• 한국연소학회지
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• 제7권3호
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• pp.47-54
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• 2002

The propagation speed of tribrachial flame in laminar propane jets has been investigated experimentally under normal and micro gravity conditions. The displacement speed was found to vary nonlinearly with axial distance because flow velocity along stoichiometric contour was comparable to the propagation speed of tribrachial flame for the present experiment. Approximate solutions for velocity and concentration accounting density difference and virtual origins have been used in determining the propagation speeds of tribrachial flame. Under micro gravity condition, the results showed that propagation speed of tribrachial flame is largely affected by the mixture fraction gradients, in agreement with previous studies. The limiting maximum value. of propagation speeds under micro gravity conditions are in good agreement with the theoretical prediction, that is, the ratio of maximum propagation speed to the stoichiometric laminar burning velocity is proportional to the square root of the density ratio of unburned to burnt mixture.

• 한국자동차공학회논문집
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• 제10권4호
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• pp.23-32
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• 2002

Combustion and flame propagation characteristics of the liquid phase LPG injection (LPLI) engine were investigated in a single cylinder optical engine. Lean bum operation is needed to reduce thermal stress of exhaust manifold and engine knock in a heavy duty LPG engine. An LPLI system has advantages on lean operation. Optimized engine design parameters such as swirl, injection timing and piston geometry can improve lean bum performance with LPLI system. In this study, the effects of piston geometry along with injection timing and swirl ratio on flame propagation characteristics were investigated. A series of bottom-view flame images were taken from direct visualization using an W intensified high-speed CCD camera. Concepts of flame area speed, In addition to flame propagation patterns and thermodynamic heat release analysis, was introduced to analyze the flame propagation characteristics. The results show the correlation between the flame propagation characteristics, which is related to engine performance of lean region, and engine design parameters such as swirl ratio, piston geometry and injection timing. Stronger swirl resulted in foster flame propagation under open valve injection. The flame speed was significantly affected by injection timing under open valve injection conditions; supposedly due to the charge stratification. Piston geometry affected flame propagation through squish effects.

• 대한기계학회논문집B
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• 제20권1호
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• pp.244-254
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• 1996

Flow velocity was measured by, use of hot wire anemometer. Turbulence intensity was in proportion to mean flow velocity regardless of swirl velocity. And integral length scale has proportional relation with swirl velocity regardless of measurement position. Turbulent burning speed during flame propagation which was determined by flame photograph and gas pressure of combustion chamber was increased with the lapse of time from spark and was decreased a little at later combustion period. Because of combustion promotion effect, turbulent burning speed was increased according to increase of turbulence intensity. Burning speed ratio i.e. ratio of turbulent burning speed ($S_BT$) to laminar burning speed ($S_BL$) was found out by use of turbulence intensity u' and integral length scale $l_x$ , $\delta_L$ is width of preheat zone in laminar flame.

• 오토저널
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• 제1권1호
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• pp.28-41
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• 1979

Propane-Air premixed combustible gas was ignited by the conventional current break system inside the open combustion chamber under the atmospheric pressure and the room temperature to measure the flame propagating speed and the burning speed, also to elucidate the history of the propagating flame behavior and wall effects to flame shape by using Ion Gap Method and High Speed Schlieren Photography. The results obtained show that the maximum flame propagating speed and maximum burning speed are approximately 292 cm/sec and 36 cm/sec at the mixture ratio 4.6%, respectively. The cellular flame structures can be observable in the rich mixture region, moreover, the cellular structures become finer, with increasing the mixture strength.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1998년도 제17회 KOSCI SYMPOSIUM 논문집
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• pp.139-154
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• 1998

Under certain circumstance, premixed turbulent flame can be treated as wrinkled thin laminar flame and its motion in a hydrodynamic flow field has been investigated by employing G-equation. Past studies on G-equation successfully described certain aspects of laminar flame propagation such as effects of stretch on flame speed. In those studies, flames were regarded as a passive interface that does not influence the flow field. The experimental evidences, however, indicate that flow field can be significantly modified by the propagation of flames through the volume expansion of burned gas. In the present study, a new method to be used with G -equation is described to include the effect of volume expansion in the flame dynamics. The effect of volume expansion on the flow field is approximated by Biot-Savart law. The newly developed model is validated by comparison with existing analytical solutions of G -equation to predict flames propagating in hydrodynamic flow field without volume expansion. To further investigate the influence of volume expansion, present method was applied to initially wrinkled or planar flame propagating in an imposed velocity field and the average flame speed was evaluated from the ratio of flame surface area and projected area of unburned stream channel. It was observed that the initial wrinkling of flame cannot sustain itself without velocity disturbance and wrinkled structure decays into planar flame as the flame propagates. The rate of decay of the structure increased with volume expansion. The asymptotic change in the average burning speed occurs only with disturbed velocity field. Because volume expansion acts directly on the velocity field, the average burning speed is affected at all time when its effect is included. With relatively small temperature ratio of 3, the average flame speed increased 10%. The combined effect of volume expansion and flame stretch is also considered and the result implied that the effect of stretch is independent of volume release.

