Oxidation Of Unburned Hydrocarbons Research Articles

Technology for obtaining a deposited catalyst based on an aluminosilicate matrix modified with europium oxide

The number of cars used worldwide is constantly growing. In this regard, the problem of combating atmospheric pollutants - exhaust gases of internal combustion engines is of particular relevance. Over the years, automakers have made many improvements to car engine design and fuel systems to meet pollution limits. One of the best solutions to this problem is the use of a so-called catalytic converter (converter) or simply a catalyst with a high content of noble metals, the main function of which is the simultaneous oxidation of unburned hydrocarbons and CO, as well as the reduction of nitrogen oxides. It was found that the addition of rare earth metals to Pd, Pt catalysts improves their properties and reduces the proportion of noble metals in the composition of catalysts. The paper presents the results of a study of complexation in the Eu3+-ligand system, where the ligand is an organic acid, by photocolorimetric and potentiometric methods. In the Eu3+-gallic acid system, a stable complex of the composition MeLnx – 1:2 is formed. In the Eu3+- oxalic acid system, a stable complex of the composition MeLnx – 1:1 is formed. In the Eu3+-valine system, a stable complex of the composition MeLnx – 1:2 is formed. A new technique for obtaining complex compounds is shown, consisting in adding hydrogen peroxide H2O2 to a solution containing solutions of Eu3+ salt and organic acid in an aqueous-alcoholic medium to block the reduction of Eu3+→Eu2+. A technology for obtaining a automotive catalyst has been developed, consisting of successive stages: obtaining complex compounds, applying the obtained complex compounds to ceramic block matrices, drying, applying platinum (palladium) acid, calcination. The presence of the Eu3+ ion in the ceramic matrix is proved by the method of elemental analysis. The technology can be applied to solve the problem of environmental pollution, such pollutants as exhaust gases of cars containing a lot of harmful substances in their composition.

Modified one-step reaction equation for modeling the oxidation of unburned hydrocarbons in engine conditions

The oxidation of unburned hydrocarbons from piston crevices was modeled using a modified one-step reaction equation. This new one-step oxidation model was developed by modifying the Arrhenius reaction rate coefficients of the conventional one-step reaction equation. The predictions of the new one-step oxidation model agree well with the results of the detailed chemical reaction mechanism in terms of the 90% oxidation time of the fuel. The effects of pressure and intermediate species in the burnt gas on the oxidation rate were also investigated and included as additional multiplying factors in the modification of the equation. To simulate the oxidation process of unburned hydrocarbons from a piston crevice, a two-dimensional computational mesh, based on the conventional engine geometry, was constructed with a fine mesh density at the regions of the piston crevice and cylinder wall. The number of cell layers in the cylinder was controlled according to the piston motion to model the out-flow of unburned hydrocarbons from the piston crevice during the expansion stroke. The effects of engine operational conditions on the oxidation rate were examined at several engine speeds and load conditions, and the sensitivity of the oxidation rate to the piston crevice volume was also evaluated. Finally, the new one-step oxidation model was applied to a three-dimensional computational mesh that modeled the three-dimensional engine geometry and piston-valve motions to simulate the oxidation of unburned hydrocarbons in a real engine condition.

Dual-catalyst aftertreatment of lean-burn natural gas engine exhaust

A dual-catalyst system for the reduction of NO with CH4 under lean conditions was investigated. The system is comprised of a mixed bed containing a Co/ZrO2 catalyst, active for the oxidation of NO to NO2, and a Pd/sulfated zirconia (SZ) catalyst that is active for the reduction of NO2 with CH4. Such a system is capable of taking advantage of higher reduction rates for NO2, as compared to NO, that have been previously observed. When simulated exhaust streams from lean-burn natural gas engines are used as feed, the dual-catalyst system is simultaneously active for the reduction of NOx and the oxidation of unburned hydrocarbons and CO.

The Effect of an Oxidation Precatalyst on the NOx Reduction by Ammonia SCR

The performances of oxidation and SCR catalysts were investigated individually and as a combined system for the removal of NOx by ammonia. Experiments were carried out with synthetic gas mixtures matching the composition of diesel exhaust. Introducing an oxidation catalyst upstream of the SCR catalyst enhances the removal of NOx at low temperatures. The beneficial effects of combining the two catalysts are the oxidation of unburned hydrocarbons that inhibit the SCR reaction and the conversion of NO to NO2 on the oxidation catalyst. NO2 fractions up to 50% of total NOx enhance the NOx conversion at temperatures below 300 °C. However, excess NO2 should be avoided because the reaction of NO2 with ammonia is slow, resulting in a decreased NOx conversion. Above 350 °C, the NOx conversion essentially does not depend on the ratio NO2/NOx or on the presence of hydrocarbons in the feed. A simple mathematical prediction of the NOx conversion for the combined system is also possible. The parameters used in this calculation are the ratio NO2/NOx behind the oxidation catalyst and the experimentally determined conversions of pure NO or NO2 over the SCR catalyst.

