Experimental Investigation on Gasoline and Diesel Fuels Surrogates Designed Via Computation and Property Integration Methods

Abstract

Automotive researchers attempts to simulate combustion of fuels in order to improve engine performance.[1] Conventional fuels are difficult to represent in these simulations due to their complex composition. Surrogates that meet American Society of Testing and Materials (ASTM) standards are a good alternative to conventional fuels. This study aims at design and analyzing surrogate mixtures for both gasoline and diesel. Surrogates were designed through a computer aided model developed at the Technical University of Denmark.[2] The model architecture has four structures viz., (i) problem definition (ii) property model identification (iii) mixture blend design and (iv) model-based verification.Surrogate diesel, comprised of five paraffinic compounds viz., n-dodecane, n-tetradecane, tetralin, cyclo-octaneand iso-cetane in different volumetric ratios. Surrogate gasoline comprised of six different chemicals viz. n-butane, n-heptane, iso-octane, 1-pentene, methyl cyclopentane and toluene in different volumetric ratios. Target physical properties of these fuel surrogates were measured using advanced analytical equipment and experimental techniques developed at Texas A&M University at Qatar.[3] Diesel surrogate was tested for the target properties employed in the model viz. density, viscosity, heat content, flash point, vapor pressure, pour point, cloud point and distillation curve. Butane present in the gasoline surrogate hampers handling and testing since it is extremely critical to prepare a homogeneous blend that comprises of both liquids and a permanent gas. Also, the conventional sampling technique was found to be ineffective to prevent loss of permanent gas in the surrogate. Therefore, a novel sampling methodology and advanced blending technique was developed to minimize loss of butane and volatile components such as 1-pentene. Detailed Hydrocarbon Analysis (DHA) for gasoline surrogate was carried out by Gas Chromatography (GC) according to ASTM D6730 to verify the efficacy of blending technique as well as sampling method. The composition analysis through DHA confirmed that the blending and sampling methodology was accurate with maximum relative standard deviation of approx. 5.82%. Subsequently gasoline surrogate was tested for density, viscosity, vapor pressure, heat content, distillation curve and compositional attributes.The surrogate mixtures prepared in this study complied well with their respective ASTM standards for the properties measured. The work would further be continued to investigate the engine performance and emission characteristics for diesel surrogate. Engine performance will be evaluated in terms of Power/Torque and Theoretical Brake Specific Fuel Consumption (BSFC). Emissions of Carbon Monoxide (CO), Hydrocarbon (HC) and Nitrogen Oxides (NOx) will be determined. Results of this study provide a basis to further improving the computer aided models used to design the surrogates and for design of future generations of efficient fuels of different composition obtained from both conventional sources (petroleum) and non-conventional sources (e.g. from natural gas via gas-to-liquid (GTL), coal via coal-to-liquid (CTL) or biofuels). Also, the outcome of this study will be used to optimizing the design of fuel blends obtained from the aforementioned sources.