• Title/Summary/Keyword: Autoignition model

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Simplified Reaction Scheme of Hydrocarbon Fuels and Its Application to Autoignition of Gasoline with Different Octane Numbers (탄화수소계 연료의 축소반응모델과 가솔린연료의 옥탄가 변화에 따른 자발화 지연시간)

  • 여진구
    • Transactions of the Korean Society of Automotive Engineers
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    • v.11 no.3
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    • pp.13-19
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    • 2003
  • Mathematically simplified reaction scheme that simulates autoignitions of the end gases in spark ignition engines has been studied computationally. The five equation model is described, to predict the essential features of hydrocarbon oxidation. This scheme has been calibrated against autoignition delay times measured in rapid compression machines. The rate constants, activation temperatures, Ta, Arrhenius preexponential constants, A, and heats of reaction for stoichiometric n-heptane/air, iso-octane/air, and their mixtures have all been optimised. The optimisation has been guided by Morley's correlation of the ratio of chain branching to linear termination rates with octane number. Comparisons between computed and experimental autoignition delay times have validated the Present simplified reaction scheme and the influences of octane number upon autoignition delay times have been computationally investigated. It has been found that both cool flame and high temperature direct reactions can have an effect on autoignition delay times.

Numerical Analysis for Autoignition Characteristics of Turbulent Gaseous Jets in a High Pressure Environment (고압 분위기하에 분사된 메탄가스 제트의 자연발화 및 화염전파 특성 해석)

  • Kim, Seong-Ku;Yu, Yong-Wook;Kim, Yong-Mo
    • 한국연소학회:학술대회논문집
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    • 2002.06a
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    • pp.24-32
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    • 2002
  • The autoignition and subsequent flame propagation of initially nonpremixed turbulent system have been numerically analyzed. The unsteady flamelet modeling based on the RIF (Representative Interactive Flamelet) concept has been employed to account for the influences of turbulence on these essentially transient combustion processes. In this RIF approach, the partially premixed burning, diffusive combustion and formation of pollutants(NOx, soot) can be consistently modeled by utilizing the comprehensive chemical mechanism. To treat the spatially distributed inhomogeneity of scalar dissipation rate, the multiple RIFs are employed in the framework of EPFM(Eulerian Particle Flamelet Model) approach. Computations are made for the various initial conditions of pressure, temperature, and fuel composition. The present turbulent combustion model reasonably well predicts the essential features of autoignition process in the transient gaseous fuel jets injected into high pressure and temperature environment.

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Numerical analysis for Autoignition Characteristics of Turbulent Gaseous Jets in a High Pressure Environment (고압 분위기하에 분사된 메탄가스 제트의 자연점화 및 화염전파 특성 해석)

  • 김성구;유용욱;김용모
    • Transactions of the Korean Society of Automotive Engineers
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    • v.10 no.5
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    • pp.81-89
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    • 2002
  • The autoignition and subsequent flame propagation of initially nonpremixed turbulent system have been numerically analyzed. The unsteady flamelet modeling based on the RIF (representative interactive flamelet) concept has been employed to account for the influences of turbulence on these essentially transient combustion processes. In this RIF approach, the partially premixed burning, diffusive combustion and formation of pollutants(NOx, soot) can be consistently modeled by utilizing the comprehensive chemical mechanism. To treat the spatially distributed inhomogeneity of scalar dissipation rate, the multiple RIFs are employed in the framework of EPFM(Eulerian particle flamelet model) approach. Computations are made for the various initial conditions of pressure, temperature, and fuel composition. The present turbulent combustion model reasonably well predicts the essential features of autoignition process in the transient gaseous fuel jets injected into high pressure and temperature environment.

Investigation of Autoignition of Propane and n-Butane Blends Using a Rapid Compression Machine

  • Kim, Hyunguk;Yongseob Lim;Kyoungdoug Min;Lee, Daeyup
    • Journal of Mechanical Science and Technology
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    • v.16 no.8
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    • pp.1127-1134
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    • 2002
  • The effects of pressure and temperature on the autoignition of propane and n-butane blends were investigated using a rapid compression machine (RCM) , which is widely used to examine the autoignition characteristics. The RCM was designed to be capable of varying the compression ratio between 5 and 20 and minimize the vortex formation on the cylinder wall using a wedge-shaped crevice. The initial temperature and pressure of the compressed gas were varied in range of 720∼900 K and 1.6∼ 1.8 MPa, respectively, by adjusting the ratio of the specific heat of the mixture by altering the ratio of the non-reactive components (N$_2$, Ar) under a constant effective equivalence ratio (ø$\_$f/= 1.0) The gas temperature after the compression stroke could be obtained from the measured time-pressure record. The results showed a two-stage ignition delay and a Negative Temperature Coefficient (NTC) behavior which were the unique characteristic of the alkane series fuels. As the propane concentration in the blend were increased from 20% and 40% propane, the autoignition delay time increased by approximately 41 % and 55% at 750 K. Numerical reduced kinetic modeling was performed using the Shell model, which introduced some important chemical ideas, represented by the generic species. Several rate coefficients were calibrated based on the experimental results to establish an autoignition model of the propane and n-butane blends. These coefficients can be used to predict the autoignition characteristics in LPG fueled Sl engines.

