Premixed Combustion Characteristics Research Articles

Study on the effect of hydrogen fraction on the premixed combustion characteristics of syngas/air mixtures

Effect of hydrogen fraction on the combustion characteristics of syngas/air mixtures was experimentally investigated at various hydrogen fractions and equivalence ratios in a turbulent combustion bomb under atmospheric temperature and pressure. The laminar burning velocity and turbulent burning velocity at various hydrogen fractions were measured, and the promotion of turbulence on the burning velocity at various hydrogen fractions was systematically investigated. The results show that the laminar burning velocity of the H2/CO/air mixture exhibits a non-linear increasing trend with increasing hydrogen fraction. With increasing equivalence ratio, the laminar burning velocity increases remarkably. Reaction CO + OH = CO2 + H is identified as the most dominate chain branching reactions and reaction H + OH + M = H2O + M is the most dominant chain termination reaction. The laminar burning velocity exhibits linear and non-linear growth with the maximum concentration of radical H and OH, respectively. With increasing the hydrogen fraction, the value of uT/uL shows a non-linear decreasing trend as a whole and the growth rate gradually decreases. As the equivalence ratio increases, the uT/uL value decrease. When the hydrogen fraction is more than 50%, the promoting effect of turbulence on the burning velocity decreases gradually.

Numerical study of the physical and chemical effects of hydrogen addition on laminar premixed combustion characteristics of methane and ethane

Methane and ethane are taken as the research objects. Using H2 as diluent, based on Chemkin II/Premix Code and modified detailed chemical reaction mechanism: GRI 3.0*-Mech (introducing three hypothetical substances of FH2, FO2 and FN2), the physical and chemical effects of hydrogen on laminar burning velocities (LBVs), adiabatic flame temperatures (AFTs), net heat release rates (NHRRs) and elementary reactions responsible for temperature changes of two alkanes under different equivalence ratios were analyzed and determined. Results showed that the chemical effect of H2 promotes the LBVs and ATFs of methane and ethane, while the physical effect decreases the two parameters. In addition, the physical effects of H2 inhibit the chemical reactions of methane and ethane, resulting in the decrease of NHRRs. The chemical effect of H2 accelerates the process of chemical reaction and obviously increases the NHRRs. The two most vital elementary reactions that promote the temperature rise of methane and ethane are H + O2 <=> OH + O and CO + OH <=> H + CO2. The important reactions responsible for inhibiting the temperature rise are H + CH3(+M) <=> CH4(+M) and H + O2 + H2O <=> HO2 + H2O.

Influence of controllable slit width and angle of controllable flow on hydrogen/air premixed combustion characteristics in micro combustor with both sides–slitted bluff body

To improve the combustion stability of micro combustor, both sides-slitted bluff body is applied to the micro combustor. The H2/O2 reaction mechanism is used to study the influence of controllable slit width (d) and angle of controllable flow (β) on combustion characteristics of the micro-combustor. The result shows that the reduction of d can significantly improve the combustion efficiency. Under the same controllable flow ratio (γ), the reduction of d can effectively expand the recirculation region. However, the blow-off limit will be reduced if d is too large or too small. With the same γ, the recirculation region and low-velocity zone expand when β decreases, which can entrain more high-temperature gas and increase the residence time of fuel in the low-velocity zone, thus improving the combustion efficiency. The residence time of fuel in the combustor will be reduced when β is too large or small, resulting in lower combustion efficiency and blow-off limit. Therefore, it is significant to choose the parameter of d and β.

