Air Coefficient Research Articles

Study on Mechanisms of NOx Formation and Inhibition during the Combustion of NH3/CH4 and NH3/CO Mixtures

Ammonia is an ideal renewable, carbon-free fuel and hydrogen carrier, which produces nitrogen and water after complete combustion in the presence of oxygen. However, ammonia has low reactivity, slow flame-propagation speed, and carries risks of high nitrogen oxide (NOx) emissions. Co-firing ammonia with an industrial by-product gas (with CH4 and CO being the main combustible materials) is a cost-effective and convenient method of improving the combustion characteristics of ammonia, but attention still needs to be paid to the NOx generation. Currently, the research on NOx formation during co-firing of ammonia with other fuel gases is still insufficient. In this study, a high-temperature furnace reaction system was used to investigate the NOx formation and inhibition mechanisms during the combustion of NH3/CH4 and NH3/CO mixtures. By varying the ammonia blending ratio, excess air coefficient (α), temperature, residence time, and fuel concentration, the key factors influencing NOx generation and inhibition were further analyzed. The results showed that when α was no less than 1, the production of NOx initially increased and then decreased with an increasing proportion of ammonia in the fuel gas. Within the temperature range of 900 °C to 1500 °C, the amount of NOx generated during the combustion of the mixed gas gradually decreased with the increase in temperature. Under the conditions of NH3/CH4 and NH3/CO, the emissions of NOx were higher than those during pure ammonia combustion.

Study on combustion characteristics of fully premixed water-cooled biogas burner

Biogas is a renewable gas produced by the fermentation of biomass and is an environmentally friendly alternative to traditional fossil fuels. To overcome the problems of traditional biogas burner, such as unstable combustion, easy flameout and backfire, and low thermal intensity, a new water-cooled biogas burner based on fully premixed combustion technology was designed and developed. Then, numerical simulations and experimental investigations were conducted to explore the effects of CO2 content, excess air coefficient, heat load, and cooling water temperature on the combustion characteristics of the burner. The results revealed that the designed burner exhibited good adaptability to simulated biogas with methane concentrations ranging from 55 % to 80 %. Increasing CO2 content resulted in decreased combustion temperatures and reduced NOx and CO emissions concentration at the burner outlet. In addition, reducing the excess air coefficient enhanced the combustion heat intensity and reduced combustion heat loss. Nevertheless, excessively low excess air coefficients yielded elevated levels of NOx and CO in the flue gas. The results showed that the designed burner demonstrated stable operation at a minimum heat load of 35 %, exhibited a favorable load regulation ratio, and had low emissions. It is a promising solution for utilizing biogas as a clean and sustainable energy source.

Effects of hydrogen blending ratio on combustion and emission characteristics of an ammonia/hydrogen compound injection engine under different excess air coefficients

Currently, hydrogen and ammonia are the best green, zero-carbon energies worldwide. Applying ammonia and hydrogen to internal combustion engines is a top priority for achieving the dual-carbon goal for the automotive industry. However, both ammonia and hydrogen have disadvantages that make them unsuitable for use as fuels on their own. Hydrogen internal combustion engines can suffer from abnormal burning, such as premature ignition, backfiring, and detonation. At the same time, the difficulty of hydrogen storage, transportation, and refilling can also lead to the problem of high cost of use. Ammonia suffers from high ignition energy, poor flame-spreading speed, and inadequate burning stabilization. When used alone, it causes incomplete combustion of large amounts of ammonia. Therefore, our group uses the spray pattern of “hydrogen direct injection (HDI) plus ammonia port injection (API). ” The influence of hydrogen blending ratio (HBR) on the combustion and emission characteristics of an ammonia/hydrogen compound injection engine with various excess air coefficients (λ) is investigated. The blending ratios of hydrogen are 6.1 %, 16.8 %, 27.3 %, 37.7 %, 47.8 %, and 57.7 %, respectively. The experimental data suggests that the indicated mean effective pressure (IMEP) shows an incremental trend as the hydrogen blending ratio grows. Not only CA0-10 but also CA10-90 have been reduced. The whole combustion process is shortened. The temperature and pressure rise. When the ratio of hydrogen blending is higher than 27.3 %, the enhancement of the burning characteristics by hydrogen is not apparent. NOX emissions rise with the ratio of hydrogen blending. NH3 emissions tend to drop as the blending ratio of hydrogen rises. Combining the emission and combustion characteristics, the general engine performance is better when the λ is 1.2 and the ratio of hydrogen blending is 27.3 %.

