Reduced Ignition Delay Research Articles

Karakteristik Pembakaran Droplet Campuran Metil Oleat – Etanol dengan Penambahan Multi -Walled Carbon Nanotubes

This research intended to investigate the combustion characteristics of methyl oleic – ethanol blend with OH functionalized multi-walled carbon nanotubes (MWCNT-OH) addition. Methyl oleic is an unsaturated fatty acid methyl ester, which is a constituent of various biodiesels. The observed fuel was a mixture of Methyl oleic with 20% vol of ethanol. MWCNT-OH content was varied by 100 ppm, 200 ppm, 300 ppm, 400 ppm, and 500 ppm (wt based). The presence of ethanol in the droplets is intended to promote the microexplosion phenomenon, generating smaller droplets and a shorter burning time. The experimental results show that the MWCNT-OH addition on the droplet of Methyl oleic – ethanol blend decreased the ignition delay and droplet burning time, while the constant burning rate and droplet temperature (and flame temperature) were increased. Reducing ignition delay time due to the higher thermal conductivity of nanofluid droplets results in more effective heat absorption from the environment and better heat transport inside the droplet. Hence, droplet vaporization, flammable mixture formation and ignition occur in a shorter time. Furthermore, this condition encourages a higher burning rate and a lower droplet burning time. The higher droplet and flame temperatures are related to the higher heating value of the methyl oleic – ethanol – MWCNT-OH mixture and higher droplet burning rate, which results in a higher heat release rate.

A Comprehensive Review on the Hydrogen–Natural Gas–Diesel Tri-Fuel Engine Exhaust Emissions

Natural gas (NG) is favored for transportation due to its availability and lower CO2 emissions than fossil fuels, despite drawbacks like poor lean combustion ability and slow burning. According to a few recent studies, using hydrogen (H2) alongside NG and diesel in Tri-fuel mode addresses these drawbacks while enhancing efficiency and reducing emissions, making it a promising option for diesel engines. Due to the importance and novelty of this, the continuation of ongoing research, and insufficient literature studies on HNG–diesel engine emissions that are considered helpful to researchers, this research has been conducted. This review summarizes the recent research on the HNG–diesel Tri-fuel engines utilizing hydrogen-enriched natural gas (HNG). The research methodology involved summarizing the effect of engine design, operating conditions, fuel mixing ratios and supplying techniques on the CO, CO2, NOx and HC emissions separately. Previous studies show that using natural gas with diesel increases CO and HC emissions while decreasing NOx and CO2 compared to pure diesel. However, using hydrogen with diesel reduces CO, CO2, and HC emissions but increases NOx. On the other hand, HNG–diesel fuel mode effectively mitigates the disadvantages of using these fuels separately, resulting in decreased emissions of CO, CO2, HC, and NOx. The inclusion of hydrogen improves combustion efficiency, reduces ignition delay, and enhances heat release and in-cylinder pressure. Additionally, operational parameters such as engine power, speed, load, air–fuel ratio, compression ratio, and injection parameters directly affect emissions in HNG–diesel Tri-fuel engines. Overall, the Tri-fuel approach offers promising emissions benefits compared to using natural gas or hydrogen separately as dual-fuels.

Optical study on the single and multiple regions of flame propagation and combustion characteristics of methane/air mixture ignited by pilot diesel

The combustion characteristics of lean methane/air mixtures ignited by single and multiple diesel sprays were investigated using an optical RCEM test bench. The experimental approach included flame natural luminescence photography, pressure data acquisition, and heat release analysis. The results revealed that the relationships of ignition delay and orifice diameter varied under single diesel and dual fuel combustion mode. Under dual fuel mode, increasing the orifice diameter of the single-orifice nozzle resulted in a reduction in ignition delay, an acceleration in flame propagation, and an increase in the heat release rate. Increasing the number of orifices multiplied the flame regions, expanded the flame propagation pathways, and enhanced the promoting effect between the flames, resulting in faster flame propagation and increased heat release. The orifice axis angle significantly affected the ignition position and flame propagation direction. An appropriate axis angle would shorten the flame propagation distance, optimize the flame propagation direction and mitigate the impediment effect between flames.

