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Comparative study of the effects of nitrous oxide and oxygen on ethylene ignition Fuquan Deng, Youshun Pan, Wuchuan Sun, Feiyu Yang, Yingjia Zhang, and Zuohua Huang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01425 • Publication Date (Web): 30 Oct 2017 Downloaded from http://pubs.acs.org on November 1, 2017

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Energy & Fuels

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Comparative study of the effects of nitrous oxide

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and oxygen on ethylene ignition

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Fuquan Denga, Youshun Pana,Wuchuan Suna, Feiyu Yanga Yingjia Zhanga*1, Zuohua Huanga*

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a. State Key Laboratory of Multiphase Flows in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China

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Abstract: To explore the effects of N2O and O2 on C2H4 ignition, ignition delay times

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of stoichiometric C2H4/O2/N2O/Ar mixtures with mole blending ratios of N2O:(N2O +

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O2) = 0%, 50%, 80% and 100% were measured in a high-pressure shock tube.

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Reflected shock conditions cover a range of pressures from 1.2 to10 atm and

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temperatures from 1090 to 1760 K. In addition, ignition delay times of C2H4/N2O/Ar

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mixtures are measured at pressures of 1.2 – 10 atm, equivalence ratios of 0.5– 2.0 and

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temperatures of 1214 – 1817 K. The results indicate that, in the studied conditions, the

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ignition delay times of C2H4 greatly increase as N2O concentration increases at a

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given pressure and temperature. Five recent literature models are tested against the

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new measured ignition delay times, and show very small discrepancies among each

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other for the C2H4/N2O/Ar mixtures, but exhibit significant discrepancies for the

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C2H4/N2O/O2/Ar mixtures. Moreover, the kinetic analysis are performed to reveal the

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reason for the discrepancies among the five models and to investigate the different

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effects of N2O and O2 on the C2H4 ignition.

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Corresponding author: Yingjia Zhang, [email protected], State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China.

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1. Introduction

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As main power source, propellants directly affect the performance of rocket and

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missile engines1-3. Most of propellant molecules contain nitro- and/or nitrate-groups,

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which decompose to produce small hydrocarbons (CH4, C2H6, C2H4, C2H2 and C3H6)

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and NOx (N2O, NO2 and NO)4,5,27. Clearly, the interaction chemistry between NOx

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and small hydrocarbons is very importance for understanding of gas-phase

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combustion of solid propellants. For internal combustion engines with exhaust gas

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recirculation (EGR), the NOx (NO, NO2 and N2O) formed during fuel combustion will

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be recirculated in the next cycle, and then influence the combustion of the fresh

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mixtures. Previous researchers6-14 has demonstrated that NOx shows great influence

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on the ignition of hydrocarbons.

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An amount of studies have been performed on the combustion of

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NO2/hydrocarbons mixtures15-23. However, the studies on the interaction chemistry of

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small hydrocarbons and N2O are very limited. Recently, Mével et al.24-26 performed

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systematic experimental and modeling studies of the interactions between H2 and N2O

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behind the reflected shock waves. They measured the ignition delay times of H2/N2O

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mixtures at the pressures of 256 – 910 kPa, equivalence ratios of 0.5 – 2.0 and

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temperatures of 1300 – 2356 K. A sequence of three-step reactions was proposed to

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describe the formation of OH* in H2/N2O/Ar mixtures, which proceeded in the

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flowing orders: N2O (+ M) N2 + Ö (+ M), Ö + H2 Ḣ + ȮH and N2O + Ḣ

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N2 + ȮH*. Besides, they developed a detailed kinetic model to describe the

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interaction chemistry of H2/N2O. Mével and Shepherd27 measured the ignition delay

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times of small hydrocarbons (CH4, C2H6, C2H4 and C2H2)/N2O mixtures with and

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without oxygen at a pressure around 3.0 atm and φ = 0.78 – 1.8. They reported that

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R2775 and R2774 almost dominate the ignition of fuel/N2O/Ar, and that R2775 and

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R5 play the predominant role for the fuel/N2O/O2/Ar. More recently, Mathieu et al.16

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investigated the effect of N2O on the ignition of CH4/O2 mixtures behind the reflected

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shock waves. Their experiments were performed at T = 1250 – 2095 K, p = 1 – 28 atm

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and φ = 0.5 – 2.0. The results indicated that the presence of N2O significantly

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promoted the ignition of CH4/O2 mixtures. Together, Mathieu et al.

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detailed C1/NOx model to examine the influence of N2O on the methane ignition.

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Santner et al.12 recently conducted research on the influences of fuel chemistry and

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reaction temperature history on the production of oxides of nitrogen in methane and

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ethylene combustion. They systematically investigated the influence of fuel chemistry

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on the NOx emissions in the methane and ethylene flames.


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proposed a

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Moreover, in our previous studies regarding the promoting-effect of NO2 on the

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methane8 and ethane28 ignition, we found that the interactions between NO2 and

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methane/ethane are very violent. However, in our previous study on the N2O/CH4

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chemistry9, the results suggested that the interactions between N2O and CH4 played a

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small role on the methane ignition. In this study, we want to see whether the

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interactions between N2O and unsaturated hydrocarbons have great influence on the

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fuel’s ignition. Ethylene which contains a carbon-carbon double bond is also an

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important intermediate in the combustion of large hydrocarbons29,

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selected the N2O/C2H4 system as the target to conduct this experimental and modeling

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study.

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. Hence, we

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From these studies, it can be found that there are few data for the ignition of

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C2H4/N2O mixtures except in the work of Mével and Shepherd27. But they carried out

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only at p = around 3.0 atm and ϕ = 1.4. Consequently, one of the purposes of this

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study is to measure the ignition delay times of C2H4/N2O mixtures with and without

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oxygen over a wide range of conditions to extend the database. Besides, five literature

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models are tested against the experimental data to evaluate model performances. At

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last, the detailed kinetic analysis is conducted to explore the different effects of N2O

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and O2 on the ethylene ignition.

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2. Experimental

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The double-diaphragm high-pressure shock tube used in this study has been

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described in our previous studies8, 9. Briefly, the shock tube has an internal diameter

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of 11.5 cm with a 4.0 m long driver section and a 4.8 m long driven-section, and is

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divided by double Polyethylene terephthalate (PET) diaphragms. At the end 1.3 m of

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the driven section, four pressure transducers (PCB 113B26) were mounted to obtain

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the incident shock velocities, which are used to calculate the reflected shock

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temperature using a chemical equilibrium software Gaseq31 developed by NUI

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Galway. In most experiments, the largest uncertainty in the temperatures is evaluated

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to be less than 25 K8. A pressure transducer (PCB 113B03) equipped with acceleration

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compensation and a photomultiplier (HAMAMATSU CR131) with a 307 ± 10 nm

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narrowband filter located at the end-wall of the driven section were used to monitor the

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reflected shock pressure and OH* light emission during ignition.

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The ignition delay times were defined as the time interval between the arrival of

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the incident shock wave at the end-wall and the extrapolation of the maximum slope of

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OH* light emission to the baseline, as shown in Fig. 1. It is clear to observe a pressure


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rise (dP*/dt = around 100 s-1) caused by the propagation of reflected shock wave into a

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nonuniform flow field as mentioned by Petersen et al.32. According to the uncertainty in

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the temperature, the uncertainty in the measured ignition delay times were evaluated to

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be within 20%33.

