Coordinated Electric Supercharging and Turbo-Generation for a Diesel Engine 2010-01-1228
Exhaust gas turbo-charging helps exploit the improved fuel efficiency of downsized engines by increasing the possible power density from these engines. However, turbo-charged engines exhibit poor transient performance, especially when accelerating from low speeds. In addition, during low-load operating regimes, when the exhaust gas is diverted past the turbine with a waste-gate or pushed through restricted vanes in a variable geometry turbine, there are lost opportunities for recovering energy from the enthalpy of the exhaust gas. Similar limitations can also be identified with mechanical supercharging systems.
This paper proposes an electrical supercharging and turbo-generation system that overcomes some of these limitations. The system decouples the activation of the air compression and exhaust-energy recovery functions using a dedicated electrical energy storage buffer. Its main attributes fast speed of response to load changes and flexibility of control. A causal simulation model of the proposed system, including that of the Diesel engine, electrically driven compressor, energy buffer battery and power electronics, and the turbo-generation system are developed and analyzed. A coordinated control scheme is then implemented for the electric compressor and turbo-generator considering load demand fluctuations on the engine and enforcing battery state of charge constraints. The proposed system is evaluated on standard test cycles and compared with conventional turbo-chargers. The results show the potential of the system in improving transient performance, in general, and the cycle equivalent fuel efficiency over a standard city driving cycle.