Increase In Ignition Delay Research Articles

The impact of carbon quantum dots derived from spent coffee grounds on the droplet combustion of diesel/n-butanol blend

As global concerns surrounding climate change mount and fossil fuel reserves diminish, the application of additives in internal combustion engines is increasingly prevalent. Butanol and carbonaceous nanomaterials, such as carbon quantum dots (CQD), are being employed as additives to increase engine efficiency and mitigate the emission of pollutants. Nevertheless, understanding the impact of these additives on combustion behavior at the droplet scale through combustion assessments before their use in engines is crucial. In this study, our main objective was to assess the impact of incorporating CQD dispersed in n-butanol as additives to conventional diesel fuel on the combustion characteristics at the droplet scale. CQD were obtained from spent coffee grounds (SCGs) using n-butanol as a solvent. The product obtained was mixed with Colombian commercial diesel (10 % vol. palm oil biodiesel), and its combustion was evaluated using the droplet combustion method. Before the CQD synthesis, SCGs were characterized by thermogravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM). CQD were characterized via Fourier transform infrared (FTIR) spectroscopy, Transmission Electron Microscopy (TEM), UV–vis, and fluorescence spectroscopy. Results indicated that adding n-butanol and CQD to commercial diesel leads to a 5.4 % and 16.5 % increase in droplet ignition delay, respectively. These additives also cause droplet contraction and expansion cycles, resulting in unstable combustion. However, CQD reduces the frequency of microexplosions caused by boiling n-butanol inside the droplet, which mitigates instabilities during droplet combustion. Including CQD can enhance fuel evaporation by increasing the density of nucleation sites for bubble formation and preventing micro-explosions, thereby leading to stable combustion. These attributes can significantly influence the performance of blends in Compression Ignition (CI) Engines.

Alcohols as Biofuel for a Diesel Engine with Blend Mode—A Review

In the era of decarbonization driven by environmental concerns and stimulated by legislative measures such as Fit for 55, the industry and transportation sectors are increasingly replacing petroleum-based fuels with those derived from renewable sources. For many years, the share of these fuels in blends used to power compression ignition engines has been growing. The primary advantage of this fuel technology is the reduction of GHG emissions while maintaining comparable engine performance. However, these fuel blends also have drawbacks, including limited ability to form stable mixtures or the requirement for chemical stabilizers. The stability of these mixtures varies depending on the type of alcohol used, which limits the applicability of such fuels. This study focuses on evaluating the impact of eight types of alcohol fuels, including short-chain (methanol, ethanol, propanol) and long-chain alcohols (butanol, pentanol, hexanol, heptanol, and octanol), on the most critical operational parameters of an industrial engine and exhaust emissions. The engines being compared operated at a constant speed and under a constant load, either maximum or close to maximum. The study also evaluated the effect of alcohol content in the mixture on combustion process parameters such as peak cylinder pressure and heat release, which are the basis for parameterizing the engine’s combustion process. Determining ignition delay and combustion duration is fundamental for optimizing the engine’s thermal cycle. As the research results show, both the type of alcohol and its concentration in the mixture influence these parameters. Another parameter important from a usability perspective is engine stability, which was also considered. Engine performance evaluation also includes assessing emissions, particularly the impact of alcohol content on NOx and soot emissions. Based on the analysis, it can be concluded that adding alcohol fuel to diesel in a CI engine increases ignition delay (up to 57%), pmax (by approximately 15–20%), HRRmax (by approximately 80%), and PPRmax (by approximately 70%). Most studies indicate a reduction in combustion duration with increasing alcohol content (by up to 50%). For simple alcohols, an increase in thermal efficiency (by approximately 15%) was observed, whereas for complex alcohols, a decrease (by approximately 10%) was noted. The addition of alcohol to diesel slightly worsens the stability of the CI engine. Most studies pointed to the positive impact of adding alcohol fuel to diesel on NOx emissions from the compression ignition engine, with the most significant reductions reaching approximately 50%. Increasing the alcohol fuel content in the diesel blend significantly reduced soot emissions from the CI engine (by up to approximately 90%).

