Predicting flammability limits for hydrocarbons gases and mixtures with nitrogen as inert gas
Translated title
Forudsigelse af brandbarhedsgrænser for kulbrinter og blandinger med nitrogen som inert gas
Author
Ottosen, Jonas Blom
Term
4. semester
Education
Publication year
2019
Submitted on
2019-05-31
Pages
35
Abstract
At kende en gas' antændelighedsgrænser (det koncentrationsområde i luft, hvor en blanding kan antændes og brænde) er afgørende for sikker håndtering af brændbare kulbrinter. Selvom teorien på området ikke er fuldt afklaret, bruges simple tilgange som Le Chateliers blandingsregel ofte for blandinger. Dette speciale udvikler en model af en forbrænder til at forudsige antændelighedsgrænser for kulbrinter og for blandinger fortyndet med inert (ikke-reaktiv) gas. Opsætningen anvender masseflowkontrollere til at indstille molfraktionerne (andelene) af hver gas i blandingen, og antændelse initieres med en kort puls af hydrogenradikaler (meget reaktive brint-radikaler). De kemiske reaktioner beskrives med mekanismen GRI-Mech 3.0 (gri30), som omfatter metan, ethan, propan samt andre gasser, der indgår i forbrænding. Modelresultaterne sammenlignes med eksperimentelle data rapporteret af Kuchta og Zhao. Modellen genskaber antændelighedsadfærden for mindre kulbrinter godt, men viser markante afvigelser, når ethan er til stede.
Knowing a gas's flammability limits (the range of concentrations in air where a mixture can ignite and burn) is essential for the safe handling of flammable hydrocarbons. Although the theory is not complete, simple approaches such as Le Chatelier's mixing rule are often used for mixtures. This thesis develops a combustor-based model to predict flammability limits for hydrocarbons and for mixtures diluted with inert (non-reactive) gases. The setup uses mass flow controllers to set the molar fractions (proportions) of each gas in the mixture, and ignition is initiated by a brief pulse of hydrogen radicals (highly reactive hydrogen species). Chemical reactions are described with the GRI-Mech 3.0 (gri30) mechanism, which covers methane, ethane, propane and other common combustion gases. Model predictions are compared with experimental data reported by Kuchta and Zhao. The model reproduces the flammability behavior of small hydrocarbons well, with notable deviations when ethane is present.
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