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Cooled LPL EGR is a proven means of improving the efficiency of a Gasoline Turbocharged Direct-Injection engine. One of the most significant hurdles to overcome in implementing a LPL EGR system is dealing with condensation of water near the entrance of the turbocharger's compressor wheel. A gasoline engine, and to a greater extent a spark ignition engine running on Natural Gas, will encounter enough water condensation at some steady-state conditions to damage the compressor wheel due to the high-speed collision between the compressor blades and the water droplets. As an alternative to not utilizing beneficial EGR at the condensing conditions, the team at BorgWarner have developed a LPL EGR mixer that is effective at condensing and collecting the water droplets and routing the water around the compressor wheel. The new Condensing EGR mixer was developed from the known concept of utilizing a mild venturi section to enhance EGR delivery and mixing.

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.

Prior work with the concept of dividing the exhaust process into an early and late phase has shown the potential of applying only the early stage (blow-down) of the exhaust period directly to a turbocharger or turbocharger system, and the later stage (scavenge) arranged to bypass the turbine. In this manner, the exhaust backpressure required to extract high turbine work from the engine can be isolated from the displacement phase of the exhaust stroke and thereby greatly reduce the exhaust pumping work and Residual Gas Fraction. In previously-published efforts, the challenges of valve-event control and high turbine inlet temperature have been revealed. The BorgWarner Engine Systems Group, in conjunction with Presta, has applied a cam-phaser controlled concentric camshaft system to the exhaust side of a divided exhaust port 4-valve per cylinder DOHC GDI engine, to enable variable phasing between the Blow-down and Scavenge cam profiles.

It has been clearly demonstrated separately, that the application of both Dual Cam Phasers (DCP) and External Cooled EGR systems are highly beneficial to improving the efficiency of highly-boosted GDI engines. DCP systems can optimize the volumetric efficiency at WOT conditions, improve boost and transient response at low engine speeds, and provide internal EGR at low RPM part-load conditions. External cooled EGR has been demonstrated to dramatically improve the fuel consumption, lower turbine inlet temperature, and improve emissions at high power conditions. In previous investigations by the BorgWarner Engine Systems Group, we showed that full engine speed/load range EGR coverage can be obtained by combining High Pressure Loop and Low Pressure Loop external EGR systems with a DCP strategy.

As CO2 legislation tightens, the next generation of turbocharged gasoline engines must meet stricter emissions targets combined with increased fuel efficiency standards. Recent studies have shown that the following technologies offer significant improvements to the efficiency of turbocharged GDI engines: Miller Cycle via late intake valve closing (LIVC), low pressure loop cooled EGR (LPL EGR), port water injection (PWI), and cylinder deactivation (CDA). While these efficiency-improving technologies are individually well-understood, in this study we directly compare these technologies to each other on the same engine at a range of operating conditions and over a range of compression ratios (CR). The technologies tested are applied to a boosted and direct injected (DI) gasoline engine and evaluated both individually and combined.