We have studied cyclic heat release variability in a spark-ignition engine under exhaust gas recirculation (EGR), using nitrogen to simulate EGR. Five EGR levels are examined. We used wavelet analysis to identify the dominant modes of fluctuation and how these modes vary in time. It is found that at a low EGR level, the heat release variations exhibit high-frequency intermittent oscillations. As the EGR level increases, the high-frequency oscillations tend to become more persistent, occurring continuously over many cycles. When the EGR level is sufficiently high, intermittent oscillations are observed at both high and low frequencies. In addition, persistent low-frequency fluctuations are present at the high EGR level. We have fitted theoretical probability models to the empirical heat release distributions. Depending on the EGR level, a three-parameter probability density function such as the generalized logistic distribution, a four-parameter distribution such as Johnson SB, or the five-parameter Wakeby distribution is found to provide a good fit. The goodness of fit of the theoretical distributions is assessed by the Kolmogorov-Smirnov (KS) test statistics. A good understanding of cyclic variability is essential to develop effective control strategies for efficient combustion.

This study investigates the low-frequency (interannual and longer period) variability in three hydroclimatic records from east Central Europe. Two of these records consist of climate proxies derived from oak-tree rings in Bakta forest, and Balaton Highlands in Hungary, for the time interval 1783-2003. The third record consists of homogenized instrumental precipitation data from Budapest, Hungary, from 1842 to 2003. Using wavelet analysis, the three time series are analyzed and compared with one another. It is found that all three time series exhibit strong interannual variability at the 2-4 years timescales, and these variations occur intermittently throughout the length of each record. Significant variability is also observed in all the records at decadal timescales, but these variations persist for only two to three cycles. Wavelet coherence among the various time series is used to explore their time-varying correlation. The results reveal significant coherence at the 2-4 years band. At these timescales, the climatic variations are correlated to the tree-ring signal over different time intervals with changing phase. Increased (decreased) contribution of large-scale stratiform precipitation offers a potential explanation for enhanced (faded) coherence at the interannual timescale. Strong coherence was also observed occasionally at decadal timescales, however these coherences did not appear uniformly. These results reinforce the earlier assertion that neither the strength nor the rank of the similarity of the local hydroclimate signals is stable throughout the past two centuries.

Long instrumental records of meteorological variables such as temperature and precipitation are very useful for studying regional climate in the past, present, and future. They can also be useful for understanding the influence of large-scale atmospheric circulation processes on the regional climate. This paper investigates the monthly, winter, and annual temperature time series obtained from the instrumental records in Zagreb, Croatia, for the period 1864–2010. Using wavelet analysis, the dominant modes of variability in these temperature series are identified, and the time intervals over which these modes may persist are delineated. The results reveal that all three temperature records exhibit low-frequency variability with a dominant periodicity at around 7.7 years. The 7.7-year cycle has also been observed in the temperature data recorded at several other stations in Europe, especially in Northern and Western Europe, and may be linked to the North Atlantic Oscillation (NAO) and/or solar/geomagnetic activity.

A field experiment was conducted to study the growth, yield and economic potential of rice as influenced by different age of seedlings, cultivars and weed management under system of rice intensification on sandy-clay-loam soil at Agricultural Research Farm of Institute of Agricultural Sciences, Banaras Hindu University during the two consecutive kharif (rainy) seasons of 2010 and 2011. The experiment was laid out in split-plot design with two ages of seedlings with two cultivars assigned to main plots and seven weed management treatments were allocated as sub- plot treatments has replicated thrice. Transplanting of younger age seedling (10 days) of PHB 71 recorded significantly higher growth attributes, viz. plant height, no. of green leaves/hill and dry matter accumulation with yield attributing characters. Similarly, ten days old seedlings of PHB 71 also produced significantly higher yield (grain and straw) that fetched maximum benefit in respect to gross return, net return and B: C ratio over old aged seedling (15 days) of NDR 359 during 2010 and 2011. Among weed management, cono-weeding 4 times at 10, 20, 30 and 40 days after transplanting (DAT) recorded significantly higher growth attributes, yield attributes and yield, but sequential application of pre and post-emergence herbicides, i e pretilachlor + bispyribac-Na was found economically feasible under SRI due to lesser labour requirement.

This study investigates the pattern of variability in the precipitation time series reconstructed from tree ring records in the Xiaolong Mountain in central China for the period 1629-2003 AD. Using a continuous wavelet transform, the dominant modes of variation and the time intervals over which these modes may persist are delineated. It is found that the precipitation in this region varies over multiple timescales, and exhibits multiscale dynamics. The different modes may be coupled to large-scale atmospheric circulation patterns such as the Pacific Decadal Oscillation (PDO), and El-Nino Southern Oscillation (ENSO). The results reveal that the reconstructed precipitation time series has strong variations with periodicities in the 37-53 year periodic band. This periodic band persists approximately from 1690 to 1790 AD, and may be linked to PDO. In addition, strong interannual variations (4-8 years) with the highest power around the period of 6.9 years persists from 1945 to 1970 AD. This periodic band may be associated with ENSO. These atmospheric teleconnections of the reconstructed precipitation time series are explored using cross-wavelet analysis.

