• Transactions of the Korean hydrogen and new energy society
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• v.24 no.2
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• pp.136-141
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• 2013

In order to achieve simultaneously the ultra-low NOx, the high power and the high efficiency in a hydrogen-fueled engine with SI and the external mixture, the effects of low temperature combustion, performance and exhaust are compared and analyzed by the application of the lean boosting. As the results, the decrease rate of the high temperature in the hydrogen is less decreased than the other fuels by high constant-volume specific heat. However, when the conditions of 1.7bar and ${\Phi}=0.33$ are reached by the lean boosting, the maximum gas temperature of hydrogen is decreased under the temperature of NOx formation and it is possible to stabilize combustion below 2% of COVimep. Also, at that condition, it is feasible to achieve simultaneously NOx-free and the power of gasoline level. Therefore, it is found that the lean boosting is useful in the hydrogen-fueled engine.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.853-858
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• 2001

The knowledge of flame structure is essential for control of combustion instability phenomena. Some results of an experimental study on mechanism of naturally occurring combustion oscillations with a single dominant frequency are presented. Tests were conducted in a laboratory-scale dump combustor at atmospheric pressure. Sound level meter was used to track the pressure wave inside the combustor. The observed instability was a longitudinal mode with a frequency of $\sim341.8Hz$. Instability map was obtained at the condition of inlet temperature of $360^{\circ}C$, mean velocities of $8.5\sim10.8m/s$ and well premixed mixture. It showed that combustion instability was susceptible to occur in the lean conditions. In this study, unstable flame was observed from stoichiometric to 0.7 in overall equivalence ratio. At selected unstable conditions, phase-resolved OH chemiluminescence images were captured to investigate flame structure with various mean velocities. As mean velocity is increased, the flame grows and global heat release was changed. Due to these effects, combustion instability can be maintained at more lean air-fuel ratio. Also, these results give an insight to the controlling mechanism for an increasing heat release at maximum pressure.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.3
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• pp.106-112
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• 2012

Since air pollution problem by emissions from automotive vehicles has become social issues, lean-burn gasoline direct injection (GDI) engine is focused as an alternative to meet the requirement of reinforced emission regulation and improved fuel consumption. Spray-guided type DI combustion is promising technology, which characterized by the centrally mounted injector and closely positioned spark plug, since stable lean combustion can be realized even at ultra-lean mixture condition. In the present study, the effect of multi-ignition with developed charge coil on combustion and emission characteristics was investigated in optical accessible single cylinder engine. In order to fully understand the in-cylinder phenomena and the mechanisms of emission production, optical diagnostics, such as flame visualization was also carried out at frequently using operating condition. Multi-ignition is effective to improve fuel economy but increase NOx emission at flammability limit.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.3
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• pp.7-12
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• 2003

Mixture formation in the cylinder of a lean bum engine has been observed by Laser Induced Fluorescence technique. XeCl laser (308nm) was used to produce a laser sheet. 3-pentanone has been added to iso-octane fuel to produce fluorescence, the intensity of which is proportional to the concentration of the fuel. The laser sheet was introduced through the piston window and the fuel distribution in the vertical plane was observed through a side window. Comparison has been made for the cases of selected fuel injection timing as 0, 360, 405, and 450 CA. For the case of 0 and 360 CA injection, uniform fuel distribution in the combustion chamber has been obtained at the ignition time which is favorable for the high load mode. And the late injection cases, 405 and 450 CA, revealed the stratified formation of rich mixture around the spark plug. That extends the lean misfire limit and reduces cyclic variation in the low load mode.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1682-1685
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• 2004

Gas Turbine combustors for power plant can be reduced NOx emissions using lean premixed combustion technology. But the combustors are likely to occur combustion oscillations which damage operation reliability and mechanical life of the gas turbines. In this paper, characterizations of oscillation in a gas turbine combustor for power plant are presented. Combustion dynamics occur $1{\sim}1.5$ psi in amplitude with low frequency less than 140Hz during normal operation. An abnormal high level dynamics, 2.0 psi amplitude occur at 125 Hz frequency. Abnormal combustion oscillation is reduced by modulation of fuel supply valve control schedule.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.425-432
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• 2004

