An uncertainty analysis of the time-resolved fuel injection pressure wave based on BOSCH method for a common rail diesel injector with a varying current wave pattern

A system capable of measuring the time-resolved fuel injection rate of an injector with a varying current pattern supplied to the injector was constructed. The control of the driving of a common rail diesel injector is achieved by controlling the current waveform supplied to the injector. In order to control various current waveforms flowing in the common rail injector, 80 V of power supplied to the injector was switched using a negative-positive-negative (NPN) 2N3055 transistor. The transistor-transistor logic (TTL) switching signal supplied to the base terminal of the NPN 2N3055 transistor was generated from the capture compare PWM (CCP) terminal of a microcontroller. The PWM signal generated from the CCP pin creates five patterns of waveforms by combining the peak-and-hold conditions. In the first part of the 1ms injection period, the duty ratio is 100 %, while the remaining part has a waveform with a greatly reduced duty ratio. The duty ratio used in this study was 10 % or 30 %. The time-resolved pressure wave caused by fuel injection in the Bosch method was repeatedly measured. For an uncertainty analysis, 39 repetitive measurements were taken per fuel injection condition. The rail pressures used in this study were 80, 110 and 140 MPa. With five pick-and-hold current waves supplied to the injector under a rail pressure condition, the time-resolved pressure waves caused by the fuel injection tended to be almost equal during the peak duration, whereas those during the hold duration differed. The duration of the pressure wave caused by the fuel injection is prolonged at a high hold current. When the common rail pressure is high, the slope of the pressure wave in the pick interval is steeper. A parameter that can effectively evaluate the optimal current control pattern for lower power consumption and thermal dissipation of the injector solenoid is also presented.