Excess Air Ratio Research Articles

Design, energy efficiency, and CO2 emissions analysis of a power generation process of coking dry gas reforming coupled with solid oxide fuel cell and organic Rankine cycle

Coking dry gas is a kind of refinery dry gas, which is rich in H2 and light hydrocarbon resources, but it’s often used as fuel, resulting in inefficient utilization of dry gas resources and a large amount of air pollutants emissions. Solid oxide fuel cell can efficiently convert the chemical energy of hydrogen into electricity. Therefore, this work establishes a model of a power generation process of coking dry gas reforming coupled with the solid oxide fuel cell and organic Rankine cycle. Process simulation is used to analyze the influence of key operating parameters on the system output performance. The obtained results indicate that the net electrical efficiency of the proposed system is increased from 45.45 % of the coking dry gas direct combustion for power generation system to 56.89 %. In terms of environmental impact, the CO2 emissions of the new system is 373.31 kg/MWh, 20.12 % lower than that of the direct combustion process. Besides, the effect of air excess ratio on system performance is evaluated and the net electrical efficiency of the proposed system increases to 63.73 % as the air excess ratio decreases from 2.0 to 1.1. The above results show that the proposed hybrid power system can provide an effective way for efficient and clean utilization of coking dry gas.

The effect of hydrogen additives on fuel consumption and hydrocarbon emissions in gasoline fuelled Wankel rotary engine

Experimental data for Wankel rotary engine performance on hydrogen blends with hydrocarbon fuel is presented. Researches are performed on partial loads and idle. Hydrogen mass fraction additions to the fuel mixture didn’t exceed at partial loads 5% and idle mode 9%. The excess air ratio was stoichiometric. It is shown that for partial loads (20% of full load) and engine speed 2000 rotary per minute 5% hydrogen addition yields to 4.2% decrease of brake specific fuel consumption (hydrogen consumption was converted to gasoline consumption computed proportionally to their combustion heats ratio). Amount of unburned hydrocarbons for the conditions mentioned reduces in a factor of 1.8 and emission of carbon monoxide in a factor of 2.3. Hydrogen addition notably increase effective leaning limit, thus for idle mode tests Wankel rotary engine showed steady performance even for excess air ratio 1.16, while in the absence of addition instability displayed itself for excess air ratio exceeding 0.95.

Математическое моделирование детонации в двигателях с искровым зажиганием

Adjusting engines with a high compression ratio operating on traditional gasoline grades is simplified by the application of mathematical models of the operating cycle that predict the self-ignition of the fuel-air mixture. Mathematical simulation of detonation based on the analysis of a computational model of the thermodynamic cycle of a spark-ignited piston engine, which is close to the actual cycle, can be used to determine with sufficient accuracy in time the change in the current cycle pressure and the temperature of the unburned part of the charge. The model takes into account the heat exchange between the combustion zones of the charge and the walls of the combustion chamber. The onset of detonation is associated with the point of self-ignition of the unburned part of the charge and is determined depending on the thermodynamic parameters of the unburned part of the charge and the kinetic mechanism of pre-ignition chemical processes in the fuel-air mixture. It is shown that mathematical modeling of the self-ignition of the unburned part of the charge in a spark-ignition piston-type internal combustion engine can be performed in the same way as the modeling of self-ignition of the fuel-air mixture under continuing compression in units with a free-sliding piston. The accuracy of the self-ignition calculation using the cycle model has been experimentally verified by indicating it at different speeds and at different excess air and charge volume ratios, as well as different mixture temperatures in the intake manifold. The simulation results were verified experimentally on isooctane and octane blends (60% isooctane) and on commercial gasoline. It was found that at low compression ratios (up to 5 to 7), the low-temperature mechanism of self-ignition prevails, while at higher compression ratios, the high-temperature mechanism prevails. The detonation limit of an internal combustion engine can be determined by the point of self-ignition (explosion) in the unburned part of the charge at a residual cycle fraction of unburned fuel of at least 10%.

