Experimental Measurement of the Isothermal Bulk Modulus of Compressibility and Speed of Sound of Conventional and Alternative Jet Fuels

Abstract

The use of jet fuels in compression–ignition engines with pump–line–nozzle (PLN) fuel injection systems requires consideration of differences in bulk modulus and speed of sound versus diesel fuels, thus requiring thorough characterization of jet fuels before they are applied. In this study, we measured the isothermal bulk modulus of compressibility of three different petroleum-based jet fuels (i.e., POSF 4658, POSF 6169, and POSF 10325) at 313 K (0–4000 psig) and of three different alternative jet fuels (i.e., Farnesane, hydrotreated renewable jet-derived from Camelina (HRJC), and Alcohol-to-Jet (ATJ)) at 308 K (0–4000 psig). Measured isothermal bulk modulus is used to calculate the specific heat ratio of each test fuel by comparing it to the isentropic bulk modulus referenced from previous literature. Measurement results show that the bulk modulus of petroleum-based jet fuels is ∼20%–25% lower than that of the petroleum-based diesel fuel: 984, 932, and 953 MPa for POSF 4658, POSF 6169, and POSF 10325, respectively, at 0.1 MPa. The bulk modulus of Farnesane (982 MPa at 0.1 MPa) was similar to that of petroleum-based jet fuels while those of the other alternative jet fuels were ∼4% (HRJC) and 14% (ATJ) lower than that of the petroleum jet fuels. We also measured the pseudoisothermal speed of sound of these jet fuels using a pair of fuel line pressure sensors installed on the fuel supply line of a diesel engine in a temperature range between 318 K and 338 K. Results showed a lower pseudoisothermal speed of sound for both petroleum-based (1114–1122 m/s at 328 K) and alternative jet fuels (1038–1116 m/s at 328 K) relative to petroleum-based diesel fuel. Isentropic speed of sound estimated by applying the conversion factor to the pseudoisothermal speed of sound measurement showed a similar trend: a lower isentropic speed of sound for jet fuels relative to petroleum-based diesel fuel. This suggested an unintended retarding in the actual fuel injection timing when these jet fuels are used in a CI engine in lieu of regular diesel fuel without the adjustment in nominal fuel injection timing.

High Pressure Injection Pump Operating with Renewable Diesel Fuels

“…Diesel fuel exhibits an intermediate behavior between HVO and WCO. In all cases, the concavity of both the compression and expansion phases is evident, aligning with the increasing function of the compressibility modulus of liquids with pressure [19]. The characteristics of the delivery phase remain consistently similar across different fluids.…”

“…Figure 2 resumes their features. Information about density and viscosity are derived by the producers' datasheets, whereas bulk modulus is found in the literature [17][18][19]. Bulk modulus of diesel fossil fuel, FAME diesel and HVO according to [18] Figure 2.…”

Characteristics of High-Pressure Injection Pump Operated with Renewable Fuel for Diesel Engines

“…Diesel fuel exhibits an intermediate behavior between HVO and WCO. In all cases, the concavity of both the compression and expansion phases is evident, aligning with the increasing function of the compressibility modulus of liquids with pressure [25]. The characteristics of the delivery phase remain consistently similar across different fluids.…”

“…Table 3 summarizes their features. Information about density and viscosity are derived from the producers' datasheets, whereas information on bulk modulus is found in the literature [23][24][25] and reported in Figure 3, according to [24]. according to [24].…”