Increase In Combustion Temperature Research Articles

Non-adiabatic effect on NOx emissions for premixed H2-blended NH3/air combustion under rich-lean-staged conditions

The non-adiabatic effect on NOx emission for the swirl premixed NH3/H2/air combustion under fuel-rich/quick-mix/fuel-lean (RQL) conditions was experimentally studied. The wall temperature of the quartz combustor was controlled by surrounding heating. Results showed that both H2-blending and thermal insulation were in favor of enlarging the low-NOx range and lowering the valley NOx, due to the less NO and unburnt NH3, and smaller flow rate from the primary stage. In the post-flame zone of the primary stage, increasing combustion temperature significantly enhanced NO reduction, Thus, for low NOx emission, it is essential to keep enough thermal insulation there. Experimental measurements also found remarkable N2O could be formed in the secondary stage when combustion temperature was low and much unburnt NH3 was excessive. Kinetic analyses showed this phenomenon was due to the high combination rate of NH and NO, and low reduction rate of H radical.

Measurement report: In-flight and ground-based measurements of nitrogen oxide emissions from latest-generation jet engines and 100 % sustainable aviation fuel

Abstract. Nitrogen oxides, emitted from air traffic, are of concern due to their impact on climate by changing atmospheric ozone and methane levels. Using the DLR research aircraft Falcon, total reactive nitrogen (NOy) in-flight measurements were carried out at high altitudes to characterize emissions in the fresh aircraft exhaust from the latest-generation Rolls-Royce Trent XWB-84 engine aboard the long-range Airbus A350-941 aircraft during the ECLIF3 (Emission and CLimate Impact of alternative Fuels 3) experiment. The impact of different engine thrust settings, monitored in terms of combustor inlet temperature, pressure and engine fuel flow, was tested for two different fuel types: Jet A-1 and, for the first time, a 100 % sustainable aviation fuel (SAF) under similar atmospheric conditions. In addition, a range of combustor temperatures and an additional blended SAF were tested during ground-based emission measurements. For the data measured during ECLIF3, we confirm that the NOx emission index increases with increasing combustion temperature, pressure and fuel flow. We find that as expected, the fuel type has no measurable effect on the NOx emission index. These measurements are used to compare to cruise NOx emission index estimates from three engine emission prediction methods. Our measurements thus help to understand the ground to cruise correlation of current engine emission prediction methods while serving as input for climate modelling and extending the extremely sparse data set on in-flight aircraft nitrogen oxide emissions to newer engine generations.

Soot evolution in ethylene combustion catalyzed by electric field: experimental and ReaxFF molecular dynamics studies

In this study, an electric field (E-field) was used to regulate the formation and oxidation of soot in combustion. In the procedure, an E-field is applied to the ethylene non-premixed flame, the flame is stretched horizontally and the flame height is reduced. By comparing the partially premixed flame to eliminate the effect of the E-field on the increase of combustion temperature caused by premixing, transmission electron microscope (TEM) detection revealed that the soot particles were more dispersed in the action of E-field, the “core-shell” structure of soot disappeared, and the markedly improved oxidation rate of soot in the flame. The evolution process of soot in ethylene combustion was studied by reactive molecular dynamics. The 9 ns simulation was performed at E-field strengths of 0, 0.001, and 0.1 V/Å by three successive modelings. The results showed that the E-field reduced the growth of the largest molecule in the system and increased the coagulation time of the initial soot particles. With increasing E-field strength, the “core-shell” structure of soot gradually broke. An increased hydrogen-carbon ratio and decreased number of six-membered rings are the internal factors for the more scattered structure of soot, which allows the soot to be more easily oxidized.

Estimation of soot refractive index from its nanostructural parameters with the dispersion model

Particles derived from combustion processes, mainly composed of soot agglomerates, are acknowledged to be among the main contributors to climate change. Their effects depend mostly on their size, shape, and internal structure. Specifically, the latter has a significant effect on their optical properties, mainly through the refractive index. This index has been widely evaluated, but scarcely correlated with the soot internal characteristics. In this work, relationships between the nanostructural parameters (such as the degree of graphitization, among others) obtained with conventional analytical techniques and the input parameters of the dispersion model (a representation of the electromagnetic radiation through the Lorentz-Drude approach) are proposed with the aim to determine the refractive index. From experiments in a chassis dynamometer, it has been observed that as the vehicle speed increases, the soot samples have, in general, higher degree of graphitization, due to increased combustion temperature. The method proposed allows quantifying how both the real and imaginary parts of the complex refractive index increase as the degree of graphitization increases. Much lower dependence on the average crystal length has been observed. Different combinations of techniques can be used to determine the nanostructural parameters, depending on the analytical technique used. As far as the resulting parameters are reliable, the effect of the technique selected is minor, thus providing flexibility to the application of the method.