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Before each experiment, the shock tube was evacuated to below 25 Pa using a

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mechanical vacuum pump and was subsequently vacuumed to below 1 Pa using a roots

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vacuum pump. The leak rate is typically less than 1 Pa/min. The tested mixtures were

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prepared in a stainless steel tank (evacuated to below 25 Pa) using Dalton's Law of

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partial pressure, and the pressure was monitored by a pressure transmitter (Rosemount

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3051, with an accuracy of 0.75%). The components in the test mixtures were He

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(>99.999%), N2 (> 99.999%), Ar (> 99.99%), O2 (>99.99%), C2H4 (> 99.99%) and

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N2O (> 99.99%). Detailed compositions of the tested mixtures are listed in Table 1.

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The mixtures were named as Na/b-c, where a/b indicates the mole blending ratio of

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N2O than O2 and c indicates the equivalence ratio.

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3. Results and Discussion

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3.1 Comparison the effects of N2O and O2 on the ethylene ignition

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3.1.1 Effect of blending ratios on the ignition of C2H4/O2/N2O/Ar mixtures

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In order to compare the effects of N2O and O2 on C2H4 ignition, the ignition

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delay times of the stoichiometric mixtures with different blending ratios of N2O:O2

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(0:100, 50:50, 80:20 and 100:0) are compared at pressures of 1.2, 4.0 and 10 atm, Fig.

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2. It is observed that the ignition delay times increase remarkably with increasing N2O

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concentrations. This means that the reactivity of N2O/C2H4 system is much weaker

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than that of O2/C2H4 system. Moreover, the ignition delay times increase more

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significantly when the mole fraction of N2O grows from 50% to 100%, notably at

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higher pressures (10.0 atm) and lower temperatures condition.

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To quantitatively illustrate the effect of N2O addition on the ethylene ignition, the 34-40

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Aramco-Z model, which is combined by Aramco Mech 2.0

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sub-model developed by Zhang et al41, was used to calculate the ignition delay times

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of stoichiometric C2H4/N2O/O2/Ar mixtures with the blending ratios of N2O:O2

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changing from 0 to 100 at 10.0 atm and 1350 K, Fig. 3. Obviously, the ethylene

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ignition is inhibited moderately by small amount of N2O addition (XN2O < 60%),

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whereas it is inhibited dramatically by more addition of N2O (XN2O > 60%).


and the NOx

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3.1.2 Effect of pressure on the ignition delay times of the four stoichiometric mixtures

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Figure 4 shows the influence of pressure on the ignition delay times of the four

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stoichiometric mixtures (N0/100-1.0, N50/50-1.0, N80/20-1.0 and N100/0-1.0) at pressures of 1.2

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– 10 atm. For the N0/100-1.0 mixture, Fig. 4 (a), an “S” curve temperature-dependence

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can be observed due to the change in dominant kinetics at different temperature

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regions. It means that the global activation energies (Ea) of the mixtures change with

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the temperature. This behavior of ethylene ignition was also observed by Kopp et al.30.

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As a result, the pressure shows a significant effect on the ignition delay times at

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higher temperatures (T > 1250 K), but just gives a very little impact at lower

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temperatures (T < 1250 K). As shown by Kopp et al.42, this phenomenon is mainly

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caused by the competition between the chain-branching reaction (R5: Ḣ + O2 Ӧ

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+ȮH) and the chain termination reaction (R34: Ḣ + O2 (+ M) HȮ2 (+ M)). At the

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higher pressures and lower temperatures condition, R34 becomes the most significant

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leading to an increase in the ignition delay times of C2H4/O2/Ar mixture.

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For the cases with N2O addition (Fig. 4 (b-d)), an interesting feature is that the

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N2O presence changes the temperature-dependence of C2H4 ignition. When N2O is

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added into the mixtures, the ignition delay times of the tested mixtures essentially

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conform Arrhenius correlation at each pressure meaning no change in the activation

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energy at current conditions. It is different from the results observed in H2/O2/NOx

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system performed by Ahmed et al.13.

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temperature-dependence for the H2/O2/NOx ignition. Specifically, for the N50/50-1.0

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mixture (Fig. 4 (b)), Ea do not changes with temperature at each pressure but Ea

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greatly varies with pressure. The Ea at the higher pressures (p > 4.0) are much larger

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than that at 1.2 atm resulting in that the pressure effect at higher temperatures is more

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remarkable than that at lower temperatures. It can be inferred that the reaction R34

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remains play an important role at the higher pressure and C2H4/O2 chemistry still

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dominates the ignition kinetics of the tested mixtures. However, the pressure change

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shows little or no effect on the Ea as the N2O concentration continues to increase, see

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in Figs. 4 (c) and 4 (d). It is believed that C2H4/N2O chemistry begins to dominate the

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ignition.

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3.2 Equivalence ratio-dependence of ignition delay times for the C2H4/N2O/Ar

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mixtures

Ahmed et al. found a non-typical Arrhenius

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Figure 5 shows the effects of equivalence ratios on the ignition of C2H4/N2O/Ar

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mixtures at pressures of 1.2 – 10 atm. Generally, the increase in equivalence ratio


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inhibits the reactivity of mixtures and this inhibiting-effect appears more evident at

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higher pressures (> 4 atm). Specifically, at p = 1.2 atm and T = about 1500 K, Fig. 5 (a),

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the ignition delay times reduce by 47.4% and 35.9% when the equivalence ratio varies

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from 2.0 to 1.0 and from 1.0 to 0.5, respectively. However, the reductions in the

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ignition delay times increase up to 50.3% and 40.4% at 4.0 atm and 52.1% and 56.7%

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at 10.0 atm, respectively. Clearly, this equivalence ratio-dependence of the ignition

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delay times is similar with most hydrocarbons/O2 systems.

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4. Kinetic mechanism evaluation

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The CHEMKIN program43 with SENKIN code44 is used to calculate ignition

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delay times. The SENKIN/VTIM approach proposed by Chaos et al.45 is used to

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consider the effect of dP*/dt = around 100 s-1. The definition of equivalence ratio

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proposed by Mével et al.27 is adopted in this study:

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ϕ=

2 xC + 0.5 xH (1) xO

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where ϕ is the equivalence ratio, xc , xH and xO are the mole fractions of C, Ḣ and Ö

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atoms, respectively. Aramco Mech 2.0 is adopted to reproduce the ethylene chemistry

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because it has been tested by numerous experimental data performed by different

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facilities. Figure 6 illustrates the comparisons of the model predictions and the

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experimental measurements for stoichiometric C2H4/O2/Ar mixtures. It is visible that

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the predictions of Aramco Mech 2.0 are in an excellent agreement with the

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experimental data. Usually, different literature NOx models contain different ethylene

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sub-models. Consequently, the direct comparisons of the literature NOx models will

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be influenced by the ethylene sub-models and the NOx sub-models. In addition, to

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study the influences of the NOx sub-models is the focus in this study. Therefore, five

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literature NOx sub-models (Zhang et al.41, Sivaramakrishnan et al.20, Giménez-Lópezet

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et al.46, Mathieu et al.16 and Konnov et al.47) are assembled with Aramco Mech 2.0 to

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eliminate the impact of ethylene chemistry. The five assembled models are entitled as

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Aramco-Z, Aramco-S, Aramco-G, Aramco-M and Aramco-K, respectively.

