Increase Of Excess Air Ratio Research Articles

Research on the Impact of Blending Dissociated Methanol Gas on the Performance and Emissions of Marine Medium-Speed Methanol Engines

This study conducts a detailed analysis of the mixed combustion of dissociated methanol gas (DMG) and methanol in a marine medium-speed methanol engine through numerical simulation methods. The research focuses on the impact of partially replacing methanol with DMG on engine combustion characteristics and emissions under both stoichiometric and lean-burn conditions. Employing the MAN L23/30H diesel engine as the experimental model, direct injection of DMG is achieved by installing gas injectors on the cylinder head. Utilizing the CONVERGE software, we simulate the injection and combustion processes of methanol and DMG and subsequently analyze the effects of varying DMG blending ratios on in-cylinder pressure, heat release rate, mean chamber temperature, as well as NOx, HC, CO, and soot emissions. The research findings indicate that, under stoichiometric combustion conditions at both rated and idle speeds, the incorporation of DMG leads to increases in the peak in-cylinder pressure, peak heat release rate, and peak in-cylinder temperature, with these peaks occurring earlier. Additionally, it is observed that emissions of HC, CO, and soot are reduced. Under lean combustion conditions at rated speed, in the absence of DMG blending, increasing the excess air ratio results in an initial increase followed by a decrease in both fuel-indicated and overall-indicated thermal efficiency. However, with the blending of DMG, these efficiencies improve as the excess air ratio increases. Notably, the highest efficiencies are achieved when the excess air ratio is 1.8 and the blending ratio of DMG is 30%.

Comparative study on combustion and emission characteristics of methanol/gasoline blend fueled DISI engine under different stratified lean burn modes

Combining stratified lean-burn techniques with methanol offers a promising path to achieving high efficiency and low emissions in direct-injection spark-ignition (DISI) engines. This work compares the stratified and homogeneous-stratified lean-burn characteristics of methanol/gasoline fuels on a DISI engine. Combustion and emissions characteristics under two stratified lean-burn strategies were investigated. The results indicate that compared to double-injection stratified lean-burn (DISL), single-injection stratified lean-burn (SISL) leads to more timely combustion, which deteriorates more slowly as the excess air ratio increases. Using M20 fuel with SISL achieves a higher tolerance for air dilution. At the same excess air ratio, SISL results in higher maximum in-cylinder pressure and combustion temperature, but lower exhaust temperature. The economic zone for SISL occurs with M40 fuel at λ = 1.3–1.6, whereas DISL's economic zone is within λ = 1.1–1.3. When λ is below 1.5, SISL produces higher hydrocarbon (HC) emissions but lower nitrogen oxides (NOx) emissions. However, as λ exceeds 1.5, HC emissions from DISL increase sharply while NOx emissions decrease significantly. The particle concentration from SISL is at least an order of magnitude higher than that from DISL, with particle size distribution forming a unimodal curve centered around accumulation mode particles. Conversely, DISL exhibits a quasi-bimodal distribution.

Experimental and numerical study on a SI engine fueled with gasohol and dissociated methanol gas blends at lean conditions

Hydrogen-rich dissociated methanol gas (DMG) and ethanol are both promising alternative fuels for engines. The study investigates the performance of a spark ignition engine using various gasohol-DMG blends under lean conditions, aiming to evaluate the influence of fuel composition, excess air ratio, and operational parameters including engine load and speed. The results demonstrate that the introduction of DMG substantially enhances the engine's fuel economy, combustion efficiency, combustion stability, and the HC and CO emissions. The addition of ethanol has a distinct impact on engine performance, including increased peak cylinder pressure at lower DMG ratios and a subsequent decrease at higher DMG ratios. It also leads to substantial reductions in HC and NOx emissions but shows a non-linear effect on CO emissions with an increasing ethanol blending ratio. An increase in excess air ratio results in simultaneous reductions in peak cylinder pressure, HC, CO, and NOx emissions. Moreover, variations in engine load and speed respectively impact the cylinder's thermal environment and gas flow, consequently influencing combustion and emission characteristics.