Numerical analysis of various combustion chamber bowl geometries on combustion, performance, and emissions parameters in a diesel engine

In this paper, numerical analysis of a diesel engine with various combustion chamber bowl geometries was investigated. Numerical analyses of asymmetrical bowl forms were carried out using the Ansys Forte software. Analyses were done for three different piston bowl geometries in a single-cylinder, air-cooled diesel engine at 1500 rpm engine speed. Three different bowl geometries were created, the piston-1 model is a commercial one for used engine, in the piston-2 pedestal area is removed from the piston, and in the cylindrical model bowl geometry has more straight borders. The results of the numerical study were confirmed with the results of experiments which is carried out for the piston-1 model. Simulation results showed a good correlation with experimental results. According to the results of the numerical study, the highest in-cylinder temperature was determined as 1213 K for the piston-1 model. In the piston-1 model, the combustion efficiency was improved with the increase of the swirl by the increased combustion temperature. As a result of the analysis, the thermal and combustion efficiencies of the piston-1 model were higher than the other models. The maximum turbulence velocity was observed at -12 CA for three different piston bowl models as 4.1 m/s, 4.06 m/s, and 3.9 m/s for piston-1, piston-2, and cylindrical respectively.

Feasibility of co-disposal of lignite and eucalyptus wood in coal-fired power plants: thermogravimetric characterization, typical gaseous pollutant emission characteristics, and economic analysis

ABSTRACT Energy issues are becoming increasingly prominent, and biomass blending in coal-fired power plants can improve combustion performance and reduce gaseous pollutant emissions, thereby improving economic efficiency. In this study, a thermogravimetric analyzer, a horizontal tube furnace, and an infrared flue gas analyzer were used to investigate the combustion behavior and gaseous pollutant emissions of the co-combustion of LC and EW. The results show that blending EW into LC cofiring can inhibit the release of volatile matter and promote the decomposition of fixed carbon and lignin simultaneously. The HHV of EW (15.88 MJ/kg) reaches 63.7% of LC’s (24.90 MJ/kg), indicating EW has a high energy utilization value. With increasing combustion temperature, the average value of CR S increased from 47.09% to 59.94%, and the average value of CR Cl increased from 26.15% to 52.15%, leading to a significant increase in SO2 and HCl emissions. The decrease in combustion temperature slightly promoted the release of N (CR N increased from 11.76% to 14.45%). The results of the economic analysis show that the cost of CaO and NH3·H2O used for removing gaseous pollutants decreased the most, and the economic efficiency increased the fastest to 14,000 RMB/day when the EW blending ratio increased from 10% to 20%.

Ash melting and slagging and residual K ion content in biomass pellet combustion

ABSTRACT Combustion of biomass pellets is an effective way to reduce greenhouse gas emissions and achieve carbon neutrality. However, the alkali metal content (represented by K) in ash directly affects its slagging behavior, which can corrode the reactor and shorten its service life. In this study, the ash fusion slag and residual K ion contents were investigated at different combustion times (2, 5, 10, 20, 30 and 60 min) and temperatures (600, 700, 800, 900 and 1000°C). At the same combustion temperature, the residual content of K ions in ash decreases as the combustion time increases; at the same combustion time, the residual content of K ions decreases as the combustion temperature increases. The addition of 5% CaO promotes K precipitation, but at 10% CaO addition, the K precipitation rate is less than that at 5% CaO addition, indicating that the addition of CaO is beneficial to K ion precipitation only within a certain range. Adding CaO also generates high-melting-substances, such as CaSiO3 and calcite, which improve the overall slag resistance of the fuel.