Experimental study on the turbulent premixed combustion characteristics of 70%H2/30%CO/air mixtures

Abstract To investigate the effect of equivalence ratio and turbulence intensity on the combustion characteristics of syngas/air mixtures, experiments involving premixed combustion of 70% H2/30% CO/air mixtures at various equivalence ratios and turbulence intensities were conducted in a turbulent combustion bomb at atmospheric temperature and pressure. The turbulent burning velocity and flame curvature were used to study turbulent combustion characteristics. The results show that the turbulent burning velocity grew nonlinearly as the equivalence ratio increased, while the normalized turbulent burning velocity tended to decrease. When the equivalence ratio was relatively low, the turbulence intensity was a greater determinant of the burning velocity. The normalized turbulent burning velocity increased as the turbulence intensity increased. Re and Da were found to be directly and inversely proportional to u’/uL, respectively. A linear relationship was observed between uT/uL and ln Re. As the turbulence intensity increased or equivalence ratio decreased, the wrinkle degree of the flame front increased, and the maximum and minimum values of flame front curvature increased and decreased, respectively. Meanwhile, the range of the flame front curvature increased gradually. The proportion of components with smaller absolute value of flame front curvature gradually decreases.

Particle number size distribution from direct-injection premixed combustion engine fueled with gasoline/diesel blends

The organizing of combustion process in the advanced internal combustion engine is developing toward unified combustion mode of gasoline-engine-like premixed gas formation and diesel-engine-like compression ignition. Gasoline/diesel blended fuel has received extensive attention for its suitability for this combustion characteristic, owing to its relatively poor ignitability and high volatility. In order to more comprehensively evaluate the application of the blended fuel on this combustion mode, an experiment was conducted to characterize the particle size distribution and total number concentration of exhaust particles from the gasoline/diesel blended fuel. The premixed combustion characteristics and relatively high hydrocarbon emission were confirmed first and their effects on the particle size distribution were determined subsequently. Combustion control parameters such as exhaust gas recirculation and injection pressure were also taken into account. Results indicated that gasoline/diesel blended fuel had significant effect on the particle size distribution due to the higher premixed combustion ratio and more unburned hydrocarbon emission. Under high load condition, as the proportion of gasoline blending increased, the accumulation mode particle decreased while the nucleation mode particle and total particle number increased significantly. The geometric mean diameter of exhaust particle decreased with the addition of gasoline. The effect of exhaust gas recirculation and injection pressure on the particle size distribution of gasoline/diesel blended fuel was less than that of pure diesel. That meant the gasoline/diesel blends were beneficial for carbonaceous particle (&gt;22 nm) reduction. However, the nucleation mode as well as total particle number were still higher for gasoline/diesel blends than that for pure diesel.

Characteristics of turbulent premixed oxy-fuel combustion - A DNS study

A 3D DNS numerical study with detail chemistry mechanism has been carried out to investigate turbulent premixed combustion with oxyfuel mixtures under similar operating conditions as happened in spark ignition Internal Combustion Engine (ICE). H2O and CO2 are adopted as the dilution in oxy-fuel combustion. The temperature profiles of oxy-H2O and oxy-CO2 combustion are consistent with those of air-fired conditions in laminar premixed flame when the molar fraction of H2O and CO2 are 73% and 66% in oxidizer, respectively. 79%, 67% molar fraction of H2O and 79%, 56% molar fraction of CO2 are also conducted to learn the effects of the dilution molar fraction on the process of flame propagation. With the molar fraction of dilution increases, the mass of C2H2 increases the flame propagation speed and the mass of CO does an opposite influence. With the investigation for effects of turbulent intensity under conditions of 73% H2O and 66% CO2 with the initial u′ of 0.8, 1.6 and 2.4 m/s, respectively, results show that the turbulent intensity has little effect on the formation of CO. It is also demonstrated that for oxy-fuel combustion, due to the disparity in laminar flame speed, an appropriate u′ is necessary to keep consistent with the flame propagation speed meanwhile to maintain suitable temperature profiles.

