Excess Air Ratio Research Articles

The Impact of Hydrogen Admixture into Natural Gas on Residential and Commercial Gas Appliances

Hydrogen as a carbon-free fuel is commonly expected to play a major role in future energy supply, e.g., as an admixture gas in natural gas grids. Which impacts on residential and commercial gas appliances can be expected due to the significantly different physical and chemical properties of hydrogen-enriched natural gas? This paper analyses and discusses blends of hydrogen and natural gas from the perspective of combustion science. The admixture of hydrogen into natural gas changes the properties of the fuel gas. Depending on the combustion system, burner design and other boundary conditions, these changes may cause higher combustion temperatures and laminar combustion velocities, while changing flame positions and shapes are also to be expected. For appliances that are designed for natural gas, these effects may cause risk of flashback, reduced operational safety, material deterioration, higher nitrogen oxides emissions (NOx), and efficiency losses. Theoretical considerations and first measurements indicate that the effects of hydrogen admixture on combustion temperatures and the laminar combustion velocities are often largely mitigated by a shift towards higher air excess ratios in the absence of combustion control systems, but also that common combustion control technologies may be unable to react properly to the presence of hydrogen in the fuel.

A novel vortex combustion device: Experiments and numerical simulations with emphasis on the combustion process and NOx emissions

Experimental and numerical studies of combustion process in a vortex flow device have been developed. The modelling part of the study has been performed by means of ANSYS Fluent package. Fuel droplet trajectories and the flow pattern on their motions have been modeled by the function ?injection?. The combustion process utilized the k-? turbulence model. A special trend on the effect of the vortex generator blade orientation on the gross process has been developed. It has been established that optimal process performance (high air excess ratio and low NOx emissions) could be attained with an angle of the vortex generator blade orientation, especially with respect to the minimization of NOx emissions.

Effect of Excessive Air Ratio on Hydrogen-Fueled Spark Ignition Engine with High Compression Ratio Using Direct Injection System Toward Higher Brake Power and Thermal Efficiency

Effect of Excessive Air Ratio on Hydrogen-Fueled Spark Ignition Engine with High Compression Ratio Using Direct Injection System Toward Higher Brake Power and Thermal Efficiency

Effects of Excess Air Ratio and Spark Timing on Performance and Gaseous Pollutant Emissions of Fuel Reforming Natural Gas Engine

Effects of Excess Air Ratio and Spark Timing on Performance and Gaseous Pollutant Emissions of Fuel Reforming Natural Gas Engine

Influence of Nitric Oxide and Other Factors on Acoustic Knock Onset for Lean DISI Engine Operation

Spark-ignition (SI) engine efficiency can be increased by operating lean and with increased compression ratio (CR), but both of these measures tend to increase the propensity for undesirable acoustic knock generation. It is well known that increased CR makes the engine more prone to knock due to increased combustion pressures and temperatures, but it may be less well understood why lean operation would exacerbate knock generation. For typical gasoline-range fuels, the laminar flame speed becomes very low (roughly only 20% compared to stoichiometric conditions) for an air-excess ratio (λ) of 2. Indirectly, this exacerbates the knock challenge in two ways; a) it may necessitate operation with a combustion phasing near Top Dead Center (TDC) to complete the combustion before expansion cooling occurs, b) it increases cycle-to-cycle variations, making it more challenging to operate near the knock limits. In addition, the high intake pressure required for lean operation (nearly a factor of two higher for λ = 2 compared to λ = 1) increases the oxygen concentration which promotes end-gas autoignition and knock generation.

Hybrid draft direct-combustion with secondary air jets in cross-flow for reducing CO and PM2.5 emissions in biomass cookstoves

CO and PM2.5 emissions in household biomass cook stoves are affecting billions of lives and millions are suffering from related fatal diseases. An air supply configuration was proposed and tested experimentally to reduce emissions from a prototype biomass cook stove. The hybrid draft staged combustion with primary air by natural draft and preheated secondary air by forced draft was tested in a wood-burning cook stove. The secondary air jets were arranged in cross-flow to the primary flue. A mathematical model to predict the performance of a hybrid draft cook stove was developed and validated experimentally. The effect of different parameters such as excess air ratio (λ), Primary air to secondary air ratio (PA/SA) and Momentum flux ratio (J) was investigated. All three variables have shown a profound effect on CO and PM2.5 emissions. Optimum values of these parameters for minimum CO emissions were identified as λ = 3, PA/SA = 1.9 and J = 94 respectively. However, the mechanism of CO and PM2.5 destruction was found to be different and no such optimum was identified for PM2.5 emissions. The hybrid draft configuration resulted in a significant reduction of CO and PM2.5 emissions, achieving emissions performance corresponding to the Tier 4 level.