The effect of multiple factors on changes in organic-inorganic fractions of condensable particulate matter during coal combustion

Condensable particulate matter (CPM) from coal combustion is the focus of current pollutant emission studies, and CPM can be divided into inorganic and organic fractions according to the component characteristics. At present, the effects of different factors in the combustion process on the organic and inorganic components of CPM have not been discussed systematically. Here, we conducted combustion experiments collected the generated CPM on a well-controlled drip tube furnace, and investigated the effects of different factors on the generation of organic and inorganic components of CPM by varying the furnace wall insulation temperature, the ratio of gas supply components and the water vapor content in the flue gas. The results showed that the increase in combustion temperature (1300–1500 °C) and oxygen concentration (15–25%) reduced the total CPM generation by 9.8% and 19.98%, respectively, and the intervention of water vapor increased the ability of the whole CPM sampling device to capture ultrafine condensable particles. The generation of CPM organic components decreased with the enhancement of combustion temperature and oxygen content on combustion characteristics, and alkanes shifted to low carbon content. The amount of CPM inorganic components increased with the increase of water vapor content in the flue gas, and this change was dominated by SO42−. The above results provide a feasible idea for the next step of the precise reduction of CPM components.

Heavy metals behavior of co-combustion ash from sewage sludge and coal slime: Temperature and mixing ratio dependence, interactions and speciation

Co-combustion of municipal sludge (SS) and coal slime (CS) is an effective route to achieve the co-disposal of solid wastes. This work addresses the problem of heavy metal pollution in co-combustion ash, aiming to reveal the effect of interactions in SS-CS co-combustion on the behavior of heavy metals and the control mechanism of minerals using the inductively coupled plasma mass spectrometry (ICP-MS) technique and the Community Bureau of Reference (BCR) method. The residual rate of heavy metals in CS ash monotonically decreased with increasing combustion temperature, while the residual rate of heavy metals in SS tended to increase when it was burned at high temperatures. Increased temperature enhanced the effect of SS-CS interaction on heavy metals. The interaction significantly inhibited the volatilization of As, and the As residue of the blend containing 50% CS (5SS5CS) at 1000 °C was 14.9% higher than the theoretical value. Typical minerals in SS had significant effects on heavy metal migration in CS, and the effects of CaO and Fe2O3 on heavy metals were mainly due to chemical interactions, in which CaO fixed As in the form of Ca3(AsO4). Density functional theory calculations show that the optimal adsorption sites for both As and As2O3 on the CaO(001) surface were O-top sites, and the presence of O defect on the surface led to enhanced interaction of As2O3 with the surface. Co-combustion led to an increase in the residual fractions of heavy metals, but the exchangeable and acid soluble fraction of As in 5SS5CS was still as high as 19.3%, so the ecological impact of As should be considered in further utilization of the co-combustion ash.

A review on the performance of non-additive blended fuel (ethanol-gasoline) in spark ignition engines

The use of effective fuel additives can improve fuel and engine efficiency, but some non-additive or incompatible additives can cause engine problems. Ethanol-gasoline blends offer advantages as an alternative to regular gasoline, but high-dose blends with non-additives can lead to issues such as deposits in the engine, increased combustion temperature, emissions, and power loss. This paper reviews various fuel additives and their impacts on engine performance. Early anti-knock additive based on organometallic compounds were used in the past but faced concerns regarding cost, legislation, health effects, and environment. Ethanol and other oxygenated additives have been used to increase research octane numbers, improve combustion and fuel economy. While ethanol has benefits of improved efficiency and reduced emissions, it is not considered an additive. Therefore, finding a chemical additive that enhances fuel efficiency, combustion, and reduces greenhouse gas emissions is crucial. This research aims to explore and provide solution in this area.

Development of a Thermodynamic Model for Supercharged Diesel Engine Performance and Combustion Characteristics Study

ABSTRACT Development of a model that allows performance and combustion characteristics for a supercharged diesel engine was the main objective sought by the present work. Thus, the developed model is used, to examine the impact of start combustion, combustion duration, compression ratio, and heat flux, as well as intake conditions such as pressure and temperature, on the combustion characteristics of the supercharged diesel. For this purpose, a one zone thermodynamic prediction model was adopted with Wiebe function for combustion sub-model. The heat transfer was correlated using Woschni correlation. A numerical simulation is developed considering the crankshaft angle as the independent variable. Validation of the computational code has been favorably evaluated using our experimental data. To give a more general aspect to the developed model, experimental data found in the literature, are also used for this purpose. The results show that the addition of a turbocharger increases low-speed airflow and hence fuel consumption. In addition, an increase in intake pressure contributes to the rise of the heat flux released during combustion, while an increase in intake temperature leads to a strong increase in combustion temperature. Moreover, an increase in the compression ratio leads in a remarkable increase in all parameters simultaneously. However, maximum combustion pressure limits must not be exceeded. This is because the pressure has an effect with the engine mechanical strength.

