Andrew A. Adamczyk

A numerical study of laminar flame wall quenching

Abstract Laminar flame quenching at the cold wall of a combustion chamber has been studied, using a numerical model to describe the reactive flow. The model combines an unsteady treatment of the fluid mechanics and a detailed chemical kinetic reaction mechanism. Fuels considered included both methane and methanol. Catalytic reactions at the wall surface are not included in the kinetic model. The one-dimensional case of flame propagation perpendicular to the wall was studied. Two reference cases are described in detail for flame quenching at 10 atm pressure and a wall temperature of 300°K with stoichiometric mixtures of methane-air and methanol-air. In each case a conventional laminar flame propagates toward the wall, approaching to within a distance determined by the thermal flame thickness. Chemical kinetic factors, particularly differences between the temperature dependence of radical recombination reactions and conventional chain branching and chain propagation reactions, are shown to be responsible for quenching the flame near the wall. The flame stagnates, but fuel remaining near the wall diffuses out of the boundary region and is rapidly oxidized away from the wall. Subsequent model calculations demonstrate the effects of variations in pressure, fuel-air equivalence ratio, wall temperature, and type of fuel. Computer results from these methane and methanol flame quenching models indicate that the total unburned hydrocarbon content is considerably smaller than is commonly believed and that thermal wall quenching may not be the major source for hydrocarbon emissions from internal combustion engines at near-stoichiometric conditions.

The Effect of Oil Layers on the Hydrocarbon Emissions from Spark-Ignited Engines

Abstract Measured amounts of oil were added to the engine cylinder of a single-cylinder CFR engine to determine the effect of oil layers on exhaust hydrocarbon emissions. The exhaust hydrocarbon concentration increased in proportion to the amount of oil added when the engine was fueled on isooctane. Addition of 0·6 cm3 of oil produced an increase of 1000 ppmC in exhaust hydrocarbon emissions at a coolant temperature of 320°K. Gas chromatographic analysis of the exhaust determined that fuel and fuel oxidation species, not oil oxidation products, were responsible for most of the increase. Similar experiments performed with propane fuel showed no increase in exhaust emissions when oil was added to the cylinder. These measurements have determined that the increase in tailpipe hydrocarbon concentration consists of fuel related species and is proportional to both the amount of oil added and the solubility of the fuel in the oil. Thus, we believe that the principal source of this increase in exhaust hydrocarbon ...

A combustion bomb study of the hydrocarbon emissions from engine crevices

Abstract Two combustion bombs manufactured from a Ford 1.6L Escort production engine were used to determine the effects of engine crevice volumes on hydrocarbon emissions. Since these combustion bombs were used as static reactors, the results cannot be directly applied to an operating engine but they focus attention on the major hydrocarbon-producing crevices in an actual engine geometry. During Ihis propane-fueled experiment, the crevices were sequentially filled with epoxy or viton rubber, and after filling each crevice, the exhaust hydrocarbon emission was measured by gas chromatography. This provided a quantitative measurement of the hydrocarbon emission from each crevice. For these reactors, the ring-pack crevices produced approximately 80.5 percent of the total scaled hydrocarbon emission, while the head gasket and spark plug threads produced approximately 12.5 percent and 5 percent, respectively. All other hydrocarbon sources produced less than 2 percent of the total scaled hydrocarbon emissionfrom...

An experimental study of hydrocarbon emissions from closed vessel explosions

Two combustion bombs are used to determine the exhaust hydrocarbon emission after laminar flame propagation through the reactors. Propane and air are used as fuel and oxidizer, and gas chromatography is used to analyze, the emission, gases. Data are taken over an initial pressure range from 50 kPa to 400 kPa and from an equivalence ration of 0.7 to the soot limit at 2.0. During experimentation, extreme care is taken to keep the reactor vessels clean while reducing crevice storage volumes using indium seals and displacement materials. The results under lean conditions indicate that the charging and subsequent outgassing of fuel molecules from storage volumes into a relatively cold bulk gas is the primary cause of exhaust emissions. This is consistent with recent numerical results under near stoichiometric conditions, indicating that flame quench hydrocarbons rapidly diffuse and oxidize, producing less unburnt material than previously thought. Under these conditions, the levels of exhaust hydrocarbons are observed to be two orders of magnitude lower than previously reported in the literature. Furthermore, under rich conditions, >1.2, the results indicate that processes other than storage effects and wall-quenching—possibly occurring in the bulk gas—may be the cause of the exhaust hydrocarbon emission from clean vessels.

LAMINAR HEAD-ON FLAME QUENCHING - A THEORETICAL STUDY.

Results of a numerical investigation of one-dimensional laminar flame quenching with constant and time-dependent pressure variations are reported. A description of flame quenching and postflame oxidation processes for a global reaction is obtained by solving a simplified form of nonlinear conservation of mass, momentum, and energy equations in a planar flow field. These equations are reduced to finite difference form, and time-dependent pressure is input via an integrated form of the energy equation or a third-order polynomial law. Numerical calculations were performed at constant-pressure, combustion bomb-type conditions and under rapid decompression during quenching. One-dimensional head-on quenching distances, hydrocarbon concentration levels, and gas properties were derived for various stoichiometric values in a propane/air-type mixture. Results indicate that quenching distance is primarily controlled by the thermal conduction process; however, residual hydrocarbon levels are intimately related to postquenching diffusion, oxidation kinetics, and the thermodynamic cycle during which they occur. Model calculations exhibit good agreement with experimental flame speed and demonstrate single-wall quench thicknesses which closely follow known experimental trends for the two-plate quench distance. Effects of transient pressure changes on postquench burn-up are examined, and results indicate that pressure variations on a time scale similar to that of the quenching process can account for a factor increase in predicted hydrocarbons, as compared with constant pressure calculations. Additional research is recommended to devise a multistep reduction reaction scheme that adequately describes the quenching process.

