Quench Distance Research Articles

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...

Entropy production in flames

Thermodynamic foundations of the thermal entropy production are rested on the concept of lost heat , ( Q T ) δT. The thermomechanical entropy production is shown to be in terms of the lost heat and the lost work as δS 8= 1 T Q T δT+δW l where the second term in brackets denotes the lost (dissipated) work into heat. The dimensionless number Π s describing the local entropy production s‴ in a quenched flame is found to be Π s ∼(Pe d 0) −2, where Π s = s‴l 2 k , l = α S u 0 (a characteristic length), k thermal conductivity, α thermal diffusivity, S u 0 the adiabatic laminar flame speed at the unburned gas temperature, Pe d 0 = S u 0D α the flame Peclet number, and D the quench distance. The tangency condition ∂ Pe d 0 ∂θ p = 0 , where θ b = T b T b 0 , T b and T b 0 denoting, respectively, the burned gas (nonadiabatic) and adiabatic flame temperatures, is related to an extremum in entropy production . The distribution of entropy production between the flame and burner is shown in terms of the burned gas temperature and the distance from the burner.

Radiative entropy production—lost heat into entropy

Heat flow δQ of the First Law of Thermodynamics is expressed in terms of the entropy flow δ( Q/ T) δQ  δ[ T( Q/ T)] = Tδ( Q/ T)+( Q/ T) dT where Tδ( Q/ T) denotes the energy equivalent of the entropy flow, and ( Q/ T) dT introduces the concept of lost heat into entropy production. Here Q = Q K + Q R where superscripts K and R indicate conduction and radiation, respectively. In terms of the lost heat, dimensionless entropy productions on the wall of a thermal boundary layer and in a quenched laminar flame are respectively shown to be П x ~ (1+q x R/q x K)Nu x 2 and П s ~ (1+q R/q K)Pe −2 where q R and q K are the one-dimensional fluxes associated with Q R and Q K , Nu x is a local Nusselt number, and Pe is a Peclet number based on the laminar flame speed at the adiabatic flame temperature. The tangency condition, ∂Pe/ ∂T b = 0, customarily used in the evaluation of minimum quench distance without any physical justification, is shown to correspond to an extremum in entropy production.

Modelling of combustion process in a spark ignited hydrogen engine

This paper reports the relative merits of the Eddy Entrainment model over the Reynolds Parameter model in describing the combustion process in a spark ignition engine using hydrogen as fuel. The relative performance of each model is analysed with reference to the experimental data obtained from a single-cylinder engine. From the present investigation and in comparison of the performance of these models with other fuels it is found that both the models are capable of satisfactorily predicting the performance of hydrogen fuel engines due to (a) higher laminar flame speeds and (b) small quench distance.

Fundamental Study on Quenching Distance Measured by Flanged Electrode Method

Fundamental Study on Quenching Distance Measured by Flanged Electrode Method

On laminar flame quenching and its application to spark ignition engines

Analyses are made of flame quenching in flows both perpendicular and parallel to a heat sink. A fundamental question is raised about the characteristic length over which a flame in a tube loses heat. Two possibilities are examined, the radius and the flame thickness. By using a functional form prescribed by the theoretical analyses a correlation of laminar flame speed, quenching diameter, and lean limit flame temperature is developed. The correlation suggests that the characteristic length for heat loss is the flame thickness. Laminar flame speeds of isooctane and propane have been correlated and used to compute quench distances in an engine. The agreement is reasonable and leads to speculation that quenching in an engine is basically laminar and dependent upon the free stream unburned gas temperature rather than the wall temperature.

Flame-quench distance measurements in a CFR engine

A method has been devised which uses ion probe detection of flames burning through a gap inside the combustion chamber to provide rapid and convenient measurement of two-surface flame-quench distances in an operating engine. This method has been used to establish that such quench distances range from about 0.01 cm to > 0.2 cm, depending in decreasing order on equivalence ratio, manifold pressure, wall temperature, spark timing, and fuel type. A comparison between these experimental findings and the results from one- and two-surface measurements performed by others indicates that two-surface quench values are 2.5 to 12 times greater than one-surface values. The steep dependence on lean equivalence ratio of the measured two-surface quench values imitates to some extent the known behavior of lean hydrocarbon emissions (HCE), but more detailed single-surface quenching data is now needed to fully appreciate the mechanism involved in exhaust HCE.