Effects of various discharge strategies on ignition and combustion of lean natural gas mixture under the static and turbulent conditions

Diluted combustion can promote thermal efficiency and decrease NOx emissions for natural gas engines, but also presents high cycle-by-cycle variations. Enhancing the in-cylinder flow field is beneficial for the combustion stability, but brings challenges for the stable ignition. Therefore, advanced ignition strategies are critical for extending the diluted limit. In this work, by using the constant volume combustion vessel, rapid compression and expansion machine, and multi-cylinder natural gas engine, the lean methane/air or natural gas/air mixtures under the static and turbulent conditions are established to compare various discharge strategies. The comparisons include: (1) different discharge energies, (2) power and duration enhancements with similar discharge energies, (3) the continuous discharge and multi-strike. For the static condition, once the flame kernel can be successfully established, enhancing discharge power or duration has few effects on ignition. The continuous discharge and multi-strike show no clear differences. At the lean limit, the multi-strike shows better performance than the continuous discharge. For the turbulent condition, increasing discharge energy can promote the initial flame propagation. When the flow velocity around the spark plug increases to some extent, enhancing the discharge duration shows better performance than enhancing the discharge power. Moreover, the continuous discharge is better for the ignition processes than the multi-strike. For the multi-cylinder engine tests, compared to the single strike of one coil, the continuous discharge and multi-strike extend the lean limit from the excess air ratio of 1.51 to 1.61. The multi-strike is more beneficial for the combustion phase stability than the continuous discharge.

HARDWARE AND SOFTWARE OF AUTOMATIC CONTROL SYSTEM OF FUEL COMBUSTION PROCESS IN LOW AND MEDIUM POWER BOILERS. PART 2. ALGORITHMIC SOFTWARE

The efficiency of the functioning of boiler units depends on the availability of reliable information on the progress of technological processes. The lack of control and measuring systems for the composition of the exhaust gases leads to low efficiency of the boiler unit, in particular, due to poor-quality fuel combustion. Therefore, in modern operating conditions of boiler units, it is relevant to develop technological solutions focused on finding and minimizing the causes and mechanisms of the formation of harmful substances in exhaust gases.
 Due to the fact that replacement of outdated boiler units with new ones requires significant capital investments, a promising direction is the modernization of existing boiler units. It is a low-cost and efficient way of rational use of fuel while simultaneously reducing the level of harmful substances in exhaust gases. It remains relevant to ensure the functioning of the control systems for the composition of the air-fuel mixture (AFM) with a given speed and high reliability of maintaining the excess air ratio (EAR) at the stoichiometric level.
 In the article the high-quality algorithm is proposed for the operation of an automatic control system for the combustion of fuel in boilers of medium and low power by regulating the ratio of the components of the AFM for the burner with feedback according to the signals of the oxygen sensor. The algorithms for the operation of the frequency regulator of the ratio of the components of the AFM in various operating modes are considered. The developed algorithms allowed maintaining the stoichiometric air-fuel ratio in the boiler furnace, reducing the level of toxic emissions into the atmosphere and increasing the boiler efficiency by optimizing the fuel combustion process. The AFM ratio programmer is made in the LM Programmer technical programming environment and works with Windows operating systems (XP, Vista, 7, 8, 10) and oxygen sensors manufactured by Bosch. The visualization of the control process of the fuel combustion process is made in the technical programming environment LogWorks 3 and operates in the environment of Windows operating systems.

Analysis of the effect of syngas substitution of diesel on the Heat Release Rate and combustion behaviour of Diesel-Syngas dual fuel engine

