Optimizing Steady State Diesel Efficiency and Emissions Using a SuperTurbo ^TM on an Isuzu 7.8L Engine

A driven turbocharger offers many benefits for internal combustion engines over traditional turbochargers or superchargers. One type of driven turbocharger, a SuperTurbo, is an amalgamation of supercharger, turbocharger, and turbo-compounder all in one device. This is accomplished through the combination of a high-speed traction drive that transfers bi-directional torque between the turbo shaft and a CVT, which then allows for overall ratio control between the turbo and the crankshaft. High efficiency turbine designs become feasible through the removal of overspeed and turbo lag design restrictions. Isuzu recognized the benefits of a driven turbocharger and the two companies have worked to evaluate it against more conventional turbochargers. This paper documents years of simulation, development, and engine testing, with a focus on steady state optimization of a 7.8L diesel engine. While improved transient response and drive cycle efficiency have previously been published, this paper will explain how the driven turbocharger functions differently than a normal turbocharger and how it improved steady state performance by precisely controlling and balancing boost pressure, air fuel ratio, high pressure EGR, and supercharging or compounding power. The increased flexibility of the driven turbo has shown unique approaches to using controls to balance or focus benefits per the manufacturer objectives. The results shown will include the effects on emissions and the way in which both the fundamental aero design of the turbine and compressor and the control system strategy worked to minimize those emissions.