Kernel Growth Rate Research Articles

How pulse energy affects ignition efficiency of DBD plasma-assisted combustion

This work aims to find how coupled energy per pulse influences the ability of a pulsed dielectric barrier discharge (DBD) plasma to ignite fuel-lean methane–air flow. For that, experiments are performed on a custom-built DBD flow reactor with a variable dielectric thickness and the discharge is operated by bursts of 10 ns duration pulses at 3 kHz repetition rate. With an increase in dielectric thickness, we observe that the coupled energy per pulse decreases even though applied voltage conditions are similar and so more pulses are required to ignite the lean mixture. Interestingly, we observe a significant increase in the minimum ignition energy (MIE) with an increase in the thickness beyond 3 mm. Moreover, the ignition kernel growth rate is much slower in the thicker dielectric cases even though total energy coupling per burst is similar. This phenomenon is investigated further by evaluating plasma parameters using electrical and optical diagnostics. Effective dielectric capacitance, discharge current, and voltage drop across the gas gap are derived from an equivalent circuit analysis, whereas plasma gas temperature and effective reduced electric field ( E/N ) are estimated from optical emission spectroscopy. From these analyses, we conclude that a thicker dielectric limits the discharge current and so the plasma filament temperature. For more than 3 mm thick dielectric cases, the filament heating per pulse is too low to achieve strong enough plasma pulse-to-pulse coupling which eventually leads to higher MIE and slower ignition kernel growth rate or the inability to ignite at all.

Responses of Physiological Traits and Grain Yield to Short Heat Stress during Different Grain-Filling Stages in Summer Maize

Maize kernel growth is sensitive to heat stress, which is predicted to result in yield loss. However, the response of maize to short-term heat stress during different kernel-growth stages is still not clear. A 3-year field experiment, included two heat-stress treatments (LSH, lag-stage heat stress; FSH, effective-filling-stage heat stress), was conducted in 2019–2021. The results showed that LSH and FSH significantly reduced the grain yield by 8.7–14.9% and 11.6–17.6%, respectively, compared with the control (CK). LSH mainly reduced the kernel number per ear, and FSH mainly reduced the kernel weight. Heat stress reduced the SPAD and chlorophyll content during the effective-filling stage, but not in the lag stage. Photosynthesis was obviously reduced under heat stress during both stages; however, the photosynthesis rate during the lag stage was higher than during the effective-filling stage. The decreased amplitude of dry matter under LSH was higher than under FSH during the heating period. However, there was no difference between the CK and LSH samples in terms of dry-matter accumulation from the end of heat stress to harvest, which was significantly reduced under FSH. Additionally, decreased starch-synthesis-related enzyme activity, i.e., adenosine diphos-phoglucose pyrophosphprylase, contributed to the kernel number and kernel weight loss in LSH and FSH, respectively. The kernel-growth rate (per ear) was lowered, but the growth duration was not shortened in this study. Consequently, LSH mainly reduced the photosynthesis rate (Pn), resulting in kernel abortion and yield penalty. FSH mainly reduced the Pn and chlorophyll content, which reduced the kernel weight, and increased yield loss.

Interactive effect of branch source-sink ratio and leaf aging on photosynthesis in pistachio.

Tree source-sink ratio has a predominant and complex impact on tree performance and can affect multiple physiological processes including vegetative and reproductive growth, water and nutrient use, photosynthesis, and productivity. In this study, we manipulated the branch level source-sink ratio by reduction of photosynthetic activity (partial branch defoliation) or thinning branch fruit load early in the growing season (after fruit set) in pistachio (Pistacia vera) trees. We then characterized the leaf photosynthetic light response curves through leaf aging. In addition, we determined changes in leaf non-structural carbohydrates (NSC) and nitrogen (N) concentrations. In leaves with high source-sink ratios, there was a gradual decrease in maximum net photosynthetic rate (ANmax) over the growing season, while in branches with low source-sink ratios, there was a sharp decline in ANmax in the first two weeks of August. Branches with high-sink showed an up-regulation (increase) in photosynthesis toward the end of July (at 1,500 growing degree days) during the period of rapid kernel growth rate and increased sink strength, with ANmax being about 7 μmol m-1 s-1 higher than in branches with low-sink. In August, low source-sink ratios precipitated leaf senescence, resulting in a drastic ANmax decline, from 25 to 8 μmol m-1 s-1 (70% drop in two weeks). This reduction was associated with the accumulation of NSC in the leaves from 20 to 30 mg g-1. The mechanisms of ANmax reduction differ between the two treatments. Lower photosynthetic rates of 8-10 μmol m-1 s-1 late in the season were associated with lower N levels in high-sink branches, suggesting N remobilization to the kernels. Lower photosynthesis late in the season was associated with lower respiration rates in low-source branches, indicating prioritization of assimilates to storage. These results can facilitate the adaptation of management practices to tree crop load changes in alternate bearing species.