Based on the simulations developed in research groups over the past years, Introduction to Quasi-dimensional Simulation of Spark Ignition Engines provides a compilation of the main ingredients necessa

Hydroclimate variations since 1300 in central and monsoonal Asia and their interplay on interannual and interdecadal timescales are investigated using the tree-ring based Palmer Drought Severity Index (PDSI) reconstructions. Both the interannual and interdecadal variations in both regions are closely to the Pacific Decadal Oscillation (PDO). On interannual timescale, the most robust correlations are observed between PDO and hydroclimate in central Asia. Interannual hydroclimate variations in central Asia are more significant during the warm periods with high solar irradiance, which is likely due to the enhanced variability of the eastern tropical Pacific Ocean, the high-frequency component of PDO, during the warm periods. We observe that the periods with significant interdecadal hydroclimate changes in central Asia often correspond to periods without significant interdecadal variability in monsoonal Asia, particularly before the 19th century. The PDO-hydroclimate relationships appear to be bridged by the atmospheric circulation between central North Pacific Ocean and Tibetan Plateau, a key area of PDO. While, in some periods the atmospheric circulation between central North Pacific Ocean and monsoonal Asia may lead to significant interdecadal hydroclimate variations in monsoonal Asia.

This study investigates the cycle-to-cycle variations (CCV) of heat release in a simulated spark ignition engine fueled by gasoline–ethanol blends. The equivalence ratio of the combustible mixture is changed from 0.7 to 0.9 and 1.0, i.e., from very lean to stoichiometric. Ethanol is added in the volumetric proportions of 5–25 %. For each equivalence ratio and for each ethanol fraction added, we calculate the coefficient of variation (COV) of the heat release time series. From the values of COV, we find that at a fixed equivalence ratio, the CCV of heat release decreases as the amount of ethanol addition is increased. We also find that for a fixed volume fraction of ethanol, the CCV increases with leaner mixtures. In addition, we use a continuous wavelet transform (CWT) to analyze the heat release time series. From the CWT, the dominant modes of the CCV are identified and the engine cycles over which these modes may persist are delineated. The results reveal that the CCV of heat release occur on multiple timescales and exhibit complex dynamics. With no ethanol added, high-frequency intermittent fluctuations together with more persistent low-frequency variations are observed. As the volume fraction of ethanol is increased, the low-frequency variations tend to become less persistent and more intermittent. Furthermore, at a fixed equivalence ratio, when ethanol fraction is increased, the overall spectral power is found to decrease significantly indicating that ethanol has a pronounced effect on reducing the CCV. An advantage of using a simulated model engine is that the computations can be easily carried out to a large number of cycles and thus determine the long term dynamics of the cyclic variations.

Oxygenates may be added to diesel oil to help reduce exhaust emissions from diesel engines. This study evaluates the effect of adding ethyl-tert-butyl ether (ETBE) to diesel oil on the physicochemical properties of the mixture. ETBE is added in volumetric proportions of 5%, 10%, 20%, 30%, and 40%, and its effects on density, viscosity, lubricity, surface tension, miscibility, and cetane number are investigated. While the effects of ETBE addition on density, viscosity, and cetane number have been examined earlier, this is the first study to investigate the effects of ETBE addition on surface tension, lubricity, and miscibility. The impact of ETBE addition on particulate matter (PM) and smoke emissions is also investigated. The results reveal that ETBE addition can significantly reduce PM emission. In particular, it was found that only 10% ETBE can decrease PM emission by 36%. ETBE addition was also found to reduce the smoke opacity, resulting in 70% reduction with 40% ETBE fraction at the engine speed of 1400rpm and a load of 80Nm. This is the first study that reports the effect of ETBE addition on PM emission from an engine fueled by diesel–ETBE blends.

Based on the simulations developed in research groups over the past years, Introduction to Quasi-dimensional Simulation of Spark Ignition Engines provides a compilation of the main ingredients necessary to build up a quasi-dimensional computer simulation scheme. Quasi-dimensional computer simulation of spark ignition engines is a powerful but affordable tool which obtains realistic estimations of a wide variety of variables for a simulated engine keeping insight the basic physical and chemical processes involved in the real evolution of an automotive engine. With low computational costs, it can optimize the design and operation of spark ignition engines as well as it allows to analyze cycle-to-cycle fluctuations. Including details about the structure of a complete simulation scheme, information about what kind of information can be obtained, and comparisons of the simulation results with experiments, Introduction to Quasi-dimensional Simulation of Spark Ignition Engines offers a thorough guide of this technique. Advanced undergraduates and postgraduates as well as researchers in government and industry in all areas related to applied physics and mechanical and automotive engineering can apply these tools to simulate cyclic variability, potentially leading to new design and control alternatives for lowering emissions and expanding the actual operation limits of spark ignition engines

We have analyzed the variations in cutting force during milling of a fiber-reinforced composite material. In particular, we have investigated the multiscale dynamics of the cutting force measured at different spindle speeds using multifractals and wavelets. The multifractal analysis revealed the changes in complexity with varying spindle speeds. The wavelet analysis identified the coexistence of important periodicities related to the natural frequency of the system and its multiple harmonics. Their nonlinear superposition leads to the specific intermittent behavior. The workpiece used in the experiment was prepared from an epoxy-polymer matrix composite reinforced by carbon fibers.

