Ignition and combustion characteristics of gasoline-biodiesel blend in a constant volume chamber: Effects of the operation parameters

The GB20 combined from 20% biodiesel and 80% gasoline showed the excellent potential for engine fuel application due to utilizing superior lubrication ability, renewables, environmental friendliness, high ignitability from the biodiesel and high volatility from the gasoline. However, there has been no quantitative evaluation of ignition and combustion characteristics for the GB20 spray combustion by the optical investigation, yet. In this work, we performed a comprehensive study focused on the lift-off length and ignition delay of the GB20 in a constant volume chamber under a wide range of experimental conditions simulating engine operating conditions. The GB20 was injected into the combustion chamber under different conditions: gas density (5 kg/m(3) and 15 kg/m(3)), ambient temperature (800 K-1200 K), and oxygen content (10%-21%). The single-hole injector with a 0.2mm diameter was used to inject the fuel sample at various injection pressures (30 MPa-130 MPa) and injection durations (400 mu s-3500 mu s). The ignition delay and lift-off length were determined via broadband chemiluminescence imaging, which was obtained using a high-speed camera. A self-written LabVIEW code was made to separate and smoothen the flame from background noise in the image processing. As a result, the ignition delay and lift-off length heavily depend on the operating conditions. The increase of ambient temperature, ambient gas density, or oxygen concentration significantly decreases the ignition delay and lift-off length. The injection parameters, including the injection pressure and injection duration, also influence the airfuel mixing process, thus changing the local ambient temperature and local air-fuel ratio, resulting in increasing/decreasing the ignition delay and lift-off length. The ambient temperature is lower than 1000 K for the gas density of 5 kg/m(3) and 900 K for the gas density of 15 kg/m(3) at an oxygen concentration of 10%, the lift-off length result disappears due to the very few soot particles formation under the deficient oxygen condition.