低燃油中的硫的氧化模型高速二冲程柴油发动机英文文献和中文翻译

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Abstract: In large marine two stroke Diesel engines during combustion of sulfur containing fuel, the sulfur is oxidised to SO2, mainly, although substantial amounts of SO3 and H2SO4 will form as well. These latter species may cause corrosional wear of the cylinder liner if not neutralised by lube oil additives. Potential attacks is due to either condensation of sulfuric acid on the cylinder liner lube oil film or direct dissolution of oxidised sulfur species in the lube oil film in which reaction with dissolved water may be the source of acidic species. In order to evaluate and predict corrosional wear of the liner material, it is pivotal to have realistic estimates of the distribution/concentration of oxidised sulfur species as well as a reliable model of formation, transport and destruction of acidic species in the oil film. This paper addresses the former part by invoking a detailed reaction mechanism in order to simulate the oxidation of fuel bound sulfur and predicting the concentration of SO2 as well as the conversionfraction into SO3 and H2SO4. The reaction mechanismis coupled to a realistic model of the combustion processin which the air entrainment into the combustion zone is accounted for. The results of the simulation are evaluated with respect to previously applied models as well as existing data on the conversion fraction of SO2 to SO3 and H2SO4. The conversion fraction is

found to be in a range of 2.6-6.7 %.52555

INTRODUCTION

During the combustion of sulfur containing fuel, the sulfur will be oxidised mainly to SO2 but significant fractions of SO3 and H2 SO4 will also form [1]. While emissions of CO, HC and NOx to some extent can be controlled through the combustion conditions e.g. air excess ratio, combustion temperature etc.the total emission of sulfur can only be controlled through the sulfur content of the fuel [2] or by appropriate exhaust gas after treatment e.g. By scrubbing technologies [3]. From an environmental point of view SOx emissions are undesired,primarily due to the formation of atmosphericH2SO4, which is the main source of acid rain.From a technical/engineering point of view the problems related to the sulfur content of the fuel are mainly corrosional wear due to sulfuric acid

(produced from fuel sulfur, oxygen and moisture)attacking various parts of the engine and auxiliaries[4, 5, 6]. Especially the corrosional wear of the cylinder liner has received special attention in the past [7, 8, 9, 10, 11, 12, 13]. Sulfuric acid may potentially cause corrosion either by condensation,if the liner temperature drops below the dew point of the combustion gas [7, 12] or by direct transport of acidic gas phase species into the cylinder liner lube oil film [13]. The acidic species may diffuse through the cylinder lube oil and reach the metal surface eventually leading to corrosional wear. This can be avoided through neutralisation of sulfuric acid with alkaline lube oil additives. Further it has been proposed that SO2 is absorbed in the lube oil film in which further reaction with water leads to acid formation [11].Standard textbooks on the topic of internal combustion engines and combustion in general only surface the topic of sulfur oxide formation during combustion of sulfur containing fuels[2, 14, 15]. To the best of our knowledge no results on experimental measurements of SOx in the exhaust gas from large two-stroke diesel engines have been published in peer reviewed journals in the past. Engel et al. reported measurements of both SO2 and SO3 in the exhaust gas of a range of heavy duty four stroke diesel engines [4]. They found that approx. 3 % (volumetric) of the SO2 was converted to SO3 on average. Previous modelling studies devoted to the prediction of diesel engine in-cylinder formation of sulfur oxides including sulfuric acid [7] has been based either on the assumption that SO2, SO3, and H2SO4 are in equilibrium at temperatures above 1000∘C, viz. The reactions responsible for their formation are much faster than the time scales being considered. Below1000∘C the reaction systems are considered frozen i.e. the amount of the species already formed will be constant, or ii) a fixed instantaneous conversion ratio of SO2 to SO3 of e.g. 5% [12, 13]. In order to provide a deeper understanding of corrosional wear of the cylinder liner through modelling studies it is pivotal to have reasonable concentrations of bothSO2, SO3 and H2SO4 as input.In contrast to diesel engines the published research on formation of SOx and H2SO4 from aircraft turbines has been significantly more extensive both experimentally as well as theoretically [16, 17, 18, 19, 20] (and references therein). The modelling studies reported are based on large detailed reaction mechanisms describing the oxidation of fuel bound sulfur formation[18, 17, 19].In this preliminary study it will be investigated how both chemical kinetics and thermodynamics influence the distribution of oxidised sulfur species during combustion of sulfur containing fuel in large two-stroke diesel engines. The main motivation for this study is the fact that the current knowledge about the in-cylinder formation of SO3 and H2 SO4in large two-stroke diesel engines is very limited.Improving the understanding in this field will indeed be helpful in evaluating potential in-cylinder corrosional wear both for engines in service,especially considering choice of lube oil type and lube oil consumption, but certainly also for engines in the design phase. Furthermore, exhaust gas recirculation (EGR) is becoming an emerging method for NOx reduction for large two-stroke marine diesel engines running on heavy fuel oil(sulfur content up to 4.5 w.w %) [21, 22]. A detailed