Poster Presentation

Dr. Katherine Ilie, RMIT University, Australia

FISITA 2008 ABSTRACT

PARAMETER SELECTION AND MODELLING FOR COMPONENT MATCHING AND PERFORMANCE ENHANCEMENT OF A TWINCHARGER SYSTEM ON VEHICLE IC ENGINES

Ilie, Katherine* RMIT University - School of Aerospace, Mechanical and Manufacturing Engineering, Melbourne, Australia

KEYWORDS - supercharger, compressor, turbine, component matching, performance, engine design, parametric modelling, automotive

ABSTRACT

Due to fuel resources and environmental concerns, the IC engine has been lately under close scrutiny aiming improvements in efficiency, cost and emissions. Addition of power boosting devices to an IC engine is not a new topic; however, it is of interest in that better or improved solutions are still required. The twincharger systems were developed in this context, but their potential has been mainly exploited with small capacity engines, that reach high power outputs by operating at higher volumetric efficiency, although being small displacement engines.

The twincharger construction relies on the combination of a turbocharger with a supercharger used to produce boost as a positive manifold pressure to eliminate or minimize the turbolag. Currently a twincharging system integrates a turbocharger and a Roots blower. The supercharger of Roots type is expected to provide pressure and response at low speeds so that the turbocharger spooling can be minimised or eliminated. It is recognised that while the turbocharger, developed as an exhaust gas-driven supercharger, cannot reach the high-response required by the engine performance over the whole range of operational speed; by design and operation the conventional Roots blower cannot achieve the high-pressure and high-efficiency at low speed ranges expected from the twincharger system.

The research introduced by this paper focused on a new twincharger system matching a turbocharger with an optimised supercharging compressor of Lysholm type. The twin-screw supercharging compressor has good response and high-performance in high-pressure ratio ranges and at low speed it can be optimised to achieve volumetric and thermal efficiency better than the Roots blower. Although good attributes have been assigned to turbochargers, they have undesirable characteristics such as poor performance at low engine speeds and loads that influence their design and matching to a particular engine. Practically, changes in the exhaust flow through the turbine modify the turbine inlet temperature, pressure changes and the turbine rotational speed changes, the inlet mass flow rate and pressure ratio developed by the compressor change, and so on until the engine reaches a steady state operating condition. Possible to be used with different engine types, the basic components of a twincharger have been treated independent of each other so far. The method of component matching proposed provides this type of supercharging system with better response. As the turbocharger starts to generate a pressure ratio, the total pressure ratio to the engine is a result of the compound charging (serial via supercharging compressor, then through the turbocharger as shown in the generic Figure 1), and it can be very high for high torque at low engine speeds.

The major topic of this paper is the system approach to component matching and the selection and modelling of the basic components and their parameters or parameter group relationships describing their behaviour and effects on changing operating conditions on engine. This materialises as an economic and practical solution for downsized power trains with high specific power, with new enhanced functionality and performance including fuel economy-boosting and reduction of the emissions level. Ultimately, this new twincharger system may be integrated in the strategy for future ultra low exhaust emission.

Figure 1: Generic twincharging system (detailed in the attached PDF file format of the ABSTRACT)

This abstract is supplemented by a PDF, which can be viewed here.

Poster presentation: Future powertrain solutions