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Figure 7 depicts the comparisons of the experimental measurements and the

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model predictions of the five assembled models for the C2H4/N2O/O2/Ar mixtures

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(N50/50-1.0 and N80/20-1.0) at pressures of 1.2, 4.0 and 10.0 atm. For the N50/50-1.0 mixture,

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Fig. 7 (a), Aramco-Z agrees with the measured data over the whole conditions. The

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other four models well reproduce the experimental data at 1.2 atm but they are around


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1.5 times lower than the measured data at the elevated pressures (p > 4.0 atm) and

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lower temperatures (T < around 1200 K). This means that the Aramco-S, Aramco-G,

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Aramco-M and Aramco-K are incapable of reproducing the pressure-dependence

200

behavior of ignition delay times for the N50/50-1.0 mixture. For the N80/20-1.0, Fig. 7 (b),

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Aramco-Z remains show acceptable predictions at all pressures and temperatures in

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despite of a slight over-prediction at 1.2 atm. In contract, the Aramco-S, Aramco-G,

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Aramco-K and Aramco-M well capture the experimental data at p < 4.0 atm whereas

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under-predict by around 2.5 times at 10 atm and 1200 K.

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For the C2H4/N2O/Ar mixtures, Fig. 8, the five assembled models acceptably

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agree with the measured data in consideration of the experimental error at all

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conditions. The results suggest that the discrepancies between the model predictions

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and the experimental measurements are typical within 35%. In general, the Aramco-Z

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remains the best one to reproduce the auto-ignition behavior for the tested mixtures.

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The Aramco-Z model is thus selected to perform sensitivity and flux analyses to

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explore the effect of N2O addition on the ignition of the mixtures with and without O2.

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As discussed above, the discrepancies between the experimental data and the

213

model predictions are very small for C2H4/N2O/Ar mixtures but are quite remarkable

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for C2H4/N2O/O2/Ar mixtures. As shown in Figure 9, the rate constants of reaction

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R2775 (N2O + Ḣ N2 + ȮH) in the Aramco-S, Aramco-G, Aramco-K and

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Aramco-M are around 2 times larger than that in the Aramco-Z. However, such a

217

small discrepancy exerts a great effect on the consumption of Ḣ atom, see in Figure

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10. For Aramco-Z, more than half of the Ḣ atom react with C2H4 via R247 to produce

219

Ċ2H5, most of which react with O2 and return to form ethylene + HȮ2 radical via

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R217 (Ċ2H5 + O2 C2H4 + HȮ2). The total effects of R247 and R217 translate the

221

reactive Ḣ atom into the unreactive HȮ2 radical. For the other four models, R2775

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plays greater than or equal to R247 effect on the consumption of Ḣ atom.

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Consequently, the Ḣ atoms translated into HȮ2 are much less, which significantly

224

promotes the reactivity of system and reduces the ignition delay times of the mixtures.

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After replacing the rate constant of R2775 by that in Aramco-Z, the predictions

226

simulated by these models are very similar with that by Aramco-Z except for

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Aramco-K. Aramco-K under-predicts the ignition delay times of N80/20-1.0 even

228

through the influence of R2775 is eliminated. Aramco-K considers the reaction

229

between N2O and ĊH3 (N2O + ĊH3 CH3Ȯ + N2), which is not added in the other

230

four models. And the rate constant of reaction (N2O + ĊH3 CH3Ȯ + N2) in

231

Aramco-K is a few orders of magnitude larger than that recommended by Tomeczek


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et al.48, which may be the another reason why the predictions of Aramco-K are below

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the measured data.

234

5. Kinetic analysis

235

To compare the effects of N2O and O2 on C2H4 ignition, flux and sensitivity

236

analyses are conducted for the four stoichiometric mixtures at 10 atm and 1450 K.

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Together, the kinetic analyses are performed for the C2H4/N2O/Ar mixtures at the

238

same conditions to investigate the effect of equivalence ratio on the ignition of the

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mixtures without O2. The sensitivity coefficient indicates the effect of the perturbation

240

of the rate constant on the ignition delay times and is defined as following49: Si =

241

τ ( 2ki ) − τ ( 0.5ki ) 1.5τ ( ki )

242

Where Si and ki are the sensitivity coefficient and rate constant of ith reaction,

243

respectively, and τ is the ignition delay time. Negative value denotes a

244

promoting-effect, and vice versa.

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5.1 Comparison of the effect of N2O and O2 on the ethylene ignition

246

As shown in Figure 11, the top 15 of the largest sensitive reactions are identified at

247

10 atm and 1450 K for the four stoichiometric mixtures. For N0/100-1.0, the sensitivity

248

coefficient of the chain-branching reaction R5 (O2 + Ḣ Ö + ȮH) are more than 3

249

times larger than the second largest promoting reaction. This indicates that R5 controls

250

the ignition of ethylene at this condition. For the N50/50-1.0 (Fig. 11 (b)), R5 remains the

251

top promoting reaction, and the sensitivity coefficients of the other 14 top reactions

252

are still quite small than that of R5. It can be concluded that N2O gives very small

253

effect on the C2H4 ignition and the C2H4/O2 chemistry is predominant with less than

254

50% N2O addition. With more N2O addition (N80/20-1.0), Fig. 11 (c), a great change in

255

the top promoting reactions can be observed. R2775 exceeds R5 to become the most

256

promoting reaction, and R2774 (N2O (+ M) N2 + Ö (+ M)) becomes the third

257

most promoting reactions. It is therefore inferred that the interaction of C2H4/N2O

258

begins to dominate the ignition kinetic. Nevertheless, R5 remains the second most

259

promoting reaction and shows a considerable promoting effect on the ethylene

260

ignition. It indicates that even very little O2 (< 20%) can significantly affect the

261

ignition of the C2H4/O2/N2O/Ar mixture. For the N100/0-1.0, Fig. 11 (d), R2774 and

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R2775 are the two most promoting reactions. As addressed by Mével and Shepherd27,

263

the ignition is principally driven by R2774 and 2775 for fuel/N2O/Ar mixtures, and by


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2775 and R5 for the fuel/N2O/O2/Ar mixtures. In this study, for the C2H4/N2O/Ar

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mixture, R2774 and 2775 dominate the ethylene ignition which is consistent with the

266

results observed by Mével and Shepherd. For the C2H4/N2O/O2/Ar mixtures, 2775 and

267

R5 control the ethylene ignition even with little O2 addition (< 20%), whereas the

268

O2/C2H4 chemistry will dominate the ignition with over than 50% O2 addition.

