Improve Combustion Performance Research Articles

Performance characteristics of a thin‐layered radial porous burner with different strategies for fuel‐air mixture supply

A recent surge of interest is focused on developing radiant burners that may replace traditional open flame burners because of their ability to interchangeably use a wide range of fuels with improved emissions and the overall efficiency of combustion appliances. This research focuses on identifying conditions under which a radiant burner with a thin‐layered radial porous emitter operates in the internal combustion mode with increased radiation efficiency alongside decreased noise and NOx emission. The way the fresh mixture distributes over the cylindrical cavity of the emitter is the main factor affecting the burner performance. Two strategies for fuel‐air mixture supply were considered: (i) co-axial feed of turbulent flow through the open end of the cylindrical emitter using a divergent annular nozzle; (ii) distributed radial feed of laminar flow through a thin‐layered conical porous insert located inside the cavity of the emitter. The burner performance (radiation efficiency, NOX, and noise emissions) was experimentally studied in the ranges of thermal power of 4.0–9.1 kW and equivalence ratio of 0.5–1.0, which corresponds to the range of the emitter temperature from 500 to 1190 K. It was established that the distributed radial feed of fresh mixture dramatically reduced the noise emission, markedly improved the uniformity of the emitter temperature, and slightly increased the radiation efficiency of the burner. The improved combustion performance makes the thin‐layered radial porous burners relevant for application in domestic heating appliances.

Correlation between needle behavior and fuel flow rate for gasoline direct injection injector using X-ray phase contrast imaging technique

To meet strong emission regulations such as Euro-7, which is expected to be implemented in 2025. The multiple-injection strategy is one of well-known solutions to reduce exhaust gas and improve combustion performance on GDI engine. In order to realize multiple-injection strategy, it is necessary to secure excellent flow rate repeatability within short period. Therefore, the purpose of this study was to analyze the flow rate repeatability of GDI injector under various multiple injection conditions and to correlate with needle behavior of GDI injector and flow rate repeatability. To analyze flow rate repeatability, the injection rate data was obtained by the Bosch method and the individual flow rates of 110 shots were analyzed under several experimental conditions. The movements of the ball and armature inside the injector were visualized using the X-ray phase contrast imaging (XPCI) technique, and the individual behaviors of the ball and the armature were quantitatively analyzed by image post-processing analysis. In this study were used two test GDI injectors with same structure. Whereas Flow rate results were different on shorter dwell time conditions. This study revealed that a specific injector had unstable injection rate and worse Shot to Shot (STS) deviation under dwell time 0.7 ms. In addition, armature bouncing appeared in a specific GDI injector. This armature bouncing affects unstable flow rate characteristics because when armature lift up again, the position of armature was different at every time.

Stone Fruit Seed: A Source of Renewable Fuel for Transport

This study investigated the suitability of stone fruit seed as a source of biodiesel for transport. Stone fruit oil (SFO) was extracted from the seed and converted into biodiesel. The biodiesel yield of 95.75% was produced using the alkaline catalysed transesterification process with a methanol-to-oil molar ratio of 6:1, KOH catalyst concentration of 0.5 wt% (weight %), and a reaction temperature of 55 °C for 60 min. The physicochemical properties of the produced biodiesel were determined and found to be the closest match of standard diesel. The engine performance, emissions and combustion behaviour of a four-cylinder diesel engine fuelled with SFO biodiesel blends of 5%, 10% and 20% with diesel, v/v basis, were tested. The testing was performed at 100% engine load with speed ranging from 200 to 2400 rpm. The average brake specific fuel consumption and brake thermal efficiency of SFO blends were found to be 4.7% to 15.4% higher and 3.9% to 11.4% lower than those of diesel, respectively. The results also revealed that SFO biodiesel blends have marginally lower in-cylinder pressure and a higher heat release rate compared to diesel. The mass fraction burned results of SFO biodiesel blends were found to be slightly faster than those of diesel. The SFO biodiesel 5% blend produced about 1.9% higher NOx emissions and 17.4% lower unburnt HC with 23.4% lower particulate matter (PM) compared to diesel fuel. To summarise, SFO biodiesel blends are recommended as a suitable transport fuel for addressing engine emissions problems and improving combustion performance with a marginal sacrifice of engine efficiency.

