Lower Ignition Delay Research Articles

NOx emission reduction using permanent/electromagnet-based fuel reforming system in a compression ignition engine fueled with pine oil

In this experimental study, pine oil is identified as low viscous low cetane (LVLC) fuel for compression ignition engine replacing diesel. Numerous advantages of LVLC fuels include improved combustion due to favorable physical properties than diesel. This leads to reduced hydrocarbon, smoke and carbon monoxide emissions with improved thermal efficiency. However, utilization of pine oil as a drop in fuel is challenging, due to its low cetane index. This leads to higher nitrogen oxide (NOx) emission due to prominent heat release rate. A novel fuel reforming system based on the principle of electrochemical liquid vortex ionization was used with permanent magnet/electromagnet to reduce NOx emission with pine oil as base fuel. Electrochemical liquid vortex ionization system converts the fuel molecules to ions; this leads to enhanced atomization and faster air–fuel mixing process leading to lower ignition delay. A two-cylinder commercial CI engine was used for this experimental study. Performance, emission and combustion characteristics were studied for pine oil with and without ionization system at 3, 6, 9 and 12 kW power output and compared with diesel. According to engine test results, compared to diesel, brake thermal efficiency for pine oil is higher and further improved with ionization system. Emissions like smoke, hydrocarbon, carbon monoxide and carbon dioxide are reduced for pine oil in comparison with diesel and further reduce with the ionization system. Longer ignition delay with pine oil operation leads to higher NOx emission compared to diesel. Nevertheless, the use of magnetic-based fuel reforming system reduces the ignition delay leading to lower NOx emission.

Autoignition and flame propagation in non-premixed MILD combustion

Direct Numerical Simulation (DNS) data of Moderate or Intense Low-oxygen Dilution (MILD) combustion are analysed to gather insights on autoignition and flame propagation in MILD combustion. Unlike in conventional combustion, the chemical reactions occur over a large portion of the computational domain. The presence of ignition and flame propagation and their coexistence are studied through spatial and statistical analyses of the convective, diffusive and chemical effects in the species transport equations. Autoignition is observed in regions with lean mixtures because of their low ignition delay times and these events propagate into richer mixtures either as a flame or ignition. This is found to be highly dependent on the mixture fraction length scale, ℓZ, and autoignition is favoured when ℓZ is small.

Low temperature ignition delay times measurements of 1,3,5-trimethylbenzene by rapid compression machine

Due to the increased interest on understanding the combustion chemistry of the larger alkyl aromatic as jet fuel surrogate component, we provide new ignition delay time data of 1,3,5-trimethylbenzene/O2/Ar mixtures, for the temperature range between 880 and 1090 K, at the pressure of 20.0 and 30.0 bar and for different mixture equivalence ratio and fuel concentration, by using a well validated rapid compression machine with heating system. Measurements show that no negative temperature coefficient behavior was observed for this fuel. Subsequently, these low temperature ignition delay time data were used to validate several kinetic mechanisms including those of Gudiyella and Brezinsky (Combust Flame 2012), Diévart et al. (Fuel 2013), and Wang et al. (Combust Flame 2018), all of which significantly overestimate the reactivity of 1,3,5-trimethylbenzene in this temperature range. Sensitivity analysis at typical condition and comparisons of the rate constants of the ignition dominant reactions in different models indicate that a more complete reaction scheme for 1,3,5-trimethylbenzene (T135MB) and more accurate rate constant should be further pursued, especially for the reactions of H abstraction from T135MB and fuel radical consumption reactions. Finally, ignition delay times of toluene is lower than T135MB and n-propylbenzene at the same condition, which indicate that the larger number of side chain and the longer side chain length enhances the low temperature reactivity. In addition, for the same fuel isomer, the effect of the side chain length is stronger than the number of side methyl in accelerating ignition since n-propylbenzene presents an even shorter ignition delay times than T135MB. We believe the present work will be of merit for future jet fuel surrogate model development.