Surface-Hydrophobic Al@COFs Core-Shell structured Composites: A class of efficient high-energy fuels

Aluminum powder is a metal fuel with numerous advantages, but it is susceptible to oxidation, which poses challenges for both ignition and combustion efficiency. Addressing these issues in the application of Al powder is crucial for enhancing the specific impulse of rockets and other related applications. By employing the concept of preparing composite materials and combining multiple materials, it is possible to enhance the stability of long-term storage of Al powder and improve ignition and combustion efficiency. This paper delves into the innovative synthesis and application of Al@COFs-based core–shell structured composites filled with AP to enhance stability, reduce ignition delay time, and improve the combustion efficiency of Al powder. To further enhance the water repellency of the composites, fluoroalkylsilanes were used to coat the Al@COFs@AP composites. The fluoroalkylsilane coating not only improves the oxidation resistance of Al but also introduces F, which disrupts the alumina shell of Al during combustion, generating AlF3 and increasing the heat of combustion. The findings presented in this paper will pave the way for the development of advanced aluminum-based materials with enhanced combustion characteristics and broadens the application areas of COFs.

Preparation of MXene-type C-TiO2 nanocatalysts for enhancing the combustion performance of AP/HTPB propellants

With the vigorous development of aerospace technology and the continuous improvement of the mobility of solid rockets, the combustion performance, especially the combustion rate, of AP-based propellants as power source of solid rockets has also been constantly improved. Due to the influence of AP thermal decomposition performance on the combustion rate of AP-based propellants, it has become necessary to develop new catalysts for AP thermal decomposition. A novel MXene-type C-TiO2 (M-TiO) nanomaterial has been successfully prepared by regulating the oxidation degree of MXene. Modern characterization technologies were used to investigate M-TiO nanomaterials. The analysis results indicated that M-TiO-2 nanomaterial exhibited the MXene-type C-TiO2 structure with large BET-SSA (126.8 m2/g). The catalytic experiments showed that HD temperature of AP with 2.0 wt% M-TiO-2 could be reduced by 68.2 °C and heat release was increased by about four times. The Ea of AP with M-TiO-2 (2.0 wt%) was significantly reduced by 54.5%. As for the combustibility of AP/HTPB propellant, M-TiO-2 (2.0 wt%) reduced ignition delay by 72.2% and enhanced combustion rate by 2.0 times. The reasons why M-TiO-2 improved the thermal decomposition performance of AP and the combustion performance of AP/HTPB propellant were the synergistic effect of catalysis and combustion support provided by the MXene-type C-TiO2 structure of M-TiO-2.

Combustion characteristics of water-oil emulsion droplets with special additives

Relevance. Fuel oil application in power plants is characterized by increased values of underburning and anthropogenic emissions. One way to reduce anthropogenic emissions is the use of oil-water emulsions. Also, additional specialized additives are used to reduce anthropogenic emissions and improve fuel combustion characteristics. Aim. To determine the optimal fuel oil additive to reduce anthropogenic emissions and ignition delay times. Methods. The following additives: ION-M, Rosneft R503V3, Rosneft R502V1 (relative mass concentration 0.5%) were added to the water-oil fuel. The physicochemical properties of fuel oil M-100, as well as the elemental composition of CHNSO, were determined. The rheological characteristics of water-oil fuel compositions were established. Using high-speed photography, the droplet ignition delay times were determined. Using the gas analyzer, it was possible to prevent anthropogenic emissions. Results and conclusions. The results of the study showed that the additive based on a special combination of positively and negatively charged ions (ION M) reduces ignition delay times by 20–60%, when the gas temperature varies in the range from 700 to 900 °C. The addition of the additive based on fatty vegetable acids (P502B3) reduced the ignition delay times by 7–10%, when the temperature changed in the range from 700 to 900 °C relative to water-oil fuel. It was found that when using the P502B1 additive in water-oil fuel, it was possible to reduce the ignition delay times by 15–50%. It was determined that in the presence of combustion catalysts, water binds with heavy hydrocarbons and thus the release of volatile substances occurs faster, i. e. the supplied heat is not wasted on heating water into droplets, but evenly affects the entire volume of fuel. The results of the study of anthropogenic emissions showed that the use of additives when burning water-oil fuel reduces the concentrations of CO, CO2, NO, SO2 by 8, 6, 10 and 13%, respectively, compared to fuel oil.