Feasibility Study of Bio-Sludge Hydrochar as Blast Furnace Injectant

Hydrothermal treatment can convert paper mill biological (bio-) sludge waste into more energy-dense hydrochar, which can achieve energy savings and fossil CO2 emissions reduction when used for metallurgical applications. This study assesses the basic, combustion and safety performance of bio-sludge hydrochar (BSHC) to evaluate its feasibility of use in blast furnace injection processes. When compared to bituminous and anthracite coals, BSHC has high volatile matter and ash content, and low fixed carbon content, calorific value and ignition point. The Ti and Tf values of BSHC are lower and the combustion time longer compared to coal. The R0.5 value of BSHC is 5.27 × 10−4 s−1, indicating a better combustion performance than coal. A mixture of BSHC and anthracite reduces the ignition point and improves the ignition and combustion performance of anthracite: an equal mixture of BSHC and anthracite has a R0.5 of 3.35 × 10−4 s−1. The explosiveness of BSHC and bituminous coal is 800 mm, while the explosiveness of anthracite is 0 mm. A mixture of 30% BSHC in anthracite results in a maximum explosiveness value of 10 mm, contributing to safer use of BSHC. Mixing BSHC and anthracite is promising for improving combustion performance in a blast furnace while maintaining safe conditions.

Gas emission characteristics of sewage sludge co-combustion with coal: Effect of oxygen atmosphere and feedstock mixing ratio

Rapid urbanization brings increasing production and accumulation of sewage sludge (sludge for short) challenging ecological environment sustainability. Combustion can achieve sludge reduction and harmless treatment, but faces pollutant emission problems. This work explored gas emission characteristics of sludge co-combustion with coal in oxygen atmosphere. The results showed that sludge combustion in oxygen atmosphere could worsen SO2 and CO emission. The optimum desulfurization temperature for sludge combustion was 800 °C in oxygen atmosphere. Due to relatively low N and S contents in coal, NO and SO2 emission were significantly reduced when adding 25% coal in co-combustion. However, increasing oxygen content in oxygen atmosphere induced NO and SO2 emission in co-combustion. An oxygen atmosphere with 30% of oxygen content was recommended for co-combustion, which had less effect on emission performance and improved combustion performance.

Co-Combustion Characteristics And Ash Melting Behavior Of Sludge/High-Alkali Coal Blends

ABSTRACT Liquid slagging is an important solution for the problem of high-alkali coal slagging. The blending of low-melting-point fuel for combustion can effectively reduce the ash melting point of mixed fuel, improving the efficiency of liquid slagging. In this study, highly active sludge is mixed with Zhundong (ZD) coal. Then, co-combustion characteristics and ash melting behavior are studied by combining thermogravimetric analysis, thermodynamic analysis, ash melting analysis and ash composition analysis. The following results are observed. Ignition temperature is significantly reduced with an increase in sludge blending ratio, and combustion performance deteriorates rapidly when sludge proportion exceeds 20 wt.%. The burn out temperature initially decreases and then increases, reaching its minimum value when the sludge blending ratio is 10 wt.%. The blending of sludge causes the apparent activation of the sample to decrease, enhancing the combustion activity of the mixed fuel. The mixed fuel has lower ash melting point. A eutectic system with low melting point is produced due to the reaction of a large amount of sludge Fe2O3 with SiO2 in coal. The ash melting point is only 1080°C when 10 wt.% sludge is mixed. On the basis of the two considerations for improving combustion performance and reducing the melting point of ash, the recommended optimal blending ratio of sludge is 10 wt.%.

A Double-Wiebe Function for Reactivity Controlled Compression Ignition Combustion Using Reformate Diesel

AbstractReactivity controlled compression ignition (RCCI) combustion has previously been proposed as a method to achieve high fuel conversion efficiency and reduce engine emissions. A single-fuel RCCI combustion strategy can have decreased fuel system complexity by using a reformate fuel for port fuel injection and the parent fuel (diesel) for direct injection. This paper presents a one-dimensional computational model of a compression ignition engine with single-fuel RCCI. A Wiebe function is used to predict the combustion process by representing the mass fraction burned (MFB) on a crank angle resolved basis. One single-Wiebe function (SWF) and two double-Wiebe functions(DWFs) were fitted to experimentally derive MFB data using the least-square method. The fitted results were compared with MFBs calculated from experimental data to verify the accuracy. The SWF did not fully capture the MFB curve with high fidelity while the detailed DWF captured the MFB curve within a root mean square error of 1.4%. The reduced double-Wiebe function (RDWF) also resulted in a predicted combustion profile with similar accuracy. Hence, the RDWF was used in a GT-power thermodynamic study to understand the effects of the low-temperature heat release (LTHR) fraction and combustion phasing on combustion characteristics. At optimum phasing of 5–10 crank angle degree after the top dead center, increasing the LTHR fraction from 20% to 60% resulted in the fuel conversion efficiency increasing from 39.5% to 41.1%, thus suggesting that the reformate fuel-based RCCI strategy is viable to unlock improved combustion performance.