The Heat Release Rate (HRR) model of ICEs is known to be most sensitive to the ratio of specific heats, γ, which is known to be depended on temperature and the excess air ratio, λ. The HRR of ICEs cannot be measured directly. As such, accurate HRR models, as well as accurate expressions of γ and λ are required to model the HRR behaviour of ICEs mathematically. In this work, an improved HRR model based on γ(T,λ) was used to investigate the effect of syngas substitution of diesel at constant energy on the Heat Release Rate (HRR) behaviour and the combustion phasing in a 5.7 kW engine out and 4.3 kW generator output, single cylinder, dual fuel, Reactivity Controlled Compression Ignition (RCCI) mode CI engine. An improved global excess air ratio, λg was used in the HRR analysis of the dual fuel engine. The engine was run on 10, 25, and 45% syngas substitution (by energy) and at 1, 2, 3, and 4 kW loads (generator output) for each syngas substitution. The improved dual fuel engine HRR model was validated by comparing the measured fuel consumption by energy (input energy) per (thermodynamic) cycle to the predicted fuel consumption by energy per cycle for the tested conditions. The values of the fuel consumption predicted by the Leeds HRR model were also compared to the predictions of the HRR models that were based on γ(T). The overall average error in the predictions of the fuel input energy by the Leeds HRR model was 2.41% with a standard deviation of 1.65. The overall average errors in the other models ranged from 6.26 to 8.29%. The SoC, MFB50, PP, and PHRR occurred later for the diesel-syngas dual fuels compared to baseline diesel due to increased ignition delay as the fraction of syngas was increased. The current work showed that the use of diesel-syngas dual fuel in diesel engines in Nigeria (a developing country) can potentially reduce CO2 emissions by up to ∼0.26 million tonnes.

Estimates of the air-fuel ratio at the time of ignition in a pre-chamber using a narrow throat geometry

The benefits of pre-chamber combustion (PCC), such as improved engine efficiency and reduced NOx emissions, are primarily observed when operating at lean conditions with an active pre-chamber, where auxiliary fuel is supplied directly to the pre-chamber. Estimating the pre-chamber excess air ratio (λ) is important in the active pre-chamber concept to gain insights into the pre-chamber combustion phenomenon. Experimental investigations were performed using a narrow-throat pre-chamber at global-λ 1.6, 1.8, and 2.0. The fraction of fuel energy injected in the pre-chamber over the total fuel energy was fixed at 3%, 7%, and 13% for each global-λ. The mixture formation process inside the pre-chamber is first simulated using the 1-D simulation software GT-Power to analyze the pre-chamber λ at the ignition timing. However, the 1-D results were unable to reproduce the experimental observations on the pre-chamber pressure buildup accurately. Upon simulating the same conditions using the 3-D CFD software CONVERGE, the pre-chamber λ estimated from the CFD model is well-correlated to the experimental data. The CFD results indicate that the amount of fuel trapped in the pre-chamber at the inlet valve closing timing is over-predicted by the 1-D simulations. A correlation between the injected and the trapped fuel in the pre-chamber is proposed by theoretical scavenging models and applied to the 1-D simulation results to improve pre-chamber λ prediction accuracy.

Computational optimization of a hydrogen direct-injection compression-ignition engine for jet mixing dominated nonpremixed combustion

Hydrogen (H2) nonpremixed combustion has been showcased as a potentially viable and preferable strategy for direct-injection compression-ignition (DICI) engines for its ability to deliver high heat release rates and low heat transfer losses, in addition to potentially zero CO2 emissions. However, this concept requires a different optimization strategy compared to conventional diesel engines, prioritizing a combustion mode dominated by free turbulent jet mixing. In the present work, this optimization strategy is realized and studied computationally using the CONVERGE CFD solver. It involves adopting wide piston bowl designs with shapes adapted to the H2 jets, altered injector umbrella angle, and an increased number of nozzle orifices with either smaller orifice diameter or reduced injection pressure to maintain constant injector flow rate capacity. This work shows that these modifications are effective at maximizing free-jet mixing, thus enabling more favorable heat release profiles, reducing wall heat transfer by 35%, and improving indicated efficiency by 2.2 percentage points. However, they also caused elevated incomplete combustion losses at low excess air ratios, which may be eliminated by implementing a moderate swirl, small post-injections, and further optimized jet momentum and piston design. Noise emissions with the optimized DICI H2 combustion are shown to be comparable to those from conventional diesel engines. Finally, it is demonstrated that modern engine concepts, such as the double compression-expansion engine, may achieve around 56% brake thermal efficiency with the DICI H2 combustion, which is 1.1 percentage point higher than with diesel fuel. Thus, this work contributes to the knowledge base required for future improvements in H2 engine efficiency.

Structured composite catalyst Pd/Ce0.75Zr0.25O2-x/θ-Al2O3/FeCrAlloy for complete oxidation of methane

Structured catalyst Pd/Ce0.75Zr0.25O2-x/Al2O3/FeCrAl was prepared via multistep solution synthesis. The prepared catalyst was characterized by X-Ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), the specific surface area was measured by N2 adsorption (BET). The catalyst was tested in the deep oxidation of methane at excess air ratio ranging from 1.05 to 2. During the tests, the catalyst ensured complete methane conversion and zero CO content in the exhaust gases.