Effects of turbulence on variations in early development of hydrogen and iso-octane flame kernels under engine conditions

The understanding and prediction of the early development of flame kernels are of high practical importance for the robust relight of aviation gas turbines and the control of cycle-to-cycle variations (CCV) of spark-ignition engines. CCV are known to correlate strongly with early flame kernel development and complicate the optimization of such engines in terms of safety, thermal efficiency, and engine emissions. The flame kernel initiated by a spark is initially small, in the very early combustion phase typically smaller than the size of the turbulent integral length scales. Therefore, the development of the flame kernel is dominated by local, intermittent flow fluctuations and can vary under the same nominal conditions. In this study, the effects of turbulence on the early development of premixed iso-octane and hydrogen turbulent flame kernels under realistic engine conditions are investigated through direct numerical simulations. Multiple realizations were simulated under the same nominal conditions for both fuels. Significant variations in flame kernel interactions with turbulence can be identified among different realizations. The fuel consumption rate varies by a factor of two, which is remarkable considering that only statistical differences in the local flow field are present between different realizations. Effects of different flow features of the initial flow fields on the flame kernel development were analyzed. It was found that the flow motion on the scale of the ignition radius, specifically the fluid deformation, which is characterized by the invariants of the strain rate tensor, determines the global shape of the kernel, while the variations of the kernel growth rate are mostly driven by the variations of the smallest turbulent scales. In particular, turbulence influences the flame surface area growth mainly through the tangential strain rate at the flame surface, which is shown to result from the small-scale turbulent motion. Due to differential diffusion effects, hydrogen and iso-octane exhibit significantly different flame responses to curvature, which is comprehensively studied for both fuels. The findings in this study will guide the development of combustion models that are capable to capture variations of the early flame kernels based on the local turbulence dissipation rate.

Experiments and modeling of forced ignition in methane/air mixtures with added NO

Ignition of fuel/oxidizer mixtures containing combustion products is important to the operation of advanced combustors. Previous work indicates that the presence of NO can reduce ignition delay times, yet the influence of NO on forced ignition is not clear. This work examines ignition kernels generated by spark discharges in CH4/air flows diluted with a mixture of NO and N2. Differences in chemistry initiated by the presence of NO are examined by comparing mixtures diluted with only N2 to mixtures diluted with both NO and N2. Ignition probability and kernel growth rates are determined using measurements of infrared radiation emissions from the developing ignition kernels. The presence of NO in the unburned mixture does not affect ignition probability. However, the addition of small quantities of NO on the order of 300–1200 parts per million increases the size of ignition kernels relative to those generated in mixtures diluted with pure N2 by up to 20%. Numerical modeling is performed to examine the role of low temperature chemistry on ignition behavior. The sensitivity of ignition kernel growth to the presence of NO is attributed to increased CH4 oxidation rates caused by low-temperature chemistry activated in the early stages of kernel development.

Diallel analysis of kernel weight and grain‐filling traits in maize grown under contrasting nitrogen supply

