Morio Hori

An experimental and kinetic calculation of the promotion effect of hydrocarbons on the NO-NO2 conversion in a flow reactor

Experimental and detailed chemical kinetic modeling work has been performed to investigate the role of hydrocarbon oxidation in NO-NO 2 conversion. An atmospheric pressure., quartz flow reactor was used to examine the dependence of NO oxidation to NO 2 by hydrocarbon type, reaction temperature, and residence time. The five hydrocarbons examined were methane, ethylene, ethane, propene, and propane. In the experiment, probe measurement of the species concentrations was performed in the flow reactor using a mixture of NO(20 ppm)/air/hydrocarbon(50 ppm) at residence times from 0.16 to 1.46 s and temperatures from 600 to 1100 K. In the chemical kinetic calculation, the time evolution of NO, NO 2 , hydrocarbons, and reaction intermediates were evaluated for a series of the hydrocarbons and the temperatures. The chemical mechanism consisted of 639 reversible reactions and 126 species. Experimental results indicate that, in general, ethylene and propane effectively oxidize NO to NO 2 while methane is less effective. The calculation indicates the important chemical kinetic features that control NO-NO 2 conversion for each hydrocarbon type. The dependence of NO-NO 2 conversion with hydrocarbon type and temperature is qualitatively reproduced by the calculation. The calculation indicates that all five hydrocarbons oxidize NO to NO 2 predominantly through NO+HO 2 ahNO 2 +OH and that the contribution of oxidation by RO 2 and HORO 2 is minor. Highest effectiveness comes from hydrocarbons that produce reactive radicals (i.e., OH, O atom) that promote hydrocarbon oxidation and lead to additional HO 2 production. On the other hand, if hydrocarbons produce radicals, such as methyl and allyl, which resist oxidation by O 2 , then these radicals tend to reduce NO 2 to NO. Experimental results show that the effectiveness of hydrocarbons varies appreciably with temperature and only within the low-temperature range. Propane shows the greatest NO-NO 2 conversion for the lowest temperatures. This ability is primarily due to the hydroperoxy-propyl plus O 2 reactions as indicated by the sensitivity analysis results.

The effect of low-concentration fuels on the conversion of nitric oxide to nitrogen dioxide

The effect of low-concentration fuels on the conversion of NO to NO 2 is studied by an experiment and a chemical kinetic calculation. In the experiment, the NO and NO 2 concentrations are measured for the mixing process of hot combustion gas with cold air in which nine types of fuel (seven hydrocarbons from C1 to C4, H 2 and CO) are added. The hot combustion gas contains from 6 ppm to 79 ppm NO. The experimental results show that the conversion of NO to NO 2 in the mixing process is strongly promoted by the addition of small amount of all nine types of fuel. For example, the addition of only 40 ppm of C 3 H 8 raises the proportion of NO 2 to NO x from 0.24 to 0.90. The effectiveness of promotion strongly depends on the type of fuel. For seven types of fuel showing a similar pattern of promotion, the effectiveness increases as H 2 4 2 H 6 2 H 4 3 H 8 i -C 4 H 10 n -C 4 H 10 . In the chemical kinetic calculation, in order to understand the fundamental chemical kinetic aspect of the effect of fuel on the conversion of NO to NO 2 , a constant-temperature air premixed with NO and a low concentration of hydrocarbons is assumed as a simple model. The reaction mechanism includes 115 reactions for C3 hydrocarbons and NO-NO 2 . The conversion of NO to NO 2 is indicated to proceed mainly through the HO 2 mechanism (NO+HO 2 =NO 2 +OH) even in the presence of fuel. Therefore, high effectiveness is obtained by the fuels which are most easily decomposed to produce HO 2 . Also, the promotion is shown to proceed strongly in a certain temperature range. It is suggested from the results that the presence of fuel in the cool region of the flow in a combustion system should be prevented in order to reduce NO 2 exhaust emission.

