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Exhaust Gas Recirculation (exhaust + gas_recirculation)
Selected AbstractsComposite adaptive and input observer-based approaches to the cylinder flow estimation in spark ignition automotive enginesINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 2 2004A. Stotsky Abstract The performance of air charge estimation algorithms in spark ignition automotive engines can be enhanced using advanced estimation techniques available in the controls literature. This paper illustrates two approaches of this kind that can improve the cylinder flow estimation for gasoline engines without external exhaust gas recirculation (EGR). The first approach is based on an input observer, while the second approach relies on an adaptive estimator. Assuming that the cylinder flow is nominally estimated via a speed-density calculation, and that the uncertainty is additive to the volumetric efficiency, the straightforward application of an input observer provides an easy to implement algorithm that corrects the nominal air flow estimate. The experimental results that we report in the paper point to a sufficiently good transient behaviour of the estimator. The signal quality may deteriorate, however, for extremely fast transients. This motivates the development of an adaptive estimator that relies mostly on the feedforward speed-density calculation during transients, while during engine operation close to steady-state conditions, it relies mostly on the adaptation. In our derivation of the adaptive estimator, the uncertainty is modelled as an unknown parameter multiplying the intake manifold temperature. We use the tracking error between the measured and modelled intake manifold pressure together with an appropriately defined prediction error estimate to develop an adaptation algorithm with improved identifiability and convergence rate. A robustness enhancement, via a ,-modification with the ,-factor depending on the prediction error estimate, ensures that in transients the parameter estimate converges to a pre-determined a priori value. In close to steady-state conditions, the ,-modification is rendered inactive and the evolution of the parameter estimate is determined by both tracking error and prediction error estimate. Further enhancements are made by incorporating a functional dependence of the a priori value on the engine operating conditions such as the intake manifold pressure. The coefficients of this function can be learned during engine operation from the values to which the parameter estimate converges in close to steady-state conditions. This feedforward learning functionality improves transient estimation accuracy and reduces the convergence time of the parameter estimate. Copyright © 2004 John Wiley & Sons, Ltd. [source] Energy efficiency improvement strategies for a diesel engine in low-temperature combustionINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2009Ming Zheng Abstract The lowered combustion temperature in diesel engines is capable of reducing nitrogen oxides and soot simultaneously, which can be implemented by the heavy use of exhaust gas recirculation (EGR) or the homogeneous charge compression ignition (HCCI) type of combustion. However, the fuel efficiency of the low-temperature combustion (LTC) cycles is commonly compromised by the high levels of hydrocarbon and carbon monoxide emissions. More seriously, the scheduling of fuel delivery in HCCI engines has lesser leverage on the exact timing of auto-ignition that may even occur before the compression stroke is completed, which may cause excessive efficiency reduction and combustion roughness. New LTC control strategies have been explored experimentally to achieve ultralow emissions under independently controlled EGR, intake boost, exhaust backpressure, and multi-event fuel-injection events. Empirical comparisons have been made between the fuel efficiencies of LTC and conventional diesel cycles. Preliminary adaptive control strategies based on cylinder pressure characteristics have been implemented to enable and stabilize the LTC when heavy EGR is applied. The impact of heat-release phasing, duration, shaping, and splitting on the thermal efficiency has also been analyzed with engine cycle simulations. This research intends to identify the major parameters that affect diesel LTC engine thermal efficiency. Copyright © 2008 John Wiley & Sons, Ltd. [source] Influence of high rates of supplemental cooled EGR on NOx and PM emissions of an automotive HSDI diesel engine using an LP EGR loopINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2008A. Maiboom Abstract Previous experimental studies on diesel engine have demonstrated the potential of exhaust gas recirculation (EGR) as an in-cylinder NOx control method. Although an increase in EGR at constant boost pressure (substitution EGR) is accompanied with an increase in particulate matter (PM) emissions in the conventional diesel high-temperature combustion (HTC), the recirculation of exhaust gases supplementary to air inlet gas (supplemental EGR) by increasing the boost pressure has been suggested as a way to reduce NOx emissions while limiting the negative impact of EGR on PM emissions. In the present work, a low-pressure (LP) EGR loop is implemented on a standard 2.0 l automotive high-speed direct injection (HSDI) turbocharged diesel engine to study the influence of high