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Research Papers: Internal Combustion Engines

Effect of Exhaust Gas Temperature Limits on the Peak Power Performance of a Turbocharged Gasoline Engine

[+] Author and Article Information
Amey Y. Karnik

Powertrain R&A, Ford Motor Company, 2101 Village Road, Dearborn, MI 48121akarnik@ford.com

Michael H. Shelby

Powertrain R&A, Ford Motor Company, 2101 Village Road, Dearborn, MI 48121mshelby@ford.com

In a separate test, the inlet air (before the air cleaner) temperature was swept to evaluate its effect on the peak power performance, when the turbine inlet temperature was fixed. It was observed that maintaining the turbine inlet temperature required maintaining a constant CA50. For those tests, constant CA50 was maintained by reducing the airflow with increased inlet air temperature that made the engine more knock limited. These data are not included in this paper.

Equation 2 can be derived by using the equations for indicated power and indicated specific air consumption, as follows: Indicatedpower(kW)=IMEP(kPa)Vd(m3)N(rpm)/120. ISAC(kg/kWh)=airflow(kg/h)/Indicatedpower(kW)

At the high speed and load conditions, the CA50 at MBT was observed to be closer to top dead center. The value used for CA50 at MBT was obtained through evaluation of multiple spark sweeps.

The extrapolation of IMEP at MBT and LBT versus volumetric efficiency was obtained using the data from both 11:1 AFR and 12:1 AFR, shown by the dash-dotted lines in Fig. 5.

J. Eng. Gas Turbines Power 132(11), 112801 (Aug 10, 2010) (7 pages) doi:10.1115/1.4000856 History: Received May 11, 2009; Revised November 06, 2009; Published August 10, 2010; Online August 10, 2010

Peak power of an engine is typically constrained by the maximum obtainable airflow. This constraint could arise directly from the airflow limitation imposed by the throttle restriction (typical for a naturally aspirated engine), or indirectly from other factors, such as various temperature limits for component protection. In this work, we evaluate the airflow limit for a turbocharged gasoline engine as dictated by the constraints on the turbine inlet temperature. Increasing the limit on the turbine inlet temperature requires the exhaust manifolds and turbine to be made out of more expensive materials that withstand higher temperatures. This expense is justifiable if operating with higher turbine inlet temperature allows noticeably higher power output, and not merely increases the allowable airflow. Experimental data show that under some conditions the increase in airflow does not increase the peak power. The effects of increasing airflow on the peak power and turbine inlet temperatures are systematically analyzed through individual accounting for the different losses affecting the engine torque. The breakdown analysis presented in this work indicates combustion phasing as a major contributing factor to whether increasing the flange temperature limit would increase the peak power.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of a turbocharged gasoline engine

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Figure 2

Sweep in turbine inlet temperature limit for the maximum BMEP with constant air fuel ratio. The lines with circular and square markers correspond to 11:1 AFR and 12:1 AFR, respectively.

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Figure 3

(a) Combustion phasing versus volumetric efficiency with respect to ambient conditions, and (b) turbine inlet temperature versus combustion phasing, for 11:1 AFR and 12:1 AFR

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Figure 4

Effect of equivalence ratio (lambda) and combustion phasing on the indicated specific air consumption

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Figure 5

The progression from the maximum IMEP at a given airflow to the BMEP obtained. The squares represent the 12:1 AFR and the circles represent 11:1 AFR.

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Figure 6

Expected CA50 and turbine inlet temperature versus volumetric efficiency

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Figure 7

BMEP predictions for 10:1 AFR with increase in the volumetric efficiency with respect to ambient conditions

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