Effect of hydrogen injection coupled with high-energy ignition on the combustion stability of a lean-burn gasoline engine

The shortage of fossil energy and the aggravation of environmental pollution have led to stricter requirements for energy conservation and environmental protection of automobiles. The development of new energy vehicles still needs time and space. The internal combustion engine is still the power source that automobiles will need to rely on in the future. Lean combustion is one of the key research directions for efficient and clean combustion technology for gasoline engines. In this paper, the effects of high-energy ignition coupling hydrogen blending on the combustion stability of lean-burn gasoline engines were studied by means of multi-point high-energy ignition and gasoline/hydrogen double direct injection. Through the combination of gasoline and hydrogen injection timing, a suitable stratified mixture can be formed in the cylinder. Combined with high-energy ignition, the fire core can be formed smoothly, and the flame spreads rapidly. The introduction of hydrogen increases the concentration of H in the reaction system, enhances the activity of the reaction system, and accelerates the oxidation process of fuel molecules. Compared with a pure gasoline engine, hydrogen blending can expand the lean burn limit by 66.2% and increase ITE (Indicated Thermal Efficiency) by 6.5%. NOx emission increases first and then decreases with the increase in excess air ratio, but when λ > 1.6, NOx emission is much lower than that of the equivalence ratio condition. HC (Hydrocarbons), CO, and CO2 emissions are also lower than the equivalent ratio conditions.

A study of the local entropy generation rate in a porous media burner

In this paper, the work and performance of the premixed methane-air porous axisymmetrical burner have firstly been simulated numerically using the CFD tools. For this purpose the set of governing equations has been enriched by an additional energy equation in porous solid, and the chemical species transport has been extended onto the multi-step mechanism (GRI-2-11). This numerical model has been verified on the base of available benchmark experiments. Next, we have studied the local entropy generation problem taking into account not only classical contributions like viscous and turbulent dissipation but also, the porous combustion of gases. The results showed that the greatest portion of entropy generation in the porous medium burner is related to chemical reactions, followed by heat transfer, mass diffusion (mixing) and friction (viscous dissipation), respectively. According to the results, as the excess air ratio increases, the local entropy generation rate due to heat transfer and friction increases and the local entropy generation rate due to chemical reactions is decreased. Also, by increasing the volumetric heat transfer coefficient, the local entropy generation rate due to heat transfer decreases and the local entropy generation rate due to friction and chemical reactions increases. Also, the local entropy generation rate due to mixing does not show a significant change with the changing excess air ratio and volumetric heat transfer coefficient.

Research on the performance of a hydrogen/methanol dual-injection assisted spark-ignition engine using late-injection strategy for methanol

A dual-fuel spark-ignition engine that was equipped with a hydrogen (H2) port-injection and methanol direct-injection fuel-supply system was used to study the power, combustion and emission performances in a methanol late-injection strategy. The test was operated at a spark timing of a 20° crank angle before top dead center, engine speed of 1200 rpm and 1800 rpm with a manifold absolute pressure of 70 kPa and 68 kPa, respectively, and H2 addition ratio of 0% and 3%, respectively, under different excess-air ratios. The indicated mean effective pressure decreased with an increase in excess-air ratio at an engine speed of 1200 rpm and 1800 rpm. H2 enrichment could expand the lean-burn limits of a methanol engine without or with H2 addition from excess-air ratio 1.6 to 2.2. H2 addition could shorten the flame-development angle and rapid-burning angle, and advance the combustion central angle closer to top dead center. The coefficient of variation in the indicated mean effective pressure was increased significantly as the excess-air ratio was increased over 1.4 for no H2 addition and 1.8 for H2 addition from a 3% methanol engine at an engine speed of 1800 rpm. Brake-specific nitrogen-oxide emissions decreased as the excess-air ratio was increased. The BSNOX emissions for lean-burn conditions are average 90% lower than for excess-air ratio 1.0. The maximum soot emission for 3% H2 addition at engine speed of 1200 rpm and 1800 rpm is 59% and 30% lower than for no H2 addition, respectively.

