Increase Of Hydrogen Addition Research Articles

Effect of hydrogen addition on CO emission and thermo-chemical state near wall during head-on quenching of laminar premixed methane/air flame

A computational model for premixed methane-air flame under the flame-wall interaction was established based on CFD software and experimentally verified. The head-on quenching process of premixed methane-air flame under different hydrogen additions was simulated. The changes in CO emission, quenching distance, and the distribution of CO near the wall under different hydrogen additions were obtained. With the increase of H2 addition, the mass fraction of HCO and the generation of CO increase. Moreover, the consumption of OH in R79: OH+H2=H+H2O increases, resulting in the weakening of the oxidation of OH to CO in R94: OH+CO=CO2+H, and the EICO increases. With the increase of H2 addition, the heat release rate increases, the quenching distance decreases, and the Peclet number (Pe) increases. With the increase of hydrogen addition, the mole fraction of CO in Region A gradually decreases, the mole fraction of CO in Region B first increases and then decreases, and the mole fraction of CO in Region C increases. The temperature drops first and then rises. Near the wall (y < 0.3 mm), the convection term and diffusion term dominate, and the heat transfer time is less than the generation time and oxidation time of CO, and the generation branch and oxidation branch of CO move to the low-temperature region. Far from the wall (y ≥ 0.3 mm), the reaction source term dominates, the heat transfer time is greater than the generation time of CO, less than the oxidation time of CO, and the oxidation branch of CO moves to low temperature. With the increase of hydrogen addition, the chemical time scale of CO decreases, and the generation branches and oxidation branches of CO move to higher temperatures.

Study on Combustion Characteristics of Diesel/Natural Gas/Hydrogen RCCI Engine

Abstract With the increasing environmental and energy problems, the development of new combustion technology has become a hot topic in the research of internal combustion engine. Reactivity controlled compression ignition (RCCI) combustion mode is the most promising combustion mode at present, which can solve the problems of combustion ignition controllability, and expand the engine load range. In this paper, optical diagnostics and numerical simulation are used to study the diesel/natural gas/hydrogen tri-fuel RCCI engine performance. Results show that hydrogen can significantly improve in-cylinder combustion and emission characteristics. With the increase of hydrogen addition, the combustion efficiency is increased accordingly, and the afterburning is prevented, which makes the exhaust energy loss decrease.

Effects on the performance of domestic gas appliances operated on natural gas mixed with hydrogen

As an environmentally friendly fuel, hydrogen is one of the research hotspots of renewable energy currently, but transportation and utilization of pure hydrogen remain to be improved due to vast investments and high risk. Therefore, as a transitional program before the implementation of large-scale applications, mixing hydrogen into natural gas pipeline is an effective and feasible method. The paper studied the influence of natural gas mixed with hydrogen at 0%, 5%, 10%, 15% and 20% by volume on the performance of domestic gas appliances including domestic gas stoves and gas water heaters. The experiments show that the flame length shortened with increasing proportion of hydrogen. Flashback can be obviously observed when hydrogen addition reaches to 23% in gas water heaters. It is concluded that the measured heat inputs of domestic gas appliances decrease gradually with the increase of hydrogen addition, but the thermal efficiency increases. The increasing proportion of hydrogen mixed with natural gas promotes the emission reduction of CO and NOx for most test samples. When hydrogen addition fraction is up to 20%, annual CO2 emission reduction can reach 9.33% in gas water heaters, but when the hydrogen is produced by water electrolysis, the annual fuel cost will increase 32.7% on average.

Experimental study on self-acceleration characteristics of unstable flame of low calorific value gas blended with hydrogen

The self-acceleration characteristics of cellular flame of low calorific value (LCV) gas in a constant volume combustion bomb were studied, the propagation process of spherical flame with different hydrogen (H2) addition and initial pressure was analyzed, and the flame radius versus time was also discussed. The experimental results show that the self-acceleration of the cellular flame of LCV gas blended with hydrogen appears at high pressure, high hydrogen ratio and lean burn. The acceleration index increases with the increase of hydrogen addition and the reduction of equivalence ratio, and increases with the increase of initial pressure, but the acceleration index does not infinitely increase with the increase of initial pressure. With the increase of the hydrogen addition and the reduction of the equivalence ratio, the critical radius of the cellular flame decreases, which is shown that increase of the hydrogen addition and the lean burn will make appearance of cellular flame in advance. When the ratio of hydrogen is less than 60%, the critical Peclet number decreases with increase of hydrogen addition, when the ratio of hydrogen continues to increase to 80%, it increases slightly. The research in this paper provides an experimental basis for the in-depth study of engine combustion of LCV gas blended with hydrogen.

