EFFECTS OF INJECTION TIMING ON PERFORMANCE AND DROPLET CHARACTERISTICS OF A 16-VALVE 4-CYLINDER ENGINE

The performance and droplet characteristics of a sixteen-valve, four c ylinder engine operating with combustion in one cylinder have been mea sured with part load, a speed of 1200 rpm and a stoichiometric mixture of gasoline and air. The indicated mean-effective cylinder pressure w as found to be constant with initiation of injection from 150 degrees to 630 degrees of crank angle after top-dead-centre of intake and with a 10% reduction between 30 degrees and 60 degrees which coincided wit h maxima in the covariance in pressure and in the emissions of unburne d hydrocarbon. There was also a tendency for performance to decline wi th injection after 660 degrees. Measurements with laser- and phase-Dop pler velocimeters showed that the number of droplets entering the cyli nder was much reduced with injection at crank angles corresponding to closed inlet valves due to evaporation, and that the few large droplet s which emerged did not survive until top-dead-centre of compression. In contrast, some of the many droplets associated with injection with the valves open survived to the crank angle of ignition and it is like ly that these led to an inhomogeneous charge with poorer flame-front p ropagation responsible for reduction in performance.