Research On Improving Geometric Compression Ratio Of Boosted Sidi Engine Using Miller Cycle And EGR

With the increasing of global vehicle parc, automotive industry isfacing more and more serious environment and energy problems. Thus,engine fuel economy improvement and emission reduction have becomethe focus of global attention. Under this background, downsizedspark-ignition direct-injection (SIDI) engine with boosting has become oneof the mainstream technologies to improve gasoline engine fuel economy.However, continuing downsize these engines requires a higher boost ratio,resulting in a reduction in lower geometric compression ratio (CR) tocontrol abnormal combustion such as knock. As a higher compression ratioleads to higher fuel conversion efficiency, it is essential to developeffective knock control strategy in order to improve fuel economy.In this paper, we first investigate knock suppression potential of threedifferent miller cycle strategies in a2.0L boosted SIDI engine and find65CAD LIVC strategy shows the best anti-knock performance. However,40CAD LIVC shows better performance in terms of knock suppresion, fueleconomy, emission and boost requirement. Hence, the knock suppressionpotential by40CAD LIVC strategy is further evaluated with the intentionto increase geometric compression ratio. The geometric compression ratiois sucessfully improved to12.0without the sacrafice of serious knockcombustion as compared to baseline CR. Meanwhile, the fuel economoy isimproved by up to9%. Although40CAD LIVC improves engine performance in many aspects, we also found that it causes severe sootemission problem. In order to reduce the high soot emission caused byLIVC strategy, the effect of cooled exhaust gas recirculation (EGR) isfurther investigated. By combining EGR with LIVC strategy, sootemission is reduced by up to62%. Fuel economy is further improved by upto13.5%compared to baseline engine.