Excess Air Coefficient Research Articles

Effects of different hole structures of pre-chamber with turbulent jet ignition on the flame propagation and lean combustion performance of a single-cylinder engine

Turbulent jet ignition is an advanced pre-chamber approach for improving combustion rates and extending lean burn limitations. The hot flows jetted from the pre-chamber through jet hole act as a distributed ignition source, igniting the mixture in the main chamber. In this paper, the effects of structures on flame propagation and engine performance are systematically studied based on an optical constant volume combustion chamber and a single cylinder engine. Firstly, the visualization of the effects of pre-chamber hole apertures and jet hole numbers on flame propagation is realized. Then, the effects of pre-chamber hole structures on engine performance are studied. The results show that small jet hole aperture could lead to flame quenching while too large aperture may cause low flame speed, both of which will decrease combustion rates. Moreover, the disturbance zone formed by cold jet flow could help maintain the jet flame speed induced by hot jet. Meanwhile, adopting multi jet hole structure could improve combustion in main chamber while modifying jet hole structure considering combustion chamber of real engine helps to achieve lower fuel consumption and emissions. TJI engine has great potential for achieving low fuel consumption and low NOx emissions without severe engine knock when the excess air coefficient ranges from 1.4 to 1.7.

Simulation of soot formation in a tractor diesel engine running on rapeseed oil methyl ether and methanol

The mass content of soot (C) in the cylinder of a tractor diesel engine (TDE) is directly affected by the temperature conditions, the excess air coefficient, and the chemical composition of the fuel. Methanol (M) does not form C particles during combustion. As the C chain in the fuel molecule increases, the propensity to C formation during combustion increases. However, in the presence of oxygen atoms in the initial fuel molecule, it significantly slows down the rate of nucleation of primary particles. During the evolution of the particle in the cylinder of a TDE when working on rapeseed oil methyl ether and methanol (ROMEM), a number of characteristic stages are identified.

Application study on plasma ignition in aeroengine strut–cavity–injector integrated afterburner

To increase the thrust-weight ratio in next-generation military aeroengines, a new integrated afterburner was designed in this study. The integrated structure of a combined strut–cavity–injector was applied to the afterburner. To improve ignition characteristics in the afterburner, a new method using a plasma jet igniter was developed and optimized for application in the integrated afterburner. The effects of traditional spark igniters and plasma jet igniters on ignition processes and ignition characteristics of afterburners were studied and compared with the proposed design. The experimental results show that the strut–cavity–injector combination can achieve stable combustion, and plasma ignition can improve ignition characteristics. Compared with conventional spark ignition, plasma ignition reduced the ignition delay time by 67 ms. Additionally, the ignition delay time was reduced by increasing the inlet velocity and reducing the excess air coefficient. This investigation provides an effective and feasible method to apply plasma ignition in aeroengine afterburners and has potential engineering applications.

Effects of light naphtha utilization on engine performance in an homogeneous charged compression ignition engine

In the current study, the effects of light naphtha utilization were experimentally investigated in a diesel engine operated with HCCI mode. Engine load, fuel consumption, in-cylinder pressure and emissions were measured in the experiments. 100 % light naphtha, 90% light naphtha +10% gasoline, 80% light naphtha +20% gasoline, 70% light naphtha +30% gasoline and 50% light naphtha +50% gasoline fuel blends were used as test fuels. Experiments were conducted between 7 and 14 ms injecton duration and 1100 and 1900 rpm engine speed with the intervals of 0.5 ms and 200 rpm respectively. The lowest fuel consumption was obtained as 584.42 g/kWh at 1500 rpm and 2.39 air excess coefficient with 90% light naphtha +10% gasoline and 12.5 ms injection duration. The highest engine torque was measured as 4.18 Nm at 1500 rpm and 2.31 air excess coefficient with 80% light naphtha +20% gasoline test fuel and 13.5 ms injection duration. Almost zero NO emission was observed for all HCCI operating conditions.

