Sensitivity Of Delay Time Research Articles

Experimental Investigation on Auto-Ignition Characteristics of Kerosene Spray Flames

To facilitate the better use of RP-3 kerosene in compression ignition engines, the auto-ignition behaviors of RP-3 kerosene spray were experimentally investigated in an optical rapid compression machine. Results show that most of the tests have good ignitability and combustion performance. For all the successful ignited cases, the flame kernel was found to be formed before the steep rise of pressure, which explained that image-based ignition delay time is always shorter than the pressure-based ignition delay time. The effects of ambient environment, injection pressure, and injection delay time on the pressure history, ignition intensity, combustion duration, heat release rate, and other parameters were investigated individually. The ambient environment has a strong influence on ignition delay time by accelerating the chemical reactions, whereas the high injection pressure helps the better vaporization of fuel spray. The effect of injection delay time is non-monotonic as the trade-off relation between heat loss and blending of fuel and oxygen. The heat release rate histories under different conditions were compared and analyzed, and the two-stage heat release phenomenon was observed in the negative temperature coefficient region. The ignition intensity region was determined based on the measured ignition delay times of RP-3 kerosene spray, and multiple linear regression correlation was used to study the ignition delay time sensitivity to multi-factors.

Influence of the double bond position in combustion chemistry of methyl butene isomers: A shock tube and laser absorption study

AbstractShock tube experiments have been carried out on 2‐methyl‐1‐butene (2M1B), 2‐methyl‐2‐butene (2M2B), and 3‐methyl‐1‐butene (3M1B)—the three isomers of methyl butene compound. Carbon monoxide (CO) time‐histories and ignition delay times are obtained behind reflected shockwaves over the temperature range of 1350‐1630 K and pressures of 8.3‐10.5 atm with stoichiometric mixtures of 0.075% fuel in O2/Ar. Comparative ignition study reveals that 3M1B ignites significantly faster than the other two isomers, while 2M1B dissociates earlier but ignites later than 2M2B. Possible mechanisms for this behavior are discussed with ignition delay time sensitivity and reaction path analysis. In addition, time‐resolved CO measurements are compared with three different reaction mechanisms from the literature. Sensitivity analyses have been carried out to identify important reactions that need attention to accurately predict the chemistry of these isomers. Further investigation into the rates of unimolecular fuel decomposition reactions and C3H3 + O2 = CH2CO + HCO reaction are suggested based on the current investigation.

Ignition delay time sensitivity in ignition quality tester (IQT) and its relation to octane sensitivity

Cetane number (CN) is a commonly used metric to rate the ignition quality of distillate fuels. In this work, a concept of sensitivity in ignition delay time (IDT) obtained with an ignition quality tester (IQT) is proposed, which is correlated to octane sensitivity (OS), i.e., the difference between research octane number (RON) and motor octane number (MON). The concept is based on the determination of IDT using the ASTM D6890 standard and IDT obtained at a temperature lower than that prescribed by the standard. The IDT measured at this lower temperature is referred to as IDTl, which is obtained via a calibration procedure similar to the ASTM D6890 standard, but with a higher value of reference IDT for calibration with n-heptane. The IDTh (measured at the derived cetane number (DCN) ASTM D6890 condition) of a given test fuel and a binary primary reference fuel (PRF) mixture of iso-octane and n-heptane was measured to identify a PRF with matching IDTh as the test fuel. The ratio of low temperature IDTs of the non-PRF test fuel and PRF, i.e., IDTl,non-PRF/IDTl,PRF was defined as IDT sensitivity (IDS), which was correlated with the OS of the test fuel. The RON and MON values of a wide range of fuel classes including surrogate fuels and fully blended practical fuels were estimated, and showed satisfactory agreement with measured RON/MON values. The RON values of many pure components that could not be measured with the standard test method ASTM D2699 were also estimated. Two certification diesels and Saudi Arabian pump grade diesel were also tested.

Route Choice Behavior Analysis with Unexpected Delay Information

Route choice behavior analysis has been widely adopted to promote intelligent traffic systems running efficiently. For better grasp the route choice behavior characteristic under some uncertain environments, a practical influential factor of unexpected delay is proposed and invested for urban travel in daily. The parameter of unexpected delay not only can well describe the travelers’ sensitivity of travel time and its accurate, but also greatly influence traveler's judgment for different travel modes. It is important for route choice behavior analysis under uncertain conditions. According to the above, this paper sets multi-subject probability to construct uncertainly traffic environment to analyze the attitude of route choice combine with MEU (maxmin expected utility) theory under risky scenario. The experiments indicate that 95% travelers show risky preference when they in a route choice setting. Furthermore, the sensitivity of delay time is closely relation in proportion to the entire travel time refer to diminishing marginal utility by travelers. Finally, the results also elaborate the phenomenon of the small probability overestimate contrast to the high probability underestimate of the delay probability.