SIMULATION OF KNOCK WITH DIFFERENT PISTON SHAPES IN A HEAVY-DUTY LPG ENGINE

  • CHOI H.;LIM J.;MIN K.;LEE D.
    • International Journal of Automotive Technology
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    • v.6 no.2
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    • pp.133-139
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    • 2005
  • In this study, a three-dimensional transient simulation with a knock model was performed to predict knock occurrence and autoignition site in a heavy-duty LPG engine. A FAE (Flame Area Evolutoin) premixed combustion model was applied to simulate flame propagation. The coefficient of the reduced kinetic model was adjusted to LPG fuel and used to simulate autoignition in the unburned gas region. Engine experiments using a single-cylinder research engine were performed to calibrate the reduced kinetic model and to verify the results of the modeling. A pressure transducer and a head-gasket type ion-probe circuit board were installed in order to detect knock occurrences, flame arrival angles, and autoignition sites. Knock occurrence and position were compared for different piston bowl shapes. The simulation concurred with engine experimental data regarding the cylinder pressure, flame arrival angle, knock occurrence, and autoignition site. Furthermore, it provided much information about in-cylinder phenomena and solutions that might help reducing the knocking tendency. The knock simulation model presented in this paper can be used for a development tool of engine design.

Simplified Reaction Scheme of Hydrocarbon Fuels and Its Application to Autoignition of n-Heptane (탄화수소계 연료의 축소반응모텔과 노말-헵탄(n-Heptane)의 자발화 현상)

  • 여진구
    • Transactions of the Korean Society of Automotive Engineers
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    • v.10 no.1
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    • pp.76-83
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    • 2002
  • Mathematically and chemically simplified reaction scheme for n(heptane that simulates autoignitions of the end gases in spark ignition engines has been developed and studied computationally. The five(equation model is described, to predict the essential features of hydrocarbon oxidation. This scheme has been calibrated against autoignition delay times measured in rapid compression machines. The rate constants, activation temperatures, Ta, Arrhenius pre-exponential constants, A, and heats of reaction for stoichiometric nheptane/air has all been optimized. Comparisons between computed and experimental autoignition delay times have validated the present simplified reaction scheme. The influences of heat loss and concentration of chain carrier at the beginning of compression upon autoignition delay times have been computationally investigated.

A Numerical Study of Autoignition in a Confined Cylindrical Spray Combustor (밀폐된 원통형 분무 연소기내의 자연발화 현상에 관한 수치적 연구)

  • Choi, Ji Hun;Baek, Seung Wook
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.6
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    • pp.778-787
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    • 1999
  • In this study, the autoignition process of liquid fuel, injected into hot and stagnant air in a 2-D axisymmetric confined cylindrical combustor, has been investigated. Eulerian-Lagrangian scheme was adopted to analyze the two-phase flow and combustion. The unsteady conservation equations were used to solve the transition of the gas field. Interactions between two phases were accounted by using the particle source in cell (PSI-Cell) model, which was used for detailed consideration of the finite rates of transports between phases. And infinite conduction model was adopted for the vaporization of droplets. The results have shown that the process of the autoignition consists of heating up of droplets, vaporization, mixing and ignition. The ignition criteria could be determined by the temporal variations of temperature, reaction rate and species mass fraction. And the effects of various parameters on ignition phenomena are examined. These have shown that the increasing the reaction rate and/or the vaporization rate can reduce the ignition delay time.

Characteristics of the Ignition Delay for Hydrocarbon Fuels by Reduced Chemical Kinetics Modeling (축소 화학반응 모델링에 의한 탄화수소 연료의 점화지연 특성)

  • 김형욱;배상수;민경덕
    • Transactions of the Korean Society of Automotive Engineers
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    • v.9 no.4
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    • pp.44-49
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    • 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.

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A study on knock model in spark ignition engine (스파크 점화 기관의 노크 모델에 관한 연구)

  • 장종관;이종태;이성열
    • Journal of the korean Society of Automotive Engineers
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    • v.14 no.5
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    • pp.30-40
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    • 1992
  • Spark knock obstructs any improvement in the efficiency and performance of an engine. As the knock mechanism of spark ignition engine, the detonation and the autoignition theory have been offered. In this paper, the knock model was established, which was able to predict the onset of knock and knock timing of spark ignition engine by the basis of autoignition theory. This model was a function of engine speed and equivalent air-fuel ratio. When this established knock model was tested from 1000rpm to 3000rpm of engine speed data, maximum error was crank angle 2 degrees between measured and predicted knock time. And the main results were as follows by the experimental analysis of spark knock in spark ignition engine. 1) Knock frequency was increased as engine speed increased. 2) Knock amplitude was increased as mass of end gas increased. 3) Knock frequency was occured above minimum 18% mass fraction of end gas.

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Study on Spray Vaporization and Combustion in High Pressure Environment (고압에서의 분무의 증발 및 연소 현상에 관한 연구)

  • Wang, Tae-Joong;Baek, Seung-Wook
    • 한국연소학회:학술대회논문집
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    • 2002.11a
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    • pp.193-207
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    • 2002
  • The present study is mainly motivated to investigate the vaporization, autoignition, and combustion of liquid fuel spray injected into high pressure environment. In order to represent these phenomena realistically, discrete droplet model (DDM) which simulates the spray using finite number of representative droplets was adopted for detailed consideration of the finite rate of uansport between liquid and gas phases. The Eulerian-Lagrangian formulation was used to analyze the two-phase interactions. The high pressure vaporization model was applied using the thermodynamic and phase equilibrium at droplet surface. The high pressure effect as well as high temperature effect was considered in the calculation of liquid and gas properties. The characteristics of spray in high pressure environment were explained by comparison with normal pressure case.

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