Effect of direct injection of small amounts of ethanol on port-injected hydrogen internal combustion engines

Hydrogen is a renewable fuel with excellent combustion characteristics. However, the direct use of hydrogen in existing engines faces obstacles such as abnormal combustion and high NOx emissions. This study proposes a strategy for controlling the combustion and emissions performance of a port-injection (PI) hydrogen internal combustion engine using ethanol direct injection (DI). The test conditions are 1000 rpm, 1500 rpm, and 2000 rpm respectively, the excess air coefficient is 1, 1.5, and 2, and 3%, 6%, and 9% ethanol is added. The results showed that the addition of ethanol can significantly reduce the pressure rise rate of the hydrogen engine and prolong CA0-10 and CA10-90. The addition of ethanol can promote the BMEP and BTE of the hydrogen engine. The addition of ethanol can reduce NOx emissions under lean burn conditions by 18%. The disadvantage is that the addition of ethanol increases the hydrocarbon emissions of hydrogen engines by about 50%, but the total amount is less. After the addition of ethanol, the flashback phenomenon of the hydrogen engine was significantly improved.

Experimental Study on the Impact of Hydrogen Injection Strategy on Combustion Performance in Internal Combustion Engines.

Hydrogen is an ideal alternative fuel for internal combustion engines due to its fast combustion rate and near-zero carbon emissions. To further investigate the impact of the injection strategy on combustion performance under various excess air coefficients and loads, experimental methods were employed to systematically study injection timing, injection pressure, and dual injection. The results demonstrate that appropriately delaying hydrogen injection timing can improve the thermal efficiency by up to 2.6% and reduce NOx emissions of equivalent combustion by nearly 88%. While increasing the hydrogen pressure to 8 MPa does not directly enhance the thermal efficiency and emissions, it can reduce the injection pulse width by approximately 75%, allowing for more flexibility in delaying the injection timing. Delaying the secondary end of injection (SEOI) leads to a reduction of over 47% in NOx emissions for λ (excess air coefficient) values of 1.5 and 1.0. The combustion duration and ignition delay initially increase and then decrease with the delay in SEOI, depending on the movement state of the fuel jet. With the increase in secondary injection proportion (SIP), brake thermal efficiency increases by no more than 1%, but NOx is reduced by more than 43% for λ values of 1.5 and 1.0. In the case of ultralean conditions (λ = 2.3), increasing the SIP from 0 to 30% results in a nearly 14% increase in the peak heat release rate (HRR) and a 19% reduction in combustion duration.

Validation of the Townsend criterion for ignition of volume gas discharges

An eigenvalue problem governing ignition of volume discharges is formulated in the drift approximation with account of photoionization and the presence of multiple ion species with various reactions. The Townsend ignition (self-sustainment) criterion is deduced by partial integration of this eigenvalue problem neglecting the photoionization, and, in the case of electronegative gases, also the detachment. The Townsend criterion is applied to three examples of discharge ignition in high-pressure air, two of them referring to negative coronas in concentric-cylinder and point-to-plane configurations and one to a configuration with weakly nonuniform electric field. The comparison of the results obtained from different forms of the Townsend criterion with those given by the accurate numerical solution of the full eigenvalue problem shows that the neglect of the diffusion of the charged particles produces an error in the ignition voltage of the order of or less. The effect of photoionization for these configurations is also weak as expected. The lower and upper estimates of the effect of negative ions over the ignition voltage are obtained from different forms of the Townsend criterion. A form of the Townsend criterion, which employs an effective attachment coefficient in air and takes into account, in an approximate way, also the detachment, gives a virtually exact value of the inception voltage in all the cases considered. Practical recommendations are given on when one can use the Townsend self-sustainment criterion, and when one should resort to a numerical solution of the general eigenvalue problem governing discharge inception.

Optimization of low-NOx Burner Under the Combined Influence of Multiple Factors

ABSTRACT The influence degree of structural parameters and operating parameters on the low NOx performance of burners was studied by numerical simulation and orthogonal experiment. Excess air coefficient (factor A) and flue gas circulation rate (factor B) were used as operating factors, fuel nozzle diameter (factor C), cyclone blade end deflection angle (factor D), flame-stabilizer inclination angle (factor E), and internal circulation tube diameter (factor F) were used as structural factors, the average temperature (T av), maximum temperature (T max) of the combustion chamber, and NO emission value at the combustion chamber outlet (M NO) were used as indicators. Range analysis and variance analysis were used to analyze the specific influence of the above factors on the indicators. In the studied cases, the most significant factor affecting T av and M NO is the factor B, followed by the factor C. The more significant factor affecting T max is the factor A, followed by the factor C. The coupling of multiple parameters has a significant effect on the distribution of flow field in the combustion chamber. Vortices are produced in all the cases studied. The vortices are basically symmetrical, but the number of vortices varies from 2 to 6. The results show that the burner has good flame stability.