Thermal management of solid oxide fuel cells with liquid metal

Effective thermal management of SOFCs is necessary for their long life and highly efficient operation, while the conventional method through excess air cooling is limited due to the inherently low thermal conductivity and capacity of air. In this study, a novel temperature control strategy is proposed by using liquid metal as a new kind of coolant that can work in both the stable operation stage and start-stop stage of an SOFC stack. A three-dimensional model is developed considering chemical/electrochemical reactions, mass, momentum and heat transfer processes to assess the effect of liquid metal cooling. The simulation results show that liquid metal has an excellent ability to improve the temperature uniformity and electric performance of the cell unit. The temperature difference of the cell unit cooled by air cooling is 60 K, which can be decreased to 15 K with liquid tin cooling. Furthermore, inlet air has little effect on the performance of the cell unit when liquid metal is chosen as coolant. The pumping powers of the air and liquid metal are compared at different excess air ratios and inlet velocities of liquid metal. The total pumping power consumption could be dramatically decreased when liquid metal is utilized as the coolant. Furthermore, the variations in the conductivity, heat capacity and convective resistance at different liquid metal inlet velocities are discussed.

Influence of primary reference fuels on isobaric combustion in a heavy-duty optical diesel engine

Previous studies on isobaric combustion achieved using n-heptane/diesel fuel have shown the potential for higher engine efficiency compared to conventional diesel combustion. This was due to the lower heat transfer losses thanks to the lower rate of heat release and in-cylinder temperature, along with exhaust losses when coupled with a split cycle concept. However, the close-coupled injections implemented in isobaric combustion led to spray-flame interactions resulting in higher soot emissions. Potential ways to reduce the soot emissions are either employing multiple injectors, which helps to avoid the spray-flame interaction, or, as investigated in this study, burning higher octane or low reactivity fuels to increase the pre-combustion mixing time. This study investigated the effect of fuels on isobaric combustion in both all-metal and optical configurations of a heavy-duty optical diesel engine. Isobaric combustion was achieved using multiple injections from a single central injector; the engine performance, exhaust emissions, particle size distributions, and in-cylinder flame and soot distributions have been compared for three different primary reference fuels (PRFs) i.e., PRF0 (n-heptane), PRF50 (volumetric mixture of 50 % n-heptane and 50 % isooctane), and PRF100 (isooctane). High-speed combustion luminosity, OH* chemiluminescence, and planar laser-induced incandescence of soot (soot-PLII) have been performed at a fixed air-excess ratio and peak cylinder pressure for all three fuels. The results demonstrated that PRF100 being the least reactive fuel out of the three tested fuels led to longer ignition delay resulting in more premixed combustion. PRF100 resulted in 4 % higher gross indicated efficiency, 48.8 % lower heat transfer losses, 17.6 % lower exhaust losses, and 87.4 % lower soot emission than PRF0; however, isobaric combustion using PRF100 was difficult to achieve. PRF50 is a promising candidate for isobaric combustion with slightly lower gross indicated efficiency than PRF100 but lower uHC/CO/soot/NOx emissions. Overall, PDI of Soot-PLII indicates initial soot is formed near the nozzle holes, and grow along the flame direction, until they hit the bowl-wall and flow along it due to flame-wall interactions. The soot PDI values are comparatively lower as we move axially away from the top of the cylinder.

Experimental investigation of the effect of supply airflow position, excess air ratio and thermal power input at burner pot on the thermal and emission performances in a pellet stove

In this study, the effect of burner pot design by changing supply airflow position at three different excess air ratios and three different thermal power inputs on thermal performance and emissions at pellet stove experimentally researched. In this context, burner pots with four different supply airflow distances of 15, 30, 60 and 75 mm above the burner pot base were designed, manufactured and performance tests were made. Considering all excess air conditions, at 6 kW, the efficiencies in the 75 mm distance showed the worst performance; at 9 kW, the 30 and 60 mm distances were better, and at 12 kW, the 30 mm distance reached the highest efficiency with the value of 80.80–89.48%. The highest CO emissions obtained at the supply airflow distance of 15 mm and λ = 1.7 conditions at 12 kW with the value of 2982 ppm. It is hard to make a general inference on the thermal and emission performances to propose optimal conditions. However, it can be said that optimal conditions for the use of the stove produce high efficiencies with low polluting emissions were in the range of 6–9 kW thermal power, λ = 1.7–2.2 excess air ratios and 30 mm supply airflow distance.