AbstractUnderstanding the inheritance of maize (Zea mays L.) kernel weight (KW) under contrasting nitrogen (N) supply is crucial for obtaining high KW across diverse N conditions. This work evaluated broad‐sense heritability (H2), general combining ability (GCA), and specific combining ability (SCA) under contrasting N levels for (i) KW and kernel number per plant and (ii) grain‐filling traits represented by the duration of lag and effective filling phases, kernel growth and desiccation rates, maximum water content and volume, and moisture content at physiological maturity. A six‐parent full diallel cross generated via Griffing's method 3 was tested under high (N200) and low (N0) N supply in 2 years (Y). For the various traits: (i) F1 hybrid, and F1 by Y and/or N interactions were significant (p < 0.05); (ii) GCA was significant at both N levels and affected (p < 0.05) by the Y effect; (iii) SCA was important (p < 0.05) only at N200; and (iv) GCA sum of squares was higher than those of SCA (except for KW). For KW and grain‐filling traits, H2 and GCA/SCA ratios were higher at N0 than at N200, suggesting low‐N environments would be more advantageous for developing genetic selection. Lag‐phase duration (LPD), kernel desiccation rate (KDR), and kernel maximum water content (KWCMAX) had higher H2 (≥0.70) and GCA/SCA ratio than KW, particularly under N0. Thus, the highest KW hybrid (LP2×LP662) was composed of inbreds with high GCA for LPD, KDR and KWCMAX, revealing superior KW hybrids could be selected from the GCA of mentioned traits.

Schlieren imaging and spectroscopic approximation of the rotational-vibrational temperatures of a microwave discharge igniter with a resonating cavity.

A microwave discharge igniter (MDI) with a resonating cavity was developed and optimized for practical applications in an internal combustion engine. In contrast to the typical microwave ignition, the resonating cavity of the MDI induces a discharge through dielectric resonance. Its source of microwave (MW) is a 2.45GHz semiconductor oscillator that is capable of numerous oscillation patterns. To verify and demonstrate the optimum ignition performance and combustion, we varied the oscillation parameters (signal factors) of the MW to optimize the performance of the MDI using the Taguchi method. Plasma spectroscopy was used for ignition condition analysis. Two sets of microwave pulses, a first pulse followed by a second set of pulse bursts, were used to ignite a propane-air fuel. The flame kernel growth rate and O I species generation were used as the response outputs, which were obtained, respectively from Schlieren imaging and emission spectroscopy experiments. The extended pulse periods and higher MW pulse numbers of the second set of pulses improved the response outputs of the MDI. To further analyze the effect of MW oscillation patterns on plasma properties and performance, measurements were done on MW superimposed operation with the high-voltage ignition from spark plugs. The MW transmission on a typical spark plug enhanced the air plasma ignition. Higher input MW energy and more extended MW pulse widths results in increased spectral intensity and radical generation of OH, O, and N 2. An inverse relation between the temperature and spectral intensity functions of the MW pulse width was observed, which was attributed to the cutoff density of the MW-enhanced plasma.

Prediction of the flame kernel growth rate in spark ignition engine fueled with natural gas, hydrogen and mixtures

The knowledge of combustion duration is a key tool in the development of engines, specially nowadays for engines adapted to new fuels with low C/H ratio such as natural gas and hydrogen. This work is aimed to develop a correlation that predicts the duration of the first phase of combustion until the process becomes turbulent in a SI engine. The flame kernel radius when this transition occurs, Rtr, is the study variable.To determine this variable from the experimental pressure records, a flame kernel growth predictive model is used. The predictive model is adjusted to the experimental data, determining the most appropriate Rtr value.The pressure records of 500 consecutive cycles of 48 test points have been processed. The averaged values of Rtr of each test point have been correlated with the characteristic parameters of the process: turbulence and properties of the fuel–air mixtures. Finally, Rtr and integral length scale ratio is correlated with Damköhler number.A wide range of operating conditions have been studied, reaching the novel conclusion that it is possible to analyze the kernel growth phenomenon from a spatial point of view rather than from a temporal point of view, as had been studied in many previous works.The developed correlation can be used in combustion predictive modeling to support SI engine design. Other practical conclusion from the work, that can be used in SI engine development, is that decreasing the integral length scale reduces the time of the first phase of combustion.

Effect of Dilution on Forced Ignition of Jet-A/Air Mixtures

Consistent ignition in environments where combustion products are present is critical for the safety and reliability of some propulsion applications. Prior research has shown that residual can reduce the probability of forced ignition of mixtures by decreasing the concentration of H radicals. However, the applicability of these observations to larger hydrocarbon fuels, such as jet-A, is not known. Ignition probabilities and volumetric kernel growth rates for vaporized jet-A/air/diluent mixtures were determined from radiation intensity measurements collected using an FLIR SC6700 infrared camera. Measurements of ignition probability of jet-A/air mixtures showed no appreciable reduction in ignition probability for mixtures with similar and . Mixtures diluted with showed no statistical change in average growth rates compared to undiluted and diluted mixtures. One-dimensional reacting flow simulations were conducted to help identify why no apparent chemical sensitivity to was observed for the jet-A/air mixtures, in contrast to results reported for . A greater concentration of H radicals was predicted for jet-A/air mixtures when compared to mixtures, even when is present. Further analysis showed that different reaction pathways exist for jet-A when compared to and that these reaction pathways are affected differently in the presence of residual .