Operation strategy optimization of lean combustion using turbulent jet ignition at different engine loads

Turbulent jet ignition is an important method to achieve lean combustion in spark ignition engines by using a pre-chamber to ensure reliable ignition and a high burning rate. In this work, a TJI device is designed with additional fuel supply in the pre-chamber, the combustion characteristics of TJI are analyzed, and its operation strategy optimization over wide engine loads is performed on a single-cylinder engine. The results show that a stable combustion process with an excess air coefficient in the range of 1.0–2.2 is achieved, reducing the fuel consumption rate by up to 9.6% under a part load compared with that of the baseline engine. However, under high loads, lean combustion cannot effectively maintain the required power output, and under low loads, excessive lean combustion results in a significant reduction in the combustion efficiency. Therefore, a technical solution involving different intake strategies for different loads, including intake boost, Miller cycle, throttle adjustment, and negative valve overlap, is proposed to flexibly regulate the air/fuel ratio and maintain the in-cylinder excess air coefficient in the optimal range (1.5–2.0). The results show that the fuel consumption rate of boosted lean combustion strategy is reduced by 10–12.5% under high loads compared with that of the baseline engine. Under medium-to-low loads, a reasonable intake strategy reduces the intake air mass and helps avoid excessive lean combustion, and the fuel consumption can be reduced by more than 9.6%. The present work demonstrates the potential of TJI application to enhance the thermal efficiency through lean combustion.

Experimental observation of lean flammability limits using turbulent jet ignition with auxiliary hydrogen and methane in pre-chamber

The combustion characteristics of CH4-air mixture under the lean-fuel conditions ignited by different methods including SI, unfueled pre-chamber ignition and fueled pre-chamber ignition were investigated experimentally in a constant volume combustion chamber (CVCC) through high-speed schlieren photography. And a self-designed fueled pre-chamber turbulent jet ignition (TJI) combustion system with a single orifice configuration and small volume was employed. Results show that TJI could enhance combustion including the rapid increases of flame tip velocity and flame area growth rate, which also was manifested by increasing peak pressure and shortening time to peak. The pre-chamber ignition fueled with hydrogen can greatly extend the lean flammability limit in the main chamber and reduce the sensitivity of flame development with the excess air coefficient. However, the oscillations in flame propagation and pressure evolution due to the flame-shock interaction were obvious under the pre-chamber fueled with hydrogen. Overall, in the present work, the turbulent flame development in the main chamber depends on the flame consumption velocity in pre-chamber, orifice size of pre-chamber, and the mixture concentration in main chamber. These results are of great help to achieve the highly-efficient combustion and to shorten the combustion duration in practical SI engines.

Effect of excess air coefficient on the combustion characteristics of a multi-stage dual swirl burner

This study proposed a multi-stage dual swirl burner for heating furnaces to achieve low nitrogen oxide (NOx) emissions based on swirling combustion and staging combustion technology. The effect of excess air coefficient on combustion characteristics and NOx emissions was studied by numerical simulation. The flow field, temperature field, oxygen concentration, and the NOx concentration distributions of the burner were discussed and analysed in detail. The simulated results showed that two recirculation zones for entrained flue gas formed in the reaction process by swirl blades. Meanwhile, increasing the excess air coefficient can improve the fuel/air mixing rate and diffusion effect in the combustion chamber, reducing the maximum combustion temperature and NOx emissions. Furthermore, when the excess air coefficient increased from 1.1 to 1.4, the maximum flame temperature was reduced from 1918.3 K to 1819.6 K, and the mole fraction of NOx at the outlet decreased from 1.67×10-6 to 0.77×10-6, which revealed the potential of the burner for the clean combustion.

Rotating gliding arc discharge plasma-assisted combustion from ignition hole

Plasma-assisted combustion (PAC) is a potential method to improve the performances of aero-engine combustion chambers. A plasma-assisted combustion actuator (PACA) that operates without an additional air supply device was designed to improve the performance of the combustion chamber. To validate the feasibility of using the PACA to enhance the annular combustor performance, a plasma-assisted combustion test platform was established. It was found that the PACA could improve combustion performance in many aspects. Experimental results showed that the average outlet temperature of the combustion chamber increased from 1386 to 1652 K when the excess air coefficient (α) was 0.8 after PAC. Compared with the normal conditions, the uniformity of the outlet temperature field was improved. The combustion efficiency of the PAC could be increased by up to 10.98% under fuel-rich conditions. In addition, the lean blowout performance was improved, which meant the flame could continue burning under leaner fuel conditions. In other words, PAC greatly improved the stability of combustion.