Involvement of the organics in aqueous phase of bio-oil in hydrothermal carbonization of lignin

Aqueous phase of bio-oil (APBO) is water-rich but also contains some sugar-derivatives and phenolics. APBO has little potential as feedstock for producing biofuel, but can be potentially used as medium for hydrothermal carbonization (HTC) of biomass. In this study, the HTC of lignin in APBO was conducted, aiming to probe the influence of the organics in APBO on property of the hydrochar. The results indicated that the organics in APBO cross-polymerized with lignin derivatives, resulted in the yield of hydrochar to exceed 100%. In addition, APBO promotes the deoxygenation but does not promote dehydrogenation. More aliphatic structures are generated in the hydrochar, reducing its thermal stability. In addition, the hydrochar from APBO also shows the improved combustion performance by lowering the activation energy and the ignition temperature (180 vs 240 °C).

Research on application of asymmetrical Pre-chamber in Air-Assisted direct injection kerosene engine

• Effects of asymmetric jet pre-chamber on combustion process of kerosene AADI engines were studied. • The simulation of jet pre-chamber schemes was conducted for combustion optimization. • Engine test on combustion comparison of different ignition schemes was performed. • The asymmetric jet pre-chamber was found to be advantageous to improve combustion performance. Aiming at the power improvement of the aviation kerosene engine caused by the mixture preparation, and slow combustion rate, this paper introduced the design and application of the asymmetric jet pre-chamber on a spark ignition piston-type aviation engine equipped with the kerosene low-pressure air-assisted direct injection (AADI) system. Simulation calculation was conducted on combustion differences between the asymmetric pre-chamber and the traditional symmetrical pre-chamber. Meanwhile, the impacts on the flame combustion duration and heat release process in the main combustion chamber, which was divided into zone A and zone B, by the different jet nozzle orifice diameters and spatial distribution angles in the asymmetric jet pre-chamber were analyzed in the paper; and engine bench tests were performed on the influence of the combustion characteristics and power performance by the asymmetric jet pre-chamber ignition scheme under different control strategies. The simulation results showed that the asymmetric pre-chamber could further improve the combustion reaction rate by 7% and the cumulative heat release rate by 17%, thereby effectively promoting the engine combustion efficiency. And an optimal orifice diameter by 2.00 mm of the two jet nozzle in the zone B existed. Compared with the spatial angle α of these two jet nozzle in zone B by 80°, the spatial angle α of 50° can further be helpful to strengthen the heat transfer between the jet flame in the pre-chamber and the mixture in the main combustion chamber. The test results showed that the asymmetric pre-chamber was beneficial to improve the engine combustion performance by 11.4% under low load and by 16.7% under heavy load conditions. The optimal combustion performance can be obtained by the asymmetric pre-chamber at the condition of λ = 0.7, which resulted in higher jet flame ignition energy and faster combustion progression at the condition of richer mixture. As a conclusion, it is benefit to increase the initial heat release and enhance heat work transfer efficiency in the main combustion chamber of the AADI aviation kerosene engine.

Tuning the reactivity of Al–Ni by fine coating of halogen-containing energetic composites

In this paper, various core-shell structured Al–Ni@ECs composites have been prepared by a spray-drying technique. The involved ECs refer to the energetic composites (ECs) of ammonium perchlorate/nitrocellulose (AP/NC, NA) and polyvinylidene fluoride/hexanitrohexaazaisowurtzitane (PVDF/CL-20, PC). Two Al–Ni mixtures were prepared at atomic ratios of 1:1 and 1:3 and named as Al/Ni and Al/3Ni, respectively. The thermal reactivity and combustion behaviors of Al–Ni@ECs composites have been comprehensively investigated. Results showed that the reactivity and combustion performance of Al–Ni could be enhanced by introducing both NA and PC energetic composites. Among which the Al/Ni@NA composite exhibited higher reactivity and improved combustion performance. The measured flame propagation rate (v = 20.6 mm/s), average combustion wave temperature (Tmax = 1567.0 °C) and maximum temperature rise rate (γt = 1633.6 °C/s) of Al/Ni@NA are higher than that of the Al/Ni (v = 15.8 mm/s, Tmax = 858.0 °C, and γt = 143.5 °C/s). The enhancement in combustion properties could be due to presence of the acidic gaseous products from ECs, which could etch the Al2O3 shell on the surface of Al particles, and make the inner active Al to be easier transported, so that an intimate and faster intermetallic reaction between Al and Ni would be realized. Furthermore, the morphologies and chemical compositions of the condensed combustion products (CCPs) of Al–Ni@ECs composites were found to be different depending on the types of ECs. The compositions of CCPs are dominated with the Al–Ni intermetallics, combining with a trace amount of Al5O6N and Al2O3.

