The Design And Development Of Diesel-LNG Dual Fuel Engine Electronic Control System Based On Single Point Fuel Injection System

The application of diesel-LNG dual fuel technology for the existing diesel engine can not only reduce the pollutant emissions,but also obviously save lots of money of fuel cost for vehicles.Relied on the research project "conversion of diesel-fueled engines to natural gas",an integral electronic control system for diesel-LNG dual fuel engine is wholly developed.The primary control method is combined with mechanical and electronic means.As a result,the pilot fuel quantity is adjusted by mechanical fuel injection pump of conventional diesel engine and the volume of natural gas injection is controlled by gas injectors.Aiming at the development of retrofitting technology for diesel-LNG dual fuel engine,the main research content is listed as follows:1.The PCB for ECU and the related hardware circuits of entire electronic control system are designed and developed.On the basis of module strategy,the main circuit is devised on the rules of separating digital signals and analog signals,separating regions of signal detecting and power driving,which could avoid the signal interference effectively.The main circuits for ECU are comprised of minimum working module of chip unit,input,output and communication circuit.In addition,signals detecting circuits of engine speed,coolant temperature and air pressure and temperature,and driving circuits of natural gas injectors and stepper motor are developed.2.The control strategy for diesel-LNG dual fuel engine is investigated.The control strategy consists of operating condition management strategy and running strategy.At operating condition management strategy,different kinds of working mode and the mutual transformation relationship are determined,then the judgment strategy of working mode is created accordingly.For running strategy,the operating conditions are divided into starting-idling condition,steady-state condition,transition condition,speed limiting condition,acceleration condition and deceleration condition respectively,then develop the corresponding control strategy in terms of the operating features of each condition.3.The Codewarrior software is applied as the development platform for Freescale MC9S12XET256,and the program of speed interrupt service,analog signals acquisition and process for sensors in different working conditions are coded.The incremental PID control algorithm is applied to correct and adjust the injection pulse width at steady state condition,and the fuzzy control algorithm is put forward to control the pulse width at acceleration condition.4.The experiment results of bench test for dual fuel engine verify the effectivety of the electronic control system,which supports the dual fuel system running in reliable and smooth way.At the same time,the data of engine external characteristics and load characteristics demonstrated:(1)the established control strategy of diesel-LNG dual fuel engine is feasible to ensure the dual-fuel engine running well;(2)The dynamic performance of dual fuel engine at medium and high load condition is similar to the conventional diesel engine;(3)The natural gas and air mixture plays a significant role to improve the fuel economy of diesel engine;(4)Compared with the conventional diesel engine,the emissions of NOx and smoke decline remarkably,while the emission of CO increase obviously.