Effects of preheating temperature, O2 distribution concentration and combustion temperature on the formation of PM during preheating-low NO combustion

Clarifying the mechanism of multi-mode PM formation during pulverized coal preheating-combustion is expected to facilitate the synergistic control of NO and PM, and a significant low carbon way to achieve clean combustion. In this study, combustion experiments under different preheating-combustion conditions were conducted in a preheating-combustion furnace. Based on this, a system coupling design was explored by combining preheating-combustion with air staging. The results demonstrated a significant simultaneous reduction in both PM and NO during preheating-combustion, achieving a synergistic control of PM and NO emissions. With an increase in preheating temperature(Tp), the NO formation decreased, while the PM10 formation increased. Increasing the excess air coefficient(αp) reduced the PM10 formation, while the NO exhibited a trend of initially decreasing and then increasing. The impact of the combustion temperature(Tc) on NO and PM was more pronounced, especially with a significant increase of 80.59% in the PM0.3 (from 1300 K to 1700 K). Furthermore, the effect of the interaction of the three factors on NO: αp and Tc > αp and Tp > Tp and Tc. After coupling preheating-combustion with air staging, the formation of NO and PM0.3 decreased by 33.27% and 17.43%, respectively, compared to the preheating-combustion baseline.

Air distribution and coal blending optimization to reduce slagging on coal-fired boiler water wall based on POD reduced order modeling for CFD

Slagging is a common phenomenon interfering with the safe and efficient operation of coal-fired boilers. Due to the lack of monitoring methods for species and temperature distribution near the water wall, which is critical for slagging formation, it is a tricky problem to detect and reduce the slagging in real time. A method for slagging distribution prediction and anti-slagging optimization of a 330 MW tangentially coal-fired boiler is developed in this paper. Proper orthogonal decomposition (POD) reduced order modeling and support vector machine (SVM) are used to predict the distribution of temperature and O2 near the water wall by taking 15 variables as input parameters (load, coal types, primary air rate, secondary air rate, excess air coefficient, and secondary air velocities). Next, fuzzy comprehensive evaluation (FCE) is employed to quantify the slagging occurrence and distribution on the water wall. Furthermore, the real time slagging prediction is realized with the combination of POD, SVM, and FCE. Finally, the conventional genetic algorithm (CGA) and simulated annealing genetic algorithm (SAGA) are adopted to optimize the air distribution schemes and coal blending schemes to reduce the slagging ratio, and their performances are compared. The results indicate that the predictions of temperature and O2 with POD show a good agreement with CFD simulations. In the optimization process, whether air distribution is optimized alone or both coal blending and air distribution are optimized simultaneously, the performance of SAGA is better than that of CGA. After optimizing the air distribution with SAGA, the slagging ratio of a typical operating condition with a load of 330 MW is reduced from 14.21% to 7.16%. The slagging ratio is further reduced to 5.36% after optimizing air distribution and coal blending schemes simultaneously. The proposed slagging prediction and optimization for anti-slagging opens a new perspective to alleviate slagging of water walls effectively.

Effects of intake conditions on a dual-fuel spark-assisted compression ignition engine with polyoxymethylene dimethyl ether and methanol as fuels

Dual-fuel spark-assisted compression ignition (DF-SACI) is an advanced engine combustion mode. The use of polyoxymethylene dimethyl ether (PODE) and methanol as fuel can reduce the carbon emissions of the DF-SACI engine. To improve the combustion continuity and minimize the knocking and emissions of DF-SACI engines, the effects of intake heating and boosting were investigated. The results showed that the combination of intake heating and delayed spark ignition promoted fuel diffusion and prevented multi-peak heat release. Intake boosting promoted the transformation of compression ignition into flame propagation ignition. Intake heating and boosting allowed engine combustion optimization. The brake thermal efficiency was 41.4 % and 44 % when the brake mean effective pressure was 0.6 and 0.8 MPa, respectively, and the maximum pressure rise rate, coefficient of cyclic variation in the indicated mean effective pressure, and emissions were within reasonable ranges. A high intake air temperature combined with delayed spark ignition reduced the enrichment of PODE, thereby reducing the self-ignition probability of the fuel mixture, which can reduce knocking. When intake boosting was applied, the adoption of an excess air coefficient (λ) of 1.8 eliminated knocking under most conditions. Intake heating improved fuel reactivity and increased the ratio of compression ignition, to allow for the simultaneous reduction of hydrocarbon (HC) and NOx emissions. The effects of intake boosting on NOx and HC emissions were related to the energy ratio of PODE. As the energy ratio of PODE is between 47 % and 68 %, the appropriate increase in λ reduced both HC and NOx emissions. The results are conducive to the development of low-carbon engines and can provide a new direction for engine research.

