Closed-loop control method and system of rear oxygen sensor of natural gas engine

Abstract

The invention discloses a closed-loop control method and system of a rear oxygen sensor of a natural gas engine. The closed-loop control method comprises the steps that a response model of the rear oxygen sensor is constructed, and the response time of the sensor is calculated through the response model of the rear oxygen sensor; according to the response time of the sensor and the output correction amount of a PID controller, the undelayed air-fuel ratio is calculated; a pure lag time model of a catalyst is constructed, the pure lag time is calculated through the pure lag time model of the catalyst; a model of a Simth predictive controller or an internal model controller is constructed, the model of the Simth predictive controller or the internal model controller calculates the delayed air-fuel ratio according to the undelayed air-fuel ratio and the pure lag time; and the difference between the undelayed air-fuel ratio and the delayed air-fuel ratio is fed back to the input end of thePID controller of a PID closed-loop control loop, namely the pure lag of the oxygen storage capacity of the catalyst and the response lag of the rear oxygen sensor are introduced into the closed-loopcontrol loop, the time-lag link of the closed-loop control loop of the rear oxygen sensor is eliminated, and the stability and emission consistency of the closed-loop control are improved.

Description

technical field [0001] The invention relates to the technical field of engines, in particular to a closed-loop control method and system for a rear oxygen sensor of a natural gas engine. Background technique [0002] With the upgrading of emission regulations, the emission limits of natural gas engines are becoming increasingly stringent. For equivalent combustion natural gas engines, the quality of emissions largely depends on the accuracy of air-fuel ratio control. At present, natural gas engines are equipped with oxygen sensors before and after the catalytic converter. The front oxygen sensor is used to control the efficiency window of the catalytic converter and the closed-loop air-fuel ratio. At the same time, when the front oxygen sensor deviates, it has a certain correction effect on the catalytic converter window to avoid serious deterioration of emissions. The current control strategy uses PID to control the rear oxygen sensor closed loop. For natural gas engines,...

AI Technical Summary

Problems solved by technology

For natural gas engines, due to the large amount of oxygen stored in the catalytic converter, the control of the air-fuel ratio can only be fed back to the rear oxygen sensor after a certain period of time. When the oxygen sensor detects it, it has already overshooted a lot, which makes it difficult to stabilize the rear oxygen closed loop using PID control, the air-fuel ratio has been fluctuating, and the emission results are not ideal

[0003] That is, due to the large amount of oxygen stored in the catalytic converter of the natural gas engine, there is a time lag in the closed-loop control of the rear oxygen sensor, which makes the system difficult to stabilize

With the aging of the catalytic converter and the aging of the rear oxygen sensor, the oxygen storage capacity of the catalytic converter gradually decreases, the response of the rear oxygen sensor gradually slows down, the time-delay model of the fresh catalyst and the response time of the new rear oxygen sensor slow down, thereby affecting the stability of the post-oxygen closed loop

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