Computational Fluid Dynamics (CFD) Assessment of the Internal Flue Gases Recirculation (IFGR) Applied to Gas Microturbine in the Context of More Hydrogen-Enriched Fuel Use

Renewable energy is a promising substitute for fossil fuels when corelated with P2G technology. To optimise P2G efficiency, there is a need to increase hydrogen fraction in the fuel stream. Simultaneously gas microturbines are widely applied in many industry sectors. These devices are often equipped with diffusion combustors. This situation was investigated in this paper. The P2G and gas microturbines may be integrated together in the future leading to the application of hydrogen-enriched fuel. Hydrogen-enriched fuel causes increase in combustion temperature and velocity. In a nonadapted combustor, these phenomena could result in an increase of NOx emissions and risk of material overheating and failure. In order to adapt the combustors for hydrogen-enriched fuel, the concept of autonomous internal flue gases recirculation (IFGR) system was applied to this issue. In this paper, the IFGR system applied to gas microturbine was studied in terms of hydrogen-enriched fuel application. The obtained exhaust gases recirculation ratios were too low to affect the combustion process as it was expected. The observed combustion modifications in the combustor were hardly linked to the air flow modification in the liner, due to IFGR system implementation. After CFD studies, the proposed IFGR system does not seem to provide the expected effects.

Three-Dimensional Numerical Modeling and Analysis for the Municipal Solid-Waste Incineration of the Grate Furnace for Particulate-Matter Generation

A 3D numerical model of the municipal solid waste incineration (MSWI) process was constructed based on a grate furnace with a daily processing capacity of 800 tons. Fluent was used for analyzing key factors affecting the concentration and diffusion level of particulate matter (PM). According to the actual MSWI plant working condition, a 3D model of the incinerator and the waste heat boiler has been constructed under benchmarks. Key factors affecting PM generation were determined by combining mechanistic knowledge and experts’ experience. They were the combustion temperature of solid phase municipal solid waste (MSW), the wall’s PM collision mode, and the second baffle length. Subsequently, the process of resolving the 3D numerical model was delineated. Then, a univariate analysis of the aforementioned 3D model was conducted for the three pivotal factors mentioned above. Conclusively, the effect of the important factors on the number of particles at the outflow of the incinerator was analyzed via orthogonal experiments to obtain the optimal combination. PM concentration initially diminished and then rose with the increased combustion temperature of the solid-phase MSW. Furthermore, a noteworthy reduction in PM concentration was observed when the second baffle length was 12.45–12.95 m. The greatest influence on the PM concentration of the outlet was posed by the wall’s PM collision mode, followed by the second baffle length. The appropriate adjustment of the combustion temperature of the solid-phase MSW, selection of wall materials, and design of the second baffle length were beneficial for diminishing PM concentration and ensuring long-term stable operation of the MSWI process. The combinative optimality of the three key factors was acquired via orthogonal experiments, which proved the subsequent optimal control of PM concentration at the outlet.

Mineral transformations and molten mechanism during combustion of biomass ash

With continuous expansion of the heat produced from biomass energy, the problems of biomass ash melting and slagging have become increasingly prominent. Studies of mineral transformations and melting behaviour in biomass ash are helpful for understanding the slagging process fully. In this paper, ash samples prepared from corn straw, sawdust and rice husk were studied with an ash melting point analyser, simultaneous thermal analyser, XRD and SEM‒EDS. The results showed that the deformation temperature (DT) of corn straw was the lowest, while that of rice husk was the highest. The variations in ash weight loss and temperatures indicated that the two main paths for ash loss were decomposition and volatilization. With increasing combustion temperature, eutectic salts with low melting points were formed in the ash, such as potassium silicate and calcium silicate, and the liquid phase and crystalline phase coexisted at 1000 °C. In this paper, the influence of different elements on the ash structure and the changes occurring in ash structure during combustion and ash melting point tests are explained by considering the silicate network structure. The ash melting behaviour observed during biomass combustion is clarified, which provides a theoretical basis for preventing biomass ash from melting and slagging.

