Model simulations of fuel sulfur conversion efficiencies in an aircraft engine: Dependence on reaction rate constants and initial species mixing ratios

Abstract

The fuel sulfur conversion efficiency ε behind the combustor of a JT9D-7A aircraft engine in flight has been simulated using an extended exhaust plume chemistry model. The model simulations start in the hightemperature intra-engine regime behind the combustor. The simulations show that the sulfur conversion efficiency is sensitively dependent on model assumptions like reaction rate constants and initial mixing ratios. Sensitivity studies to demonstrate the effect of the uncertainties and variabilities of these parameters on ε are presented. Among the rate constants k, the uncertainty of the reaction rate constant for SO 2 + OH + M → HSO 3 + M has the greatest effect on ε: The uncertainty of k(SO 2 + OH) results in an uncertainty range of 1.1% < ε < 6.2% for our simulation scenario, with a most probable value around 3.8%. The effect of the reaction SO 2 + O + M → SO 3 + M on ε is very small if the initial mixing ratio of O is smaller than that of OH. Among the initial mixing ratios, the variation of the initial OH mixing ratio OH 0 has the greatest effect on ε. For our simulation scenario, the uncertainty range of 5.7 ppmv < OH 0 < 14.7 ppmv (inferred from measurements) leads to an uncertainty range of 2.7% < ε < 5.0%. © 1999 Éditions scientifiques et médicales Elsevier SAS fuel sulfur conversion efficiency / aircraft engine / uncertainty / sensitivity study Zusammenfassung Modellsimulationen der Schwefel-Konversionseffizienz in einem Flugzeugtriebwerk: Abhängigkeit von Geschwindigkeitskonstanten und Anfangs-Mischungsverhältnissen. Die Treibstoffschwefel-Konversionseffizienz ε hinter der Brennkammer eines JT9D-7A-Triebwerkes unter Flugbedingungen wurde mit einem detaillierten Abgasfahnen-Chemiemodell simuliert. Als Referenzwert wurde eine Schwefelumwandlung von ε = 3.8% gefunden. Die berechnete Schwefelumwandlung hängt dabei ganz entscheidend von den Modellannahmen wie z.B. den Geschwindigkeitskonstanten und den Anfangskonzentrationen ab. Es werden Sensitivitätsstudien präsentiert, die den Einfluß dieser Parameter auf ε verdeutlichen sollen. Unter den Geschwindigkeitskonstanten k hat k(SO 2 + OH) den größten Einfluß auf ε: ihr Fehlerbereich führt zu einer Schwankungsbreite von ε zwischen 1.1 und 6.2% für unser Szenario. Der Effekt der Reaktion SO 2 + O ist dagegen eher klein, wenn das Mischungsverhältnis von O kleiner als das von OH ist. Unter den Anfangs-Mischungsverhältnissen hat die Variation des Mischungsverhältnisses von OH den größten Einfluß auf ε. Für unser Simulations-Szenario führt der Fehler bei der Bestimmung des anfänglichen OH-Wertes (OH liegt nach einer Abschätzung aus Messungen für dieses Szenario zwischen 5.7 und 14.7 ppmv) zu einem Bereich von 2.7% < ε < 5.0%.

Evolution of Carbonaceous Aerosol and Aerosol Precursor Emissions Through a Jet Engine

“…The small fractions of HONO compared to NO and NO x are expected [2,3]. These ratios also show no dependence on sulfur loading, and a decrease in going from cruise to uprated cruise power.…”

“…SGA measurements indicate an average NO 2 =NO y ratio of 0.03. This is equivalent to approximately 1500 ppbv of NO 2 and may help explain the difference between measured and calculated NO 2 , particularly if the postcombustor oxidation is independent of upstream oxidation [3]. This also suggests that for this engine, the combustor is an important source for NO 2 .…”

“…Aerosol precursor species evolve due to postcombustor oxidative processes driven by O and OH. Thus, SO 3 and HONO are particularly good indicators of the degree of oxidation occurring in the turbine and exhaust nozzle and are the focus of the measurements in this study. SO 3 is of added interest due to its role as an intermediate in forming H 2 SO 4 , which has been implicated in the formation of additional volatile sulfate aerosol after the exhaust has left the engine.…”

“…SO 3 is of added interest due to its role as an intermediate in forming H 2 SO 4 , which has been implicated in the formation of additional volatile sulfate aerosol after the exhaust has left the engine. Because SO 2 and NO are the source gases for SO 3 and HONO produced in the turbine, their measurement is important for complete quantification of SO x and NO y [2,3]. SO x consists of SO 2 and its oxidation products, especially SO 3 and H 2 SO 4 in aircraft exhaust.…”

Emission of ions and charged soot particles by aircraft engines

“…In the post-combustion zone, the temperature and pressure varied according to the simple law given by Tremmel and Schumann (1999), i.e. the temperature decreases lin- (2000) has been used for the the ion-ion recombination coefficients k ii .…”