Analysis of the Turbocharger Speed to Estimate the Cylinder-to-Cylinder Injection Variations - Part 2 - Frequency Domain Analysis

Abstract

For the development of a very high efficiency engine, the continuous monitoring of the engine operating conditions is needed. Moreover, the early detection of engine faults is fundamental in order to take appropriate corrective actions and avoid malfunctioning and failures. The in-cylinder pressure is the most direct parameter associated to the engine thermodynamic cycle. The cost and the intrusiveness of the dynamic pressure sensor and the harsh operating condition that limits its life-time, make the direct measurement of the in-cylinder pressure not suitable for mass production applications. Consequently, research is oriented on the measurement of physical phenomena linked to the thermodynamic cycle to obtain useful information for the ICE control. For turbocharged engine application, the direct connection between the thermo-dynamic and fluid-dynamic conditions at the engine cylinder exit and the turbocharger behavior suggests that turbocharger instantaneous speed could give useful information about the engine cycle. By considering diesel engines, strong attention is paid to the injectors, which operating characteristics vary with respect to the nominal one usually due to the injector individual tolerance and the time degradation. The correct operation of the injectors and the control of the injected fuel quantity, allow ensuring the right combustion process and consequently maintaining engine performance at design-level in the long term. In previous studies, a preliminary investigation of the relationship between the engine performance and the turbocharger speed of a four-stroke multi-cylinder turbo-diesel engine was carried out. It was assessed that a condition monitoring and fault detection strategy based on the turbocharger (TC) speed measurement can be defined. Both the numerical and experimental results confirm that the instantaneous TC speed is a potentially suitable indicator for the detection of the cylinder-to-cylinder injection variation. In the present study, by exploiting the calibrated numerical model, several cylinder-to-cylinder injection variations were considered in the whole engine operating range in order to define a robust injection monitoring strategy based on the instantaneous TC speed for the estimation of the actual injected fuel quantity in each cylinder. The results of the Fast Fourier Transform (FFT) processing methodology are here reported. The method is based on the frequency analysis of the instantaneous TC speed signal. By taking advantage of the periodicity of the signal, its treatment on the frequency domain could simplifies the injection monitoring strategy. Indeed, the FFT has a low computational cost and has been used successfully in many other applications

Innovative Control Strategies for the Diagnosis of Injector Performance in an Internal Combustion Engine via Turbocharger Speed

“…The reliability of the acceleration methodology for the injector performance monitoring is, however, limited by the engine speed. In previous studies [30,31], it was shown in fact that at high engine rotational speeds (3000 rpm and above), the correlation between the TCAF parameter and the injected fuel in one of the cylinders is no longer stable and exploitable, due to the following reasons:  at high engine rotational speeds, the scavenging phase (if present) managed by the valve overlap makes the pressure wave coming from the inlet duct (i.e., from the compressor) affect the pressure at the turbine inlet and the instantaneous TC speed;  high engine speeds are connected to strong pressure pulsations, and consequently to instantaneous TC speed oscillations, characterized by very high frequency, as testified by Eq. 3, where is the number of cylinders, N is the average engine speed and T is the number of strokes of the engine.…”

“…The consideration above is true as long as the engine speed is kept constant. The coefficient of the linear proportionality does change, however, by varying the engine rotational speed, as discussed in [31]. Conversely, it is indeed true that the sensitivity on the F4 module grows by reducing the engine speed.…”

“…Upon examination of the sensitivity of the instantaneous TC speed to the cylinder-to-cylinder and to the global injection variation, two methodologies have been theoretically conceived in the recent past [30,31] with the aim of detecting the actual fuel quantity injected in each cylinder during engine operation. In previous studies, the methodologies were set up making use of a 1D numerical model of the same engine that was then tested in the present study.…”

“…The reliability of the acceleration methodology for the injector performance monitoring is, however, limited by the engine speed. In previous studies [30,31], it was shown in fact that at high engine rotational speeds (3000 rpm and above), the correlation between the TCAF parameter and the injected fuel in one of the cylinders is no longer stable and exploitable, due to the following reasons:…”

“…The developed methodology makes use of different order in the engine functioning to get a complete representation of different phenomena. A brief description of each significant order used is reported following [30,31]:…”