Engine performance, emission and bio characteristics of rice bran oil derived biodiesel blends

The present work involves the investigation of biodiesel characteristics derived from rice bran oil via heterogeneous basic catalytic transesterification path as the rice husk contains about 16–20% of crude rice bran oil by its weight. Engine performance and emission characteristics of rice bran oil derived biodiesel blends during fueling a four-stroke, single-cylinder, direct-injection engine at 1500 rpm were investigated. The results indicate that 20% biodiesel blend leads to a lower ignition delay at higher loads which in turn increases the rate of vaporization of the fuel as it has higher cetane umber. This fuel blend has a high in-cylinder peak pressure and heat release rate (HRR) of about 72.1 bar and 70.826 J/°CA respectively, during the pre-mixed combustion phase in rapid combustion due to the higher oxygen content. Even though, it has high viscous nature, it possesses highest brake thermal efficiency (BTE) which adds absolute combustion. The exhaust gas temperature (EGT: 7.8221%) increases with load and the observed values were matched with other biofuels. Moreover, the HCs, COx and NOx emissions decrease as the load increases since the increase in fuel atomization promotes the combustion process and thereby decreases the amount of unburnt biodiesel components. At 100% load, the smoke cloudiness level was decreased by about 21.62%. The rice bran oil and the blended (20, 30 and 40%: B20, B30 and B40) samples were tested for their notable in vitro microbial, antioxidant and nuclease bio activities due to the presence of certain bioactive components in the rice bran derived biodiesel. If the rice bran oil (RBO) is converted effectively into biodiesel, thereby it will not only satisfy 60–70% of our diesel requirement but also facilitate a green environment.

Combustion Characteristics of Physically Mixed 40 nm Aluminum/Copper Oxide Nanothermites Using Laser Ignition.

This paper reports on the ignition and flame propagation characteristics of aluminum/copper oxide (Al/CuO) nanothermite at different packing density, manufactured from 40 nm commercial Al and CuO nanopowders. A 3.5 W continuous wave laser was used to ignite the samples in argon at atmospheric pressure, and a high speed camera captured the flame propagation. The high speed images revealed that the fast laser heating creates significant material ablation, followed by heat transfer along the heated surface. The bulk ignition occurs near the edge of the top surface, followed by the self-sustained burning. Lightly pressed powders (90% porosity) ignited in ~0.1 ms and the burning front propagated at around 200 m/s, while the dense pellets (40–60% porosity) ignited in ~1 ms and the burning front propagated at around 10 m/s. These results indicate that the reaction mechanism changes from mass convection to heat diffusion with increasing the packing density. The ignition and burn speeds of these Al/CuO nanothermites at different equivalence ratios (ERs), along with SEM images of pre- and post-combustion, illustrate that the homogeneity of the mixture is a critical parameter for optimizing the performance. The Al rich mixtures show significantly lower ignition delays and higher burn speeds.

Combustion characteristics of linseed (Linum usitatissimum) methyl ester fuelled biodiesel blends in variable compression ratio diesel engine

ABSTRACTIn this article, the overall combustion characteristics of non-edible linseed (Linum usitatissimum) biodiesel blended with petrodiesel (PD) are presented. The objective of the present study is to investigate the effect of a fraction of biodiesel in the blends, the variation of load (20 to 100% in a step of 20%) and compression ratio (CR) (14:1, 16:1, and 18:1) on combustion characteristics. The obtained result, compared with baseline fuel PD, is operated at rated CR 17.5:1. The result shows the higher value of cylinder combustion pressure (CP), a rate of pressure rise (RPR), cumulative heat release, combustion duration, and combustion mean gas temperature and lower ignition delay (ID) for biodiesel and its blends compared with PD. On an average, the ID increased by 30% and 3.3% at CR 14:1 and 16:1, respectively, and reduced by 28.3% at CR 18:1 for LB blends.

Study of combustion, performance and emissions of a diesel engine fueled with ternary fuel in blended and fumigation modes

