SwRI’s D-EGR demo car wows SAE engines symposium with 42% BTE
Aside from the colorful decals plastered on its body, the 2012 Buick Regal GS appears to be stock. But underneath its skin is an advanced gasoline combustion system that promises significant fuel-efficiency improvements with ultra-low exhaust emissions. And the combustion system, developed by Southwest Research Institute (SwRI), is headed for production at a major European OEM.
The so-called EGR Car was displayed at the 2014 SAE High-Efficiency IC Engine Symposium, held April 6-7 in Detroit. The SAE audience attending the event showed keen interest in its 2.0-L dedicated-EGR (D-EGR) concept engine, so named because one of its four cylinders is dedicated exclusively to producing high levels of exhaust gas recirculation and hydrogen/CO reformate. The engine has achieved brake-thermal-efficiency (BTE) levels exceeding 42% in idle-to-full-load testing, according to Dr. Terry Alger, SwRI’s Assistant Director.
For an SwRI video of the vehicle, go to http://www.swri.org/vidclip/html/d-egr-demo-vehicle.htm.
Dr. Alger and Chris Chadwell, SwRI’s Manager of SI Engine Research, presented their organization’s latest research in natural-gas-engine developments and advanced boosting technologies, respectively, at the fourth annual SAE event, held at the Westin Book Cadillac Hotel. Along with SwRI colleagues Jacob Zuehl and Raphael Gukelberger, Alger and Chadwell are co-authors of a new SAE Technical Paper, A Demonstration of Dedicated EGR on a 2.0 L GDI Engine (SAE 2014-01-1190).
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Using one cylinder as an “EGR factory” (it is possible to dedicate more, depending on total cylinder count) operating under a sophisticated control strategy, helps increase the engine’s tolerance for EGR (up to 25% dilution) and eliminates many of the losses typically seen in typical external reforming devices, according to the engineers.
The hydrogen and carbon-monoxide-rich reformate is recirculated with the rest of the exhaust gas. The reformate combustion properties help offset the drawbacks of cooled EGR alone. Reformate improves the engine’s EGR tolerance by increasing burn rates. It thus improves combustion stability at high EGR levels. It also has a low minimum-ignition energy, providing improved fuel oxidation for reduced emissions of unburned HC and improved combustion efficiency.
Earlier this year, PSA Peugeot Citroën announced that a patented D-EGR system developed in collaboration with SwRI will be featured on a new range of gasoline engines the automaker will introduce for MY2018 production. The new engines will offer a fuel-consumption reduction of 10% versus incumbent engines, according to the automaker.
The SwRI EGR Car’s engine is running an 11.7:1 compression ratio, increased from the stock engine ratio to optimize the knock-resistance properties of the concentrated EGR and reformate. It has run naturally aspirated over a large portion of the operating map at a 14:1 compression ratio, the test results showing significant fuel-efficiency gains over a low-compression-ratio baseline engine, with reduced engine-out emissions from the other three cylinders.
SwRI engineers explain that the knock response of the engine using regular-grade (87 AKI) gasoline is the same as for the baseline engine using premium (greater than 93 AKI) grade fuel. A two-stage boosting system combines turbocharger and supercharger to deliver smooth transient response while enabling the engine to achieve its torque targets at a minimum 17-bar BMEP (brake mean effective pressure), from 1500-5500 rpm, with low engine-out emissions.
Besides the dedicated circuit and two-stage boost system, additional modifications to create the D-EGR engine include a high-energy ignition system and an additional fuel injector for delivering extra fuel for reformation.
For an SwRI animation of the D-EGR engine, go to http://www.swri.org/vidclip/html/d-egr.htm.
The demonstrator engine currently is delivering approximately 13% improvement on the FTP cycle and 10% on the EPA’s Highway Fuel Economy Test (HwFET) cycle, Dr. Alger said. Brake-specific fuel consumption (BSFC) measured at 2000 rpm (BMEP at 2 bar) was improved from 385 g/kW·h in the baseline production engine to 330 g/kW·h. The lowest BSFC achieved was 212 g/kW·h compared with 236 g/kW·h for the base engine. SwRI testing has shown fuel efficiency improvements greater than 30% under certain operating conditions.
SwRI’s D-EGR program is a spinoff of its HEDGE (High Efficiency Dilute Gasoline Engine) consortium projects, initiated to equal or beat diesel fuel efficiency at gasoline-engine emissions levels, using a gasoline engine with cooled EGR. D-EGR development will continue in the latest phase, HEDGE III (High-Efficiency Dilute Gasoline Engine), which is managed by Chadwell.
The program, planned through 2018, aims to achieve the stringent LEV3 emission levels. (See video at http://www.swri.org/vidclip/html/hedge-iii.htm).