Flame detection via active plasma probing

Combustion diagnostics of highly diluted air fuel mixtures are of great importance for reducing the carbon footprint of various types of combustion systems. Flame detection techniques, such as ion sensing and optical diagnostics, have been reported for diagnosing combustion status. In this paper, a flame front detection technique based on active plasma probing is introduced and analyzed. Unlike the conventional ion sensing used in internal combustion engines, a separate electrode gap is used to detect the flame front arrival. Further, the voltage potential across the electrodes of the spark plug probe is modulated actively to be slightly below the breakdown threshold prior to flame arrival. At the arrival of the flame front, the ions in the flame tend to decrease the breakdown voltage threshold and trigger a breakdown event. An optically accessible constant volume combustion vessel is employed to investigate the efficacy of such active plasma probing for the detection of the flame front under quiescent and flow conditions. Three types of fuels are used in the tests, including methane, propane, and DME, with an air fuel ratio sweep (from stoichiometric to extremely lean) for each fuel. Efforts are made to characterize the probing criteria of minimum, yet adequate voltage to succeed in the detection of the arrival and departure of the flame front most sensitively and reliably, for all three types of fuels under various mixture strengths. For comparison, conventional ion current measurements are conducted under identical background conditions to benchmark the efficacy of flame detection. Results show that the active plasma probing can promptly detect the arrival and departure of the flame front, robustly regardless of the fuel type and excess air ratios. The precise control of the detecting voltage is key for reliable flame detection with high sensitivity.

The Characteristics of a Novel After-Burner Used for Metal-Supported Planar SOFC System

Abstract A novel after-burner used for the heat-up and normal operating conditions of a metal-supported planar solid oxide fuel cell (SOFC) system, is designed and experimentally studied in this paper. The burner construction and the calculation of maximum burner power are shown in detail. Meanwhile, its static characteristics are researched through the influence of excess air ratio (ER), air velocity, inlet air temperature, and fuel utilization rate (Uf) and its transient characteristics are researched through the processes of burner start-up, burner operating state switch, and stack start-up. The results suggest that the best ER value gets larger with the increased burner power. The air velocity is better controlled within 3 m/s to prevent the influence of a lifted flame. High inlet air temperature can extend the lean combustion range and reduces incomplete combustion products, but large ER mutations should still be avoided. In the case of anode off-gas combusting with cathode off-gas, there are nearly zero emissions. Meanwhile, the flue gas temperature decreases to about 760 °C because of enlarged heat loss, but it is minimally influenced by Uf. Under the static condition, the optimal point with both controlled temperature and lowest emissions can be obtained in a wide range, and the after-burner can well adapt to various operating states of the stack. Under the transient condition, the after-burner has good response performance with much shorter time in burner start-up and burner operating state switch than conventional porous media ones. It can start up the stack in 1715 s.

Co-firing characteristics and fuel-N transformation of ammonia/pulverized coal binary fuel

As a feasible way to decarbonize coal combustion under the background of carbon neutrality in recent years, ammonia co-firing with pulverized coal is receiving considerable critical attention from the academic and industrial communities. This paper investigates the effects of coal type, NH3 injection mode, temperature, excess air ratio (α) and NH3 co-firing ratio (ENH3) on combustion characteristics and fuel-N transformation of ammonia/pulverized coal in a 6 kW drop tube furnace. Emission of O2, CO2, CO, NO, NO2 and NH3 at the furnace exit was monitored online. The unburned carbon (UBC) content and elementary composition in fly ash were also tested. Results show that NOx generation behaviors of premixed and staged modes are significantly different. Typically, NOx emission peaks at ENH3 = 20 % under high temperature and staged mode. As for NH3/coal cases at 1000 °C, NOx level is even lower than pure coal combustion, but NH3 residue is higher. The water gas shift reaction (WGSR) under fuel-rich condition generates more CO, and the conversion ratio from fuel-N to NOx decreases when α diminishes. Ammonia co-firing can achieve lower CO emission with anthracitic coal from Gongyi (GY-coal) while lower NOx emission with bituminous coal from Inner Mongolia (IM-coal). Ammonia co-firing can considerably improve the transformation from fuel-N to N2. From the perspective of emission control and decarbonization, ENH3 = 40 % is an optimal ammonia co-firing ratio which not only can reduce half of CO2 but also brings the conversion ratio from fuel-N to NOx and residual NH3 to the minimum level. The micromorphology of ash samples is greatly affected by coal/ammonia co-firing. In premixed mode, the surface of ash sample is porous and adhered to each other; while in staged mode, obvious fractures and cuts exist between the ash particles due to the sharp decrease of local gas temperature.