The objective of this study is a qualitative comparison between line-integrated OH chemiluminescence(OH$\^$*/) image and its Abel inverted image to investigate the flame structure at different phase of the oscillating pressure field. PIV(Particle Image Velocimetry) measurements were conducted under non-reacting conditions to see the global flow structure and NOx emission was measured to investigate the effect of fuel-air premixing on combustion instability and emission characteristics. Experiments were carried out in an atmospheric pressure, laboratory-scale dump combustor operating on natural gas. Combustion instabilities in present study exhibited a longitudinal mode with a dominant frequency of ∼341.8㎐, which corresponded to a quarter wave mode of combustor. Heat release and pressure waves were in-phase when instability occurred. Results gave an insight about the location where the strong coherence of pressure and heat release existed. Also an additional information on active control to suppress the combustion instabilities was obtained. For lean premixed combustion, strong correlation between OH$\^$*/ and NOx emissions was expected largely due to the exponential dependence of thermal NOx mechanism on flame temperature.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.149-152
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• 2012

The laboratory experiments have been conducted to investigate the effects of air preheated temperature on the emission characteristics by a model gas turbine burner with a hybrid/dual swirl jet flames configuration. The concentration of NOx and CO emissions, and flue gas temperature at combustor exit were measured with varying the equivalence ratio for different air preheated temperatures of 300, 400, 500K at atmospheric pressure. It was overall shown that the NOx and CO emissions, and flue gas temperature were decreased according to the decreasing of equivalence ratio due to the effects of lean premixed combustion regardless of the air preheated temperature. Experimental results of a lean premixed flames configuration indicated that the NOx emission was increased with higher inlet air temperature and air flow rate, which is attributed to the increasing of flue gas temperature and heat release related to the thermal NOx mechanism. But the CO emission was shown the opposite tendency, that is, the CO emission was decreased with increasing of inlet air temperature and flow rate.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.704-709
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• 2000

Laminar burning velocities of propane- and iso-octane-air mixtures have been numerically modelled over a wide range of equivalence ratio, pressure and temperature. These correlations are applicable to the modelling of stratified charged combustion like that of lean bum and GDI engine combustion. The numerical models are based on the results calculated by PREMIX code with Sloane's detailed chemical reaction mechanism for propane and FlameMaster code with Peters' for iso-octane. Laminar burning velocity for two fuels showed a pressure and temperature dependence in the following form, in the range of $0.1{\sim}4MPa$, and $300{\sim}1000K$, respectively. $S_L={\alpha}\;{\exp}[-\xi({\phi}-{\phi}_m)^2-{\exp}\{-{\xi}({\phi}-{\phi}_m)\}-{\xi}({\phi}-{\phi}_m)]$ where ${\phi}_m=1.07$, and both of ${\alpha}$ and ${\xi}$ are functions of pressure and temperature. Compared with the results of the existing models, those of the present one showed the good agreement of the recent experiment data, especially in the range of lean and rich sides. Judging from the calculated results of the stratified charged combustion by using STAR-CD, the above modelling prove to be more suitable than the other ones.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.356-361
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• 2003

The objective of this study is a qualitative comparison between line-integrated OH chemiluminescence ($OH{\ast}$) image and its Abel inversion image at different phase of the oscillating pressure field. PIV(Particle Image Velocimetry) measurements were conducted under non-reacting conditions to see the global flow structure. Also NOx emission was measured to investigate the effect of fuel-air premixing on combustion instability and emission characteristics. Experiments were carried out in an atmospheric pressure, laboratory-scale dump combustor operating on natural gas. Combustion instabilities in present study exhibited a longitudinal mode with a dominant frequency of ${\sim}341.8$ Hz, which corresponded to a quarter wave mode of combustor. Heat release and pressure waves were in-phase when instability occurred. Results gave an insight about the location where the strong coherence of pressure and heat release existed. Also an additional information on active control to suppress the combustion instabilities was obtained. For lean premixed combustion, strong correlation between $OH{\ast}$ and NOx emissions was expected largely due to the exponential dependence of thermal NOx mechanism on flame temperature.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.97-100
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• 2014

The combustion and emission characteristics of propane and n-butane which are the main components of LPG were compared with gasoline. The experiment was performed in a stratified DISI engine under lean combustion conditions. Mixtures of propane and n-butane wre more homogeneous because propane and n-butane have better evaporation characteristics. As a result, combustion speeds of n-butane and propane were slower, and emission levels of NOx and PM were lower. However, in spite of better evaporation, PM from propane was higher.