel ratio in multi-fuel engines, then the control system is simple, but the air-fuel ratio cannot be maintained precisely within a narrow range of stoichiometry
Solution Approach 1:
The patent implements a closed-loop control system that continuously monitors the air-fuel ratio using oxygen sensors in the exhaust stream and adjusts fuel injection quantities accordingly. The control module receives feedback signals from the sensors and dynamically modifies the quantities of pilot fuel and main fuel to maintain the air-fuel ratio within the desired narrow range around stoichiometry, thereby achieving precise control through continuous feedback correction.
Solution Approach 2:
The control system segments the fuel injection control into two independent controllable components: pilot fuel injection quantity and main fuel injection quantity. By separately controlling these two fuel sources rather than treating them as a single fuel stream, the system can independently adjust each fuel quantity to achieve precise air-fuel ratio control while maintaining system manageability.
2Adaptability or versatility
If the fuel composition is adjusted significantly under varying load conditions, then the engine adapts to different loads, but the air-fuel ratio becomes difficult to control precisely
Solution Approach 1:
The control system dynamically adjusts both the fuel composition ratio and the total fuel injection quantity based on real-time operating conditions. The control module continuously modifies the relative quantities of pilot fuel and main fuel according to engine load, speed, and air-fuel ratio feedback, enabling the system to adapt to varying loads while maintaining precise air-fuel ratio control through dynamic parameter adjustment.
Solution Approach 2:
The system changes multiple parameters simultaneously - the proportion of pilot fuel to main fuel, the total fuel injection quantity, and the injection timing - to adapt to different load conditions while maintaining precise air-fuel ratio control. By coordinating changes in these parameters based on feedback from oxygen sensors, the system achieves both adaptability to load variations and precision in air-fuel ratio maintenance.
3Speed
If fast transient response is achieved through aggressive fuel adjustment, then the engine responds quickly to load changes, but the air-fuel ratio may overshoot or become unstable
Solution Approach 1:
The control system applies partial fuel adjustment strategies during transient conditions, making incremental changes to fuel quantities rather than aggressive large-step adjustments. By using proportional control with appropriate gain settings and integral control to eliminate steady-state error gradually, the system achieves sufficiently fast response while preventing overshoot and maintaining air-fuel ratio stability through controlled, progressive fuel quantity modifications.
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 enables precise control of air-fuel ratio, providing fast transient response and stable steady-state operation, maintaining the desired lambda value even under varying load conditions, thereby optimizing engine performance and reducing emissions.
Implementation Method 1
a diesel pilot fuel is often employed since the auto-ignition temperature of natural gas is greater than that of diesel. A small amount of diesel, normally around 5% of total fuel introduced to the combustion chamber, is injected along with the main natural gas fuel. The diesel ignites due to compression heat and subsequently the natural gas is ignited due to the combustion of diesel.
Data Source
AI summary
A technique for controlling air-fuel ratio in an internal combustion engine consuming more than one fuel type includes determining a target air-fuel ratio as a function of engine operating conditions; determining an actual air-fuel ratio from the engine operating conditions; determining a first fuel quantity of a first fuel to introduce into a combustion chamber as a function of the engine operating conditions; determining a second fuel quantity of a second fuel such that the actual air-fuel ratio equals the target air-fuel ratio to within a predetermined range of tolerance when the first fuel quantity and the second fuel quantity are introduced into the combustion chamber, the second fuel quantity being determined as a function of the engine operating conditions, the target air-fuel ratio, the actual air-fuel ratio and the first fuel quantity; and introducing the first fuel quantity and the second fuel quantity into the combustion chamber.