Measurements and kinetic study on ignition delay times of propane/hydrogen in argon diluted oxygen

Measurements on ignition delay times of propane/hydrogen mixtures in argon diluted oxygen were conducted for hydrogen fractions in the fuel mixtures (XH₂)$\left(X_{{\text{H}}_2}\right)$ from 0 to 100%, pressures of 1.2, 4.0 and 10 atm, and temperatures from 1000 to 1600 K using the shock-tube. Results show that for XH₂$X_{{\text{H}}_2}$ less than 70%, ignition delay time shows a strong Arrhenius temperature dependence and it decreases with the increase of pressure, while for XH₂$X_{{\text{H}}_2}$ larger than 90%, there is a crossover pressure dependence of the ignition delay time with increasing temperature. Numerical studies were made using the selected kinetic mechanisms and results show that the predicted ignition delay time gives a reasonable agreement with the measurements. Both measurements and predictions show that for XH₂$X_{{\text{H}}_2}$ less than 70%, the ignition delay time is only moderately decreased with the increase of XH₂$X_{{\text{H}}_2}$, indicating that hydrogen addition has weak effect on ignition enhancement. Sensitivity analysis reveals the key reactions that control the simulation of ignition delay time. Kinetic study is made to interpret the ignition delay time dependence on pressure and XH₂$X_{{\text{H}}_2}$.     

Kinetic study on nonisothermal dehydrogenation of TiH2 powders

The nonisothermal dehydrogenation of TiH₂ powders was studied using thermogravimetry and differential scanning calorimetry. The reaction model was established by estimating the activation energy. The results show the nonisothermal dehydrogenation occurred in a four-step process. The hydrogen released from the TiH_1.5∼2$\text{Ti}{\mathrm{H}}_{1.5\sim 2}$ phase in the first step, which led to the decrease of activation energy. The second step was derived from the formation of βH${\beta }_H$ in δ$\delta$ phase and the reaction model was Phase boundary reaction. In the third step, the hydrogen started to release from the βH${\beta }_H$ phase, and then the βH→αH${\beta }_{\mathrm{H}}\to {\alpha }_{\mathrm{H}}$ phase transformation happened. So the activation energy Eα$E_{\alpha }$ underwent a decrease followed by a quick increase. The fourth step corresponded to the formation of αH${\alpha }_H$ in βH${\beta }_H$ phase, and the slight oxidation resulted in the small fluctuation of activation energy.     

Intake charge dilution effects on control of nitric oxide emission in a hydrogen fueled SI engine

Though hydrogen fueled spark ignition engine can operate at high thermal efficiency with almost zero emission of HC and CO, the high level of _NOx${\mathrm{NO}}_x$ poses problems. The high combustion temperature and lean mixtures used are the reasons. In this work, the effect of _N2${\mathrm{N}}_2$, _CO2${\mathrm{CO}}_2$ and hot EGR gas as diluents in the intake charge to suppress NO emission in a manifold injected hydrogen fueled SI engine was studied. Nitrogen as a diluent is not so effective at low loads while inducting smaller amounts, but very effective at higher loads where the mixture becomes richer and the dilution effect (oxygen depletion) is significant. On other hand, carbon dioxide is a good diluent with relatively better thermal effect and diluent effect and effectively controls NO emission at all output regions. However this is at the expense of thermal efficiency. Recirculating hot exhaust gas which contains both _N2${\mathrm{N}}_2$ and steam comes in between _N2${\mathrm{N}}_2$ and _CO2${\mathrm{CO}}_2$ in terms of its effectiveness. On the whole _N2${\mathrm{N}}_2$ is the most effective as it has minimum impact on thermal efficiency for a given level of permissible NO emission. Thus it is felt that cold EGR could be a good option. In all cases, a good control system is necessary to supply correct quantity of diluent.     