The present study aimed to compare the combustion, performance and emissions of a diesel engine fueled with diesel, biodiesel and ethanol in the blended and fumigation modes. In addition, a combined fumigation and blended mode (F + B) of fueling was introduced to understand its behavior in comparison with the blended and fumigation modes. In the blended mode, the fuel was composed of 80% diesel, 5% biodiesel and 15% ethanol (DBE), by volume. In the fumigation mode, a mixture of biodiesel and ethanol (BE) was injected into the intake manifold and diesel fuel was used as the main fuel. In the F + B mode, half of the BE mixture was injected into the intake manifold and another half of the DB mixture was mixed with diesel to form the main fuel. The experiments were conducted at a speed of 1800 rpm with five engine loads at a constant mixture percentage of D80B5E15 for the three fueling modes to provide the same fuel composition for comparing the effects of the three fueling modes.According to the average of five loads, compared to the pure diesel operation, the blended mode causes increases in peak heat release rate (HRR), ignition delay (ID), BSFC, CO, HC and NO2; drops in duration of combustion (DOC), CO2, NOX, PM, total number concentration (TNC) and geometric mean diameter (GMD); and similar peak in-cylinder pressure and BTE. While the fumigation mode leads to higher peak HRR, DOC, BSFC, CO, HC, NO2 and TNC; lower ID, BTE and NOX; and similar peak in-cylinder pressure, CO2, PM and GMD in comparison with the diesel mode. In addition, the F + B mode has the effects between those of the fumigation and blended modes. Among the three fueling modes, the blended mode gives the highest engine performance and lowest emissions, except for NOX. In contrast, the fumigation mode gives the worst engine performance and emissions, except for NOX.

Investigation of steam effect on ignition of dispersed coal particles in O2/N2 and O2/CO2 ambiences

In this paper, we intensively investigate the influence of steam on the hetero-homogeneous joint ignition of dispersed coal particle streams in both O2/N2 and O2/CO2 conditions of an optically accessible flat-flame burner. Two differently ranked coals and one bituminous char were tested for a comparison. The effects of moisture content in the raw coal, steam content or diluents (N2/CO2) in the ambience, and fuel types were systematically examined under isothermal conditions. First, it is seen that the moisture content in raw coal delays its ignition because of endothermic vaporization, which becomes weakened at the high ambient temperature. Secondly, three main mechanisms are categorized to explore the profound effects of ambient steam content on ignition of coal particles, i.e., (i) the promotion effect of OH radical on the oxidation of volatile hydrocarbons, (ii) the inhibition effect of gaseous H2O molecule on the equilibrium of hydrocarbon oxidation, (iii) the negative effect of endothermic surface gasification reaction (C-CO2/C-H2O). In O2/N2 ambience (1500 or 1800 K), as the steam content increases, the ignition delay of coal particles is rapidly reduced in an early stage of 0%–5% due to the positive effect of OH radicals, followed by an inappreciable reduction in 5%–13% stage because of both the steam inhibition effect and the endothermic surface gasification. However, in O2/CO2 ambience with sufficiently high steam content (5%–18%), the ignition delay even becomes longer with the further increment of steam. It is because of the synergistic effect between C-H2O and C-CO2 reaction at high temperatures (1500 K and 1800 K). Finally, for fuel types, the OH radical promotion effect of two lignite samples is obviously higher than that of low-volatile char samples, whereas with steam addition the sodium-rich Zhundong coal exhibits lower ignition delay than Hulunbel lignite due to catalytic effect.

Comparative evaluation of physical and chemical properties, emission and combustion characteristics of brassica, cardoon and coffee based biodiesels as fuel in a compression-ignition engine

This study have been considered the effects of the three type of biodiesel (brassica, cardoon and coffee) on the performance, tailpipe emissions and combustion characteristics of a single cylinder direct injection compression ignition engine operated in four different speeds (1200, 1700, 2200, 2700 rpm) and three different engine loads (15, 30 and 45%). The differences in combustion and performance parameters and exhaust emissions of engine fueled by these fuels have been compared. The free fatty acid profile of the biodiesels has been considered. The properties of the biodiesels according to the ASTM D6751 have been analyzed. Highest degree of unsaturation is achieved for biodiesel produced from brassica (94.64%) compared to biofuels derived from cardoon and coffee, 79.81% and 57.65%, respectively. The high value of the erucic acid (C22:1) in the brassica biodiesel (48.7 wt%) is the reason of higher unsaturation degree than the other biodiesels. The components of the free fatty acid profile of the considered biodiesels mostly include long chain free fatty acids (C18 and higher). The physical properties of the biodiesel fuel is influenced by the fatty acid profile. The CN of the brassica, cardoon and coffee is 56.44, 56.11 and 57.44, respectively. The surface tension of the brassica, cardoon and coffee biodiesel fuel is 42.05, 40.99 and 37.62 mN/m. The oxygen content of the brassica, cardoon and coffee is 13.44, 10.91 and 7.77%, accordingly. Dynamic viscosity of the brassica, cardoon and coffee was 6, 5.7 and 9.5 cSt, respectively. The ignition delay of the brassica, cardoon and coffee biodiesel diesel fuel blends at 15% engine load is 9.52, 11.05, 5.07% and at 30% engine load is 12.88, 13.85, 15.78% lower than diesel fuel on average, respectively. The additional oxygen have decreased the CO and THC emissions. The highest reduction of the THC emission than standard diesel fuel was 41.19%. The maximum BTE (brake thermal efficiency) obtained for different biodiesel diesel blends fuels was lower than that of standard diesel fuel. The CA50 of the biodiesel diesel fuels was lower than diesel fuel due to their lower ignition delay.