On pulse energy and energy distribution for ignition of flowing mixtures

The effects of energy distribution on ignition during a burst of nanosecond-pulsed high-frequency discharges (NPHFD) are investigated in methane-air mixtures at a nominal flow velocity of 5.7 m/s, equivalence ratio of 0.61 and inter-electrode gap distance of 2 mm. These effects were considered in the context of three pulse-coupling regimes, occurring at different inter-pulse time (IPT) conditions: fully-coupled (short IPT, high PI), partially-coupled (intermediate IPT, low PI), and decoupled (long IPT, variable PI). High-speed schlieren imaging was used to analyze ignition probabilities (PI) and kernel growth characteristics. Two approaches were utilized to explore the effects of energy distribution. First, four nominal levels of energy per pulse (Epp) were explored across a wide range of IPTs using a fixed number of pulses. In the fully-coupled regime, Epp did not show any influence over PI or kernel growth rate. Outside of the fully-coupled regime, PI drops to 0 for the lowest level of Epp, whereas the highest level of Epp has PI of 1 for the entire range of IPTs. For intermediate levels of Epp, a partially-coupled regime characterized by significant drops in PI is observed, with recovering PI in the decoupled regime at longer IPT. Second, the energy per pulse (Epp), inter-pulse time (IPT), and the number of pulses are varied such that their individual effects could be isolated while maintaining constant total deposited energy or total discharge duration. In this exploration, IPT is found to be the driving parameter determining the inter-pulse coupling regimes and PI. Lastly, single kernel analysis clarifies the effect of destructive kernel interactions in the partially-coupled regime, which, against intuition, results in increasing minimum ignition power for higher Epp. In conclusion, high-frequency, low-energy discharge pulses can be the optimal ignition method for NPHFD ignition with high PI and optimal energy efficiency.

Kernel weight responses to the photothermal environment in maize dent × flint and flint × flint hybrids

AbstractMaize (Zea mays L.) grain yield is assumed to be source limited during the flowering period but sink limited during grain growth; however, environmental restrictions during active grain filling may strongly affect final kernel weight (KW). In this study, we evaluated the effect of natural changes in photothermal conditions during lag phase (LP) and effective grain‐filling period (EGFP) on KW, its physiological determinants, and the post‐flowering source–sink relationships of flint and semident germplasm. F1 hybrids of flint × flint and dent × flint background were tested during four seasons (Y1, Y2, Y3, and Y4). Across years, the highest KW (286 mg) was obtained under the maximum photothermal quotients during LP (PTQLP = 1.18 MJ m−2 °C−1) and EGFP (PTQEGFP = 1.07 MJ m−2 °C−1) of Y2, whereas the smallest KW (252 mg) and source–sink ratio during grain filling was obtained under the lowest PTQEGFP (.79 MJ m−2 °C−1) of Y3. Supra‐optimum temperatures during LP of Y3 negatively affected potential KW determination, and hence kernel growth rate (P < .001) as a result of reduced assimilate availability per kernel. Hybrids dent × flint exhibited higher grain yield, kernel number, and plant growth around flowering than flint × flint throughout evaluated seasons but had reduced source–sink relationship during grain filling (P < .05) and increased KW sensitivity (P < .001) to changes in the photothermal conditions. Results emphasized the importance of the photothermal environment during grain filling on KW determination (particularly for seasons with great photothermal imbalance between filling subphases) as well as the dependency of KW responses on the genetic background.