Kinetic characteristics of sodium borohydride formation when sodium meta-borate reacts with magnesium and hydrogen

Sodium borohydride is attracting considerable interests as a hydrogen storage medium. In this paper, we investigated the effects of hydrogen pressure, reaction temperature and transition metal addition on sodium borohydride synthesis by the reaction of sodium meta-borate with Mg and _H2${\mathrm{H}}_2$. It was found that higher _H2${\mathrm{H}}_2$ pressure was beneficial to _NaBH4${\mathrm{NaBH}}_4$ formation. The increase in reaction temperature first improved _NaBH4${\mathrm{NaBH}}_4$ formation kinetics but then impeded it when the temperature was raised to near the melting point of Mg. It was also found that some additions of transition metals such as Ni, Fe and Co in the _NaBO2+Mg+_H2${\mathrm{NaBO}}_2+\mathrm{Mg}+{\mathrm{H}}_2$ system promoted the _NaBH4${\mathrm{NaBH}}_4$ formation, but Cu addition showed little effect. The activation energy of the _NaBH4${\mathrm{NaBH}}_4$ formation from Mg, _NaBO2${\mathrm{NaBO}}_2$ and _H2${\mathrm{H}}_2$ was estimated to be 156.3 kJ/mol _NaBH4${\mathrm{NaBH}}_4$ according to Ozawa analysis method.     

Flame balls in mixing layers

We present a study of flame balls in a two-dimensional mixing layer with one objective being to derive an ignition criterion (for triple-flames) in such a non-homogeneous reactive mixture. The problem is formulated within a thermo-diffusive single-reaction model and leads for large values of the Zeldovich number β$\beta$ to a free boundary problem. The free boundary problem is then solved analytically in the asymptotic limit of large values of the Damköhler number, which represents a non-dimensional measure of the (square of the) mixing layer thickness. The explicit solution, which describes a non-spherical flame ball generalising the classical Zeldovich flame balls (ZFB) to a non-uniform mixture, is shown to exist only if centred at a single location. This location is found to be precisely that of the leading-edge of a triple-flame in the mixing layer, and typically differs from the location of the stoichiometric surface by an amount of order β^-1${\beta }^{-1}$ depending only on a normalised stoichiometric coefficient Δ$\Delta$.     

Hydrogen as an ignition-controlling agent for HCCI combustion engine by suppressing the low-temperature oxidation

Homogeneous charge compression ignition (HCCI) combustion enables internal combustion engines to achieve higher thermal efficiency and lower _NOx${\mathrm{NO}}_x$ emission than with conventional combustion systems. Controlling the ignition timing in accordance with the operating conditions is crucial for utilizing HCCI combustion engines. Adding hydrogen-containing gas is known to retard the autoignition of dimethyl ether (DME) considerably. The effective ignition control by hydrogen can expand the operation range of equivalence ratios and engine loads in HCCI combustion. This research investigated the mechanisms in the ignition control by the chemical kinetics analysis. The results show that the retarded ignition can be attributed to a consumption of OH by hydrogen during low-temperature oxidation of DME. The decreased OH concentration leads to retarded heat release and delays the onset of the high-temperature oxidation.     

Hydrogen injection as additional fuel in gas turbine combustor. Evaluation of effects

Industrial gas turbines fuelled by fossil fuels have been used widely in power generation and combined heat and power for many years. However they have to meet severe _NOx${\mathrm{NO}}_x$, CO and _CO2${\mathrm{CO}}_2$ (greenhouse effect) emissions legislation in many countries. This paper reports a study on injection of small quantities of hydrogen in a hydrocarbon fuelled burner like additionally fuel to reduce the pollutants emissions. Hydrogen is injected in the primary zone, premixed with the air. Using this injection together lean primary zone, it is possible to reduce the _NOx${\mathrm{NO}}_x$ level while CO an HC levels remains approximately constant.     

Productive energy in the US economy

In this paper, methods of separation of primary work _EP$E_{\mathrm{P}}$, which is needed to provide the genuine work of production equipment, from the total amount of primary energy E$E$ are proposed. Direct estimates of primary work of production equipment _EP$E_{\mathrm{P}}$ on the base of available data for the US economy for the 20th century are compared with alternative evaluations of the same quantity calculated from time series for consumption of labour and primary energy. The relationship among primary energy E$E$, primary work of production equipment _EP$E_{\mathrm{P}}$, and genuine work of production equipment P$P$ (productive energy) is considered. The results allow one to estimate coefficient of efficiency of primary work of production equipment.     

