Turbocharger Rotational Speed Research Articles

Reducing emissions of harmful substances in rally cars

Currently discussed changes in the automotive sector, which are aimed at significantly reducing emissions of harmful substances in road transport, also affect the directions of development of motorsport. One of them is the use of electric drive systems. Currently produced electric cars are not technically prepared to compete in car rallies, both due to their performance and safety reasons. For this reason, rallies still use combustion engines and attempts are made to implement hybrid drive systems. Bearing in mind the above-mentioned limitations of electric drive technology, combustion engines will remain in car rallies for a longer time. Taking the above into account, the article focuses on the issues of exhaust gas treatment systems in rally cars. Tests were carried out to determine exhaust emissions from a car using a catalytic converter approved according to FIA guidelines and compare them to the current standards for mass-produced cars. Thanks to them, it was also possible to estimate the level of exhaust emissions on the approach sections of the car rally. A separate issue was the analysis of how much the use of an electrically driven compressor could reduce fuel consumption by limiting the operation of the ALS system, which is designed to maintain the turbocharger's rotational speed at a constant level. Reducing fuel consumption on the special stage would also have a positive impact on reducing emissions of harmful substances from the rally car.

Surge Prevention Techniques for a Turbocharged Solid Oxide Fuel Cell Hybrid System

Abstract Pressurized solid oxide fuel cell (SOFC) systems are one of the most promising technologies to achieve high energy conversion efficiencies and reduce pollutant emissions. The most common solution for pressurization is the integration with a microgas turbine, a device capable of exploiting the residual energy of the exhaust gas to compress the fuel cell air intake and, at the same time, generating additional electrical power. The focus of this study is on an alternative layout, based on an automotive turbocharger, which has been more recently considered by the research community to improve cost effectiveness at a small size (<100 kW), despite reducing slightly the top achievable performance. Such a turbocharged SOFC system poses two main challenges. On one side, the absence of an electrical generator does not allow direct control of the rotational speed, which is determined by the power balance between turbine and compressor. On the other side, the presence of a large volume between compressor and turbine, due to the fuel cell stack, alters the dynamic behavior of the turbocharger during transients, increasing the risk of compressor surge. The pressure oscillations associated with such event are particularly detrimental for the system because they could easily damage the materials of the fuel cells. This paper aims is to investigate different techniques to drive the operative point of the compressor far from the surge condition when needed, reducing the risks related to transients and increasing its reliability. By means of a system dynamic model, developed using the transeo simulation tool by Thermochemical Power Group (TPG), the effect of different antisurge solutions is simulated: (i) intake air conditioning, (ii) water spray at compressor inlet, (iii) air bleed and recirculation, and (iv) installation of an ejector at the compressor intake. The pressurized fuel cell system is simulated with two different control strategies, i.e., constant fuel mass flow and constant turbine inlet temperature. Different solutions are evaluated based on surge margin behavior, both in the short and long terms, but also monitoring other relevant physical quantities of the system, such as compressor pressure ratio and turbocharger rotational speed.

A phenomenological model for the description of unburned hydrocarbons emission in ultra-lean engines

The adoption of lean-burn concepts for internal combustion engines working with a homogenous air/fuel charge is under development as a path to simultaneously improve thermal efficiency, fuel consumption, nitric oxides, and carbon monoxide emissions. This technology may lead to a relevant emission of unburned hydrocarbons (uHC) compared to a stoichiometric engine. The uHC sources are various and the relative importance varies according to fuel characteristics, engine operating point, and some geometrical details of the combustion chamber. This concern becomes even more relevant in the case of engines supplied with natural gas since the methane has a global warming potential much greater than the other major pollutant emissions. In this work, a simulation model describing the main mechanisms for uHC formation is proposed. The model describes uHC production from crevices and flame wall quenching, also considering the post-oxidation. The uHC model is implemented in commercial software (GT-Power) under the form of “user routine”. It is validated with reference to two large bore engines, whose bores are 31 and 46 cm (engines named accordingly W31 and W46). Both engines are fueled with natural gas and operated with lean mixtures (λ > 2), but with different ignition modalities (pre-chamber device or dual fuel mode). The engines under study are preliminarily schematized in the 1D simulation tool. The consistency of 1D engine schematizations is verified against the experimental data of BMEP, air flow rate, and turbocharger rotational speed over a load sweep. Then, the uHC model is validated against the engine-out measurements. The averaged uHC predictions highlight an average error of 7% and 10 % for W31 and W46 engines, respectively. The uHC model reliability is evidenced by the lack of need for a case-dependent adjustment of its tuning constants, also in presence of relevant variations of both engine load and ring pack design.

