Impact of Physical and Chemical Properties of Alternative Fuels on Combustion, Gaseous Emissions, and Particulate Matter during Steady and Transient Engine Operation

Abstract

Properties of alternative fuels, such as cetane number, aromatic content, bulk modulus, etc., can vary significantly; thus, a detailed investigation is conducted to assess the impacts on engine combustion, efficiency, and emissions during steady-state and transient engine conditions. Insights can be used to maximize the benefits of alternative fuels or to avoid potential problems that stem from differing ignition and combustion characteristics of particular fuels. In this work, biodiesel (20%, 50%, and 100% biodiesel blends), jet fuel JP8, and synthetic jet fuel S8 are compared to diesel #2 (ULSD). Comparisons are made on ignition, combustion, particulate matter, particulate size spectra, and NO X emission at steady state under harmonized operating conditions, that is, with equalized fuel energy input. All experiments are conducted using the same baseline calibration originally developed for diesel fuel. Ignition delay and combustion phasing trends suggest the need for possible adaptation of ECU calibration. The impact of alternative fuels on particulate emission depended strongly on fuel aromatic content and oxygenation. NO X emission was correlated to multiple physical and chemical fuel properties. While the significance of different properties on NO X emission varied with engine condition, the CA50 location was strongly correlated at all conditions. This paper also includes detailed insight into particulate spectra obtained for all six fuels. Transient engine operation over a driving schedule was characterized with the engine-in-the-loop setup. The use of alternative fuels caused more aggressive cyber-driver behavior as a reaction to their lower energy densities. Different fueling histories were recorded with the alternative fuels and led to marked changes in instantaneous emissions traces. In particular, spikes of particulate emission in the exhaust that typically occur at accelerator tipin were reduced with biodiesel, while extended high load operation was observed in order to follow the demanded vehicle velocity trace and led to higher NO. Cumulative results over the complete FTP 75 driving schedule indicate that transient engine operation reduces the particulate matter benefits of the alternative fuels. JP8 and S8 show slight NO emission benefits with biodiesel showing slightly worse NO emission when compared to steady state. The more aggressive driver behavior led to worse fuel economy.

Effects of fuel components and combustion particle physicochemical properties on toxicological responses of lung cells

“…Differences in fuel can have a significant effect on cdPM properties, including size distribution, surface area, ability to generate reactive oxygen species, and volatile content. [10–13]…”

Effects of fuel physical properties on direct injection spray and ignition behavior

“…Wu et al [15] observed that the viscosity of oxygenated fuels influenced spray atomization behavior. Other experimental comparisons have been made to assess the sensitivity of engine performance, emissions, and spray characteristics to the properties of alternative diesel fuels, such as dimethyl ether (DME), biodiesel, and jet fuel, which are significantly different from those of petroleum derived diesel fuel [16][17][18][19][20].…”

Effect of Oxygenated Fuels on Physicochemical and Toxicological Characteristics of Diesel Particulate Emissions

“…The different physicochemical properties of blended fuels could in turn affect the fuel injection and combustion process, and thus probably lead to major differences in DPM properties and their toxicity. 14 However, no systematic study has been conducted to make a comparative evaluation of fundamental changes in the physicochemical characteristics of particulate emissions resulting from the combustion of diesel blended with several oxygenates with different thermophysical properties and to relate these changes to the toxicity of particulates in an integrated manner, to the best of our knowledge.…”