Injector Characterisation Measurement Technology for a Production Environment

The performance of Heavy-Duty common rail injectors is directly responsible for the power, efficiency, and emission levels of diesel engines. The variance in injector measurements, negatively impact performance and emissions characteristics of engines in real world applications. The main objectives of this work were to identify sources of injection measurement variance in a rate tube injection meter, and to gain insight into how to characterise high pressure multiple injection events for near future applications. Experimental schemes were developed using existing production injector test equipment to investigate sources of injector performance measurement variance. The investigations were carried out using standard production measurement equipment. This research identified sources of variance in a rate tube meter, as: zero value baseline variance originating from pressure wave activity in the fluid medium, high frequency cavitation activity in the injection event, accuracy of the temperature to speed of sound transfer function, cumulative signal offset driven by fluid dependant properties during the injection event, and artefacts in the characteristic injection rate profile after the end of the injection event. A 1D hydraulic model of a rate tube was constructed to identify the source of the experimental observations. The knowledge gained from the analysis of the model informed the design of a three-month trial under production conditions, to improve the accuracy of the temperature to speed of sound transfer function using large datasets. Results from the experimental schemes were used to construct normalised datasets for feature selection using data mining and correlation analysis. This led to the discovery of a source of previously unknown injector performance variance caused by high pressure supply resonant wave activity. Major contributions to the field of automotive fuel injector performance characterisation from the research included an optimised hydraulic design approach that eliminates previously unknown low frequency resonant zero value variance, a unique data set on high frequency resonance spectrograms of an unfiltered rate tube signal, and demonstration that post injection rate distortion is a product of fluid friction from the tube walls before the sensor port. Additional contributions of this work included a 1D rate tube model, novel cepstrum signal noise and fluid properties analysis, distortion free injection rate signal processing, improved accuracy of temperature to speed of sound signal magnitude calibration, identification of the criteria for the repeatability of thermal signal offsets, and automated feature selection algorithms that reveal novel sources of variance. This knowledge transferred to the production environment in 2018, enabling reduced cycle times and an order-of-magnitude improvement in consecutive mass measurement repeatability, leading to a 10% increase in Overall Equipment Effectiveness