Effect of quenching region characteristics on the performance of two-region porous inert medium burners at low-power operation

Although the effects of quenching and combustion regions on the performance of two-region porous inert medium (PIM) burners are different, only the combustion regions have received the utmost consideration. This study focuses on quenching regions by exploring the effect of varying their characteristics on the performance of PIM burners operated at low powers (1–5 kW). Therefore, the axial real-time temperature distributions and the steady-state CO– and NOx-emissions due to the combustion of wide ranges of well-premixed LPG-air mixtures within a well-designed PIM burner were measured. To vary the quenching region characteristics, two different materials of alumina and cordierite and three different thicknesses of the alumina material were used. The combustion stability limits were extracted from the measured stable temperature distributions and presented as a function of the applied power. Both the lower and higher stability limits decayed toward lower excess air ratios. However, the higher limit decayed at a faster rate, thereby causing the modulation ability of the excess air ratio to shrink continuously, which limited the burner’s adaptability and capacity. Meanwhile, using the alumina material instead of the cordierite improved the entire lower stability limit by at least 0.1. Conversely, using the cordierite material improved the higher stability limit by 0.1, but only for the two lower powers of 1 and 2 kW. In addition, increasing the alumina material’s thickness from 13 to 20 mm enhanced the whole modulation ability by 0.2, where each limit was entirely improved by 0.1. Therefore, these findings emphasize the effects of quenching region characteristics on the performance of two-region PIM burners, revealing the importance of optimizing this region during their design for actual practical applications. Finally, except for the CO-emission at 1 and 2 kW, outstanding insignificant CO– and NOx-emissions were observed.

Effects of excess air ratio and spark timing on performance and gaseous pollutant emissions of fuel reforming natural gas engine

The combustion and emission characteristics as well as the economic performance of partial oxidation fuel reforming (POFR) natural gas engines were investigated by adjusting the fuel reforming ratios and the engine load. The performance of the POFR engine with a 12% fuel reforming ratio was compared with that of the original engine. The results showed that the fuel-partial-reforming was effective in reducing the cycle-to-cycle variations over the whole range of the operating conditions. The THC and NOX emissions decreased at almost all operating conditions, but showed different decreasing trends at different loads and equivalence ratios, while the CO emissions increased at all operating conditions. It was found that reducing the advancement of ignition timing of the POFR-engine can further reduce the gaseous pollutant emissions without reducing the economic performance of the engine. In conclusion, blending reforming gas improved the overall performance of the natural gas engine at low to medium load conditions.

Effects of isopropanol ratio at different excess air ratios on combustion and emissions characteristics of an isopropanol/gasoline dual-fuel combined injection SI engine

Energy crises and environmental issues require the development of green fuels for engines. Isopropanol is an excellent performance renewable alternative fuel for SI engines. It can be prepared by IBE fermentation. However, there have been few studies on the use of isopropanol/gasoline dual fuel in SI engines, especially based on the combined injection technology. For dual-fuel engines, the combined injection technology can further achieve clean combustion by flexibly controlling the fuel composition in the cylinder. Therefore, it is significant to combine the isopropanol/gasoline dual-fuel with the combined injection technology. The effects of the isopropanol ratio at different λ values on combustion and emissions characteristics of an isopropanol/gasoline dual-fuel combined injection SI engine were studied in this paper. The injection mode is isopropanol direct injection plus gasoline port injection. Six isopropanol ratios (0 %, 20 %, 40 %, 60 %, 80 %, 100 %) and five λ values (0.9, 1, 1.1, 1.2, 1.3) are set. The engine was tested at 1500 rpm with an intake pressure of 50 kPa. It is shown that isopropanol addition improves combustion, increases Pmax and maximum heat release rate, and shortens ignition delay period, rapid combustion period, and combustion duration. As the isopropanol ratio increases, the IMEP increases and the COVIMEP decreases. The improvements in combustion, IMEP and COVIMEP brought by the addition of isopropanol were more obvious under lean-burn conditions. Isopropanol addition effectively reduces unburned HC emissions, CO emissions, and NOx emissions. A higher isopropanol ratio in the mixture leads to better power and emissions performance. Isopropanol is a promising alternative fuel for engines, but its corrosive properties can damage the rubber parts of engines.

