The potential of direct injection in spark-ignition engines regarding the significant reduction of fuel consumption and pollutant emission as well as advantages in the field of torque characteristic and acceleration behavior induced a remarkable development of GDI engines for automobile applications. The mentioned advantages are of special interest for motorcycle four-stroke engines as well. However, in compact cylinder units, respectively in a wide speed range as for motorcycle engines, the adaptation of direct injection gains on complexity.
The paper presents the development results of a GDI four-stroke four-valve single cylinder motorcycle engine with 125 cc. The pressure pulse direct injection system developed for this application is presented from the fluid-dynamic behavior up to the obtained injection spray characteristics.
The mixture formation process is analyzed for different load and speed values, respectively for favorable combinations of parameters such as the injector location, the opening pressure and the injection start, using a numerical simulation method.
The results of the engine tests confirm the adaptability of this concept for motorcycle engine applications.