91̽»¨

Abstract:

Self-ignition of hydrocarbon fuels, which causes engine knock, initiates at localized sites called hot-spots. The occurrence of such hot-spots was studied using double-pulse planar laser induced fluorescence of unburned hydrocarbons in the end-gas of an optically accessible internal combustion (IC) engine. The IC engine was fuelled with a mixture of iso-octane (90%) and n-heptane (10%) and equipped with quartz windows allowing optical access into the combustion chamber. The pulsed radiation of two XeCl Excimer lasers at 308 nm was formed into planar sheets, which are subsequently overlapped and directed into the combustion chamber of the operating engine. An intensified CCD camera was used per laser to image the resulting fluorescence. An image pair was obtained to allow the temporal development of hot-spots to be studied. A large number (around 20,000) of image pairs was observed. The boundary curves of the hot-spots and the velocity of hot-spot expansion from image pairs were extracted and stored in a database. Probability density functions (pdfs) of such measures as hot-spot spatial distribution, boundary curvature, and expansion velocity, can be derived from this database. Preliminary pdfs for hot-spot spatial distribution, boundary curvature, and expansion velocity are presented and compared with numerical one-dimensional simulations of self-ignition in hydrogen-oxygen mixtures, where the interaction of two closely neighboring hot-spots was modelled using a detailed chemical mechanism. Original is an abstract.