269

As shown in Fig. 12, the flux analysis based on the rates of production for the

270

fuels is performed for the four stoichiometric mixtures at 10 atm, 1450 K and the time

271

of 10% consumption of ethylene. For the N0/100-1.0 mixture, C2H4 mainly undergoes

272

H-atom abstraction reactions to produce vinyl radicals (Ċ2H3). The formed Ċ2H3

273

radicals subsequently either react with O2 to produce ĊH2CHO and Ö atoms (30.0%)

274

or to form CH2O and HĊO (22.8%); or directly decompose to generate Ḣ atoms and

275

C2H2 (17.6%). At the presence of N2O, the C2H4 are also mainly consumed through

276

the H-atom abstraction reactions. However, the mole fraction of radical pool (total

277

radicals = Ḣ atoms + Ö atoms + ȮH radicals) decreases with increasing the N2O mole

278

fraction at the time of 10% consumption of fuel, see in Fig. 13. Therefore, the

279

consumption rate of C2H4 reduces with increasing N2O concentration resulting in an

280

increase in the ignition delay times. In addition, the N2O addition dramatically

281

perturbs the branching ratios of Ċ2H3. The branching ratio of Ċ2H3 decomposes to

282

produce C2H2 greatly increases at the presence of N2O. C2H2 is significant unreactive

283

resulting in an increase in the ignition delay times. As shown in the NO2/hydrocarbons

284

systems8, 28, the interactions between NO2 and hydrocarbons is very violent. NO2

285

reacts violently with fuels and almost all its intermediates. But the interaction between

286

N2O and C2H4 shows very small effect on the ethylene ignition.

287

To better clarify the effect of N2O addition, the mole fractions of radical pool are

288

simulated by Aramco-Z model at 10 atm and 1450 K, Fig. 13. When the reaction time >

289

10 µs, the concentration of radical pool for N0/100-1.0 is much larger than those for the

290

mixtures doped with N2O. Besides, the concentration of radical pools reduces as the

291

N2O concentration increases. Moreover, the reduction appears to be more distinct when

292

the concentrations of N2O changed from 50% to 100%. As a result, the growth in τing

293

when the N2O mole fraction increases from 50% to 100% is more significant than that

294

of N2O mole fraction changes from 0 to 50%

295

Interestingly, the concentration of radical pool for N0/100-1.0 is several orders of

296

magnitude smaller than that of the mixtures doped with N2O at reaction time < 2 µs

297

whereas it quickly catches up with and surpasses at reaction time > 8 µs. As shown in

298

Table. 2, for the N0/100-1.0 at the reaction time < 2 µs, the initiating Ḣ atoms mainly


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

299

come from R163 and R244, which feed R5 to produce ȮH radicals. And the Ö atoms

300

mainly come from R271 (Ċ2H3 + O2 ĊH2CHO + Ö). It is concluded that the

301

development of radical pool is closely related to R163, R244 and R271. The mole

302

fraction of radical pool is very small due to the very high reaction activation energy of

303

R244 and the small concentration of HĊO or Ċ2H3 at this condition. However, for the

304

mixtures doped with N2O, the development of radical pool is initiated by

305

decomposition of N2O via R2774. N2O quickly decomposes to produce abundant Ö

306

atoms and largely increases the mole fraction of radical pool.

307

At the reaction times = around 8 µs, the concentration of radical pool for the

308

C2H4/O2/Ar mixture rapidly exceeds that for the mixtures doped with N2O. For the

309

N0/100-1.0, R5 plays the most predominant role on the development of radical pool. In

310

addition, almost all the Ḣ atoms feed R5 to produce two radicals, so the mole fraction

311

of radical pool for N0/100-1.0 keeps an explosive growth. However, R5 plays a small role

312

for the N2O addition cases. This can be attributed to the two-fold effects: 1) R2775

313

competes with R5 for the Ḣ radicals; 2) the decrease of oxygen concentration

314

significantly reduces reaction rate of R5.

315

5.2 Effect of equivalence ratio on ignition of C2H4/N2O/Ar mixtures

316

Figure 14 and Figure 15 show the sensitivity and flux analysis for the

317

C2H4/N2O/Ar mixtures at p = 10 atm and T = 1450 K, respectively. Clearly, at all

318

conditions R2775 (N2O + Ḣ N2 + ȮH) and R2774 (N2O (+ M) N2 + Ö (+ M))

319

are the two most promoting reactions while R247 (C2H4 + Ḣ Ċ2H3 + H2) and

320

R302 (Ċ2H3 + Ḣ C2H2 + H2) are the two most inhibiting reactions. It means that

321

there is no change in controlling-kinetic of the C2H4/N2O/Ar mixtures with the change

322

in equivalence ratio. Consequently, the ignitions of all the tested C2H4/N2O/Ar

323

mixtures are mainly driven by R2775 and R2774, which is consistent with those

324

reported by Mével and Shepherd

325

resulting in an increase in the reaction rates of R2774 and R2775 and a reduction in

326

the ignition delay times. As shown in Fig. 16, the concentrations of free radicals at

327

fuel-lean condition are much bigger than those at fuel-stoichiometric and fuel rich

328

condition. The bigger concentration of radical pools clearly benefits to fuel

329

consumption that corresponds to shorter ignition delay times.

330

6. Conclusions

331

27

. The N2O is more at the fuel-lean condition

In this study, C2H4/N2O/ Ar mixtures with and without O2 have been investigated


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Energy & Fuels

332

experimentally in a high pressure shock tube and modeling with five literature N2O

333

models. The main conclusions are summarized as follows:

334

1) For stoichiometric C2H4/N2O/O2/Ar mixtures, the C2H4 ignition is inhibited

335

by N2O addition at a given pressure and temperature. The increase in the

336

ignition delay times is moderate when the concentration of N2O is less than

337

60%, whereas it becomes significant when the concentration of N2O is more

338

than 60%. In addition, the inhibiting effect of N2O is closely related to

339

temperature and pressure. Specifically, the influence of N2O is significant for

340

i) higher T and XN2O < 50% and ii) lower T and XN2O > 50%.

341

2) Five assembled models are tested against the measured data. Overall, the five

342

models show small discrepancies for the C2H4/N2O/Ar mixtures, but great

343

discrepancies for the mixtures with both O2 and N2O. The Accurate rate

344

constant of R2775 (N2O + Ḣ N2 + ȮH) is very vital and twice the

345

difference in the rate constant of R2775 can significantly influence the

346

performances of the models.

347

3) Unlike the violent interactions between NO2 and hydrocarbons, the

348

interactions between N2O and C2H4 have no effect on the ethylene ignition.

349

The kinetic analysis results show, first that, R2774 and 2775 dominate the

350

ethylene ignition for the C2H4/N2O/Ar mixtures, and second that, for the

351

C2H4/N2O/O2/Ar mixtures, the ignition is mostly driven by 2775 and R5 with

352

small O2 addition (< 50%), but by the O2/C2H4 chemistry with more than 50%

353

O2 addition.

354

Acknowledgement

355

This work is supported by the National Natural Science Foundation of China (No.

356

91541115, 91441203) and the Fundamental Research Funds for the Central

357

Universities.

358

(JCKY2016212A501).

359

References

360 361 362 363 364 365

[1] Atwood, A.; Boggs, T.; Curran, P.; Parr, T.; Hanson-Parr, D.; Price, C.; Wiknich, J. Burning rate of solid propellant ingredients, part 1: Pressure and initial temperature effects. J. Propul. Power 1999, 15, 740-747. [2] Tanaka, S.; Kondo, K.; Habu, H.; Itoh, A.; Watanabe, M.; Hori, K.; Esashi, M. Test of B/Ti multilayer reactive igniters for a micro solid rocket array thruster. Sen. and Act. A Phys. 2008, 144, 361-366.

