DEVELOPMENT OF THE HIGH PRESSURE DIRECT INJECTION (HPDI) SYSTEM FOR TWO-STROKE OUTBOARD MOTOR

摘要

Two-stroke internal combustion engine, characterized by lightweight and high output power, is suitable for outboard motors with larger horsepower. The High Pressure Direct Injection (HPDI) system was developed and applied to this type of production outboard motor. The HPDI system has different arrangement from the conventional Orbital or FICHT system. The outboard motor equipped with the system reduces the exhaust emission level to approximately two-thirds of the EPA (U.S.) 2006 emission standard. The HPDI is non-air-assist-type gasoline direct injection system, in which the fuel pressure is raised to 5MPa (700psi) by crankshaft-driven high-pressure fuel pump and then injected directly into the cylinder without air assistance. Research and development for the relevant areas including combustion chamber configuration and injector orientation have resulted in successful homogeneous combustion utilizing the scavenging flow of the two-stroke engines. High-pressure injection of the HPDI system effectively reduces exhaust emission especially in higher engine speeds, and at the same time it substantially improves the fuel economy. This HPDI system design had been released publicly in Japan at the end of 1999.