• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.127-130
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• 2003

This paper presents the numerical thermal analysis for regeneratively cooled rocket thrust chambers. An integrated numerical model incorporates computational fluid dynamics for the hot-gas thermal environment, and thermal analysis for the liner and coolant channels. The flow and temperature fields in rocket thrust chambers is assumed to be axisymmetric steady state which is presumed to the combustion liner. The heat flux computed from nozzle flow is used to predict the temperature distribution of the combustion liner. As a result, we present the wall temperature of combustion liner and the temperature change of coolant.

• Journal of Environmental Health Sciences
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• v.22 no.3
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• pp.28-36
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• 1996

The objects of this study were to investigate emissions of air pollutant the particles as well as the combustibility of the low grade domestic anthracite coal and imported high-calorific bituminous coal in the fluidized bed coal combustor. The production of air pollution from anthracite-bituminous coal blend combustion in a fluidized bed coal combustor was evaluated. The effects of air velocity and anthracite fraction on the reaching time of steady state condition was also evaluated. We used coal samples the domestic low grade anthracite coal with heating value of 2,010 kcal/kg and the imported high grade bituminous coal with heating value of 6,520 kcal/kg. The experimental results are presented as follows. The time of reaching to steady state was affected by the temperature variation. The steady state time was about 120 minute at 0.3 m/s which was the fastest. It has been found that $O_2$ and $CO_2$ concentration were reached steady state at about 100 minute. As the height of fluidized bed becomes higher, the concentration s of $SO_2$ and $NO_x$ mainly increased. The concentration of freeboard was the highest and emission concentration was diminished. Also, as anthracite fraction increased, the emission of $SO_x$ concentration was increased. But, it has been found that the variation of $NO_x$ concentration with anthracite fraction was negligible and the difference of emission concentration according to air flow rates was negligible, too. It has been found that $O_2$ concentration decreased and $CO_2$ concentration increased as the height of fluidized bed increased. As anthracite fraction increased, the mass of elutriation particles increased, and $CO_2$ concentration decreased. Also, as air velocity increased, $O_2$ concentration decreased and $CO_2$ concentration increased. Regardless-of anthracite fraction and flow rate, the combustible weight percentage in elutriation particles were high in the case of fine particles.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.2
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• pp.41-49
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• 2000

To understand the signal fluctuation of a wide-range oxygen sensor installed at the exhaust confluence point, when a misfiring is triggered in a cylinder, the steady state and the transient response characteristics of the sensor to the flow of the misfired gas were investigated quantitatively. It was recognized that the steady state output voltage of the sensor increased higher when it contacted the misfired gas even though the fueling condition was the same as the normal combustion case and this characteristic enabled the application of the wide-range oxygen sensor for the misfire detection. The transient response was compared at different engine speeds and it was found that the response speed increased with the engine speed. The signal fluctuation was also estimated quantitatively, using these steady state and transient response of the sensor, and the estimated signal showed satisfactory correlation with the measurements.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3300-3305
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• 2007

Ignition delay of second injection of HSDI diesel engine was usually much shorter than that of first injection. It is due to the interaction between radicals generated during the combustion process, and mixed gas of second injection. In this paper, To analyze combustion phenomena of multiple injection mode in HSDI diesel engine effectively, two-dimensional flamelet combustion model was modified. To reduce calculation time, two-dimensional flamelet equations were only applied near stoichiometric region. If this region was ignited, species and temperature of other region were changed to the steady-state solutions of one dimensional flamelet equations. By this method calculation time for solving flamelet equations was reduced to 20 percents, thought the results were almost same. Modified flamelet combustion model was coupled to commercial CFD code interactively using user subroutine.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.218-225
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• 2008