Dynamics and control of a turbocharged solid oxide fuel cell system

• A cold bypass valve control can comply with the fuel cell system constraints. • Four controllers were tested on the system during load variation scenarios. • The cascade controllers with feed-forward approaches are the most promising. • A proportional-integrative cannot control the system properly for quick transients. The purpose of this paper regards the design and testing of control systems for a 30-kW turbocharged solid oxide fuel cell system fuelled with biogas. The adoption of a turbocharger, instead of a micro gas turbine, for the fuel cell stack pressurisation, is an innovative solution that is expected to decrease the capital cost of such systems and to facilitate their penetration into the energy market. However, not being connected to an electric generator, the turbocharger rotational speed, and thus the air mass flow, cannot be directly controlled as in microturbines. The control of turbocharged solid oxide fuel cell systems is a novel topic, characterised by many technical challenges that have not been addressed before. To regulate the stack temperature, a cold bypass valve is included, connecting the compressor outlet to the turbine inlet. A dynamic model of this system was developed in Matlab-Simulink® to analyse the response of the turbocharged solid oxide fuel cell system to a cold bypass valve opening step change. System information obtained from this analysis was used to design and tune four controllers: a conventional proportional integral controller and three different cascade controllers. The controller performance was evaluated under two different scenarios, considering quite aggressive power ramps. The best results were obtained with a cascade controller, where the feedback loop was complemented by a feed-forward contribution based on power demand. This analysis demonstrated that such a control system effectively tracks the fuel cell maximum temperature target, complying with all the system operative constraints.

Improvement of instantaneous turbine efficiency through late intake valve phase (LIVP) in a turbocharged-gasoline direct injection (T-GDI) engine

The effects of a late intake valve phase (LIVP) strategy on crank-angle resolved real-time turbocharger efficiency were analyzed. The research is composed of experiments and simulations. In the experiments, an engine test was conducted with a downsized 2.0 L 4-cylinder turbocharged-gasoline direct injection (T-GDI) engine. In order to evaluate the effects of LIVP on the instantaneous turbocharger efficiency, the intake valve phase was retarded from its reference phase to 30 crank angle degrees (CADs) by steps of 10 CADs, while maintaining the fixed position of the other engine control parameters. Pressure in the intake and exhaust systems and turbocharger rotational speed were also measured in the experiments. In the simulation, a 1-D simulation model was built to simulate the same conditions as in the experiments. Instantaneous turbine mass flow rate as well as, temperature upstream and downstream of the turbine were extracted from the model in the units of CAD. This was done because it is inherently impossible to measure these data in the units of CAD with the existing real-world mass flow meter and thermocouples. The instantaneous blade speed ratio (BSR), turbine efficiency, and mass flow parameter were calculated by combining the results of the experiment and the 1-D simulation. In the results, the instantaneous turbine efficiency was divided into two phases and analyzed. First, in the filling phase, the effects of exhaust blow-down pulse arrival on the instantaneous turbine efficiency were analyzed. Second, in the emptying phase, the effects of exhaust gas scavenged from the cylinder on the instantaneous turbine efficiency were analyzed. The instantaneous turbine efficiency showed strong unsteady characteristics and deviated from the quasi-steady performance line. This was due to large fluctuations in the turbine inlet conditions. With the application of the LIVP strategy, the instantaneous turbine efficiency was increased. This was because of a decrease in the amount the waste-gate opened while meeting the same engine load lead to more exhaust gas energy entering the turbine, and the turbine’s operating conditions were changed to more efficient conditions. Finally, correlation of the engine thermal efficiency rising according to the instantaneous turbine efficiency rising was confirmed.

