Title: Simulations of droplet combustion under gas turbine conditions

Abstract

In various applications with recirculation, liquid droplets can be immersed in gases that may have a wide range of possible compositions, from pure air to hot combustion products. In order to gain fundamental understanding of the behaviour of individual droplets in vitiated air, numerical simulations of kerosene single droplet evaporation, autoignition, and combustion in conditions relevant to gas turbines have been performed. The droplet autoignition behaviour has been analysed in both physical and mixture fraction space for a wide range of vitiated air compositions and initial droplet diameters. Results show that the autoignition time delay decreases with increasing level of dilution with hot combustion products and decreasing initial droplet diameter. Chemistry is confined up to a radius of almost 10 initial droplet diameters and the location of autoignition is influenced by both the initial droplet diameter and the level of dilution. The time evolution of species in the gaseous phase after autoignition shows similar trends for all the diameters and dilution levels investigated here with the peak of temperature and OH mass fraction moving towards the droplet surface as a consequence of the balance between fuel production and consumption. In mixture fraction space, the location of the peaks of temperaturemore » and OH mass fraction after autoignition do not change in time whereas other intermediate species such as CH₂O and pyrolysis products still exhibit a quite variable behaviour. The long-time flame structure has been compared with gaseous laminar counterflow simulations and, although qualitatively similar, the flame structure in the two configurations has differences with implications for flamelet combustion models used in spray combustion. The droplet evaporation, autoignition, and combustion behaviour has been summarized through a regime diagram showing the evaporation and autoignition time delays as a function of both initial droplet diameter and vitiated air dilution. This allows the identification of different states in the droplet combustion scenario and the introduction of critical values of dilution and initial droplet diameter beyond which single droplet rather than cloud combustion can occur, which can be exploited in the design of lean burn gas turbine combustion systems. In conclusion, the approach presented here can be easily extended to other conditions and fuels allowing the generation of regime diagrams for various operating conditions.« less

Authors:

Giusti, Andrea  ^[1];

• Search DOE PAGES for author "Giusti, Andrea"
• Search DOE PAGES for ORCID "0000-0001-5406-4569"

Sidey, Jennifer A.M. ^[1]; Borghesi, Giulio ^[2]; Mastorakos, Epaminondas  ^[1]

• Search DOE PAGES for author "Mastorakos, Epaminondas"
• Search DOE PAGES for ORCID "0000-0001-8245-5188"

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+ Show Author Affiliations

1. Univ. of Cambridge (United Kingdom)
2. Sandia National Lab. (SNL-CA), Livermore, CA (United States)

Publication Date:

Sat Jul 29 00:00:00 EDT 2017

Research Org.:

Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Sandia National Lab. (SNL-CA), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1870507

Alternate Identifier(s):

OSTI ID: 1566228

Report Number(s):

SAND2022-4985J
Journal ID: ISSN 0010-2180; 705283

Grant/Contract Number:  

NA0003525; AC04-94AL85000; AC0494AL85000

Resource Type:

Accepted Manuscript

Journal Name:

Combustion and Flame

Additional Journal Information:

Journal Volume: 184; Journal ID: ISSN 0010-2180

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

42 ENGINEERING; kerosene; single droplet combustion; hot products; MILD combustion; regime diagram