Role of soluble nano-catalyst and blends for improved combustion performance and reduced greenhouse gas emissions in internal combustion engines

Biofuels were getting an enormous attention to be used as fuel for diesel engines. This paper examines the effect of addition of nanoparticles in biofuel on diesel engines. The biofuel used for conducting tests was canola oil. Corn oil was mixed with titanium dioxide (TiO2) at different proportions as 25 ppm, 50 ppm, 75 ppm and 100 ppm. These nanoparticles mixed with biofuel and diesel. The nanoparticles were dispersed with biodiesel at the concentration of B10T25 (10% cornoil + 90% diesel + TiO225), B10T50, B10T75, B10T100, B20T25, B20T50, B20T75, and B20T100 and plain biodiesel are B10 and B20. All tests were carried at different speeds 1800 rpm, 2000 rpm, 2200 rpm, 2400 rpm, 2600 rpm and 2800 rpm. Performance and emission characteristics were estimated for all fuel blends. Results were compared to each other to characterize the fuel blend quality. The addition of titania with biofuel increased the performance qualities such as brake thermal efficiency (BTE), exhaust gas temperature (EGT), Torque and Power. Further this combination reduced the Greenhouse gas emissions such as CO, CO2, and UHC. The specific fuel consumption (SFC) was also reduced and proved to be the better alternative to existing fossil fuel. However, the emission of NOx was increased.

Upgrading of banana leaf waste to produce solid biofuel by torrefaction: physicochemical properties, combustion behaviors, and potential emissions.

This study is the first report that focuses on investigating the effects of torrefaction on the bioenergy-related properties, combustion behavior, and potential emissions of banana leaf waste (BLW). Experiments were first conducted in a bench-scale fixed-bed reactor operating at light (220 °C), mild (250 °C), and severe (280 °C) torrefaction conditions to torrefy the raw BLW. Torrefaction pretreatments reduced the weight of the raw BLW by about 60%, but the resulting solid biofuel can preserve up to 77% of the energy content of the raw biomass. It was found that torrefied BLW contains more concentrated fixed carbon than the raw BLW, volatile matter content of up to 59.8 wt.%, and a higher HHV of up to 20.7 MJ kg-1 with higher concentrations of carbon, nitrogen, and ash. Bulk density increased 13.0% over the raw BLW, and the torrefied BLW became a solid biofuel with 51.5% greater energy density under the severe torrefaction condition. The upgrading of BLW by torrefaction enhanced its combustion performance in terms of comprehensive combustion, ignition, burnout, and flammability indices. Compared with commercial hard coal, BLW torrefied at the mild condition (250 °C) had lower potential emissions per unit of energy, 25.3% less CO2 emission, 3.1% less CO emission, 96.4% less SO2 emission, and 18.4% less dust emission, except for NOX emission. This study conclusively indicates that BLW after torrefaction has enhanced bioenergy-related properties, improved combustion performance, and reduced emissions potential, proving to be a promising method for its valorization.

Comparative Studies on Combustion Characteristics of Blended Crude Jatropha Oil with Magnetic Liquid Catalyst and DEX under Normal Gravity Condition

A comparative study on the combustion characteristics of a single droplet fueled by DEX, crude jatropha oil (CJO), and a mixture of CJO with a magnetic liquid catalyst of rhodium trisulfate has been carried out under normal gravity conditions. The high viscosity of crude jatropha oil makes it difficult to burn under normal conditions (room temperature and atmospheric pressure), therefore the addition of a magnetic liquid catalyst rhodium trisulfate is needed to improve the properties of crude jatropha oil. As a catalyst, rhodium trisulfate has the potential to improve combustion performance while improving the physical properties of crude jatropha oil as an alternative fuel for the better. Furthermore, performance tests were also carried out with DEX fuel with a cetane number (CNs) 53. The results showed that compared to DEX, it was seen that the liquid metal catalyst rhodium trisulfate succeeded in making crude jatropha oil more charged so that the combustion process was better. This is evidenced by a significant change in the dimensions of the flame and an increase in the combustion temperature. Moreover, it is also seen that the burning rate increases and the ignition delay become faster.

