A direct numerical simulation of cool-flame affected autoignition in diesel engine-relevant conditions

Conference · Fri Nov 11 04:00:00 EST 2016 · Proceedings of the Combustion Institute

DOI:https://doi.org/10.1016/j.proci.2016.08.043· OSTI ID:1345580

Krisman, Alex ^[1]; Hawkes, Evatt R. ^[2]; Talei, Mohsen ^[3]; Bhagatwala, Ankit ^[4]; Chen, Jacqueline H. ^[4]

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1. Sandia National Lab. (SNL-CA), Livermore, CA (United States); The Univ. of New South Wales, Sydney, NSW (Australia)
2. The Univ. of New South Wales, Sydney, NSW (Australia)
3. The Univ. of Melbourne, Melbourne, VIC (Australia)
4. Sandia National Lab. (SNL-CA), Livermore, CA (United States)

In diesel engines, combustion is initiated by a two-staged autoignition that includes both low- and high-temperature chemistry. The location and timing of both stages of autoignition are important parameters that influence the development and stabilisation of the flame. In this study, a two-dimensional direct numerical simulation (DNS) is conducted to provide a fully resolved description of ignition at diesel engine-relevant conditions. The DNS is performed at a pressure of 40 atmospheres and at an ambient temperature of 900 K using dimethyl ether (DME) as the fuel, with a 30 species reduced chemical mechanism. At these conditions, similar to diesel fuel, DME exhibits two-stage ignition. The focus of this study is on the behaviour of the low-temperature chemistry (LTC) and the way in which it influences the high-temperature ignition. The results show that the LTC develops as a “spotty” first-stage autoignition in lean regions which transitions to a diffusively supported cool-flame and then propagates up the local mixture fraction gradient towards richer regions. The cool-flame speed is much faster than can be attributed to spatial gradients in first-stage ignition delay time in homogeneous reactors. The cool-flame causes a shortening of the second-stage ignition delay times compared to a homogeneous reactor and the shortening becomes more pronounced at richer mixtures. Multiple high-temperature ignition kernels are observed over a range of rich mixtures that are much richer than the homogeneous most reactive mixture and most kernels form much earlier than suggested by the homogeneous ignition delay time of the corresponding local mixture. Altogether, the results suggest that LTC can strongly influence both the timing and location in composition space of the high-temperature ignition.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Sandia National Laboratories, Livermore, CA; Energy Frontier Research Centers (EFRC) (United States). Combustion Energy Frontier Research Center (CEFRC)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 1345580
• Report Number(s): SAND2016-5709C; 643524
• Conference Information: Journal Name: Proceedings of the Combustion Institute Journal Issue: 3 Journal Volume: 36
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY