Arindrajit Chowdhury

The Simultaneous Reduction of NOx and PM Using Ultra-Cooled EGR and Retarded Injection Timing in a Diesel Engine

Now-a-days, diesel engines are more popular over gasoline engines due to their undisputed benefit of fuel economy and higher torque output. However, meeting the stringent emission norms without affecting fuel economy is a major challenge with diesel engines. In this paper, optimization of various parameters like injection parameters, compression ratio (CR) and amount of ultra-cooled exhaust gas recirculation (EGR) has been done for a variable CR (VCR) engine, to achieve low-temperature combustion (LTC) mode by which simultaneous reduction of NOx and soot may be obtained. Taguchi analysis was employed to carry out minimum number of experimental runs and still get the essence of large number of test cases. Effect of those parameters on engine performance and exhaust emissions has also been studied with the help of signal-to-noise (SN) ratio analysis. Results of SN ratio analysis indicate that injection timing, CR and ultra-cooled EGR are the dominant factors while the effect of injection pressure, in range of study, is not much significant for chosen response variables. Flatter and wider HRR traces, hence simultaneous reduction in NOx and PM emissions has been observed for runs having optimized input parameters. NOx and soot found to be reduced by 98% and 60%, respectively, with an increase in brake thermal efficiency (BTE) by 5%. Higher values of HC and CO emissions were found for runs with optimized parameters, but these can be easily reduced by using a catalytic converter, a simple device.

Nitro-Substituted Bishomocubanes: Synthesis, Characterization, and Application as Energetic Materials

Several high-energy-density strained polycyclic compounds nitromethyl-l,3-bishomocubane (NMBHC), nitromethylene-1,3-bishomocubane (NMyBHC), and bis(nitromethyl)-1,3-bishomocubane (DNTMBHC), which were synthesized for the first time from bishomocubanone, hold potential for application as standalone fuels in liquid bipropellant systems or as additives in liquid and solid propellant formulations. DFT analysis at the B3LYP/6-31G(d) level of theory was employed to optimize the geometries of the compounds and to determine their densities, heats of formation, and various thermodynamic properties. The density specific impulse, determined by using equilibrium thermodynamics, demonstrated an improvement of 75 s for NMBHC and NMyBHC over standard hydrocarbons. The specific impulse with ammonium perchlorate showed an improvement of 25-30 s over hydroxy-terminated polybutadiene. Thermogravimetric analysis revealed that NMBHC, NMyBHC, and DNTMBHC evaporated readily with activation energies of 58.8, 69.2, and 74.5 kJ mol(-1), respectively.

Synthesis and energetic properties of high-nitrogen substituted bishomocubanes

Synthesis, thermodynamic characterization, and energetic properties of three novel high-nitrogen bishomocubane-based compounds DADMBHC, DTetzBHC and DPTrizDMBHC are reported here. These compounds have higher heats of formation (HoFs) and higher energy densities as compared to traditional hydrocarbon fuels. Densities, gas phase HoF and their optimized molecular structure geometries were calculated with various levels of theory. In general, the calculated HoFs of these compounds turn out to be extremely high. Ballistic properties such as vacuum specific impulse and density vacuum specific impulse were calculated using the NASA Chemical Equilibrium and Applications utility. Propulsive properties were compared with liquid bipropellants (RP1) and solid propellants (AP) and explosive properties were compared with RDX. The density specific impulse demonstrated an improvement of 35 s for DADMBHC and DTetzBHC over standard liquid hydrocarbon HTPB, thus showing promise as possible monomers to replace HTPB as a fuel-binder. The density specific impulses of these compounds were also found to be significantly higher than that of RP1, e.g. that of DADMBHC was found to be higher by 84 s, making them potentially good candidates as propellants for use under volume-limited conditions. The detonation properties showed that these compounds have low potential as explosives. TGA, coupled with IR spectroscopy, revealed that DADMBHC and DPTrizDMBHC evaporate readily while DTetzBHC decomposes partially.

Analysis of RDX-TAGzT pseudo-propellant combustion with detailed chemical kinetics

A detailed model of steady-state combustion of a pseudo-propellant containing cyclotrimethylene trinitramine (RDX) and triaminoguanidinium azotetrazolate (TAGzT) is presented. The physicochemical processes occurring within the foam layer, comprised of a liquid and gas bubbles, and a gas-phase region above the burning surface are considered. The chemical kinetics is represented by a global thermal decomposition mechanism within the liquid by considering 18 species and eight chemical reactions. The reactions governing decomposition of TAGzT were deduced from separate confined rapid thermolysis experiments using Fourier transform infrared spectroscopy and time-of-flight mass spectrometry. Within the gas bubbles and gas-phase region, a detailed chemical kinetics mechanism was used by considering up to 93 species and 504 reactions. The pseudo-propellant burn rate was found to be highly sensitive to the global decomposition reactions of TAGzT. The predicted results of burn rate agree well with experimental burn-rate data. The increase in burn rate by inclusion of TAGzT is due in part from exothermic decomposition of the azotetrazolate within the foam layer, and from fast gas-phase reactions between triaminoguanidine decomposition products, such as hydrazine, and oxidiser products from the nitramine decomposition.

