Studies On Flame Spread Characteristics Of Diesel And Diesel Blends

With the rapid development of the economy,the problems like energy shortage and environmental pollution have become more and more serious.Although many researchers have been studying the clean renewable energy,petroleum fuels still dominate.In recent years,diesel engines are widely used due to its high drivability and economy.However,the increasing number of diesel vehicles brings serious emission problems,which triggers many researches of diesel replacement.Previous studies on diesel and diesel blends were mainly focused on the physical and chemical characteristics,combustion and emission characteristics.However,little research has focused on its flame spread characteristics.Flame spread is a fast and dangerous phenomenon,which plays a significant role in catastrophic accidents.Based on the status above,a set of flame spread experiments was carried out for diesel and diesel blends,the following aspects were studied in this work:A set of experiments was conducted to investigate the initial temperature effect on the flame spread characteristics of diesel and gasoline-diesel blend(dieseline).The results showed that the flame spread rate of both fuels increased with initial fuel temperature while the dieseline flame spreaded almost twice that of diesel.During flame spread,the front temperature and velocity of subsurface flow increased with initial fuel temperature and the velocity of dieseline increased faster due to longer subsurface flow.Furthermore,it was found that the pulsation amplitude of diesel flash flame increased with initial fuel temperature while the dieseline decreased initially and then increased with the increased initial fuel temperature.The pulsation frequency and velocity of flash flame were found to be independent of the initial fuel temperature.A set of experiments was conducted to study the effects of fuel depth and ullage height on flame spread over diesel and ethanol-diesel.Results showed that as the fuel depth increased under ullage effect,the flame spread rate increased first and then maintained constant.The flame spread rate of diesel changes with increasing non-dimensional ullage height,and presents a local minimum dividing the experimental range with different control mechanisms.Prior to this minimum point,the flame spread rate is entrainment-controlled,while it is radiation-controlled after this minimum value.For ethanol-diesel,the flame spread rate decreases monotonously and then tends to be unchanged with non-dimensional ullage height due to the higher combustion efficiency and oxygen content of ethanol-diesel.For deep pools,the subsurface flow velocity,which is independent of ullage height,increases with fuel depth.Moreover,the flash flame pulsation frequency is weakly affected by the fuel depth and presents a negative relationship with ullage height.A set of experiments with various sidewall heights was conducted to study the sidewall flame spread more in-depth.It was found that,there were two sections along the whole spread region when flames adherently spread on one side.The one section is called as the flame spread section,where exists near the front flame;the other is called as the sidewall fire section,following the former one.In flame spread section,the flame burns away from the sidewall.As a result,the fuel surface temperature in adherent position is lower than that of center and outer position.However,in sidewall fire section,the adherent temperature is higher than the center one.In vertical direction,the fuel temperature at the adherent position decreases along the vertical height while the temperature at the outer side shows obvious stratification.And as the depth increases,the growth rate of temperature at the adherent wall gradually decreases,while it remains nearly unchanged for outer position.In addition,with the increasing of the non-dimensional sidewall height,both flame spread rate and subsurface flow velocity increase first and then decrease.And when the ratio of sidewall height to pan width reaches 1,both velocities reach the maximum.