Effect of hydrogen addition on the laminar premixed combustion characteristics the main components of natural gas

With the increasing use of natural gas, improving the thermal efficiency and reducing emissions has become the major goals in its combustion. The objective of the present work is to investigate the effect of hydrogen addition on the combustion characteristics of natural gas. A ChemkinⅡ/Premix Code with the detailed chemical reaction mechanisms was employed with the Soret effect taken into account in all the calculations. With the mole fraction of hydrogen in the fuel varied from 0 to 40% at different initial temperatures (298–500 K) and pressures (1–8 atm), the results showed that the laminar burning velocities (LBVs) and the adiabatic flame temperatures of the C1C4 four alkanes increased with increasing hydrogen-doping ratio. The LBV and the adiabatic flame temperature of methane displayed the maximum increase with the hydrogen-doping ratio. Additionally, the generation of active radicals H, O, and OH during the combustion process was strongly correlated with the LBV. The sensitivity of the flame temperature in four alkane fuels present in the natural gas at the maximum temperature gradient was analyzed. At a constant hydrogen-doping ratio, the LBV and the adiabatic flame temperature increased significantly with the increasing initial temperature. With increasing the pressure, the LBV gradually decreased while the adiabatic flame temperature increased.

Study on premixed combustion characteristics of co-firing ammonia/methane fuels

Ammonia is believed to eventually play an important role in substituting conventional fossil fuels for future energy systems. In this study, to gain a deep insight into the combustion properties of co-firing ammonia/methane fuel blends for the power and steel industry, a detailed chemical-kinetics mechanism model was developed for comprehensively modelling ammonia/methane fuels combustion. Characteristics of ignition delay time, unstretched laminar flame speed and NO, CO2 and CO emissions in the exhaust gas were obtained over a wide range of equivalence ratios and ammonia fractions. High NO emissions will be a main problem as CO and CO2 emissions tend to drop when adding ammonia into methane. To gain a further understanding of the effect of ammonia substituting methane for combustion use, analyses of laminar premixed flame structures were performed. The impact of ammonia substitution was illustrated by analysing relevant specific radicals. Furthermore, to study the combustion characteristics of ammonia/methane under more practical conditions, effects of engine relevant conditions (elevated pressure and initial temperature) were also studied. Results indicate that pressure has a more prominent effect than initial temperature and there is a good potential that unwanted emissions can be reduced significantly under industrial conditions.

Modeling Combustion of Ammonia/Hydrogen Fuel Blends under Gas Turbine Conditions

To utilize ammonia as an alternative fuel for future power generation, it is essential to develop combustion chemical kinetic mechanisms which can describe in some detail the reaction characteristics and combustion properties. In the present study, a detailed chemical-kinetics mechanism is developed to validate premixed combustion characteristics of ammonia and hydrogen fuel blends comprehensively. In order to obtain a useful model for gas turbine applications, the proposed kinetic mechanism is verified in terms of NOx emission, laminar burning velocity, and ignition delay times, focusing particularly on elevated conditions which are encountered during gas turbine operation. Results have shown that the proposed kinetic model performs with satisfactory accuracy under different practical equivalence ratio conditions. The comparison with other mechanisms from the literature also demonstrates that the model can comprehensively describe the reaction process of ammonia/hydrogen fuels in terms of different combu...

Comparative experimental study of ethanol-air premixed laminar combustion characteristics by laser induced spark and electric spark ignition

An experimental study of laminar combustion characteristics of ethanol-air premixed mixtures was conducted with different ignition methods, including laser induced spark ignition (LISI) and electric spark ignition (SI) at an initial condition of 358 K temperature and 0.1MPa pressure. Flame propagation with the two different ignition methods was analyzed and discussed. The laminar flame speed was extrapolated with a nonlinear extrapolation method. Results indicate that the laminar speed of ethanol-air mixtures with LISI is faster than that with SI at lean mixtures, but slower at stoichiometric and rich mixtures. The peak values of the laminar burning velocity for SI and LISI with nonlinear extrapolation are 50.1 cm/s and 47.6 cm/s at the equivalence ratio of 1.1, respectively. Laser-induced spark ignition is able to ignite leaner ethanol-air mixtures.