An Adaptive Frequency-Locked-Loop Approach for the Turbocharger Rotational Speed Estimation via Acoustic Measurements

Obtaining accurate measures of the turbocharger rotational speed is a key task to achieve good powertrain control performance in turbocharged combustion engines. However, direct access to the rotating parts of a turbocharger requires expensive sensors that present long-term reliability issues. In view of this, this article focuses on the design of measurement architectures for the estimation of the turbocharger shaft rotating speed via the numerical processing of the overall sound emissions acquired by a microphone placed in the vehicle hood. This kind of signal represents an extremely rich source of information about the operating conditions of all noisy powertrain subsystems. The core of the scheme is represented by an adaptive discrete-time nonlinear frequency locked-loop (FLL) filter that is properly designed to extract the useful frequency content from the acquired audio signal. The whole architecture is innovative, flexible, and extremely low cost by requiring, for its implementation, the additional installation of a single microphonic capsule only. Moreover, it exhibits such a modest computational burden to be directly implementable in commercial engine control units (ECUs) without requiring additional computing hardware. Reported experimental assessments show that the accuracy of the estimate is excellent in all allowed rotational speed regimes.

Vibration analysis to estimate turbocharger speed fluctuation in diesel engines

The optimum management of the engine system has a crucial role in order to achieve high efficiency and reduced pollutant emissions. Advanced methods have been proposed, in which several types of sensors are used to directly/indirectly sense the combustion and to provide a feedback signal to optimize the engine management.In turbocharged engines, it has been demonstrated that a relationship exists between the rotational speed of the turbocharger and the thermo-fluid dynamic condition of the gases at the exhaust valve opening. Such a relation allows to establish a link between the engine operating conditions in terms of speed, load and injection settings and the turbocharger speed.A research activity was performed aimed at developing a methodology in which the signal from an accelerometer mounted on the compressor housing was used to extract information about the turbocharger speed value. The activity was organized in two subsequent steps, each one focused on one specific objective:– estimation of the mean turbocharger rotational speed– evaluation of the turbocharger speed fluctuations.Tests were performed on a small displacement two-cylinder diesel engine mainly used in urban vehicles that was equipped with a turbocharger. The results obtained during the first step of activity demonstrated the opportunity of further investigations in order to compute the turbocharger speed fluctuation from the accelerometer signal processing. This paper is devoted to present the results of the second step of the research activity, with the final aim of realizing a non intrusive control of combustion process, in which the variation of combustion development as regards nominal condition is detected via the estimation of the turbocharger speed.

Turbocharger speed estimation via vibration measurements for combustion sensing

Monitoring of engine operating condition is essential to comply with severe limitations of harmful exhaust emissions and fuel consumption. Several strategies have been proposed, in which different types of sensors are used for the direct/indirect combustion sensing and to provide a feedback signal to optimize the process.It has been demonstrated that in a turbocharged engine a relationship exists between the rotational speed of the turbocharger and the thermo-fluid dynamic condition of the gases at the exhaust valve opening. Such a relation allows to establish a link between the engine operating conditions in terms of speed, load and injection settings and the turbocharger speed.This work presents a methodology devoted to extract from an accelerometer signal, the mean turbocharger rotational speed with the final aim of realizing a non intrusive control of combustion process, in which the variation of combustion development as regards nominal condition is detected via the estimation of the turbocharger speed.

