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Simulation studies on the influence of other combustible gases on the characteristics of methane explosions at constant volume and high temperature

Luo Zhenmin, Liu Litao, Gao Shuaishuai, Wang Tao, Su Bin, Wang Lei, Yang Yong, Li Xiufang

Archives of Mining Sciences

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2021

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Vol. 66, no. 2

279--295

EN

Gas explosions are major disasters in coal mining, and they typically cause a large number of deaths, injuries and property losses. An appropriate understanding of the effects of combustible gases on the characteristics of methane explosions is essential to prevent and control methane explosions. FLACS software was used to simulate an explosion of a mixture of CH4 and combustible gases (C2H4, C2H6, H2, and CO) at various mixing concentrations and different temperatures (25, 60, 100, 140 and 180℃). After adding combustible gases to methane at a constant volume and atmospheric pressure, the adiabatic flame temperature linearly increases as the initial temperature increases. Under stoichiometric conditions (9.5% CH4-air mixture), the addition of C2H4 and C2H6 has a greater effect on the adiabatic flame temperature of methane than H2 and CO at different initial temperatures. Under the fuel-lean CH4-air mixture (7% CH4-air mixture) and fuel-rich mixture (11% CH4-air mixture), the addition of H2 and CO has a greater effect on the adiabatic flame temperature of methane. In contrast, the addition of combustible gases negatively affected the maximum explosion pressure of the CH4-air mixture, exhibiting a linearly decreasing trend with increasing initial temperature. As the volume fraction of the mixed gas increases, the adiabatic flame temperature and maximum explosion pressure of the stoichiometric conditions increase. In contrast, under the fuel-rich mixture, the combustible gas slightly lowered the adiabatic flame temperature and the maximum explosion pressure. When the initial temperature was 140℃, the fuel consumption time was approximately 8-10 ms earlier than that at the initial temperature of 25℃. When the volume fraction of the combustible gas was 2.0%, the consumption time of fuel reduced by approximately 10 ms compared with that observed when the volume fraction of flammable gas was 0.4%.

2

Measurement of flame temperature and soot amount for effective NOx and PM reduction in a heavy duty diesel engine

Aoyagi Yuzo

Combustion Engines

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2019

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R. 58, nr 4

32--39

EN

To reduce exhaust NOx and smoke, it is important to measure flame temperature and soot amount in combustion chamber. In diesel combustion it is effective to use the two-color method for the measurement of the flame temperature and KL factor, which is related with soot concentration. The diesel flame was directly and continuously observed from the combustion chamber at running engine condition by using a bore scope and a high-speed video camera. The experimental single cylinder engine has 2.0-liter displacement and has the ability with up to five times of the boost pressure than the naturally aspirated engine by external super-charger. The devices of High Boost, Wide Range and High EGR rate at keeping a relatively high excess air ratio were installed in this research engine in order to reduce exhaust NOx emission without smoke deterioration from diesel engines. The video camera nac GX-1 was used in this study. From observed data under the changing EGR rates, the flame temperature and KL factor were obtained by the software of two-color method analysis. The diesel combustion processes are understood well by analyzing high-speed movies of the diesel flame motion and its temperature. The NOx and smoke are mutually related to maximum flame temperature and also it is possible to reduce simultaneously both NOx and soot emissions by high EGR rate in a single cylinder diesel engine.

3

Investigation on effect of air velocity in turbulent non-premixed flames

Namazian Z., Hashemi H., Namazian F.

Archive of Mechanical Engineering

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2016

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Vol. LXIII, nr 3

355--366

EN

In this study, the turbulent non-premixed methane-air flame is simulated to determine the effect of air velocity on the length of flame, temperature distribution and mole fraction of species. The computational fluid dynamics (CFD) technique is used to perform this simulation. To solve the turbulence flow, k-ε model is used. In contrast to the previous works, in this study, in each one of simulations the properties of materials are taken variable and then the results are compared. The results show that at a certain flow rate of fuel, by increasing the air velocity, similar to when the properties are constant, the width of the flame becomes thinner and the maximum temperature is higher; the penetration of oxygen into the fuel as well as fuel consumption is also increased. It is noteworthy that most of the pollutants produced are NOx, which are strongly temperature dependent. The amount of these pollutants rises when the temperature is increased. As a solution, decreasing the air velocity can decrease the amount of these pollutants. Finally, comparing the result of this study and the other work, which considers constant properties, shows that the variable properties assumption leads to obtaining more exact solution but the trends of both results are similar.

PL

W pracy przeprowadzono symulację turbulentnego płomienia metanowo-powietrznego bez mieszania wstępnego w celu wyznaczenia wpływu szybkości powietrza na długość płomienia, rozkład temperatur oraz ułamek molowy składników spalin. Do przeprowadzenia symulacji wykorzystano technikę obliczeniowej dynamiki płynów (CFD). Przy rozwiązaniu przepływu turbulentnego zastosowano model k-ε. W przeciwieństwie do poprzednich prac, w prezentowanym studium założono zmienne właściwości materiałów w każdej z symulacji, a wyniki symulacji porównywano. Rezultaty badań pokazują, że przy określonej prędkości przepływu paliwa, przy wzroście szybkości powietrza uzyskuje się cieńszy płomień, o wyższej temperaturze, podobnie jak w przypadku gdy zakłada się stałe właściwości. Wzrasta przy tym penetracja tlenu do płomienia, a także zużycie paliwa. Warto zauważyć, że większość powstających szkodliwych substancji to tlenki azotu (NOx), silnie zależne od temperatury. Zawartość tych zanieczyszczeń rośnie ze wzrostem temperatury. Rozwiązaniem jest zmniejszenie szybkości powietrza, co może zmniejszyć zawartość zanieczyszczeń. Ostatecznie, porównując wyniki tego studium i poprzedniej pracy gdzie założono stałe właściwości materiałów, pokazano, że założenie zmiennych właściwości prowadzi do otrzymania dokładniejszych rozwiązań, niemniej, wyniki wykazują w obydwu przypadkach ten sam trend.