Fuel-rich methane oxidation in a high-pressure flow reactor studied by optical-fiber laser-induced fluorescence,multi-species sampling profile measurements and detailed kinetic simulations

A versatile flow-reactor design is presented that permits multi-species profile measurements under industrially relevant temperatures and pressures. The reactor combines a capillary sampling technique with a novel fiber-optic Laser-Induced Fluorescence (LIF) method. The gas sampling provides quantitative analysis of stable species by means of gas chromatography (i.e. _CH4${\mathrm{CH}}_4$, _O2,CO,_CO2${\mathrm{O}}_2\text{,}\mathrm{CO}\text{,}{\mathrm{CO}}_2$, _H2O,_H2${\mathrm{H}}_2\mathrm{O}\text{,}{\mathrm{H}}_2$, _C2${\mathrm{C}}_2$_H6${\mathrm{H}}_6$, _C2${\mathrm{C}}_2$_H4${\mathrm{H}}_4$), and the fiber-optic probe enables in situ detection of transient LIF-active species, demonstrated here for C_H2${\mathrm{H}}_2$O. A thorough analysis of the LIF correction terms for the temperature-dependent Boltzmann fraction and collisional quenching are presented. The laminar flow reactor is modeled by solving the two-dimensional Navier–Stokes equations in conjunction with a detailed kinetic mechanism. Experimental and simulated profiles are compared. The experimental profiles provide much needed data for the continued validation of the kinetic mechanism with respect to _C1${\mathrm{C}}_1$ and _C2${\mathrm{C}}_2$ chemistry; additionally, the results provide mechanistic insight into the reaction network of fuel-rich gas-phase methane oxidation, thus allowing optimization of the industrial process.     

Hydrogen production by autothermal reforming of LPG for PEM fuel cell applications

Indirect partial oxidation, or oxidative steam reforming, tests of a bimetallic Pt–Ni catalyst supported on δ$\delta$-alumina were conducted in propane–n  -butane mixtures (LPG) used as feed. _H2${\mathrm{H}}_2$ production activity and _H2/CO${\mathrm{H}}_2/\mathrm{CO}$ selectivity were investigated in response to different S/C, C/_O2$\mathrm{C}/{\mathrm{O}}_2$ and W/F ratios. It was confirmed that higher steam content in the reactant stream increases both the activity and the _H2/CO${\mathrm{H}}_2/\mathrm{CO}$ selectivity of the process. Low residence times created a positive impact on catalyst activity not only for hydrogen but also for carbon monoxide production due to the increased amount of fresh hydrocarbon in the feed stream. Hence, the highest selectivity level was obtained at intermediate residence times. The response of the system to C/_O2$\mathrm{C}/{\mathrm{O}}_2$ ratio was found to depend on the available steam content due to the complex nature of IPOX. The Pt–Ni catalyst was very prone to catalyst deactivation at low S/C ratios accompanied by high C/_O2$\mathrm{C}/{\mathrm{O}}_2$ ratios, but this problem was not encountered at high S/C ratios. A comparison of catalyst performance for different propane-to-n-butane ratios in the LPG feed indicated that the Pt–Ni catalyst has slightly better activity and selectivity at higher n-butane contents at the expense of becoming more sensitive to coke deposition.     

