Research On Control And Optimazation Of Common Rail Based Diesel Ignited Natural Gas Engine

Diesel ignited natural gas engine is regarded as a promising approach toimprove emission and fuel economy of diesel engine. However, diesel ignitednatural gas engine suffers from low efficiency, poor fuel economy and high HCemission under low load conditions. Besides, it can only use natural gas from aspecified source. This is mainly because the existing diesel ignited natural gasengine is lack of effective method of mixture air-fuel ratio control, and usessimple fuel injection strategy. In order to solve this problem, a new enginesystem configuration is developed in this paper. Both the hardware and softwareof a distributed electronic control system with new control methods for dieselignited natural gas engine is developed. At the end of this paper, a research wasdone on the engine performance optimization in diesel ignited natural gas modeunder low load condition.By analyzing diesel ignited natural gas engine system requirements, a dieselignited natural gas engine system configuration which consists of common rail dieselsupply system, inlet single-point mixture natural gas supply system and air system withelectronic throttle valve is developed.The distributed electronic control system for diesel ignited natural gasengine contains diesel ignited natural gas engine control system and electronicthrottle control system. The former is used for real-time engine data acquisitionand control, including air-fuel ratio close-loop control. The latter is used foractual control of throttle position. The real-time communication between thetwo systems is through CAN bus.The diesel ignited natural gas engine control system is based ontorque-based control strategy, and coordinately controls diesel injection, naturalgas injection and target throttle percentage. The Air-fuel ratio close loop controluses variable parameter PID controller which is quite fit for engine real-timecontrol, and achieved good control effect. The throttle control also uses variableparameter PID controller based close-loop control, and the steady-state error isless than1%and transient response is fast with small overshoot.Taking lambda as the feedback signal and natural gas volume heating value as the characteristic parameter, a natural gas constituent identification method isdesigned. A natural gas constituent adaptive control method which holdingmixture heating value unchanged is also designed, which includes a constituentidentification based open-loop control method and an air-fuel ratio close-loopcontrol based close-loop control method.Aiming at reducing HC and NOxemissions under optimal economy condition,taking coordinately controlling throttle percentage and diesel injection strategy ascontrol means, a research was done on the diesel ignited natural gas engineperformance optimization under low load condition, and the effect of throttlepercentage and diesel injection strategy on the combustion and engineperformance. Results indicated that comparing with the existing one, the dieselignited natural gas engine electronic control system raised in this paper couldsignificantly improve engine efficiency and fuel economy, reduce HC emissionand maintain NOxemission almost unchanged under low load condition.