rates of supplemental cooled EGR on NOx and PM emissions. Contrary to initial high-pressure (HP) EGR loop, the gas flow through the turbine is unchanged while varying the EGR rate. Thus, by closing the variable geometry turbine (VGT) vanes, higher boost pressure can be reached, allowing the use of high rates of supplemental EGR. Furthermore, recirculated exhaust gases are cooled under 50°C and water vapour is condensed and taken off from the recirculated gases. An increase in the boost pressure at a given inlet temperature and dilution ratio (DR) results in most cases an increase in NOx emissions and a decrease in PM emissions. The result of NOx,PM trade-off, while varying the EGR rate at fixed inlet temperature and boost pressure depends on the operating point: it deteriorates at low load conditions, but improves at higher loads. Further improvement can be obtained by increasing the injection pressure. A decrease by approximately 50% of NOx emissions while maintaining PM emission level, and brake specific fuel consumption can be obtained with supplemental cooled EGR owing to an LP EGR loop, compared with the initial engine configuration (HP moderately cooled EGR). Copyright © 2008 John Wiley & Sons, Ltd. [source] Effects of exhaust gas recirculation on exergy destruction due to isobaric combustion for a range of conditions and fuelsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2008Hari Shanker Sivadas Abstract This study was directed at examining the effects of exhaust gas recirculation (EGR) on the exergy destroyed due to combustion in a simple constant pressure combustion system. Both cooled and adiabatic cases of EGR were studied. Higher ,cooled EGR' fractions lead to higher exergy destruction for reactant temperatures less than 2000,K. For the base case, the percentage of the reactant exergy destroyed for 0,,20, and 40% EGR at 300,K was found to be 28,,32, and 36%, respectively. Neglecting the chemical exergy in the products, the equivalence ratio and reactant temperature that corresponded to the lowest exergy destruction varied from 0.9 to 1.0 and 800,1300,K, respectively, depending on the EGR fraction. The fraction of the reactant exergy destroyed increased with increase in the molecular mass of the fuel for the alkanes examined. The exergy destroyed due to combustion was the least for acetylene and the highest for the alcohols. The trends stayed the same for the different EGR fractions for the eight fuels that were analyzed. For the ,adiabatic EGR' case, the percentage destruction of exergy decreased with increase in the EGR fraction with a 40% ,adiabatic EGR' fraction corresponding to a destruction of exergy of 14%. Copyright © 2008 John Wiley & Sons, Ltd. [source] Pressure and temperature-based adaptive observer of air charge for turbocharged diesel enginesINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 6 2004A. G. Stefanopoulou Abstract In this paper we design an adaptive air charge estimator for turbocharged diesel engines using intake manifold pressure, temperature and engine speed measurements. This adaptive observer scheme does not depend on mass air flow sensors and can be applied to diesel engines with no exhaust gas recirculation (EGR). The performance of the adaptive scheme is shown in simulations to be comparable to conventional air charge estimation schemes if perfect temperature measurements are available. The designed scheme cannot estimate fast transients and its performance deteriorates with temperature sensor lags. Despite all these difficulties, this paper demonstrates that (i) the proposed scheme has better robustness to modelling errors because it provides a closed-loop observer design, and (ii) robust air charge estimation is achievable even without air flow sensors if good (fast) temperature sensors become available. Finally, we provide a rigorous proof and present the implementation challenges as well as the limiting factors of this adaptation scheme and point to hardware and temperature sensor requirements. Copyright © 2004 John Wiley & Sons, Ltd. [source] Influence of novel cycle concepts on the high-temperature corrosion of power plantsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 5 2008Bettina BordenetArticle first published online: 29 MAY 200 Abstract The aim to reduce CO2 emissions has triggered the evaluation of new cycle concepts for power plants. CO2 -capture concepts are also evaluated to add on new and existing power plants. For combined cycle power plants (CCPP), different cycles are investigated such as integrated gasification (IGCC) or oxy-fuel firing. Besides the difference in combustion compared to a conventional CCPP, the environmental boundary conditions are changed and will affect the oxidation and corrosion life of the materials in the hot-gas path of the gas turbine and the heat-recovery steam generator. For the circulating fluidised bed power plants, the biomass co-firing and the oxy-fuel firing are also foreseen for CO2 -emission reduction. The fireside corrosion of the water walls will be influenced by these concepts and the changed fuel. The corrosion risk has been evaluated for two new power plant concepts: combined cycle with exhaust gas recirculation and pulverised coal-fired boiler with oxy-fuel firing. Based on this evaluation, the consequences for the testing conditions and the material selection have been discussed in detail. [source] | ||||||||||