• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.5
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• pp.35-44
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• 2011

In a spark ignition engine, a variable valve lift (VVL) system has been developed for high fuel efficiency and low power loss. However, changes in valve lift cause deviations of cylinder air charge which lead to individual cylinder equivalence ratio maldistribution. In this study, in order to reduce the maldistribution, we propose individual cylinder equivalence ratio estimation and control algorithms. The estimation algorithm calculates the equivalence ratio of each cylinder by using a mathematical engine model which includes air charging, fuel film, exhaust gas, and universal exhaust gas oxygen sensor (UEGO) dynamics at various valve lifts. Based on the results of estimated equivalence ratio, the injection quantity of each cylinder is adjusted to control the individual cylinder equivalence ratio. Estimation and control performance are validated by engine experiments. Experimental results represented that the equivalence ratio maldistribution and variation are decreased by the proposed algorithms.

• Journal of the Korean Society of Combustion
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• v.16 no.3
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• pp.52-58
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• 2011

The purpose of this paper is to investigate the effect of equivalence ratio on the combustion and emission characteristics of a compression ignition engine fueled with biodiesel. In this research, a single-cylinder direct injection engine with 373.3 cc of displacement volume was tested on DC dynamometer. In order to investigate the effect of biodiesel equivalence ratio on combustion characteristics, the experiments were conducted at various equivalence ratios and injection pressures of 40~120 MPa. For investigating engine performance, lambda meter was connected and equivalence ratios was varied from 0.6 to 1.0. In addition, the exhaust emissions such as oxides of nitrogen($NO_X$), hydrocarbon(HC) and carbon monoxide(CO) were measured by exhaust gas analyzer under the various air/fuel ratios. The experimental results show that maximum IMEP was measured at the 0.8 of equivalence ratio. Furthermore, $NO_X$ emission was rapidly decreased as the increase of equivalence ratio. However soot emission was significantly increased according to the increase of equivalence ratio.

• Journal of the Korean Society of Combustion
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• v.1 no.1
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• pp.51-55
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• 1996

An experimental investigation has been made with the objective of studying the limits of equivalence ratio on mixing enhancement in a tone excited jet flame. The jet is pulsed by means of a loudspeaker-driven cavity and rich flames(${\phi}>1.5$) are used. The excitation frequency is chosen for the resonant frequency identified as a pipe resonance due to acoustic excitation. Methane, propane and butane are used to examine the effect of mixture property on the limit of equivalence ratio. Mixing is always enhanced in a methane/air flame as the excitation intensity increases. Constant lower limits of equivalence ratio for mixing enhancement are present in cases of propane/air and butane/air flames irrespective of mean mixture velocities. The equivalence ratio limits are also found to be related to the flame instability ; the lower Le, the higher the limit of equivalence ratio. Under the equivalence ratio limits, cellular flames are generated as the excitation intensity increases. The amplitude of oscillating velocity for generating a cellular flame in the equivalence ratio limit is proportional to a mean mixture velocity irrespective of fuels.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.242-250
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• 2006

The impacts of equivalence ratio on the flow structure and flame dynamics in a model gas turbine combustor are investigated using large eddy simulation(LES). Dynamic k-equation model and G-equation flamelet model are employed as LES subgrid model for flow and combustion, respectively. As a result of mean flow field for each equivalence ratio, the increase of equivalence ratio brings about the decrease of swirl intensity through the modification of thermal effect and viscosity, although the same swirl intensity is imposed at inlet. The changes of vortical structure and turbulent intensity etc. near flame surface are occurred consequently. That is, the decrease of equivalence ratio can leads to the increase of heat release fluctuation by the more increased turbulent intensity and fluctuation of recirculation flow. In addition, the effect of inner vortex generated from vortex breakdown on the heat release fluctuation is increased gradually with the decrease of equivalence ratio. Finally, it can be identified that the variations of vortical structure play an important role in combustion instability, even though the small change of equivalence ratio is occurred.

• Journal of the Korean Society of Combustion
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• v.11 no.4
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• pp.27-35
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• 2006

The impacts of equivalence ratio on flow structure and flame dynamic in a model gas turbine combustor are investigated using large eddy simulation(LES). Dynamic k-equation model and G-equation flamelet model are employed as LES subgrid model for flow and combustion, respectively. As a result of mean flow field for each equivalence ratio, the increase of equivalence ratio brings about the decrease of swirl intensity through the modification of thermal effect and viscosity, although the same swirl intensity is imposed at inlet. The changes of vortical structure and turbulent intensity etc. near flame surface are occurred consequently. That is, the decrease of equivalence ratio can leads to the increase of heat release fluctuation by the more increased turbulent intensity and fluctuation of recirculation flow. In addition, the effect of inner vortex generated from vortex breakdown on the heat release fluctuation is increased gradually with the decrease of equivalence ratio. Finally, it can be identified that the variations of vortical structure play an important role in combustion instability, even though the small change of equivalence ratio is occurred.

