Srithar Rajoo

Variable Geometry Mixed Flow Turbine for Turbochargers: An Experimental Study

This paper investigates a variable geometry (VG) mixed flow turbine with a novel, purposely designed pivoting nozzle vane ring. The nozzle vane ring was matched to the 3-dimensional aspect of the mixed flow rotor leading edge with lean stacking. It was found that for a nozzle vane ring in a volute, the vane surface pressure is highly affected by the flow in the volute rather than the adjacent vane surface interactions, especially at closer nozzle positions. The performance of the VG mixed flow turbine has been evaluated experimentally in steady and unsteady flow conditions. The VG mixed flow turbine shows higher peak efficiency and swallowing capacity at various vane angle settings compared to an equivalent nozzleless turbine. Comparison with an equivalent straight vane arrangement shows a higher swallowing capacity but similar efficiencies. The VG turbine unsteady performance was found to deviate substantially from the quasi-steady assumption compared to a nozzleless turbine. This is more evident in the higher vane angle settings (smaller nozzle passage), where there are high possibility of choking during a pulse cycle. The presented steady and unsteady results are expected to be beneficial in the design of variable geometry turbochargers, especially the ones with a mixed flow turbine.

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.

Comparison between the steady performance of double-entry and twin-entry turbocharger turbines

Most boosting systems in internal combustion engines utilize ‘pulse turbocharging’ to maximize the energy extraction by the turbine. An internal combustion engine with more than four cylinders has a significant overlap between the exhaust pulses which, unless isolated, can decrease the overall pulse energy and increase the engine pumping loss. Thus, it is advantageous to isolate a set of cylinders and introduce the exhaust gases into two or more turbine entries separately. There are two main types of multiple entry turbines depending on the method of flow division: the twin-entry and the double-entry turbine. In the twin-entry design, each inlet feeds the entire circumference of the rotor leading edge regardless of inlet conditions. In contrast, the double-entry design introduces the flow from each gas inlet into the rotor leading edge through two distinct sectors of the nozzle. This paper compares the performance of a twin and double-entry mixed flow turbine. The turbines were tested at Imperial College for a range of steady-state flow conditions under equal and unequal admission conditions. The performance of the turbines was then evaluated and compared to one another. Based on experimental data, a method to calculate the mass flow under unequal admission from the full admission maps was also developed and validated against the test results.Copyright

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%.

Numerical Assessment of Unsteady Flow Effects on a Nozzled Turbocharger Turbine

In order to extract maximum amount of energy possible from the automotive reciprocating engine exhaust gas, the turbocharger usually installed closely downstream the exhaust valve thus exposing it to highly pulsating flow conditions. This condition induces highly complex flow field within the turbocharger stage and significantly impact its performance characteristics which is not fully understood. The main objective of this paper is to provide understanding of unsteady flow feature using a Computational Fluid Dynamics (CFD) approach validated with experimental data. Despite focusing on unsteady feature of the flow, this research also emphasizes the importance of accurately modelled geometry in the early section of the paper. A steady state validation against experimental data is performed prior to unsteady calculations. The effect of different phase shifting methods is described and the relationship of instantaneous efficiency with incidence angle is established. In the final section of this paper, the turbocharger stage is sectioned where its instantaneous performance is evaluated individually in each section. The unsteady simulation is performed at fixed 30 000 RPM with 20Hz pulsing flow.Copyright