The

authors

also

appreciate

the Science Challenge Project


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[3] Singh, G.; Felix, S.P. Studies of energetic compounds, part 29: effect of NTO and its salts on the combustion and condensed phase thermolysis of composite solid propellants, HTPB-AP[J]. Combust. flame 2003, 132. 422-432. [4] Oommen, C.; Jain, S., Ammonium nitrate: a promising rocket propellant oxidizer. J. Hazard. Mater. 1999, 67, 253-281. [5] Kishore, K.; Sunitha, M.R. Comprehensive view of the combustion models of composite solid propellants[J]. AIAA J. 1979, 17, 1216-1224. [6] Zheng, M.; Reader, G.T.; Hawley, J.G. Diesel engine exhaust gas recirculation––a review on advanced and novel concepts. Energy Convers. Manage. 2004, 45, 883-900. [7] Tsolakis, A.; Megaritis, A.; Wyszynski, M.; Theinnoi, K. Engine performance and emissions of a diesel engine operating on diesel-RME (rapeseed methyl ester) blends with EGR (exhaust gas recirculation). Energy 2007, 32, 2072-2080. [8] Deng, F.; Yang, F.; Zhang, P.; Pan, Y.; Bugler, J.; Curran, H.J.; Zhang, Y.; Huang, Z., Towards a kinetic understanding of the NOx promoting-effect on ignition of coalbed methane: A case study of methane/nitrogen dioxide mixtures. Fuel 2016, 181, 188-198. [9] Deng, F.; Yang, F.; Zhang, P.; Pan, Y.; Zhang, Y.; Huang, Z., Ignition Delay Time and Chemical Kinetic Study of Methane and Nitrous Oxide Mixtures at High Temperatures. Energy Fuels 2016, 30, 1415-1427. [10] Lipardi, A.C.; Versailles, P.; Watson, G.M.; Bourque, G.; Bergthorson, J.M., Experimental and numerical study on NOx formation in CH4–air mixtures diluted with exhaust gas components. Combust. Flame 2017, 179, 325-337. [11] Watson, G.M.; Munzar, J.D.; Bergthorson, J.M., Diagnostics and modeling of stagnation flames for the validation of thermochemical combustion models for NOx predictions. Energy Fuels 2013, 27, 7031-7043. [12] Santner, J.; Ahmed, S.F.; Farouk, T.; Dryer, F.L., Computational Study of NOx Formation at Conditions Relevant to Gas Turbine Operation: Part 1. Energy Fuels 2016, 30, 6745-6755. [13] Ahmed, S.F.; Santner, J.; Dryer, F.L.; Padak, B.; Farouk, T.I., Computational Study of NOx Formation at Conditions Relevant to Gas Turbine Operation, Part 2: NOx in High Hydrogen Content Fuel Combustion at Elevated Pressure. Energy Fuels 2016, 30, 7691-7703. [14] Mueller, M.; Yetter, R.; Dryer, F., Flow reactor studies and kinetic modeling of the H2/O2/NOx and CO/H2O/O2/NOx reactions. Int. J. Chem. Kinet. 1999, 31, 705-724. [15] Herzler, J.; Naumann, C., Shock tube study of the influence of NOx on the ignition delay times of natural gas at high pressure. Int. J. Chem. Kinet. 2012, 184, 1635-1650. [16] Mathieu, O.; Pemelton, J.M.; Bourque, G.; Petersen, E.L., Shock-induced ignition of methane sensitized by NO2 and N2O. Combust. Flame 2015, 162, 3053-3070. [17] Dayma, G.; Dagaut, P., Effects of air contamination on the combustion of hydrogen—effect of NO and NO2 addition on hydrogen ignition and oxidation kinetics. Combust. Sci. Technol. 2006, 178, 1999-2024. [18] Faravelli, T.; Frassoldati, A.; Ranzi, E., Kinetic modeling of the interactions between NO and hydrocarbons in the oxidation of hydrocarbons at low temperatures.


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[34] Li, Y.; Zhou, C.; Somers, K.P.; Zhang, K.; Curran, H.J., The oxidation of 2-butene: a high pressure ignition delay, kinetic modeling study and reactivity comparison with isobutene and 1-butene. Proc. Combust. Inst. 2016, 36, 403-411, [35] Zhou, C.; Li, Y.; O'Connor, E.; Somers, K.P.; Thion, S.; Keesee, C.; Mathieu, O.; Petersen, E.L.; DeVerter, T. A.; Oehlschlaeger, M.A.; Kukkadapu, G.; Sung, C-J.; Alrefae, M. Khaled, F.;A. Farooq, F.; Dirrenberger, P.; Glaude, P-A.; Battin-Leclerc, F.; Santner, J.; Ju, Y.; Held, T.; Haas, F.M.; Dryer, F.L.; Curran, H.J. A Comprehensive experimental and modeling study of isobutene oxidation. Combust. Flame 2016, 167, 353-379. [36] Burke, U.; Metcalfe W.K.; Burke, S.M.; Heufer, K.A.; Dagaut, P.; Curran, H.J. A Detailed Chemical Kinetic Modeling, Ignition Delay time and Jet-Stirred Reactor Study of Methanol Oxidation. Combust. Flame 2016, 165, 125-136.. [37] Burke, U.; Mc Donagh, R.; Mathieu, O.; Osorio, I.; Keesee, C.; Morones, A.; Petersen, E.L.; Wang, W.; DeVerter, T.A. Oehlschlaeger, M.; Rhodes, B.; Hanson, R.; Davidson, D.; Weber, B.; Sung, C.; Santner, J.; Ju, Y.; Haas, F.; Dryer, F.; Volkov, E.; Nilsson, E.; Konnov, A.; Alrefae, M.; Khaled, F.; Farooq, A.; Dirrenberger, P.; Glaude, P; Battin-Leclerc, F. An experimental and modeling study of propene oxidation. Part 2: Ignition delay time and flame speed measurements. Combust. Flame 2015, 162 (2), 296-314. [38] Burke, S.M.; Metcalfe, W.; Herbinet, O.; Battin-Leclerc, F.; Haas, F.M.; Santner, J.; Dryer, F.L.; Curran, H.J. An experimental and modeling study of propene oxidation. Part 1: Speciation measurements in jet-stirred and flow reactors. Combust. Flame 2014, 164 (11), 2765-2784 [39] Metcalfe W K, Burke S M, Ahmed S S, Curran, H.J. A hierarchical and comparative kinetic modeling study of C1–C2 hydrocarbon and oxygenated fuels. Int. J. Chem. Kinet. 2013, 45 (10), 638-675. [40] Kéromnès A, Metcalfe W K, Heufer K A, Donohoe, N.; Das, A.K.; Sung, C.J.; Herzler, J.; Naumann, C.; Griebel, P.; Mathieu, O.; Krejci, M.C.; Petersen, E.L.; Pitz, W.J.; Curran, H.J. An Experimental and Detailed Chemical Kinetic Modelling Study of Hydrogen and Syngas Mixtures at Elevated Pressures. Combust. Flame 2013, 160, 995-1011. [41] Zhang, Y.; Mathieu, O.; Petersen, E.L.; Bourque, G.; Curran, H.J., Assessing the predictions of a NOx kinetic mechanism on recent hydrogen and syngas experimental data. Combust. Flame 2017, 182, 122-141. [42] Kopp, M.M.; Petersen, E.L.; Metcalfe, W.K.; Burke, S.M.; Curran, H.J., Oxidation of Ethylene—Air Mixtures at Elevated Pressures, Part 2: Chemical Kinetics. J. Propul. Power 2014. [43] Kee, R.J.; Rupley, F.M.; Miller, J.A. Chemkin-II: A fortran chemical kinetics package for the analysis of gas-phase chemical kinetics. Sandia Report SAND89-8009B 1989. [44] Lutz, A.E.; Kee, R.J.; Miller, J.A. SENKIN: A fortran program for predicting homogeneous gas phase chemical kinetics with sensitivity analysis. Sandia Report