A comparative study on effects of homogeneous or stratified hydrogen on combustion and emissions of a gasoline/hydrogen SI engine

A comparative study on effects of homogeneous or stratified hydrogen on combustion and emissions was presented for a gasoline/hydrogen SI engine. Three kinds of injection modes (gasoline, gasoline plus homogeneous hydrogen and gasoline plus stratified hydrogen) and five excess air ratios were applied at low speed and low load on a dual fuel SI engine with hydrogen direct injection (HDI) and gasoline port injection. The results showed that, with the increase of excess air ratio, the brake thermal efficiency increases firstly then decreases and reaches the highest when the excess air ratio is 1.1. In comparison with pure gasoline, hydrogen addition can make the ignition stable and speed up combustion rate to improve the brake thermal efficiency especially under lean burn condition. Furthermore, it can reduce the CO and HC emissions because of more complete combustion, but produce more NOX emissions due to the higher combustion temperature. Since, in the gasoline plus stratified hydrogen mode, the hydrogen concentration near the sparking plug is denser than that of homogeneous hydrogen, the ignition is more stable and faster, which further speed up the combustion rate and improve the brake thermal efficiency. In the gasoline plus stratified hydrogen mode, the brake thermal efficiency increases by 0.55%, the flame development duration decreases by 1.0°CA, rapid combustion duration decreases by 1.3°CA and the coefficient of variation (COV) decreases by 9.8% on average than that of homogeneous hydrogen. However, in the gasoline plus stratified hydrogen mode, due to the denser hydrogen concentration near the sparking plug and leaner hydrogen concentration near the wall, the combustion temperature and the wall quenching distance increase, which make the NOX and HC emissions increase by 14.3% and 12.8% on average than that of homogeneous hydrogen.

Numerical investigation of the effect of air supply and oxygen enrichment on the biomass combustion in the grate boiler

The characteristics of biomass combustion in industrial scale grate boiler under different operating conditions are investigated based on the numerical model. On account of the one-dimensional dynamics assumption, a fuel bed model is developed to simulate the biomass incineration on the grate bed, while interacting with three-dimensional CFD furnace model to provide a thoughtful representation of the whole boiler. The model validation is performed based on the experimental data and is used as the standard basis for further investigation. The effect of air supply is analyzed with a combination of numerical results and efficiency analysis. Under constant excess air ratio, the thermal efficiency of the boiler is raised greatly when the primary air supply is elevated to 43% of the total air supply, but the improvement is limited when the ratio of primary air is further increased to 50%. The influence of redistribution of primary air supply in zone 4 and zone 5 on the thermal efficiency is dependent on the conversion rate of fuel in the first three zones, although the bottom ash temperature can be reduced through increasing the air flow in zone 5. An increase in excess air ratio contributes to better burnout but stack loss increase simultaneously, so an optimum ratio is found to be 1.6. Oxygen-enriched combustion is also explored in this study. The combustion improves obviously by enriching the volume fraction of O2 in primary air to 25%, and the highest temperature in the grate bed is below 1400 K, which is the limitation from the design specification of this commercial grate boiler.

Effects of Air-fuel Ratio and Hydrogen Fraction on Combustion Characteristics of Hydrogen Direct-Injection Gasoline Engine

Effects of air-fuel ratio and hydrogen fraction on engine combustion at the conditions of locally rich hydrogen and lean-burn mode have been experimentally carried out on a hydrogen direct-injection (HDI) and gasoline port-injection engine. The test results showed that both excess-air ratio and hydrogen affect the HDI combustion. The peak cylinder pressure was decreased by 45% (3.9% hydrogen fraction) and 23% (10.5% hydrogen fraction) when the excess-air ratio was increased from 1 to 1.5. Hydrogen, which compensates the loss of cylinder pressure and heat release rate caused by lean burn, effectively improves the engine performance at lean burn operation. In addition, when the excess air ratio was set at 1.2, the rise in hydrogen fraction from 3.9% to 10.5% caused a 51.2 % increase in peak cylinder pressure and 101% increase in maximum heat release rate. The maximum cylinder temperature and exhaust temperature was increased firstly and then decreased afterwards with an increase in excess-air ratio. The increase in hydrogen fraction resulted in the acceleration of maximum cylinder temperature, but the exhaust temperature is not that much affected.