Model-free daily inversion of NOx emissions using TROPOMI (MCMFE-NOx) and its uncertainty: Declining regulated emissions and growth of new sources

Current approaches to estimate NOx emissions fail to account for new and small sources, biomass burning, and sources which change rapidly in time, generally don't account for measurement error, and are either based on models, or do not consider wind, chemistry, and dynamical effects. This work introduces a new, model-free analytical environment that assimilates daily TROPOMI NO2 measurements in a mass-conserving manner, to invert daily NOx emissions. This is applied over a rapidly developing and energy-consuming region of Northwest China, specifically chosen due to substantial economic and population changes, new environmental policies, large use of coal, and access to independent emissions measurements for validation, making this region representative of many rapidly developing regions found across the Global South. This technique computes a net NOx emissions gain of 118% distributed in a see-saw manner: a more than doubling of emissions in cleaner regions, chemical plants, and regions thought to be emissions-free, combined with a more than halving of emissions in city centers and at well-regulated steel and powerplants. The results allow attribution of sources, with major contributing factors computed to be increased combustion temperature, atmospheric transport, and in-situ chemical processing. Furthermore, sensitivity runs that represent the range of uncertainties in the TROPOMI NO2 retrievals themselves are performed, and it is determined that the differences between the errors in TROPOMI NO2 lead to smaller errors in the emissions estimates, due to non-linear buffering built in from the physical bounds on the underlying physical and chemical driving factors. It is also observed that errors in the priori dataset contribute more than the uncertainties in the TROPOMI retrievals, opening a new door to recursive iteration between this approach and new emissions dataset development. It is hoped that these findings will drive a new look at emissions estimation and how it is related to remotely sensed measurements and associated uncertainties, especially applied to rapidly developing regions. This is especially important for understanding the loadings and impacts of short-lived climate forcers, and provides a bridge between remotely sensed data, measurement error, and models, while allowing for further improvement of identification of new, small, and rapidly changing sources.

Influence of FeCl3/Fe3(PO4)2/CaO in sludge on the migration pattern of heavy metals during coal slime combustion

The influence of minerals (FeCl3, Fe3(PO4)2, CaO) contained in SS(Sewage Sludge) on the migration and mechanism of Pb, As, Cu, Cr, Cd in CS(Coal Slime) during the co-combustion process was studied by electric heating tube furnace. Studies have shown that the interaction of minerals in SS with minerals and heavy metals in CS is an important factor affecting the migration of heavy metals in the co-combustion process of SS-CS. The heavy metals combine to form volatile heavy metal-Cl compounds. Compared with the single combustion of CS, the retention rates of Pb, As, Cu, and Cd are reduced by 89.6%, 45.1%, 70.4%, and 89.2% at 900 °C. When CS is blended with Fe3(PO4)2, Fe3(PO4)2 decomposes a large amount of Fe2O3 and P with the increase of combustion temperature to react with As, Cu, and Cr in CS, which makes the retention rate of the three heavy metals increase by 30.6%, 194.1%, and 1726.4% under the combustion condition of 900 °C compared with CS alone. When CS was burned with CaO, CaO had a competitive adsorption effect on Pb and Cd, which reduced the retention rate of Pb and Cd by 12.2% and 58.2% at 900 °C compared with CS alone. Meanwhile, CaO reacted with As, which increased the retention rate of As by 1.3% and 38.9% at 700 °C and 900 °C.The effects of Cl on the migration of Pb, Cu, Cr, and Cd were stronger than those of CaO and Fe3(PO4)2, and Fe2O3 and CaO had the greatest effect on the sequestration of As.

ENHANCE THE HEAT AND FLAME CHARACTERISTICS OF SAGO BRIQUETTES WITH AND WITHOUT ADJUSTERS

Experimental investigations were conducted to assess the impact of an adjuster on the heating efficiency and flame stability of sago waste briquettes. The adjuster was introduced to maintain a consistent burning distance, thereby enhancing the combustion heat of the fuel. Infrared thermometry was employed to monitor the temperature evolution within the briquette and the combustion load, represented by water in a pan. The findings demonstrate that adding an effective adjuster significantly improves the performance of both the briquettes and the stove, resulting in enhanced effectiveness and efficiency. This is evident from the observed increase in combustion temperature and faster boiling time of the water. The consistent burning distance ensures a stable and uniform heat supply to the briquettes, facilitating more efficient fuel utilization as all parts of the fuel can undergo complete combustion and transfer heat to the pan. Molecular analysis reveals that the stability of the burning distance weakens the Van der Waals bonds within the carbon chain, thereby increasing the reactivity of the fuel molecules. Consequently, the fuel exhibits improved heat absorption capability and becomes highly combustible.