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507

Page 16 of 24

Table 1. Detail components of the tested. No. Mix

Mole blending ratio

φ

C2H4

N2O

O2

Ar

(%)

(%)

(%)

(%)

1

N0/100-1.0

0% N2O/100% O2

1.0 1.0

0.0

3.0

96.0

2

N50/50-1.0

50% N2O/50% O2

1.0 1.0

3.0

1.5

94.5

3

N80/20-1.0

80% N2O/20% O2

1.0 1.0

4.8

0.6

93.6

4

N100/0-1.0

100%N2O/0% O2

1.0 1.0

6.0

0.0

93.0

5

N100/0-0.5

100%N2O/0% O2

0.5 1.0

12.0

0.0

87.0

6

N100/0-2.0

100%N2O/0% O2

2.0 1.0

3.0

0.0

96.0

508 509

Table 2. Main production and consumption channels of Ḣ, Ӧ and ȮH radicals during

510

the reaction time < 2 µs period. Time = 0.01 microsecond

Ḣ N0/100-1.0

production

consumption

Reaction

Ratio

R163:HĊO +MḢ+CO+M

86

R244:Ċ2H3+Ḣ(+M)C2H4(+M)

8

R5:O2+ḢӦ+ȮH

38

R207:C2H4+Ḣ(+M)Ċ2H5(+M)

35

R247:C2H4+ḢĊ2H3+H2

N50/50-1.0 production

consumption


consumption


consumption

ȮH

Ӧ

18

Ḣ

Reaction

Ratio

R5:O2+ḢӦ+ȮH R271: Ċ2H3+O2ĊH2CHO+Ӧ

Reaction

Ratio

18 82

R5:O2+ḢӦ+ȮH

96

R255: C2H4+ӦĊH3+ HĊO

55

R248: C2H4+ȮHĊ2H3+H2O

87

R256: C2H4+ӦĊH2CHO+Ḣ

45

R261: C2H4+ȮHC2H3OH+Ḣ

8.0

57 40

ȮH

Ӧ

R256:C2H4+ӦĊH2CHO+Ḣ R163:HĊO+MḢ+CO+M

81 15

R2774: N2O(+M)N2+Ӧ(+M)

100

R2775:N2O+ḢN2+ȮH R5:O2+ḢӦ+ȮH

R2775:N2O+ḢN2+ȮH

24

R255: C2H4+ӦĊH3+HĊO

55


79

R207:C2H4+Ḣ(+M)Ċ2H5(+M) R5:O2+ḢӦ+ȮH R247:C2H4+ḢĊ2H3+H2

39 17 15


45


6.0

Ḣ

ȮH

Ӧ


81 14

R2774: N2O(+M)N2+Ӧ(+M)

100

R2775:N2O+ḢN2+ȮH R5:O2+ḢӦ+ȮH

85 15

R207:C2H4+Ḣ(+M)Ċ2H5(+M)

37

R255: C2H4+ӦĊH3+HĊO

55


86

R2775:N2O+ḢN2+ȮH R247:C2H4+ḢĊ2H3+H2 R5:O2+ḢӦ+ȮH

36 15 6


45


8.0

Ḣ

ȮH

Ӧ


79 16

R2775:N2O+ḢN2+ȮH

45

R207:C2H4+Ḣ(+M)Ċ2H5(+M)

36

R247:C2H4+ḢĊ2H3+H2

12

R2774: N2O(+M)N2+Ӧ(+M) R255: C2H4+ӦĊH3+HĊO R256: C2H4+ӦĊH2CHO+Ḣ

100

54 45


R2775:N2O+ḢN2+ȮH R248: C2H4+ȮHĊ2H3+H2O R261: C2H4+ȮHC2H3OH+Ḣ R262: C2H4+ȮHPC2H4OH

100

86 7.0 6.0

Page 17 of 24

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Energy & Fuels

511

Table 3. Main production and consumption channels of Ḣ, Ӧ and ȮH radicals at the

512

reaction time = around 8 µs. Time = around 8 microsecond

Ḣ N0/100-1.0

Reaction

Ratio

R363: ĊH2CHO(+M)ĊH2CO+Ḣ(+M)

27

R256:C2H4+ӦĊH2CHO+Ḣ

23

R163:HĊO+MḢ+CO+M

22

R266:C2H2+Ḣ(+M)Ċ2H3(+M)

10

R5: O2+ḢӦ+ȮH

51

R247:C2H4+ḢĊ2H3+H2

23

R207:C2H4+Ḣ(+M)Ċ2H5(+M)

10

Production

Consumption

N50/50-1.0

Ḣ

N80/20-1.0

Production

Consumption

N100/0-1.0

Production

Reaction

Ratio


21

R163:HĊO+MḢ+CO+M

23


14

R266:C2H2+Ḣ(+M)Ċ2H3(+M)

17

R2775:N2O+ḢN2+ȮH

28

R5: O2+ḢӦ+ȮH

18

R247:C2H4+ḢĊ2H3+H2

17

Ḣ

R5: O2+ḢӦ+ȮH

89

R271: Ċ2H3+O2ĊH2CHO+Ӧ

30

R27:HȮ2+Ḣ2OH

6.0

R255:C2H4+ӦĊH3+HĊO

54


86


45


7

ȮH

R5: O2+ḢӦ+ȮH

50


41


6

ȮH

28


17

27


12

R2774: N2O(+M)N2+Ӧ(+M)

R2775:N2O+ḢN2+ȮH

48


R247:C2H4+ḢĊ2H3+H2

19 R256:C2H4+ӦĊH2CHO+Ḣ

R5: O2+ḢӦ+ȮH

8.0

R2775:N2O+ḢN2+ȮH

79

R5: O2+ḢӦ+ȮH

13

52


83

42


7.0

40

ȮH

Ӧ

R2775:N2O+ḢN2+ȮH R247:C2H4+ḢĊ2H3+H2

11

79

R5: O2+ḢӦ+Ӧ

8.0

R27:HȮ2+Ḣ2OH R248: C2H4+ȮHĊ2H3+H2O

18


33

50

R163:HĊO+MḢ+CO+M

10

R5: O2+ḢӦ+ȮH


31

R163:HĊO+MḢ+CO+M

48

42

R266:C2H2+Ḣ(+M)Ċ2H3(+M)

59

R2775:N2O+ḢN2+ȮH


Ӧ

R266:C2H2+Ḣ(+M)Ċ2H3(+M)

Ratio

69


Ḣ

Reaction

R5: O2+ḢӦ+ȮH

Ӧ

Production

Consumption

ȮH

Ӧ

R2774: N2O(+M)N2+Ӧ(+M)

100

63


52

20


43

Consumption


R2775:N2O+ḢN2+ȮH

R248: C2H4+ȮHĊ2H3+H2O R261: C2H4+ȮHC2H3OH+Ḣ

99

85 7.0

Energy & Fuels

513 514 (a)

8

End-wall pressure trace 30

End-wall OH* emission

20 4

10

OH* emission

Pressure / atm

6

2

τ = 1435 µs

0

0

1000

1500

2000

515

2500

3000

3500

Time / µs 1.50

(b) Normalized pressure P* (p/p0)

1.25

1.00

0.75

Pressure

Ideal

Reflected shock

0.50

0.25

0.00 1000

516 517 518

1500

2000

2500

Time (µs)

Fig.1. Typical traces of end-wall pressure and OH* light emission for C2H4/N2O/Ar mixture at 10 atm and 1215 K and at ϕ = 0.5.