Effect of hydrogen addition on the combustion and emission of a diesel free-piston engine

The free-piston engine (FPE) is a new crankless engine, which operates with variable compression ratio, flexible fuel applicability and low pollution potential. A numerical model which couples with dynamic, combustion and gas exchange was established and verified by experiment to simulate the effects of different hydrogen addition on the combustion and emission of a diesel FPE. Results indicate that a small amount of hydrogen addition has a little effect on the combustion process of the FPE. However, when the ratio of hydrogen addition (RH2) is more than 0.1, the RH2 gives a positive effect on the peak in-cylinder gas pressure, temperature, and nitric oxide emission of the FPE, while soot emission decreases with the increase of hydrogen addition. Moreover, the larger RH2 induces a longer ignition delay, shorter rapid combustion period, weaker post-combustion effect, greater heat release rate, and earlier peak heat release rate for the FPE. Nevertheless, the released heat in rapid combustion period is significantly enhanced by the increase of RH2.

The Effect of Hydrogen Addition on the Combustion Characteristics of RP-3 Kerosene/Air Premixed Flames

Experimental studies have been performed to investigate the effects of hydrogen addition on the combustion characteristics of Chinese No.3 jet fuel (RP-3 kerosene/air premixed flames. Experiments were carried out in a constant volume chamber and the influences of the initial temperatures of 390 and 420 K, initial pressures of 0.1 and 0.3 MPa, equivalence ratios of 0.6–1.6 and hydrogen additions of 0.0–0.5 on the laminar burning velocities, and Markstein numbers of Hydrogen (H2)/RP-3/air mixtures were investigated. The results show that the flame front surfaces of RP-3/air mixtures remain smooth throughout the entire flame propagation process at a temperature of 390 K, pressure of 0.3 MPa, equivalence ratio of 1.3 and without hydrogen addition, but when the hydrogen addition increases from 0.0 to 0.5 under the same conditions, flaws and protuberances occur at the flame surfaces. It was also found that with the increase of the equivalence ratio from 0.9 to 1.5, the laminar burning velocities of the mixtures increase at first and then decrease, and the highest laminar burning velocity was measured at an equivalence ratio of 1.2. Meanwhile, with the increase of hydrogen addition, laminar burning velocities of H2/RP-3/air mixtures increase. However, the Markstein numbers of H2/RP-3/air mixtures decrease with the increase of hydrogen addition, which means that the flames of H2/RP-3/air mixtures become unstable with the increase of hydrogen addition.

Effect of intake hydrogen addition on performance and emission characteristics of a diesel engine with exhaust gas recirculation

This article presents the potential of improving engine performance and pollutant emissions of a ZS195 Diesel engine by exhaust gas recirculation (EGR) and intake hydrogen enrichment. The effect of EGR level and hydrogen addition on the engine performance and pollutant emissions has been investigated through detailed experiments at rated speed. The experimental results have shown that when EGR level is constant, the peak pressure and maximum rate of pressure rise increase with the increase of hydrogen addition. The intake hydrogen enrichment can reduce HC, CO, and soot level and increase NOX emission, but EGR technique can offset this effect. The combustion speed and thermal efficiency increase with the increase of hydrogen addition when EGR technique has been adopted.

Effect of hydrogen addition on lean burn performance of a spark-ignited gasoline engine at 800 rpm and low loads

To reduce the fuel consumption and emissions of spark-ignited (SI) engines, hydrogen enrichment was used to improve the performance of a lean burn SI engine operating at low speed and load conditions. A hydrogen port-injection system was mounted on the intake manifolds to introduce hydrogen into the intake ports sequentially while keeping the original gasoline injection system unchanged. A hybrid electronic control unit (HECU) was adopted to control injection timings and durations of gasoline and hydrogen, accomplishing four excess air ratios of 1.00, 1.18, 1.43 and 1.67 and three hydrogen volume fractions in the intake of 3%, 5%, 8%. The experimental results showed that engine brake thermal efficiency and torque output were increased, combustion durations were shortened, cyclic variation and HC emissions were reduced, but NOx emissions were increased with the increase of hydrogen addition. CO emission was also reduced under lean conditions with hydrogen enrichment.