Temperature dependence of NO to NO2 conversion by n-butane and n-pentane oxidation

An experimental and detailed chemical kinetic modeling investigation of the temperature-dependentrole of n-butane and n-pentane oxidation on the NO to NO2 conversion is presented. An atmospheric pressure, quartz flow reactor was used to examine the NO oxidation to NO2 behavior for the 600 to 1100 K temperature range and residence times from 0.16 to 1.46 s. In the experiment, probe measurement of the species concentrations was performed in the flow reactor using a mixture of NO (20 ppm)/air/hydrocarbon (10 ppm). In the chemical kinetic calculation, the time evolution of NO, NO2, hydrocarbons, and reaction intermediates were evaluated using a n-butane oxidation model coupled with a nitrogen oxides submechanism for all temperatures. The detailed chemical kinetic model consisted of 897 reactions and 158 species. The experimental results show n-pentane promoting the NO to NO2 conversion to a greater extent thann-butane for the entire temperature range. This may be explained by n-pentane oxidation exhibiting a vigorous chain-branched hydroperoxy-pentylperoxy radical isomerization kinetic system more so than found in n-butane. Kinetic calculations performed on the n-butane oxidation system revealed that the NO to NO2 conversion is strongly temperature dependent. The NO+HO2=NO2+OH and alkylperoxy +NO=alkyloxy+NO2 reactions play an important role in converting NO to NO2 at the lower temperatures in this study. However, as the temperature increases toward 800–900 K, the butyl+O2 and hydroperoxy-butyl+O2 network of reactions undergoes reaction reversal and allows other reaction channels to be accessed which heavily promotes NO to NO2 conversion. Above 900 K, the decrease in NO2 concentration is attributed to NO2+HO2=HONO+O2, HONO(+M)=NO+OH(+M), and NO2+O=NO+O2 destruction reactions. Consequently, the change of HO2 formation with temperature plays the most important role for the temperature dependence of the NO to NO2 conversion.

Unified approach to correlating the viscosities of H2O and D2O in the liquid and gaseous phases

Unified correlation for the thermophysical properties of H2O and D2O is useful for studying the isotope effects, for checking the consistency of available data and also for predicting the properties of other H2O isotopes. A unified approach has been studied in the present paper for correlating the viscosities of H2O and D2O both in the liquid and gaseous phases. The analysis of the experimental viscosity data revealed that the simple corresponding states principle held only for the excess viscosity Δη=η-η0(T) at the reduced densities ρr=ρρc⪅1.5. Therefore, a functional form (T,ρ)=η0(T)+Δη(T,ρ) has been adopted for the correlating equation and the excess term Δη(T,ρ) at ρr⪅1.5 has been generalized between H2O and D2O. In the density range ρrGap;1.5, the equation has been based only on the H2O data and the interpretation of the isotope effect has been tried by using the extended corresponding states principle. The applicability of the present equation to the estimation of the viscosity of T2O is also discussed.

Reactive Absorption of NO2 by Water in the NOx Measurement System

In this study, firstly it was demonstrated that the absorption of NO2 by condensed water in the sampling system might lead to considerable errors in the measurement of NOx for combustion gases containing relatively high concentration of NO2. Secondly, the loss of NO2 into water was systematically measured using bubblers in series or an NO2 absorption tube (a horizontal tube partly full of water). NO2/air mixtures were passed through the bubblers or the NO2 absorption tube and then analyzed by a chemiluminescent NOx analyzer. The initial NO2 concentration and water temperature were varied in the ranges 20-300 ppm and 0-30°C, respectively. The ratio of the decrease in the concentration of NO2 to the initial value Δ [NO2] / [NO2] 0 is found to be proportional to the surface area of water and inversely proportional to the volume flow rate of the mixture but practically independent of the residence time in the NO2 absorption tube. Also, Δ [NO2] / [NO2] 0, gradually increases with increasing the initial concentration of NO2 but it is independent of those of NO and O2. The temperature dependence of Δ [NO2] / [NO2] 0 is found to be negative and of an Arrhenius relationship. The species balance between the gaseous and liquid phases was also verified. Finally, based on a simple model and the present experimental data, an equation for estimating the magnitude of the loss of NO2 was developed.