Estimation of excess air coefficient on coal combustion processes via gauss model and artificial neural network

It is no doubt that the most important contributing cause of global efficiency of coal fired thermal systems is combustion efficiency. In this study, the relationship between the flame image obtained by a CCD camera and the excess air coefficient (λ) has been modelled. The model has been obtained with a three-stage approach: 1) Data collection and synchronization: Obtaining the flame images by means of a CCD camera mounted on a 10 cm diameter observation port, λ data has been coordinately measured and recorded by the flue gas analyzer. 2) Feature extraction: Gridding the flame image, it is divided into small pieces. The uniformity of each piece to the optimal flame image has been calculated by means of modelling with single and multivariable Gaussian, calculating of color probabilities and Gauss mixture approach. 3) Matching and testing: A multilayer artificial neural network (ANN) has been used for the matching of feature−λ.

Effect of thermal input, excess air coefficient and combustion mode on natural gas MILD combustion in industrial-scale furnace

To promote the application of MILD scheme in furnace, the present work was performed to evaluate the effect of thermal input, excess air coefficient and combustion mode on the MILD combustion at high thermal level (thermal input varies from 600 to 786 kW); meanwhile, the heat from the utilized furnace was extracted by an annular water jacket and a corundum tube was installed in the furnace tube to create the high temperature atmosphere. The results were presented on flow field using numerical simulations and on global flame signatures, temperature/species distribution and exhaust emissions using experiments. Better combustion performance of MILD mode than conventional swirling diffusion combustion mode was verified in the present work. The positive effect of increased thermal input and excess air coefficient on gas recirculation, thermal uniformity and exhaust emissions reduction was observed. In the MILD combustion regime, the switching from nonpremixed to premixed combustion resulted in lower oxygen level and reduced reaction temperature in the combustion region, also much lower NOx emissions and slightly higher CO emission were observed. At 786 kW thermal input, the reaction zone covers the entire combustion chamber; meanwhile, low NOx emission level of 32 ppm@3%O2 are achieved for premixed MILD combustion mode. The MILD regime was established for natural gas fueled furnace with colorless distributed combustion and suppressed NOx and CO emissions.

Influence of Operating Parameters on Chlorine Release and Pollutant Emission Characteristics of a 130 t/h BCFB Combustion System.

A 130 t/h biomass circulating fluidized bed (BCFB) boiler combustion system model, considering the chloride release and pollutant emissions during the biomass combustion, was established using the Modelica language. The effects of the biomass feed amount, limestone amount, excess air coefficients, and different ratios of primary and secondary air on the boiler furnace temperature and flue gas composition (O2, CO2, SO2, HCl, and KCl) were investigated. Upon the biomass feed amount step change, the variation ranges of NO and KCl concentrations were very large, which were 18.58 and 21.16% of the before step value, respectively. The step change of the limestone input had little effect on b ed temperature in the dense phase zone, but it could obviously reduce the SO2 concentration. The concentration of SO2 in flue gas decreased by 22.56% when the limestone input increased by 50%. The removal rate of SO2 gradually decreased with the increase of the limestone amount. The SO2 desulfurization rate decreased by 68.30% when the amount of limestone increased from 0.0275 to 0.0825 kg/s. More NO would be generated and KCl concentration would be significantly reduced with the increase of the excess air coefficient. When the ratio of primary and secondary air was 4:6, the NO concentration in flue gas was lower than 86.06 mg/Nm3.

Technology for Optimizing Flue Gas Pollutant Emission Reduction in Oil Field Heating Furnace Combustion

The energy consumption of the heating furnace is an important part of the energy consumption of the oilfield gathering and transportation system. The low energy efficiency of the heating furnace will directly lead to the increase of oilfield production costs. In response to the national energy-saving and emission-reduction policy, the oilfield has implemented energy-saving practices in heating furnace load adjustment, efficient combustion, excess air coefficient control, flue gas waste heat utilization, and furnace modification. It is clear that the energy efficiency of oilfield heating furnaces is still lower than foreign advanced levels. There is an urgent need for further energy conservation and efficiency enhancement. MVR low-temperature flue gas heat recovery technology, flame shape matching technology, nanofluid heat transfer enhancement technology, solar auxiliary heating technology and other new technologies that can be used for energy saving and consumption reduction of oilfield heating furnaces provide a reference for oilfield heating furnaces to tap the potential and increase efficiency.

