Study On Gas Injection Closed-loop Control Of CNG Engine

CNG (compressed nature gas) engine is completely divorced from diesel and petrol,which is an effective means to solve today’s energy problems and environmental pollutionproblems. Electronic control technology is the main direction of CNG engine performanceresearches in the future, good gas injection control system and the air-fuel ratio controlstrategy could achieve precise control of the air-fuel ratio, which can significantly increase thenatural gas engine power, fuel economy and emissions performance.This paper designs and constructs a CNG engine experimental platform,2135G dieselengine is transformed into a single fuel gas engines, and a gas injection control system isdesigned independently, the hardware circuit adopts MC9S12XEP100microcontroller as thecore, including signal acquisition circuits, drive circuits of UEGO (Universal exhaust gasoxygen sensor), injectors, electronic throttle and communication circuits, UEGO can achievethe continuous acquisition of the air-fuel ratio signal, to complete the closed loop control ofthe air-fuel ratio as a feedback unit, controlling the gas injection amount.PID control algorithm is simple and functional, and has good stability, so this paper usesPID algorithm as the core control strategy of the gas injection system. There are twodrawbacks of this control algorithm: under different conditions of engine, PID parameters areinconsistent, using different PID parameters increases complexity; due to the delay caused bythe sensor, filter and gas transmission factors in the natural gas engine systems, the control islag. For the former, this paper uses fuzzy algorithm to form a fuzzy self-tuning PID controlstrategy, for the latter, this paper uses a feed-forward control based on speed density method,eventually forming the feed-forward fuzzy self-tuning PID control strategy.In the last part of this article, experiments of startup and experiments of the air-fuel ratioclosed-loop control for steady state and transient state are done. Due to the limitations of theexperimental conditions, the advantage fuzzy self-tuning PID can not be reflected, so PIDcontrol strategy based feedforward is used. In steady state, using gas injection systemdesigned in this paper can precisely stable air-fuel ratio in the vicinity of the target air-fuelratio, in transient state, throttle changes, gas injection system will be adjusted according to theactual air-fuel ratio of the amount of gas injection, then the air-fuel ratio will be transferredback to the target value in a short period of time. In addition, experiments are done to analysis the relevant factors of the gas engine combustion process, in the injection system, the resultsshow that the air-fuel ratio and throttle opening greater impact on the combustion process, andinjection advance angle almost has no effect on the combustion process.