Developing Surrogates for Liquid Transportation Fuels: The Role of Spherically Symmetric Droplet Combustion

The finite supply of transportation fuels has generated renewed interest to improve their performance in power and propulsion devices. However, the complexity of real fuels prohibits developing their combustion chemistries and property databases needed for simulating performance in engines to identify operational regimes for improving fuel efficiency. Surrogates offer the means to address these concerns if they can be shown to replicate certain combustion targets of the real fuel, and to result in combustion properties similar to real fuels when burned in a suitable configuration that is amenable to detailed numerical modeling. This paper examines the role which droplet combustion can play in the development of surrogates for complex transportation fuels. Recognizing that spray combustion is far too difficult to model and that droplets represent the fine-grid structure of sprays, the combustion dynamics of fuel droplets are examined in an environment that seeks to remove external convective influences to simplify the transport field and produce spherical symmetry in the droplet burning process that can be modeled using a detailed numerical simulation approach. The one-dimensional flames and transport dynamics that result are shown to be well positioned to evaluate the efficacy of surrogate fuel performance. Recent efforts are summarized that have used the spherical droplet flame configuration to evaluate the performance of surrogate fuel blends. Experiments are discussed for promoting spherical symmetry, and results are presented to show the efficacy of some surrogate blends to replicate the performance of gasoline and jet fuels using the spherical droplet configuration. Some results are also included from detailed numerical modeling of biodiesel droplets that incorporate complex combustion chemistry, and unsteady transport, vaporization, and variable property effects that illustrate the potential for high fidelity predictions needed for developing surrogates using the spherically symmetric droplet flame configuration. This paper is based on a presentation given at the Indo-US International Workshop on Novel Combustion for Sustainable Energy Development, Kanpur, India, January 2–4, 2014. C.T. Avedisian (&) Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853-7501, USA e-mail: [email protected] © Springer India 2014 A.K. Agarwal et al. (eds.), Novel Combustion Concepts for Sustainable Energy Development, DOI 10.1007/978-81-322-2211-8_16 379