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SwRI engineers win SAE award for paper on impact of octane and cooled EGR on engine performance and efficiency
3 July 2014
A team of engineers from Southwest Research Institute (SwRI) has received the prestigious SAE International Harry L. Horning Memorial Award for a 2012 technical paper (2012-01-1149) investigating different octane-rated gasolines and exhaust gas recirculation (EGR) levels.
Institute Engineer Dr. Charles Roberts, Assistant Director Dr. Terry Alger and Research Technologist Barrett Mangold, all of SwRI’s Engine, Emissions and Vehicle Research Division, received the award at the SAE World Congress in Detroit in April. Former SwRI employee Jess Gingrich is also a co-recipient.
Their paper, “The Interaction of Fuel Anti-Knock Index and Cooled EGR on Engine Performance and Efficiency,” looked at different octane-rated gasolines and different EGR levels to examine the benefit of EGR on octane levels. Tests outlined in the paper also allowed the authors to compare the dilution impacts of EGR and fuel dilution on knock.
In the paper, they reported on experiments performed on a 2.4L boosted, MPI gasoline engine, equipped with a low-pressure loop (LPL)-cooled EGR system and an advanced ignition system, using a pump grade 87 AKI (anti-knock index) gasoline, a certification grade 93 AKI gasoline and a 105 AKI racing fuel.
They performed ignition timing and EGR sweeps at a variety of EGR levels and a variety of high load conditions, including knock-limited peak torque and WOT as well as some knock-limited, part load conditions. In addition, they examined the combustion difference between fuels to determine the effect that fuel reactivity—in the form of anti-knock index (AKI—has on EGR tolerance and burn rate.
Broadly, they found that:
The improvement in effective AKI of the fuel from using EGR is constant across commercial grade gasolines at about 0.5 ON per % EGR. I.e., to achieve a given combustion phasing in an engine, one could either increase the fuel AKI by 6 or the EGR level by 12%.
Higher AKI fuels gave better peak torque results and improved combustion phasing at fixed EGR levels. However, they also noted that the hardware limitations of the engine were also considerable, suggesting that a high-dilution engine built for a variety of markets may not be able to only rely on calibration changes to take full advantage of geographical fuel differences.
Where EGR allowed equivalent combustion phasing between fuels, a lower AKI fuel often had superior BTE results. The highest AKI fuel, which achieved its high octane rating using high levels of aromatics, had significantly worse combustion efficiencies and slower burn rates.
Using high octane fuels allows a broader torque range on a single boosting device, potentially mitigating some of the challenges of boosting high-dilution engines.
Lower octane fuels benefited more from high levels of EGR than did the high octane fuels. While low octane fuels saw a monotonic increase in BTE with EGR rate, the highest AKI fuel saw a peak BTE at approximately 25% EGR and then a decrease in performance with increased EGR.
At the only condition where all three fuels could be compared on an equal basis, no detectable difference was found in EGR tolerance between fuels.
Emissions results confirm the effect of higher fuel reactivity on burn rate, with lower AKI fuels leading to higher NOx emissions at a constant EGR level and load.
The award. The Horning award, established in 1938, recognizes the authors of the best paper regarding the better mutual adaptation of fuels and internal combustion engines. It is given in the memory of Harry L. Horning, president of SAE in 1925.
Roberts joined SwRI in 1997. He manages and conducts research and development for SwRI’s Clean High-Efficiency Diesel Engine (CHEDE-VI) consortium, one of the world’s longest-running diesel engine research programs. He holds 20 patents in engine and emissions technology and is an original patent holder and former manager of the SwRI High-Efficiency Dilute Gasoline Engine (HEDGE) consortium.
Alger joined SwRI in 2003. He is the manager of SwRI’s HEDGE III consortium (earlier post), which is focused on improving gasoline engine efficiency through the use of cooled EGR, advanced ignition systems and other efficiency-enhancing technologies. He has been awarded 11 patents. He previously was a recipient of SAE’s McFarland Award for being “instrumental in establishing a forum through SAE to foster improved discussions on high-efficiency internal combustion engine technologies.”
Mangold, who joined SwRI in 2003 has designed, fabricated and operated a broad range of test experiments related to engine and vehicle research. He has authored numerous articles.
Alger, T., Mangold, B., Roberts, C., and Gingrich, J. (2012) “The Interaction of Fuel Anti-Knock Index and Cooled EGR on Engine Performance and Efficiency,” SAE Int. J. Engines 5(3):1229-1241 doi: 10.4271/2012-01-1149
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