Feasibility study on supercritical fuel cooled solid oxide fuel cell stack with internal reforming

Solid oxide fuel cell (SOFC) is regarded as a promising energy conversion device because of its advantages such as high efficiency and fuel flexibility. With the advent of aviation electrification era, SOFC has been gradually studied as aviation power system. However, the high temperature operation and temperature gradient of SOFC bring challenges to practical application. Nowadays SOFC systems often use excessive air as coolant to reduce the temperature gradient of SOFC, which leads to the increases of the fuel consumption and reduction of the power generation efficiency. In order to maintain a lower temperature gradient with less air, a supercritical fuel cooled SOFC scheme is proposed in this paper. By establishing a one-dimensional model of conventional air-cooled fuel cell and fuel cell with fuel cooling channel. Through calculating the fuel cell temperature gradient under different working conditions, the results show that when the excess air coefficient (EAC) is 3, the temperature gradient of air-cooled SOFC reaches 22.7K/cm, while the temperature gradient of SOFC with fuel channel decreases to 8.35K/cm. Therefore, the SOFC with fuel channel can effectively reduce the use of air, reduce parasitic power consumption and improve the efficiency of the system while maintaining a lower temperature gradient.

The energy performances of an elastocaloric device for air conditioning through numerical investigation

The urgent needing to address global warming and the rapid depletion of fossil fuel reserves has led to a demand for immediate research in sustainable and clean energy technologies. Elastocaloric cooling is a promising proposal for clean refrigeration because of the zero global warming potential of the shape memory alloys, which are solid-state materials showing elastocaloric effect. The latter manifests when the shape memory alloys are stressed through a mechanical loading, transforming from the austenite phase toward the martensite one and releasing heat, dually transforming from the martensite phase into the austenite phase and absorbing heat. The updated literature accounts for 15 elastocaloric cooling devices, but none is close to commercialization. The efforts are devoted to making this decisive step by implementing new efficient devices.This paper analyses the energy performances of an elastocaloric rotary prototype employing binary NiTi wires through the first rotary bidimensional numerical model based on the finite element method to attain the device's potential cooling and heating capacities. In this paper, the energy performances of an elastocaloric rotary prototype employing binary NiTi wires are analyzed through a 2D numerical model based on the finite element method to attain the device's potential cooling and heating capacities. The model reproduces the thermo-fluid-dynamic behaviour of an experimental rotary device for air conditioning; meanwhile, the secondary fluid in the device is air. The accuracy of the rotary model easily allows to optimize the operating parameters of the elastocaloric prototype under construction.Results in terms of outlet air temperature, cooling power and coefficient of performance are presented for different air velocities inside the air channel and different rotation frequencies of the device. A performance map has been obtained by exploring the device's behaviour in the cooling mode under variable working conditions to identify the optimal configuration. A maximum COP of 6.22 (corresponding to a second law analysis efficiency of 60%) was evaluated under an airflow speed of 6 m s−1 and a frequency of 0.3 Hz, corresponding to ϕ∗=0.44. 28.5 K and 5400 W kg−1 are the reached peaks of temperature span and cooling power.

Numerical study of heat transfer characteristics of organic heat carrier furnace chamber

The heat transfer oil in the organic heat carrier furnace (OHCF) is prone to deterioration and deterioration at higher operating temperatures, resulting in overheating of the furnace tube and bursting of the tube, resulting in safety accidents. Therefore, it is necessary to study and analyze the flowing heat transfer characteristics of organic heat carriers in the furnace tube. The paper takes YY(Q)W-180(15) OHCF as the research object, mainly through ANSYS CFX numerical simulation method, to analyze the influence of influencing factors: inner and outer spiral tube spacing R, oxygen content, air preheating degree T and excess air coefficient on the temperature field, velocity field and NOx concentration inside the OHCF, and found that the organic heat carrier in the oxygen concentration of 25%, air preheating The thermal efficiency of the furnace is higher and the pollutant content emitted at the exit of the furnace is lower when the oxygen concentration is 25%, the air preheating temperature is 498 K and the excess air coefficient is 1.10. Also, the smaller the inner coil spacing R1 and the outer coil spacing R2 from the furnace wall, the higher the overall furnace chamber temperature.