Modeling kernel weight of hybrid maize seed production with different water regimes

Kernel weight (KW) is the key to ensuring seed vigor in hybrid maize (Zea mays L.) production, and irrigation is important for ensuring KW in arid regions. Irrigation experiments were conducted in an arid region of Northwest China to investigate the effects of water deficit on KW, plant growth rate per kernel after silking (PGRKAS), lag phase duration (LPD), kernel growth rate during effective grain filling (KGREGF), and effective grain filling duration (EGFD), which included a 50% water deficit at the vegetative stage, and a 50% and 100% water deficit at the flowering and grain-filling stages in 2018 and 2019. A restricted pollination treatment and two defoliation treatments (three and six leaves were removed from the top 14 days after silking) were conducted under each irrigation treatment in 2019 to obtain a wide range of data on grain filling characteristics and aboveground biomass. The results showed that a 50% water deficit at the vegetative stage shortened EGFD and LPD in both years. The 50% and 100% water deficit at the grain-filling stage decreased KW, PGRKAS, EGFD, and KGREGF in 2019, but had no significant differences in each indices in 2018 due to heavy rainfall. We found a bilinear plateau relationship between relative KGREGF (RKGREGF) and relative PGRKAS (RPGRKAS) as well as a logistic relationship between relative EGFD and RPGRKAS/RKGREGF. Combined with the Jensen model to simulate biomass characteristic parameters (the maximum aboveground biomass, the day of year of the maximum absolute growth rate, and the initial growth rate), the KW–water model performed well in predicting the KW of hybrid maize seed production under different irrigation treatments. This research provides a quantitative method for modeling the KW of hybrid maize seed production, which considers the source-sink relationship under different water regimes in arid areas.

Spark and flame kernel interaction with dual-pulse laser-induced spark ignition in a lean premixed methane–air flow

The growth rate of flame kernels from dual-pulse laser-induced spark (DPLIS) ignition was compared to that from single-pulse laser-induced spark (SPLIS) ignition in a flowing premixed methane–air mixture. The flow speed ranged from 3.75 m/s to 12.5 m/s with equivalence ratios of 0.57–0.67. The pulse energy ranged from 10 mJ to 30 mJ, with each DPLIS pulse having half of the SPLIS pulse energy. High-speed schlieren imaging captured ignition and flame propagation. Two regimes were identified depending on the location of the first laser-induced spark (LIS) kernel: direct interaction and flame combination. The direct interaction regime occurred when the second LIS immediately combined with the first LIS. In the direct interaction regime, DPLIS ignition had faster flame kernel growth rates than SPLIS ignition when the second LIS occurred near the boundary of the first LIS expansion prior to the first LIS igniting the fuel–air mixture. The flame combination regime occurred when each LIS separately ignited the fuel–air mixture and then combined into a single flame kernel. DPLIS ignition had faster flame kernel growth rates in the flame combination regime than did SPLIS ignition when each DPLIS had fully developed into a self-sustaining flame.

Effect of CO2 dilution on forced ignition and development of CH4/air ignition kernels

Reliable ignition of reactant mixtures containing combustion products is important to the function of many practical combustion devices. Prior work has considered the influence of CO2 on ignition delay times and laminar flame speeds. This work examines the effects of dilution with CO2 on forced ignition and development of ignition kernels in CH4/air mixtures. Ignition kernels were initiated by a high voltage spark discharge in CH4/air/diluent mixtures with a bulk velocity of 5 m/s and with 0.7 ≤ Φ ≤ 0.8. Ignition probabilities and kernel growth rates were determined from radiation intensity measurements collected using a Telops MS-IR FAST infrared camera. Nitrogen was used as an inert in a subset of conditions to facilitate identifying changes in chemistry associated with dilution by CO2. Chemistry effects of diluents on ignition were isolated by examining undiluted, N2 diluted, and CO2 diluted flows with equivalent adiabatic flame temperatures. Dilution with CO2 reduced the probability of ignition relative to undiluted and N2 diluted conditions with the same adiabatic flame temperature. Ignition kernels diluted with CO2 also tended to be smaller than those initiated in both undiluted and N2 diluted mixtures, with reduced growth rates.

