Laminar flame characteristics of cyclopentanone at elevated temperatures

Cyclopentanone, a product of biomass pyrolysis of agricultural waste, has certain advantages as a biofuel candidate but so far little is known about its combustion characteristics. In this paper, the laminar flame characteristics of cyclopentanone, including stretched flame propagation speed, unstretched flame propagation speed, and laminar burning velocity, were measured and compared with gasoline and ethanol, using the outwardly propagating spherical flame method and the high-speed Schlieren photography technique. The experiments were conducted in a constant-volume vessel using various fuel-air equivalence ratios (ϕ = 0.8–1.6) at elevated initial temperatures (T₀ = 423, 448 and 473 K) and a fixed initial pressure (P₀ = 0.1 MPa). Linear and non-linear extrapolations were used to characterise the relationship between the stretch rate and the stretched flame propagation speed when Markstein length was near to or away from zero respectively. Empirical functions were obtained to calculate the laminar burning velocities of cyclopentanone for various fuel-air equivalence ratios and initial temperatures. The results show that Markstein length of cyclopentanone decreases when equivalence ratio is increased, and the turning point of equivalence ratio at which it changes from positive to negative is slightly below 1.4. The maximum laminar burning velocity of cyclopentanone appears at the equivalence ratio of approximately 1.2, regardless of the initial temperature. The laminar burning velocity of cyclopentanone has a smaller difference to that of ethanol and gasoline when equivalence ratio is leaner than stoichiometric, but when equivalence ratio increases from 1.0 to 1.4, it becomes increasingly lower than that of ethanol and higher than that of gasoline. The maximum laminar burning velocity of cyclopentanone is 0.82 m/s; for gasoline it is 0.72 m/s and for ethanol it is 0.86 m/s, at an initial temperature of 423 K and pressure of 0.1 MPa.