An Experimental Technique for Determining Cycle-Resolved Pre-Combustion in-Cylinder Composition and its Application Towards the Understanding of Diesel Engine Emissions during Transient Operation.

[摘要] This study introduces an experimental technique to quantify cycle-resolved values of pre-combustion in-cylinder compositions during transient engine operation.The work is motivated by increased particulate and NOX emissions during transient engine operation, which contribute significantly to overall cumulative diesel emissions.The study is divided into three major tasks:technique development, validation, and application to demonstrate its capability to provide new insight into transient engine behavior.One cylinder of a 6.0L V-8 diesel engine is instrumented to obtain cycle-resolved masses of three in-cylinder pre-combustion constituents:fuel, air, and stoichiometric combustion products.Fuel is determined through use of an instrumented fuel injector and cylinder pressure.The mass of air is determined through calculation of the air/fuel ratio of each cycle from measurements of CO2 concentrations in the exhaust and in the cylinder.Stoichiometric combustion product mass is quantified through the pre-combustion in-cylinder measurement of CO2.Validation of the technique is accomplished by first determining that the methodology does not significantly alter combustion.Error and sensitivity analysis confirm that the technique provides accurate results.The masses of fuel, air, and stoichiometric combustion products are known to ±0.74%, ±2.82%, and ±3.93%, respectively, with a 95th percentile confidence interval.The technique provides data on a cycle-by-cycle basis, a resolution that is unattainable with traditional test cell hardware. This allows insight into engine behavior that was previously impossible, especially during transient operation.Engine data is taken in three separate investigations:steady-state conditions, constant-speed load sweeps, and realistic in-vehicle engine behavior during an FTP 75 driving schedule.Cycle-resolved NO emissions and fast particulate measurements are also made to characterize transient emissions.During the first few cycles of intense accelerations, excessive levels of over-fueling occur, resulting in cycles with equivalence ratios as high as 1.4.These cycles cause extremely high particulate emissions.High levels of NO emissions occur 3-4 cycles into strong accelerations and are attributed to intensely-premixed combustion with high levels of in-cylinder oxygen.In summary, this study demonstrates that tighter cycle-resolved control of fuel injection and EGR systems, including internal residual, are necessary prerequisites for realizing the full potential of low-emissions transient engine operation strategies.

[发布机构] University of Michigan

[效力级别] Cycle-resolved

[关键词] Transient Diesel Emissions;Cycle-resolved;In-cylinder Measurement;Pre-combustion In-cylinder Composition;Mechanical Engineering;Engineering;Mechanical Engineering