Investigating the effect of flue gas temperature and excess air coefficient on the size distribution of condensable particulate matters

Primary particles emitted from fuel combustion mainly involve filterable particulate matter (FPM) and condensable particulate matter (CPM). Particularly, CPM has emerged as a subject for further emission control. This study investigated the effects of the sampling temperature and excess air coefficient (EAC) on the total mass, chemical speciation, and particle size distribution of CPM by integrating Electrical Low-Pressure Impactor+ (ELPI+) sampling devices with the EPA Method 202 (dry impinger method). The total mass of CPM increased with the sampling temperature and EAC. Specifically, the total concentration of CPM was 10.51–39.93 mg/m3, in which the mass fraction of organic species varied between 8.74 and 49.80%, and the organic components in CPM followed the ranking order of alkanes/alkenes (62.6–78.6%), oxygen-containing volatile organic compounds (OVOCs) (19.7–35.4%), and aromatics (5.6%). Compared with other inorganic species such as HCl and NOX, SO3 had a higher migration tendency from the flue gas to CPM. The particle size distribution suggested that heterogeneous condensation was responsible for the whole size range of particles in CPM, whereas the homogeneous condensation led to the increase of finer particles (smaller than 0.2 µm). Accordingly, adjusting the emission temperature and EAC could help to control the emission of CPM.

Theoretical and experimental investigation on the effect of CO on N migration and conversion during air-staged coal combustion

Air-staging combustion is the widely-used low-nitrogen combustion technology. In this process of NOx reduction, the role played by CO resulted from the air-staged combustion cannot be ignored. In this study, quantum chemistry method is used to investigate the effects of the CO on the NOx generation/reduction and on the char surface. Theoretical calculations indicate that CO is involved in nitrogen fixation during the migration and transformation of N. During the oxidation of N-containing char, CO increases the binding energy of N of pyridine with adjacent C atoms, which is not conducive to the N precipitation. During reduction of NOx by char, CO decreases the desorption energy barrier of N2 and promotes NO heterogeneous reduction. On the other hand, CO promotes the re-embedding of N in generated NO into the char to form char-N. XPS experiments are carried out for the coal char samples after the air-staged combustion. The experimental results show that high CO concentration is conducive to retention N. When the excess air coefficient (α) is 0.8, the increase of N-6 content is 7.2% larger than that of α = 0.9. This work discovers the nitrogen fixation of CO, enriches and expands the understanding of the role of CO.

Effects of mixture formation strategies on combustion in dual-fuel engines – a review

The article presents an overview of technical solutions for dual fuel systems used in internal combustion engines. It covers the historical and contemporary genesis of using two fuels simultaneously in the combustion process. The authors pay attention to the value of the excess air coefficient in the cylinder, as the ignitability of the fuel dose near the spark plug is a critical factor. The mixture formation of compression ignition based systems are also analyzed. The results of research on indirect and direct injection systems (and their combinations) have been presented. Research sections were separated based to the use of gasoline with other fuels or diesel oil with other fuels. It was found that the use of two fuels in different configurations of the fuel supply systems extends the conditions for the use of modern combustion systems (jet controlled compression ignition, reactivity controlled compression ignition, intelligent charge compression ignition, premixed charge compression ignition), which will enable further improvement of combustion efficiency.

Energy Efficiency Analysis of Hot Oil Heater System with Waste Heat Recovery Device

In this paper, the energy efficiency analysis of a hot oil heater system with waste heat recovery device is carried out by using the counter balance method. The influence of different excess air coefficient and different flue gas recirculation percentage on the energy efficiency is studied. Through comparative analysis, it is concluded that: as excess air coefficient increases, the exhaust gas heat loss increases, the dissipation heat loss decreases, the overall heat loss increases, and the system thermal efficiency decreases; as flue gas recirculation percentage increases, the exhaust gas heat loss increases, the dissipation heat loss decreases, the overall heat loss increases, and the system thermal efficiency decreases. These conclusions provide some reference for improving the design and operation of hot oil heater system with waste heat recovery device.

Universal Combustion Chamber for Utilization of Petroleum Gases of Different Composition and Heat Output

When developing micro-gas turbine power plants, it is necessary to have universal two-zone combustion chambers for utilizing petroleum gases of different composition and heat output at different oil deposits. In the combustion zone, the excess air ratio is selected from the interval between the lower and upper concentration limits of combustion. In the dilution zone by supplying secondary air, the working fluid with specified parameters is prepared for supply to the turbine. The excess air coefficient at the exit from the combustion chamber is determined from the energy balance equation and depends on the air and fuel gas parameters at the entrance to the combustion chamber and on the temperature of the working fluid at the entrance to the turbine. The purpose of this work is to develop recommendations for creating a universal combustion chamber for combustion of fuel gases of different composition and heat output. This goal is achieved by selecting the diameter of the chamber in order to ensure the required ratios between the average flow rate of the combustible air mixture and the rate of turbulent combustion, at which a stable position of the flame front is observed. The most noticeable result of the research conducted is substantiation of the possibility of using a universal combustion chamber with constant dimensions in utilization gas turbine installations designed for burning nonstandard fuel gases with ballasting components content up to 70%, which will reduce the time and cost of development and implementation of these installations.