High-Speed Imaging and Measurements of Ignition Delay Times in Oxy-Syngas Mixtures With High CO2 Dilution in a Shock Tube

In this study, syngas combustion was investigated behind reflected shock waves in order to gain insight into the behavior of ignition delay times and effects of the CO2 dilution. Pressure and light emissions time-histories measurements were taken at a 2 cm axial location away from the end wall. High-speed visualization of the experiments from the end wall was also conducted. Oxy-syngas mixtures that were tested in the shock tube were diluted with CO2 fractions ranging from 60% to 85% by volume. A 10% fuel concentration was consistently used throughout the experiments. This study looked at the effects of changing the equivalence ratios (ϕ), between 0.33, 0.5, and 1.0 as well as changing the fuel ratio (θ), hydrogen to carbon monoxide, from 0.25, 1.0, and 4.0. The study was performed at 1.61–1.77 atm and a temperature range of 1006–1162 K. The high-speed imaging was performed through a quartz end wall with a Phantom V710 camera operated at 67,065 frames per second. From the experiments, when increasing the equivalence ratio, it resulted in a longer ignition delay time. In addition, when increasing the fuel ratio, a lower ignition delay time was observed. These trends are generally expected with this combustion reaction system. The high-speed imaging showed nonhomogeneous combustion in the system; however, most of the light emissions were outside the visible light range where the camera is designed for. The results were compared to predictions of two combustion chemical kinetic mechanisms: GRI v3.0 and AramcoMech v2.0 mechanisms. In general, both mechanisms did not accurately predict the experimental data. The results showed that current models are inaccurate in predicting CO2 diluted environments for syngas combustion.

Studies on piston bowl geometries using single blend ratio of various non-edible oils.

The depletion of fossil fuels and hike in crude oil prices were some of the main reasons to explore new alternatives from renewable source of energy. This work presents the impact of various bowl geometries on diesel engine with diesel and biodiesel samples. Three non-edible oils were selected, namely pumpkin seed oil, orange oil and neem oil. These oils were converted into respective biodiesel using transesterification process in the presence of catalyst and alcohol. After transesterification process, the oils were termed as pumpkin seed oil methyl ester (PSOME), orange oil methyl ester (OME) and neem oil methyl ester (NOME), respectively. The engine used for experimentation was a single-cylinder four-stroke water-cooled direct-injection diesel engine and loads were applied to the engine using eddy current dynamometer. Two bowl geometries were developed, namely toroidal combustion chamber (TCC) and trapezoidal combustion chamber (TRCC). Also, the engine was inbuilt with hemispherical combustion chamber (HCC). The base line readings were recorded using neat diesel fuel with HCC for various loads. Followed by 20% of biodiesel mixed with 80% neat diesel for all prepared methyl esters and termed as B1 (20% PSOME with 80% diesel), B2 (20% OME with 80% diesel) and B3 (20% NOME with 80% diesel). All fuel samples were tested in HCC, TCC and TRCC bowl geometries under standard injection timing and with compression ratio of 18. Increased brake thermal efficiency and reduced brake specific fuel consumption were observed with diesel in TCC geometry. Also, higher heat release and cylinder pressures with lower ignition delay were recorded with TCC bowl geometry. TCC bowl geometry showed lower CO, HC and smoke emissions with B2 fuel sample than diesel and other biodiesel samples. But, higher NOx emission was observed in HCC and TCC than that in TRCC bowl geometry. Graphical abstract ᅟ.

