Post-Flame Oxidation and Unburned Hydrocarbon in a Spark-Ignition Engine PDF Download
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Author: K. Song
Publisher:
ISBN:
Category :
Languages : en
Pages : 16
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Many recent publications indicate that spark ignition (SI) engines equipped with the conventional port-injection fuel system (PIF) seem to have serious fuel-maldistribution problems, including the formation of liquid layers over the combustion chamber surfaces. It is reasonable to expect that such a maldistribution is an unfavorable condition for the flame propagation in the cylinder. The in-cylinder flame behaviors of a PIF-SI engine as fueled with gasoline are investigated by using the Rutgers high-speed spectral infrared imaging system. These results are then compared with those obtained from the same engine operated by gaseous fuels and other simple fuels. The results from the engine operated by gasoline reveal slowly burning fuel-rich local pockets under both fully warmed and room-temperature conditions. The local pockets seem to stem from the liquid layers formed over the surfaces during the intake period. The (invisible) post-flame oxidation of the rich pockets is observed to continue even after the exhaust valve opens. On the contrary, the same engine run with a gaseous fuel exhibits some predictable and 'clean' flame propagations. The new results obtained from the present study suggest that such a late oxidation of locally fuel-rich liquid pockets may be a significant cause for the emission of the engine-out unburned hydrocarbon (UHC). The sluggish consumption of the fuel there may also be a factor for reducing the thermal efficiency of the engine. A parametric study of this observation is performed to obtain a better understanding of the findings. (AN).
Author: K. Song
Publisher:
ISBN:
Category :
Languages : en
Pages : 16
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Book Description
Many recent publications indicate that spark ignition (SI) engines equipped with the conventional port-injection fuel system (PIF) seem to have serious fuel-maldistribution problems, including the formation of liquid layers over the combustion chamber surfaces. It is reasonable to expect that such a maldistribution is an unfavorable condition for the flame propagation in the cylinder. The in-cylinder flame behaviors of a PIF-SI engine as fueled with gasoline are investigated by using the Rutgers high-speed spectral infrared imaging system. These results are then compared with those obtained from the same engine operated by gaseous fuels and other simple fuels. The results from the engine operated by gasoline reveal slowly burning fuel-rich local pockets under both fully warmed and room-temperature conditions. The local pockets seem to stem from the liquid layers formed over the surfaces during the intake period. The (invisible) post-flame oxidation of the rich pockets is observed to continue even after the exhaust valve opens. On the contrary, the same engine run with a gaseous fuel exhibits some predictable and 'clean' flame propagations. The new results obtained from the present study suggest that such a late oxidation of locally fuel-rich liquid pockets may be a significant cause for the emission of the engine-out unburned hydrocarbon (UHC). The sluggish consumption of the fuel there may also be a factor for reducing the thermal efficiency of the engine. A parametric study of this observation is performed to obtain a better understanding of the findings. (AN).
Author:
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Languages : en
Pages : 0
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The post-flame oxidation of unburned hydrocarbons (HC) released from the ring-pack crevice in spark-ignition engines was investigated. Experimental data was collected in two engines running at steady-state, fully warmed-up condition, fixed load and fixed speed. Nitrogen was injected into the intake manifold to dilute the charge in order to maintain the average burned gas temperature as the equivalence ratio varied. For a given operating condition, similar in-cylinder pressure and burned gas temperature profiles were obtained at different equivalence ratio. Two models for post-flame oxidation were proposed: 1) a mixing-controlled model, based on an empirical correlation of two parameters, and 2) a kinetically controlled model, based on a zero-dimensional model using detailed chemical kinetic. The mixing-controlled model consisted of a linear correlation between the peak mass flow rate of crevice gas returning to the combustion chamber and a post-oxidation metric defined as Global HC Consumption Rate (GCR). Using this correlation, the engine-out HC emissions were estimated. In general, the results were satisfactory, but the main shortcoming of the model was that the constant of the linear correlation needed to be derived empirically for each engine and each air-fuel ratio. A kinetically controlled model was developed to study the effect of the mixture composition and temperature in the post-oxidation process. To account for the mixing between the unburned crevice gas and the burned gas in the cylinder, two approaches were taken: 1) an optimized mixing rate based on a constant (with time) value for the mass of burned gas entrained into an unburned gas parcel, and 2) a time-varying mixing rate, in which the crevice outgassing process was modeled using a self-similarity solution for both a turbulent round jet and a wall jet. Using both approaches, the engine-out HC emissions were calculated. The results were compared to the measured HC emission. In general, satisfactory (or expected) results were found for cases in which the engine was run rich or near stoichiometric. For the lean combustion cases, the results were unsatisfactory (or unexpected) with both mixing approaches. A hypothesis that explain the discrepancy in the lean combustion side was suggested. For a given operating condition, the potential to reduce actual engine-out HC emission was identified. The results showed that during the crevice outgassing process, there was a relatively narrow period of time in which it is feasible to increase the overall rate of post-oxidation. It is suggested that improving the mixing rate during this window of time can boost the level of post-oxidation within the cylinder and subsequently reduce the engine-out HC. This insight can be used to develop strategies for engine-out HC emission reduction by focusing on the period of the engine cycle that matter the most.