Modeling of RDX/TAGzT Propellant Combustion with Detailed Chemical Kinetics

A detailed model of steady -state combustion of a pseu do -propellant containing cyclotrimethylenetrinitramine and triaminoguanidinium azotetrazolate is presented. The physicochemical processes occurring within the foam layer , comprised of a liquid and gas bubbles, and a gas -phase region above the burning surf ace are considered. The chemical kinetics is represented by a global thermal decomposition mechanism within the liquid by considering 18 species and 8 chemical reactions. The reactions governing decomposition of TAGzT were deduced from separate confined r apid thermolysis experiments using Fourier transform infrared spectroscopy and time -of -flight mass spectrometry. Within the gas bubbles and gas -phase region, 76 species and 468 reactions are considered. The model predicts a burn enhancement due in part f rom exothermic decomposition of the azotetrazolate within the foam layer, and from fast gas -phase reactions between triaminoguanidine decomposition products, such as hydrazine , and oxidizer products from the nitramine decomposition.

Ignition Behavior of Novel Hypergolic Materials

The complex interplay of various physical and chemical phenomena occurring during the ignition of dicyanamide -based novel ionic liquids as fuels and nitric acid as the oxidizer was probed. The pre -ignition condensed phase chemistry was analyzed by a modified confined rapid thermolysis set up under isothermal conditions. The major gases accumulating in the ignition zone were found to be CO 2, N 2O, H 2O, and HNCO, within the temperature range 30 �50oC. A reaction mechanism initiated by an exothermic neutralization, followed by formation of cyano -nitro -urea and dinitrobiuret, leading to the smaller molecular weight gases, was formulated. A conventional drop test setup was utilized to determine the temperatures in the gas phase in both the pre -ignition and post -ignition stages. High speed videos of the ignition event were acquired to further aid in the resolution of the separate events leading to ignition as a droplet of fuel collides with a pool of oxidizer. The videos showed the expulsion of small droplets of condensed phase matter into the igniti on zone due to vigorous condensed phase reactions prior to the formation of the ignition kernel. The global ignition delay for the ionic liquid 1 -ethyl -3-methyl -imidazolium dicyanamide (EmimDCA) was approximately doubled from 35 ms by substituting white fu ming nitric acid (WFNA) with 90% HNO 3 as the oxidizer.

Theoretical studies on the propulsive and explosive performance of strained polycyclic cage compounds

Compounds consisting of a carbon-based cage have a highly strained molecular structure and have become the subject of interest in recent years because they possess high heat of formation and so are highly energetic. In the present work, ab initio molecular modelling calculations have been used for analysing 28 carbon-cage structures with the aim of identifying the best candidates for synthesis particularly for use in propellant compositions. Density functional theory (B3LYP) was employed for the geometry optimisation of the proposed molecules using the 6-311++G(d,p) basis set. Calculated heats of formation and densities of the compounds have been used from the optimized structures to compute their specific impulses and density specific impulses in various configurations (solid and liquid) with an eye on propulsion applications. Detonation properties of the compounds have also been reported and comments have been made correlating the properties of the cage compounds with their molecular structures.

Apparatus for probing preignition behavior of hypergolic materials

The determination of the condensed-phase preignition chemistry of hypergolic bipropellant pairs has been considerably challenging due to toxicity and reactivity of the used materials. In this work, we describe a new experimental technique for characterizing preignition behavior of hypergolic materials. Small quantities of the bipropellant pair are brought in contact under isothermal conditions, and spectral transmission measurements on the evolved products are performed using Fourier transform infrared spectroscopy. The gaseous products are subsequently quantified to yield species concentration profiles at various temperatures, hence facilitating the elucidation of the detailed condensed-phase chemical kinetics responsible for the ignition in the gas phase.

Development of custom-made engine control unit for a research engine

In this paper, hardware development, software coding using embedded C programming language for an Arduino ATMEGA microcontroller, calibration of electronic control unit (ECU) was tested for a research engine to control the fuel injection flow rate with respect to the suction top dead center (TDC) of the engine. The system could control the fuel flow rate with a variable reluctance sensor, an Arduino microcontroller and a solenoid operated injector in a closed loop domain with a varying pulse width modulator controlled exclusively by the engine operator. The injection flow rates were measured and calibrated with the calculated fuel flow rates for different equivalence ratios (Ø) of the engine. The results showed a very close match between the measured fuel flow rates after calibration and the calculated fuel flow rates at 1500 RPM. The gasoline mass flow rate error was reduced from 40% to 3.25% by compensating the ON/OFF time of the pulse width.

Burn Rate Characterization of Iso-propyl Nitrate Blends: Part II

An experimental investigation was conducted to characterize the strand combustion of pure isopropyl nitrate (IPN) blended with a known de-sensitizer dibutyl sebacate (DBS). The blend was prepared with 75% IPN mixed with 25% DBS by weight so as to mimic the composition of Otto fuel II. Quartz tubes of 3, 5, 7.5, and 9 mm in diameters were utilized to create the strands of various diameters. The experiments were conducted in a quiescent atmosphere of air and the ambient pressure was varied from 5 to 40 bar in steps of 5 bar. Ignition of the strands was achieved by using a heated 60 μm Nichrome wire dipped in the liquid. The dependence of the linear burning rate of IPNDBS blends on ambient pressure as well as the strand diameter was elucidated. The temperatures in the flame zone were measured with K-type thermocouples of 250 μm diameter. The ambient pressure variation was investigated for a strand diameter of 5 mm while, the tube diameter variation was studied at 5 and 40 bar pressure. The linear burning rate of IPN-DBS blends in 5 mm diameter tube was found to rise with pressure. The gas phase temperature above the tip of the tube was measured using 250 μm K-type thermocouple. The burning rate of IPN-DBS blends was found to be lower than that of pure IPN as well as Otto fuel II.