Research of the efficiency of gas ice’s under various load modes

When changing the load modes of gas internal combustion engines, the efficiency and economy of operation of such engines change significantly. The article discusses five main modes of operation of a gas internal combustion engine: start-up mode, idle mode, average (optimal) stroke mode, maximum (full) stroke mode, high speed mode (acceleration, acceleration). The article also discusses the parameters of the internal combustion engine: coefficient of performance, specific fuel consumption, excess air coefficient, degree of severity. Keywords: start mode, idle mode, medium mode, full flow mode, extreme conditions mode, excess air coefficient

The effect of ignition diesel injection conditions on the combustion process of natural gas engine

As transportation is a major contributor to carbon emissions, the significance of researching dual-fuel engines lies in their potential to substantially reduce such emissions. Based on the experimental engine of diesel micro-ignition and air intake channel injection natural gas engine, the effects of pilot diesel quality, diesel injection timing and excess air coefficient on combustion process were studied. The test was performed on a single-cylinder engine modified with the WP12 natural gas engine at 1000 rpm under medium load condition. The results revealed that there is a critical pilot energy proportion that affects the combustion stability and that increasing the pilot diesel mass below the critical value improves the combustion stability. The critical diesel energy share increases as the diesel injection moment is delayed and the λ is increased. From the combustion process analysis early ignition diesel injection time is beneficial to improve the thermal efficiency, reduce THC and CO emissions, but sometimes worsen the NOx emissions. Reasonably improving the quality of pilot diesel can accelerate the combustion process and improve thermal efficiency by up to 47.7%.

Experimental Study on NOX Formation Characteristics in Flue Gas Recirculation Combustion Process of S-CO2 Coal-Fired Boiler

ABSTRACT Flue gas recirculation technology and air-staged combustion technology are both effective methods for reducing the production of NOX in coal-fired boilers. However, the synergistic effect of air-staged combustion technology and flue gas recirculation technology on NOX generation characteristics in S-CO2 boilers needs further study. The formation characteristics of NOX in the main combustion zone of coal combustion were studied experimentally when flue gas recirculation and air-staged combustion were combined. The results indicate that as the recirculation flue gas is injected at deeper levels, there is a gradual decrease in the concentration of NOX along the path, And the concentration of O2 also decreases gradually. The concentration of NOX decreases as the excess air coefficient decreases. The concentration of O2 increases as the excess air coefficient increases. Additionally, the NOX concentration at the furnace outlet increases with the increase of the excess air coefficient. Along the axial direction of the one-dimensional flame combustion furnace, the NOX production along the way and the NOX concentration at the outlet decrease with the increase of the flue gas recirculation position. Flue gas recirculation in air-staged combustion is an effective method for reducing NOX emissions. The positioning of flue gas recirculation significantly impacts NOX emissions. The NOx concentration is lowest when the flue gas recirculation rate is 27% and the mixing position of the recirculated flue gas is 300 mm with an excess air coefficient of 0.8.

The Development and Investigation of the Diffusion-Stabilizing Burner with the Niche

The article presents the results of researches of the development and field tests in bench conditions of the microdiffusion stabilizer burner device of a rectangular slot type with a niche deepening along the entire perimeter of the burner. The air passes through a rectangular slot, gaseous fuel for combustion is supplied to the recirculation zone through a system of holes in the end wall of the stabilizer. On the side of the output end of the stabilizer, there is a niche deepening. As studies have shown, the niche deepening is an additional source of stabilization and intensification of torch burning. The experimental data and calculated dependences on the stabilization of the torch in the modes of “poor” disruption are obtained. It is shown that the stable operation of the burner on the lean limit expands – the coefficient of excess air increases with an increase in the width of the stabilizer, the diameter of the gas distribution holes, the coefficient of shading of the burner and air temperature, as well as with a decrease in the speed of the air flow. The research results showed that “rich” flame failure – flame failure with a gradual increase in gas flow occurs at air excess ratios less than unity. This ensures the reliable operation of the burner at the calculated operating modes with respect to the coefficient of excess air a = 1.15 – 6.0 and the air flow speed Wp = 12.0 m/s. A dependence was obtained that determines the influence of regime and design factors on the characteristics of a rich flare failure. The sustainability of the burner operation on the rich limit increases – the coefficient of excess air decreases, with an increase in the width of the stabilizer, the shading coefficient of the burner, air temperature and a decrease in air velocity. The experimental data and calculated dependences on the length of the combustion zone in the burner device are obtained. It was established that at the calculated coefficient of excess air a = 2.0 and higher coefficients, complete combustion of fuel occurs on the length of the combustion space X = 1000 mm. The relative length of the flame decreases when the shading coefficient of the burner and the air temperature increases. Measurements of harmful nitrogen oxides showed that the maximum content of oxides is observed at the coefficient of excess air a = 1.0 and is 125 mg/m3, which is less than the limit values which allowed by regulatory documents.