Predicting Kernel Growth of Maize under Controlled Water and Nitrogen Applications

The availability of water and nitrogen (N) to maize during its flowering stage affects the growth of individual kernels. The present study reports the variability of maize kernel dry weight under different levels of water and N applications. Two consecutive-year experiments were conducted during 2009 and during 2010 to study the interaction between three irrigation regimes and five N application rates on weekly maize kernel growth. Logistic and regression equations were fitted to kernel moisture content and kernel dry weight as a function of thermal time (TT) during critical crop stages. Kernel moisture content and growth rate increased non-linearly from 1 week after silking to physiological maturity. By applying logistic function we were able to improve simulation of kernel moisture content and daily increases in kernel dry weight. The logistic curve showed kernel moisture contents linearly correlated with kernel dry weight. Similarly, regression analyses of kernel dry weight showed a significant positive correlation with kernel moisture content for the 2009 (R2 = 0.86 NRMSE = 23%) and 2010 growing seasons (R2 = 0.92; NRMSE = 19%). Therefore, the logistics curves derived from the observed data may be helpful for predicting daily kernel growth for the semi-arid conditions. The results showed that the optimal N rate for maximum kernel dry weight was 250 kg ha−1 under 525 mm delta of water application ha−1. This rate might be considered in formulating good agricultural practices for optimum maize kernel growth in the semi-arid regions. Thus, our results contribute to better understanding of best management practices of N fertilizer and irrigation water for optimum maize productivity under semiarid region.

Response of kernel growth of barley genotypes with different row type to climatic factors before and after inflection point of grain filling

Abstract Changes in patterns of rainfall and rising temperatures during grain development have already negatively affected yield gains of temperate cereals. This article reports on barley field trials with 15 two- and 10 six-row barley genotypes evaluated in eight environments where terminal drought was simulated by leaf defoliation applied seven days after heading. The experimental years were contrasting in terms of temperatures during grain filling. The focus of the study was to determine which barley type was more sensitive to terminal drought and high temperatures. The grain filling period was divided in two sub-periods: before (P1) and after (P2) inflection point (IP) of the growth curve, which occurs at the instant when the rate of accumulation ceases to accelerate and begins to slow down. For each period, climatic factors were calculated and their effects on the mean kernel growth rate (RG) were analyzed. To explore genotype × environment interactions for production per spike (PPS), the regression approach was adopted using climatic data in P1 and P2 as explanatory variables. Two-row barley had a significantly longer IP than six-row barley. IP was in a negative relationship with RG and PPS in both barley types. Six-row barley showed higher RG sensibility than two-row barley to drought stress during the period of the extensive kernel growth (P1). The number of days with moderately high (between 25 and 30 °C) and high (over 30 °C) temperatures had a higher negative effect on RG of two-row barley than six-row barley, particularly in P2. On the other hand, minimum temperatures were more negative for RG of the six-row barley than two-row barley, particularly under control conditions. In general, two-row barley showed better adaptation to low yielding environments, while six-row barley was more responsive to high yielding environments.

Analysis of high-speed broadband flame chemiluminescence imaging in a SI engine

This study investigates the characteristics of flame propagation in a gasoline S.I engine through a combined thermodynamic and optical approach. Two high-speed CMOS camera were used together with an endoscopic system to visualize the early flame in a spark-ignited engine. An unintensified high-speed (20 kHz) imaging of early flame kernel formation and turbulent flame propagation for hundreds of consecutive combustion cycles has been analysed and compared to pressure-derived heat release rates and mass fraction burn (MFB) profiles. At very low light levels, the patterned read-out noise on the detector becomes significant. Filtering in the Fourier domain was effective in suppressing this noise component to acceptable levels. In this paper, a previously-developed algorithm with automatic dynamic thresholding was used to separately detect spark ignition and flame kernel in the image sequences. The detected flame boundary was post-processed to compute basic flame characteristics such as flame area and turbulent flame speed based on spherical flame propagation assumption. Ignition and flame propagation are compared for fast combustion cycles and slow combustion cycles based on the optical flame speed and crank angle resolved mass fraction burned profile. The good burn (fast) cycles show higher spark stretch caused by local tumble flow-field, greater early flame growth rate, and nearly spherical flame propagation at the center of combustion chamber. In contrast, the poor (slow) cycles show slower flame kernel growth rate, and mostly asymmetric flame propagation near the spark-plug and pent-roof of the combustion chamber. The analysis shows a good correlation between thermodynamics and optical data.

