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Research Papers

Comparison Between the Steady Performance of Double-Entry and Twin-Entry Turbocharger Turbines

[+] Author and Article Information
Alessandro Romagnoli

e-mail: a.romagnoli@imperial.ac.uk

Colin D. Copeland

e-mail: c.copeland@imperial.ac.uk

Ricardo Martinez-Botas

e-mail: r.botas@imperial.ac.uk
Department of Mechanical Engineering,
Imperial College,
London, United Kingdom

Martin Seiler

ABB Turbo Systems Ltd.,
Baden, Switzerland
e-mail: martin.a.seiler@ch.abb.com

Srithar Rajoo

Department of Mechanical Engineering,
Universiti Teknologi Malaysia,
Malaysia
e-mail: srithar@fkm.utm.my

Aaron Costall

Caterpillar Inc.,
Peterborough, United Kingdom
e-mail: Costall_Aaron@cat.com

Unequal admission refers to the condition where the flow is not equally shared between the two entries. Partial admission instead refers to the conditions when no flow is going through one limb.

The velocity ratio is defined as the ratio between the rotor tip velocity (U) divided by the velocity of the gas that would result from an isentropic expansion between the inlet and outlet (Cis). This parameter is used to define the operating point of a turbine since the peak efficiency occurs at approximately the same velocity ratio regardless of speed.

In order to evaluate the mass flow parameter, the air pressure, temperature, and mass flow rate were measured. Each of these measurements is associated with an uncertainty due to the instrumentation used. Pressure was measured through two strain gauge pressure transducers, Druck PDCR 23D and Druck PDCR 22, for low and high pressure range respectively. Temperatures were monitored at the measurement plane with two T-type thermocouples (−200 to 350 °C). The air mass flow rate was measured according to British Standards as already reported before. The overall uncertainty for the mass flow parameter is calculated by using the root-sum-square method (RSS), which results in an uncertainty of ±0.9% to ±2.3% for the test points range [20]. The overall uncertainty in the steady pressure measurement is ±470 and ±90 Pa for the high and low pressure transducer respectively. The root-sum-square (RSS) uncertainty in the pressure ratio is between ±0.1% and ±0.3% for the test points range [20].

Note that the rotor tip speed U and the flow velocity C are related by the flow angle which changes for each operating point. However, the similarity approach in Eq. (13) helps to divide out its influence.

In the case of a radial machine there will be a speed dependency due to centrifugal head.

Similar mass flow pattern to those shown in Figs. 8 and 9 was observed for all the other test conditions of Table 2; these are not reported in the current paper but more details can be found in [19].

For the double-entry turbine a fourth order polynomial curve would provide better fit. However it was preferred to maintain a power trend curve for consistency of analysis with the twin-entry turbine.

It is worth noting that the temperatures T0,fa and T0,ff simplify since similar total temperatures were set during testing.

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 16, 2011; final manuscript received August 26, 2011; published online October 31, 2012. Editor: David Wisler.

J. Turbomach 135(1), 011042 (Oct 31, 2012) (11 pages) Paper No: TURBO-11-1184; doi: 10.1115/1.4006566 History: Received August 16, 2011; Revised August 26, 2011

Most boosting systems in internal combustion engines utilize “pulse turbocharging” to maximize the energy extraction by the turbine. An internal combustion engine with more than four cylinders has a significant overlap between the exhaust pulses which, unless isolated, can decrease the overall pulse energy and increase the engine pumping loss. Thus, it is advantageous to isolate a set of cylinders and introduce the exhaust gases into two or more turbine entries separately. There are two main types of multiple entry turbines depending on the method of flow division: the twin-entry and the double-entry turbine. In the twin-entry design, each inlet feeds the entire circumference of the rotor leading edge regardless of inlet conditions. In contrast, the double-entry design introduces the flow from each gas inlet into the rotor leading edge through two distinct sectors of the nozzle. This paper compares the performance of a twin and double-entry mixed flow turbine. The turbines were tested at Imperial College for a range of steady-state flow conditions under equal and unequal admission conditions. The performance of the turbines was then evaluated and compared to one another. Based on experimental data, a method to calculate the mass flow under unequal admission from the full admission maps was also developed and validated against the test results.

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References

Figures

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Fig. 1

Turbine configurations: (a) twin-entry and (b) double-entry

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Fig. 2

Imperial College test facility

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Fig. 3

Turbine performance parameters: comparison between Imperial College and conventional test range [17]

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Fig. 4

Twin-entry turbine: partial admission analysis

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Fig. 5

Double-entry turbine: partial admission analysis

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Fig. 6

Unequal admission mass flow parameter for the twin-entry turbine

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Fig. 7

Unequal admission mass flow parameter for the double-entry turbine

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Fig. 8

Mass flow parameter under unequal admission and in the free flow limb for the twin-entry turbine

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Fig. 9

Mass flow parameter under unequal admission and in the free flow limb for the double-entry turbine

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Fig. 10

Flow mixing and equivalence of the turbine with an adiabatic nozzle

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Fig. 11

Mass flow parameter ratio versus unequal expansion ratio for the twin-entry turbine

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Fig. 12

Mass flow parameter ratio versus unequal expansion ratio for the double-entry turbine

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Fig. 13

Flow chart for the calculation of the mass flow parameter in one limb

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Fig. 14

Twin-entry: prediction of mass flow in the free flow limb by mean of Eq. (20) at N/√T ≈ 43.0 rev/s√K

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Fig. 15

Twin-entry: prediction of mass flow in the free flow limb by mean of Eq. (20) at N/√T ≈ 27.9 rev/s√K

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Fig. 16

Double-entry: prediction of mass flow in the free flow limb by mean of Eq. (20) for U/Cis ≈ 0.65 and 0.5

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