Co-combustion of municipal solid waste and coal gangue in a circulating fluidized bed combustor

Mixed incineration of municipal solid waste (MSW) in existing coal gangue power plant is a potentially high-efficiency and low-cost MSW disposal way. In this paper, the co-combustion and pollutants emission characteristic of MSW and coal gangue was investigated in a circulating fluidized bed (CFB) combustor. The effect of MSW blend ratio, bed temperature and excess air ratio was detailedly studied. The results show the NOx and HCl emission increases with the increasing MSW blend ratio and the SO2 emission decreases. With the increase of bed temperature, the CO emission decreases while the NOx and SO2 emission increases. The HCl emission is nearly stable in the temperature range of 850–950 °C. The increase of excess air ratio gradually increases the NOx emission but has no significant effect on the SO2 emission. The HCl emission firstly increases and then decreases with the increase of excess air ratio. For a typical CFB operating condition with excess air ratio of 1.4, bed temperature of 900 °C and MSW blend ratio of 10%, the original CO, NOx, SO2 and HCl emissions are 52, 181, 3373 and 58 mg/N m3 respectively.

Idle performance of a hydrogen rotary engine at different excess air ratios

Rotary engine has flat chamber and longs for fuel with high flame speed and small quenching distance. Hydrogen has many excellent characteristics that are suitable for the rotary engine. In this paper, the performance of a rotary engine fueled with pure hydrogen at different excess air ratios was experimentally investigated. The investigation was carried out on a single-rotor hydrogen-fueled rotary engine equipped with port fuel injection system. An online electronic control module was used to govern the hydrogen injection duration and excess air ratio. In this study, the engine was operating at the idle speed of 3000 rpm and different excess air ratios varied from 0.993 to 1.283. The test results demonstrated that the fuel energy flow rate of the hydrogen rotary engine and engine stability were reduced with the increase of excess air ratio. When the excess air ratio increased from 0.993 to 1.283, the hydrogen energy flow rate was decreased from 14.91 to 11.55 MJ/h. Both the flame development and propagation periods were increased with excess air ratio. CO emission was negligible, but HC, CO2 and NOx emissions were still detected due to the evaporation and possible burning of the lubrication-used gasoline, and oxidation reaction of nitrogen of the intake air.

Improving the lean performance of an n-butanol rotary engine by hydrogen enrichment

The present paper introduced an experiment survey focusing on exploring the impact of hydrogen enrichment on improving the lean-burn performance of an n-butanol rotary engine. During the test, the engine speed and intake pressure were roughly set at 4000 rpm and 35 kPa, respectively. A constant spark advance of 45 °CA was adopted through the test. Hydrogen volumetric fraction of the total intake was severally kept at 0% and 3%. The testing results manifested that the brake thermal efficiency and peak chamber temperature were heightened with hydrogen addition. Besides, the ignition delay and rapid combustion duration were both reduced with the hydrogen additive. Engine running stability gained an improvement by hydrogen supplement. Moreover, HC and CO emissions from the original n-butanol rotary engine were reduced after hydrogen adding. NOx emissions were increased with hydrogen enrichment while reduced with the increase of excess air ratio. This indicated that NOx emissions from both the n-butanol and hydrogen-blended n-butanol rotary engines could be reduced by lean combustion strategies.

Experimental study on combustion and pollutants emissions of oil sludge blended with microalgae residue

Experimental study on co-combustion of oil sludge (OS) and microalgae residue (MR) was conducted with a thermogravimetric analyzer and a designed fluidized bed reactor system. Combustion process of OS blended with MR could be divided into four stages, water evaporation, volatiles release and combustion, fixed carbon combustion and minerals decomposition. With MR ratio increasing, combustion performance of the mixture became better. MR addition can help improve the combustion performance of OS. NOx and SO2 concentrations increased firstly and then decreased with the increase of combustion temperature which ranged from 800 to 1100 °C. With the increase of excess air ratio α, NOx and SO2 emissions increased. Generally, NOx and SO2 emissions decreased with MR ratio increased at 800 °C, which is caused by the catalysis effect of ash and heavy metals in OS. OS blended with MR could both improve combustion performance and help reduce NOx and SO2 emissions during OS combustion, which provides an effective approach to massive synergistic disposal of waste resources.