519 (a) p = 1.2 atm, ϕ = 1.0

103

N0/100-1.0 N50/50-1.0 N80/20-1.0

102

0.55

520

(b) p = 4.0 atm, ϕ = 1.0

Ignition delay times (µs)


N100/0-1.0 Solid lines: Aramco-Z 0.60

0.65

0.70

0.75

0.80

0.85

3

10

2

10

0.90

0.95

0.60

1000/T (K-1)

0.65

0.70

0.75

3

10

2

10

0.60

521

-1

1000/T (K )

(c) p = 10.0 atm, ϕ = 1.0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 24

0.65

0.70

0.75

0.80

0.85

0.90

-1

1000/T (K )


0.95

0.80

0.85

0.90

Page 19 of 24

522 523

Fig.2. Effect of the blending ratio of N2O/O2 on the ethylene ignition at pressures of 1.2 atm (a), 4.0 atm (b) and 10 atm (c). (a)


1000

ϕ = 1.0 10.0 atm

800

Calculated by the Aramco-Z

600

400

200

0 0:100

80:20

100:0

Fig. 3. Effect of mole blending ratios of N2O/O2 on the stoichiometric ethylene ignition at 10 atm and 1350 K using Aramco-Z model. (a) N0/100-1.0

(b) N50/50-1.0

1.2 atm 4.0 atm 10.0 atm

103



102

103

23.91 Kacal/mol·K 33.39 Kcal/mol·K 102

31.89 Kcal/mol·K

Solid lines: Aramco-Z 0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

0.55

0.60

0.65

1000/T (K-1)

(c) N80/20-1.0

31.66 Kcal/mol·K

29.57 Kcal/mol·K

103

0.85

0.90

0.95

29.31 Kcal/mol·K

29.31 Kcal/mol·K

35.21 Kcal/mol·K 0.60

0.80

29.31 Kcal/mol·K

2

0.55

0.75

(d) N100/0-1.0

103

10

0.70

1000/T (K-1)


524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547

60:40

40:60

20:80

Mole mixing ratio of N2O/O2


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.65

0.70

1000/T (K-1)

0.75

102

0.80

0.85

0.55

0.60

0.65

0.70

0.75

0.80

1000/T (K-1)

Fig. 4. Effect of N2O addition on the pressure-dependence of ignition delay times of N0/100 (a), N50/50 (b), N80/20 (c) and N100/0 (d).


Energy & Fuels

(a) p = 1.2 atm

10

3

(b) p = 4.0 atm

C2H4/N2O/Ar mixtures ϕ = 2.0 ϕ = 1.0 ϕ = 0.5

Lines: Aramco-Z



103

102

102 0.55

0.60

0.65

0.70

0.75

0.55

0.60

0.65

0.70

0.75

0.80

1000/T (K-1)

1000/T (K-1)

548


(c) p = 10.0 atm

103

10

2

0.60

549 550 551

0.65

0.70

0.75

0.80

0.85

1000/T (K-1)

Fig. 5. Effect of equivalence ratio on the ignition delay times of C2H4/N2O/Ar mixtures at various equivalence ratios and at (a) 1.2 atm, (b) 4.0 atm and (c)10 atm. ϕ = 1.0 Ignition delay times (µs)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 24

10

3

1.2 atm 4.0 atm 10.0 atm

102

Solid lines : Aramco Mech 2.0 0.60

552 553 554

0.65

0.70

0.75

0.80

0.85

0.90

1000/T (K-1)

Fig.6. Comparison between the measured data and the predictions with Aramco Mech 2.0 for stoichiometric C2H4/O2/Ar mixture at different pressures.


Page 21 of 24

(b)

1.2 atm 4.0 atm 10.0 atm

3

10

Aramco-Z Aramco-S Aramco-G Aramco-M Aramco-K

102

0.60

0.65

0.70

0.75

0.80

0.85

103

102

0.90

0.60

0.65

0.70

0.75

0.85

Fig. 7. Comparisons between the measured data and the predictions for C2H4/N2O/O2/Ar mixtures at p of 1.2, 4.0 and 10 atm. (a) N50/50-1.0, (b) N80/20-1.0.

3

10

(b)

Ν100/0−0.5 1.2 atm 4.0 atm 10.0 atm

Ν100/0−1.0

103


2

10

0.55

0.60

0.65

0.70

0.75

0.80

102 0.85

1000/T (K-1)

558


(c)

0.55

0.60

0.65

0.70

1000/T (K-1)

0.75

0.80

Ν100/0−2.0

103

2

10

0.55

0.60

0.65

1000/T (K-1)

0.70

0.75

Fig.8. Comparison between the measured data and the predictions with five assembled models for C2H4/N2O/Ar mixtures at various pressures with ϕ = 0.5 (a), ϕ = 1.0 (b), and ϕ = 2.0 (c).

Rate constant (cm3/mole·s)

Reaction: N2O + H = N2 +OH 1E12


1E11

1E10 1000

563

0.80

1000/T (K-1)

1000/T (K-1)

(a)

559 560 561 562

N80/20-1.0


555 556 557



(a) N50/50-1.0 ϕ = 1.0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1200

1400

1600

1800

Temperature (K)


2000

Energy & Fuels

Fig.9. Comparisons of the rate constants in the five models for the reaction (N2O + Ḣ N2 + ȮH). 0

0

(b)

-20

-20

(a) Mixtures: N80/20-1.0 T = 1150 K

p = 10.0 atm

-40

-40

Simulated by Aramco-Z R2775:N2O+H=N2+OH

-60

-60

R207:C2H4+H(+M)=C2H5(+M) R247:C2H4+H=C2H3+H2

-80

R34:H+O2(+M)=HO2(+M) 0

20

40

60

Aramco-M Aramco-G Aramco-S Aramco-K

-80

R5:H+O2=O+OH

-100

-100

567 568 569 570

Normalized consumption ratio for H atom (%)

564 565 566

Normalized consumption ratio for H atom (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 24

80

0

100

20

40

Times (µs)

60

R302: C2H3+H=C2H2+H2

R302: C2H3+H=C2H2+H2

(a)