A new software program for monitoring the energy distribution in a thermal waste treatment plant system

The paper presents a novel system for monitoring the operation of a thermal waste treatment plant. The computer program is based on measurements of pressure, temperature, and mass flow rate of the working medium. The boiler efficiency is calculated using an indirect method. Thermal online calculations of the boiler combustion chamber make it possible to determine the heat flow rate to the evaporator. Based on the energy balance of the boiler evaporator, the superheated steam mass flow rate is determined, taking into account the mass flow rates of water injected into steam attemperators. By comparing the calculated and measured value of steam mass flow rate, the calorific value of the fuel fed is determined. The developed system enables monitoring of energy flow rates in individual elements of the power unit, taking into account losses in the boiler and turbine condenser. The following parameters are determined online, the efficiency of the boiler and the entire incinerator, heat losses in the boiler and the turbine condenser, as well as the heat flow rate, supplied to the municipal district heating system. By monitoring the plant operation, it is possible to adjust online the optimum excess air ratio.

Experimental investigation on NO emission and burnout characteristics of high-temperature char under the improved preheating combustion technology

In order to avoid the formation of NO from the nitrogen-containing pyrolysis components in the main combustion zone under preheating combustion technology, an improved preheating combustion technology was proposed. A two-stage drop-tube furnace was built to study the NO emission and combustion characteristics of high-temperature char (HTC) under the improved preheating combustion technology. The char was first heated to the initial pyrolysis temperature(600℃,800℃ and 1000℃) in the upper furnace under the atmosphere of nitrogen, before being burned in the second furnace. The influence of important operating parameters such as HTC temperature(600℃,800℃ and 1000℃), combustion temperature (1200℃,1300℃ and 1400℃)and excess air ratio (0.6 ∼ 1.4)were analyzed. The results show that raising the HTC temperature helps to reduce NO emissions. The maximum NO reduction efficiency is 21.1 % when the excess air ratio(α) = 1.0, which differs from the reported literature results of room-temperature char (RTC). In HTC, there is no absolute correlation observed between the BET area and NO reduction. The release of C and N is altered by pre-ignition of char at HTC; additionally, the evolution of nitrogen functional groups during the pyrolysis process is more key influencing factors. The stoichiometric ratio has a considerable influence on the effects of combustion temperature on NO emission. When there is a lack of oxygen, NOx emissions decrease as the temperature rises, whereas under oxygen-rich situations the converse is true. With the increase in HTC temperature from 600 °C to 1000 °C, the critical excess air ratio steadily increases from 0.75 to 0.85. The carbon concentration of fly ash can be reduced by increasing both the HTC and the combustion temperature. The largest reduction in carbon content in fly ash is 28.6 % at α = 1.0.

Combustion of kerosene sprayed with a jet of superheated steam

In the present work, the effect of forced air supply on the combustion process of liquid hydrocarbons was studied using diesel fuel as an example. The content of the flame intermediate components and temperature distribution along the flame symmetry axis were studied using an atmospheric burner in which liquid fuel is atomized by a steam jet. The gas composition of equilibrium combustion products and heat release were also investigated. The influence of the excess air ratio in the combustion chamber of the burner device on the thermal and environmental characteristics was shown.

Engine Performances of Lean Iso-Octane Mixtures in a Glow Plug Heated Sub-Chamber SI Engine

Due to the difficulty to directly study ammonia, the present work investigated the engine performance of lean iso-octane/air mixture to approximate ammonia combustion behaviour. The study was conducted using a single cylinder modified diesel engine that features a spark plug and glow plug in the sub-chamber. The investigations varied the engine speeds (1000 and 1500 RPM), glow plug voltages (6 and 10 volts), excess air ratios (1.4 to 1.8), and ignition timings (-2 to -5 °BTDC). The results suggested improved engine performances with a lower excess ratio and higher glow plug voltage due to more complete and stable combustion. By increasing the engine speed, the lean burn limit was extended and improved the engine performances. Because of the sub-chamber feature, delaying the ignition timing improved the engine performances. A larger excess air ratio was found to increase the sensitivity of the engine performances with the ignition timing. The brake mean effective pressure for all conditions has a coefficient of variation of less than 7%, indicating stable combustion. The results suggested that the current setup can be used to investigate ammonia blended fuel and direct ammonia combustion in future works.