• 한국산업융합학회 논문집
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• 제22권5호
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• pp.511-517
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• 2019

Two type pistons which had different configuration were made to find out the effects on combustion and flame propagation. Flame propagation speed was obtained by use of the cylinder head gasket ionization probe. Ionization Probe voltage output and flame propagation speed were increased according to the air fuel mixture ratio increase. Exhaust direction flame propagation speed was fastest in combustion chamber and next was front direction, rear direction and intake direction cause of tumbling motion in cylinder. In case of remove the valve pocket in piston, average flame propagation speed changed slowly and spark timing was advanced. Also emission was decreased.

• 한국자동차공학회논문집
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• 제11권3호
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• pp.48-57
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• 2003

A cylindrical constant volume combustion chamber was used to investigate the flow characteristics at spark plug and the combustion characteristics of homogeneous charge methane-air mixture under various initial pressure, excess air ratio and ignition times in quiescent mixture. The flow characteristics such as mean velocity and turbulence intensity was analyzed by hot wire anemometer. Combustion pressure development measured by piezoelectric pressure transducer and flame propagation acquired by ICCD camera were used to investigate the effect of initial pressure, excess air ratio and ignition times on pressure, combustion duration, flame speed and burning velocity. Mean velocity and turbulence intensity had the maximum value at 200 or 300ms and then decreased to near 0 value gradually after 3 seconds. Combustion duration, flame speed and burning velocity were observed to be promoted with excess air ratio of 1.1, lower initial pressure and ignition time of 300ms.

• 한국연소학회지
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• 제13권3호
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• pp.9-16
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• 2008

In this study, a cylindrical constant volume combustion chamber is used to investigate the flow and combustion characteristics of methane-air homogeneous mixture under various initial charge pressure, excess air ratios and ignition times. The flame and burning speed, mean gas speed are calculated by numerical analysis to analyze the combustion characteristics. It is found that the mean gas velocity during combustion has the maximum value around 300 ms and then decreased gradually on the condition of 10000 ms, and that the combustion duration is shorten and flame speed and burning velocity have the highest value under the conditions of an excess air ratio 1.1, an initial charge pressure of 0.2 MPa and an ignition time of 300 ms in the present study. And, the initial pressure and burning speed are in inverse proportion, so that it is in agreement with Strehlow who presented that the initial pressure and burning speed are in inverse proportion when the burning speed is under 50cm/s.

• 대한기계학회논문집B
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• 제20권2호
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• pp.659-669
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• 1996

To clarify the effects of equivalence ratio, initial pressure and temperature on the flame propagation and radicals characteristics, a series of the experimental study were conducted in a quiescent methane-air premixture using a constant volume chamber. The development of the flame was visualized following the start of ignition using high speed schlieren photo and radical images by intensified CCD camera. Combustion pressure and ion current were recorded simultaneously according to the experimental conditions which were equivalence ratio with 0.7 to 1.2, initial pressure with 0.08 MPa to 0.40 MPa and initial premixture temperature with 3l3.2K to 403.2K. The results showed that the flame speed by ion current and mass fraction burned by combustion pressure characterized the effects of flame propagation very well. And increased combustion duration due to lean combustion condition that was below equivalence ratio, 0.8 caused cycle variation and decreasing the power of engine.

• 한국추진공학회지
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• 제19권4호
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• pp.45-51
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• 2015

정상초음파의 영향을 받는 메탄-공기 예혼합화염의 주파수-당량비 상관도 분석을 위한 실험적 연구가 수행되었다. 슐리렌가시화기법을 이용하여 예혼합화염의 전파영상을 획득하였으며, 영상 후처리를 통해 화염의 구조변이 및 전파거동을 면밀히 관찰하였다. 정상초음파가 개재할 때, 화염선단과 기연부에서 구조적 변이와 연소반응 촉진으로 인한 화염의 전파속도의 증가를 가져온다는 사실에 더하여, 초음파 구동주파수와 당량비에 대한 화염거동의 종속성을 확인하였다.