In-situ synthesis of MEMS compatible Al/Cu2HIO6/PVDF Metastable composites film with high combustion performance

To address the challenges related to significant pressure loss and weakened combustion performance of energetic materials when ignited on Micro-Electro-Mechanical Systems (MEMS), periodate-based MICs (Metastable Intermolecular Composites) have emerged as promising candidates due to their high energy density and combustion pressure. However, the integration of periodate-based MICs onto MEMS has not been effectively achieved thus far. Herein, we propose a simple, environmentally friendly, and cost-effective approach to fabricate a MEMS-compatible Al/Cu2HIO6/PVDF (polyvinylidene difluoride) energetic composite film. Our method involves utilizing a Cu(OH)2 array as a template and employing an in-situ and spin-coating process. The resulting Al/Cu2HIO6/PVDF film was characterized using various techniques including SEM, TEM, XRD, and XPS. These analyses reveal a tightly packed nano array morphology with a porous structure. DSC-TG analysis was conducted to investigate the thermal reaction of the Al/Cu2HIO6/PVDF composite film. The results demonstrate that the thermal reaction involved a complex multi-step process, with higher heat release (1121 J g-1), a faster reaction rate, and a lower initial reaction temperature (294.5 °C) compared to the Al/CuO/PVDF composite film. the reaction process of Al/Cu2HIO6/PVDF film was also been proposed by analyzing the products at different temperatures. combustion diagnostic tests were carried out to evaluate the combustion performance of the Al/Cu2HIO6/PVDF composite film. The results indicate that as CuO transformed into Cu2HIO6, the film exhibits a reduced ignition delay (8 ms) and combustion duration (50 ms), higher combustion temperature (3710 K), and stronger flame intensity (8630 a.u.).

A shock tube study of the ignition delay time of DME/ammonia mixtures: Effect of fuel blending from high temperatures to the NTC regime

An experimental and chemical kinetic investigation has been conducted to understand the effect of dimethyl ether (DME) blending on the ignition delay time of ammonia (NH3) from high temperatures to the negative temperature coefficient (NTC) regime in a shock tube with the DME fractions of 0 %, 5 %, 25 %, 50 %, and 100 %, temperatures of 690–1810 K, pressures of 1.2 and 10 atm, and equivalence ratio of 1.0. Four representative literature chemical kinetic models were validated against our measurements, however none of the above models can provide reasonable predictions of the experimental data in the NTC regime. A chemical kinetic model was developed in this study, the model was also been validated by the ignition delay times, laminar flame speeds and specie profiles data of DME/ammonia mixtures in the literature. Experimental results show that the ignition delay times of NH3 can be obviously shorten by 5 % DME addition in both high temperature and the NTC region. Chemical kinetic analyses reveal that the addition of 5 % DME can rapidly generate OH radical through the reaction pathway of HO2 → H2O2 → OH at 1250 K. At 800 K, the blended DME can be rapidly consumed via the reaction pathway of R → RO2 → QOOH → OOQOOH to promote the production of OH radical in the early stage, thus lead to the reduced ignition delay time of DME/NH3 mixture.

Combustion Behavior of Fuel Droplets with Metallic, Non-Metallic and Organo-Metallic Boron Additives

ABSTRACT There is considerable interest in the utilization of fuels derived from boron materials, with their high calorific value, in various applications ranging from propellants to pyrotechnics. Conversely, their impact on the combustion behavior of conventional hydrocarbon fuels remains largely unclear. In this study, ignition, combustion, micro-explosion and simultaneous atomization behaviors of gasoline-based alternative fuels containing metallic (28–35 µm MgB2), nonmetallic (1 µm amorphous boron, 10 µm AlB12 with 86–88% and 95–97% purity) and organo-metallic boron derivatives (triethyl borate (TEB) containing C2H5 groups and trimethyl borate (TMB) containing CH3 groups) were investigated. The experiments were carried out at droplet scale and recorded using a high-speed camera and a thermal camera. The findings revealed a systematic reduction in ignition delay for each gasoline fuel enriched with boron derivatives. 2.5%AlB12/G and pure TMB droplets were the fastest extincting fuel droplets (0.9678 s and 1.245 s, respectively). The highest maximum flame temperature was recorded as 626 K and 610 K for pure TMB and 80%TEB/G, respectively. Droplet diameter regression analyses showed that the diameters of fuel droplets containing predominantly metallic and nonmetallic boron derivatives decreased in accordance with the d 2 -law. This study demonstrated that cost-effective and easily producible amorphous boron and organometallic boron derivatives are promising energy carriers for hydrocarbon fuels.

