New Mapping Method of a Radial Turbine

Abstract

Turbocharging is one of the most essential techniques in internal combustion engine technology, and they are often modeled as look-up tables in 1D engine models by using the mapping data collected under steady-state conditions. However, turbochargers are often used with internal combustion engines where the reciprocating motion results in unsteadiness.

The thesis proposes a new mapping method for a radial turbine in numerical and experimental ways, where this method involves the usage of pulsations and different wastegate openings.

A detailed literature review of the up-to-date mapping methods for turbocharger turbines will be illustrated by highlighting research gaps:

• There is a lack of a precise and accurate experimental methodology to quantify the instantaneous behaviors of the turbine.

• How will unsteady behavior of a radial turbine differ from steady state mapping results and how to quantify it by using a robust model?

• Without unsteady data, is CFD possible to use as a model to predict mapping results with the correction of mechanical loss and heat loss?

• How to model a wastegate accurately and is it possible to map a turbine with different wastegate openings?

Conventional gas stand mapping data were collected for a specific turbocharger with a fixed geometry that comes from a production of a 1.5 L gasoline engine, extended data are captured by using a closed-loop configuration. The experimental data collected is then used as a baseline to compare with 1D model with pulsations and steady CFD models.

The author also analyzed a dual-orifice model which was validated by engine test data. The model’s results give a detailed comparison of how the turbine will react under pulsating conditions in a range of different frequencies versus steady data. The model also gives the feasibility of assessing unsteady mapping by modeling different sensors.

A computational fluid dynamics (CFD) model was also built and analyzed as an alternative to the mapping experiments. This 3D CFD turbine model is built based on the geometry of the turbine. The results show good agreement with the use of a mechanical loss model that this author built, thus in this way, a CFD model coupled with a mechanical loss model can be used in turbine mapping work.

What is more, the use of a wastegate in turbine mapping is also explored. The thesis collected the mapping results of this radial turbine with different wastegate openings by using a set of two hotwire probes to measure the mass flow rate that passed through the turbine inlet volute as well as the wastegate in different wastegate positions. The results are then validated with a CFD model with the wastegate open. A wastegate flow coefficient model is then built based on the data collected, which is able to give a prediction of the turbine under different wastegate opening positions.

Date of Award	13 Sept 2023
Original language	English
Awarding Institution	University of Bath
Supervisor	Richard Burke (Supervisor) & Aaron Costall (Supervisor)