Analysis of the possibility of landfill gas use as additional fuel for combustion of solid municipal waste with different moisture content

The paper suggested the calculation method of combustion for solid and gaseous fuel cofiring. The calculation is suggested to carry out for per unit of generated during combustion total capacity instead of per unit of weight or volume of fuel. This method was tested during combustion parameters examination at cofiring of solid municipal waste, which is the main fuel, and landfill gas (biogas) which is the additional fuel for thermal mode stabilization. The calculation has been conducted for waste with the moisture content of 50%, 30% и 10%, which are solid fuel, methane, as a reference fuel, common biogas with a methane content of 60%, and biogas with a low methane content of 35%. It was established that additional input of biogas is effective for the combustion of unprepared waste with high moisture content, moreover, it is possible to use common biogas as well as biogas with low methane content. The required combustion product temperature (900-1000°C) for unprepared waste can be achieved at the excess air coefficient of 116 or more. In summary, solid fuel and biogas cofiring allows operative control of the combustion process and sustain combustion product temperature and heat output of units at a constant level. The combustion process regulation should be based on the given temperature of combustion products by changing two parameters: landfill gas flow rate and flow rate of air supplied for combustion.

Underground coal fire emission of spontaneous combustion, Sandaoba coalfield in Xinjiang, China: Investigation and analysis.

Long-term spontaneous combustion of coal has caused serious ecological and environmental problems. Only in recent years has it received growing popularity to undertake relevant researches. In order to study the impact of combustion by-products on atmosphere in the Sandaoba fire field, Xinjiang, a region-scale field survey was firstly conducted to investigate the gaseous-solid emissions in separated fire sections. The evaluation method and model have been proposed to describe the underground combustion and the related air pollution. Every year, the total estimates of the gaseous emission are approximately 4030t of CO2, 113.6t of SO2 and 57.3t of CO. The emission pollution varies considerably from regions, and is substantially attenuated with the advancement of fire control. Principal component analysis (PCA) refines the thermophysical parameters into three attributions: the intrinsic thermophysical property, atmospheric dynamics, and combustion degree. PCA score distribution shows that thermophysical parameter is dominated by the combustion condition at severely polluted areas. Factor Analysis is used to extract four contaminant indicators, which suggests the local air suffers sulfur oxides pollution the most. The air quality index of the eight study sections calculated are all below 60, ranging from 24 to 58. It indicates that coal fire air pollution is in the medium-to-severe stage. By Canonical Correlation Analysis, it is noted that thermophysical indicator performs outstanding explanatory for contaminant variates. On the whole, the higher the level of thermophysical properties in the fire area, the greater the intensity of pollutant emission. Underground coalfield fire is dominated by smoldering, and the overall combustion efficiency is lower than 0.8 which generally declines as the excess air coefficient increasing.

Study on the mixing characteristics of circular transverse jet in crossflow

With the development of combustion technology, transverse jets have received extensive attention, especially as the method of fuel-air mixing and flame stabilization. This paper studies circular transverse jet in crossflow and develops a new kind of transverse jet device. By injecting gas fuel into crossflow through a Laval-shaped annular gap, the device generates a circular aerodynamic barrier and forms a recirculation zone downstream the jet to obtain the flame stabilization. In this paper, numerical simulations and experimental methods are used to study the mixing characteristics of the circular transverse gas fuel jet in crossflow. The numerical simulations show that the circular transverse jet mixes quickly with crossflow in its near field region, and forms a well-mixed mixture in the recirculation zone. In the experiment, the mixing coefficient and the gas composition in the burning region were quantitatively measured. Results show that the measured excess air coefficient at each measuring point in the back half of the recirculation zone is roughly uniform and the local combustion efficiency at the end of recirculation zone approaches to 99% at atmospheric pressure and normal temperature conditions. This provides reference and basis for the research and design of circular transverse jet as fuel-air mixer and flame stabilizer.