Experimental study on ammonia-diesel co-combustion in a dual-fuel compression ignition engine

Ammonia, as a carbon-free renewable fuel and a potential hydrogen carrier, is gaining increasing interest in addressing greenhouse gas emissions in industrial applications and transportation. This paper presents experimental studies on the co-combustion of ammonia with diesel fuel in a single-cylinder industrial compression ignition engine operating in dual-fuel mode. The energy share of ammonia ranged from 0 to 60%. Increasing the proportion of ammonia compared to diesel fuel in the compression ignition engine leads to a change in the combustion process character, increasing the kinetic combustion phase at the expense of diffusive combustion. However, it does not result in an increase in the peak pressure rise (PPR) beyond the permissible value of 1 MPa/deg for piston engines. It increases ignition delay and shortens the combustion duration, while also increasing thermal efficiency and decreasing specific energy consumption. An increase in the NH3 share results in a decrease in combustion efficiency, a reduction in unit emissions of NO, CO2, and soot, and an increase in CO emissions. Beyond 42% ammonia share, it reduces unit THC emissions. At a 42% ammonia share, the dual-fuel engine achieves the highest indicated thermal efficiency (ITE), lowest specific energy consumption (SEC), shortest combustion duration, and lowest unit soot emissions.

Numerical Investigation on Energetic, Combustion, and Emissions Parameters of a Diesel Engine Fueled With Diesel/Butanol and Diesel/Pentanol

Abstract In this article, the effect of butanol/diesel and pentanol/diesel blended fuel with different proportions on the energetic, combustion, and emissions parameters of a diesel engine was studied. First, an engine model was established using Diesel-RK software. The modeled engine was a direct injection diesel engine having a fixed compression ratio, injection timing, and speed of 17.5:1, 23 degbTDC, and 1500 rpm, respectively. After that, a set of experiments was conducted using a 5% pentanol and 95% diesel by volume fuel blend maintaining the same operating conditions as the simulation, and the results of the experiment were compared with the numerical result using the same blend. The simulated results were found to be in respectable agreement with experimental findings. The analysis of the simulated results shows that at 100% load using 15% butanol and 85% diesel by volume and 15% pentanol and 85% diesel by volume brake thermal efficiency was increased by 0.96% and 0.8%, respectively. The emission of NOx was reduced by 24.4% and 10.75% on average using butanol and pentanol blends, respectively. The instantaneous heat release rate and ignition delay increase with the higher alcohol–diesel blends, whereas the peak pressure rise and combustion temperature decrease. Smoke emissions were reduced by 3.31–8.75%, and specific particulate matter emissions decreased by 20.9% and 15.07%, respectively, on average with the addition of butanol/pentanol in neat diesel.

CO2, Ar, and He dilution effects on combustion dynamics and characteristics in a laboratory-scale combustor

This study aimed to investigate the impact of CO2, Ar, and He addition on combustion instability under varying acoustic frequencies, dynamic pressure amplitudes, and light emission intensities. Experiments involved using pure methane as fuel at a 1.0 equivalence ratio, with three distinct acoustic frequencies. The burner operated at 5 kW, and the combustion chamber was excited at frequencies of 90 Hz, 160 Hz, and 320 Hz. It was observed that with dilution, the temperatures decreased more from the burner exit temperature to the exhaust section. As the oxygen concentration in the oxidizer decreases in Ar, He, and CO2 dilution, CO emissions increase, but CO2 emissions decrease. The addition of Ar, He, and CO2 causes an effect that reduces the flame temperature and brightness while causing the flame length to extend due to the diluting effect. While a decrease in instability was observed in He-Ar-CO2 dilution in 20 % oxygen, instability increased again in the three 19 % cases. It is observed that mixtures under the diluent effect approach the blowoff limit due to the increase in ignition delay. It has been determined that the addition of diluent increases the tendency for the flame to go out, especially due to the thermal effect. The methane fuel with an 18 % oxygen concentration in the oxidizer of Ar remained below lean extinction limits, undergoing blowoff. The temperature was measured as 1156 K at 21 % oxygen concentration, 584 K at 19 % oxygen concentration for carbon dioxide, 877 K for Helium, and finally 777 K for argon. In the case of pure air for the combustion of methane, CO emissions were measured at 140 ppm. Average CO levels at 20 % oxygen concentration in the oxidizer are 1254 ppm, 356 ppm, and 308 ppm with carbon dioxide, argon, and helium, respectively. The study also shows that an increase in O2 in oxidizing air leads to a decrease in CO emissions, while an increase in He/Ar/CO2 gases leads to an increase in CO emissions. Regarding NOX emissions, undiluted conditions measured a value of 14 ppm. NOX emission levels approached 0 ppm in all dilution cases and achieved its goal.

