Mruthunjaya Uddi

Temperature measurements in a rapid compression machine using mid-infrared H2O absorption spectroscopy near 7.6 μm.

A method for measuring the temporal temperature and number density in a rapid compression machine (RCM) using quantum cascade laser absorption spectroscopy near 7.6 μm is developed and presented in this paper. The ratios of H(2)O absorption peaks at 1316.55 cm(-1) and 1316.97 cm(-1) are used for these measurements. In order to isolate the effects of chemical reactions, an inert mixture of argon with 2.87% water vapor is used for the present investigation. The end of compression pressures and temperatures in the RCM measurements are P(C)=10, 15, and 20 bar in the range of T(C)=1000 to 1200 K. The measured temperature history is compared with that calculated based on the adiabatic core assumption and is found to be within ±5 K. The measured temporal number density of H(2)O to an accuracy of 1%, using the absolute absorption of the two rovibrational lines, show that the mixture is highly uniform in temperature. A six-pass, 5.08 cm Herriott cell is used to calibrate the line strengths in air and broadening in an Ar bath gas.

On the Effect of Nonequilibrium Plasma on the Minimum Ignition Energy—Part 1: Discharge Model

The mathematical model of a repetitive nanosecond pulse discharge at atmospheric-pressure conditions has been presented. The influence of initial gas temperature, chemical kinetics, and vibrational nonequilibrium on the ignition of methane-air and ethylene-air mixtures has been analyzed.

Studies of C2H6/ air and C3H8/ air Plasma assisted combustion kinetics in a nanosecond discharge

The paper presents the studies of ethane and propane/air plasma assisted combustion at a pressure of 60 torr and temperature 300K. O atoms in the plasma have been measured as a function of time after a single discharge pulse using TALIF (Two photon laser induced fluorescence) at 60 torr and temperature of 300 K for these mixtures at various equivalence ratios. A plasma chemistry model of hydrocarbons has been developed. This is done by combining a reduced mechanism of the latest low temperature hydrocarbon mechanism with plasma air chemistry along with plasma and flame NO formation chemistry. The reaction rates of excited nitrogen species with hydrocarbons are not know accurately and have not been included. O atoms measured in air are compared with the new mechanism predictions. The O atom measurements compare well with the mechanism predictions. The O atoms decay slightly faster in the case of ethane than predicted. For the case of propane, the O atoms decay much faster than predicted by the mechanism. A better mechanism for low temperature hydrocarbon combustion is required for the plasma. The O atoms begin chain reactions giving rise to OH and H radicals. H 2O is formed during these chain reactions. But soon all the radicals decay in ~1.5msec. After the end of chain reactions, species such as CH 2O, CH 4, C 2H4, H 2O2, O 3 begin to accumulate. CO and CO 2 are formed only at the end of these chain reactions through slow oxidation. The mechanism has been used to study ignition by a single discharge for air/fuel mixtures at high temperatures in the range 500-700K and pressures in the range 300-500 torr. An initial mole fraction of O atoms (~5 x 10 -5 ) has been added without a nanosecond discharge and the mixture is observed in time. It is found that for higher pressures of ~ 400torr, 700K, there is a two stage ignition in ~28msec for stoichiometric air while it is 43msec for same mixture at 300 torr showing that there is a dependence on initial pressure and temperature to be studied to take advantage of the nanosecond discharge.

On the Effect of Nonequilibrium Plasma on the Minimum Ignition Energy: Part 2

A mathematical model for the calculation of the minimum ignition energy (MIE) of the nanosecond-pulsed discharge ignition is presented. The model is based on the kinetic and transport equations for a multicomponent reacting mixture combined with the equations for translational and vibrational temperatures. The analysis of the influence of a pulsewidth, the reduced electric field of the discharge, the energy stored in the vibrational degrees of freedom, and the mixture composition on the MIE is conducted.