Optical investigation of the influence of high-reactivity iso-octane turbulent jet ignition on the combustion characteristics of ammonia/air mixtures

Ammonia has attracted considerable attention as a zero-carbon fuel; however, challenges such as ignition difficulty and slow flame propagation persist. These challenges can be addressed by employing a highly reactive fuel in the pre-chamber to initiate the ignition of ammonia. This work aims to experimentally investigate the influence of pre-chamber fuel composition and concentration on ammonia combustion characteristics across various equivalence ratios. The results are as follows: elevating iso-octane equivalence ratios in the pre-chamber enhances stoichiometric ammonia combustion characteristics, reducing ignition delay and burn duration. However, excessive values result in significant delays and a decrease in flame speed. At an iso-octane equivalence ratio of 0.8, the main chamber exhibited the shortest combustion duration. By utilizing the optimal pre-chamber total equivalence ratios of 2.0 and 2.3, the ammonia lean combustion limit was achieved at an excess air ratio of 1.89 under experimental conditions (0.8 MPa, 440 K). As main chamber equivalence ratios decreased, ignition delay shortened. The pre-chamber total equivalence ratios exert a more pronounced impact on the main chamber ignition delay. In contrast, the main chamber equivalence ratios substantially influence the middle and later stages of combustion.

Effects of pilot injection on ignition performance for F-24/Gasoline fuel blends

This study experimentally investigates the effects of pilot injection on first stage and overall ignition behavior for different fuel blends. A conventional petroleum-derived fuel (F-24) with a Derived Cetane Number (DCN) of 48.5 and gasoline (GAS), which has a low DCN of 21.4 but high volatility, were blended at different volumetric ratios. These blends were injected into a high temperature, pressure vessel using either a single or pilot-main injection strategy. Four optical diagnostics (formaldehyde PLIF, OH* chemiluminescence, schlieren, and Mie scattering) were employed to visualize the ignition process and to evaluate liquid length, penetration distance, heat release rate, the first stage, and overall ignition delays. It is shown that the higher GAS blend ratios result in longer ignition delay and less overall heat release attributed to the poor reactivity of GAS. In such cases, the contributions of the extended first stage ignition delay to the extended overall ignition delay decrease with GAS blend ratio. Furthermore, some of the high GAS blend fuels exhibit no overall ignition at all due to the excessive fuel-air mixing. The study then shows that this decrease in ignition performance with GAS can be mitigated by introducing pilot injection, which shortens the ignition delays and provides more overall heat release. Specifically, at low GAS blend ratios, the ignition exhibits mixing controlled combustion where the ignition of pilot fuel-air mixture induces the main fuel ignition. For pilot-main injections, the decrease in first stage ignition delay accounts for the average of 87 % of the reduced overall ignition delay, suggesting that the reduced ignition delay with pilot injection is primarily due to the reduced time for fuel atomization, vaporization, and decomposition of the main fuel. These results will contribute to the development of ignition models capable of capturing the impact of fuel composition and pilot injection on ignition performance.

An experimental evaluation of novel biofuel and biodiesel from Ziziphus mauritiana seeds in DICI engine

The engine community is searching for novel fuels concerning sustained availability with superior properties to traditional engine fuels. From the seeds of Ziziphus mauritiana, vegetable oil is extracted and transesterified for improvement in its properties as engine fuel. The properties of the oil qualify it for engine applications. This investigation has been carried out on a 5.2 kW, 1500 r/min, eddy current loading compression ignition engine. Engine runs at different loads on neat Ziziphus mauritiana oil biofuel and on Ziziphus mauritiana biodiesel. Both fuels developed power at all loads of the engine. Z iziphus mauritiana oil has a lesser calorific value, elevated density, viscosity, and least brake thermal efficiency, highest emissions except for NOx. Z iziphus mauritiana oil properties were improved through transesterification. At maximum load, compared to Ziziphus mauritiana oil biofuel, Ziziphus mauritiana biodiesel has a percentage variation of 2.1%, 6.0%, 24.4%, 14.5%, and 31.4% increase in brake thermal efficiency, peak pressure, heat release rate, NOx, and carbon dioxide, respectively. A percentage variation of 40%, 26.1%, 33%, and 4% reduction in ignition delay, CO, HC, and smoke is observed, respectively for Ziziphus mauritiana biodiesel operation. Compared to Ziziphus mauritiana oil biofuel, the Ziziphus mauritiana biodiesel produced better results with lesser and nearly equal diesel emissions except NOx and smoke. Therefore, Ziziphus mauritiana biodiesel fuel can be used as a replacement fuel.

