Research On Transient Air-fuel Ratio Control Of Compressed Natural Gas Engine

In serious environmental pollution of the environment and energy conservation, thedevelopment of alternative fuel vehicles has become the new hot spot. Compressed naturalgas (CNG) has a good quality of economy, security, and combustion emissions performance,coupled with the gradual improvement of the filling stations in the current facilities. Naturalgas will be as the main alternative fuel engine in a long period of time. As natural gas enginesare quite different in terms of the mechanical structure and air-fuel ratio control strategy withgasoline or diesel engines, the research for natural gas engines is very necessary. Transientconditions occupy the entire engine operating conditions in a large proportion, as engineoperating conditions change quickly, it is difficult to accurately control the transient air-fuelratio, so it is the core and difficult about air-fuel ratio control.This paper analyzed the characteristics of natural gas engines, based on the intake airflow control and precise calculations, the closed-loop fuel injection amount correction andtransient correction, in order to achieve precise control of the air-fuel ratio. In this process, onthe basis of traditional PID controller, it optimized the design of the electronic throttlenonlinear PID controller, throttle opening for more precise control, to achieve precise controlof intake air flow; besides it comparatively analyzed the mass flow method and speed-densitymethod to analyze the factors affecting fuel injection duration. In the analysis of theopen-loop air-fuel ratio control and transient causes of error based on the error model,compensation transient air-fuel ratio control strategy was proposed; it was combined with theaverage model engine, electronic throttle controller model, analyzed the failure ofMATLAB/simulink/stateflow to establish a security policy with natural gas engine air-fuelratio control system model.This paper focuses on the research for the electronic throttle, air-fuel ratio controlstrategy and fail-safe strategy. The application of higher accuracy nonlinear PID controllerhelped to build a electronic throttle control system hardware platform, and conduct responsecalibration experiments; the steady-state conditions used "feed forward and closed loop"control strategy, while transient conditions adaptive compensation control strategy; on theaspect of fail-safe control strategy, which focuses on the throttle sensor failure, speed signalfailure, intake manifold pressure sensor failure, and oxygen sensor failure, it designs anappropriate security controls strategy and tactics during the corresponding verification.Finally, the imperfect contents are presented in this paper, where the summary andoutlook were made.