Automotive Turbochargers Power Estimation Based on Speed Fluctuation Analysis

Turbocharging technology will play a crucial role in the near future as a way to meet the requirements for pollutant emissions and fuel consumption reduction.However, optimal turbocharger control is still an issue, especially for downsized engines fitted with a low number of cylinders. As a matter of fact, automotive turbochargers are characterized by wide operating range and unsteady gas flow through the turbine, while only steady flow maps are usually provided by the manufacturer. In addition, in passenger cars applications, real-time turbocharger optimal control is even more difficult because of the lack of information about pressure/temperature in turbine upstream/downstream circuits and turbocharger rotational speed.In order to overcome these unknowns, this work presents a methodology for instantaneous turbocharger rotational speed determination through a proper processing of the signal coming from one accelerometer mounted on the compressor diffuser, or one microphone facing the compressor. The presented approach can be used to evaluate both turbocharger speed mean value and the amplitude of turbocharger speed fluctuations caused by the pulsating gas flow in turbine upstream and downstream circuits. Once turbocharger speed has been determined, it can be used to estimate power delivered by the turbine.The whole estimation algorithm has been developed and validated for a light duty turbocharged Common-Rail Diesel engine mounted in a test cell. However, the developed methodology is general and can be applied to different turbochargers, both for Spark Ignited and Diesel applications.

Estimation Methodology for Automotive Turbochargers Speed Fluctuations Due to Pulsating Flows

Turbocharging technique, together with engine downsizing, will play a fundamental role in the near future as a way to reach the required maximum performance while reducing engine displacement and, consequently, CO2 emissions. However, performing an optimal control of the turbocharging system is very difficult, especially for small engines fitted with a low number of cylinders. This is mainly due to the high turbocharger operating range and to the fact that the flow through compressor and turbine is highly unsteady, while only steady-flow maps are usually provided by the manufacturer. In addition, in passenger cars applications, it is usually difficult to optimize turbocharger operating conditions because of the lack of information about pressure/temperature in turbine upstream/downstream circuits and turbocharger rotational speed. This work presents a methodology suitable for instantaneous turbocharger rotational speed determination through a proper processing of the signal coming from an accelerometer mounted on the compressor diffuser or a microphone faced to the compressor. The presented approach can be used to evaluate turbocharger speed mean value and turbocharger speed fluctuation (due to unsteady flow in turbine upstream and downstream circuits), which can be correlated to the power delivered by the turbine. The whole estimation algorithm has been developed and validated for a light-duty turbocharged common-rail diesel engine mounted in a test cell. Nevertheless, the developed methodology is general and can be applied to different turbochargers, both for spark ignited and diesel applications.

Total Pressure Loss Mechanism of Centrifugal Compressors

To develop the turbocharger matching system, a compressor model and turbine model need to be developed independently and coupled. This paper describes the construction of the centrifugal compressor model and its validation with the experimental data. The compressor model in this paper uses One-dimensional (1D) thermo-fluid equations to analyse the compressor side of a turbocharger. Under a specified set of turbocharger geometry, atmospheric conditions, rotational speed, and fluid mass flow rate, the model can calculates the static and total temperatures, velocities, static and total pressures, pressure losses, and isentropic efficiencies for each compressor component. Instead of using lumped loss parameters, the compressor model includes established loss models found in the open literature. Not only in the impeller, the losses in the diffuser and the volute are modelled. With the model, it is possible for a parametric study on the effect of each loss mechanism on the performance, and which can aid the designer in justifying design decisions minimising the magnitude of the losses and thus positively influence the overall performance. The compressor model can also be applied to investigate the two stage Turbocharging or Variable Geometry Turbocharger (VGT) in the future.

