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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.

This paper describes a gas-dynamic model for the basic elements of exhaust mufflers in a spark ignition (SI) engine. Attention has been paid in particular to the modelling of the concentric tube resonator with a perforated pipe inside, since this element has been a problem for gas dynamic modelling (GDM) of mufflers. The model was coupled with a previously developed engine simulation code, ENGWA-1, for both acoustic and gas dynamic performance analysis of mufflers. Measured pressures in the positions of interest in a practical exhaust system and exhaust noise spectra from a tail pipe were compared with simulations for validating the model. Results show that the model can satisfactorily predict measurements. Moreover, how to use the computer code for muffler design has been discussed for the point of engineering application.