Apostolos Pesiridis

Mild Hybridization via Electrification of the Air System: Electrically Assisted and Variable Geometry Turbocharging Impact on an Off-Road Diesel Engine

Electric turbocharger assistance consists in incorporating an electric motor/generator within the turbocharger bearing housing to form a mild-hybrid system, without altering other mechanical parts of the engine. This makes it an ideal and economical short to medium term solution for the reduction of CO2 emissions.The scope of the paper is to assess the improvements in engine energy efficiency and transient response correlated to the hybridization of the air system. To achieve this, an electrically assisted turbocharger with a variable geometry turbine has been compared to a similar, not hybridized, system over step changes of engine load. The variable geometry turbine has been controlled to provide different levels of initial boost, including one optimized for efficiency, and to change its flow capacity during the transient. The engine modeled is a 7-litre, 6-cylindres diesel engine with a power output of over 200 kW and a sub-10 kW turbocharger electric assistance power. To improve the accuracy of the model, the turbocharger turbine has been experimentally characterized by means of a unique testing facility available at Imperial College and the data has been extrapolated by means of a turbine meanline model.Optimization of the engine boost to minimize pumping losses has shown a reduction in brake specific fuel consumption up to 4.2%. By applying electric turbocharger assistance, it has been possible to recover the loss in engine transient response of the efficiency optimized system, as it causes a reduction in engine speed drop of 71% to 86% and of 79% to 94% in engine speed recovery time. When electric assistance is present in the turbocharger, actuating the turbine vanes to assist transient response has not produced the desired result but only a decrement in energy efficiency. If the variable geometry turbine is opened during transients, an improvement in specific energy efficiency with negligible decrement in engine transient performances has been achieved.Copyright

Investigation of Cylinder Deactivation and Variable Valve Actuation on Gasoline Engine Performance

Increasingly stringent regulations on gasoline engine fuel consumption and exhaust emissions require additional technology integration such as Cylinder Deactivation (CDA) and Variable valve actuation (VVA) to improve part load engine efficiency. At part load, CDA is achieved by closing the inlet and exhaust valves and shutting off the fuel supply to a selected number of cylinders. Variable valve actuation (VVA) enables the cylinder gas exchange process to be optimised for different engine speeds by changing valve opening and closing times as well as maximum valve lift. The focus of this study was the investigation of effect of the integration of the above two technologies on the performance of a gasoline engine operating at part load conditions. In this study, a 1.6 Litre in-line 4-cylinder gasoline engine is modelled on an engine simulation software and its data were analysed to show improvements in fuel consumption, CO2 emissions, pumping losses and effects on CO and NOx emissions. A CDA and VVA operating window is identified which yields brake specific fuel consumption improvements of 10-20% against the base engine for speeds between 1000rpm to 3500rpm at approximately 12.5% load. Highest concentration of CO emissions was observed for BMEP inbetween 4 bar to 5 bar at 4000rpm, and highest concentration of NOx found at the same load range but at 1000rpm. Findings based on simulation results point towards significant part load performance improvements which can be achieved by integrating cylinder deactivation and variable valve actuation on gasoline engines.

Effects of mechanical turbo compounding on a turbocharged diesel engine

This paper presents the simulation study on the effects of mechanical turbo-compounding on a turbocharged diesel engine. A downstream power-turbine has been coupled to the exhaust manifold after the main turbocharger, in the aim to recover waste heat energy. The engine in the current study is Scania DC13-06, which 6 cylinders and 13 litre in capacity. The possibilities, effectiveness and working range of the turbo compounded system were analyzed in this study. The system was modeled in AVL BOOST, which is a one dimensional (1D) engine code. The current study found that turbo compounding could possibly recover on average 11.4% more exhaust energy or extra 3.7kW of power. If the system is mechanically coupled to the engine, it could increase the average engine power by up to 1.2% and improve average BSFC by 1.9%.