Effect of Al2O3 nanoparticles in biodiesel-diesel-ethanol blends at various injection strategies: Performance, combustion and emission characteristics

The current experimental work focusses on influence of Alumina (Al2O3) nanoparticle on various injection strategies. Experiments were conducted with three different injection timings (IT) namely, original timing (ORG IT) of 23deg bTDC, advanced timing (ADV IT) of 27deg bTDC and retarded timing (RET IT) of 19deg bTDC. The base fuel used is a blend of biodiesel (20%), diesel (70%), and ethanol (10%) (known as BDE). Alumina nanoparticles were synthesized, characterized by SEM and XRD analysis and blended with BDE blend at a fraction of 25ppm using ultrasonicator. The effect of 25ppm Al2O3 in BDE blend at ORG IT, ADV IT and RET IT were experimented in a single cylinder diesel engine and the following results were obtained. Al2O3 addition at ADV IT resulted in higher peak pressure and heat release rate occurring nearer to TDC, higher hydrocarbon (HC), higher carbon monoxide (CO), lower carbon dioxide (CO2), higher nitrogen oxides (NOx), higher exhaust gas oxygen (EGO), higher combustion duration (CD) and lower ignition delay (ID). Whereas, Al2O3 addition in RET IT causes lower cylinder pressure and heat release away from TDC, followed by simultaneous reductions of HC, CO, NOx and smoke opacity. In addition, higher levels of EGO and ID along with lowered brake specific fuel consumption (BSFC) and CD were observed with Al2O3 addition in RET IT. Overall, the influence of 25ppm Al2O3 in RET IT of 19deg bTDC resulted in better engine performance, combustion and emission characteristics.

Ionic Liquid and Biofuel Blend: A Low–cost and High Performance Hypergolic Fuel for Propulsion Application

AbstractHypergolic fuel has unique importance in missiles and satellite launch vehicles. Hydrazine and its derivatives (Monomethyl hydrazine, MMH and Unsymmetrical Dimethyl Hydrazine, UDMH) are the continuous choices of fuel in bipropellant though it is carcinogenic and toxic. Development of new, green and cost‐effective fuel blends based on trust‐worthy, ionic liquid and biofuel in different volume proportion have been reported. The blends exhibit reasonably good stability (chemical and thermal), low viscosity (η < 15 mPa⋅s), high density (ρ > 1 g/cm3), low ignition delay and high performance in comparison with UDMH ‐ a proven liquid fuel presently being used as promising fuels for liquid rocket application. The reported blends appear to be a technologically promising, eco‐friendly and affordable fuel blend to replace currently used liquid toxic fuels.

Impact of fuel spray angles and injection timing on the combustion and emission characteristics of a high-speed diesel engine

This paper presents effect of fuel spray angles such as narrow (60°) and conventional (156°) spray angles on spray behavior, combustion and emissions characteristics. To achieve research objectives, fuel spray images measured using a visualization system and two injectors at spray angles of 60° and 156° were analyzed for spray tip penetration and spray development processes as a function of injection timing and injection pressure. The spray angle effects on combustion and emission characteristics, and engine performance were analyzed.Results revealed that 60° injector exhibited higher maximum combustion pressure, higher maximum heat release rate, and lower ignition delay than 156° injector. Under various injection timings with 156° spray angle, it is shown based on the experimental results that peak value of combustion pressure decreased when injection timing of 30° BTDC (before top dead center) was advanced. Regarding emission characteristics, the use of narrow spray angle injector is advantages in case of an early injection combustion strategy because it yields low ISHC (indicated specific hydrocarbon), ISCO (indicated specific carbon monoxide), and ISNOx (indicated specific nitrogen oxides) emissions. In addition, the IMEP (indicated mean effective pressure) in a narrow spray angle injector is higher than that in conventional spray angle injector.