Blending effects on ignition delay times of methyl octanoate/n-nonane/methylcyclohexane

Ignition delay times were measured behind reflected shock waves under highly dilute conditions (99% Ar) for 10 ternary blends of methyl octanoate, n-nonane, and methylcyclohexane (MCH), using a Design of Experiments approach, namely an L9 array. Measurements were obtained over a wide range of temperature (1258<T (K)<1630), pressure (1.5<P (atm)<9.5), and equivalence ratio (ϕ=0.5, 1.0, 2.0). The series of experiments focused on the effects of variation in relative fuel volume fractions to assess respective influence of hydrocarbon class (i.e. methyl ester, n-alkane, cycloalkane) on ignition delay times of blended fuel. The L9 array utilized for the design of the experimental test matrix led to the development of an empirical ignition delay time correlation which was then employed for a broad series of calculations examining the effects of fuel-ratio variation. Results of the calculations show that addition of methyl octanoate to blends of n-nonane and MCH lowers the power-law pressure dependence of ignition delay times of such blends (the latter two species share similar dependence on pressure). The correlation also shows MCH as the most dominant of the three fuels in the blends studied with respect to controlling ignition delay time, a finding supported by ignition delay time-sensitivity calculations. Calculation of blending effects, defined herein as deviation from neat-fuel behavior, using the correlation indicated several key features of the studied blends. First, for fixed MCH concentration in a ternary blend, correlation calculations revealed an insensitivity of ignition delay time to variation in the ratio of methyl octanoate to n-nonane for all conditions. Second, blending effects on ignition delay times depend strongly on blend composition and on experimental conditions (pressure, equivalence ratio, temperature), indicating fuel- and condition-specific complexities, although were generally more pronounced at lower temperature. Third, of the three experimental conditions varied, ignition delay times of fuel blends exhibited the most sensitivity to equivalence ratio. To support experimental results, the study also involved compilation of a detailed chemical kinetics mechanism (4815 reactions, 1082 species) by integrating pertinent reaction chemistry from two independently validated mechanisms into a base model for n-nonane oxidation from a previous study by the authors. Model-based calculations indicate that under stoichiometric conditions near 10atm, blending effects are negligible above 1350K yet become increasingly significant towards lower temperature. Lastly, to assess the importance of blending effects, ignition delay times of fuel blends measured experimentally were compared against times calculated using a linear combination method (i.e. superposition of constituent-fuel ignition delay times). In general, superposition of neat-fuel trends cannot be utilized to reproduce ignition trends of the fuel blends herein, highlighting the importance of and continued need for blended-fuel studies.

Three-dimensional Frechet differential kernels for seismicdelay times

Summary Seismic traveltimes are the most widely exploited data in seismology. Their Frechet or sensitivity kernels are important tools in tomographic inversions based on the Born or single-scattering approximation. The current study is motivated by a paradox posed by two seemingly irreconcilable observations in the numerical calculations for the sensitivity kernels of the traveltime perturbations. Calculations of kernels for 2-D media by the normal-mode approach indicate that traveltimes are most sensitive to the structure on and around the geometrical ray paths corresponding to the seismic arrivals, whereas calculations for 3-D media by geometrical ray theory predict exactly zero sensitivities on the ray paths. In the current work, we employ these two completely different wave-propagation approaches, the more efficient geometrical ray theory and the more accurate normal-mode theory, to investigate the 3-D sensitivities of the delay times to shear-wave speed variations. Expressions for the delay-time Frechet kernels are presented for both methods, and extensive numerical experiments are conducted for various types of seismic phases as well as for different reference earth models. The results show that the contradictory observations are but two examples of a wide range of behaviours in the delay-time sensitivity. For most of the seismic phases in realistic reference models with multiple discontinuities, wave-speed gradients and low-velocity zones, the wavefields are highly complicated and ray theory, which describes the response by the contributions of a few geometrical rays between the source and receiver, produces qualitatively different delay-time kernels from those obtained by the normal-mode theory, which includes essentially all contributions.

Delay time sensitivity analysis of multi-generation BiCMOS digital circuits

The speed sensitivity of BiCMOS circuits to changes in the key MOS/BJT device parameters is analysed. The study takes into account the changes in the forward transit time, the knee current, the collector resistance, the base resistance, and the current gain of the bipolar transistor and the channel length and width, threshold voltage, and oxide thickness of the MOS transistor. The relationships between the key process parameters and the overall speed sensitivity are reported. The analysis also covers the effects of the output load capacitance, scaling the technology, and the quality of the bipolar device on the delay sensitivity. Sensitivity coefficients are defined and generated for the conventional BiCMOS circuit as well as two recently reported circuits designed for low-voltage operation. A method to calculate the worst case speed degradation for a given set of device and process parameters&apos; tolerances is described. HSPICE is used to generate the numerical results for the three technologies (5 V, 0.8 µm), (3.3 V, 0.5 µm), and (2.2 V, 0.2 µm).

Delay time sensitivity in nonlinear monotone RC trees

The sensitivity of delay time (time required to achieve a given target voltage) at any node of a nonlinear monotone RC tree is studied using the adjoint-network approach. It is shown that the sensitivity of tau with respect to changes in a parameter of the resistors or the capacitors of the tree can be expressed as an integral of the solutions of the network and its adjoint network. Using this integral it is then established that tau increases for some nodes (depending upon location of a node) due to the decrease in a given resistor value, when tau is small. For other nodes tau would decrease. However, if the target voltage is close to the steady-state value then tau decreases for all the nodes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Delay-time sensitivity in linear RC tree

The study of RC networks is important to understand digital MOS integrated circuits. Several authors studied these networks from the point of view of bounds on voltage waveform [1], [2], signal delay [3], etc. Wyatt [4] developed a qualitative theory of RC meshes having monotone elements. He showed that for a monotone exitation <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u(t)</tex> , the sensitivity of the output node voltage of a nonleaky line is monotonic due to any conductance on the line.