Insights into in-situ sulfur retention by co-combustion of dyeing sludge and wood sawdust

Dyeing sludge (DS) incineration is a promising strategy to achieve waste reduction and waste-to-energy conversion efficiency; however, the poor-combustion performance and high-emission level of the gaseous sulfur of DS limit its applications. This study attempts to introduce wood sawdust (WS) to improve combustion performance and inhibit the sulfur emission during DS incineration. The combustion characteristics and release behavior of sulfur gas products of DS-WS mixtures were investigated using thermogravimetry and mass spectrometry (TG-MS), as well as the influence of WS on sulfur fate of DS and the in-situ retention mechanism to sulfur were revealed by ash analysis. Results indicated that WS addition restrained the devolatilization of light volatiles and facilitated the degradation of heavy volatiles and fixed carbon. WS addition improved the combustibility, burnout performance and combustion stability of DS. Organic sulfur species occupied most sulfur-containing compounds in DS, the thermal degradation of organic matter was responsible for emitting SO2, CH3SH, H2S, COS. SO2 contributed > 40% of sulfurous gas emissions. WS addition (30%) significantly reduced the normalized sulfur content from DS, and the in-situ retention ratio to sulfur reached 16.72%. The in-situ retention mechanism to sulfur was explained as potassium iron sulfate and calcium hydrogen sulfate jointly retained the release of sulfur. Moreover, Ca-based sulfate was more stable, indicating that the newly formed mineral contributed to preventing the re-emission of sulfur from incineration residue.

Ilmenite as alternative bed material for the combustion of coal and biomass blends in a fluidised bed combustor to improve combustion performance and reduce agglomeration tendency

Co-firing coal and biomass has the potential to reduce GHG emissions. However, high levels of alkali and alkaline metals in biomass ash can bring additional issues to the operation of coal-fired boilers. This study investigates the effects of ilmenite as the bed material on CO and NOx emissions and combustion efficiency of a coal and biomass blend, and the agglomeration tendency of the bed material with a pilot-scale (30 kWth) bubbling fluidised bed combustor. The experiments were carried out at 900 °C using a bituminous coal blended with wheat straw pellets at 40 wt% as the fuel and silica sand as the baseline bed material. Samples of agglomerates collected from the combustor and cyclone ash were characterised by SEM-EDS, XRD, and XRF. The results revealed that ilmenite could reduce the level of excess air required to achieve complete combustion due to lower CO emissions and less efficiency loss compared to silica sand. However, ilmenite increased NOx emissions. Furthermore, the characterisation of the obtained agglomerates and cyclone ash showed that ilmenite could hinder the K-rich molten substance attachment to the bed material, leading to significantly smaller agglomerates and hence less tendency towards defluidisation in comparison to silica sand.

Surface fluorination of n-Al particles with improved combustion performance and adjustable reaction kinetics

Surface composition plays a crucial role for the energy output performance of nanosized aluminum (n-Al) based metallic fuels. However, effective surface modification strategy with integrated functions and mild preparation conditions remains being exploited. Herein, a polydopamine fluoride (PF) coating was successfully constructed by covalent decoration of polydopamine (PDA) with thiol-terminated organic fluoride for surface engineering of n-Al under ambient conditions. The uniform coating of PF shell on the n-Al surface enabled the Al@PF composites optimized contact area between reactive components (Al and F). Concomitantly, the generation of fluoride gaseous species from PF coating facilitated the mass transport and self-activation of n-Al particles. It resulted in a substantially enhanced burning rate (196.4 mm s−1), which is 8.1 and 3.6 times than that of pristine n-Al (24.2 mm s−1) and physically mixed samples (54.7 mm s−1), respectively. Additionally, the reaction kinetics could be readily adjusted by tailoring the diffusion distance of reactants, as exhibited by varied heat release (0.24–1.43 kJ g−1), ignition delay (79–427 ms), and pressurization rate (6.3 × 101–2.3 × 103 kPa s−1). On this basis, the surface reaction mechanism was further clarified by combining theoretical simulation and experimental results. The current study provided a general approach for improving combustion performance and modulating reaction kinetics of advanced energy materials by elaborate surface design.