Partially premixed combustion based on different injection strategies in a light-duty diesel engine

The performance of partially premixed combustion (PPC) relies heavily on the proper mixing between the fuel and the in–cylinder gas. In this paper, two injection strategies, including single and multiple injection, were investigated to achieve PPC in a four-cylinder light-duty diesel engine, and were evaluated in terms of heat release rate, combustion phase, emissions and thermal efficiencies. The combustion process is dominated by premixed combustion and the diffusion combustion process is quite short at the early single injection mode. It shows the characteristics of both premixed combustion and low temperature combustion. However, the ratio of diffusion combustion increases at high load. NOx and smoke emissions reduce at the same time with late injection mode. For the multiple injection strategy, the cylinder pressure and peak pressure rise rate is lower. As the pilot-main interval increases, the mixture is more homogeneous due to sufficient premixing time. However, diffusion combustion plays the dominant role in the double pilot injection mode. The BSFC (brake specific fuel consumption) and brake thermal efficiency are considerably improved with pilot injection mode at low load condition, compared with late injection mode. The NOx decreases dramatically in double pilot injection PPC, while the smoke and CO increase, compared with single early injection mode.

Hydrogen/oxygen premixed combustion characteristics in micro porous media combustor

The micro-combustor is a major component of the micro thermophotovoltaic (TPV) system. In order to improve the stability of combustion and efficiency of the micro-TPV conversion device, porous media combustor was designed. Porous media combustion can increase flame stability and gain higher conversion efficiency compared with the free flame combustor. In this work, the influence of several major parameters on micro combustion, namely material of porous media, hydrogen to oxygen equivalence ratio, porosity of porous media and mixture flow rate were investigated using the numerical simulation method. Results indicate that, even though at three different equivalence ratio conditions, SiC is still one of the most suitable porous media materials. Besides, high flow velocity and big porosity both induce high temperature gradient and big pressure drop. The interaction between these two parameters plays an important role in external wall temperature. Analyses in this paper reveal that with the appropriate parameters: ϕ=0.8, v=6m/s, porosity is 0.5 and porous media material is SiC, micro combustor with porous media structure could greatly increase combustion efficiency. Present research will facilitate the optimization and improvement of micro-TPV conversion device.

Heat Release Analysis of Hydraulic Free Piston Diesel Engine

A simplified method is used to calculate the Rate of Heat Release (RoHR), some notice details are considered. The data is smoothed to get the final curves, we analyze the parameters of original formula of Wiebe and they are fitted the well except several cycles. Not all the cycles are conformed to the complete premixed combustion characteristics. We get several cycles to distinguish the factors of premixed combustion and diffusion combustion in HFPDE, a parameter J is quoted to describe the possibility of diffusion combustion. And then we analyze the working process of HFPDE based on the characteristics of the curves. Fortunately, we find that the stability of ignition can be improved by changing the fuel injection time appropriately. Finally, we find the most suitable fuel injection quality of HFPDE, and the optimum proposals are presented. However, the specific method to reach the goal and internal cause of RoHR characteristics are not given.

Impact of DME as an Oxygenated Alternative Fuel on Combustion and Emissions Reduction in a Transportation Vehicle at Low Load Condition

AbstractThis study investigates the impact of dimethyl ether (DME) on the combustion and exhaust emission characteristics at low engine load operating and pilot injection conditions in a four-cylinder diesel engine that was modified for DME application. The combustion characteristics were analyzed based on the combustion pressure, the rate of heat release, the accumulated heat release, and the premixed combustion characteristics. The emission characteristics were analyzed through the analysis of the nitrogen oxides (NOx), soot, hydrocarbon (HC), and carbon monoxide (CO). The heat release amount per unit crank angle in DME combustion is higher than that in diesel combustion in a pilot injected combustion mode. The accumulated heat release of DME during the main combustion is higher than that of diesel fuel. The pilot injection combustion of DME fuel started earlier than single-injection combustion does. The advanced pilot injection timing caused a decrease of premixed combustion duration and a retardation ...