Numerical investigation on pyrolysis and ignition of ammonia/coal blends during co-firing

Co-firing ammonia with coal is a promising and feasible technology for reducing coal-related carbon emissions. Pyrolysis and ignition of ammonia-coal blended fuels are the key steps for flame stability and boiler operation safety throughout the conversion process but remain unclear. In this work, an extended Euler–Lagrange framework coupled to detailed solid-phase pyrolysis kinetics and gas-phase reactions mechanism is introduced and validated against experimental results for ammonia-coal co-firing in a two-stage flat flame burner. First, the CRECK-S coal pyrolysis model was validated with TGA experiments and the CPD model at different heating rates to determine parameters for a competing two-step model for CFD simulations. Second, a detailed gas-phase mechanism with 116 species and 1513 elementary reactions was derived from the volatile and ammonia reaction mechanisms. Thirdly, the co-firing simulations were validated for the ignition delay time for various ammonia co-firing ratios. The results show that increasing the co-firing ratios from 0.0 to 1.0 results in gradually increasing ignition delay times in a low-oxygen atmosphere. Further analysis demonstrates that adding ammonia accelerates the coal particle heating rate due to the reduced coal particle number density and ammonia reaction induced gas-phase temperature increase, and thus the coal devolatilization rate is increased. The latter plays a dominant role. Hydrogen produced from ammonia pyrolysis is negligible, so ammonia predominantly participates in the ignition. Time scale analysis shows that homogeneous ignition is dominant during the ignition process. The presence of ammonia inhibits the inward oxygen diffusion and causes the reaction zone to move away from the pulverized coal particle flow. The oxygen diffusion inhibition and low reactivity of ammonia compared to volatiles lead to an increase in ignition delay time for ammonia co-firing, even though pulverized coal devolatilization is accelerated.

Future zero carbon ammonia engine: Fundamental study on the effect of jet ignition system characterized by gasoline ignition chamber

Ammonia is a carbon-free fuel with tremendous potential for clean internal engine applications in the future. However, the combustion and emissions limitations of ammonia fuel have impeded the development of ammonia engine. As a combustion enhancement technology, the ignition chamber (pre-chamber) jet ignition system has emerged as an effective solution to address the challenges associated with ammonia combustion. This study utilized a high-speed camera to capture the evolution of jet and the combustion processes of ammonia. The combustion method entailed the injection of gasoline into the ignition chamber, while ammonia was injected into the main chamber. The experimental results demonstrated that ignition chamber jet ignition system significantly enhanced ammonia combustion and shortened the combustion duration as compared to spark plug ignition system. The study involved evaluating the ammonia combustion performance under different equivalence ratios (1.0 and 0.8) while comparing it to various gasoline energy percentages (2.5%, 2.0%, 1.5%, and 1.0%). The results revealed that the combustion performance at 1.5% was superior to other gasoline energy percentages. Additionally, in comparison to ignition chamber outlet diameter of 4.5 mm and 6.0 mm, it was found that the 3.0 mm diameter exhibited weak ignition capability, resulting in a 107.1% and 40.3% increase in ignition delay at the equivalence ratio of 0.8, and ignition failure at the equivalence ratio of 0.6. However, its high jet velocity induced a more homogeneous mixing of radicals with ammonia/air, leading to a 30.6% reduction in rapid combustion and a 43.1% decrease in combustion duration at the equivalence ratio of 0.8. Additionally, the investigation of equivalence ratios (0.8, 1.0, and 1.1) demonstrated that the fastest initial combustion of ammonia occurred at the equivalence ratio of 0.8, with an ignition delay of only 4.7ms. Therefore, an appropriate reduction in the equivalence ratio could enhance the ammonia combustion efficiency to some extent. The findings of this study provide a fundamental ignition technique for future applications of zero carbon ammonia engines.