The apparent rate of troponin (Tn) dissociation from myofibrils has been used as a method to study thin filament regulation in striated muscle. The rate is dependent upon calcium and strong crossbridges and supports the three-state model for thin filament regulation. The dissociation rate of Tn is extremely low so it is not intuitively clear that such a slow process would probe thin filament regulation. We have investigated this issue by developing a simple kinetic model to explain the Tn dissociation rate measured by labeled Tn exchange in the myofibrils. Tn is composed of three interacting subunits, TnC, TnI and TnT. In our model, TnI's regulatory domain switches from actin-tropomyosin to TnC followed by TnT dissociation from actin-tropomyosin. This TnI regulatory domain switching is linked to the transition of the thin filament from the blocked state to the closed state. It is calcium dependent and several orders of magnitude faster than TnT dissociation from actin-tropomyosin. By integrating the dimensionless rate equations of this model, we have computed the time course of each of the various components. In our numerical simulations, the rate constant for TnI switching from actin-tropomyosin to TnC was varied from 10 s(-1) to 1000 s(-1) to simulate the low calcium, blocked state to high calcium, closed state. The computed progress curves for labeled Tn exchange into the myofibrils and the derived intensity ratio between the non-overlap and overlap regions well explains the intensity ratio progress curves observed experimentally. These numerical simulations and experimental observations reveal that the apparent rate of In dissociation probes the blocked state to closed state equilibrium of the myofibrillar thin filament. (C) 2012 Elsevier Inc. All rights reserved.

LPG is the most widely used fuel in spark ignition (SI) engines after gasoline. In SI engines, temperature of the fuel-air charge affects the engine performance and exhaust emission characteristics. At higher engine loads and speeds, LPG can be overheated. This will cause an increase in the charge temperature, and a decrease in engine performance. NOx emissions will also increase as the charge temperature increases. By controlling the LPG temperature, some advantages can be gained. In this study, some preliminary results of a fuel temperature control system on engine performance and emission characteristics will be discussed. As the temperature of the engine cooling fluid changes, a valve controlled by LabVIEW adjusts the mass flow rate of the fluid to hold the LPG temperature in a band before injecting it to the engine intake manifold.

The purpose of this study is to investigate the effect of adding small amounts of hydrogen to gasoline–air mixtures on the performance and exhaust emission characteristics of a spark ignition engine. Four air–fuel ratios are used ranging from stoichiometric to very lean. The amount of hydrogen added is varied from 0% to 2.14%, 5.28%, and 7.74% by volume. The test engine is operated at 2000rpm, and measurements are made over 1000 consecutive engine cycles. From the experimental observations, the effect of hydrogen addition on (a) thermal efficiency, (b) specific fuel consumption, (c) cyclic variations of the indicated mean effective pressure (IMEP), and (d) emissions of CO, NO and unburned hydrocarbons are analyzed. The cyclic IMEP variations are analyzed using the coefficient of variation (COV) and wavelet analysis. An advantage of wavelet analysis is that it can identify the dominant modes of variability and delineate the engine cycles over which these modes may persist.

This study investigates the effect of exhaust gas recirculation (EGR) on the cycle-to-cycle variations (CCV) in combustion in a natural gas spark ignition engine. The engine is operated at 2000 rpm and a stoichiometric fuel-air mixture is used. The EGR level is changed from 0% to 5%, 10%, 15%, and 20%. For each EGR level, a continuous wavelet transform is used to analyze the time series of the indicated mean effective pressure (IMEP) over 200 cycles. The dominant oscillatory modes of the CCV are identified and the engine cycles over which these modes may persist are delineated. The results reveal that the CCV of the IMEP occur on multiple timescales and exhibit complex dynamics. With no EGR, mainly high frequency intermittent fluctuations are observed. As the EGR level is increased, more persistent low frequency variations tend to develop. In addition, the spectral power increased with an increase in the EGR level. At the EGR level of 20%, the spectral power is found to increase significantly indicating that EGR has a pronounced effect on increasing the CCV. Knowledge of the dominant modes of variability may be useful to develop effective control strategies for reducing the CCV and improving engine performance in the presence of EGR. (C) 2011 Elsevier Ltd. All rights reserved.