Open cycle CFD investigation of SI engine fueled with hydrogen/methane blends using detailed kinetic mechanism

Hydrogen/methane mixtures have been considered as viable alternative fuels to gasoline, due to overall lower emissions and much better lean burn capabilities. Nevertheless, due to different combustion characteristics of hydrogen compared to conventional fuels, its utilization in SI engines requires further investigations. The current study investigates the effect of hydrogen addition to methane SI engines using an open cycle Computational Fluid Dynamics (CFD) simulation coupled with chemical kinetics. The Eddy dissipation concept (EDC) model is used in combination with a two-equation turbulence model (k-ε) and GRI-Mech 3.0 kinetic mechanism. The effect of various volume fractions of hydrogen from 0 to 0.5 on methane combustion is investigated and results are validated with experimental data in literature. A good insight of combustion, turbulence flow and species consumption inside combustion chamber is obtained. A sensitivity analyses is also performed in order to get profound understanding of combustion phenomena. The results showed that hydrogen addition reduces combustion duration, improves flammability range, and reduces carbon monoxide and carbon dioxide amounts. Hydrogen also has a great effect on initiation of combustion process due to its lower ignition delay and higher flame propagation speed. Hydrogen addition does not affect NOx levels considerably, which is on the other hand much affected by combustion air and maximizes at 20–30 percent excessive air. The results also indicate that at Maximum Brake Torque (MBT) condition, all fuel is consumed up to 10 degrees after Top Dead Center (TDC), while carbon monoxide which is maximum at this point will transmute to carbon dioxide afterwards.

PROPERTIES AND PERFORMANCE OF E-BIODIESEL WITH CETANE IMPROVER ON VARIABLE COMPRESSION RATIO ENGINE

In the transport sector, a Major source of energy is from diesel engine. Karanja oils have a great potential to be alternative fuel for diesel engines. Use of non-edible oil is helpful for food security. Blend of biodiesel, ethanol and diesel fuel improve some properties compared with biodiesel diesel blends and ethanol biodiesel blends. Addition of ethanol (CN-6 to 8) lowers cetane number of blend with the addition of cetane improver it can be overcome. This paper consist of investigation of properties of karanja biodiesel, karanja biodiesel with 15% ethanol and cetane improver(3ml) and karanja biodiesel with 20% ethanol and cetane improver (3ml). Also the performance of these blends investigated with the help of variable compression ratio engine taking 15,16,17,18 as a compression ratio. Addition of cetane improver (2-EHN), lower ignition delay and improve combustion quality. The effect of these blends on Brake Specific Fuel Consumption (BSFC), Brake Thermal Efficiency (BTE), Indicated Thermal Efficiency (ITE), Volumetric Efficiency, Mechanical Efficiency, Exhaust Gas Temperature (EGT) is Studied. From experimental result it is found that additional lubricity gives better output with minimum frictional loss as compared with conventional diesel. Cetane improver which gives better combustion characteristics reduces ignition delay and maximum amount of fuel burnt nearer to TDC and no fuel remain for the after combustion stage or exhaust pipe combustion. Lower heating value give less heat generation which causes lower exhaust gas temperature.

Amine-boranes: green hypergolic fuels with consistently low ignition delays.

Complexation of amines with borane converts them to hypergols or decreases their ignition delays (IDs) multifold (with white fuming nitric acid as the oxidant). With consistently low IDs, amine-boranes represent a class of compounds that can be promising alternatives to toxic hydrazine and its derivatives as propellants. A structure-hypergolicity relationship study reveals the necessary features for the low ID.

Measuring the Impact of Engine Oils and Fuels on Low-Speed Pre-Ignition in Downsized Engines

© 2014 SAE International. One of the limits on the maximum fuel efficiency benefit to be gained from turbocharged, downsized gasoline engines is the occurrence of low speed pre-ignition (LSPI). LSPI may lead to high pressures and extreme knock (megaknock or superknock) which can cause severe engine damage. Though the mechanism leading to megaknock is not completely resolved, LSPI is thought to arise from local auto-ignition of areas in the cylinder which are rich in low ignition delay “contaminants” such as engine oil and/or heavy ends of gasoline. These contaminants are introduced to the combustion chamber at various points in the engine cycle (e.g. entering from the top land crevice during blow-down or washed from the cylinder walls during DI wall impingement). This paper describes a method for testing the propensity of different contaminants to cause a local pre-ignition in a gasoline engine. During one cycle, a small amount of contaminant is injected into one cylinder of a 4 cylinder engine. The spark is suppressed during this or the following cycle to allow detection of local pre-ignition events after spark timing. If the contaminant is injected on the cycle before, it is the cycle following the injection that has the missed spark. By detecting auto-ignition events before and after spark timing, it is possible to compare contaminants over a broad range of ignition tendencies. Sensitivities of pre-ignition tendencies to intake pressures and temperatures, the amount of contaminant introduced, and fuelling ratios are discussed. Additionally, the importance of contaminant stratification is shown, and pre-ignition is demonstrated to result from the introduction of contaminant as early as the beginning of blow-down of the preceding cycle.

