The Study of the Dynamics of Diesel Engine Fuel Injectors with Alternative Fuels for Diagnosis

With the oncoming energy crisis in fossil fuels, the study of alternative fuels has become a topic of much concern for industry in recent years. Among the alternative fuels, biodiesel shows huge potential for solving the crisis as it can be used in traditional diesel engine systems with minimal modifications.
The injector has the highest failure rate in diesel engines, which has more potential for using biodiesels that have higher viscosity and bulk modulus. However, the influence of biodiesel on the injector’s dynamics and diagnostics has rarely been reported. In practice, the injector operation is influenced by many factors and it is hard to extract its dynamic characteristics for the purpose of detection and analysis by using the traditional techniques like the vibration and the airborne sound (AS), which are highly affected by other processes in the engine systems, such as combustion. As a non-intrusive condition monitoring (CM) technique, acoustic emissions (AE) can detect a very high frequency event, which means it has good localized performance and is less likely to be interfered by noises from other engine process such as combustion. Thereafter, as a promising nonintrusive technique, AE measurement is employed in this project to study the injector dynamics for the purpose of diagnosis. At the same time, to verify this method, conventional intrusive monitoring methods, such as cylinder pressure and injector pressure are also investigated.
A series of analytic studies and experiments are carried out based on a four-stroke diesel engine system by changing the running of the engine with different loads, speeds and fuel types. The signals are converted to the angular domain to help understand the behavior of the injection process. From the results analysis, it has been found that the injection parameters, such as starting angle, closing angle and impact strength, have high correlation with AE signals. Moreover, current study results show that the envelope of the AE signal has good performance in estimating the injection open angle for all fuel types. Therefore, AE can be employed as a non-intrusive method for monitoring the injection behaviour of different fuels. In addition, AE amplitudes of injecting pure biodiesels show little increase although the injection pressures are clearly higher in comparison with normal diesel fuel. This may be accounted by the softening effect of high viscosity.