1D Simulation and Experimental Analysis of a Turbocharger Turbine for Automotive Engines Under Steady and Unsteady Flow Conditions

Turbocharging technique is more and more widely employed on compression ignition and spark ignition internal combustion engines, as well, to improve performance and reduce total displacement. Experimental studies, developed on dedicated test facilities, can supply a lot of information to optimize the engine-turbocharger matching, especially if tests can be extended to the typical engine operating conditions (unsteady flow). A specialized components test rig (particularly suited to study automotive turbochargers) has been operating since several years at the University of Genoa. The test facility allows to develop studies under steady or unsteady flow conditions both on single components and subassemblies of engine intake and exhaust circuit.In the paper the results of an experimental campaign developed on a turbocharger waste-gated turbine for gasoline engine application are presented. Preliminarily, the measurement of the turbine steady flow performance map is carried out. In a second step the same component is tested under unsteady flow conditions. Instantaneous inlet and outlet static pressure, mass flow rate and turbocharger rotational speed are measured, together with average inlet and outlet temperatures.A numerical procedure, recently developed at the University of Naples, is then utilized to predict the steady turbine performance map, following a 1D approach. The model geometrically schematizes the component basing on few linear and angular dimensions directly measured on the hardware. Then, the 1D steady flow equations are solved within the stationary and rotating channels constituting the device. All the main flow losses are properly taken into account in the model. The procedure is able to provide the sole “wheel-map” and the overall turbine map. After a tuning, the overall turbine map is compared with the experimental one, showing a very good agreement.Moreover, in order to improve the accuracy of a 1D engine simulation model, the classical map-based approach is suitably corrected with a sequence of pipes that schematizes each component of the device (inlet/outlet ducts, volute and wheel) included upstream and downstream the turbine to account for the wave propagation and accumulation phenomena inside the machine. In this case, the previously computed “wheel-map” is utilized. The turbine pipes dimensions, are automatically provided by the geometrical module of the proposed procedure to correctly reproduce the device volume and the flow path length.

Pulsating flow performance of a turbocharger compressor for automotive application

Downsizing with turbocharging is the most promising way, especially in terms of cost, to get reduced fuel consumption and CO2 emissions particularly in the case of Spark Ignition engines. In automotive applications the turbocharger turbine usually operates under heavy unsteady flow conditions due to the opening and closing of engine valves. However, in the case of extremely downsized engines with a reduced number of cylinders and a small intake circuit volume also the compressor performance can be affected by the unsteady flow generated by the engine intake valves.To make simulation models able to accurately predict engine performance, a better understanding of compressor and turbine pulsating flow performance can be accomplished through measurements performed on specialized test facilities, using suitable measuring equipment. As regards the turbocharger compressor, the surge line position under pulsating flow conditions is another important aspect to be considered.In the paper the results of a broad experimental investigation performed on a small turbocharger compressor matched to a downsized gasoline engine are presented. Measurements were developed on the test facility operating at the University of Genoa, which allows investigations on automotive turbochargers both under steady and unsteady flow conditions. Tested turbocharger compressor was coupled to the automotive engine intake circuit and the pulsating flow was generated by a motor-driven cylinder head fitted with a variable valve actuation system.Different levels of turbocharger rotational speed and different intake valve opening strategies were considered. For each operating condition compressor unsteady performance was evaluated starting from measurement of several instantaneous parameters (inlet and outlet static pressure, mass flow rate and turbocharger rotational speed). A significant deviation of compressor instantaneous performance from steady state was observed, resulting in a hysteresis loop surrounding the steady state curve.

Experimental analysis of unsteady flow performance in an automotive turbocharger turbine fitted with a waste-gate valve

Downsizing and turbocharging is today an effective way of enhancing fuel economy in automotive engines. However, more information on compressor and turbine behaviour when working under unsteady flow conditions typically occurring in automotive turbocharged engines is still required to improve simulation models. The results of an experimental investigation into a small turbocharger turbine fitted with a waste-gate valve are presented in this paper. Turbine performance was measured under both steady and unsteady flow operation. Particular attention was given to pulsating flow performance, evaluated starting from the measurement of instantaneous parameters (inlet and outlet static pressure, mass flowrate, and turbocharger rotational speed). The effect of flow unsteadiness on turbine behaviour is analysed, referring to different pulse frequencies and waste-gate settings. The paper highlights that steady and unsteady turbine performance when the waste-gate valve is partially or totally open should be known in order to improve engine-turbocharger matching calculations.