Combustion characteristics of oxymethylene dimethyl ether-diesel blends: An experimental investigation using a constant-volume combustion chamber

The combustion characteristics of oxymethylene dimethyl ether (OMEx) and its blends with diesel have been investigated using a multi-hole injector in a constant-volume combustion chamber. The results show OMEx addition can reduce the ignition delay, especially when blends of more than 50 vol% are used, at low chamber temperature. Two individual heat-release peaks are observed for OMEx during premixed combustion at 750 K, due to a pronounced low-temperature heat-release phase. The chamber temperature of 800 K can be regarded as a transition point for the behavior of burn duration as well as maximum ROHR peak, mostly caused by combustion regime transition from premixed- to diffusion combustion. It appears that there is an approximate linear relation between maximum ROHR peak and the time at which this peak occurs with injection pressure. The ignition delay of OMEx is almost insensitive to a decrease in ambient oxygen concentration. And the premixed ROHR profile, due to its high oxygen content, is very similar and only ignition delay and burn duration increase slightly. Additionally, comparisons of natural luminosity results for OMEx and diesel indicate that OMEx produces near-zero soot values. Luminosity is expected to be caused by chemiluminescence alone, which increases with injection pressure.

Diesel-natural gas dual fuel injection strategy effects on engine ignition delay and cylinder pressure evolution

Diesel pilot high-pressure direct injection (HPDI) natural gas technology has been noticed and applied in medium and heavy-duty engines due to its outstanding economy and power performance. However, the combustion of two kinds of fuels will involve more injection parameters, which increases the difficulty of designing injection strategy and calibrating injection parameters. This paper investigates comprehensively the effects of three key engine injection parameters (injection timing, injection duration of the pilot diesel, interval of injection between diesel and natural gas) on the engine ignition delay and cylinder pressure evolution using the experimentation method, which are utilized to guide the design of injection strategy and optimize injection parameters. Results show that the maximum in-cylinder pressure and its position are determined by the injection timing of natural gas, but little affected by the injection parameters of diesel. As the injection timing advances and the duration of diesel injection shortens, the ignition delay increases. To avoid rough combustion in the cylinder, it is necessary to optimize the injection timing, injection interval, and ignition diesel injection duration to ensure that the pressure rise rate does not exceed the threshold.

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.

Experimental Measurements of Ignition Delay Times of Iso-octane/n-Butanol Blend Mixtures in Rapid Compression Machine (RCM)

Among oxygenated alternative fuels, n-butanol is considered as a promising alternative biofuel which can partially (or fully) replace conventional transportation fuels currently in use. However, before n-butanol can be commercially utilised, its fundamental combustion characteristics need to be fully understood. In this work, the effect of adding n-butanol on autoignition property of iso-octane was studied. Measurements of ignition delay times for the two blends of n-butanol proportions of 30% and 50% by mole weight were made in a Rapid Compression Machine for stoichiometric mixtures at 2.0 MPa and temperature range 651-918 K. n-butanol increased ignition delay times of iso-octane at lower temperatures and hence acted as an octane enhancer, while at higher temperatures delay times were reduced. In the intermediate temperatures there was visually no difference in delay times between the two blends. Throughout the temperature range studied, the delay times of both blends were much closer to those of pure n-butanol which suggests that the combustion chemistry of n-butanol was dominant over that of iso-octane. These results have shown that n-butanol can enhance fuel octane rating and therefore can potentially improve thermal efficiency of SI engines, whilst CI engines can benefit from the reduced delay times at higher temperatures.