Author: Kuo-Chun Wu
Publisher:
ISBN:
Category :
Languages : en
Pages : 187
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Author: Javier A. Vera
Publisher:
ISBN:
Category :
Languages : en
Pages : 226
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Author: Kevin David Cedrone
Publisher:
ISBN:
Category :
Languages : en
Pages : 191
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Gasoline consumption and pollutant emissions from transportation are costly and have serious, demonstrated environmental and health impacts. Downsized, turbocharged direct-injection spark ignition (DISI) gasoline engines consume less fuel and achieve superior performance compared with conventional port fuel injected spark ignition (PFI-SI) engines. Although more efficient, turbocharged DISI engines have new emissions challenges during cold start. DISI fuel injection delivers more liquid fuel into the combustion chamber, increasing the emissions of unburned hydrocarbons. The turbocharger slows down activation (warm-up) of the catalytic exhaust after-treatment system. The objective of this research is to find a control strategy that: 1. Accelerates warm-up of the catalyst, and 2. Maintains low emissions of unburned hydrocarbons (UBHCs) during the catalyst warm-up process. This research includes a broad experimental survey of engine behaviour and emission response for a modern turbocharged DISI engine. The study focuses on the idle period during cold-start for which DISI engine emissions are worst. Engine experiments and simulations show that late and slow combustion lead to high exhaust gas temperatures and mass flow rate for fast warm-up. However, late and slow combustion increase the risk of partial-burn misfire. At the misfire limit for each parameter, the following conclusions are drawn: 1. Late ignition timing is the most effective way to increase exhaust enthalpy flow rate for fast catalyst warm-up. 2. By creating a favourable spatial fuel-air mixture stratification, split fuel injection can simultaneously retard and stabilize combustion to improve emissions and prevent partial-burn misfire. 3. Excessive trapped residuals from long valve overlap limit the potential for valve timing to reduce cold-start emissions. 4. Despite their more challenging evaporation characteristics, fuel blends with high ethanol content showed reasonable emissions behaviour and greater tolerance to late combustion than neat gasoline. 5. Higher exhaust back-pressure leads to high exhaust temperature during the exhaust stroke, leading to significantly more post-flame oxidation. 6. Post-flame oxidation in the combustion chamber and exhaust system play a critical role in decreasing the quantity of catalyst-in emissions due to hydrocarbons that escape primary (flame) combustion. A cold start strategy combining late ignition, 15% excess air, and high exhaust backpressure yielded the lowest cumulative hydrocarbon emissions during cold start.
Author: Haifeng Liu
Publisher:
ISBN:
Category :
Languages : en
Pages :
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The influence of different post-flame fuel oxidation rates on the hydrocarbon emission formation process in a spark ignition engine was investigated using both experimental measurements and model simulations. Because the engine was fueled by gaseous fuels, the investigation focused on the combustion chamber crevices, in particular the piston top-land crevices as a source of hydrocarbon emissions. An engine test system was set up, from which the regular exhaust emissions 'CO'2, 'CO', 'O '2, 'NOx', total hydrocarbon, as well as the speciated hydrocarbons from 'C'1 to 'C'6, were measured under different engine operating conditions for a variety of fuels including pipeline natural gas, pure methane, ethane, propane, and iso-butane. Three stages were found for the in-cylinder hydrocarbon development during the post-flame period, namely the blowdown process, the displacement process before the hydrocarbon vortex reaches the vicinity of the exhaust valve, and exit of the vortex through the exhaust valve. The computational model can reasonably predict the regular exhaust emissions and speciated hydrocarbon emissions. The fuel's oxidation chemistry plays a complicated and critical role in the eventual hydrocarbon emission formation. Although the main component of the mixture of engine-out hydrocarbons is fuel itself, the fraction of the intermediate hydrocarbons increases as the fuel carbon number increases. Most of the intermediate hydrocarbons are generated and flow out of the cylinder during the blowdown and the displacement process. Most of the hydrocarbons in the vortex remain unoxidized. The cut-off temperatures, i.e. the temperature below which hydrocarbons that are intermediates in the fuel oxidation process begin to appear in the bulk gas, for different fuels are 1480 K for methane, 1300 K for ethane, 1400 K for propane, 1450 K for n-butane, and 1470 K for iso-butane. A strong interaction between hydrocarbon emissions and 'NO x' emissions was identified using the model. Direct interaction and indirect interaction mechanisms were defined. It was found that the reactions between radicals 'CH'3, 'CH' 2 and 'NO', and reactions between radicals 'O, H' and 'NO' are the dominant reasons for the interaction for low carbon number hydrocarbon fuels. (Abstract shortened by UMI.).
Author: Stani V. Bohac
Publisher:
ISBN:
Category :
Languages : en
Pages : 464
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Author: John V. Mendillo
Publisher:
ISBN:
Category : Combustion gases
Languages : en
Pages : 13
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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![The Influence of Post-flame Fuel Oxidation Rates on Hydrocarbon Emissions in SI Engines [microform] PDF](https://books.google.com/books/content/images/frontcover/l_ZDXwAACAAJ?fife=w80-h100)
Author: Haifeng Liu
Publisher: National Library of Canada = Bibliothèque nationale du Canada
ISBN: 9780612590151
Category :
Languages : en
Pages : 424
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