Multi-objective optimization of a hydrogen-fueled Wankel rotary engine based on machine learning and genetic algorithm

Hydrogen is a promising way to achieve high efficiency and low emissions for Wankel rotary engines. In this paper, the intake and exhaust phases and excess air ratios (λ) were optimized using machine learning (ML) and genetic algorithm (GA). Firstly, a one-dimensional model was built and verified under various λ. Secondly, the variables were determined using sensitivity analysis method, and the sample for training models was generated using the Latin hypercube sampling. Finally, a prediction model for performance and emissions was built using ML and combined with GA for multi-objective optimization. The results show that the timing of intake port full closing (IPFC) and exhaust port start opening (EPSO) exhibits the most significant influence on performance and emissions, while the other phases are less influential. Both indicated mean effective pressure (IMEP) and indicated specific nitrogen oxides (ISNOx) increase as the IPFC timing is advanced, while indicated specific fuel consumption (ISFC) decreases as EPSO timing is delayed. Compared with the original engine, the optimized IMEP is improved by 0.18%, ISFC is reduced by 2.39%, and ISNOx is reduced by up to 65.43%. It is an efficient way to use ML combined with GA to improve performance and reduce emissions simultaneously.

Analysis of combustion characteristics under cooled EGR in the hydrogen-fueled Wankel rotary engine

Hydrogen-fueled Wankel rotary engine (HWRE), as a high power density and eco-friendly internal combustion engine, has the potential to become an alternative for gasoline-fueled piston engines. Cooled EGR, as an effective means of improving engine performance, is less studied based on HWRE. However, due to the different operating way and structure, the flame development and propagation of WRE are significantly different from those of the piston engine, so may the effect of cooled EGR. Hence, the goal of present work is to analyze the effect of cooled EGR on the combustion characteristics of HWRE. This work is conducted under 1500 r/min and wide-open throttle conditions. The results show that when the ignition timing and excess air ratio are fixed at 5°CA ATDC and 1, the cooled EGR level has a significant influence on the combustion process and operating stability. In addition, when maximum brake torque CA50 is employed, within test range, whether stoichiometric or lean combustion, both the brake torque and brake thermal efficiency are monotonous to the cooled EGR level. And cooled EGR can achieve high brake thermal efficiency compared with lean combustion at the same brake torque. Compared with the hydrogen-fueled piston engine, HWRE allows for a higher cooled EGR level whether in terms of efficiency or power output considerations. In general, the cooled EGR can be used as an excellent load control means to achieve high efficiency of HWRE.

Experimental Study on the Effects of Hydrogen Injection Strategy on the Combustion and Emissions of a Hydrogen/Gasoline Dual Fuel SI Engine under Lean Burn Condition

Hydrogen addition can improve the performance and extend the lean burn limit of gasoline engines. Different hydrogen injection strategies lead to different types of hydrogen mixture distribution (HMD), which affects the engine performance. Therefore, the present study experimentally investigated the effects of hydrogen injection strategy on the combustion and emissions of a hydrogen/gasoline dual-fuel port-injection engine under lean-burn conditions. Four different hydrogen injection strategies were explored: hydrogen direct injection (HDI), forming a stratified hydrogen mixture distribution (SHMD); hydrogen intake port injection, forming a premixed hydrogen mixture distribution (PHMD); split hydrogen direct injection (SHDI), forming a partially premixed hydrogen mixture distribution (PPHMD); and no hydrogen addition (NHMD). The results showed that 20% hydrogen addition could extend the lean burn limit from 1.5 to 2.8. With the increase in the excess air ratio, the optimum HMD changed from PPHMD to SHMD. The maximum brake thermal efficiency was obtained with an excess air ratio of 1.5 with PPHMD. The coefficient of variation (COV) with NHMD was higher than that with hydrogen addition, since the hydrogen enhanced the stability of ignition and combustion. The engine presented the lowest emissions with PHMD. There were almost no carbon monoxide (CO) and nitrogen oxides (NOx) emissions when the excess air ratio was, respectively, more than 1.4 and 2.0.