Exhaust Oxidation of Unburned Hydrocarbons from Lean-Burn Natural Gas Engines

Post cylinder oxidation of unburned hydrocarbons (UHC) was studied using a 35 kW lest engine. The engine was equipped with an insulated exhaust reactor to extend the residence time. The exhaust reactor performance has been characterised under the basic engine operating conditions, and under conditions where temperature and composition (NOx level) of the exhaust were modified independent of engine settings. The experiments studied spanned a wide range of moderately lean-bum conditions. The composition at the exhaust port was as follows: O2 5-9% (engine excess air ratios of 1.28-1.75), UHC 1000-7000 ppm, CO 550 ppm, NOx0-1400 ppm. The temperature varied from 600 to 700°C, In addition, experiments with injection of hydrogen peroxide to promote UHC oxidation in the exhaust system were conducted. The amount of UHC oxidised in the exhaust system depended closely on the exhaust temperature, residence time and concentration of nitrogen oxides in the exhaust gas. The increased reaction time in the exhaust reactor caused an oxidation of the exhaust hydrocarbons of up to 90% with CO as the major oxidation product, but the reactor efficiency decreased as the engine was operated at leaner conditions, due to lower temperatures and lower NO, levels. Levels of nitrogen oxides above 300 ppm were shown to strongly promote the extent of UHC oxidation. Injection of hydrogen peroxide increased the degree of exhaust reactor oxidation and extended the oxidation further into the lean operation range. A field engine was tested at increased NOx levels, obtained by addition of ammonia to the air intake. No physical modifications of the engine or the settings were performed. The ammonia addition resulted in a reduction of unburned hydrocarbons by approximately 30% with CO2 as the major product. Due to the comparatively low temperature and short residence time of the field engine exhaust system, as well as the absence of CO production, the UHC reduction was attributed to processes occurring in the cylinder or exhaust port, rather than in the exhaust system. Similar levels of UHC reduction prior to the exhaust reactor were observed in the test engine. A detailed chemical kinetic model was used for simulation of the exhaust oxidation experiments. The modelling predictions were in fairly good agreement with the observations, confirming the catalytic role of NOx in the oxidation of hydrocarbons. The model was used to extrapolate the test engine results to conditions representative of co-generation engines and the practical implications are discussed.

3-Dimensional Modeling of Hydrocarbon Oxidation in the Exhaust Port of a Spark Ignition Engine

A three-dimensional model for oxidation of unburned hydrocarbons at the SI engine exhaust port has been developed. The computational mesh with a moving grid for the valve motion is constructed for the port geometry of a single-cylinder research engine. A 4-step oxidation model is used to predict the HC oxidation and the coefficients of the model are modified for the port oxidation environment with the results of a full chemical kinetic mechanism. The measured THC concentrations at the cylinder exit (3 positions) are used as the inlet concentration for the simulation and the temperatures of the core gases and boundary zone gases in the cylinder are obtained from a three-zone cycle simulation. The simulation result shows that the degree of the THC oxidation in the exhausl port at 1,000 rpm, IMEP 550 kPa, stoichiometic condition is 31.5%. The effects of inlet gas temperature, oxygen concentration, heat transfer, and engine operating conditions on the THC oxidation have been investigated. THC oxidation in the exhaust port is predicted to be between 14% and 46% depending on the engine operating conditions. The simulation results are in good agreement with other research results.

