The studies of an electronically controlled CNG system for dual fuel engines

In order to improve the engine's emission performance and convert diesel engine to dual fuel engine, an electronically controlled natural gas injection system is developed for the X6130 naturally aspirated bus diesel engine. The system includes gas supply, electronic control unit(ECU) and auxiliary systems, which consists of harness, sensors, mechanical diesel control system and diagnostic system. The injection natural gas pressure is 1 MPa and six high-speed solenoid valves(HSV) are used to control natural gas injection timing and quantity of each cylinder at each work cycle. The ECU is based on the MC68HC811A1 microcontroller unit(MCU) and the system software is edited by MOTOROLA assembly language. The test results show that the system has great advantage in the aspects of emission and economy. Adopting multi-point electronic control injection for dual fuel system can get as high as 92% of CNG substitution at rated power and reduce NOx and PM emissions greatly. Then we conduct the environment test for ECU and make road-running test on bus. The test results show that the dual fuel system is a practical system and that using dual fuel system to convert diesel engine is an important way to exert the advantage of natural gas in improving the emission of a bus engine.