Study of Low-Pressure Premixed Dimethyl Ether/Hydrogen/Oxygen/Argon Laminar Flames with Photoionization Mass Spectrometry

Laminar premixed fuel-rich (equivalence ratio of 1.5) dimethyl ether/hydrogen/oxygen/argon flames with different hydrogen fractions (0%, 20%, 40%, 60%, and 80%) were investigated with tunable synchrotron vacuum-ultraviolet photoionization and molecular-beam mass spectrometry. The flame temperature profile was measured. Through measurement of the signal intensities at different distances from the burner surface, the mole fraction profiles of major intermediates are derived. A comparison of the flame temperature profiles or mole fraction profiles is made among these flames. The influences of hydrogen addition on the flame temperature and mole fractions of major species and intermediates are analyzed. The results show that the flame temperature in the flame zone decreases with an increase of hydrogen addition. The mole fractions of major species and intermediates are decreased with an increase of the hydrogen fraction. This might be attributed to the decrease of the C/H ratio of the fuel blend by hydrogen ad...

Numerical study on laminar burning velocity and NO formation of premixed methane–hydrogen–air flames

Abstract Numerical study on laminar burning velocity and NO formation of the premixed methane–hydrogen–air flames was conducted at room temperature and atmospheric pressure. The unstretched laminar burning velocity, adiabatic flame temperature, and radical mole fractions of H, OH and NO are obtained at various equivalence ratios and hydrogen fractions. The results show that the unstretched laminar burning velocity is increased with the increase of hydrogen fraction. Methane-dominated combustion is presented when hydrogen fraction is less than 40%, where laminar burning velocity is slightly increased with the increase of hydrogen addition. When hydrogen fraction is larger than 40% , laminar burning velocity is exponentially increased with the increase of hydrogen fraction. A strong correlation exists between burning velocity and maximum radical concentration of H + OH radicals in the reaction zone of premixed flames. High burning velocity corresponds to high radical concentration in the reaction zone. With the increase of hydrogen fraction, the overall activation energy of methane–hydrogen mixture is decreased, and the inner layer temperature and Zeldovich number are also decreased. All these factors contribute to the enhancement of combustion as hydrogen is added. The curve of NO versus equivalence ratio shows two peaks, where they occur at the stoichiometric mixture due to Zeldovich thermal-NO mechanism and at the rich mixture with equivalence ratio of 1.3 due to the Fenimore prompt-NO mechanism. In the stoichiometric flames, hydrogen addition has little influence on NO formation, while in rich flames, NO concentration is significantly decreased. Different NO formation responses to stretched and unstretched flames by hydrogen addition are discussed.

Study of cyclic variations of direct-injection combustion fueled with natural gas–hydrogen blends using a constant volume vessel

Cyclic variations of direct-injection combustion fueled with natural gas–hydrogen fuel blends were experimentally studied using a constant volume vessel. Direct-injection combustion was realized by injecting the high-pressure fuel into the vessel. Flame propagating photographs and pressure history in the vessel were recorded at various hydrogen volumetric fractions in the fuel blends (from 0% to 40%) under the same lean-burn conditions where the overall equivalence ratios are 0.6 and 0.8, respectively. The effect of fuel–air mixture inhomogeneous distribution and hydrogen addition on the cyclic variations was analyzed via flame development photographs and pressure-derived combustion parameters. The results indicated that the cyclic variations were initiated at the early stage of flame development. The flame kernel is closely concentric to the spark electrode and flame pattern has less irregular with hydrogen addition. Direct-injection natural gas combustion can achieve the stable lean combustion along with low cyclic variations due to the mixture stratification in the vessel. The cyclic variations decreased with the increase of hydrogen addition and this trend is more obvious at ultra-lean-burn condition. Hydrogen addition weakened the effect from turbulent flow on flame propagating process, thus reduce the cyclic variations related to the gas flow. There exists interdependency between the early combustion stage and the subsequent combustion process for direct-injection combustion.