Optical investigation of methane, ethane, or propane and diesel at low load RCCI conditions

Natural luminosity (NL) imaging diagnostics were employed to investigate the effects of natural gas (NG) components on reactivity-controlled combustion, using an ultra-low sulfur diesel fuel and three NG major components (methane, ethane, and propane). The experiments were performed in a single-cylinder heavy-duty optical compression-ignition (CI) engine at 500 bar diesel injection pressure, 1000 RPM, ∼ 6.6 bar IMEP, and ∼ 64% energy-based diesel substitution ratio. NL confirmed the premixed nature of the combustion, which started inside the squish area and propagated towards the center of the combustion chamber. The high intensity NL regions that appeared towards the end of the premixed combustion were the result of the diffusive combustion of end-of-injection fuel dribble or of the diesel fuel that condensed on the bowl window surface or accumulated in the bowl straight corners (typical of an optical engine piston). The time it took for the spatially integrated NL (SINL) to decrease from its maximum to its minimum was similar for all investigated cases, suggesting that the gas addition did not change the fraction of the diesel fuel that participated in the diffusion-controlled combustion. Differences in oxidation properties between NG components affected the RCCI combustion at these low load conditions. Propane RCCI was characterized by 1 crank angle (CA) to 3 CA more advanced combustion phasing (despite an increased ignition delay) and higher SINL compared to methane and ethane RCCI. However, as NL for the propane RCCI was lower at similar combustion phasing, it suggests that propane addition created a more stratified diesel-gas mixture, with a richer mixture inside the squish volume, supported by faster and more intense combustion compared to the other two RCCI cases. As a result, the flame speed slowed as it progressed from the squish volume towards the center of the combustion chamber, therefore the delay in capturing the premixed combustion in the NL images. The amount of fuel that burned after the premixed combustion completely engulfed the piston bowl was relatively low compared to fraction of the fuel that burned before it. Finally, the results suggest the importance of tailoring the low–high fuel reactivity ratio of the dual-fuel combustion based on the operating condition.

Optical characterization of ethanol spray flame on a constant volume combustion chamber

Studying pure ethanol spray flame has the potential to achieve the carbon neutrality vision. This paper studies the effects of fuel injection masses (12, 24, 36 mg) and fuel injection pressures (30, 40, 50 MPa) on ethanol spray flame on an optically visualized constant volume combustion chamber. Further compared with the spray flame of methanol and n-butanol. The combustion characteristics and flame development process were revealed by flame self-illumination high-speed imaging method, and the soot distribution was revealed by wavelength integration two-color method. Results show that ethanol spray flame presents an unstable yellow flame with many wrinkles. Small injection masses exist a partial flame-quenching phenomenon. As injection mass increases, the soot lift-off length decreases, and the flame brightness, soot concentration, and ignition delay increase. The high soot concentration areas locate upstream of the flame, and there is almost no soot downstream. Increased injection pressure increases the soot lift-off length and decreases the flame brightness. The ignition delay is shortened from 8.388 ms to 6.955 ms when injection pressure increases from 30 MPa to 40 MPa. But higher injection pressure has a negligible effect on reducing ignition delay. Finally, an ethanol spray combustion conceptual model is proposed. This paper gives particular guiding significance to the future use of carbon-neutral ethanol in diesel engines.

Experimentally investigating the influence of biodiesel blend (Bio20) injection instead of diesel in methanol dual-fuel HCCI engine performance

ABSTRACT This paper aims to examine the effect of a biodiesel blend (Bio20) substitute for diesel on methanol dual-fuel HCCI engine performance. In this work, the existing CI engine is modified into a dual-fuel HCCI engine by attaching the carburetor to the inlet manifold for the supply of methanol. Fuel Jet No. 60 in the carburetor was used to provide a predetermined amount of methanol fuel. The mixture of methanol and air is ignited by diesel/Bio20 injection at the end of the compression stroke. Experimental results showed that methanol with diesel increased ignition delay (ID) and reduced NOX. However, HC, smoke opacity and CO emissions increased drastically compared to a conventional diesel engine. Conversely, methanol with Bio20 reduced ID and promoted combustion helping to reduce smoke opacity, HC and CO emissions. In terms of brake thermal efficiency (BTE) Bio20 instead of diesel gave better performance for a methanol dual-fuel HCCI engine.