Investigation on the structure and electrochemical properties of the laser sintered La0.7Mg0.3Ni3.5 hydrogen storage alloys

The structure and electrochemical properties of the _{La0.7Mg0.3Ni3.5}${\mathrm{La}}_{0.7}{\mathrm{Mg}}_{0.3}{\mathrm{Ni}}_{3.5}$ alloys laser sintered at different powers were investigated. It is found that all alloys contain three phases _La3MgNi14${\mathrm{La}}_3{\mathrm{MgNi}}_{14}$ with the _Ce2Ni7${\mathrm{Ce}}_2{\mathrm{Ni}}_7$ structure, _LaNi5${\mathrm{LaNi}}_5$ and _LaMgNi4${\mathrm{LaMgNi}}_4$. The abundance of the main phase _La3MgNi14${\mathrm{La}}_3{\mathrm{MgNi}}_{14}$ is 43, 68 and 63 wt%, respectively, when sintering power varies from 1000 to 1200 and 1400 W. The laser sintered _{La0.7Mg0.3Ni3.5}${\mathrm{La}}_{0.7}{\mathrm{Mg}}_{0.3}{\mathrm{Ni}}_{3.5}$ alloys can be activated to their maximum discharge capacity within three cycles. The discharge capacities of those alloys prepared by laser sintering at 1000, 1200 and 1400 W are 324.6, 352.8 and 340.5 mAh/g, respectively. The _{La0.7Mg0.3Ni3.5}${\mathrm{La}}_{0.7}{\mathrm{Mg}}_{0.3}{\mathrm{Ni}}_{3.5}$ alloy laser sintered at 1200 W has a best cyclic stability (_S100=58.4%)$(S_{100}=58.4\%)$ and high-rate dischargeability (_HRD800=79.4%)$({\mathrm{HRD}}_{800}=79.4\%)$ due to the high amount of the main phase _La3MgNi14${\mathrm{La}}_3{\mathrm{MgNi}}_{14}$.     

Experimental study on thermal efficiency and emission characteristics of a lean burn hydrogen enriched natural gas engine

In order to analyze the effect of hydrogen addition on natural gas (NG) engine's thermal efficiency and emission, an experimental research was conducted on a spark ignition NG engine using variable composition hydrogen/CNG mixtures (HCNG). The results showed that hydrogen enrichment could significantly extend the lean operation limit, improve the engine's lean burn ability, and decrease burn duration. However, nitrogen oxides (NO_x)$({\text{NO}}_x)$ were found to increase with hydrogen addition if spark timing was not optimized according to hydrogen's high burn speed. Also found when spark timing was set at constant was that hydrogen addition actually increases heat transfer out of the cylinder due to smaller quenching distance and higher combustion temperature, thus is not good to improve thermal efficiency if combined with the effect of non-ideal spark timing. But if spark timing was retarded to MBT, taking advantage of hydrogen's high burn speed, _NOx${\mathrm{NO}}_x$ emissions exhibited no obvious increase after hydrogen addition and engine thermal efficiency increased with the increase of hydrogen fraction. Unburned hydrocarbon always decreased with the increase of hydrogen fraction.     

An experimental study on performance and emission characteristics of a hydrogen fuelled spark ignition engine

In the present paper, the performance and emission characteristics of a conventional four cylinder spark ignition (SI) engine operated on hydrogen and gasoline are investigated experimentally. The compressed hydrogen at 20  MPa has been introduced to the engine adopted to operate on gaseous hydrogen by external mixing. Two regulators have been used to drop the pressure first to 300 kPa, then to atmospheric pressure. The variations of torque, power, brake thermal efficiency, brake mean effective pressure, exhaust gas temperature, and emissions of _NOx${\mathrm{NO}}_x$, CO, _CO2${\mathrm{CO}}_2$, HC, and _O2${\mathrm{O}}_2$ versus engine speed are compared for a carbureted SI engine operating on gasoline and hydrogen. Energy analysis also has studied for comparison purpose. The test results have been demonstrated that power loss occurs at low speed hydrogen operation whereas high speed characteristics compete well with gasoline operation. Fast burning characteristics of hydrogen have permitted high speed engine operation. Less heat loss has occurred for hydrogen than gasoline. _NOx${\mathrm{NO}}_x$ emission of hydrogen fuelled engine is about 10 times lower than gasoline fuelled engine. Finally, both first and second law efficiencies have improved with hydrogen fuelled engine compared to gasoline engine. It has been proved that hydrogen is a very good candidate as an engine fuel. The obtained data are also very useful for operational changes needed to optimize the hydrogen fueled SI engine design.