Efforts to establish Malaysian urban drive-cycle for fuel economy analysis

Emissions from motor vehicles are known to be the major contributor of air pollution. Pollutants that are commonly concerned and regulated for petrol engines are Hydrocarbons, Carbon Monoxide, Nitrogen Oxides and Particulate Matter. One of the most important factor that vary these pollutants is the engine operating condition such as cold start, low engine loads and high engine loads which are found during actual driving. In actual driving conditions, particularly in urban areas, vehicles regularly travel at idle, low or medium speeds which signify the engine part load operations. Thus urban driving carries a crucial weight on the overall vehicle fuel economy. Understanding the implications of urban driving conditions on fuel economy will allow for trategic application of key technologies such as cylinder deactivation in the efforts towards better efficiency. This paper presents the measurement and analysis of engine condition during Malaysian actual urban driving in an attempt to formulate representable fuel consumption data. The measurements were conducted through multiple on-road urban driving with an instrumented 1.6 litre car. Data was collected using the “chase” technique. Driving conditions were recorded over different routes within the selected urban areas, with considerations on the level of population, density and traffic congestion. The on-road driving was performed to measure vehicle speed, engine speed, accelerator pedal traces, engine torque and fuel consumption. The fact that high traffic congestion in urban area dictates the vehicle movements and the engine running conditions were analysed by clustering the variables. The analyses show that idling and cyclic speed ranging up to 25km/h were the most frequent conditions captured in the Malaysian urban driving. Using the cluster analysis, 10 important conditions were identified in developing a framework for the Malaysian actual urban driving conditions, towards representable fuel economy analysis.

Unsteady Performance Prediction of a Single Entry Mixed Flow Turbine Using 1-D Gas Dynamic Code Extended With Meanline Model

Turbochargers are widely regarded as one of the most promising enabling technology for engine downsizing, in the aim to achieve better specific fuel consumption, thermal efficiency and most importantly carbon reduction. The increasing demand for higher quality engine-turbocharger matching, leads to the development of computational models capable of predicting the unsteady behaviour of a turbocharger turbine when subjected to pulsating inlet flow. Due to the wide range of engine loads and speed variations, an automotive turbocharger turbine model must be able to render all the frequency range of a typical exhaust pulse flow. A purely one-dimensional (1-D) turbine model is capable of good unsteady swallowing capacity prediction, provided it is accurately validated. However, the unsteady turbine power evaluation still heavily relies on the quasi-steady assumption. On the other hand, meanline model is capable of resolving the turbine work output but it is limited to steady state flow due to its zero dimensional nature.This paper explores an alternative methodology to realize turbine unsteady power prediction in 1-D by integrating these two independent modelling methods. A single entry mixed-flow turbine is first modelled using 1-D gas dynamic method to solve the unsteady flow propagation in turbine volute while the instantaneous turbine power is subsequently evaluated using a mean-line model. The key in the effectiveness of this methodology relies on the synchronization of the flow information with different time-scales. In addition to the turbine performance parameters, the common level of unsteadiness was also compared based on the Strouhal number evaluations. Comparison of the quasi-steady assumption using the experiment results was made in order to further understand the strength and weaknesses of corresponding method in unsteady turbine performance prediction. The outcomes of the simulation showed a good agreement in the shape and trend profile for the instantaneous turbine power. Meanwhile the predicted cycle-averaged value indicates a positive potential of the current turbine model to be expanded to a whole engine simulation after few minor improvements.Copyright

Nozzle Steam Piston Expander for Engine Exhaust Energy Recovery

This paper presents a concept for new piston expander utilizing nozzle as part of a secondary steam cycle to recover exhaust energy. A commercial 1D simulation tool, AVL BOOST, was used to model the system, and comparison study was carried out between the conventional and nozzle piston expanders. It was found the nozzle piston expander could increase output power from a minimum of 0.73kW up to a maximum of 4.75kW. The simulation study has shown that the concept of using nozzle to admit steam into the piston expander has potential to improve engine system level efficiency.

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.

Current Issues and Problems in the Joining of Ceramic to Metal

Ceramics and metals are two of the oldest established classes of technologically useful materials. While metals dominate engineering applications, ceramics have some attractive properties compared to metals, which make them useful for specific applications. The properties of individual ceramics and metals can vary widely; however, the characteristics of most materials in the two classes differ significantly. Joints between a metal and ceramic are becoming increasingly important in the manufacturing of a wide variety of technological product. But joining ceramics to metallic materials often remains an unresolved or unsatisfactorily resolved problem. This chapter deals with problems of various studies in recent years on the joining between two materials.