High-Resolution Two-Dimensional Numerical Simulation of n-Heptane/Air Autoignition Under the Influence of Temperature Fluctuation

ABSTRACT High-resolution two-dimensional numerical simulations are performed to investigate n-heptane/air autoignition process under different initial temperatures with varied levels of temperature fluctuations. It is found that temperature fluctuation has an important impact on the autoignition process, and its effects depend on the initial mean temperature. When is located at the upper turning point of the negative temperature coefficient (NTC) regime, as the temperature fluctuation increases, the autoignition mode evolves from a single-stage ignition mode controlled by high-temperature chemistry (HTC) to a mode characterized by the coexisting of multi-stage and single-stage ignition. Both the first-stage heat release and ignition delay increase, but the overall heat release and the total ignition delay decrease. In the presence of a large temperature fluctuation, the low-temperature chemistry (LTC), and HTC reactions, single-stage and two-stage ignitions could coexist in the domain. Chemical explosive mode and sensitivity analyses are performed to identify the reaction mode and the key element reactions in the mutli-stage autoignition process. The temperature fluctuation has a significant promotion effect on the overall ignition except when is located at the lower turning point of the NTC regime. Overall, the NTC phenomenon is weakened under the influence of temperature fluctuation, approaching to zero temperature coefficient (ZTC) phenomenon.

Combustion and emission characteristics of hydrotreated pyrolysis oil on a heavy-duty engine

Second-generation biofuel is promising to be applied in the field of long-haul transportation, aviation, and marine shipping. This work focuses on the ignition behavior, combustion process, and emission characteristics of hydrotreated pyrolysis oil. This biomass-derived oil was blended with marine gas oil from 10 to 30 wt% without a co-solvent or emulsifier. Tests were performed both on a combustion research unit and a commercial heavy-duty diesel engine setup. The results from the combustion research unit reveal that ignition delay increase as hydrotreated pyrolysis oil blend ratio increases at tested ambient conditions. Engine tests were first performed under factory settings at representative load/speed points based on the European stationary test cycle for benchmarking. Then start of injection and fuel pressure are varied to check the controllability and engine sensitivity of hydrotreated pyrolysis oil blends. It is shown that under engine conditions, the combustion characteristics and heat release are quite identical among hydrotreated pyrolysis oil blends and diesel. Though all cases present ultra-low particulate matter emissions, hydrotreated pyrolysis oil blends yield higher particulate matter emissions, which increase as the blend ratio increases. The particulate matter/NOx tradeoff is observed both for benchmarking tests and parameter study. The results indicate that the engine can run with HPO blends smoothly and safely without major modification.

Ignition and combustion characteristics of boron-based nanofluid fuel

With its high gravimetric and volumetric heat value, boron-based nanofluid fuel is potentially well suited for future high-energy propulsion systems. In this experimental study, we investigate the ignition and combustion of boron-based nanofluid fuel, with a focus on the effects of oleic acid (OA) concentration (0 to 10 wt.%), boron particle concentration (2.5 to 20 wt.%), and boron particle size (300 nm to 13 µm). Thermogravimetry−differential scanning calorimetry and laser ignition tests reveal that adding boron nanoparticles to a fuel can improve its combustion intensity, but without much affecting the oxidation and ignition characteristics, primarily because of agglomeration and thicker oxide layer properties relative to boron microparticles. Pure kerosene droplets are found to undergo pre-ignition heating and classic combustion, whereas OA or boron addition promotes puffing and micro-explosions, accelerating the classic combustion process. The co-existence of OA and boron is found to lead to more frequent and stronger disintegration of the nanofluid fuel droplet. The ignition delay reaches 156 ms with only 2.5 wt.% OA inclusion, compared to just 73 ms for pure kerosene. Both the ignition delay and combustion rate increase, while the solid residual decreases owing to enhanced micro-explosions as the OA concentration increases. Unlike OA, boron addition promotes ignition, with 2.5 wt.% boron yielding an ignition delay reduction of 24 ms, but this effect weakens with increasing boron concentration. The combustion rate is found to be relatively insensitive to boron addition. Although the particle size affects the ignition and combustion performance of boron powder, its effect on the combustion of the nanofluid fuel droplet is, under the present test conditions, relatively weak. Finally, a phenomenological model is presented to capture the ignition and combustion of a boron-based nanofluid fuel droplet. The predicted ignition delay and combustion rate are found to be within 7.15% of their experimental values. This study contributes to an improved understanding of boron ignition and combustion in high-energy liquid fuel systems.

