• Transactions of the Korean Society of Automotive Engineers
• /
• v.9 no.4
• /
• pp.44-49
• /
• 2001

Reduced chemical kinetics mechanism has been derived, which can be applicable for autoignition model of hydrocarbon fuels, and contains 23 reactions and 18 species. The present model is validated with the experimental data, where the ignition delays of several hydrocarbon fuels, such as n-heptane, i-octane, n-decane and DME(dimethylether) are measured as equivalence ratios are varied. Especially, the effects of different fuels on ignition delays can be explained by changing the rate constants of three reactions among the present model. As a result, the proposed model can be applicable to two stage ignition model of Diesel combustion.

• International Journal of Automotive Technology
• /
• v.2 no.1
• /
• pp.25-31
• /
• 2001

It is necessary to understand the combustion process and cycle-by-cycle variation in combustion to improve the engine stability and consequently to improve the fuel economy and exhaust emissions. The pressure related parameters instead of mass fraction burned were compared for the effect of initial combustion pressures on the following combustion and the analysis of cycle-by-cycle variation in combustion for two pen injected SI engines. The correlation between IMEP and pressures at referenced crank angles showed almost the same trends for equivalence ratios, but the different mixture preparations indicated different tendency. The dependency of IMEP on pressure at the referenced crank angles increases as the mixture becomes leaner for both engines. The mixture distribution in the combustion chamber was varied with the coolant temperature and intake valve deactivation due to the evaporation of fuel and air motion. The correlation between pressure related parameters were also compared for the coolant temperatures and air motion.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2001.11a
• /
• pp.50-53
• /
• 2001

Flame propagation during the initial stages of ignition in a non-premixed swirl, having some of characteristics of the primary zone of an aero gas turbine combustor, has been investigated. Nd:YAG laser was adopted as the principal ignition source to allow arbitrary placing of the ignition site i subsequent flame development was monitored using a natural light high speed filming technique for many ignition site at two different swirl ratios and an overall equivalence ratio of 0.9. For ignition offset from the burner centreline, buoyancy force associated with radial pressure gradient produced a strong inward movement of the flame kernel. At the burner exit. flame kernels invariably developed into cylindrical form and a 'radial confinement /axia expansion' (RCAE) process was observed.

• 한국전산유체공학회:학술대회논문집
• /
• 2003.08a
• /
• pp.126-131
• /
• 2003

A series of computational simulations have been carried out for supersonic flows in a scram jet engine with and without a cavity. Transverse injection of hydrogen, a simplest form of fuel supply, is considered in the present study with the injection pressure varying from 0.5 to 1.5 MPa. The corresponding equivalence ratios are 0.167 - 0.50. The work features detailed resolution of the flow dynamics in the combustor, which was not typically available in most of the Previous studies. In particular, oscillatory flow characteristics are captured at a scale sufficient to identify the underlying physical mechanisms. Much of the flow unsteadiness is related not only to the cavity, but also to the intrinsic unsteadiness in the flowfield. The interactions between shock waves and shear layer may cause a large excursion of flow oscillation. The role of the cavity and injection pressure are examined systematically.

• Journal of the Korean Society of Combustion
• /
• v.19 no.1
• /
• pp.11-16
• /
• 2014

Spherically expanding flames are used to measure flame speeds, which are derived the corresponding laminar flame speeds at zero stretch. Dimethyl Ether-Air mixtures at high pressure are studied over an extensive range of equivalence ratios. The classical shadowgraph technique is used to detect the reaction zone. In analytical methodology the optimization process using least mean squares is performed to extract the laminar flame speeds. It is seen that the laminar flame speed of DME-Air mixture with the increase of pressure decreases rapidly showing a similar trend to other hydrocarbon fuels. At pressure of 2 and 10 atm the experimental data from the present study agree well with results reported in the literature. Especially the laminar flame speeds at 2 atm are in good agreement with those calculated in numerical work over the full stoichiometric range. At elevated pressure of 12 atm the measured data are slightly slower at fuel lean condition and show close agreement at fuel rich condition when compared with the numerical results.

