No 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

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 two processing methodologies of the instantaneous TC speed signal in the time domain are reported in the present paper. Both methods take into account the contribution of each cylinder by considering in the first case the integral of the instantaneous TC speed signal and in the second one its derivative, whose behavior matches the upstream pressure of the turbine

In order to ensure a high level of performance and to comply with the increasingly severe limitations in terms of fuel consumption and pollution emissions, modern diesel engines need continuous monitoring of their operating conditions by their control units. With particular focus on turbocharged engines, which are presently the standard in a large number of applications, the use of the average and the instantaneous turbocharger speeds is thought to represent a valuable feedback of the engine behavior, especially for the identification of the cylinder-to-cylinder injection variations. The correct operation of the injectors and control of the injected fuel quantity allow the controller to ensure the right combustion process and maintain engine performance. In the present study, two different techniques are presented to fit this scope. The techniques are discussed and experimentally validated, leading to the definition of an integrated control strategy, which features the main benefits of the two, and is able to correctly detect the cylinder-to-cylinder injection variation and, consequently, properly correct the injection in each cylinder in order to balance the engine behavior. In addition, the possibility of detecting misfiring events was assessed.

Turbocharged engines are setting themselves as the present standard in case of high-performance engines for sport applications. The coupling of a turbomachine with an internal combustion engine poses, however, some serious challenges, especially regarding the time lags and the transitory flow conditions. In particular, focus is presently being paid to the acceleration phase of these sport vehicles, where the mass flow is much lower than that attended at maximum efficiency condition and the transitory response of the turbocharger becomes pivotal to provide promptly high compression ratios to the engine. In this view, the global optimization process of new turbochargers must be oriented not only at maximizing the aerodynamic efficiency at the best design point but also at providing good efficiency at low mass flow rates, combined with a reduced inertia to enable fast acceleration. In the study, a multi-objective methodological approach is presented aimed at designing the turbine of a high-performance turbocharged engine based on the following requirements: 1) high efficiency at the design point; 2) good efficiency at low mass flow rates, typical of the acceleration phase; 3) reduced inertia; 4) overall aerodynamic design adaptable with constructive constraints. In doing so, some design considerations are also provided, pointing out the different design choices that can be made in a design strategy focused either on maximum efficiency or on the minimization of the system inertia. The aerodynamic optimization has been carried out with an in-house CFD 3D code, while the turbine coupling with the engine has been obtained by embedding the aerodynamic maps into the 1D engine model. The analysis showed that the new focus on the transitory response modified substantially the conventional design of the turbine, leading to new geometries able to improve notably the overall performance of the turbocharger.