Research highlights

Research Team

• Kinetics of biodiesel surrogate components:

  One of our recent interests concerns with developing a kinetic scheme for a small ester, which is a potentially important candidate to represent the longer chain molecules in the real biodiesel fuel, namely methylbutanoate. A compact reaction scheme is derived for methylbutanoate from an existing detailed mechanism, revised based on recent experimental measurements and theoretical rate constant calculations. The revised kinetic model has been validated comprehensively against a wide range of experimental data along with ignition delays at intermediate temperatures measured in an RCM at PTB, Germany.
  
  Thereafter, a novel approach is used to propose surrogates to represent biodiesel fuel, consisting of methylbutanoate and n-dodecane, and assessed thoroughly (Fig. on the left). This work serves as our first step towards the development of a compact reaction scheme for a biodiesel surrogate which will be coupled with combustion studies to investigate the use of biodiesels and its blends with diesel in CI engines.
  Fig: Ignition delays in a shock tube and Species profiles in a jet stirred reactor; symbols: experiments for biodiesel, lines: Surrogate (presented at the 10th U.S. National Combustion Meeting, 2017)
  

• Extinction studies of oxygenated fuels:

  Addition to oxygenates to diesel fuel has been found to reduce soot emissions. Nonetheless, the resulting changes in the extinction and auto-ignition characteristics of the fuel mixture have not yet been fully understood. Considering two important oxygenates, dimethyl ether and methanol, we undertook a fundamental analysis, which reveals that blending small amounts of oxygenates with diesel increases its resistance to extinction, which can be of use in applications such as burners, furnaces and pre-vaporizers. We also find that the auto-ignition characteristics are not altered much due to blending. This study suggests that in the presence of oxygenate, a combustion system can be made more stable even at higher strain rates and at the same time operate with reduced emissions.
  
  In order to critically evaluate the overall combustion behaviour of DME via numerical simulations, an accurate as well as compact kinetic mechanism to describe its oxidation is most essential. A short kinetic mechanism consisting of 23 species and 88 elementary reactions is proposed to describe the oxidation of DME based on the detailed San Diego mechanism. The short mechanism accurately reproduces the available experimental data for ignition delays, laminar flame speeds, and species profiles in flow reactors as well as jet-stirred reactors.
  
  To assess the validity of this reaction mechanism in non-premixed systems, extinction strain rates of DME-air mixtures, which are not available in the literature, are measured in a counter-flow diffusion flame burner. The 23-species reaction mechanism is able to predict the experimental data for extinction within the uncertainty limits. This mechanism is further reduced by introducing quasi-steady state assumptions for six intermediate species to finally obtain a 14-step global kinetic scheme. A code is developed in MATLAB to obtain these 14 global steps and their corresponding rate expressions in terms of the elementary reaction rates. The 14-step mechanism performs as good as the 23-species mechanism for all the experimental data sets tested for.
  

• Compact kinetic model for methyl methacrylate oxidation:

  In these days, synthetic and natural polymeric esters find applications in transport and construction sectors, where fire safety is an important concern. One polymer that is wide used is poly methyl methacrylate (PMMA), which almost completely undergoes thermal decomposition into methyl methacrylate (its monomer) CH₂=C(CH₃)-C(=O)-O-CH₃ (MMA) at ~250-300^oC. In order to analyze the high temperature gas phase oxidation of PMMA, and thereby predict its fire behaviour (such as burning rate, temperature of the material and heat fluxes) with less computational effort, a compact kinetic model for the oxidation of its primary decomposition product, MMA, is most essential.
  
  As a part of this work, a compact reaction model to describe the oxidation of MMA is developed and validated against fundamental experimental datasets obtained in premixed flames, starting with a detailed mechanism proposed by the Lawrence Livermore group.
  
  Evaluating the model against these data sets point to the need to revise the kinetic model, which is achieved by adopting rate constants of key reactions from recent literature for analogous molecules. The updated compact kinetic model is able to predict the major species in the flat flame as well the burning velocity of MMA satisfactorily. The final `short MMA mechanism' consists of 88 species and 1092 reactions.
  
  
  
  
  

• Oxidation kinetics of alternative aviation fuels:

  Renewable and alternative fuels for aviation have advantages of lesser emissions and clean burning ability. To predict, assess, and understand their combustion characteristics from a fundamental approach, a kinetic model for a suitable reference mixture that mimics a chosen alternative fuel is being developed. This opens up avenues to study several `drop-in alternatives' to current day aviation fuels.
  

• Surrogates for liquid phase applications

  Surrogate mixtures are often used to emulate gas phase combustion characteristics of real fuels, such as heating value, sooting characteristics, and propensity to ignition. These cannot be used as such in liquid phase applications, where multi-phase processes, such as spray injection, are important. Typically, for these applications, surrogates are proposed by matching targets such as density, viscosity, and distillation curves between the real fuel and the surrogate. However, these targets do not pertain to a combustion environment. One attractive option to include evaporation and phase equilibrium dynamics in the surrogate definition is to study the combustion characteristics of an isolated droplet. This project involves simulating the burning process of isolated fuel droplets at low gravity for neat fuel components as well as mixtures of hydrocarbons relevant as transportation fuel surrogates. Evaporation rates of fuels in this simple configuration may be useful quantities to describe the multi-phase effects in a combusting environment.
  
  In this project, numerical solution procedure to predict the droplet burning accounting for the interface conditions will be developed. Techniques to obtain solutions with reduced computational time will be explored. The validity of the model will be ascertained based on the vast data available in the literature. Thereafter, evaporation rate rules will be developed for the surrogate mixture in terms of the components, and investigated if it is indeed an appropriate measure or if other additional parameters may be needed to come up with a good surrogate valid for liquid-phase applications.
  

Funding sources

• New Faculty Initiation Grant, Project No. MEE/15-16/845/NFIG: September 2015--2017
• Exploratory Research Project, May 2016--2017
• Indo-Russian project awarded by DST under Grant No. 16-49-02017: October 2016--2019
• InnoINDIGO BiofCFD project awarded by DST: November 2017--2020
• New Faculty Seed Grant, Project No. MEE/15-16/845/NFIG: November 2017--2020

Collaborations

• Dr. Sivaram Ambikasaran, Department of Mathematics, IIT Madras
  
• Dr. V. Raghavan, Department of Mechanical Engineering, IIT Madras
  
• Dr. K. Anand, Department of Mechanical Engineering, IIT Madras
  
• Prof. Kalyanasundaram Seshadri, University of San Diego
  
• Prof. Ravi Fernandes, Physikalisch-Technische Bundesanstalt
  
• Dr. Denis Knyazkov, Voevodsky Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences
  
• Dr. Perrine Pepiot, Cornell University
  
• Prof. Heinz Pitsch, RWTH Aachen
  

Alumni

• M. C. Sanjay (M. Tech 2017): SMILES based interface to Thermodynamic Property Estimation Using THERM
  
• T. V. Vaisakh (M. Tech 2017): Reaction mechanism optimization
  
• Kiran Kumar Yalamanchi (Dual Degree 2017)
• Ankit Jain (Dual Degree 2017)