LOW-POWER LASER IGNITION OF ALUMINUM/METAL OXIDE NANOTHERMITES

Abstract : In this study, three different types of nanothermites, i.e., Al/CuO, MoO3, and Al/Bi2O3, were produced using the widely spread wet (i.e., isopropanol based) method. In addition to the above method, the three nanothermites were also produced using a Resodyn LabRAM mixer. A paraffin-coated spherical Al nanopowder (100 nm) was used as the fuel source, while the oxidizers were nanometric powders of CuO (40 nm), MoO3 (100 nm), and Bi2O3 (200 nm). The effect of nanothermite composition on the sensitivity for the tests of electrostatic discharge (ESD), impact, and friction was investigated. Scanning electron microscopy (SEM) was used to analyze the morphology and homogeneity of the nanothermites. Next, the nanothermites were thermally analyzed in terms of energy release, ignition temperature, and flame temperature using a thermogravimetric analysis differential and scanning calorimetry (TGA/DSC) technique. A low-power diode laser was used to evaluate the ability of different laser wavelengths (661, 532, and 445 nm) to produce the ignition energy needed for a specific thermite reaction. Low ignition delays (less than 15 ms) were obtained at approximately 300 mW laser power output for both Al/MoO3 and Al/Bi2O3 thermites. Finally, a forward-looking infrared camera was used to estimate the ignition and burning temperatures of the Al/MoO3 nanothermite.

Direct numerical simulations of NOx effect on multistage autoignition of DME/air mixture in the negative temperature coefficient regime for stratified HCCI engine conditions

Direct numerical simulations (DNSs), for a stratified flow in HCCI engine-like conditions, are performed to investigate the effects of exhaust gas recirculation (EGR) by NOx and temperature/mixture stratification on autoignition of dimethyl ether (DME) in the negative temperature coefficient (NTC) region. Detailed chemistry for a DME/air mixture with NOx addition is employed and solved by a hybrid multi-time scale (HMTS) algorithm. Three ignition stages are observed. The results show that adding (1000ppm) NO enhances both low and intermediate temperature ignition delay times by the rapid OH radical pool formation (one to two orders of magnitude higher OH radicals concentrations are observed). In addition, NO from EGR was found to change the heat release rates differently at each ignition stage, where it mainly increases the low temperature ignition heat release rate with minimal effect on the ignition heat release rates at the second and third ignition stages. Sensitivity analysis is performed and the important reactions pathways for low temperature chemistry and ignition enhancement by NO addition are specified. The DNSs for stratified turbulent ignition show that the scales introduced by the mixture and thermal stratifications have a stronger effect on the second and third stage ignitions. Compared to homogenous ignition, stratified ignition shows a similar first autoignition delay time, but about 19% reduction in the second and third ignition delay times. Stratification, however, results in a lower averaged LTC ignition heat release rate and a higher averaged hot ignition heat release rate compared to homogenous ignition. The results also show that molecular transport plays an important role in stratified low temperature ignition, and that the scalar mixing time scale is strongly affected by local ignition. Two ignition-kernel propagation modes are observed: a wave-like, low-speed, deflagrative mode (the D-mode) and a spontaneous, high-speed, kinetically driven ignition mode (the S-mode). Three criteria are introduced to distinguish the two modes by different characteristic time scales and Damkhöler (Da) number using a progress variable conditioned by a proper ignition kernel indicator (IKI). The results show that the spontaneous ignition S-mode is characterized by low scalar dissipation rate, high displacement speed flame front, and high mixing Damkhöler number, while the D-mode is characterized by high scalar dissipation rate, low displacement speeds in the order of the laminar flame speed and a lower than unity Da number. The proposed criteria are applied at the different ignition stages.