Pressure, Velocity, and Geometry Effect on A12O3 Produced During Aluminized Propellant Combustion

The effect of A12O3 particles on rocket motor stability is critical, but the mechanisms of droplet formation and roles played therein by pressure, velocity, and geometry are not well characterized. An experimental study is reported which was designed to increase this understanding. Size distribution of A12O3 particles as a function of pressure and velocity along with the effects of flow geometry was determined. There was some effect on the particle size as a function of pressure. Moderate-to-low parallel flow velocity resulted in significant changes to smaller particle size distribution as did flow vortices across an otherwise perpendicular flow system. Upon quenching of combustion products as a function of distance from the end-burning propellant surface, it was found that only at quench distances less than about 1 in. was the size distribution affected. The trend was for less smoke (d< fim) to be collected after early quench.

Flame quenching during high pressure, high turbulence combustion☆

A series of experimental studies is described which confirms the theory that unreacted hydrocarbons in the combustion products of closed chamber engines which operate under conditions of high pressure and turbulence are primarily a result of flame quenching at the walls of the combustion chamber. It is shown that the effect of wall temperature on the quenching process is slight except in the special case when condensation occurs. Direct experimental evidence of the wall quenching phenomenon was obtained by varying the reaction rate through changes in the mixture turbulence and through dilution of the mixture with an inert gas, and by changing the surface area of the combustion chamber. In each case the resultant changes in the measured unreacted hydrocarbons were noted. Also, direct measurements of a representative quench distance were made and correlated with unburnt hydrocarbon measurements.

Flame quenching during high pressure, high turbulence combustion

A series of experimental studies is described which confirms the theory that unreacted hydrocarbons in the combustion products of closed chamber engines which operate under conditions of high pressure and turbulence are primarily a result of flame quenching at the walls of the combustion chamber. It is shown that the effect of wall temperature on the quenching process is slight except in the special case when condensation occurs. Direct experimental evidence of the wall quenching phenomenon was obtained by varying the reaction rate through changes in the mixture turbulence and through dilution of the mixture with an inert gas, and by changing the surface area of the combustion chamber. In each case the resultant changes in the measured unreacted hydrocarbons were noted. Also, direct measurements of a representative quench distance were made and correlated with unburnt hydrocarbon measurements.

Flame quenching at the walls of an internal combustion engine

Experimental evidence is given which indicates that wall-quenching of the combustion reaction occurs in an internal combustion engine. The apparent quench distances observed are in agreement with the quench distances calculated from burner data at approximately the same pressures and temperatures. In addition, the observed quench distances are of the right order of magnitude to account for the unburned hydrocarbons found in the exhaust gas of automobiles operated in the range of full throttle and road load.

Ignition of Explosive Gas Mixtures by Electric Sparks. I. Minimum Ignition Energies and Quenching Distances of Mixtures of Methane, Oxygen, and Inert Gases

An apparatus and experimental procedure is described for measuring capacitances and gap voltages of condensed electric spark circuits for sparks just powerful enough to ignite explosive gas mixtures. Mixtures of methane, oxygen, and inert gases are investigated. From the measured capacitances and gap voltages the minimum ignition energies are calculated. These energies are found to be independent of gap voltage. With increasing gap length they attain a minimum at critical distances which mark the farthest penetration of the flame-quenching effect of the electrode material. Above the quenching distances the energies remain constant over some range which is governed by mixture composition and pressure. Energies measured in this range may be regarded as absolute minimum energies, as defined in a subsequent paper. Data of such minimum energies and of quenching distances are presented for mixtures at room temperature and pressures ranging from 0.2 to 1 atmosphere.