The application of active control for turbocharger turbines

In this paper, the motivation behind the development of an active control turbocharger is presented, along with the initial thinking that led to the basic concept of applying active flow control at the inlet to a turbocharger turbine. In addition, the concept of active control for turbochargers is analysed in depth with the purpose of presenting a theoretical basis for any subsequent application of this type of control of exhaust gas flow into a turbocharger turbine by providing the fundamental thermo-fluids background. Secondly, the aim was not only to merely present a theory summarising the behaviour of the exhaust gas flow occurring during turbocharger turbine inlet geometrical changes, but to also present the implications from the periodic nature of these geometric changes, in particular with respect to cycle performance results both for the turbocharger and for the engine. The effects of the application of active control turbochargers were demonstrated through testing of the first prototype active control turbocharger built and tested at the aerodynamic test facility at Imperial College and through the experimental data collected. In this first attempt, at the most favourable amplitudes tested, the power recovered reached a maximum value of 7.5% increase over the equivalent variable geometry turbocharger performance, although this depended on the phasing of the turbine inlet area variation in relation to the energy content variation of the incoming exhaust pulse.

Experimental Evaluation of Active Flow Control Mixed-Flow Turbine for Automotive Turbocharger Application

In the current paper we introduce an innovative new concept in turbochargers-that of using active control at the turbine inlet with the aim of harnessing the highly dynamic exhaust gas pulse energy emanating at high frequency from an internal combustion engine, in order to increase the engine power output and reduce its exhaust emissions. Driven by the need to comply to increasingly strict emissions regulations as well as continually striving for better overall performance, the active control turbocharger is intended to provide a significant improvement over the current state of the art in turbocharging: the Variable Geometry Turbocharger (VGT). The technology consists of a system and method of operation, which regulate the inlet area to a turbocharger inlet, according to each period of engine exhaust gas pulse pressure fluctuation, thereby actively adapting to the characteristics of the high frequency, highly dynamic flow, thus taking advantage of the highly dynamic energy levels existent through each pulse, which the current systems do not take advantage of. In the Active (Flow) Control Turbocharger (ACT) the nozzle is able to adjust the inlet area at the throat of the turbine inlet casing through optimum amplitudes, at variable out-of-phase conditions and at the same frequency as that of the incoming exhaust stream pulses. Thus, the ACT makes better use of the exhaust gas energy of the engine than a conventional VGT. The technology addresses, therefore, for the first time the fundamental problem of the poor generic engine-turbocharger match, since all current state of the art systems in turbocharging are still passive receivers of this highly dynamic flow without being able to provide optimum turbine inlet geometry through each exhaust gas pulse period. The numerical simulation and experimental work presented in this paper concentrates on the potential gain in turbine expansion ratio and eventual power output as well as the corresponding effects on efficiency as a result of operating the turbocharger in its active control mode compared to its operation as a standard VGT.

Experimental testing of an active control turbocharger turbine inlet equipped with a sliding sleeve nozzle

The current paper presents the performance results of a variable-flow turbocharger turbine, called the active control turbocharger. Driven by the need to comply with increasingly strict emissions regulations as well as to strive continually for a better overall performance, the active control turbocharger is intended to provide an improvement over the current state-of-the-art turbochargers, namely the variable-geometry turbocharger. In this system, the nozzle is able to alter the throat inlet area of the turbine according to the variation in the energy (the pressure, temperature and mass flow) of each engine exhaust gas pulse with the intention of capitalising upon the untapped high-energy content of these pulses. The paper concentrates on the potential gain in the turbine expansion ratio and the eventual power output, as well as the corresponding effects on the efficiency as a result of operating the turbocharger in its active control mode compared with its operation as a standard variable-geometry turbocharger. This has meant actuation of the nozzle according to the pulse frequency, for different amplitudes and phase settings. The pulsating flow turbine power recovered increased by more than 15% compared with that from an equivalent variable-geometry turbocharger turbine, with the best phase offset between the minimum nozzle position and the start of the pulse (among the four tested) being 60°.

