La descripción química detallada de la cinética de combustión de hidrocarburos puede requerir la trazabilidad de cientos de especies químicas y miles de etapas de reacción. En el futuro previsible, el tiempo de cálculo y las limitaciones de memoria de computador impedirán una descripciones mas detallada de la química de la combustión y su simulación mediante software de dinámica de fluidos computacional (CFD) del fenómeno de la combustión. Within simulaciones CFD , el número de especies de orugas afecta el uso de memoria y tiempo de CPU . Como resultado , es importante para reducir al mínimo este número al tiempo que conserva las características esenciales de la química detallada . El número de especies necesarias para la simulación de procesos de combustión depende de la naturaleza del fenómeno, y el tipo de información que desee en el desarrollo reciente de simulation.The com integral , validados , los mecanismos detallados para la combustión de grandes hidrocarburo es un paso significativo para el barrio . Reducción de mecanismos cinéticos químicos que pueden representar im por tan tes aspectos de la conducta de estos mecanismos detallados utilizando unos escalares suficientes que puedan ser implementadas en simulaciones CFD de fer gran potencial de mejora en el modelado de dispositivos de combustión prácticos . [2] En la presente investigación fue destinados a demostrar la viabilidad de los mecanismos de reacción reducidos en la simulación de motores de combustión interna ( ICE ) . en este trabajo , tres mecanismos cinéticos químicos de combustión de metano se comparan en una configuración de ICE . El metano fue seleccionado por sus ventajas económicas y ecológicas . Estos mecanismos son : mecanismos completos detallados GRIMECH 3.0 , los mecanismos de las reacciones de cuatro pasos y un mecanismo global de una reacción.

Three chemical kinetic mechanisms of methane combustion were tested and com- pared using the inter nal combustion en gine model of Chemkin 4.02 [1]: one-step global reaction mechanism, four-step mechanism, and the standard detailed   scheme GRIMECH 3.0.This study shows good concor dances, es pecially between the four-step and the de-tailed mechanisms in the prediction of tem per ature and main species pro  files. But reduced schemes were inca pables  to predict pol  lut ant emis sions in an inter nal com-bustion en gine. The four-step mechanism can only predict CO emis sions but with-out good agreement.Key words: chemical kinetics, combustion, methane, engine

Detailed chemical kinetic descriptions of hydrocarbon combustion may require the tracking of hundreds of chemical species and thousands of reaction steps. For the foreseeable future, CPU time and computer memory limitations will prohibit implementation of fully detailed descriptions of combustion chemistry into computational fluid dynamics (CFD) simulations of combustion hardware. Within CFD simulations, the number of species tracked impacts the memory usage and CPU time. As a result, it is important to minimize this number while retaining essential features of the detailed chemistry. The number of species required for simulation of combustion processes depends on the nature of the phenomenon, and the type of information desired from the simulation.The recent development of com prehensive, validated, detailed mechanisms for combustion of large hydrocarbon is a significant step for ward. Reduced chemical kinetic mechanisms that can represent im por tant aspects of the behaviour of these detailed mechanisms using few enough scalars that they can be implemented into CFD simulations of fer large potential improvement in the modelling of practical combustion devices [2].The present research was intended to demonstrate the feasibility of the reduced reaction mechanisms in the simulation of internal combustion engines (ICE).In this paper, three chemical kinetic mechanisms

of methane combustion are compared in an ICE configuration. Methane was selected for its economic and ecological advantages. These mechanisms are: full detailed mechanisms GRIMECH 3.0, four-step reactions mechanisms, and a global one reaction mechanism.

We com pared those mechanisms for tem per ature profiles, species profiles, and when possi ble, pollutant emissions for var ious excess air ratios.Our results and discussion show that the four step reduced mechanism is feasi ble for the simulation of com bustion in ICE and can re place faithfully the full detailed one but withsome limitations.

Chemical reaction mechanisms for methane

Since methane is the sim plest hydrocar  bon fuel avail able; several studies have focusedon methane-air flames [3]. The oxidation of methane is quite well under stood and var ious de-tailed reaction mechanisms are re ported in liter ature [4]. They can be divided into full mecha-nisms, skeletal mechanisms, and reduced mechanisms. The var ious mechanisms dif fer with re-spect to the considered species and reactions. However, consider ing the uncer tainties andsim plifications included in a tur  bulent flame calculation, the var ious mechanisms agree reason-ably well [5].In liter ature, several mechanisms of methane com bustion exist. We can cite: –for detailed mechanisms: Westbrook [6], Glarborg et al  . [7], Miller and Bowman [8], andrecently, Konnov [9], Huges et al. [10], and the standard GRIMECH [11], –for reduced mechanisms: Westbrook and Dryer [12], Duterque et al. [13] (1 to 2 globalreactions), Peters [14], Hutmann et al., [15], and Jones and Lindstedt [16] (more than 2global reaction), Edelman and Fortune [17], and Edelman and Harsha [18] (1 global reactionwith many elementary reactions; these mechanisms are called quasi-global mechanisms). These last mechanisms are certainly more accurate than global mechanisms but they are also numerically expansive. All chemical models used in com bustion share the same description of elementarychemical reactions, based on an Arrhenius law, leading to a rate coefficient expressed as:

k=A T β eEa

RT

The values of  A,  Ea (or Ta =  Ea/R) and of the temperature-dependence coefficient  β are thus reaction-de pendent. Based on this ex pression, different levels of ap proximation can be de-fined to describe the kinetics.

The three following mechanisms are investigated: 

–the global one-step reaction mechanism of Duterque [13] A β Ta

CH4 + 2O2 CO2+ 2H2O 

the four-step reaction mechanism of Jones and Lindstedt [16]CH4+ ½O2 CO + 2H2

 –CH4+ H2O®CO + 3H2 –H2+ ½O2 «H2O –CO + H2O«CO2+ H2  –the standard detailed mechanism GRIMECH 3.0 (53 species,325 reactions) [11]

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.101.346&rep=rep1&type=pdf