Numerical and experimental study for a modified LPG cooking burner

A new modification of the LPG burner (NB-5) is proposed in this study. The modification combines the advantageous features that originated from three Thai commercial burners: KB-5, S-5, and EB-5. CFD techniques were used to investigate and prove the benefits each burner’s features. Combining features increase the mixing intensity and primary aeration, generates a swirling central flame, reduces heat loss, and increases secondary aeration. These enhancements cause an increase in combustion temperature and flow velocity, which significantly improves the net heat flux of the NB-5. The simulation results indicated that the NB-5 produced the highest average temperature of 929.35 K, and the highest heat flux of 58.01 kW/m2. This leads directly to an enhancement in thermal efficiency. The new modification burner (NB-5) was built and tested experimentally based on CFD results. The NB-5 burner obtained significant improvements in thermal efficiency and a reduction in CO and NOx emissions over the three commercial burners. In comparison with the traditional KB-5 burner, it was found that the NB-5, EB-5, and S-5 burners provided average energy savings of 22.37%, 8.46%, and 1.69%, respectively. This study shows the benefit of utilizing the CFD simulations to assist in designing and modifying LPG burners. This allows manufacturers to design and optimize burners more effectively at a much lower cost than the traditional water boiling tests.

A Molecular Understanding of the Flame Retardant Mechanism of Zinc Stannate/Polypropylene Composites via ReaxFF Simulations

As an important new flame retardant, zinc stannate (ZS) shows wide application prospects due to its many advantages. However, the flame retardant mechanism of composites made with polymer combined with ZS is still unclear. In particular, there is a lack of molecular level description of the micro-scale flame retardant mechanism. The combustion mechanism through molecular simulation technology has become an important research paradigm in the field of fire, which can provide new insights for the development of new materials. This work studied the flame retardant mechanism of composites consistent with polypropylene (PP) and ZS using reactive force field molecular dynamics (ReaxFF MD) simulations. A new force field incorporating Sn/Zn/C/H/O components for ZS/PP composites combustion reactions was developed. Twenty different ZS/PP composites were analyzed for their combustion reactions at various temperatures. To investigate the flame retarding mechanism of ZS in composites, the evolutions of reactants, products, and reaction intermediates at the molecular scale were collected. It was revealed that the combustion temperature controlled the degree of oxidation by regulating the consumption of molecular oxygen during PP cracking. An increased combustion temperature reduced the oxygen consumption rate and overall oxygen consumption. As the PP component of composites exceeded 56%, oxygen consumption increased. Evolutions for carbon-containing intermediates and the products in combustions of PP/ZS composites were analyzed. The small carbon-based fragments were more likely to be produced for composites with low PP contents at high temperatures. These results are beneficial to design ZS/PP composites as flame retardant materials.

Experimental and numerical study on laminar combustion characteristics of by-product hydrogen coke oven gas

The coke oven gas (COG) which mainly consists of H2, CH4 and CO is a kind of feasible by-product hydrogen that could be applied by combustion plants. This paper conducted experiments and numerical calculations to explore the combustion properties of COG. The laminar burning velocity (LBV) and flame stability of COG with different CO/CH4/H2 fractions were firstly tested. Then, based on the LBV results, a new chemical kinetic model was proposed and a mixing rule for quick estimating the LBV of COG was acquired. The influences of different COG components on LBV were obtained. The peak LBV of COG could achieve 100.2 cm/s when the highest tested hydrogen portion in COG was adopted at an equivalence ratio of 1.2. Concerning its application in real combustion plants, the exhaust emissions of CO and NO from the COG final combustion products were also detected by an emissions analyzer. The results showed that raising the hydrogen fraction in COG availed reducing CO at rich conditions through lowering the carbon fraction. The NO emission gained the peak value around the equivalence ratio of 0.9, which was found to be generally raised with the hydrogen fraction due to the increased combustion temperature.