Combustion Characteristics of Boron-Iron Powder with Micro-Zone Compounding

ABSTRACT Boron-iron composite powders with a D50 value of < 0.5 μm and iron contents of 5, 10, and 20 wt.% were prepared via a combination of electro-explosive and roll-grinding methods. High-resolution transmission electron microscopy and electron probe X-ray microanalysis revealed evidence of boron-ion micro-zone composites. Ignition tests using a 150-W laser in a pure oxygen atmosphere indicated that the boron-iron composite powder effectively reduced the ignition delay of boron (224.8 ms), with 5 wt.% boron-iron composite powder exhibiting a reduced ignition delay of 106.1 ms. Thermal analysis tests in a pure oxygen atmosphere indicated that iron not only promoted the exothermic reaction of boron but also significantly promoted its oxidation. A comparison of the oxygen bomb calorific values of the composite powder, the original boron powder, and simple mixed powder revealed that the simple mixed iron did not improve the combustion performance of boron, whereas the composite powder generally improved the boron calorific value (12967 J/g), with the 10 wt.% boron-iron composite powder exhibiting a boron calorific value of 21,189 J/g. The addition of iron improved the combustion behavior, stabilized the combustion flame, and improved the combustion quality. An elevated iron content resulted in an increased sensitivity of the powder to the ambient pressure, and an elevated pressure effectively increased the burning rate. The experimental results indicated that iron generally improved the ignition and combustion performance of boron with low and high iron contents, respectively.

Enhancing the Ignition and Combustion Performances of Solid Propellants Incorporating Al Particles Inside Oxidizers.

The combustion efficiency of Al plays a critical role in the combustion of high-energy aluminum-based solid propellants. For traditional formulations, the Al powders are dispersed in the binder matrix, leading to limited contact with the oxidizers and hence usually insufficient combustion and higher values of the pressure exponent. In this paper, various core-shell structural Al/oxidizer composites such as Al@HMX, Al@AP, and AP@Al have been prepared by a spray-drying technique based on which solid propellants with precise interfacial control between Al particles and oxidizers were realized. Compared to the control sample, the modified propellants have a greater heat of explosion of 5890 J g-1 (15% higher) and a reduced ignition delay time of 58 ms (65% decrease). Without changing the content of components, the burn rates of propellants can be easily modulated by tuning the interfacial contact of Al and oxidizers, where it varies in a wide range of 4.56-5.79 mm s-1 at the same pressure of 1 MPa. After introducing Al/oxidizer composites, the lowest pressure exponent of 0.19 within 1-15 MPa could be achieved by using Al@HMX and AP@Al composites. The agglomeration of Al was also inhibited by using Al/oxidizer composites, and the mechanism can be interpreted by using a classical "pocket" model. Moreover, the improved combustion efficiency of the solid propellants was verified by a noticeable reduction in the unreacted Al content.

An Experimental and Detailed Kinetics Modeling Study of Norbornadiene in Hydrogen and Methane Mixtures: Ignition Delay Time and Spectroscopic CO Measurements