Analysis of the exhaust hydrogen characteristics of high-compression ratio, ultra-lean, hydrogen spark-ignition engine using advanced regression algorithms

• Exhaust H 2 and NO x were investigated using heavy-duty, hydrogen spark-ignition engine. • Lower excess air ratio exhibited lower H 2 emission, but greater heat transfer loss. • The regression model achieved a high accuracy under various operating conditions. • The proposed H 2 emission model is applicable to various HICEs. Hydrogen is a leading alternative fuel for eliminating the carbon emissions of internal combustion engines. Moreover, the use of hydrogen improves the combustion owing to its high flame speed. The hydrogen selective catalytic reduction is a promising solution for the reduction of nitric oxides (NOx), which is the sole regulated gas species in hydrogen-fueled internal combustion engines. In the present study, hydrogen and NOx emissions, the crucial species for the catalyst performance, were investigated using a heavy-duty, hydrogen spark-ignition engine. The ratio of H 2 to NOx was above 100 at the excess air ratio (lambda) of 2.5 or higher. Three-dimensional, numerical simulation showed that the in-cylinder hydrogen distribution was dependent on the engine load and the lambda value. A regression analysis showed that the exhaust hydrogen quantity had a strong correlation with the seven parameters, namely engine speed, the gross indicated effective pressure (IMEPg), lambda, spark timing, total combustion duration, peak in-cylinder temperature, and peak pressure rise rate. Among these parameters, the IMEPg and the lambda value exhibited the highest weights in a neighborhood component analysis. The regression model with the seven features exhibited the highest R 2 value of 0.94 with the squared exponential Gaussian process regression. The proposed prediction model can contribute to not only reducing NOx emission with aftertreatment, but also maximizing the thermal efficiency of hydrogen-fueled internal combustion engines.

The effect of high altitude environment on diesel engine performance: Comparison of engine operations in Hangzhou, Kunming and Lhasa cities

The all-area operating performance of the vehicles requires the development of diesel engines that can operate at high altitudes without significant performance deterioration. Prior to optimizing the efficiency and emissions of highland engines, there is a necessity to investigate the underlying causes of engine performance degradation. The purpose of this paper was to study the in-cylinder activities occurring in the combustion chamber of diesel engines at high altitudes, which can help explain the effect of altitude on engine efficiency and emissions of concern to the customer. Specifically, a turbocharged direct injection compression ignition engine was operated at a constant engine speed and load, but at different altitudes. The theoretical analyses based on experimental data suggested that the mismatch between air and diesel quantities caused by the high altitude atmosphere led to the engine combustion deterioration. Specifically, the lower gas density at high altitudes during fuel injection resulted in a reduction of the injection angle and an enhancement of the penetration capability. In addition, the rise in altitude extended the ignition delay, which increased the fuel fraction mixed with air in the premixed combustion stage and raised the pressure rise rate. Moreover, at high altitudes, the reduction in excess air ratio and increased possibility of wall impingement of the fuel droplets resulted in uneven mixture concentration distribution and reduced air utility. Accordingly, combustion deterioration occurred in the combustion chamber of the plateau engines, which reduced energy release during main mixing-controlled combustion, lowered combustion efficiency, increased exhaust energy, and raised engine-out incomplete combustion emissions. All these effects resulted in a decrease in engine thermal efficiency of ∼6.5% and an increase in soot emissions of ∼4.2 times from Hangzhou to Lhasa city for the engine and operating conditions investigated in this study. Consequently, engines operating in highland areas need to be optimized in terms of efficiency and emissions.

Energy-ecological assessment of the boiler equipment modernized with the jet-niche technology

The results devoted to the issues of energy-ecological assessment of industrial boiler equipment with jet-niche combustion technology are given in the paper. The basic principles underlying this technology include: rational distribution of fuel in the oxidant stream; stable adjustable structure of fuel, oxidant and combustion products; self-regulation of the fuel mixture composition in the zone of the torch stabilization when the unit load changes. As of today, a large number of industrial gas-burning equipment has been modernized by jet-niche technology, including: boilers, furnaces, dryers, metallurgical facilities, etc. The results of industrial implementation of the technology allowed to accumulate a significant amount of technical information and gave the possibility of preliminary environmental assessment during the modernization of gas combustion equipment. As practice shows, at the present stage the main direction of the technology improvement is to enhance its environmental performance. The influence of the main regime and technical parameters of fire equipment on its emission indicators is established in the paper. Possibilities for reducing nitrogen oxides by primary technological methods, the simplest and most effective of which is the introduction of recirculation gases into the furnace space, have been identified. According to the results of the analysis of emission indicators of the modernized fire equipment with a capacity of 0.5–60 MW, data to estimate the emission indicators of low and medium power boilers depending on the main influencing factors, namely, unit size, excess air ratio and boiler load were obtained. The influence of the introduction of recirculation gases into the furnace space on the level of nitrogen oxides concentration is also taken into account. The efficiency of application of the recirculation gases introduction scheme into the primary air flow in comparison with combustion technologies based on vortex burners is shown. According to the results of the industrial experiment, the energy efficiency of the proposed measures was established on the example of the dependences of efficiency on the load of boilers PTVM-50 and KVGM-20.