Удосконалення управління процесом горіння палива в суднових котлах

Annotation – The article discusses the issues of increasing the efficiency of the combustion of liquid fuel in the furnaces of ship steam boilers using the proposed neural network system for automatic correction of the excess air coefficient. It is indicated that modern systems for automatic flame detection have a number of disadvantages, in particular, low sensitivity to extraneous illumination, etc. hot air or flue gases on the walls of the boiler furnace. Such pulsations reduce the reliability of the combustion monitoring and control system. Therefore, the task of developing and introducing on ships new, economically inexpensive and effective methods of effective control and management of the fuel combustion process in ship boilers using modern means of intelligent control is urgent. On the basis of the experiments carried out on a Mitsubishi MV 50 marine steam boiler and the collected experimental data, the values for training the neural network system of the air flow correction process, taking into account the color of the burner flame and the color of the flue gases, were obtained. The use of a trained neural network in the control system, taking into account the fuzzy expert system for monitoring the color of the flame and smoke, makes it possible to achieve the best excess air ratio depending on the steam load of the SEP units. Simulation modeling of the proposed neural system was carried out in a specialized program Matlab (Neural Networks Toolbox). The simulation results showed that the use of a neural network control system for the combustion of liquid fuel, using the example of a marine boiler, allows maintaining a given thermal regime over the entire range of steam load of the power plant units, and also allows timely correction of the excess air ratio, i.e. avoid excessive consumption of fuel.

Comparison and implementation of machine learning models for predicting the combustion phases of hydrogen-enriched Wankel rotary engines

Combustion phases, such as the development period (CA0-10) and flame propagation period (CA10-90), are the critical parameters for hydrogen-enriched Wankel rotary engines. An accurate simulation model and a suitable engine management system are required to control combustion phases. In this paper, five machine learning (ML) models, including the linear regression (LR), regression tree (TR), ensembles of trees (EnTR), support vector machine (SVM), and Gaussian process regression (GPR), are initially applied to predict combustion phases. Experiments were performed with variations of the main fuel types (gasoline and n-butanol), loads (idle and part load), ignition timing, hydrogen volume fraction, and excess air ratio. The sample data were divided into training and testing data set, and the normalization method, 5-fold cross-validation, and Bayesian optimization algorithm were used for data processing and model optimization. Among five ML models, the training speed of the LR model was the fastest; the generalization ability of the TR model was the worst. The minimum leaf size of the TR model significantly influenced regression and generalization ability. On this basis, the EnTR model improved the regression ability, but required more training time. The GPR model showed the best generalization ability among the above model, while SVM performed well in a certain data set. For CA0-10, the coefficient of determination (R2) of the best LR, TR, EnTR, SVM and GPR models was 0.9910, 0.9912, 0.9985, 0.9984 and 0.9994, respectively; for CA10-90, the R2 was 0.9348, 0.8974, 0.9873, 0.9916 and 0.9975, respectively. It is highly recommended to apply the GPR model to the combustion phases prediction and control system modeling.

Optimization and Analysis of Design Parameters, Excess Air Ratio, and Coal Consumption in the Supercritical 660 MW Power Plant Performance using Artificial Neural Network

Optimization and Analysis of Design Parameters, Excess Air Ratio, and Coal Consumption in the Supercritical 660 MW Power Plant Performance using Artificial Neural Network

Combustion performance of a two-layer porous inert medium burner at different low powers

Abstract- Improving the performance of modern combustion systems in many engineering application fields has great favorable impact on the energy conservation and global environmental pollution. This can be done through developing state of the art techniques for this purpose. One of them is the combustion within porous media burners. The two-layer porous inert medium burner (PIM) has significant merits such as high burning ratios, very low emission levels, high levels of the combustion stability, and operation at ultra-lean excess air ratios. The main work is to examine a new PIM design has a square cross-section area with two porous layers namely, aluminum oxide as the subcritical layer (quenching layer) and silicon carbide (SiC) as the supercritical layer each of 130 x 130 mm. The burner performance was estimated by recording the axial temperature profile at the selected operated thermal powers. The extent of the combustion stability limits between the flashback limit to the blow-off limit was improved. The excess air ratios of the stability limits at powers 0.7, 1.5, 2.5 kW were deduced to be (1.9-2.8), (1.8-2.6), and (1.5-2.4), respectively. The exhaust emissions were measured by a gas analyzer. The results revealed low levels of the CO emissions and decreased with increasing the operated thermal power. The CO ppm recorded the order of hundreds at powers 0.7 and 1.5 kW but reached the order of tens at power 2.5 kW. The NOx emission recorded ultra-low levels and increase with increasing the thermal power but not exceed 2 ppm.