Study on Carbonyl Emissions of Diesel Engine Fueled with Biodiesel

Biodiesel is a kind of high-quality alternative fuel of diesel engine. In this study, biodiesel and biodiesel/diesel blend were used in a single cylinder diesel engine to study the carbonyl emissions. The result shows that carbonyl pollutants of biodiesel and biodiesel/diesel blend are mainly aldehyde and ketone compounds with 1–3 carbon atoms, and formaldehyde concentration is higher than 80% of the total carbonyl pollutants for biodiesel. The formaldehyde concentration peak is reduced with the increase of intake temperature (T), intake pressure (P), and exhaust gas recirculation (EGR) ratio and increased with the increase of compression ratio (ε). When excess air coefficient (λ) is lower than 1.7, the formaldehyde concentration is increased with the increase of excess air ratio. When λ is higher than 1.7, the formaldehyde concentration is reduced with the increase of excess air ratio. The dilution of air can reduce formaldehyde concentration in the premixed flame of diesel effectively; however, it has less effect on biodiesel. Among the fuel pretreatment measures of adding hydrogen, CO, and methane, the addition of hydrogen shows the best effect on reducing formaldehyde of biodiesel.

Co-firing of pine chips with Turkish lignites in 750 kWth circulating fluidized bed combustion system

Two Turkish lignites which have different sulfur levels (2–2.9% dry) and ash levels (17–25% dry) were combusted with a Turkish forest red pine chips in a 750kW-thermal capacity circulating fluidized bed combustor (CFBC) system. The combustion temperature was held at 850±50°C. Flue gas emissions were measured by Gasmet DX-4000 flue gas analyzer. Two lignites were combusted alone, and then limestone was added to lignites to reduce SO2 emissions. Ca/S=3 was used. 30% percent of red pine chips were added to the lignites for co-firing experiments without limestone in order to see the biomass effects. The results showed that with limestone addition SO2 concentration was reduced below the limit values for all lignites. CO emissions are high at low excess air ratios, gets lower as the excess air ratio increases. During co-firing experiments the temperature in the freeboard was 100–150°C higher as compared to coal combustion experiments.

Research on cycle-by-cycle variations of an SI engine with hydrogen direct injection under lean burn conditions

Considering the improvement on combustion stability for hydrogen addition under lean burn conditions, cycle-by-cycle variations of a spark ignition gasoline engine with hydrogen direct injection were studied. Effect of hydrogen fraction of 10% on cycle-by-cycle variations for lean burn with various excess air ratio and throttle position was analyzed. The results showed that coefficient of variation in indicated mean effective pressure decreased firstly and increased afterward with the retard in ignition timing, confirming there existed a minimal cycle-by-cycle variations ignition timing for a specified excess air ratio and throttle position. It was also found that the peak cylinder pressure, the maximum rate of pressure rise and the indicated mean effective pressure increased, and their corresponding cyclic variations decreased after hydrogen addition. Interdependency between the combustion pressure parameters and their corresponding angles tended to become strongly correlated after hydrogen addition. Moreover, the pressure-derived combustion parameters and the indicated mean effective pressure decreased with the increase of excess air ratio, and coefficient of variation in both the gross indicated mean effective pressure and peak cylinder pressure increased under leaner conditions. This effect would be weakened with the enlargement of throttle position. The engine lean operating limit could be extended after hydrogen addition.