The Roles of Chemistry and Diffusion on Hydrocarbon Post-Flame Oxidation

A transient one-dimensional reactive-diffusive model is used to simulate the process of post-flame oxidation of unburned hydrocarbons in spark-ignition engines, and to identify the physical and chemical factors controlling the oxidation process. The model focuses on the oxidation processes taking place in the reactive layer between hot burned gases and cold unreacted air/fuel mixture, with initial and boundary conditions similar to those provided by the emergence of hydrocarbons from a piston land crevice. Energy and species conservation equations are solved for the entire time-dependent process, using detailed chemical kinetic mechanisms. Simulation results show that the in-cylinder process is largely controlled by diffusion rates for burned gas temperatures above a transition level )of the order of 1400–1700 K. depending on fuel type), reaction controlled for temperatures below that level, and practically frozen for temperatures below 1300K. Radicals in the burned gas are shown to be important only in initiating the reaction, as radicals concentrations generated by the oxidating fuel greatly exceed burned gas concentrations except at burned gas temperatures below 1300 K. Large differences in oxidation rates are found for different fuels for the same initial conditions of burned gas temperatures and stoichiometries. The differences can be attributed to the lengths of the reaction chain, and the diffusion of intermediate products towards the cold wall zone (which acts as a storage buffer), leading to differences in the generation of radicals in the reacting zone. In contrast with previous suggestions that oxidation is dominated by the existing radicals in the burned gas, the simulations show that the role of chemical kinetics and the self-generation of radicals are critical in determining overall oxidation rates. Further, the simulations suggest that measured hydrocarbon emission levels from operation on different fuels may be attributed to their drastically different oxidation pathways and rates, rather than simply volatility or solubility in lubricant oil.

Chemical kinetic simulation of hydrocarbon oxidation through the exhaust port of a spark ignition engine

The oxidation of unburned hydrocarbons remaining in the cylinder of a spark-ignited engine after the main combustion event takes place both in-cylinder and in the exhaust port. Hydrocarbons emerging from engine tailpipes consist of unburned fuel as well as products of incomplete combustion. This paper addresses the extent of oxidation and the production of nonfuel species in the exhaust port of a single-cylinder spark-ignition engine. Simulations of the unsteady thermal and composition state of the gases emerging from the cylinder were coupled to detailed chemistry models of the oxidation of hydrocarbons (propane, isooctane, methane, and ethane) to determine the change in the average composition of the gas as it passes through the exhaust port. The results are compared to previously measured speciated compositions of the exhaust gases at the exhaust port inlet and outlet. A stratification parameter to represent the growth of the thermal boundary layer due to heat transfer is added to the simplified unsteady plug flow simulation. Comparisons between model and experiment show that the concentration of products of incomplete combustion can only be adequately reproduced if stratification effects are taken into account.

Oxidation of hydrocarbons from lubricant oil layers in spark-ignition engines

The postflame oxidation of hydrocarbons desorbed from the lubricant oil layer in spark-ignition engines is investigated through simulations and comparison with experimental measurements. A one-dimensional reactive-diffusive model is formulated for the process of desorption and oxidation of hydrocarbons emerging from the lubricant oil layer. Energy, mass, and species conservation equations are solved through the expansion stroke, using simplified assumptions for the turbulent diffusivity, boundary layer growth, and chemical reaction rates. Simulation results show that under the current assumptions both reaction and diffusion rates are controlling. Chemical reaction rates peak over a narrow range of temperatures throughout the expansion stroke. This oxidation zone moves away from the wall during the expansion stroke due to heat transfer and volumetric expansion: Sensitivity analysis shows that the single most important parameter determining the oxidation of hydrocarbons from the oil layer is turbulent diffusion, which must be included for predictions to be of the same order of magnitude as experimental values. Other important parameters are chemical reactivity of the hydrocarbon and the initial boundary layer thickness. Good agreement is obtained regarding the sensitivity of oxidation levels to dopant type and the most sensitive operating parameters: dilution and coolant temperature. This good agreement indicates that oxidation of unburned hydrocarbons in engines may well be represented by such simplified models. However, a factor of 3 discrepancy in the prediction of absolute values for the oxidation levels suggest that substantial refinement is required in the submodels.

Storage and Partial Oxidation of Unburned Hydrocarbons in Spark-Ignited Engines - Effect of Compression Ratio and Spark Timing

Abstract The concentrations of the individual hydrocarbon species in the exhaust gases from a single-cylinder CFR engine have been measured. The effects of compression ratio and spark timing on these emissions have been observed using propane, isooctane (2,2,4-trimethylpentanerpar; and indolene clear fuels. The results show that total hydrocarbon emissions increase rapidly as the compression ratio increases and decrease sharply as the spark timing is retarded relative to MBT at a constant compression ratio. Changes in the concentration of unburned fuel in the exhaust contribute the most to these variations. These observations are consistent with the predicted increase in crevice and oil film storage of unburned hydrocarbons at higher compression ratio because of the higher peak pressures. They also agree with the predicted increase in post-flame burnup of stored hydrocarbons in the hotter cylinder gases encountered during low compression ratio or retarded spark operation.