A new design of a mixed flow variable geometry turbine is developed for the turbocharger used in diesel engines having the cylinder capacity from 1.0 to 1.5 L. An equivalent size radial flow variab...

A comparative study of the performance of the mixed flow and radial flow variable geometry turbines for an automotive turbocharger

In our previous paper, the steady-state test results of a mixed flow turbine with variable nozzle vanes for a turbocharger are reported. In this paper, the transient response of the same mixed flow...

Transient performance of the mixed flow and radial flow variable geometry turbines for an automotive turbocharger

A specific design of mixed flow variable geometry turbine for an automotive sub 1.5 litre diesel engine turbocharger is proposed in this paper. An experimental set up is developed for measuring the steady state and transient response behaviour of the turbine at different nozzle vane opening positions. The rotor speed, pressure and temperature before and after the turbine are measured and recorded using high frequency data logging system. The steady state performance for mass flow, efficiency, velocity ratio, specific speed and the transient response behaviour of the mixed flow variable geometry turbine (MFVGT) are compared against the same parameters of a radial flow variable geometry turbine (RFVGT) of similar dimensions. Typical result indicates that the transient response of the MFVGT is faster by about 350 milliseconds than the radial at turbine inlet pressure of 0.2 bar (g).Copyright © 2015 by ASME

Transient Response of Mixed Flow Variable Geometry Turbine for a Turbocharger

Turbo-compressor assembly (also called turbocharger) is added to diesel engines to increase their power density and improve performance. However, during power step-up operations, the added turbocharger system could lead to a significant delay of engine response (also called turbo-lag) which negatively impact drivability. In this paper, an external electric compressor (eBoost) is added to a turbocharged, large displacement diesel engine to significantly reduce turbo-lag, along with a bypass valve. Now, the air charge system has two control targets (boost (intake manifold) pressure and rate of exhaust-gas recirculation (EGR)) but with four control actuators including EGR valve, variable geometry turbo (VGT) vane position, eBoost speed and bypass valve, making it challenge for developing the associated control scheme. In this paper, a dual-output PID (proportional-integral-derivative) controller is proposed for controlling the boost pressure using the VGT and eBoost to reduce turbo-lag, and a transition logic is also devised to detect transient operating conditions to activate the eBoost, along with the closing and opening of the bypass valve, with maximum benefit. The EGR rate PID control remains unchanged. The addition of the eBoost is shown to improve transient response time by up to 55% and reduce transient NOx emissions by up to 42% during transitional operations without negatively impacting steady-state engine performance or emissions. Note that transient performance can be further improved for production implementation when a single engine control module is used by eliminating communication delay among multiple control systems.

Dual-output PID transient control of an electric-assisted air charge system

The vital issue of response lag and soot emission during transient operation of turbocharged engine, has been studied so far mainly on experiment in engine system rather than turbocharger basis. The study of turbocharger transient performance, however, is extremely important to manufacturers due to the stringent regulations of exhaust emission and economy for the turbocharger engine. Therefore, a general method independent of the engine for evaluating the transient response performance of a gasoline turbocharger is proposed in this paper. First, an explicit relationship between key thermodynamic parameters of turbine and compressor and the evaluation index of D x that can characterize turbocharger transient response are established. Secondly, the proposed evaluation method is tested and verified using the coupling between GT-Power and MATLAB Simulink software based on the gasoline turbocharger. The simulation results show that the appropriate conditions should be selected for the transient response test, including the starting and ending speed, the starting mass flow rate, etc. For this proposed turbocharger, the value of D x has a good consistency when the ending speed is 200,000 r/min and the initial mass flow rate is in the range of 0.0715∼0.0756 kg/s. Moreover, the influence of rotor moment of inertia, turbine efficiency and compressor efficiency on D x is analyzed in this selected condition. Finally, the evaluating method of the transient response performance of the turbocharger is conducted on a test bench. The test results are in good agreement with the simulation results, indicating that the proposed evaluation method for transient response of turbocharger has a good predictability and can be used for quantitative evaluation of transient response-ability for different turbochargers independent of engine.

Ramesh Kannan

Papers

Transient performance of the mixed flow and radial flow variable geometry turbines for an automotive turbocharger

Transient Response of Mixed Flow Variable Geometry Turbine for a Turbocharger