R164: HCO+O2=CO+HO2

R28: HO2+H=H2+O2

R28: HO2+H=H2+O2

R387: HCCO+OH=>H2+2CO

R43: CH3+H(+M)=CH4(+M)

R43: CH3+H(+M)=CH4(+M)

R364: CH2CHO(+M)=CH3+CO(+M)

R303: C2H3+H=H2CC+H2 R99: CH3+HO2=CH3O+OH

R99: CH3+HO2=CH3O+OH

N0/100-1.0

R3: H2+OH=H+H2O

N50/50-1.0

R27: HO2+H=2OH

R256: C2H4+O=CH2CHO+H

R392: HCCO+O2=>CO2+CO+H

R310: C2H2+O=HCCO+H

R248: C2H4+OH=C2H3+H2O

T = 1450 K p = 10.0 atm

R248: C2H4+OH=C2H3+H2O

R163: HCO+M=H+CO+M


R256: C2H4+O=CH2CHO+H

R2775: N2O+H=N2+OH

R5: O2+H=O+OH

-1.2

-0.8

-0.4

0.0

0.4

R5: O2+H=O+OH

0.8

-0.6

R302: C2H3+H=C2H2+H2

-0.4

-0.2

R2827: NNH+O=N2O+H


R384: CH2CO+OH=CH2OH+CO

R3: H2+OH=H+H2O

R256: C2H4+O=CH2CHO+H R3152: N2O+CH2=CH2O+N2

R248: C2H4+OH=C2H3+H2O R256: C2H4+O=CH2CHO+H

R194: 2CH3(+M)=C2H6(+M)

N100/0-1.0

R2782: N2O+CO=N2+CO2

R266: C2H2+H(+M)=C2H3(+M)

R310: C2H2+O=HCCO+H

R310: C2H2+O=HCCO+H


R3: H2+OH=H+H2O

R2774: N2O(+M)=N2+O(+M)

R2782: N2O+CO=N2+CO2

R5: O2+H=O+OH

R2774: N2O(+M)=N2+O(+M) R2775: N2O+H=N2+OH

R2775: N2O+H=N2+OH

-0.1

0.4

R389: CH+CO+M=HCCO+M

R635: C2H3+CH3(+M)=C3H6(+M)

-0.2

0.2

(d)

R302: C2H3+H=C2H2+H2

R303: C2H3+H=H2CC+H2

-0.3

0.0

R247: C2H4+H=C2H3+H2

(c)

R255: C2H4+O=CH3+HCO

N80/20-1.0

(b)



572 573 574 575

100

Fig.10. Comparisons of the normalized consumption ratios of Ḣ atom calculated by the five assembled models for the N80/20-1.0 mixture at 10 atm and 1150 K.


571

80

Times (µs)

0.0

0.1

0.2

0.3

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

Fig. 11. Normalized sensitivity analysis for the four C2H4/O2/N2O/Ar mixtures at 10 atm and 1450 K using Aramco-Z model. (a) N0/100-1.0, (b), N50/50-1.0, (c) N80/20-1.0 and (d) N100/0-1.0.


Page 23 of 24

CO 0.00 27.2 27.0 26.9 M

CH3 HCO

CH2CHO

M 70.1 70.2 70.2

0.00

0.00

0.00 9.40

7.00

18.0

16.4

10.5 13.4

16.1

12.8

25.1

20.5

16.7

30.0

17.5 17.3 H

O

O

C2H4

O2 OH 37.3 44.0 48.6 50.6 H 13.5 15.517.3 18.5

C 2 H2

M 17.6 30.4 49.8 81.5 H 9.70 8.10 6.80 5.10

C2H3

CH2CO H

6.90 4.80 3.40 0.00 OH 19.9 20.6 20.5 0.00

OH

O

63.6 6.80 63.2 7.00

H 69.0 69.3 69.7 0.00

CH2O

0.00

10.3

17.4

62.1 7.20 0.00 0.00

22.8 O2

HCCO 576 577 578 579 580

Fig. 12. The flux analysis for the four stoichiometric C2H4/O2/N2O/Ar mixtures with 10% ethylene consumption at 10 atm and 1450 K using Aramco-Z model. N0/100-1.0: black, N50/50-1.0: red, N80/20-1.0: green and N100/0-1.0: blue. (a) radical pool (H, O and OH)

0.01

(b) H radical

1E-3

1E-3

1E-5

Mole Fraction

Mole Fraction

1E-4 1E-4

N0/100-1.0 N50/50-1.0

1E-6

N80/20-1.0 1E-7

N100/0-1.0 Simulated by Aracmco-Z model

1E-5

1E-6

1E-7

1E-8 1

10

581

100

1000

1

(c) O radical

1E-3

1E-4

1E-5

1E-5

Time (µs)

100

1000

Mole Fraction

1E-4

10

(d) OH radical

1E-3

1E-6

1E-6

1E-7

1E-7

1E-8

1E-8

1E-9

1E-9 1

582 583 584 585 586

1E-8

Time (µs)

Mole Fraction

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

10

Time (µs)

100

1000

1

10

100

1000

Time (µs)

Fig.13. Evolutions of free radicals during the ignition of C2H4/O2/N2O/Ar mixtures at 10 atm and 1450 K using Aramco-Z model. Total concentration of radical pool (Ḣ, Ӧ and ȮH) (a), Ḣ atom (b), Ӧ atom (c), and ȮH radical (d).


Energy & Fuels

R247: C2H4+H=C2H3+H2 R302: C2H3+H=C2H2+H2

N100/0-0.5

R248: C2H4+OH=C2H3+H2O R303: C2H3+H=H2CC+H2

N100/0-1.0

R635: C2H3+CH3(+M)=C3H6(+M)

N100/0-2.0

R255: C2H4+O=CH3+HCO R43: CH3+H(+M)=CH4(+M) R3152: N2O+CH2=CH2O+N2

T = 1450 K p = 10.0 atm

R266: C2H2+H(+M)=C2H3(+M) R310: C2H2+O=HCCO+H R3: H2+OH=H+H2O R2782: N2O+CO=N2+CO2 R2774: N2O(+M)=N2+O(+M) R2775: N2O+H=N2+OH

587 588 589

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

Fig.14. Normalized sensitivity analysis for C2H4/N2O/Ar mixtures at 10 atm and 1450 K under different equivalence ratios using Aramco-Z model. 41.8 50.6 57.1 10.6

C2H4OH H 30.0 18.5

C2H3 M H

O 7.10

8.70

7.00

9.40

O

84.5 4.60 81.5 5.10 79.3 5.50

8.40 10.2

C2H2

CH2CHO CH3 HCO 590 591 592 593

Fig.15. Flux analysis for C2H4/N2O/Ar mixtures at 10 atm and 1450 K with ϕ = 0.5 (red), ϕ = 1.0 (blue) and ϕ = 2.0 (black) using Aramco-Z model with 10% ethylene consumption. 0.01

Radical pool Mole fraction

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 24

p = 10 atm and T = 1450 K ϕ = 0.5 ϕ = 1.0 ϕ = 2.0

1E-3

1E-4

1E-5

1E-6 1

594 595 596

10

100

1000

Time (µs)

Fig.16. Evolution of radical pool during the ignition of C2H4/N2O/Ar mixtures at 10 atm and 1450 K with varying equivalence ratios using Aramco-Z model.


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