Characteristics of ethylene and methane combustion in a range of high temperature and low oxygen environments

New understanding of turbulent jet flames of natural gas, and blends of natural gas with ethylene (C2H4), issuing into a range of preheated coflowing oxidisers with reduced oxygen (O2) concentrations are reported. Comparisons are made for coflow O2 concentrations of 3%, 4%, 5%, 6%, 9% and 11% and coflow temperatures of 1250 K, 1315 K and 1385 K. Instantaneous and simultaneously planar imaging measurements of temperature, hydroxyl radicals (OH) and formaldehyde (CH2O) were taken at eight locations ranging from 9 mm to 75 mm downstream of the jet exit plane. The experimental data is supplemented with chemical reaction modelling. It is shown that increasing the proportion of C2H4 in the fuel supply resulted in an increase in the flame front temperature. At 3% O2, CH2O signal did not very between the three fuels containing C2H4, whilst at 9%, the signal increased with increasing C2H4. OH number density was highest for a blend of 66% NG and 33% C2H4. The fuel composition made little effect on the jet spread rate. Reaction modelling found evidence of changes in the reaction process, both in the suppression of reactions with different fuels, and in the suppression of reactions, and the locations they occur, with reducing O2 concentrations. Reaction modelling also found a significant decrease in ignition delay when C2H4 was present in the fuel mixture, and an increase in ignition delay as all four fuels transition to MILD combustion.

Experimental analysis of combustion with the use of ethanol-biodiesel-diesel blends in diesel generator sets

This study aims to experimentally investigate the effects of using different percentages of ethanol-biodiesel-diesel blends in diesel internal combustion engines and to analyze energy and combustion parameters. The experiments were conducted on a single-cylinder, four-stroke, air-cooled, and constant-speed diesel generator set with a rated electrical power of 4.5 kW and 79% of full engine load (3.54kW). Temperature, fuel flow, AVL pressure, and rotation sensors were installed on the crankshaft and inside the cylinder. The fuels used were commercial diesel (S-10) and blends with 1%, 2%, and 3% of anhydrous ethanol added to diesel, changing the injection pressure in only one blend. The results show a decrease in thermal efficiency and an increase in fuel consumption, in addition to an increase in ignition delay, an increase in combustion duration, a decrease in in-cylinder pressure, and a decrease in the heat release rate as the percentage of ethanol increased.

Potential of kerosene-diesel blends as alternative fuels for diesel engines: Perspectives from spray combustion characteristics

To explore the application potential of kerosene (RP-3)/diesel blends as alternative fuels for diesel engines, the spray combustion characteristics of neat diesel, neat RP-3 and RP-3/diesel blends (varied from 25 % to 75 % of RP-3) were systematically compared in an optical constant volume combustion chamber under non-evaporating (0 % O2, 293 K), evaporating (0 % O2, 900 K) and combustion (21 % O2, 900 K) conditions. Their spray, evaporation, combustion and soot emission characteristics were visualized using various high-speed imaging techniques. The results show that RP-3/diesel blending ratio has significant effects on the spray and combustion processes. Under non-evaporating condition, higher RP-3 contents slightly decrease the spray penetration but increase the corresponding spray angle and volume. Under evaporating condition, the spray angle and volume follow the similar trend as those under non-evaporating condition except for slight fluctuations, but the liquid length decreases with the increase of blending ratio. Unexpectedly, the vapor penetrations of neat diesel and RP-3 are similar and longer than those of their blends. Under combustion condition, both the ignition delay and flame lift-off length increase with the RP-3 blending ratio. In addition, RP-3 component reduced the peak soot mass by 9.78 %, 14.7 % and 17.56 % for R25, R50 and R75, respectively. In summary, this study suggests that RP-3/diesel blends are suitable alternative fuels for diesel engines, in terms of faster evaporation and lower soot emissions. We recommend a blending ratio of 25 % as the most promising fuel for further investigations in real engines.