When the heat release and acoustic pressure fluctuations are generated in the combustor by irregular combustion, these fluctuations affect the mass flow rate of the propellants injected through the injectors. Also, the variations of the mass flow rate by these fluctuations again bring about irregular combustion and furthermore that is related with combustion instability. Therefore, it is very important to identify the mass variation for the pressure fluctuation on the injector and to investigate its transfer function. So, we first have studied quantifying the variation of mass flow rate generated in simplex swirl injector by injection pressure fluctuation. To acquire the transient mass flow rate in orifice with time, we have tried to measure of the flow axial velocity and liquid film thickness in orifice. The axial velocity is acquired through theoretical approach after measuring the pressure in orifice and the flow area in the orifice is measured by electric conductance method. As results, mass flow rate calculated by axial velocity and liquid film thickness measuring in orifice accorded with mass flow rate acquired by direct measuring method in the small error range within 1 percents in steady state and within 6 percents as average mass flow rate in pulsated state. Hence this method can be used to measure the mass flow rate not only in steady state but also in unsteady state because the mass flow rate in the orifice can acquire with time and this method shows very high accuracy based on the experimental results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.11
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• pp.2169-2180
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• 1992

Solid propellant combustion is investigated for its response to several imposed pressure histories. For this purpose, it is assumed that combustion takes place in a premixed gas evaporated from a uniform melt of solid propellant. One-dimensional unsteady problem is than numerically solved for a pressure coupling, with a steady state as an initial state. The results in response to pressure of finite sinusoidal waves show that unsteady mass fluxes are sometimes quite different from those predicted by the classical quasisteady burning law of Vieile. In addition, abnormal mass flux excursions are captured for a large pressure exponent and a lower melting point.

• Journal of the Korean Society of Combustion
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• v.9 no.4
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• pp.1-8
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• 2004

Zone conditional formulation for the Reynolds average reaction progress variable is used to derive an asymptotic expression for turbulent burning velocity. New DNS runs are performed for validation in a statistically one dimensional steady state configuration. Parametric study is performed with respect to turbulent intensity, integral length scale, density ratio and laminar flame speed. Results show good agreement between DNS results and the asymptotic expression in terms of measured maximum flame surface density and estimated turbulent diffusivity in unburned gas.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.8-23
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• 1997

Steady and unsteady numerical simulations are conducted for the comparison with the experiments performed to investigate the ram accelerator flow field by using an expansion tube facility in Stanford University. Wavier-Stokes equations for chemically reacting flows are analyzed by fully implicit and time accurate numerical methods with Jachimowski's detailed chemistry model for hydrogen-air combustion involving 9 species and 19 reaction steps. Although the steady state numerical simulation shows a good agreement with the experimental schlieren and OH PLIF images for the case of $2H_2$＋$O_2$＋$17N_2$ fails in reproducing the combustion region behind the shock intersection point shown in the case of $2H_2$＋$O_2$＋$12N_2$ mixture. Therefore, an unsteady numerical simulation is conducted for this case and the result shows all the detailed flow stabilization process. From the result of unsteady numerical simulation, the experimental result seems to be an instantaneous state during the flow stabilization process. The combustion behind the shock intersection point is the result of a normal detonation formed by the intersection of strong oblique shocks that exist at early stage of the stabilization process. At final stage, the combustion region behind the shock intersection point disappears and the steady state result is retained. The time required for stabilization of the reacting flow in the model ram accelerator is found to be very long in comparison with the experimental test time.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3288-3293
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• 2007

Compressed natural gas has good potential for alternative vehicle fuel due to its economical and clean characteristics. However, the composition of natural gas based on production location is known to affect performance and emissions of CNG engine. Thus, the objective of this paper is to clarify the effect of fuel composition on combustion and emissions of CNG engine. This paper presents combustion characteristics obtained from running a 2.5L, 4-cylinder CNG engine retrofitted IDI diesel engine with engine dynamometer. BSFC, emissions, fuel consumption and combustion pressure were measured under steady state operating conditions especially at partial load for CNG engine. Based on the experimental results, we found that CNG composition affects engine performance, fuel conversion efficiency and burning rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.8
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• pp.1097-1102
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• 2001

For the purpose of development of high performance gasoline engine, the design technique of the 5-valve(3 intake valves) combustion chamber for a subcompact vehicle has been studied. 3 intake valves cylinder heads were designed by using a 3-dimension CAD program, and steady state flow experiments have been performed with these model. The 5-valve engines, which have larger valve opening areas, have larger intake flow rates and higher flow coefficient than the 4-valve engines. The effects of intake port design parameters of a 5-valve engine on the intake flow rate and bore size were studied, and the design guidelines for the 5-valve engine were established.