Emissions of NOx, SO2, and CO from Co-Combustion of Wheat Straw and Coal Under Fast Fluidized Bed Condition

Fuel diversity and reduction in pollutant emissions are driving the increased utilization of CO2 neutral biomass. Effects of operating conditions, such as bed temperature; excess air ratio; and secondary to primary air ratio on emissions of NOx, SO2, and CO for burning different blends of wheat straw and Salt Range coal under fast fluidized bed conditions in a pilot scale test facility, are reported in this study. Emissions of NOx were found to decrease with an increase in wheat straw ratio and secondary to primary air ratio. SO2 and CO emissions were observed to decrease with an increase in excess air ratio and wheat straw ratio.

Three-dimensional modeling of olive cake combustion in CFB

A comprehensive three-dimensional numerical model which includes gas–solid flow, chemical reaction, heat transfer and mass transfer has been established, to simulate the combustion of olive cake in circulating fluidized bed (CFB) reactor. The gas flow is solved by large eddy simulation (LES) approach. The particle phase is modeled by discrete particle method, in which the drag force, gravity, particle contact force and static-dynamic friction force are taken into account. The reactive model includes pyrolysis, combustion of char and volatile matters, SO2 emission, NO and N2O emissions, which has been coupled with gas–solid flow. Simulations were carried out in a CFB riser (diameter of 0.125 m and height of 1.8 m). Flow patterns, axial and radial distributions of voidage, gas and particle velocities, profiles of temperature and gas compositions under different operating conditions were obtained. The gas pollutant emissions in a riser were highly focused on. The results showed that gas and solid temperatures increase along the riser which reveals that waste combustion mainly takes place in the upper regions of the riser. The NO and N2O concentrations reach the peak values above the fuel inlet level owing to the equilibrium between the formation and reduction reactions. The SO2 concentration peaks close to the fuel inlet. An increase in excess air ratio causes the increase of NO and N2O emissions. However, no obvious variation tendency is observed for the SO2 emission.

An Experimental and Theoretical Study of the Effects of Excess Air Ratio and Waste Gate Opening Pressure Threshold on NOx Emission and Performance in a Turbocharged CNG SI Engine

Turbocharged CNG engines produce high NOx emission due to the fuel type and high combustion temperature. In this research, the effects of lean-burn and waste gate opening pressure threshold on NOx emission are studied theoretically and experimentally at WOT condition as well as 13-mode ECE-R49 test cycle. A code is developed in MATLAB environment for predicting engine NOx and the results are validated with the research experiments. Simulations show that NOx increases by increase of excess air ratio and reaches at most to 2486ppm at excess air ratio of 1.1 and then decreases. It is also experimentally found that changing waste gate opening pressure threshold from 165mmHg to 200 and 265mmHg decreases total bsNOx at a rate of 6% and 12% respectively. Increase of the threshold to 323mmHg increases total bsNOx. Therefore, to minimize the cycle bsNOx, the threshold of 265mmHg is the optimum threshold for the engine between the four pressure thresholds experimented.

Combustion and emissions performance of a hydrogen engine at idle and lean conditions

SUMMARY Hydrogen is the most promising alternative fuel for spark-ignited engines. This paper experimentally investigated the performance of a pure hydrogen-fueled SI engine at idle and lean conditions. The experiment was carried out on a four-cylinder gasoline-fueled SI engine equipped with an electronically controlled hydrogen port-injection system and a hybrid electronic control unit which was used to govern the hydrogen injection duration. The engine original electronic control unit was used to adjust the opening of idle bypass valve and spark timing to enable the engine to be run around its target idle speed. The test results showed that the fuel energy flow rate was reduced with the increase of excess air ratio for the pure hydrogen-fueled engine at idle and lean conditions. When excess air ratio increased from 2.08 to 3.2, the hydrogen energy flow rate was decreased from 11.79 to 9.97 MJ/h. Both the flame development and propagation periods were increased with the increase of excess air ratio. Because of the increased opening of idle bypass valve and dropped cylinder temperature, both pumping and cooling losses were reduced when the engine was leaned out. NOx and CO emissions were negligible, but HC and CO2 were still existed for the pure hydrogen-fueled SI engine due to the possible burning of the blow-by lubricant oil gas. Copyright © 2013 John Wiley & Sons, Ltd.