New stringent diesel emission regulations have had the effect of limiting the acceleration rates of turbodiesel powered vehicles. A need for supercharging of turbodiesels has been well explained in the Ref. 1 SAE Paper by Mr. Thomas N. Schmitz et al workers of Mercedes Benz AG.
The proposed engine air supply system submitted in this paper, utilizes two standard type radial flow compressors staged in series. The first compressor is a supercharger driven by a miniature, very high speed, high efficiency hydraulic turbine. Kapich Engineering has developed, and extensively tested, this high efficiency hydraulic turbine supercharger that incorporates a unique hydraulic system to power and control the supercharger. The second compressor is a standard turbocharger driven by the engine exhaust.
The primary objective of the proposed system is to provide a dramatic increase of BMEP in the low engine speed range. In addition, important is the ability of the supercharger boost to gradually “fade away” as engine accelerates and the turbocharger provides most of the air supply. Thus, the supercharger duty is intermittent, providing controlled boost for acceleration, low speed torque enhancement and for the correction of high altitude effects.
Engine thermodynamic analysis has shown that at low engine speeds, the two stage compression sharply increases the turbocharger turbine pressure ratio. This leads to a nearly equivalent increase in turbocharger compressor pressure ratio. The result is an exponential effect which continues until the turbocharger balance is reached. By applying only a modest supercharger pressure ratio of 1.2 to 1.3, the calculated overall pressure ratio at the engine manifold increases by 65 to 75 percent. With the hydraulic turbine driven supercharger, the boost increase can actually be timed ahead of the engine acceleration in response to throttle position signal. With a fast responding modern fuel supply system, the turbocharger turbine can receive much needed power for its compressor acceleration quickly and ahead of actual engine acceleration.