Measurements of Extinction Limits of Methyl Decanoate Diffusion Flames and A Kinetic Study

In the present study, extinction strain rates of methyl decanoate/air diffusion flames have been measured as a function of fuel mole fraction in counterflow diffusion flames at an initial fuel temperature of 500 K and atmospheric pressure. A new high temperature detailed kinetic model is constructed for methyl decanoate oxidation based on the oxidation chemistries for methyl butanoate and n-heptane. The results show that the newly developed model reproduces experimental data from the literature, such as speciation profiles in a jetstirred reactor and diffusion flames. Model predictions also reproduce accurately the measured extinction strain rates of methyl decanoate diffusion flames. Analysis of these predictions shows that under diffusion flame conditions, the fuel is exclusively (>95%) consumed by metathesis reactions with H atoms. Formaldehyde, one of the major stable intermediates found in methyl ester oxidation, is produced via two different paths: one from the decomposition of methyl ester function group, and the other from small radicals in the core reaction zone. A comparative analysis of methyl butanoate and methyl decanoate extinction strain rate reveals that methyl decanoate exhibits a stronger resistance to extinction than methyl butanoate primarily as a result of its larger molar heating value. After accounting for the differences in the heating values and transport properties, both fuels exhibit the same extinction limit behavior, indicating the existence of an identical impact of ester kinetics present for both fuels.

Kinetic Effects of Non-Equilibrium Plasma on Partially Premixed Flame Extinction

A new plasma assisted combustion system was developed by integrating a counterflow burner with nano-second pulsed non-equilibrium discharge. The kinetic effects of plasma assisted fuel oxidization on the extinction of partially premixed methane flames was studied at 60 Torr by blending 2% CH4 into the oxidizer stream. The non-equilibrium discharge accelerated dramatically the fuel oxidation. The O production and the products of plasma assisted fuel oxidation were measured, respectively, by using two-photon absorption laserinduced fluorescence (TALIF) method, Fourier Transform Infrared (FTIR) spectrometer , and Gas Chromatography (GC). The product concentrations were used to validate an existing plasma assisted combustion kinetic model. The comparisons showed the kinetic model prediction was poor due to missing reaction pathways, such as those involving carbon formation, H2 excitation and dissociation, and interactions of excited species with hydrocarbon species. The path flux analysis determined that O was the critical species for kinetic modeling because it was generated by the discharge and dictated the oxidization process. The extinction strain rate measurements showed the non-equilibrium plasma discharge extended the extinction limit significantly. Strong emission from Ar* was observed at high plasma repetition rates and numerical modeling showed that Ar* contributed significantly to the enhancement of extinction limit.

Kinetic Interaction Effects of Methyl-Butanoate/ n-Heptane Mixture on Extinction Limits of Counterflow Diffusion Flames.

The paper presents the study of kinetic interaction of an ester molecule (Methyl Butanoate) and long chain alkane (n-Heptane). It was found that the present mechanism for Methyl butanoate (MB) over predicts the extinction strain rates in a counter flow diffusion flames by almost a factor of 5. The corrected and improved mechanism in this paper for MB predicts the extinction strain rates to within 5% of experiment values. It is also found that these rates are very sensitive to the transport parameters. A combined mechanism developed for n-heptane (nH) and Methyl butanoate (MB) predicts the extinction strain rates and flame speeds to within 5% including their blends. The extinction strain rate varies linearly from with blending fraction of MB, decreasing as MB mole fraction is increased maintaining total mole fraction of nH and MB constant. This shows that MB reduces the reactivity of n-Heptane. The combined mechanism is used to study the kinetic interaction between MB and nH. The early formation of CO2 in MB and its effect on soot precursors has also been investigated. I. Introduction

Effects of Non-Equilibrium Plasma on Counterflow Diffusion Flames

A new plasma assisted combustion system was developed by integrating a counterflow burner with nano-second pulsed non-equilibrium plasma. Xenon calibrated two-photon absorption laser-induced fluorescence was used to characterize the system by measuring the absolute atomic oxygen concentrations at the exit of the counterflow burner. The effects of plasma on the flames were examined by measuring the extinction strain rates of counterflow argon diluted methane/oxygen diffusion flames with and without plasma activation at low pressure (60 Torr). The experimental results were also compared with numerical simulations.