Effect of start timing of gasoline injection on cyclic variations,, HC and CO pollutants in part load of dual fuel gasoline-natural gas mode

Fuel system and proper fuel-air mixing are important challenges in spark ignition engines. Due to time consuming fuel atomization process, determining the best start position for fuel injection is vital in engine performance. In the present work, a single-cylinder research engine equipped with a fuel injection system for gasoline and natural gas, with the ability to adjust spark timing and start of injection positions was used at 1800 RPM and a compression ratio of 11. At a fixed fuel ratio of dual mode, the result showed 9o crank-angle difference between optimum spark advanced of full-load and half-load. At half-load fuel injection period, fuel mass fractions and engine speed were fixed and crank-angle position of start of injection (SOI) was varied along a cycle by a 45o crank-angle step. For each adjusted fuel SOI position, in-cylinder pressure of 400 successive cycles and related HC and CO emissions were collected. The obtained results showed that the emissions were changed by varying SOI position of each fuel fixing fuel injection periods. The emitted gas changes were significant for gasoline SOI variation in compared with those of natural gas. Also, from changes of standard deviation and coefficient of variation of indicated mean effective pressure, it was observed that their highest values occur when gasoline SOI is 15o crank-angle after induction top center.