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Valve-Event Modulated Boost System: Fuel Consumption and Performance with Scavenge-Sourced EGR
Abstract:
In our introductory paper on the VEMB system (SAE 2010-01-1222) we discussed the concept of a divided exhaust period turbocharging system controlled by a concentric cam system, and we presented several fixed speed/load point sets of results that demonstrated the expected BSFC benefits. The BSFC reductions (2.5% to 4%) correlated to reduction in pumping work and to improvement in combustion phasing at knock-limited points from substantial reductions in Residual Gas Fraction compared to the conventionally-boosted baseline engine. In this paper we present additional results from engine tests in the areas of full-load performance and emissions with and without Scavenge-sourced EGR.
To demonstrate the WOT performance potential of a VEMB engine, we show the effect of turbocharger matching steps, with results that exceed the baseline engine output across the engine speed range. In addition we explore the unique aspects of the EGR system of a divided exhaust period engine, for which we can take advantage of the large differentiation in enthalpy and chemistry between the Blowdown and Scavenge manifolds. The Scavenge-sourced EGR has lower temperature and pressure than the Blowdown manifold or the baseline conventionally-boosted engine. In addition, the Scavenge manifold has 3 to 5 times the HC concentration of the Blowdown manifold. Results of this investigation are presented that show significant advantages to Scavenge-Port-sourced EGR.
Finally, to complete the BSFC and emissions benefits picture, sufficient additional speed and load points have been run with and without external EGR, across the speed and load range to enable mapping the BSFC benefits across the speed and load range of a boosted GDI engine.