Theoretical Study on Premixed Flames of Nano Aluminum Particles and Water Mixture

A theoretical model is proposed to investigate premixed combustion characteristics of Nano aluminum particles - water mixture. The effects of particle size, initial pressure, and temperature were considered as well. Computational domain is divided into 3 regions; preheat zone 1, preheat zone 2, and reaction zone. No reaction occurs in either of the preheat zones. Reaction zone, consisting of nano aluminum particles–steam mixture and the combustion products, is the region where reaction and heat-release occurs. Energy conservation is considered separately at each zones. The flame speed and temperature distribution are derived by solving the energy equation in each regime and matching the temperature and heat flux at the interfacial boundaries. Combustion time correlation of nano aluminum particle is also considered to imply complex aluminum combustion kinetics. Normalized flame speed is calculated as a function of pressure, initial particle diameter, and equivalence ratio and compared with experimental data.

Fundamental Study of Spray and Partially Premixed Combustion of Methane/Air Mixture

This study presents fundamentals of spray and partially premixed combustion characteristics of directly injected methane in a constant volume combustion chamber (CVCC). The constant volume vessel is a cylinder with inside diameter of 135 mm and inside height of 135 mm. Two end of the vessel are equipped with optical windows. A high speed complementary metal oxide semiconductor (CMOS) camera capable of capturing pictures up to 40,000 frames per second is used to observe flow conditions inside the chamber. The injected fuel jet generates turbulence in the vessel and forms a turbulent heterogeneous fuel–air mixture in the vessel, similar to that in a compressed natural gas (CNG) direct-injection (DI) engine. The fuel–air mixture is ignited by centrally located electrodes at a given spark delay timing of 1, 40, 75, and 110 ms. In addition to the four delay times, a 5 min waiting period was used in order to make sure of having laminar homogeneous combustion. Spray development and characterization including spray tip penetration (STP), spray cone angle (SCA), and overall equivalence ratio were investigated under 30–90 bar fuel pressures and 1–5 bar chamber pressure. Flame propagation images and combustion characteristics were determined via pressure-derived parameters and analyzed at a fuel pressure of 90 bar and a chamber pressure of 1 bar at different stratification ratios (S.R.) (from 0% to 100%) at overall equivalence ratios of 0.6, 0.8, and 1.0. Shorter combustion duration and higher combustion pressure were observed in direct injection-type combustion at all fuel air equivalence ratios compared to those of homogeneous combustion.

Numerical study on combustion of diluted methanol-air premixed mixtures

The effect of nitrogen dilution on the premixed combustion characteristics and flame structure of laminar premixed methanol-air-nitrogen mixtures are analyzed numerically based on an extended methanol oxidation mechanism. The laminar burning velocities, the mass burning fluxes, the adiabatic flame temperature, the global activation temperature, the Zeldovich number, the effective Lewis number and the laminar flame structure of the methanol-air-nitrogen mixtures are obtained under different nitrogen dilution ratios. Comparison between experiments and numerical simulations show that the extended methanol oxidation mechanism can well reproduce the laminar burning velocities for lean and near stoichiometric methanol-air-nitrogen mixtures. The laminar burning velocities and the mass burning fluxes decrease with the increase of nitrogen dilution ratio and the effect is more obvious for the lean mixture. The effective Lewis number of the mixture increases with the increase of nitrogen dilution ratio, and the diffusive-thermal instability of the flame front is decreased by the nitrogen addition. Nitrogen addition can suppress the hydrodynamic instability of methanol-air-nitrogen flames. The decrease of the mole fraction of OH and H is mainly responsible for the suppressed effect of nitrogen diluent on the chemical reaction in the methanol-air-nitrogen laminar premixed flames, and the NOx and formaldehyde emissions are decreased by the nitrogen addition. methanol, dilution, premixed combustion, numerical analysis With increasing concern about fuel shortage and air pollution control, researches on improving engine fuel economy and reducing exhaust emissions have become the major topics in combustion and engine studies. Because of limited reserves of crude oil, the development of alternative-fuel engines has attracted more attention in the engine community. Alternative fuels usually are clean fuels compared with traditional diesel fuel and gasoline fuel in the engine combustion process. The introduction of these alternative fuels is beneficial to the solution of the fuel shortage and reduction of engine exhaust emissions. Nowadays, clean alternative fuels mainly include hydrogen, compressed natural gas (CNG), liquid petroleum gas (LPG), dimethyl ether (DME), and alcohols in internal combustion engines application

