Experimental Study on High-Load Extension of Gasoline/PODE Dual-Fuel RCCI Operation Using Late Intake Valve Closing

摘要

The dual-fuel Reactivity Controlled Compression Ignition (RCCI) combustion could achieve high efficiency and low emissions over a wide range of operating conditions. However, further high load extension is limited by the excessive pressure rise rate and soot emission. Polyoxymethylene dimethyl ethers (PODE), a novel diesel alternative fuel, has the capability to achieve stoichiometric smoke-free RCCI combustion due to its high oxygen content and unique molecule structure. In this study, experimental investigations on high load extension of gasoline/PODE RCCI operation were conducted using late intake valve closing (LIVC) strategy and intake boosting in a single-cylinder, heavy-duty diesel engine. The experimental results show that the upper load can be effectively extended through boosting and LIVC with gasoline/PODE stoichiometric operation. With the retarding of LIVC timing and increase of cyclic fuel quantity, higher boosting pressure and lower Exhaust Gas Recirculation (EGR) ratio were required to maintain sufficient available oxygen. The upper load of gasoline/PODE RCCI operation could be extended up to 23 bar indicated mean effective pressure (IMEP), while still maintaining ultra-low smoke/NO_x emissions and acceptable peak in-cylinder pressure and pressure rise rate (PRR). In addition, stoichiometric combustion also enables the application of a low-cost three-way catalyst to further reduce HC and CO emissions. However, LIVC results in slight reduction of indicated thermal efficiency (ITE) due to the lower effective compression ratio and more incomplete combustion with stoichiometric operation, thus further combustion optimization is necessary for ITE improvement. The study reveals that gasoline/PODE RCCI offers a very competitive pathway to achieve clean and highly efficient combustion over the full load conditions.