With a push to continuously develop traditional engine technology efficiencies and meet stringent emissions requirements, there is a need to improve the precision of injection rate measurement used to characterise the performance of the fuel injectors. New challenges in precisely characterising injection rate present themselves to the Original Equipment Manufacturers (OEMs), with the additional requirements to measure multiple injection strategies, increased injection pressure and rate features. One commonly used method of measurement is the rate tube injection analyser; it measures the pressure wave caused by the injection within a column of stationary fluid. In a rate tube, one of the significant sources of signal distortion is a result of the injected fluid pressure waves reflected back from the tube termination.
Cepstral analysis has shown to be a useful tool when evaluating formants in speech analysis, evaluating speaker harmonics and identifying sideband families in mechanical systems for fault identification. It is of particular usefulness in single input multiple output systems where the signal is distorted by echoes from its source. This study employs cepstrum analysis for evaluating fluid born frequencies present in a rate tube injection measurement device in order to identify sources of distortion in the injection rate signal.
A rate tube was used to measure the rate of injection from a Delphi EURO 6 commercial vehicle common rail diesel injector. Injection rate signals were acquired under stable temperature conditions then digitally processed and its cepstrum evaluated. With knowledge of the system, this study shows that it is possible to identify the influence of components on the system and sources of signal distortion present in the rate measurement using quefrency and rahmonics. This paper presents a systematic methodology used for employing cepstrum for pulsating hydraulic systems to aid system optimization and fault detection.