A data-driven method for the correction of optical distortions of depth cameras in immersion NDT

Stereoscopic cameras, also known as depth cameras, are increasingly present in robotics navigation and 3D scene reconstruction. Normally, off-the-shelf depth cameras are not suited for underwater environments and exhibit considerable distortions in the provided 3D images when operating underwater. This is mainly due to the large difference in the refractive coefficients of air and water. This issue prevents their use in subsea applications such as the inspection of oil pipelines, valves and manifolds, where these devices could be used for odometry during ultrasonic inspections as well as for 3D scanning. Aiming to allow for such applications, we present a data-driven method for the correction of distortions caused by unaccounted diffractions in depth cameras. First, the distortion is modelled via a series of detections of control points from a standard target at known underwater positions, and an approximation of the inverse distortion is obtained. Then, at runtime, a procedure takes as input the (distorted) point cloud given by the camera at each frame, applies the inverse distortion, and yields a corrected point cloud. We apply the method to data provided by a RealSense D405 camera encased in a sealed acrylic container underwater. The correction makes it possible to use the camera for odometry underwater, clearing the path for the use of off-the-shelf depth cameras in a wide range of subsea applications. The method can be applied for any other transparent fluid.

Study on mixing and combustion characteristics of solid rocket ramjet with a large angle of attack

Solid rocket ramjet faces the problems of large angle maneuvering and stage transformation in the actual operation. In order to study the effect of the change of angle of attack and excess air coefficient on the performance of boron-containing solid rocket ramjet, the fluid field with different conditions were calculated. The applicability of the numerical model was verified by ground direct-connected experiments. The results showed that as the angle of attack increases, the mixing in the head reflux area and the initial air-gas contact area are enhanced. The combustion ratio of combustible components in the front section is greatly increased, which helps to improve the combustion efficiency of the motor. When the excess air coefficient increases from less than 1 to much greater than 1, the mixing combustion in the head region is also strengthened. However, the radial impact of excess air causes the gas to deflect to the upper side of chamber, and then most of the particles move close to the wall, resulting in a lower level of combustion. The general trend is as follows, under the same mixing-dominated pattern, the average mixing at the outlet decreases with increasing angle of attack, and the combustion efficiency is reversed. Under different mixing-dominated patterns, higher combustion efficiency can be obtained at lower mixing when the head region dominates.

Combustion and emission characteristics of dimethyl ether/gasoline DFSI engine under different excess air coefficients

Dimethyl ether (DME) was a carbon neutral alternative fuel for engines.The combustion and emission characteristics of a DME/gasoline Dual Fuel Spark Ignition (DFSI) engine with various excess air coefficients (λs) at different DME ratios (ΦDME) were investigated experimentally in this study.The in-cylinder pressures along with their relevant crank angle were used for the combustion characteristics calculation. The light five component exhaust gas analyzer and particle analyzer were employed for the gaseous and particulate matter emission measurement, respectively. Results showed that the DME/gasoline dual fuel combustion strategy can enhance the Brake Mean Effective Pressure (BMEP) by up to 12.6% because the high diffusivity, superior LTR and fast LFS of DME. Although adding DME was beneficial for the reduction of gaseous emissions (HC, CO and NOx) from DME/gasoline DFSI engines, the gaseous emissions were mainly determined by the variation of λ s. Particularly, up to 93.4% of the CO emissions at stoichiometric condition can be reduced after increasing λ to 1.3. The fast evaporation rate and superior LTR of DME helped to suppress PN emissions, but larger DME ratio (ΦDME > 5%) was needed for λ >1.2.