Measurement technology and analysis of gas injection rate for the compressed natural gas(CNG)engine

The method for measuring the gas injection rate of a compressed natural gas(CNG)engine was discussed in this paper,and a test platform based on the constant volume method was established.The accuracy of the test platform was guaranteed by taking account of such characteristics as the chocking phenomenon,pressure fluctuation in the chamber and leakage from the gas injector.To develop the CNG engine YC6K400LN-C30,which was produced by YUCHAI,the gas injection rate of the injector was tested,successfully yielding the curve of injection rates under varying pressure and gas injection pulse widths.Additional important data including gas injection delay,duration,and mass flow rate of injection were also noted.The results showed that,under constant pulse width but different injection pressures,the injection delays and durations were identical;the mass flow rate of the hold phase was directly proportional to the injection pressure;injector opening times increased with increasing injection pressure;and,the injection mass and duration were linear with the pulse width after the injector had opened completely.When the injection mass was less than 40 mg,it was highly inconsistent.This study has shown that that the injection duration can be shortened by increasing the injection pressure,alleviating the problem of gas escaping into the exhaust pipe during the valve overlapping period.Gas economy,emission characteristics,and dynamic performance can be improved.