Novel method to improve engine exhaust energy extraction with active control turbocharger

A mixed-flow turbine with pivoting nozzle vanes was designed and tested to actively adapt to the pulsating exhaust flow (called the active control turbocharger). The turbine was tested at an equivalent speed of 48,000 r/min with inlet flow pulsation of 40 and 60 Hz, which corresponds to a four-stroke diesel engine speed of 1600 and 2400 r/min, respectively. The nozzle vane operating schedules for each pulse period are evaluated experimentally in two general modes: natural opening and closing of the vanes due to the pulsating flow and the forced sinusoidal oscillation of the vanes to match the incoming pulsating flow. The turbine energy extraction as well as efficiency is compared for the two modes to formulate its effectiveness. In addition, a one-dimensional commercial code was implemented, matching an active control turbocharger to an engine with equivalent characteristics to the one simulated in the laboratory. The results obtained represented an improvement over the experimental data with the engine power increasing by between 3.58% and 7.76% between 800 and 1400 r/min; the actual turbocharger power recovery required to achieve this increase in engine power was far higher and typically exceeded 20% throughout the lower half of the engine speed range while remaining higher than 10% for most of the rest. The aim of this article is to demonstrate the potential of active control turbocharger in relation to current turbocharging practice. It has shown strong potentials to improve engine performance in parts of the operational envelope, which need to be further harnessed for real-life applications.

Variable Geometry Turbocharger Active Control Strategies for Enhanced Energy Recovery

This paper describes the development of the control system for a new type of mechanical turbocharger, the Active Control Turbocharger (ACT). The main difference of ACT compared to its predecessor, the Variable Geometry Turbocharger (VGT), lies in the inlet area modulation capability which follows an oscillating (sinusoidal) profile in order to match as much as possible the similar profile of the emitted exhaust gases entering the turbine in order to capturing the highly dynamic, energy content existent in exhaust pulses. This paper describes the development of a new controller in an adaptive framework in order to improve the response of the ACT. The system has been modelled using a one-dimensional Ricardo WAVE engine simulation software and the control system which actuates the nozzle (rack) position is modelled in Matlab-Simulink and uses a map-based structure coupled with a PID controller with constant parameters. Steady-state simulations have been carried out for different speeds and a fuel-air ratios in order to determine the optimum settings for highest brake torque for a given operating point, namely the maximum rack position, the amplitude and the phase offset. Finally, an adaptive controller has been developed in Matlab-Simulink. The controller adapts its parameters according to the operating point in order to improve the system response for a wide range of operating conditions. Regarding the control system in a transient regime, the response is significantly more accurate and the discrepancy between the desired boost pressure and the actual one has been decreased by 0.5 bar to a value of less than 0.05 bar difference.

Integration of Unsteady Effects in the Turbocharger Design Process

Turbocharger development is based on performance maps arising through steady state measurements, although the flow through the engine-turbocharger system is highly unsteady. This paper investigates the potential for integrating the effects from unsteady flow in the turbine map, in order to enhance the performance of the ICE-turbocharger system. It is, also, an initial attempt to set the framework for more accurate one-dimensional turbine simulations in order to improve the selection of turbocharger components and their matching with the ICE. The development of ‘equivalent unsteady’ maps is presented, based on energy-weighted averaging of available, unsteady, experimental data and its deviations from quasi-steady performance. The maps are subsequently used for a one dimensional (1D) simulation of a turbocharged diesel engine running at 800 RPM and 1600 RPM. A comparative assessment with results from simulations using a conventional steady-state map has shown important differences in turbine parameters (up to 12% lower efficiency and 6% lower mass flow parameter) but minor differences, of less than 1% in terms of engine performance and fuel consumption.Copyright

Experimental Evaluation of the Active Control Turbocharger Prototype Under Simulated Engine Conditions

The current paper presents the results from a comprehensive set of experimental tests on the first prototype active control turbocharger allowing a final evaluation of the first prototype of the active control turbocharger to be gained in a simulated-engine test rig conditions (since hot engine exhaust flow was simulated through equivalent compressed air cold flow test conditions). Data was obtained throughout the turbocharger speed and load range during unsteady operation. Three modes of testing were employed: FGT (Fixed Geometry Turbocharger), VGT (Variable Geometry Turbocharger) and ACT (Active Control Turbocharger). FGT and VGT tests were employed as a reference (of turbochargers predominantly in use today) against which ACT performance was compared. The effects of phasing the variable area device at 30°, 60°, 90° and 240° relative to the pulse generator opening time were assessed. Overall, the Active Control Turbocharger provided encouraging results in terms of the benefit in actual power recovered. The current system is penalised by an inefficient area-regulating design, but it was the easiest and most reliable method to carry out the investigation with, in this first prototype attempt. ACT offers a distinct potential for increased internal combustion engine power output compared to current state-of-the-art, VGT-equipped engines.Copyright