High-energy-density compounds such as norbornadiene (NBD) are being considered as potential cost-effective fuel additives, or partial replacements, for high-speed propulsion applications. To assess the ability of NBD to influence basic fuel reactivity enhancement and to build a database for developing future NBD kinetics models, ignition delay times were measured in two shock-tube facilities at Texas A&amp;M University for H2/O2, CH4/O2, H2/NBD/O2, and CH4/NBD/O2 mixtures (ϕ = 1) that were highly diluted in argon. The reflected-shock temperatures ranged from 1014 to 2227 K, and the reflected-shock pressures remained near 1 atm for all of the experiments, apart from the hydrogen mixtures, which were also tested near 7 atm, targeting the second-explosion limit. The molar concentrations of NBD were supplemented to the baseline mixtures representing 1–2% of the fuel by volume. A chemiluminescence diagnostic was used to track the time history of excited hydroxyl radical (OH*) emission, which was used to define the ignition delay time at the sidewall location. Spectroscopic CO data were also obtained using a tunable quantum cascade laser to complement both the ignition and the chemiluminescence data. The CH4/O2 mixtures containing NBD demonstrated reduced ignition delay times, with a pronounced effect at lower temperatures. Conversely, this additive increased the ignition delay time dramatically in the H2/O2 mixture, which was attributed to changes in the fundamental chemistry with the introduction of molecules containing carbon bonds, which require stronger activation energies for ignition. Correlations were developed to predict the ignition delay time, which depends on species concentration, temperature, and pressure. Additionally, one tentative mechanism was tested, combining base chemistry from NUIGMech 1.1 with pyrolysis and oxidation reactions for NBD using the recent efforts from experimental and theoretical literature studies. The numerical predictions show that the rapid decomposition of NBD provides a pool of active H-radicals, significantly increasing the reactivity of methane. This study represents the first set of gas-phase ignition and CO time-history data measured in a shock tube for hydrogen and methane mixtures containing the additive NBD.

Ignition and combustion mechanism of alcohol/aluminum suspension nano-fluid droplets

The ignition and combustion of nano-fluid fuels composed of alcohol and nano-aluminum (ANP) lack atomic insights. A nanodroplet with methanol as shell and ANP as core was constructed for reactive molecular dynamic simulation. Combustion of nano-droplets can be divided into four stages: I: methanol volatilization accompanied by reaction with ANP; II: methanol fragment reacts with O2 and ANP accompanied by chain expansion; III: micro-explosion of composite aluminized phase; IV: gas phase combustion. ANP accelerates the CH3OH decomposition, reduces the ignition delay and activation energy. ANP extract hydrogen and oxygen accelerates the decomposition of CH3OH and forms H-Al and O-Al. H-Al releases H and H2, which leads to rapid generation of active fragments such as O, H, HO2, OH and CHx. It is the fundamental for reducing ignition delay. High temperature accelerates hydrogen extraction of ANP and make micro-explosion more intense. ANP increases the yield of H2O and CO2. This work explains the ignition and combustion mechanism of ANP/CH3OH, hoping to provide insights into alcohol-nanofluid fuel application in engine.

Effect of nanoparticles (Al2O3 and CeO2) blended with biodiesel on combustion, performance, and emissions of a diesel engine

The increase in the utilization of fossil fuels in almost all the energy production sector badly impacts the environment because of incomplete combustion. The incomplete combustion of fuels releases soot, unburned hydrocarbon, and greenhouse gas emissions, contributing significantly to climate change. In the current experimental work, the evaluation of the effect of the addition of aluminium oxide (Al2O3) and cerium oxide (CeO2) nanoparticles in Jatropha biodiesel (B20) has been performed on the combustion, performance, and emission characteristics of compression ignition engine. These nanoparticles have been added because they have a large surface area-to-volume ratio. The air-fuel mixture and the evaporation rate are enhanced, leading to improved burning. The increase in brake thermal efficiency has been observed with nanoparticles blended fuel, i.e. (B20 + 30 ppm Al2O3 + 30 ppm CeO2) by 9.354%. In contrast, drop-in oxides of nitrogen, carbon monoxide, HC, and smoke opacity emissions were observed by 24.67%, 33.33%, 23.08%, and 34.01%, respectively, compared with pure biodiesel. Using nanoparticles in Jatropha methyl ester reduces ignition delay, increases combustion duration, and starts earlier combustion, reducing heat release rate, cylinder pressure, and pressure rise rate by 10.53, 1.994, and 3.687%, respectively, as compared to the B20 blend.

Energy Conversion and Combustion Characteristics of Diesel and N-Alcohol Blends (N-Propanol to N-Hexanol) Under Low Ambient Temperature and Different Injection Pressures

