The work on combustion science has encompassed gaseous, liquid and solid fuels and rocket propellants.
A transient one-dimensional flame propagation code was developed at the laboratory and has been used for extracting fundamental combustion features of several gaseous fuel-oxidant mixtures. (Combustion).
Principally it was uncovered that adiabatic propagating flames do not have a flammability limit through a rigorous computation of multi-step chemistry and it is essential to invoke a minimum unavoidable heat loss to explain the experimentally observed flammability limits. (Combustion).
The code was also extended to spherical propagating flames to extract the stretch effects and these were calculated for several canonical fuel-oxidant combinations and the results compared with experimental results of stretch effects. These were used to demonstrate that full chemistry is needed to explain the stretch effects of fuel-oxidant mixtures. (Combustion).
Liquid fuel (oxidant) drop combustion behavior in the atmosphere of oxidant (fuel) was examined under several approximations and it was shown that use of variable thermodynamic and transport properties was essential to explain the observed flame-to-drop diameter ratio behavior as well other combustion properties. This aspect was shown equally important in boundary layer combustion under free or forced convection. (Combustion).
Solid sphere combustion studies have been conducted on polymeric spheres, dried distillery effluent material in the form of spheres, soft wood spheres to understand the behavior in relation to liquid droplets. All these spheres exhibit a d2 – law like liquid droplets but with different mechanisms all diffusion controlled. Principally where volatiles come out of the drop surface gas phase combustion with diffusion controlled flame results. Where volatile combustion is over and char combustion is to take place, as it happens with wood spheres, the combustion proceeds via diffusion controlled exothermic surface reaction. The combustion behavior in all these cases can be set out in a standard d2 – law format. (Combustion).
Solid combustion is by far the most difficult to accomplish in terms of extracting high combustion efficiency with minimal undesirable gaseous emissions. One of the key features of the studies and developments is hat one can obtain both high efficiency and minimal emissions by performing a two-stage combustion. In the first stage, a gasification process is initiated. This process involves flaming combustion of volatiles and subsequent reduction of the product gases by the hot char in a manner that most complex hydrocarbons are cracked into smaller molecules. This leads to a hot combustible gas that can be burnt far more effectively using gaseous combustion techniques. (Gasification).
The premixed flame propagation behavior in confined spaces was modeled along with turbulence to elucidate the combustion process in the cylinder of a reciprocating engine and predict the chamber pressure – crank angle of the engine. Comparisons of predictions of the model with experiments are excellent at moderate compression ratios up to 12. Modeling the extraordinary behavior of producer gas based gas engines namely, non-knock and smooth operation at high compression ratios (~17) has shown that the fluid dynamic behavior under these conditions involves reverse-squish of the flow and this would need three dimensional modeling of reactive flow. (Combustion).
Modeling the combustion of model solid propellants, namely, sandwich propellants has needed a complete revision of the fundamental combustion properties of the principal oxidizer, namely, Ammonium Perchlorate. (Propulsion).
Combustion of gaseous fuels with oxidants (like air) can be conducted with minimal emissions with a recently floated concept called “Mild” combustion mode, otherwise termed flameless combustion. By separating the fuel and oxidizer streams and arranging the mixing between the hot product gases and the fuel and oxidizer streams in such a way as to reduce the local concentrations of fuel and reactive component of the oxidant till substantive mixing has occurred. Such a stream with sufficiently high temperature ignites and a relatively uniform reaction occurs throughout the body of gases in the chamber. This process allows reduction of fluctuations in all quantities including the peaks in temperature that is primarily responsible for larger emissions of species like NOx . Also the burner will run with much less rough (implying emission of noise being lower). Modeling such a system and examining the physics and chemistry of the phenomenon to allow predictions has been completed. (Combustion).