모형 가스터빈 연소기에서 선회 예혼합화염의 대와동모사(LES)

본 논문에서는 대와동모사를 이용하여 모형 가스터빈 연소기에서 난류 예혼합연소의 선회 유동구조와 화염특성이 검토되었다. 비정상 화염 거동을 모사하기 위하여 G-방정식 화염편 모델이 적용되었다. 결과로서, 입구 선회수 증가에 따른 코너 및 중앙 재순환 유동이 뚜렷한 차이를 보이며, 화염의 길이도 점차 감소됨을 확인 할 수 있었다. 또한 강선회 조건에서 역화현상의 원인이 확인되었다. 정확한 비정상 화염거동의 모사를 위하여, 연소실 내 음향파 거동의 예측성능이 우선적으로 검토되었으며, 스텝 모서리 근처에서 생성된 와동이 화염면 변동에 가장 큰 영향을 주고 있음을 알 수 있었다. 마지막으로 비정상 화염-와동 상호작용에 대한 해석을 통해 선회와 음향파의 전개로부터 생성된 와동의 진동이 화염면 및 열발생의 변동과 밀접하게 관련되어짐을 체계적으로 규명하였다. In the present paper, the swirl flow structure and flame characteristics of turbulent premixed combustion in a model gas turbine combustor are investigated using large eddy simulation(LES). A G-equation flamelet model is employed to simulate the unsteady flame behavior. When inlet swirl number is increased, the distinct flow structures, such as the shapes of corner recirculation and center toroidal recirculation zone, are observed and the flame length is shorted gradually. Also, the phenomena of flashback are identified at strong swirl intensity. In order to get the accurate description of unsteady flame behavior, the predictive ability of the acoustic wave in a combustor is primarily evaluated. It is found that the vortex generated near the edge of step plays an important role in the flame fluctuation. Finally it is examined systematically that the flame and heat release fluctuation are coupled strongly to the vortex shedding generated by swirl flow and acoustic wave propagation from the analysis of flame-vortex interaction.

The Effect of Intake Boost Pressure on MK (Modulated Kinetics) Combustion

In previous work, an RSM optimization was performed to demonstrate the emission reduction capability of the combined effects of high injection pressure, boost pressure, and cooled EGR on a HSDI diesel engine equipped with a common rail injection system. The RSM optimization led optimum operating parameters to low-temperature and premixed combustion characteristics, i. e., the MK combustion region, resulting in simultaneous reductions in NOx and PM emissions without sacrificing BSFC. However, further retardation of injection timing and increase of EGR rate from the optimum point resulted in significant deterioration of the engine stability with misfire. In the present work, further RSM optimization was conducted to investigate the effect of intake boost pressure on MK combustion. It was found that the increase of intake boost pressure shortened ignition delay, which was not favorable for MK combustion. However it allowed the use of heavier EGR and later injection timings, which intensified the characteristics of MK combustion, i. e., lower-temperature and more thoroughly premixed combustion characteristics. Compared to the previous optimum point, the NOx emission level of the new optimum point was improved by 48%, and it was possible to improve PM emissions further by 71%, while retaining BSFC at the same level. At the new optimum point NOx and PM emissions were 0.54 and 0.092g/kW-hr, respectively, which met the EPA Tier II 2004 automotive diesel mandates.

522 非定常燃焼とそれを利用した制御(GS-6 燃焼(3))

Characteristics of unsteady premixed combustion were observed in two cases, the first was the self-excited oscillating combustion and the second was the combustion under the forced oscillating supply of mixture. The field noise level near the exit of exhaust pipe was measured. Pressure fluctuations in combustion chamber and OH chemiluminescence from the combustion chamber were measured simultaneously in time series. In the case of short exhaust pipe length, combustion oscillation can be controlled by a forced oscillating mixture supply with specified frequency. Furthermore, no distinct peaks was identified in the power spectrum of pressure fluctuation when combustion oscillation was attenuated despite that two dominant peaks were obtained in the case of self-excited oscillating combustion.