The Effect of Diluent Gases on High-Pressure Laminar Burning Velocity Measurements of an Advanced Biofuel Ketone

The 2,4-dimethyl-3-pentanone (DIPK) is a promising biofuel candidate for automotive applications that is produced by the endophytic fungal conversion process which can be optimized for widespread utilization. There are some studies in the literature on combustion properties of DIPK, such as ignition delay times and laminar burning velocity (LBV) measurements. However, most studies are conducted one atmospheric (atm) pressure which are far away from the high-pressure conditions present inside reciprocating engines. Therefore, we present LBV measurements at high pressures up to 10 atm for this fuel using a spherical flame speed facility. It is known that the flame in a constant volume chamber develops cellular structure (hydrodynamic instability) as the initial pressure increases because of the reduction in flame thickness. In addition, the diffusional-thermal instability prevents experiments for rich mixtures because of the reduction of Lewis number (Le). An earlier study from our lab showed that the flame instability prevented a proper extraction of LBV for stoichiometric and rich mixtures at 5 atm with nitrogen (N₂) diluent. Therefore, helium (He) and argon (Ar) were used to suppress flame instability in the present study. Several oxygen-to-diluent ratios were used at 5 atm, 403 K, and a wide range of equivalence ratios (0.8-1.6) to provide the general trend of LBV. It was observed that He provided a smooth spherical flame without cellular structure even at a rich equivalence ratio of 1.6 and delivered a wider range of data points compared to other gases. A similar observation was noticed by increasing the diluent ratio from 3.76 to 5, because of the increase in flame thickness relative to the density jump or density difference between unburned and burned gases. Since the constant volume approach is used for determining LBV, many data points can be extracted out of a single experiment (up to 10 atm and 503 K) which brings several validation targets for DIPK chemical kinetic mechanisms.