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Research Papers: Gas Turbines: Turbomachinery

Dynamic Identification of Thermodynamic Parameters for Turbocharger Compressor Models

[+] Author and Article Information
R. D. Burke

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: R.D.Burke@bath.ac.uk

P. Olmeda, J. R. Serrano

CMT-Motores Térmicos,
Universitat Politècnica de València,
Camino de Vera s/n.,
València 46022, Spain

This efficiency represents the apparent isentropic efficiency that would be observed if the compressor was operated with no heat transfer between the working fluid and the compressor housing (adiabatic conditions). Through this term, the mechanical load on the compressor rotor and the enthalpy rise of the fluid due to work addition can be correctly estimated.

This relationship is commonly used in heat transfer modeling of turbocharger compressors [5,7,8].

Adiabatic mapping is undertaken when the turbine inlet temperature, oil, and water temperatures are controlled to match the compressor outlet temperature. These are referred to as adiabatic conditions as heat transfers are minimised by removing the temperature gradients between working fluids. The turbocharger would also be insulated to avoid heat losses to ambient.

1This paper deals with both absolute and relative errors. To avoid confusion, absolute errors in compressor efficiency will be expressed in % points whereas relative errors in other quantities will be expressed in %.

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received February 27, 2015; final manuscript received March 2, 2015; published online April 21, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(10), 102603 (Oct 01, 2015) (10 pages) Paper No: GTP-15-1055; doi: 10.1115/1.4030092 History: Received February 27, 2015; Revised March 02, 2015; Online April 21, 2015

A novel experimental procedure is presented which allows simultaneous identification of heat and work transfer parameters for turbocharger compressor models. The method introduces a thermally transient condition and uses temperature measurements to extract the adiabatic efficiency and internal convective heat transfer coefficient simultaneously, thus capturing the aerodynamic and thermal performance. The procedure has been implemented both in simulation and experimentally on a typical turbocharger gas stand facility. Under ideal conditions, the new identification predicted adiabatic efficiency to within 1% point1 and heat transfer coefficient to within 1%. A sensitivity study subsequently showed that the method is particularly sensitive to the assumptions of heat transfer distribution pre- and postcompression. If 20% of the internal area of the compressor housing is exposed to the low pressure intake gas, and this is not correctly assumed in the identification process, errors of 7–15% points were observed for compressor efficiency. This distribution in heat transfer also affected the accuracy of heat transfer coefficient which increased to 20%. Thermocouple sensors affect the transient temperature measurements and in order to maintain efficiency errors below 1%, probes with diameter of less than 1.5 mm should be used. Experimentally, the method was shown to reduce the adiabatic efficiency error at 90 krpm and 110 krpm compared to industry-standard approach from 6% to 3%. However at low speeds, where temperature differences during the identification are small, the method showed much larger errors.

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References

Figures

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Fig. 1

Idealized compression and heat transfer processes in the turbine and compressor: (a) compressor and (b) turbine

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Fig. 2

Temperature evolutions over thermal transient following a rapid change in compressor operating point

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Fig. 3

Overview of turbocharger model

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Fig. 4

Gas stand configuration

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Fig. 5

Steady state mapping simulations

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Fig. 6

(a) Efficiency and (b) heat transfer identification using dynamic method versus steady state approach. All results using αA = 0 (SS: steady state mapping).

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Fig. 7

Accuracy of the identification method with respect to (a) identification period duration and (b) identification period offset with respect to thermal transient initialization

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Fig. 8

Sensitivity of dynamic identification method to correct selection of compressor housing heat transfer distribution (SS: steady state mapping; Dyn: dynamic identification)

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Fig. 9

Effect of thermocouple inertia on estimated compressor efficiency

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Fig. 10

Influence of heat transfer from the turbine to the compressor on identification accuracy

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Fig. 11

Experimental identification results for (a) efficiency and (b) heat transfer coefficient (SS: steady state mapping)

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Fig. 12

Efficiency error versus step size showing that higher accuracy is obtained with larger thermal transients

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Fig. 13

(a) Conventional and (b) proposed mapping strategies

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