Analysis of methods used to identify combustible gas and vapour-related factors contributing to explosions in the context of assigning explosion and fire safety categories to premises

Introduction . The authors have classified numerous publications, addressing the assignment of explosion and fire safety categories to premises, buildings and outdoor facilities, into the three groups: 1) sources of information that are in effect (including in-house and region-wide documents), sources that were in effect; 2) manuals and guidelines on category assignment; 3) publications that confirm (refute) or clarify some provisions, specified in regulatory sources. This article can be included into the third group of publications. Goal. Analysis of different methods, used to identify the value of Z factor; identification of strengths and weaknesses of each method, development of recommendations on the application of these methods. Objectives . The objective is to identify the substance-related factor contributing to explosions, use particular cases to demonstrate the efficiency of this or other identification method. Results and discussion. The analysis of Z factor identification methods, describing the contribution of vapours of highly flammable liquids to an explosion, has proven that three types of procedures can be used to find the Z factor value: the method of tables (that uses the maximal possible tabular value of Z = 1; for gases and aerosols Z = 0.5; for vapours of highly flammable liquids Z = 0.3); the computational method based on a pattern of three-dimensional gas and vapour spreading on the premises; however, this method, if applied, may involve a high probability of errors due to numerous conditions limiting its applicability; hence, the unexplainable value of Z may exceed 1. Besides, the computational method is extremely laborious. Its application requires the clarification of conditions for its use; the graphical method (based on the dependency graph of Z on the X parameter). This method is the simplest and the most reliable one. When the graphical method is used to find the value of Z , the excess oxidant ratio must be taken as being equal to one, and the Х parameter must be calculated according to the following formula: Х = 0.99 Р s.v / С st.c . Conclusions. The graphical method, used to find the value of Z , is simple and reliable. When the Х parameter is identified, the excess air ratio is used: φ = 1.9, which leads to the underestimation of Z , the vapour-related factor contributing to explosions. To prevent the unreasonable underestimation of Z , the excess air ratio must be disregarded or taken as being equal to 0.99.

Comprehensive optimization of a diesel-E85 engine over the full operating range using the Taguchi method in intelligent charge compression ignition (ICCI) mode

Lean combustion engines have been regarded as applicable technologies meeting the stringent emission regulations, while control parameters of these engines have become more complex with the application of new technologies. The intelligent charge compression ignition (ICCI) engine was equipped with an additional direct injection system, further complicating the optimization process. To simplify the optimization of control parameters, Taguchi design of experiment was employed based on an L18 orthogonal array. The effect degree of various parameters including engine load, speed, excess air ratio, E85 (85 % ethanol and 15 % gasoline) energy ratio, and premixed strategies were investigated, while indicated thermal efficiency (ITE), particle number (PN), and gaseous emissions as responses were discussed using the signal-to-noise (S/N) ratio and the analysis of variance. An optimized control strategy of ICCI over full operating conditions was designed based on the rules obtained by the Taguchi method. It concluded that engine load and speed had a significant influence on the upper limit of ITE while excess air ratio, E85 energy ratio, and premixed strategies had varying degrees of effect on emissions. The optimized control strategy realized that the maximum E85 substitution ratio reached 80 %, reducing CO2 emission below 500 g/kWh in most conditions. The load range of ICCI combustion reached 75 % of the original diesel engine load (21 bar IMEP) considering engine mechanical strength and noise level, while the peak ITE and the minimum NOx emissions were over 51 % and below 0.2 g/kWh respectively under conditions of low speed and high load.