Laminar burning velocities and combustion characteristics of propane–hydrogen–air premixed flames

An experimental study on laminar burning characteristics of the spherically expanding premixed propane–hydrogen–air flames was conducted at room temperature and atmospheric pressure. The unstretched laminar burning velocity, the laminar flame thickness, the Markstein number, the Zeldovich number and the global Lewis number were obtained over a range of equivalence ratios and hydrogen fractions. The influence of hydrogen addition on the laminar burning velocities and the flame front instabilities were analyzed. The results show that the unstretched laminar burning velocity increases, the laminar flame thickness decreases and the peak value of unstretched laminar burning velocity shifts to the richer mixture side with the increase of hydrogen fraction. When hydrogen fraction in the fuel is less than 60%, the Markstein number decreases with the increase of equivalence ratio, and the flame behavior is similar to that of propane–air flames. When hydrogen fraction is larger than 60%, the flame behavior is similar to that of hydrogen–air flames. At equivalence ratio less than 1.2, the Markstein number decreases with the increase of hydrogen fraction, indicating flame destabilization by hydrogen addition. At equivalence ratio larger than 1.2, the Markstein length increases with the increase of hydrogen fraction, indicating the stabilization of flame by hydrogen addition. In the case of lean mixture combustion, the Zeldovich number decreases with the increase of hydrogen addition, indicating the lowering of activation temperature of the mixture. The global Lewis number decreases with the increase of hydrogen fraction, and this indicates the increase of preferential-diffusion instabilities by hydrogen addition.

Experimental Study on Premixed Combustion of Dimethyl Ether–Hydrogen–Air Mixtures

The laminar combustion characteristics of DME–hydrogen–air premixed mixture were studied at different equivalence ratios, ratios of hydrogen to DME plus hydrogen, and initial pressures by using a constant volume combustion bomb. The influences of the equivalence ratio, the hydrogen addition, and the initial pressure on flame speed and combustion characteristics are analyzed. The results show that the flame speed, the laminar burning velocity, and the mass burning rate increase with the increase of hydrogen addition. Increasing the ratio of hydrogen to DME plus hydrogen will shorten the combustion duration. In the case of small hydrogen addition, the Markstein length decreases with the increase of equivalence ratio, and this reveals that lean mixture has better flame front stability compared with that of the rich mixture. In the case of large hydrogen addition, the Markstein length increases with the increase of equivalence ratio, and this indicates that the rich mixture has better flame front stability th...

CT2-4: Experimental Study on Premixed Combustion of Dimethyl Ether-Hydrogen-Air Mixtures(CT: Combustion, Thermal and Fluid Science,General Session Papers)

The premixed flames of DME-hydrogen-air premixed mixture were studied by the outwardly expanding flame and schlieren photography. The influences from equivalence ratio, hydrogen addition and initial pressure on the flame speed and combustion characteristics are analyzed. The results show that the flame speed, the laminar burning velocity and the mass burning rate increase with the increase of hydrogen addition. Increasing the ratio of hydrogen to DME will shorten the combustion duration. In the case of small hydrogen addition, the Markstein length decreases with the increase of equivalence ratio, and this reveals that lean mixture has better flame front stability than of rich mixture. In the case of large hydrogen addition, the Markstein length increases with the increase of equivalence ratio, and this indicates that rich mixture has better flame front stability than that of lean mixture. The initial pressure has larger influence on the combustion pressure than that from hydrogen addition. The flame development duration decreases with the increase of hydrogen addition and/or with the increase of equivalence ratio. Addition of hydrogen into DME can improve the ignitability of the mixtures and fasten the combustion.

Combustion and emission characteristics of a port-injection HCNG engine under various ignition timings

Combustion and emission characteristics of a port-injection SI turbocharged engine fueled with several H 2 / CNG blend ratios (0–50 vol%) under various ignition timings were investigated. The results show that with the increase of hydrogen addition, the maximum brake toque timing decreases and the indicated thermal efficiency increases; the MBT gets close to the top dead center and the indicated thermal efficiency increases with decreased load. The combustion duration is reduced by increasing the hydrogen fraction in HCNG (hydrogen enriched compressed natural gas) mixture. The NO x , CO and HC emissions all descend with the increase of spark advance angle, and ascend with the increase of the load. Under the same ignition timing NO x and CO emissions rises with the increase of hydrogen blend ratio, and the HC emission presents an opposite trend.