Browse Publications Technical Papers 2008-01-0838
2008-04-14

Effect of Fuel Chemical Structure and Properties on Diesel Engine Performance and Pollutant Emissions: Review of the Results of Four European Research Programs 2008-01-0838

During recent years, the deterioration of greenhouse phenomenon, in conjunction with the continuous increase of worldwide fleet of vehicles and crude oil prices, raised heightened concerns over both the improvement of vehicle mileage and the reduction of pollutant emissions. Diesel engines have the highest fuel economy and thus, highest CO2 reduction potential among all other thermal propulsion engines due to their superior thermal efficiency. However, particulate matter (PM) and nitrogen oxides (NOx) emissions from diesel engines are comparatively higher than those emitted from modern gasoline engines. Therefore, reduction of diesel emitted pollutants and especially, PM and NOx without increase of specific fuel consumption or let alone improvement of diesel fuel economy is a difficult problem, which requires immediate and drastic actions to be taken. A direct means for reducing diesel engine emitted pollutants, while preserving fuel economy, is the reformulation of conventional diesel fuel. A very promising way to improve diesel fuel behavior is the addition of synthetic or biologically renewable oxygenates. However, as the characteristics of the “parental” conventional diesel oil affect directly the behavior of resulting mixtures it is of utmost importance to first optimize its chemical composition and properties. A vast number of experimental and theoretical studies have been conducted in the past to examine the effect of diesel fuel chemical structure and properties on diesel engine exhaust emissions. The most significant fuel characteristics examined in these studies were aromatic structure and content, sulphur content, hydrocarbon molecular structure, cetane number, fuel heating value, density, viscosity and distillation temperatures. The effects of these fuel characteristics on diesel pollutant emissions have been assessed in various types of diesel engines (direct and indirect) and vehicles under diverse operating conditions (steady-state and transient). The effects of fuel properties on emissions depend on engine types and operating conditions. Moreover, it turns out that it is quite difficult to separate the effects of various fuel properties on emissions because many of them are statistically interrelated. In addition, the influence of fuel properties such as compressibility factor and surface tension on diesel performance characteristics and pollutant emissions has not been examined thoroughly. For this reason, the purpose of this study is to examine the effect of diesel fuel chemical structure and properties on diesel engine performance characteristics and pollutant emissions. To achieve these, findings of three major research programs funded by the European Commission, in which our team participated during recent years, are utilized in conjunction with pertinent results obtained from the literature. During these programs, the effect of variable aromatic content and structure and the influence of fuel physical properties on diesel engine combustion characteristics and pollutant emissions were investigated both theoretically and experimentally, in various types of diesel engines and under diverse operating conditions. Unlike other studies, emphasis will be given herein on the effects of fuel properties not only on regulated pollutant emissions but also on diesel fuel injection system, combustion evolution and in-cylinder pollutant formation. In addition, the background and the succession of various statistical approaches used in the literature to identify possible correlations between specific diesel fuel properties and exhaust emissions will be discussed. The conclusions of these evaluations will be contrasted with the statistical methods used from our research group to correlate diesel emitted pollutants and fuel characteristics. The ultimate objective of this review is to consolidate existing knowledge and discern the influence of individual conventional diesel fuel characteristics on engine performance and pollutant emissions.

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