Investigation of the Effects of Cetane Number, Volatility, and Total Aromatic Content on Highly-Dilute Low Temperature Diesel Combustion 2010-01-0337

The objective of this study is to increase fundamental understanding of the effects of fuel composition and properties on low temperature combustion (LTC) and to identify major properties that could enable engine performance and emission improvements, especially under high load conditions.

A series of experiments and computational simulations were conducted under LTC conditions using 67% EGR with 9.5% inlet O₂ concentration on a single-cylinder version of the General Motors Corporation 1.9L direct injection diesel engine. This research investigated the effects of Cetane number (CN), volatility and total aromatic content of diesel fuels on LTC operation. The values of CN, volatility, and total aromatic content studied were selected in a DOE (Design of Experiments) fashion with each variable having a base value as well as a lower and higher level. Timing sweeps were performed for all fuels at a lower load condition of 5.5 bar net IMEP at 2000 rpm using a single-pulse injection strategy. Selected fuels were also run under a higher load condition of 10 bar net IMEP at 2000 rpm with roughly 90 dB combustion noise using a split injection strategy.

For this engine and the operating conditions tested, at 5.5 bar net IMEP, results show that increasing CN reduces CO and UHC, improves ISFC and reduces combustion noise due to more favorable combustion phasing. The results at higher load with split injection indicate that the two injection timings and respective fuel quantity delivered in each injection must be varied significantly to reach optimum conditions for fuels with different CN. Numerical simulation results also demonstrate the effects of fuel property differences on combustion. In-cylinder flow fields and distributions of temperature and species depict the reasons for different combustion performance of the fuels considered in the study.