Numerical Analysis of Engine Exhaust Flow Parameters for Resolving Pre-Turbine Pulsating Flow Enthalpy and Exergy

Beichuan Hong,Andreas Cronhjort,Varun Venkataraman

doi:10.3390/en14196183

Abstract

Energy carried by engine exhaust pulses is critical to the performance of a turbine or any other exhaust energy recovery system. Enthalpy and exergy are commonly used concepts to describe the energy transport by the flow based on the first and second laws of thermodynamics. However, in order to investigate the crank-angle-resolved exhaust flow enthalpy and exergy, the significance of the flow parameters (pressure, velocity, and temperature) and their demand for high resolution need to be ascertained. In this study, local and global sensitivity analyses were performed on a one-dimensional (1D) heavy-duty diesel engine model to quantify the significance of each flow parameter in the determination of exhaust enthalpy and exergy. The effects of parameter sweeps were analyzed by local sensitivity, and Sobol indices from the global sensitivity showed the correlations between each flow parameter and the computed enthalpy and exergy. The analysis indicated that when considering the specific enthalpy and exergy, flow temperature is the dominant parameter and requires high resolution of the temperature pulse. It was found that a 5% sweep over the temperature pulse leads to maximum deviations of 31% and 27% when resolving the crank angle-based specific enthalpy and specific exergy, respectively. However, when considering the total enthalpy and exergy rates, flow velocity is the most significant parameter, requiring high resolution with a maximum deviation of 23% for the enthalpy rate and 12% for the exergy rate over a 5% sweep of the flow velocity pulse. This study will help to quantify and prioritize fast measurements of pulsating flow parameters in the context of turbocharger turbine inlet flow enthalpy and exergy analysis.

Highlights

To meet CO2 emissions legislation, accelerating the electrification of transportation is one solution, which is resulting in the demand for improving the thermal efficiencies of technology that is in-use for internal combustion engines (ICEs) [1]
These results are taken as the references to study the impacts of flow parameters regarding the quantification of flow enthalpy and exergy of the exhaust pulses
The sensitivity of flow velocity on specific enthalpy and exergy are comparable as discussed in Section 4.4, the maximum absolute percentage error (MAPE) of velocity on exergy is due to the lower magnitude of the exergy pulse compared to the enthalpy

Summary

Introduction

To meet CO2 emissions legislation, accelerating the electrification of transportation is one solution, which is resulting in the demand for improving the thermal efficiencies of technology that is in-use for internal combustion engines (ICEs) [1]. Besides developing advanced combustion concepts, exhaust energy recovery technology has been considered essential for high-efficiency ICEs. The exhaust energy recovery system driven by the ICE exhaust pulses can utilize the exhaust energy to increase the total engine efficiency by boosting the intake air or recovering the waste heat. An accurate assessment of energy contained in the engine exhaust flow is vital to indicate its work potential. Based on the evolution of exhaust energy, the working efficiency and energy losses of components through the exhaust system can be identified and improved

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Conclusion