Effects of an injector cooling jacket on combustion characteristics of compressed-ignition sprays with a gasoline-hydrogenated catalytic biodiesel blend

The fuel properties in Gasoline Combustion ignition modes (GCI) have been adapted by mixing high reactivity fuels for improving poor combustion stability with pure gasoline. Precise control of the injector tip temperature, as well as the fuel temperature, are considered as the essential boundary conditions to conduct the fundamental investigation on combustion process of GCI spray. Therefore, the impacts of an injector cooling jacket on the spray and combustion developments of a mixture contains 60% gasoline and 40% hydrogenated catalytic biodiesel are studied using a constant volume combustion chamber (CVCC) working under GCI mode. A dummy injector is equipped with a thermocouple to measure the effects of the cooling jacket and ambient temperature on tip temperature. The Schlieren imaging and Diffused Background Illumination Extinction Imaging techniques are employed to visualize the reacting spray development and in-flame soot formation. The results illustrate that the injector tip temperature is well-controlled with aiding of the cooling jacket, which only increases by 35 K with increasing ambient temperature by 250 K. Furthermore, it is found from the optical experiments that the liquid length, ignition delay and lift-off length are enlarged for the cooling mode compared to that of the uncooled one. The cooling jacket also brings in a larger overlapping area between liquid length and flame lift-off length. However, the in-flame soot production for the cooling jacket is increased more than twice compared to that of the uncooled one.