The role of the exponential and linear phases of maize (Zea mays L.) ear growth for determination of kernel number and kernel weight

Abstract Although the importance of the critical period for establishing the maize (Zea mays L.) yield components of kernel number (KN) and kernel weight (KW) is well known, there is little detailed information on how early ear development during the critical period and lag phase are influenced by hybrid improvement or N stress. Seven hybrids commercialized between 1946 and 2015 were compared under a range of N stress created by five N fertilizer treatments: no N applied or a total of 220 kg N ha−1 where N was applied either at the four-leaf stage (V4), at flowering, or a combination of these two times. Ears (cobs plus kernels) were sampled five times at weekly intervals, from approximately 14 days before until 14 days after flowering, to determine dry weight, N concentration, and N content. The dynamics of these traits were modeled using an expolinear function and parameters estimated using a non-linear mixed model. Hybrid and N treatment influences on the exponential and linear phases of ear growth were determined by comparing parameters. The greatest impact of genotype or plant N status was realized in the linear phase when modern hybrids exhibited higher linear growth rates and ears accumulated progressively more N with increasing V4 stage N rate. Neither genotype nor N stress resulted in different ear growth or N accumulation rates during the exponential phase; however, modern hybrids exhibited a longer exponential phase duration. Use of expolinear function with parameters estimated within the non-linear mixed models enabled us to gain insight on development phases modified as the result of genetic improvement or affected by N stress. During the exponential phase, which overlaps with the lag phase when cell division is a key determinant of potential kernel weight and sink strength, neither hybrid era nor N treatments substantially impacted ear growth. Instead, the most important early ear growth characteristics to differentially impact final KN and KW at maturity were the duration of the lag phase and ear growth rates during the linear phase. Future research is suggested to unravel how the duration of the exponential phase is related to cell number and kernel size determination, and how these in turn affect kernel growth rate during the linear phase.

KNMAIZE–A Model to Investigate the Dynamics of Kernel Set in Maize

Core Ideas The dynamics of kernel set in maize was modeled at the individual kernel level.Kernels survived when enough assimilate was available to meet their needs.The model captures the dynamics of ear size, plant growth rate, and kernel growth. The adjustment of kernels plant−1 to the assimilate supply is an important component of the yield production process in maize (Zea mays L.). A simulation model (KNMAIZE) was developed to better understand this process at the individual kernel level. Kernel survival was determined by comparing the assimilate supply (calculated from solar radiation) partitioned to reproductive growth during the initial stages of kernel development with the kernel assimilate requirement (based on published kernel growth curves) on a daily basis. When model parameters were optimized by maintaining the ratio of the sink (total kernel growth rate) and the source (total assimilate supply) equal to 1.0 during the linear phase of kernel growth, the model accurately mimicked the effect of plant growth rate, individual kernel growth rate, and ear size on kernels plant−1. The model also mimicked the plant density‐kernels m−2 relationship. Short‐term (3 or 5 d) variation in plant growth rate influenced kernels plant−1 11 to 15 d after the beginning of kernel growth. Modeling kernel number at the individual kernel level makes it possible to capture important aspects of the dynamics of kernel set that will lead to better predictions of kernel number and a clearer understanding of the elements of maize productivity in the field.

Flame kernel evolution and shock wave propagation with laser ignition in ethanol-air mixtures

Flame kernel evolution and shock wave propagation in ethanol/air mixtures with laser ignition in a constant-volume chamber was investigated by means of high-speed Schlieren photography. At initial pressure of 0.1 MPa and temperature of 333 K, ignition was performed using a pulsed laser at the second harmonic wavelength with six different laser energies from 75 to 200 mJ, for the equivalence ratios ranging from 0.8 to 1.4. A cross-shaped plasma spot is captured ∼3.0 µs after the laser triggering, whereas the shape of the flame kernel is initially circular and then transforms to an ellipsoid structure. Following the contraction of the plasma, the flame kernel growth rate is initially very different in the four directions and then approaches a steady flame speed. The contraction of the plasma zone is accompanied by a rapid shock wave propagation where, the wave propagation speed is found to be negligibly influenced by the variations in either laser energy or mixture equivalence ratio. Under the test conditions in this study for ethanol/air mixtures, the initial shock wave speed is ∼480 m/s which decays to ∼380 m/s after 20 µs. The shock wave front propagates with a time dependency of about t0.6 when t < 20 µs, and then it becomes an approximately linear function of time.