• Journal of the Korean Society of Combustion
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• v.10 no.1
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• pp.7-12
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• 2005

The surface flames in perforated ceramic burner are experimentally characterized to investigate the effects of equivalence ratio and heating rate. The results show that the surface flames are classified into green, red radiant and blue surface flame as the decrease of equivalence ratio. Each flame is maintained very stable at the specified equivalence ratio and represents the same flame characteristics at any orientation of ceramic burner. Particularly the blue surface flame is found to be very stable at very lean equivalence ratio at 7000kcal/hr to 20000kcal/hr heating rates. And the exhausted NOx measurement shows that blue surface flame represents the lowest NOx emission regardless of the location of burner since it sustains very stable at lean mixture ratio.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.1064-1071
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• 1994

There are three active radicals which become to the scale of flame diagnostics at the flame front. They are OH, CH and $C_2$ radical. For this, optical measurement system which could monitor simultaneously the luminous waves of three radicals, was constructed. These were analyzed statistically into the cross correlation, coherence and phase. Through such an statistical treatment, combustion characteristics was investigated at the primary zone of gas turbine combustor. The local equivalence ratio was predicted with the ratio of luminuous intensity between CH and $C_2$ radical. This result was matched up to the equivalence ratio calculated from gas composition within 5% error. In general, equivalence ratio was said to be 1.0 at flame front, but it could be increased up to about 1.2 depending on the degree of swirl intensity in case of changing properly the air amount of primary zone.

• Journal of ILASS-Korea
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• v.25 no.1
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• pp.21-26
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• 2020

The objective of this work is to numerically reveal the effect of equivalence ratio change on the simultaneous reduction of NO_X and soot emissions from the simulated-EGR compression ignition engine containing CO₂. An experiment was conducted by using a single-cylinder common-rail injection system engine, an intake control system, and exhaust emissions analyzers. The numerical analysis results were validated under the same experimental conditions. To investigate the effect of equivalence ratio by simulated-EGR containing CO₂, the O₂, N₂, and CO₂ mole fraction were changed in the initial air conditions to the cylinder. The results were analyzed in terms of peak cylinder pressure, indicated mean effective pressure, indicated specific nitrogen oxide, and indicated specific soot. It was revealed that ignition delay characteristics and heat release rate (ROHR) characteristics were not significantly different according to the equivalence ratio. However, as the equivalence ratio increased from 0.68 to 0.83, the maximum combustion pressure and IMEP decreased by about 6.5% and 9.4%, respectively. In the case of ISFC, as is well known, the trend is opposite of IMEP. In the case of ISNO, as the equivalence ratio increased, less NO was generated, and as the equivalence ratio increased by 0.05, the ISSoot value of about 10% increased.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.27-35
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• 2006

It has been observed in experiments that combustion instability of low frequency (${\sim}$ 10Hz) results form the modulation of equivalence ratio at fuel injection hole when a pressure fluctuation propagates upwards along the channel of the burner under an unchoked fuel flow condition. In this study, a commercial program was used to determine how the fuel flow rate changed with respect to the pressure, velocity of the fuel flow and the mass fraction in a choked and an unchoked condition. The calculation focus on the upstream of the dump plane to know how the forced pressure with the fuel injection conditions affects the modulation of the equivalence ratio. Therefore, it is found that pressure fluctuation leads to oscillation of mass flow rate and then results in equivalence ratio modulation under the unchoked fuel flow condition.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.127-130
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• 2015

The objective of this study is to investigate the real flame shape and characteristic of annular combustor. To identify the effects of combustor length ratio and equivalence ratio on the flame shape in annular combustion configuration, the employed parameters are combustor length ratio 0.6-1.0, equivalence ratio 0.7-1.1. The flame shape is visualized using DSLR camera and precision optic mirror. The flame intensity is analyzed by $OH^{*}$ chemiluminescence images with ICCD camera. CO and NOx emission performance is also examined using an exhaust gas analyzer. From the visualized images, it is confirmed that the different tendency appeared in combustor length ratio 0.6-0.7 and 0.8-1.0. The results of $OH^{*}$ chemiluminescence show that the flame intensity is the most uniform for equivalence ratio 0.9. The smaller equivalence ratio is, the less emission of CO and NOx will be in this investigation range.