The effect of oil layers on the hydrocarbon emissions generated during closed vessel combustion

The exhaust gas from a high pressure reactor generated during spark ignited closed vessel combustion in the presence and absence of oil has been analyzed by gas chromography. Five fuels (methane, ethane, propane, n-butane, and hydrogen) and three oils (a synthetic motor oil, a petroleum based motor oil, and a diffusion pump fluid) were tested during these experiments at a variety of fuel-air equivalence ratios (=0.7–1.6). Experiments carried out under lean (=0.9) conditions have demonstrated that the total exhaust hydrocarbon concentration increases by 30, 120, and 400 ppmC for ethane, propane, and n-butane respectively when 0.14 gm of a synthetic motor oil is placed onto a 60 cm2 surface area of the reactor. This exhaust hydrocarbon concentration consists primarily (>95%) of initial fuel in all cases and is directly proportional to both the amount of oil in the reactor and the solubility of the specific fuel in the oil. These results show that absorption of the fuel occurs in the oil prior to ignition. This dissolved fuel is then desorbed into the cooled burned gas after combustion is complete, significantly increasing the exhaust hydrocarbon concentration. In contrast to the above results for lean mixtures, when rich (=1.1–1.5) propane-air mixtures were ignited in the presence of oil, a very large increase in the total hydrocarbon concentrations (30,000 ppmC) was observed in the exhaust. Only 1% of these emissions were unburned fuel, and 20% more total carbon was observed in the exhaust than was present in the initial fuel mixture. This carbon imbalance coupled with other experimental evidence has demonstrated that the oil layer is being extensively degraded to light hydrocarbons under fuel rich conditions during passage of a single flame. This oil degradation is very sensitive to the equivalence ratio and to the type of fuel used.

The Effect of Engine Deposit Layers on Hydrocarbon Emissions from Closed Vessel Combustion

Abstract Abstract-The effects of engine deposit layers on the product gas emissions from combustion bombs manufactured from engine combustion chambers were studied for various fuel-deposit systems. Nine fuels (methane, ethane, propane, n-butane, n-pentane, n-hexane, benzene, n-heptane and iso-octane) were tested in combination with two in-situ engine deposit layers-one thin (0.0017 cm) and one thick (∼0.05-0.1 cm). Gas samples from the reactors were analyzed by gas chromatography. For the thin deposit, the results show that the principal exhaust effluent is unburnt fuel. Additionally, as the solubility of the fuel is increased, the HC emission increases in direct proportion to the change in relative solubility and the absolute HC level can be estimated from the deposit composition and estimated fuel solubility. For the thick deposit, the results show that the principal exhaust effluent is also unburnt fuel, that the exhaust HC level increases with fuel solubility and that a small fraction of the HC emissi...

Engine HC Emissions Modeling: Partial Burn Effects

Abstract A comparison of predicted and experimental HC emissions at high rates of exhaust gas recirculation (EGR), indicates that partial burning is responsible for significant changes in HC emission trends under otherwise normal, non-misfiring engine operating conditions. Ion-probe experiments show a measurable fraction of engine cycles in which the flame did not completely propagate across the chamber whenever HC emissions were high. A simple semi-empirical model is proposed to predict HC emissions from partial burning based on measured burn rate parameters.

The Effect of Oil Layers on Hydrocarbon Emissions: Low Solubility Oils

Abstract The hydrocarbon emissions from a combustion bomb were studied in the presence and absence of an oil layer coating the bottom surface of the reactor. Gas samples were analyzed by gas chromatography. Five oils (squalane, a synthetic motor oil, a petroleum-based motor oil, a polypropylene oxide oil and a polypropylene-polyethylene oxide copolymer oil) were studied in combination with three fuels (ethane, propane and butane). Glycerol was studied with propane as the fuel. The fuels were mixed with air at a fuel-lean equivalence ratio of 0.9. Under conditions ensuring saturation of the oil layer, the results show that the hydrocarbon emission is principally (>90%) initial fuel and that it varies in direct proportion to the amount of oil present in the reactor, to the initial fuel concentration and to the solubility of the specific fuel in the oil layer. The results also show that the specific composition of the oil layer can have a significant influence on the hydrocarbon emission with a polypropylene...

Hydrocarbon Emissions from an Annular Crevice: Effects of Spark/Insert Position, Equivalence Ratio and Pressure

Abstract The hydrocarbon emission (HC) from a crevice formed in the gap between a cylindrical insert and the reactor wall (similar to the piston top/bore geometry in a reciprocating engine) was determined in a combustion bomb under quiescent conditions for propane-air mixtures at four fuel-air equivalence ratios (1.0,0.9,0.82 and 0.71), initial pressures between 75 kPa and 600 kPa, several spark locations and two insert positions (edge and central location). The experiments were performed by removing product gas samples from the reactor with or without the insert in place during combustion and analyzing the samples by gas chromatography. The HC emission arose from the fuel-air mixture stored in the crevice and was related to the 2-plate quenching distance. For the centrally-mounted insert, the emission varied continuously as pressure and equivalence ratio were changed and did not instantly change when the quench distance equalled the gap spacing. For the edge-mounted insert, the emission varied significan...