# Experimental Energy and Exergy Analysis of an Automotive Turbocharger Using a Novel Power-Based Approach

^{*}

## Abstract

**:**

## 1. Introduction

_{2}-intensive processes on global warming, the need for the optimization of energy conversion systems has gained significant importance in recent decades. In particular, the global automotive industry is facing various challenges to meet emission legislation and reduce greenhouse gases. In the past few years, engine downsizing has been seen as one of the key technologies to reduce fuel consumption and emissions. This is achieved by reducing the size of the internal combustion engine (IC engine) while using the turbocharger to compensate for the power loss due to the engine size reduction. This approach consequently leads to reductions in engine weight, friction losses, fuel consumption and emissions. The key technology in question is the concept of turbocharging. A turbocharger is composed of a turbine, using the thermal energy from the hot exhaust gas from the combustion process of the IC engine and a compressor that is mechanically connected to the turbine via a rotating shaft. Recovering the mostly wasted thermal energy of the exhaust gas of the IC engine via driving the turbocharger turbine and delivering the demanded compressor power gives the required engine boost pressure.

## 2. Materials and Methods

#### 2.1. Experimental Procedure

_{3}up to 1050 °C) either via an electrical heater or a combustion chamber. The turbine mass flow rate is measured by a thermal mass flow meter (with a measuring accuracy of up to <0.8% of the measured value). Turbocharger rotational speed is captured using an eddy current measurement system. Pressures and temperatures have been recorded at the inlets and outlets of the turbine and compressor. Thermocouples of type K have been used to measure the temperatures at the exhaust side and PT100 for the compressor side, lubrication oil and coolants (for T

_{3}> 800 °C). A mixing device has been also installed in the measurement pipe downstream from the turbine to make a homogenous temperature field and increase the temperature measurement accuracy of T

_{4}, as can be seen in Figure 3 [14].

_{4}measurement point. On the right are the results of a numerical comparison between standard measurement pipe and mixing element, showing the significant improvement of the homogenized temperature field, which is more suited for reliable T

_{4}measurement.

#### 2.1.1. Adiabatic Measurement Conditions

_{3}= T

_{Oil,mean}= T

_{2}) is a viable method to approach near-adiabatic conditions. Additionally, keeping the operating temperatures low is generally favorable, to minimize thermal interactions between the turbocharger and environment. Furthermore, all measurement pipes and the turbocharger are insulated to minimize heat losses. It should be mentioned that throughout the adiabatic testing, the turbine power is mostly provided through the mass flow rather than the specific enthalpy (temperature) drop, which results in the measurement of fewer speed lines due to the pressure and mass flow limitations of the hot gas test bench. Moreover, the mentioned temperature alignments used to reach near-adiabatic conditions require a relatively longer measurement time in comparison to standard diabatic tests.

#### 2.1.2. Diabatic (i.e., Non-Adiabatic) Measurement Conditions

#### 2.2. Power–Based Approach

#### 2.3. Experimental Exergy Analysis Methodology

- Product exergy (${\dot{E}}_{P}):$ the produced (usable) work by a system;
- Exergy destruction (${\dot{E}}_{D}):$ exergy destruction due to internal irreversibilities;
- Exergy loss (${\dot{E}}_{L}$): exergy loss due to heat losses.

## 3. Results and Discussion

#### 3.1. Turbine Heat Transfer Estimation via a Power-Based Approach

#### 3.2. Exergy Analysis

_{3}, p

_{3}) to state 4 (T

_{4}, p

_{4}).

_{4,is}to measure the efficiency of the turbine. This ideal operating point is assumed to be isentropic and results in zero entropy generation. Figure 6b–d, however, clearly shows that the uncorrected ITE can exceed 1, implying that the measured temperature drops below the isentropic temperature, T

_{4,is}. I n real operating conditions, the enthalpy (or temperature) change $\Delta {H}_{T,dia}$ from the expansion can be split into the aerodynamic part ($\Delta {H}_{T,adia}$), which powers the shaft, and into the thermal part (${Q}_{T}$), which additionally contributes to the temperature drop to T

_{4,dia}. The thermal influence also causes the entropy change from $\Delta {S}_{adia}$ toward $\Delta {S}_{dia}$. Combining these with Equation (9) results in the finding that heat transfer affects the internal irreversibilities and, thus, the exergy destruction rate ${\dot{E}}_{D}$. This phenomenon is most prevalent at lower speeds, where the heat loss influence is dominant.

## 4. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## Nomenclature

Abbreviations | |

CFD | Computational Fluid Dynamics |

CHT | Conjugate Heat Transfer |

ETP | Effective Turbine Power |

IC | Internal Combustion |

ICP | Isentropic Compressor Power |

ITE | Isentropic Turbine Efficiency |

RPM | Rotation per Minute |

TIT | Turbine Inlet Temperature |

Notations | |

T | Temperature |

Q | Power |

$\dot{Q}$ | Heat transfer rate |

$\dot{m}$ | Mass Flow Rate |

${c}_{p}$ | Heat capacity at constant pressure |

η | Efficiency |

$\Pi $ | Pressure ratio |

$\dot{E}$ | Exergy rate |

$\dot{H}$ | Enthalpy rate |

$\dot{S}$ | Entropy rate |

p | Pressure |

Subscripts | |

0 | Ambiance |

1 | Compressor inlet |

2 | Compressor outlet |

3 | Turbine inlet |

4 | Turbine outlet |

C | Compressor |

T | Turbine |

B | Boundary |

eff | Effective |

ex | Exergetic |

is | isentropic |

corr | corrected |

uncorr | uncorrected |

## Appendix A

**Figure A1.**Turbocharger test bench at the Technical University Berlin (DIN EN ISO 10628-2, DIN 28000-4, DIN 28000-5).

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**Figure 5.**Power-based consideration to determine the turbine heat transfer for different TIT (

**a**) TIT = 400 °C (

**b**) TIT = 600 °C (

**c**) TIT = 800 °C.

**Figure 6.**Different turbine efficiencies, plotted over the ICP, under different operating conditions (

**a**) adiabatic (

**b**) TIT = 400 °C (

**c**) TIT = 600 °C (

**d**) TIT = 800 °C.

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**MDPI and ACS Style**

Kazemi Bakhshmand, S.; Luu, L.T.; Biet, C. Experimental Energy and Exergy Analysis of an Automotive Turbocharger Using a Novel Power-Based Approach. *Energies* **2021**, *14*, 6572.
https://doi.org/10.3390/en14206572

**AMA Style**

Kazemi Bakhshmand S, Luu LT, Biet C. Experimental Energy and Exergy Analysis of an Automotive Turbocharger Using a Novel Power-Based Approach. *Energies*. 2021; 14(20):6572.
https://doi.org/10.3390/en14206572

**Chicago/Turabian Style**

Kazemi Bakhshmand, Sina, Ly Tai Luu, and Clemens Biet. 2021. "Experimental Energy and Exergy Analysis of an Automotive Turbocharger Using a Novel Power-Based Approach" *Energies* 14, no. 20: 6572.
https://doi.org/10.3390/en14206572