• 한국연소학회:학술대회논문집
• /
• 2015.12a
• /
• pp.109-112
• /
• 2015

This article describes a cellular instability and laminar burning velocity of simulated synthetic natural gas(SNG) including 3% hydrogen. In this study, experimental apparatus is employed using cylindrical bomb combustor, and investigation is carried out with high speed camera and Schlieren system. The cellular instability is caused by the buoyancy, hydrodynamic instability. Unstretched burning velocity can be determined by extrapolated stretch rate of zero point from measured results. These results were also compared with numerical calculation by Chemkin package with GRI 3.0, USC-II, WANG, C3 Fuel mechanism. As an experimental conditions, equivalence ratios was adjusted from 0.8 to 1.3. From results of this work, the one was found that the cellular instability has occurred by effect of thermal expansion rate and flame thickness. As the other results, unstretched laminar burning velocity was best coincided with GRI 3.0 mechanism.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.34 no.6
• /
• pp.629-634
• /
• 2010

Natural gas is a promising alternative fuel that can be used to satisfy the strict engine emission regulations in many countries. To develop natural-gas engines, low emission, efficient fuel consumption, and increased power ratings have to be realized. In this study, a cylindrical constant-volume combustion chamber (CVCC) was used to investigate natural-gas combustion characteristics for different prechamber design parameters and equivalence ratios. In particular, the maximum combustion pressure and mass fraction of the burned gas were evaluated by considering orifice diameter, volume ratio of prechamber and equivalence ratio. Using this result and by analyzing the changes in combustion characteristics with variations in design parameters, the optimum prechamber parameters were determined.

• Fire Science and Engineering
• /
• v.26 no.5
• /
• pp.35-40
• /
• 2012

Numerical investigation was performed to study on the soot formation characteristics in the WSR according to the CO addition. Ethylene and pure air were used as a fuel and an oxidizer, respectively, and three different equivalence ratios (2.0, 2.5, 3.0) were used in the calculation. The resulted CO mole fraction of 10 % CO addition showed the maximum value in spite of the least CO supply. This means that the conversion of CO to soot and other carbon compounds is weakened under incipient soot formation. The soot volume fraction was decreased with increasing the CO addition because the important species for soot formation such as pyrene and acetylene, were decreased with the addition of CO. When the equivalence ratio was 2.5, the soot volume fraction shows the highest value, which results from the contribution of fuel rich condition and reacting temperature. Furthermore, surface growth rate and species concentrations justified the HACA mechanism for soot formation.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.6
• /
• pp.485-496
• /
• 2015

The present study presents experimental results on the characteristics of emission spectra of kerosene/air swirl flames. The aviation fuel Jet A-1, which is used for the liquid rocket engines of the Korea Space Launch Vehicle, is used with three different swirlers to investigate the swirl strength effects. The emission spectra from the flames are measured with a spectrometer as the swirl strength and combustion air temperature are varied. Chemiluminescence intensities of $OH^*$, $CH^*$ and $C_2{^*}$ are identified from the spectra. The chemiluminescence intensities from the kerosene flames show sensitivity to the swirl strength and are affected by changes in the combustion air temperature. Among the three radicals of interest, $C_2{^*}$ show the most significant changes in chemiluminescence intensity with the swirl strength and equivalence ratio. The intensity ratios $I_{OH^*}/I_{CH^*}$ and $I_{C_2{^*}}/I_{CH^*}$ are adequate for indicating changes in the equivalence ratio with the air and fuel mass flow rates, respectively.

• Transactions of the Korean hydrogen and new energy society
• /
• v.25 no.1
• /
• pp.47-58
• /
• 2014

The characteristics of flame shape, laminar burning velocity, emissions and heat flux of stagnation point in premixed impinging jet flame of syngas fuel with 10% hydrogen content were experimentally investigated. Also, the adiabatic temperature and burning velocity are calculated by Chemkin package with USC-II mechanism. The equivalence ratios(0.8~5.0) and dimensionless separation distance(2.0~5.0) with fixed Reynolds number(1800) are main parameters in this work. Different flame shapes and colors were observed for different impingement conditions. The experimental results of burning velocity by flame surface area have a consistent with previous works and numerical simulation of this work. The inner flame length could be predicted with the ratio of mixture velocity and burning velocity from a simple formulation by the laminar burning velocity definition. It has been observed that the heat fluxes at stagnation point are directly affected by the flame shape including the separation distance. The emission results in impinging flame of syngas fuel show that the characteristics of $NO_x$ emission traced well with adiabatic temperature trend and CO emission due to fuel rich condition increased continuously with respect to the equivalence ratio.