Next Generation Ford EcoBoost to Offer Cooled EGR

The next generation of Ford’s EcoBoost turbocharged, direct-injection gasoline engines will introduce cooled EGR (exhaust gas recirculation), enabling higher compression ratios, according to Ford executives speaking at the SAE 2010 World Congress in Detroit.

Cooled EGR as applied to an EcoBoost engine can improve efficiency, reduce the tendency for an engine to knock, and reduce PM emissions (which can be an issue with gasoline direct injection engines).

Applying cooled EGR to an EcoBoost engine results in a cleaner-running engine that develops more power and delivers as much as a 5% gain in fuel economy over current EcoBoost engines, Ford says. Other technologies being studied to further expand the potential of EcoBoost include more advanced forms of turbocharging as well as different approaches to leveraging ethanol blends.

While PM emissions have long been the concern of the diesel industry, the advent of direct injection (GDI) engines raises the PM issue for the gasoline engine sector as well. In general, GDI engines have elevated PM emissions due to the presence of liquid fuel in the combustion chamber; these deposits lead to higher HC and PM emissions, as they create locally rich areas within the combustion chamber, even when the global equivalence ratio is lean.

In a paper on the role of EGR in PM emissions from gasoline engines being presented at the SAE 2010 World Congress in Detroit this week, researchers from SwRI note that:

As modern gasoline engines move to higher specific power levels, the size of the enrichment region, in terms of percent of the total engine performance map, increases significantly. By using EGR to reduce combustion temperatures and eliminate the need for enrichment, the PM mass and number emissions were reduced substantially.

Comparisons in the enrichment regime indicated the primary benefit of EGR was from eliminating enrichment, but a significant benefit was found from using EGR even at rich conditions. EGR also reduced PM emissions at part load conditions, particularly those above 50% load.

—Alger et al., SAE 2010-01-0353

Separately, a team from AVL Powertrain Engineering, AVL List GmbH, and Ford are presenting a paper this week at the World Congress on the development of a combustion system for a flexible fuel turbocharged direct injection engine.

A logical and synergistic extension of the EcoBoost strategy is the use of E85 (approximately 85% ethanol and 15% gasoline) for knock mitigation. Direct injection of E85 is very effective in suppressing knock due to ethanol’s high heat of vaporization—which increases the charge cooling benefit of direct injection —and inherently high octane rating. As a result, higher boost levels can be archived while maintaining optimal combustion phasing giving high thermal efficiency. However, due to their different properties, optimization of a combustion system for both regular grade (91 RON) gasoline and E85 is non-trivial.

—Whitaker et al., SAE 2010-01-0585

Resources
*Terrence Alger, Jess Gingrich, Imad A. Khalek, Barrett Mangold (2010) The Role of EGR in PM Emissions from Gasoline Engines. (SAE 2010-01-0353)

*Paul Whitaker, Apoorv Agarwal, Christian Spanner, Kevin Byrd, Yuan Shen, Heribert Fuchs (2010) Development of the Combustion System for a Flexible Fuel Turbocharged Direct Injection Engine (SAE 2010-01-0585)