Effects of working conditions on the operating characteristics of an injection system applied on CNG fueled vehicles

A model-based study is conducted to examine the operating characteristics of an injection system applied on CNG fueled vehicles. This injection system is a combination of an electric pressure regulator, a rail tube, and a solenoid injector. The electric pressure regulator has a great potential to be widely used in injection systems of natural gas-fueled engines due to its flexible operation, which can help to improve the engine performance and reduce emission. This paper presents a simulation study using mathematical models to describe and analyze the operating characteristics of the gaseous fuel injection system, in which models of electric pressure regulator, solenoid fuel injector, and control model for electric pressure regulator are presented. The simulation results are compared with experimental data to validate the simulation models. Effects of working conditions, including coil resistance of the electric pressure regulator, inlet gas pressure, and set pressure in the rail tube, on the operating characteristics of the gaseous fuel injection system are investigated. Simulation results show that when the coil resistance of the electric pressure regulator is increased from 3.1 Ω to 4.1 Ω, the maximum fluctuation of the controlled gas pressure in the rail tube is reduced from 0.017 to 0.012 MPa, respectively. By decreasing the inlet gas pressure of the electric pressure regulator from 2.5 to 2.3 MPa, the controlled gas pressure in the rail tube is more stable with the maximum fluctuation significantly reduced from 0.012 to 0.002 MPa, respectively, which leads to stability in injection flow rate. The increase of set pressure in the rail tube from 0.5 to 0.7 MPa can help to improve the stability of the controlled gas pressure in the rail tube with the maximum fluctuation respectively reduced from 0.002 to 0.001 MPa.