ABSTRACT To reveal the effects of different alcohols addition to diesel on the energy conversion characteristics and combustion characteristics under low ambient temperature, diesel and four sets of blends (the volume ratio of n-propanol/diesel, n-butanol/diesel, n-pentanol/diesel, and n-hexanol/diesel being 20%/80%) were formulated. To explore the possibility of compensating for the decrease in heat value of alcohol blended fuel by increasing injection pressure, the experiments were also carried out under injection pressure of 80–160 MPa. It was discovered that the blending of alcohols into diesel significantly improved the energy conversion efficiency, and n-propanol was the most significant. In addition, the energy conversion efficiency was increased the most when the injection pressure was 120 MPa, and the energy conversion efficiency of n-propanol/diesel blend fuel was increased by 6% compared to pure diesel. However, as the carbon chain length of the alcohols increased, energy conversion efficiency gradually decreased. In addition, the impact of alcohol additives on the ignition process depends on the balance between two opposing effects, the dilution promotion effect, and the cooling inhibition effect. Both n-propanol and n-butanol blended with diesel fuel led to increased ignition delay time and combustion durations, which negatively impacted the cold start success rate and energy conversion efficiency of compression ignition engines. However, n-hexanol was found to reduce ignition delay time and combustion duration while simultaneously reducing soot radiance, making it a favorable choice as an alcohol additive for diesel fuel.

Comparison on the ignition and combustion characteristics of single Al-Li alloy and Al fuel microparticles in air

To address the resistance effect of protective oxide shell on the ignition of micron-sized aluminium (Al) and the particle agglomeration and residue deposition of Al-based fuels, aluminium-lithium (Al–Li) alloy by introducing tiny elemental Li could have a promising potential in substituting for Al. The paper presents a comparative study on the surface structure and the ignition and combustion characteristics between single Al-Li alloy and pure Al fuel microparticles in air. The Al-Li alloy with the content of 1.0 wt.% Li was prepared by gas-atomized method and characterized by multiple methods. The characterization of the surface morphology, elemental distribution, and residues of incomplete combustion show the dendritic structure of eutectic compounds like veins at the surface and interior of the Al-Li alloy microparticles. Compared to the dense oxide shell of Al, the oxide shell of Al-Li alloy provides many more pathways like cracks/openings for the Al and O2 contact as inductively heated by a highly-focused laser beam, resulting in a reduction of ignition delay. The difference of ignition delay between the two demonstrated that the addition of Li element shortened the ignition delay, especially, over 80% for the particle size of > 45 µm. The ignition delay can be reduced by minimizing the particle size or enhancing the ignition power density. Owing to the variations in reactivity, melting, and boiling points compared to pure Al, the Al-Li alloy particles exhibit distinct gas-phase flame and micro-explosion behaviour. These differences result in considerably higher flame temperatures and more intense radiation. Finally, a sequence of reaction mechanisms that potentially control the ignition and combustion of single Al-Li alloy particles (as distinct from pure Al) is proposed, the physical and chemical properties of highly reactive Li are crucial to improve the combustion performance of Al.

An optical investigation on the effects of split-injection on hydrogenated catalytic biodiesel/gasoline dual-fuel engine under cold start conditions

Reactivity-controlled compression ignition (RCCI) mode has emerged as a promising technology for internal combustion engines, offering precise combustion phase control and the potential to meet stringent emission regulations. However, RCCI mode faces challenges, particularly misfiring during cold start conditions. This study proposes a solution by utilizing hydrogenated catalytic biodiesel (HCB) as a pilot fuel for gasoline and implementing a split-injection strategy to address the challenge. Experimental research was conducted on an optical engine under cold start conditions, incorporating three split-injection strategies: P30M70 (30 % main-injection and 70 % pilot-injection), P50M50, and P70M30. The results demonstrate that although gasoline can only be ignited by the main-injected HCB under coldstart conditions, the in-cylinder environment becomes more dynamic due to the pilot-injection. Consequently, split-injection reduces ignition delay by up to 7.09 °CA and shortens the combustion stage compared to single-injection. Among the various injection strategies examined, P30M70 demonstrated outstanding in-cylinder heat release performance, surpassing other split-injection strategies by up to 26.77 J/CAD, and outperforming the single-injection by 22.94 J/CAD. Visualization tests indicate that applying the P30M70 strategy leads to higher soot production under conditions of delayed main-injection timing (-15 °CA ATDC). However, the peak flame area under cold-start conditions is 53.16 % greater than P50M50 and 71.28 % greater than P70M30, highlighting excellent flame propagation characteristics. The average in-cylinder temperature suggests that a larger visible flame area contributes to engine warming. Despite the inherent trade-off, the dual-fuel mode of HCB/gasoline proves suitable for RCCI engines, with the P30M70 split-injection strategy being recommended for the cold start stage.