Rotating gliding arc discharge plasma-assisted combustion from ignition hole

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

Thermal efficiency improvement of a range extender based on the T-GDI engine for a medium-size electric bus using on-board gasoline fuel reforming with steam addition

Electric vehicles (EVs) are becoming increasingly popular in the global automobile industry. A range extender is a generator that increases the mileage of EVs. The engine for a range extender operates in a steady state. Steady conditions are suitable for catalyst-based on-board fuel reforming operations. Hydrogen has unique properties that improve combustion performance, such as fast burning, short quenching distance, and increased flammability. We carried out experiments and analyses to improve the thermal efficiency of a range extender that uses catalyst-based on-board fuel reforming with steam addition. For this study, steam was generated from exhaust-waste heat. Based on a previous study, the power requirement for the range extender of a medium-sized city bus was calculated. Accordingly, the range extender was operated at a brake mean effective pressure (BMEP) of 10 bar and speed of 2000 rpm. The results indicate that reformed H2 has positive effects on the combustion performance and thermal efficiency of the range extender. Steam addition to the reformer improves the reforming performance and greatly influences the reduction in NOx emissions. Moreover, steam addition to the reformer leads to an increase in thermal efficiency. However, steam addition cannot affect the thermal efficiency as much as it affects the reforming performance.

The effects of particle size on flameless combustion characteristics and NOx emissions of semi-coke with coal preheating technology

The experiments of the effect of particle size on flameless combustion characteristics and NOx emissions of Shenmu semi-coke were launched on a bench-scale coal preheating combustion test rig. The results revealed that the difference of fuel particle size greatly influenced the yield of each component in high-temperature coal gas and the reactive activity of coal char, thus subsequently affecting the final combustion process and NOx emissions. The specific surface area and pore volume of Shenmu semi-coke were both significantly increased after preheated, leading to a better reactivity and the improved combustion performance, especially when d50 (the mean particle size) = 163.84 μm, where the temperature of the down-fired combustor reached the highest. The different particle size of Shenmu semi-coke resulted in different preheating temperature, which further affected the content of each component in the high-temperature coal gas. During the self-preheating process, most volatile matter and fuel bound N were separated out and the released N was mainly converted to N2 and NH3, besides the conversion rate of each component (C, H, N and V) was the highest when d50 = 100.17 µm. Additionally, all experimental conditions achieved flameless combustion, with a transparent combustion area, but no flame front visible to the naked eye, and the highest combustion efficiency was 98.23% when d50 = 163.84 µm with the brightest flame image. It was discovered in this experimental that there was a critical value (d50 = 198.54 μm) of Shenmu semi-coke particles. When the particle size was lower than or higher than the critical value, NOx generated by combustion would decrease. The lowest NOx emission was 89.46 mg/m3 (@6% O2) when d50 was 35.34 μm.

Ignition Process and Flame Lift-Off Characteristics of dimethyl ether (DME) Reacting Spray

Advanced combustion systems that utilize different combustion modes and alternative fuels have significantly improved combustion performance and emissions compared to conventional diesel or spark-ignited combustions. As an alternative fuel, dimethyl ether (DME) has been receiving much attention as it runs effectively under low-temperature combustion (LTC) modes such as homogeneous charge compression ignition (HCCI) and reactivity control combustion ignition (RCCI). Under compression-ignition (CI), DME can be injected as liquid fuel into a hot chamber, resulting in a diesel-like spray/combustion characteristic. With its high fuel reactivity and unique chemical formula, DME ignites easily but produces almost smokeless combustion. In the current study, DME spray combustion under several different conditions of ambient temperature (Tamb= 750–1100 K), ambient density (ρamb= 14.8–30 kg/m3), oxygen concentration (O2= 15–21%), and injection pressure (Pinj= 75–150 MPa) were studied. The results from both experiments (constant-volume combustion vessel) and numerical simulations were used to develop empirical correlations for ignition and lift-off length. Compared to diesel, the established correlation of DME shows a similar Arrhenius-type expression. Sensitivity studies show that Tamband Pinjhave a stronger effect on DME's ignition and combustion than other parameters. Finally, this study provides a simplified conceptual mechanism of DME reacting spray under high reactivity ambient (high Tamb, high O2) and LTC conditions. Finally, this paper discusses engine operating strategies using a non-conventional fuel such as DME with different reactivity and chemical properties.